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see OF THE
ILLINOIS STATE LABORATORY

NATURAL HISTORY

Ursana, Iniinois, U.S. A.

Wor. V1. ; NOVEMBER, 1903. ARTICLE II.

THE PLANKTON OF THE ILLINOIS RIVER, 1894-1899, WITH IN-
TRODUCTORY NOTES UPON THE HYDROGRAPHY OF THE ILLINOIS
RIVER AND ITS BASIN. PARTI. QUANTITATIVE INVESTIGATIONS AND

GENERAL RESULTS.

€. A: KQOFOID; PHD.

ay iS a ee

de

5

BUILTIN

OF THE

HANOI STATE LABORATORY

OF

NATURAL HISTORY

Urpana, I[xLutois, U.S. A.

VOL UNE NA:

1901-1903

CONTRIBUTIONS TO THE NATURAL HiIsrory SuRVEY OF ILLINOIS,

MADE UNDER THE DIRECTION OF

S. A. ForBES

GAZETTE PRESS
CHAMPAIGN, ILLINOIS
1903

VINIVERSHiN Or HEEYN@S

IBOVAIRID) Ole WSUS INE 12S)

THE GOVERNOR OF ILLINOIS,

RST CREAN) EO VZAWICES Sul aya leveracusicteiers ai sixes Selsisie Srseele Gis Seereenater eens Springfield
THE PRESIDENT OF THE STATE BOARD OF AGRICULTURE,

AIMUBS) 1X5 IDUCIRIURSOIN Gucoo¢accsondooces ecdaodcons Eee llawnencevlllle
THE SUPERINTENDENT OF PUBLIC INSTRUCTION,

PANTEHERSES DB ASVAISIS Supmevcatenieniste icici aig nem oe cesar aniiteamsroemnes: ..... pring field
ANLIN CIS, ASTON RING JANI} 84 OF Mel here cas Glo clos Gomi le ected tol eOmaemorOn cereee en Urbana
INIT IGIS JiEVMING lel. Saco csmatoerd ace bina oC ae iCrcIe mma eS Spring Grove
ANOKGUISISLOIS) 135) INIGI 8S MON GUNS coogcacous bd siasecucu ce eon Cee aot aetee Chicago
PANE XCAUN ID) FRE VEGI ES AUN eye ertentiares crelistorete cece asia syaiciom ys Ai? Wiesel a evat teelecoe Macomb
SAVVEOE e ACS WIE AURSD pene reer Oa ou er RHA OT RUC TRS oR Mes Moe Springfield
CAMRIRUOE, “10s VAIL SD. O-ANING DIS oa ga aeras Bao bcs pin eo aa GoD nee arc Rae A _. Belleville
VATE TE TAN TIS S IVUCIKSTINIE ES Vi prsersy rare cite Ssloyeieie ty Seunisi elses ema aiae cele aden Champaign
TAO NGA Sw ey KOE ClGS neat hasfetecalsepeevtestercrcitve’ “olerees rel nsateilacieie Bloomington
IL ANTOIRUA, TBs USAW INS) overae Octo omic om Sic OCS orci areca eee eect erates Taylorville

ANDREW S. DRAPER, LL.D., PRESIDENT OF THE UNIVERSITY

STATE LABORATORY OF NATURAL HISTORY

SCWEINTIIENC, SIVA, 1n6OR

STEPHEN A. FORBES, Pu.D., DIRECTOR

CHARLES A. HART, SySTEMATIC ENTOMOLOGIST

E. S. G. TITUS, M. S., FIELD ENTOMOLOGIST (to June 30)

F. M. WEBSTER, M.S., ASSISTANT ON BIOLOGICAL SURVEY

A. J. WOOLMAN, A. M., AssISTANT ON BIOLOGICAL SURVEY (to September 30)
R. E. RICHARDSON, A. M., ASSISTANT ON BIOLOGICAL SURVEY

E. P. TAYLOR, B.S., FIELD ENTOMOLOGIST (since September 30)

_CHARLOTTE M. PINKERTON, ARTIST (to August 31)
3

CONTENTS

ARTICLE I. THE DRAGON-FLIES (ODONATA) OF ILLINOIS,
WITH DESCRIPTIONS OF THE IMMATURE STAGES. PART

I, PETALURIDA, ASCHNIDA, AND GOMPHIDA:. BY ee PAGE

G. NEEDHAM AND CHARLES A. HART

noco daoeonos0050 000 I-94
IMERODWGIION G saa pogaates) obpoaonddene Socn bods nda ham ana ee Cogemmane redo I
ORDER EOD O NAT Aes ca) eee rarer oie asta eressteticrtich oj spec ravaisuasty Se uaenireton hs kvahs 3
(CGHaTaAGeTSTZCS Py lOZEILY NOMA LIAHULLES Nn Ne elciet eiele keke eel ee 3
LGOPELUTE SBo do OAS OSCE CUES Foc SODA DOU N OCC En ST Soa nDeerna cacao ters 5
Life JTPHO Mado eesusco dane sods ese: RE re a LIAN Rte ee RT ERE 7
ILiti® GYE!IGS.0500 40 Ha DOU OS OnE BHdOS ae ROSH OAD eD OFA OHNE pm may
Nymphal and adult periods, Saychecanate Spoacil nae)
Change of nymphal color at anciliar ANENGro'S'b coc osaAoOs osuGoosdwouUaT 8
IASON NS 686 Coons bug doun aoe gop osao pod Books Sem On toon aa Hane Gao 9
OWiPDOSIHMOMNs 69 6Aba volar coneaces-ooee done Guaees HHeadonmooeHm oD ma au SO ae 9
Nelative:abundance of nymphvandsimacgonepeenseeceececreee cect: 10
AGlulls el otsgae-toe no caamomao neon coed ise oon coe Crees nce mare nao II
inticKtomy Ot Oclomaia Cosenveel Ale ISlANaINA 4545 conc v0 dGc0 cuossoc0U ne AH 0000 II
WEMCPS JOE, CHAE COMPELDOS CHG? TP 3000 6090500945000 0539-000 6606 12
Nymphs inhabiting Various Kinds of Sttuations«.... 0.1 nee cece ceeeees 12
ivinceamoncusubmenrsedmeretatloner ee anera iia erica 13
ILIKE A HTS WOO Mono cadsages godsioach Sdpsougadooobsodeeaneamaooado 13
Wivingsconcealedsingmuumcdormsandybottom—- eer neeeer canoe cer 14
Nymphs inhabiting the Various Illinois Waters...........-+.-+.++--.. - I5
NEAL PS TTVENS ecto ercielvciepys oot neon ely chee SAGs cists» ats ate pistes | wise wale oid 15

Smiallenstre amSrcets cyte nstercvne Mera ache cote Rese rinae ieee oee., LO
LEV REG) a clei a bioee Bo ae ODEO OR Re ORC ET POA ETE NCRS TEN HeA 5 gate EA PoE RR (6
LEGO IRGUETOUS sa o6.0000 60006656

Pe eevsnsts rete ss icpa tate eae Simtel arcoeteren iu ieeven Senne cose cys 17
POO! Olt Ta fails Ge poo. Baron meg eee ae oe eanecE os Aistra ashe aaaneeeeie 17
INGy mn Sea SOO GA et wrsyarsrec else cpqunttacmusit dye wistesnus mules stele sresusieieis Maeeek Binese 17
A\GIWINIS: Shas. dako abe eo COO Coe Tee OO aoa RD eRe nRISe Tota e Recs cnie arais 18

COWACU TEE CLUES! RATE ao SG OCO WR ERG ARORA CEE OA UCU SORE EOLA CC Eee 18
CONEGHING 5555 cach ance WOec/8 AOS UGG OL OCS Cg ENCS Obey ru DO eB rar Oem nC 18
ES GIRVAN Caer re rei sere Pa stg oe soe lever eyes Orbe Calon mS STE Ne NHS NSP SE IA ce lela Reaves 20
ISeeaibaee le 6 amas Ot a Ga ee EH CORO ee ONE Ceasar aeccecG en Crer eo ies Cae pee heey aie 20

GHEY SHUSEOMIU A CLESSTUGALLOII A eee eI ee 21
Mlb Ire rnsy ring bnteee ver ssvarevaglsys rete rear cosy syayeses ns charter one leravare ens veruaveyreteravel cistia lalcitrsrass Alans 21
TROGIR), ad oGéeipod moomoo Rercton Soda Pot. Ce tens Sinise ee tal Reema 23

Key to Families

vi

PAGE.

INKfoN) NG edco Gags cod0 dann 0050 Good an60 obNd Doo UDCO0N doPoGoDODGGGHD 0050 7 25
Ta GOS ees ssss is Se assassin SaaS Oe Se) Oe SEE See OE EEE eee ee
Family Petalu std @ nr yacisi scr seveise osieetesonn oe NMS eI oe 27
Pian ily: AE SCRHATLE esl rele SS SRT EET LIS TREE 27
Key to“ Geme raictecs Sere cm. ain rstayes viniste telorsteverereisuerele ausrclcuede avalon alert) aye tek ea
TMA GOS ive erdievsichs sire kereitisseioitia mare evarsioetelenne lesslouetaeteeloreetclselonskste el serait 30
Nymphs 32
Niasiiceseliina sie arsjajars ares vearors «hates notes oloporsiiay slevaneyereioteiareles iioteds oanieci oastereh menetename 33
Ee pies chamial oc j.cic cee ectsie es cao cs crctotera citioiey olavesm oncictete ict Tacomas ate Velorenetet tee eres 35
BOyerlal .h.c.cc.4 008 « miealcnureievaiacsce sires Gre ojorsteneiss pie omioeasierseaseh te Geeta 36
Basizeschiiah x... cz sshusbueiacceuietevets. see uicbaatecusde ciate entttyan ae eral cree ase oaceene ie Oe ree 38
iH{cll tt me waga Are cece DEF OMA EMG COCOMADON CORO aS ODS ooGs aS'Sb000000 39
Kiéy to nymphs si ehh 8, ove alee Gosettstee cies! fie oe fs aye soos orate ee eee 40
PATNA K apsee iss ie consis rs elouayeee Boeke ud cueveiiaal ee oie jan (ets aheus al un ke esa rau ee eA 46
Family GOMBRtAO i. eres odiescd thes bo es oben Hol hoe eshte eee 50
Kieysito Gene tates isi cccise nd sates reise ent io Glens nas oe relelss oie Rese Se ae 52
TMA OSss «crstiive gro wie ole Gesnsde ever dye aryee coos buaieemieleranc reveporesePone 6/6] ACIS Oteeee SRR 52
Nymphs) soc esiaytns ore 4 sis recehers aiaiencisuatevels eyo, svausrs so ysreieventieserste oh tease) eee Ree 53

72 \)0) 0h Pipe UE eos One nne HR ERO DO RCCcrn coma crAGen Sap omc ds b:00-00000 54
Progomphus......... dsajselepeontyfayoeiere iehstal exouepora ei gasgey oilers eens ksksiene hel Spoon Rem 55
Diastatatomma and Herpetogomphus ................-.0ee cece eee eeee 57
Key tommy maplisidsoivieets. cs ocvciseceae cis chesniec sities peyote: o/s Seagal tae ett ea 58
laments: hc, jute aksste bansrnarenciels rela entele cs aetia connate pees ey tO eee eee OE 60
TGAMUWUS)iionctie aisavegiiosrtarterayet’svartieceioeramualonerone lominctleimenge tele eet eens 62
IDROLSVOROUNI NTS ooog00cceu00dac00c900000n000000 PEE ccoac | OL
GompPhusss sicicceicpecs! odur sedate wie aeelan Wieweiaieleraieionren Eaete Gallerie en eee eee 65
Tey tO. MYM P DS eraveretcielorctoverere ercte ete wren he oiesalee Suey -lovernionevepeye aekstet ate te eae 66
SPO Cles 254 aisjee yevaveseyaic,o cept myeiere evaneuaecen ie vee eine erereiais nel else) eee eee 68
MECLCTUEUTE rein si ecvese ioee tie Meche ter CterMRUEN Se HO Tia) eek eR Reo "eign eee mere)

ARTICLE II].—PLANKTON STUDIES. IV. THE PLANKTON OF
THE ILLINOIS RIVER, 1894-1899, WITH INTRODUCTORY
NOTES UPON THE HYDROGRAPHY OF THE ILLINOIS

RIVER AND ITS BASIN. PART I. QUANTITATIVE INVES- PAGE
TIGATIONS AND GENERAL RESULTS. BY C. A. KOFOID.... 95 629

INTRO DU GDION ion ahorcsass secctarsraa ehapirelelete ates 6.0) Sa ieaus eae ere Te Ee eee 95
Acknowledigements'.cisca5 dst hind Saran Once iae orleans persee eee Sake ee eee 96
THE GEOLOGICAL AND HYDROGRAPHIC FEATURES OF THE ILLINOIS
RIVER UBIASING sit nists manetoaiert aise trem ietsienda Rie elavoeia Aaa 98-251
LREOMUCLORY wail sian ce Caos Be Sears saiit Ry AES eG OR ERE eee 98
TAT dee ee SoA AS AMA ROMO Me OOM DOG G0 6.5 0.0.0 99
Geological Features of the Illinots River BaStn.... 11. cece cne en cee e eens 99
Dae 0) 0 eee mene te ee ee NU Pa eT Gs earn PA Go QiGtbiG 0.010 0 0 99
Glacial and valley Drift. 2... as. deme nese sisin scl ncialoertsecele re ree 100
eo) Va tee eae na are Acer aos, Semecmretend yo cous Bo 00 0000.0 101
Lhe Illinois: RIV CE SYSlCWES saa ices. 3 Bois dipaeie esc #8 eee eel eee Ie 102

Teength an diane ana och) Gis esally anaes) ole & oiate gree ele ete aeons een 102

PAGE
INST OUATIESS cae eaibooocoer ode cceodn Gracotorhoccerdten StOneEaaD ec aEomoE 103
(COMES dog BOO GE SINE LOGO OOM OSH ORE HORE Cre BCE et nce tae, 104
Disthibutionsotetr butanlesmecmmsrvcerrecccincreietecirearty cca srerctnienel: letter 105
UNO HOGG IRBUCF ISDH e.0.55.05600006 160040 0660 BODO HOO OHSS SODA bOONO 106
ANIME ClETESMISscconocse0 sacagedspceaon spetas ays state satan er ntoliote os Bebae ona 106
Elevation Ofsood=plain tyes sericte cis ote wrevereiea cision = suersis bits) elayevereim reise euaelere 107
PAT C Act Gum S UID CVs SI OTS jxysieyeyrscav sce sicr 2) ssevaicalc (etsce isis eye eis sim otal aise trenversra wees 107
aAnkahel Clateryeses pea sisseve orvsisisie) oa warais We lkclae 5.6 mess we aceysanaefeaye: ae eva teuars 108
Connections) with! backwaters... <5 s-ce ce naci cess sie vecae cecieseee: 109
The Illinois River Proper....0. 0.000000 POOR Ca ON 110
Direct course and undeveloped flood-plain....................-.-+-5: 110
Relation to river levels in the Mississippi River....................-05 16 e)
Dams and their relation to river levels at Havana.................... III
INAH oo co: ots Soke Deco CNS OD ORC IEEE RES CITC PTE cae Cl STCRCRE CSE LGac MCI IE CHO re eae 114
(@anagre mtperpasce ces oa cv ote vstaraies ei = asacaivisiocsivievace ers icwinlane drmaiereicawiaiels Mais Grama wate IIs
Wielocitysatalea Gran Gia <ercteyersneicteislor oy eiateres set sinfe el cise) wersja satsicuaye ethan Greimie 115
Mestimomyzotsteamboatmenteceeeresecercccicer cae acteeiac ccc 116
MES tSra teed avan alaipe rac s1ays axevty sicrs cvareye.sjejoncts: atavaveusvaie visio ayedete oi eyaiecs cterensy eels 116
IRE\ie OH itkoore| MNO INEM oes obo LasocHEUEee Gaakibedounna Doane orboeE 117
INGTON Oi CULAEINE (Ko) NET KWIN 6 6006 666000 a60000 000005 subuGOsebenAS 118
Comparison with current of Great Lakes................ 2... 000.000. II9
Ne Statement Om schroedetsilawarereetereeertciee nicer 120
ID IS@M ATE Chrencr eee aie eoe ees Slate lesa ie Nie emissary, Fisieisucugeave pare ereuereals 5 HA
rsseatia Eealllliepeesstosteveysaayoespevayes hd oy vale aera ec’tevey ar ayaya eoaiie sfaias ev ayrereroyat ole, sreyenavebatrolalayectnans 121
BOUNG ATES TOlpwatersle dycrnyrcjecicretsiereasicla soar eleieialvevnive aisles nore 121
SEARISEICS LOM UU TT OIS IE o.c ches occ eressyeraey «ve roneveyetn =: a/ai51 aimpopal'aysy i svmjeieiteahe: aie iers 122
Renodicityoburaimtallly ies cvertarss ae: s.cjoeve esis taie ciate evs sie aes eveiemune 124
Correlation between rainfall and hydrograph.................-...- 125
Sensonall chsimloninon Gt mM 5566 seaees capsenoaaecs oneonagucde 126
IRTWM-OlE. Jo Sadow ad CU CoHO GOS GOO RO A DOO DEC COER AOR. Sec cin nre ae aeIn 127
Situation of plankton station in relation to storm-tracks............ 127
Relation of flood movements to plankton..................c000000: 127
SODS: Oli, WONG Se Ie Seine Nooo Hen aoe OO erate Oe eae neae 128
Drainage lines and storage basins of tributaries................... 129
Wolumendise hate edi .i.i eter cc ispacss orepa tree overaese avacatey slarskepocimanetey a weer slots 131
AISIDES TOW corona mondo COE UR co BER DE IGOn Toor ooas Hot orned Gnor 132
WIGASITSITE NT SoG asoeatesesaccooe Udon cmt oom Gonoms omeacons 132
Comparison withyother streams ...4 4. .004-4- see see eee ce 4 133
Mascimum pl oodgdischarcerena-trcer cence ene aie 133
Minimumy discharges cy. ssisisjara Sets sislerceeiusinsies teaser eyo reheat 134
INesimentotthemlllimoismRiviet-rere- eee eee eee cee 134
Meveretusestatementer nec cee secretes sel inrerenrenrorml 35
Hydrographs at Copperas Creek and LaGrange................. 135
Compan SOnst errs spats yess ssc eoioie e ulse aiciaa) elev avs) shel nies chara 3.) wan enore 135
Effect of dams upon Havana hydrograph at low levels........ 136
Plransit ofpnlood Sea carats seas cistclayaceicye herue orssctetn ch rae ue osciamavsio tater 137
Floods and impounding action of the bottom-lands.............. 137

Bank height and bank-full capacity....................0.0005, 137

vill

PAGE.
Impounding action............... cr fet Aenean steno apt raNcaye an ea aa 138
Delay unirun=Off ascetic Relea ee eee eae 139
Durationiol ioverilowsr 2. hme eo eeene oe Ae eee 139
Effect of under-drainage upon run-off and floods.............. 140
Statistics from hydrographs at Copperas Creek and LaGrange... 144
The normals regimen ese deen peor Soe Soe ee One Oen er eeee 145
High=water period me ciMsnsacuisnccete cee eae eee 145
Maximum foodthany jmiccce meee creo oor Ra eee eee 147
MATE TLS Cis ecrs Seater stad stated Sebel Rea AMS or at ec 147
Low-water perlodiaha nace decane nar ee Oa e eee 148
Durationyandistabilityeesesener teenie shinai Sy chee 148
Minor flwetwatton's jcrts sate urate navn sciere cere eo aCe 149
MotalimovementiandirangesnelevelSeeeeee eee eer eon eereren 150
Instability of fluviatile environment.....°...............2.-.-0- I51
Description of conditions at Havana in high water............ I51
ATO Wr WA LE Test eel arabes capes Sle reais eele srcqarsiescreder sieve oem nene este eee 154
(Ghesrivierastaunitohenvwitonmenteanaee eee eeeee ee eeeEree 156
IRE ABOSOAGhINVAS Att IBEW sGcocaccccveods0e000000 aooned 157
Monthly and yearly averages of gage- -readings sace a? alevarenelea tee 163
lalyroliaopreyo Me COMGMIHOMS.6666c 6c0accagsnn0bon00 00000000 S000 0K 164
PATS OA hue tain neevbea ts ivan, eo ieee aera aes GLa et ae 164.
Mat BO Sire iae vere rheds avanale ats iar oie wile eve onle aiewotone see ahereceeion Ge aOR 164
1 Gal Col0l aR areata torn aniois MC aAO icon Bo 00.0000 165
Ooi Coley ane eee nA Aor or acetal cat a UO MeO TOS G00 cco 166
[td TBO Bsc vaves ee Havetesseve te ease aiecaversres saseae pero hae rers eT nee et eae ea 167
| Goa ¢(o lo are aa ht eae ete UCR aie it G Oo 0.610 0 6 168
TCP UAUUTE Shea eve i's Hass Se RISE RO Oe 168
Aslavtactominutherenvitoninenteeseeeerteeeco ener acre err ner en eerre 169
Temperatures records Aa.) gases Sa cto ee ee ee eee 169
Gausesloffluctuationsinitemperaturesspeeee eee eer eee eer 169
ANarowiey | Eyal Choa KEINE, ono 6500600000000 >= odbaneecgnna 000000600000 170
Monthilyzandiy.canlysavierageS meee ene Er Geer eee eter eran 171
Seasonal ‘thermograph [005s sea nae! ce erences mcrae nersineeuneleraeetare Seneca 172
Comparison of thermographs of different years...................2005- 173
SHOUMAES LUNG! lOYOAKONNN WSWOOOMANOIES 5 cos bo00 g0d0 00000009 b000 DD00 00000006 174
Instability of temperature conditions in fluviatile environment......... 174
Absence of thermocline. 4: asec saese-Cmene Oa e Eee Ee eee ene 175
swhejiceiblockadetininelationsto,planktoneeseeeneeee eee eee er eer 175
Iiceyconditionsjat Havana inirso5 n8qo nee ieee eee ener 176
OG? MIGUBDROWDETA, IECIBIOTS 36.05.9000 90090000 06800605 00006000 d000 000008 177
LUT OLALE Yad) eth Neneh dehaid aia ssstetNanavabar dete iA crclts We) raley Hote RORY eT aE AC RT TORO 179
Methodiofdetermination soos s4sc- saps sale losiecuene salce ere eer ene 179
Tim Gis RIVERS Wave everera aves ies shore cates a olernleiueer opel ouene lee er ere eye eye Se eee 179
SPOGDURAVIER Be soit lee ace ELS 2 Mee atleast Napoion arene dd stadt eae RE ciel en Crt aera 180
Phomipson's Wakes eda cae vispeaysleaya 6 oslo cteenetetelaye ayaa toe leleee eerste 180
Qaativiers Teakee ys cnctiay vetetetes sis teletahe ohertater cretion mkotoleT ote ele ceneeel ate ey Pot ere re eeet nee 180
Dogfish: Weak ey. je tuclee seein! ose eeiens or siosasiancininte Rucker oa cieetere cone eee 181

INEVERILENCOL Kea eko bape Some BDadMEotODpoDaooGOoUododD GUBmDoeasb Fodo.0s so US

1X
PAGE
TPIN@ISS ILEVEE: o cocan0008 » cos ben oop osoods cabousDSencDEsononECASaaneqSaGd0N68008 GacoodEeGcoaEoceo0 181
(Callow @F HOE WALES ror0 cco ceq cng acanosGe0aagnodcH ooanosSoDoob Soo HoBSONEDNDSaG0o00RO0R00N90000 181
(CAWSSS OH (WATCH 7o00 sonsoonon ca6ar0 sb 960 s990cn oN conopEDoDoBNAODEOAdRSOGeN99G00o89R0n000000 182
Silt in catches and method of eStimatiOn.............0ccsceesecceceecsacecrsnerereees 183
Solids in suspension as determined by Berkefeld filter................--...--+- 184
Silt and turbidity in fluviatile and lacustrine environments..............-.++. 185
(CHeetiane@l (COGP HOLES: 00080005095009900208000505606005006005068 EogI060Nd Good605008G058000000 185
SanneS WE CIA Raocree sop CAGE EC DUB RET Eco oocr Cod pCOREOEatoses soGoaneonococbasacocorea asdcoosdor 186
ACTH OWMGGCIGIENEIN IS o54950600960000000000000500000005000000009000055050000000300550005500000000 187
Comparison of chemical conditions and plankton at stations, from
AVERAGES OF alll AMEN yS@So0scoovsosacnqs00cacq0 59656 noaD996G0800000040G05000000050060 187
Residue UpOn EVaAPOFAatiON..........cc.0scoscenescensecseensecensscserenssnssseams crass 188
IRESNClME Hi SOMMMCyt\sos.005c009005G003565500000G900G0000d0 Hes cede bocaDHOboDBobbHoRooDBROHES 189
Ghlopiwereeserseteesssces conoscen 9006000900 dando 60000000 050000000 n6nd00000 eanGoBHO00 tees 190
Oxygen consumed. .......... 9060090000000200600000 090000000 a999000000050G0000000000000009 IgI
INTMPEP@FESIL ooco00000 500099 590000 DoobaGH00 900080009 066000 906056005000 60006000 do00000009n90000000C 192
Total organic nitrogen.............eee sere oposed000000009000 990000 00000087 000005000 193
AN terehn@yIGl EXTRTTRONTIo¢0000000009500000000008 006000 040600000000606006050600005000000000 194
Free ammonia.......... 900050000000 050000200000 9000000000000 pdbudGb0 Rdg: Doon oa aEdneEdee 194
INDISETLESIS 5 posoodonaco5500 niooodoane «60000000 noooaccaspea0¢ aoosgon030000D00000 {a0 900900 000000000 195
INITBFEIES):c055000;80800 cag000 000060 99060000N000000006 060000.a08050 995006088 20000900 690000 600086 196
SSWALS iad we WMMbTAONS TRa7Sie-ooscc0n¢0050009 onocoo09s0c0000D65G0000000000000000000. con006 . 198
Cities in drainage basin of river with sewage SySteMS..........-ssssseee-s0 199
Cities without Sewage SYStEMS... ........01 cscsoesescenseseceesseseensersees capsab600 200
SEWAES OF ClahGAEO) 0005000000000 00000000 000000000 sanbe000 po00n2022 cond9aDeco090000C 089 201
SWE Ol IPEOIElo5c000000060060006000608009000d00010009 49d06000000050000006 060060 ao0000b00 202
Chemical Conditions and Plankton PrOductiOt...vscrveee-coveserssasccones: Seeeeenee 203
Comparison of nitrogenous matters and plankton production on the
basis of averages Of all analySeS............-+-sccsseeesssecerecs cence: eeeeesseeees 203
INNUAONS TRIPE TPo16 000509000 cons n00G0000000 5500001000008900000900R000008 000006 Fa0DH00C 9900000 204
Spoon River....... Sdsdng tod sodoosdedcoqns8s0s0U-HesdoSHOHGoperenoasdasnn8 CUspEcC Baonenadecace 204
Q)WIRVEIP ILENE 00000000000650000000000056000800000000005000000806000 poboos pesdaxGooAse005000000 205
Thompson’s Lake.. ........2.:seceesees oe 9000000009000 p9000¢ 900000000000090000060 se-secees 200
Seasonal changes in chemical conditions and plankton production......... 206
General character of seasonal changes in chemical conditions............ 206
Comparison of the years 1896-1890............0..0sc00e 600000000 60606600088 a05000 207
Relation of chemical changes to plankton production................s100000- 208
Illinois River.............-.. 000700900000000000000 naggooenencanbenensas.qoae66 9000008000000 208
SPBOGM IRINVEiF,0020000000c0000 000000009 a9 n99c00900sn0 cHnoGnooBq0E000008 popd6006%00000% eases 209
Oitivier Wakereccs.-ceos-eens a arasielisieawiaisclgouaeetelaunesshsiseester ackeoseoteaseet onanbadosees 210
Thompson’s Lake... 00000 s0dv bo sdasseadleeeansecaecsss, 22
Comparison of nlaHkien, production one scveonall ehangean in Weare
CMOS SUIDSANAEES:cos00000000050000000 560000060000000008 onG0c0c0 HnI556005060008 640005 213
With seasonal changes in nitrates.........2..ssccssees esses 200000000 p00000000000 213
Mhe maxima m= nai nimUMI Cy Clehemeasresreeseseepsscinnroesioo loses: eee esseeeee 213
Relation to plankton maxima in the several localities..............-... 214
With seasonal changes in Nitrites........c..eseccseeece ceseee ceeceeseeeee veecenees 215
With seasonal changes in albuminoid ammonia and total organic
NILTOGEN,.....00 00000 o909600000000000 E0o0beececss6eca Sees oodtbes0 60 decuncoseaeceaes 216

PAGE
ray Hove: IMGTROMS IRI CIP 5450008600000000000000040007 SoacmaodaocosabaE000 000000000 000000 216
Iai IS yexayovaty IRUINIS Ie coo505c. Bandeobadsddade sapqouBodcodoad oBdes odaovoaad Goodandos Gosadooue 217
Iba) Qhwnihyeie IL) @ococa8n008005e0060 00000 070000060000 460040 aca0Ko sen000 DADE d00HN8 aC0000 219
In Thompson's Wak eves esc: sseesiortenrotncdeesceneascnescinesecesmsesetecaseamee se 219
Complexityiorthesprobleniesssensstossessseteseeeaset (0000600000 doa6c0 cd0000 220
Lack of a common unit Of MeaSureMENt.........-...0-cereeeeeeceeeestaeees 220
Chemical and plankton changes not proportional...........-ssese-seeees 221
Causes of absence of proportional correlation.......-......ss0eeseeeees 222
Plankton only a part of the total organic nitrogen............ ses. 222
Utilization of organic nitrogen by plankton........ ......... 6199060000 224
Observations on limnetic OrganisMS....-...:6-- seeeer eves: ponec0030 225
Cumulative character of growing plankton...... Gov00see COSbbNDOe0% 226
Some correlations between movements in nitrogenous substances
anduplanktompulSespa-csesntesssednasesctraesceteanseneccesteeeoieece eee 226
With seasonal changes in free aMMONIa.......ceceeee. seceeseerees cesses secre 227
Comparison of plankton production with seasonal changes in oxygen
(AOIMNGUNGa\eXoheconcenbaGacnos eadoonobmbaseRdaeanbe Geode" odd ooscqobdonn. EoslssSadaagecodGonaoande 228
Comparison of plankton production with seasonal changes in chlorine
in Several localities... cescnecessensenissdswsast ce coo spceseace sed snate ieopeeeeseeeere 228
Relation to sewage Of Chicago, etC......-..0.:seseeresssncecoceeerneesnsecesesers 230
Chemical anally Sesscsrsstsrecsoscicessscestescsensomse dances onan etisens caer eee 230
Bactenioloricallkexamimations-asessde-cesssccseeae eset see tease ee eteer eee 231
ANE | SIRKVELMEY so. aoobadepbobEde ocdceacns aobcEDEHb |ddEGEdes GdEeadoNe HHS 408 046000060009 231
WByenGlerejororte (60) (CrcalitteyNccossses55e00000060 90800 68000 0 B60061 DooaboDBaG0aGe0 000000 232
Seasonal changes in decay of sewage at Havana. .........sssseeeeseeeeee 233
Complete mineral analysis......... sescsseesseeee pogadvadeROOGG0G0 90000600. nDEs0 = 900000 234
Comparisons with other streams...... sssecseesecseeees severe 00900001 900000000 0000000 235
VFO Doccoccnsnenoboce psbheacACRSO oSGoAoEage. AqSe0H AeqoBeo DN aEdead aGauet condaGG9 eee Secon 236
Characteristics of aquatic vegetation at Havana........ pocconns: pooe0ee Heacwence BAD
Annotated list of aquatic plants at Havana................00+- Aro aoeREEGesbS 06600 237
Vegetation at plankton stations................ Go002s8do0s00, ood0a6 Gooohedoods go0000000 241
Dna Ein Ois MRA ertlssyadjawadesumecsscuslstiesieieeins nelscsc acuusadaneaeeeaenacce se eeeeeeee 241
IIiay Syero@In IROGWVEIE co peace dosage oc00NG60 900090008 daabG00EDGR5000.90000 O6000¢ ponons Gadec0009 243
Gay Qu whyeie ILE, 500000 cn000 0006200000" anatos GadGNs Deb abeOcHODSESSEbSHHOdEEOEOEGeGGe® coo Bildl
tiny IDYoeSIn ILA @ooac0 090000 can das oosocHnsdoobosmon 068 0Ga6ese00" nsaq9009 pedoaybosouaceécooqco 244
Ibsay 1 ovell| oxs} pli Soqs0551615000 cna 006006000 940000 05 dos Dodabo SasdoEHHseDenosGaeoasoo:GC0R0 G06 245
In’ Thompson's cake kaaivaties-iacarostoencsdslsueeusecueseensnnsme i ansehen eae eRe 245
Ia, JP lever, ILM,» ooudoooscops oso nb600 BUBUUSIDHy Hob peo ecu dou aeSbEbHandaoda on uecddes posode ance se 249
124 FW ol Ba A0) Ses ilone Ana nea sceie aaron seace sana nsoqaaananadons aemedacdandecoctaaneopasaacondcecoocotecos 0 250
INGIAUOI Ost ClSjatdla (tO), AOWES cpooa0cs aos sad ccacescosHscas0q9000009 N9D0G0G4000500000: Oa0006 250
Inapplicability of Magnin’s ClassifiCatiOm...co.....c:sccsscecceseeeseeseescen scene 250
IPGInese SCHEV IS AV CHI 51501, co0500050 95558 5d0000b00 conDae bovobeLeRbsebadcoSodcoBoddebos so0000900 251
QUANTITATIVE INVESTIGATION OF THE PLANKTON« +. ceeeeeeeeeeeeeeeeeeee ees 253-574
TPAU| XOIErgcosconases bopacadasaooqoH nsonnebbon0s soonoo900950400DNeGonDo990NGG9DBEEGCOUBOOSDOARDOE a00 AER, =
Wethod Of AC OUECLIOT siassroncse sane a scenseaasec nese sesecartooecacredeseciseneeen ee ee eee 253
Changes during progress Of the WOrk.............csccseceeeseccescesceeeer cesses eesues 253
Smithvoblique-shawlimethodeccusesssmseedcecnsseeeesck ere ssiceseeeee eee eee ereee 253

Pumipimiethodercsscarcsscsescsecscccseessecsnes cones cis ceeceeetine sae ee hs aaee see eee eee 254

nel

PAGE
Preservation And Measurentent...c..ceecccceccecerccenccccnccnecscceneeeccenceeseereerees 254
Fixing and preserving fluids...........cceeeeseeeeeceeteeeeeecee eee eee tee nee eeecee neces 254
Measurement by CentrifUge...........cceecceeseeceeteeeesee cress seen esses eereeaeeeeeees 254
Method and extent Of its USE..................00seseseesceececnecstcncesceet enc er ees ees 255
Comparison with gravity method. .............::ceseeeee eee eee eeec eee ceesee esc ees 255
Statistics of decrease in VOlUME.............2....ccseeceeseer eee sssee serene sees 255
Factors determining Gecrease..........c.ecceeecereccceserseeeseseee ees ner cen sereee 256
Compositionyofsplaniatombeseses eee lee smersiettee ene eee release eee 256
Sill sco nnaccnonasocoa9c0s n0009909900000G0s 009090 958 oP DNC cONDoUND.: EdoeBDGeoDeodaoa9000600 257
Comparisons with results of other investigators..........---2.:.ssessseseee eee 257
Formula for and computation of specific pressure.......--..:.::02 seeeeeeee ees 257
Effect upon plankton orgamismis..........-..-02e-eeceeeeenecneerseeenece: concer ese ees 258
Priority in use of centrifuge for plankton measurement.......-..-....----+- 259
Silt, @SWIMNAGIOM ccoenanosadoqc0e osacesecn GondnabseHooce 556eeq0905e0400085000de60e aonoo0R0000 260
TMae® COSA Oi iS iNCti.09600506908090009000090008 aps DoDODSEEoDOB GOTOH ooDBBDRBBoEAGEEIACASD 261
Gorrection by computed coefficient .......-......-1-cecccecceceereeeeeseereeeereres 261
Computed coefficients Of OUT MEtS.....-. ...0..-eeeeneereee eee eee ee concen eer eee eee 262
Inadequacy of such means Of COrrectiON.......--..e.seseeseeeeeeeee eee eens 262
Determination of empirical Coefficients............ceseeeeeeeeeeeeeeeeeeee tee eeeees 263
Progressive clogging of the drawn Nnet.......-.---+.-eeseseeeeee eet eee ner eetee eens 263
Reasons for adoption of empirical coefficients.........--.2:+..seseeseeseereee ees 264
Volumetric Examination of Plankton of Channel and Backwaters.......... 265
Plankton of Illinois River channel.......... nee mectehecechotr ear etc s aaaemne eae dess 266
Description of locality of Collection. ...............ccccccecceeeeeseeneceeecseenecens 266
Modifications of methods of collection at this station ...............:..c00000- 267
Ghronologyrotcolllectionstwa-cc-sce-cccsseenee eteece sess eae ests secseseeeesmesesse 268
Local distribution of plankton and its relation to limit of error in the
TANENO GE) meoancsoaoconres000 dboansnoascncHo DoD cdo HOoDSADNBADSDOAdELGBIDODNe GoooboDSRDODODS 269
IR ESN Ot GUNSie WAVSSUSANION Sho cascontecsoccocaosesqs0ne3enGs600s99000008606005000 270
Discussion of Reighard’s method of computation..........--+::.s:e000- 271
Eroblemupstatedmtorglliinoisienyera-nseserecrecscereee ceeeeacecerte tees ae: 272
Longitudinal distribution of plankton in Illinois River................... 273
ThESE TRON AACE! [VOR ccoosssccacooscassnoonoseadqoacnneases eqe0n6o0000000000 273
Comparison with Apstein’s results in German lakes............... pfobes ZA
sRestetromutloatingsboaltaacccc seat eta csticsoetcssnesscasumeetessace men esaesea 276
Companisonsjandaconelusionss--a-eeeeee cece eee eee eee 276
slestsiiromiychronolopicalisenteseceeeeetattes- eaten eee erence 277
Test in traverse of river from Hennepin to mouth.....................0. 279
MIGUNeGl OF COMETH. cosccc00sa05s0800e209480008 connoopeASovosoaddeS 9008004 0.500 279
Conclusions as to distribution in river as a whole...............000.-0 280
Sources of error and disturbing factors ................2..0.00.ce0eeceneee 280
tte chomhnydrographiceondittonsierereeeeeteeeeseeteeee eee eters 281
Distribution in minor units of environment............22....sese0seeeees 281
Transverse distribution of plankton in river......-........cssseeecesseeneevecs 283
IREIAVOM OF GAS tO joe valk osonss055 escecsasonosatooonnssadoscansannca9000006 283
Plankton in cross-section of river at Station Eu.........:ceeeecseeeeseeeee 285
WaTeiioms tha jollannllfnorn jae T1eVFs154006e2502000 000000 009602000000 0820000—0000080 286

Variations in plankton under one square mete?........ ...-..s00eee00 286

Xil

PAGE
Variations in plankton, enumerative method.................. 287
Plankton in cross-section of river below Spoon River. ........ 287
IDE Oe Syoororn INhyeke aiexal Ohorhyere IWAVKS.55500 0006000 0000000000 289
General summary of data of distribution of plankton................ 289
Validity of application of plankton method to streams. ............ 290
Plankton production in Illinois River channel....................... 291
10a sic) ier tee en GES a ANG ater In Olad a oceO HOO UG Ae oO ROtOd 2000 291
Collections, statistics, and hydrographic conditions............... 291
Seasonal distrib wt Omi scales ey ee vale elalerae evar exueietet stee een 293
(COMMPEMISCMS ANG SUITWITEIAY. o50060 6000000000 0008000900000 00000006 204.
1G cle tae cee a es Sy one Rn Ea Pe IRA ING APNE Ac Goo oC 295
Collections, statistics, and hydrographic conditions..,............ 295
Extermination of plankton under the ice in February............ 296
NVI AOITANCS Ci WErAMAll OWNS, 050000 000000950000 00000000006 208
SASMAGION jOUIISS TM |WMAEGs cctococccs0c000000 s00000c00000 DOs 0008 299
Phenomenon of recurrent pulses in production.................-. 300
Discussion of the August-December pulses.............-..-- 000+ 301
Comparisonsjandisummatyaeeeee eee eee eee eee Cee erence 306
Wn TESS Sard Sie eters cheated easisehi eens owoay rad ae REI ECE 307
Collections, statistics, and hydrographic conditions.............. 307
Theswinter plankton. 2.4. ojos cn oaerectes cletemcne eevee eee eee 307
The: vernalipullsei ce saiyenshe saree tiene oreraevers Cho sis, ols Se aCe eee 308
Discussion of May-August pulses............. 0.00. ceee ee eeeeee 310
Aotrenm ne! AOD. 05600070000 000000 000000000 Serene s 9.0.09 314
Comparisonsjandisummanyaneerere eee eee eee treet eRe ree 314
1 OU (clo Jee Rene ate are Sean Ier es Re mee a MN AEN Go 6 boo 00.00 315
Collections, statistics, and hydrographic conditions.............. 315
Plankton of. first halfcyéans cnc :cccurens cesaceneer cienose ore nena 316
Discussioniof July-December pulSestseeeeee eee eee eee teers 317
Companisonsiand sumimany ene ee eee erence 323
Ti 1808 dias date a eens ele. cia e.8 Mee es cet rai eee eae 324
Collections, statistics, and hydrographic conditions............... 324
Discussion of the January—March pulses......................--- 324
The vernal pulse in April-May. . a BRB AR ME ESonnoocs 6° S27
Description and environmental condlivore. bbD6002 6000096000 0000 9327
Factors causing the unusual vernal pulse...................... 328
IDTEE OK Woe! Om WerMaell OONIES> 56050000000 S000 00 s00000 0000000" 330
Discussion of June-December pulses....................... 0055 331
(QOMOLITISOMS BING! GwheWONEVAZ656600000600000000000005 0000000000" 337
GOW ictc\o ay Ae iY neste An re rier Mn NER Mira ors wou Coe Sood Kiad.otc0 60:0 ¢ 337
Statistics and hydrographic conditions..................-..se0:- 337
Discussion of January-March pulses................-. +2202 eee 337
Conclusionsfand@ comparisons -a--eeeieee eee eee e eee ener 340
Comparisons with tributaries and backwaters...................-.0.- 340
SpoonlRiviery Station Viana eee toetr icici eeierertnere 340
EnvironmentaleconditionSmyssaa eee ceo eee eee een 340

Goll Ct OMS ose evere ey sralisthievohars (evetorswicdellaun stetotwte a) etoteteretaxers OMS RS ree trerenee 341

PAGE
Plankton epre duct Olle gesaeracrecte pein roses atneielace at secioes aletatanatetenete tavern cnete rel oh 342
Sow Slo OSes Oa Rota Se Oca aA CORO CEC RCE Cn LER eC RES A ies Cache 342
INCU itstoy is. Sod Ont Ee oine Urea Gin orinaai tro res ian ari ecRMenes e ecio eta One: 343
Causes of the large autumnal production....................-- 345
LN BESOO— OO Remar ere cpa TTT ree int aa ars Ain aS 347
SUTIN TN Ap V pavers cays ahced we ene acuey ossasr aay erotestee Ta Suecusnre eran wah Stara ets ere eecnat ea emersteters 349
Ouiverseakes StabiamiGagnse wesc fs thy everett ter. ice baicee ae tac one rere 350
IS raWitomanemiall COMNGCHBOMS, cooodo000cenosb0000000000 0040460000 K006 350
COMMBCHONS Wo Aoi Sect analss Ra S Oo CPO HISLAR COMUNE ROS Mea en ee Mic Ne oo 352
Rlanktonyproductionisiy. ser.ns scr ho tuskiee emis Saha essinc euansne meer 353
DS TAPETS OU merece erey susie acuar ere ect eh ay Get nie Mt eae ation heh MUS SENe eee 353
Mir OG Seaestersves sa teleestocsxonseey sloseces pease tasetater ar ciaur ahaa thee ahiGhebetd seis aocarnes 354
livel “isto Osis Ge Gers Sy UO DONS UES Ole GU to Ria CLO IS FS RRC EE eRAIO OP Len ecciae 356
Comparison of plankton pulses with those of river............. 356
Cause © tinereasec! joroGlUGHOR coccoovcocagg0coodb0 000000000400 359
NiBRU SG eer seein ee ttey Acycrerecre heer cUare aiorareee leleanaicns Maimleieacnetsl terete 361
HAW BOB ere aeke Cin ere xsiee seo eye alemdar repent mlcl ere aan rave nie Perseus a aie era 363
TWAT SOO feverscee ever ce estes Soeanred salah ceeib ow staat aragoterctereoeiapincaet ae Aieveleticlatece coeciass 366
Do ghshMeake nS tationly ncenucscsseves reslsl seis aslarsisysis cceleisclevsies ders ereateve, ole 367
EMViCOMMMe MA COMGCNMOMIs ssccc coos cpad000000000nnn0 000000000000 367
(CONICS. ascrrers cintoisc nrstco ee ODOC Nm Min trae ay ar re cnercira ire aeeee 368
lam tonpproduchones ea ycetecranveseyelsors oe eiceietneme ema aeret sate eerie aye 369
[MRT OO Gysecteesvcees) )spets esscney spoiavevauchs oe wie Stas Cees Sisomeis ms euast cleo ncaa ates 369
TTS Gy Paee states eh bares series re ie Teicueore vate tore er a sarere ere hare aes sneer ore ei rch ee these 371
The vernal pulse; cause of acceleration...................... 372

Similarity of course of production to that of Quiver Lake....... 372
Relation of local factors to dissimilarities ...... ............. 374

IDSSE Ot Inifaln Wer OM jOROGIMGHOM. cos cc00000009000000G0000000 377
Companisom writin Owe ILAKC,.cccocccoodn0s0c00 s000000000800 377

Tide ROY / so oreo GRO BOD Bic te ae a ee EEO Sots Gus erent Cat peace 378
Summary of relations of Quiver and Dogfish lakes to the Illinois River. 379
nnpOminGhinye THA CINON OF JAVKES,50c200 0090 000000 d000 age ss00Gna000 HGS 379
Sflecthofivecetatione.ciigeasnerisae sues uricas wamets aetna aarrstale 379
Similarity of movement in production in lakes and river............ 380
El aoa lakers talon Ks aryacne ne sale ste eat ot ecer oo sheaece Stunts aaleraeiatere 381
EP mivsronmentalmconditionsSseeeeeeee eee eect cee 381
Colllleciiiontsaek paso sia niobe monre toi a Oe aaron tabs ee criterias ree 383
Blanktone productions aaa sess serine ae acs ie see wiekacyeom ce rere 384
[fin SN erates yore Artie leer sc) ate ASS acts aaa Sekausecencre aver es 384

DTM OG OPE yee avscch a i Too etnies co arenes, ser evayey ten esnes neeayaticl 3 avasta Mtevaliots 385
lEhrehorAyOOne COMGNMONS coe coc0 00060000 0660000000 0080 000006 386
Contnibutionsstowthemniviensenss enact eee ee aco teece 386
Similarity to other stations in movement of production......... 387
Sudden decline from vernal pulse..........................00-. 388

lm Bopp oog Go yeud ad bonmaT ome a como Od ORCS DOOR AO eaed SHO cmoeS 389

lin USlisecb oseuoss sey oonecon no debone ndiates Hoek rename ceca mancodcT 391
SUMMON sooo .c00c0se avon DoDCSHo0b0DDeDaD0DDU DU CODD DD ODDGDUODND 391

PAGE
Waonijesons Wake, Station GCGracacclsg coos cgoodes00g aban x bes00D0000 392
Dini avon nttelll COMCIMMOMNS.. ooodaaccnoo600050 000059795500 0005000006 302
Ebydrographicinelationstomtneniveleneh eee heen reece net rrtr 393
GColllic@ tions. eats see ele eel Geechee rare ne Cale ney SPA Le ot eee Ue ge 395
Plankton production in Thompson’s Lake....................0000: 396
Way LRQA, seh aha are sete tos cae Mor ee otaye ora Ora aya MFO S ea ER 396
MTN ST SOG is yes sac sccleatelc she ushtenal tobe forsestet ual te eters aes erates eee eee 307
Contributory relations to channel waters.................... «. 3098
Similaritystoyproductionelsewhere seeeee eee Eee een enne 3098
1 oe (cio Ott rnar reine cs Marie enone tare WH oO yaicdn et.o1d-6 5G G.0.00 0 400
Hydrographic conditions...... DIE Rao A LOE Sore good 5/000 b:%0 6 400
Discharge. eleven ceases oe eee oe Cee eee 400
Contributory relation to channel waters..........-.....0000- 401
Effect of access of channel water in lake.................... 401
Similarity stosproductionwelsSewherenene sere eer recreate rer 402
als Coley eee tee ea re eR UN MN Henrie DPR E ONS. ti6/05-6 0.0 403
BKChrOeAjMeS GorVEbtRCMS.cocc0c0000s0090 90000090000 000000500 403
Contributory relations to channel waters...................26- 404
Simillanityatoyproductionkelsewhienesennereeeaeeeeeeeeeernre 405
TiS Sie ckaiwncleen aire anes sect enefiahisesheueisplatnciee sinlectin eS tae See Eaeete 406
ElydirographicsconditionSteeae ean ee ee eeecete es Ceceertceeerer 406
Contributory relations to channel waters..................-... 407
Similanity toyproductionyelsewhenekmeec cee eee ee nent 408
Fol Kool ae RIE re ara eto Cin ineart rete rene te aS Io Gc O no 610.06 409
SUMIMALGY 5.4 he ics Yaad severe arse oe olatbetsite acer er oleic ete eee 409
Relatimesproductionta deg c.gesis-vaterssosieuse ae caer cleiers ore eee 410
Seasonal changes in relations of lake and river................ 410
Ico} oxoroHsKolToVes UINEMOMN so oc 50 005000000000000>b000 00000 0000000009 413
Simiullanityitosproductionkelsewhenceny reece cere 413
Phelpsiealkes Station Fw ieee us ieevevs tele) occucemeberct t=) Wate) torso Pa aeepeae 414
Environmentalliconditionss..q6-2 oc eee oer ereeee 414
COW@GtiGins i si anes A aioe pepe rsaye) soc tewnesietocre ohne CEE ree 416
Planktoniproduction\yc.sae sassoeciesen ies) cose eee ee 417
Ios (soy a ra Me siege en ee enn eM ROR earn oo dignoe O06 417
WRT BOO) es Aa As, ee ater a alee aaa ercee SALAEPe ae 417
Hydrographic conditions............. aI ate ic'o.0'0 © 417
RNelatrons#toxchanneliplanktoneeeaee eee cee eee eee rete eeee 418
Similarity to production elsewhere........................-... 15 Co)
ein Rolo sue cIa iene a ee eMa Latin anna ceraeR NOTA Se Bein cAasiaa tio’ ab 6 4 421
TTA OOS ak ckara estes om fae eninge aoe releiecenl sranst lel eWeesveissea inde Mee yt Rete 423
1 GoUE (ol oly ne Meera Re ERE SA RoI NR ORIN toma scar nA Wad Gp o.00 06 426
Summarys sta ene sls Gar sere eee gras wi toned Maser esl sleleehes GIee ee eee 427
General comparisons of years and stations......................-.- 428
TBO A calc at eter salen svs/ arose ile vevetiahe tate eis] SEEN Sey ease lope apenah ee paves ace a eS 430
gam oR ooodoO ODAC OMe nocd ges oo ODY Ono poocm cD odo co.dd c6 a coon Agi
Sele Gileioend meee ecka Monts macaramad ca Ua KOO Geo OOR Ore e090 O° 431
Effect of stable low-water at various stationS.................-.. 431

PAGE
iso Sean ghdas SOONG OSE, BUSS Hera ETON GSH NGO eaamnae acon aaetonn 435
S tatiStl CSrpscyeme iors peters ssar eres eteee aicarieliarcsstt alate eurantarste, snus ieutegemuel reyeuclaie wns 435
Effectrofmecunnent MOOdSeey. rss \ecoitcirces ciersnelciele raster tolele les aeevetot eave aes 436
Relation of production in channel and backwaters............... 437
IEC Oi coach wiiMIer MCMC. coon cuando 0600 bqueG000 Cane donDoN DUNO 438
iste y/a nomad Coot Ine CRE CO OEE See DOES noe aera noo. tee 441
SS He BTS UL CSE eae rere le ears noe wate Potierotic ah she fed tebansciototne sone ue otters Walsieeee crower ers 441
Nelatronsiombackwatersitorchanneleapeee saree cee eee e reine: 442
IEICE Ot jortoloaeal WOny WAIERPo 65000600000 0605000000 G000005008 442
Keates Glo SiGe Orc TOIL ho Cott oie rR eR OES SEG tne Che hea Ae NER en iT ere or 444
GYIEIR GEeS ate nBlOk oo Ua erao circ om Onis Ge Deere Re Caan oi cramer intr ere Ble, 444
ibhenvernallspullS ei casey ctrehachy seuss erevecieves sin sia ia ealeseyoyshie cistcimeuevacohiiete 446
Comparisonjofchannelsandsbackwaterseereeia cece eee 447
IsL0%0 \enoin dd OS a CeO REC IC RAS ODT CIO Oe CODD Cr ae ibn Peri on era OMe Cer epee 449
SHESGUKGS s gece agcnme chau go CEanide COLO ory oc Poel ERNE Sle Ceene aras RAUr aT 449
TENN SMITE OGIO 056.06 n5d00000005000000000000006000006 Soe AAG)
Gharactenizationiohwy cans sci eciye csi oe ere rere neie eee evcdiein stanchion Gueveseysi« 450
Gharacterizationioilocalitiesi-aeeeee eee ences 451
Relation of environmental factors to production............-...-....-- 454
Hydrographic conditions and plankton production.................. 454
SHASmMEME © We POON... ooonosowsgardu0ssobGEd cddewasa coun dood 454
IRIE Olt AeHIG sooae ano ade Ss HCUS SMG obo bo ne Mab onia ane Mercier are or 455
tie CtrOIMGe pth jectne sicieintsiamciyasssaorael baler) eiar a Sepa velevake whsneuavens ecehahs 456
IDOE OF AGO OF WHS WALIEIs coononsauodceconsoscssadoosaodaacuubanE 458
WAIGHS OF MECCM OIF. >c00cce 600000 00G0 00808900006 Senyeeeees 458
Time requisite for development of plankton..................... 459
Imjpoundingstunctioniotibackwatersseeaceiaa ss eater eee 460
Currentiandiratelotenemewalssmcraer eis ace a ieene aero ae saeco: 460
IDYORACH GUC Orr CHIGHSINN HS coo vo ped io a BHD ARIES 5 Ot anioe oT eam ld alae. 460
Fthectoimjaterotenene walle ysusacvsersiet crorraisesisegtertia sickens wo ecient 461
INetrette cto frun-ofaandsrenewaleenrnars aan ecmere ci ccrcem cite: 462
Fluctuations in hydrographic conditions.......................-.- 463
Importance ines uviatilletemviLonmMentesse ee eeeeeee aera 463
(CEN ONG)E GalGloxelSe nS oide motor sim ods > Weemereon Go ce oa oer teR Aron he 463
BSC OF rising levels Om EME!) . 656050 aca a000 60009000 0090006 463
Ee cuolsnisincaleyelsnnubackwatelsneretee reece rence reine 464
RECOVER yp ATO mie OOM ver deay che ste go neyo = onsiee uses caer Nein rer eee 465
Result @t cleohimimg NEVES. ccoccesscoa ocd e0ad000000 0008 gsH00c00 465
Production and total movement in levels........................ 466
High and low water periods in channel......................... 466
Levels and production in these periods during the year........ 467
SLUT TRA AY oo Someta cha Haro eee IROOM RRA ROG Gee IT Or eine 469
iightandelows water inybackwaterseneee areca seer cece: 470
Effect of season in initial stages of flood-fall.................... 470
Miemperaruneandsplanictonsproductonperee ee peeeere ree eo erceecee 471
Contrastotawannandicaldiseasonsee pepe eee eee Le ee eo cer 471
sbheavennialenisesinmremperatukeereeeeeeeerrceee coerce menace 472

Seasonal distribution of production and temperatures.............. 472

xvi
PAGE

Effect of temperature fluctuations on plankton.................... 474
Inearlycspringiol WoO. see eee Re Cee ie eee ee 475
La laterautumnvOrsreo7i-8 coon treme cece een TOC ee 476
Exceptional high production at minimum temperatures.......... 476
Effect of autumnal decline in femiperatunes semen eer ertare 477
IDOE Of TSUN OOMARY INCA FOUISES.200 000000000905 000008000005 050% 477
IDjHOCSE Ol WAS WAMUGI WESINESE, oon00 000 oo00 0500 co00G0GG NS UH OObOE 479
ightandiplanktonsproductionse- peer oe ree eEeE reece reernre ree 480
Lmpertection ol datas. .1-csaceac ena emerson ae eee eee 480
Production in periods of greater and less illumination.............. 480
Broductionyinkclearanditurbidswaterseaae eee eee ere ele tee 481
Production in clear and cloudy weather.................-e.eeeees 482
Vegetation and plankton production..................----+-- ieee 483
Greater production in vegetation-poor lakes....................... 484

Comparison of monthly means of production in lakes rich and poor

IN VEPEtALOM ck ee eeeic ee elec einem miler Gelatie He nian e eee 484
Seasonal changes in vegetation and in relative production....... 485
Combination of other factors with vegetation to depress production 486

(Cuvareintt AiG! (MOURA, WALES. 5500 can0 00000000 0000 00e0G0000n000 487

Chemical conditions.............. Pivanitls (acd. pias boa eee head 488
Corroborative evidence from Matanzas Lake.................... 489
Production in Quiver and Dogfish lakes in years of much and little

VP etatlOri iG iaeiainslnccekoesleueetete eee lel eae era ee Oe 491

Depression of production during dominance of submerged veg-

eh (OC nail er amie tees i teen cleat Gad C10 disc ove 0 493
Production in vegetation-rich waters of Flag Lake............... 494

Emergent vegetation a source of enrichment.................. 494
Struggle for existence between submerged flora and phytoplank-

LD) Celt eRe Cee ae aC er Se Ee a AS ns SIC SIceerci ty G-cl'0/016 60.0 496
Chemical conditions in the two types of lakes.................... 497
Impoverishing effect of submerged vegetation.................. 499
Obstructive effect of submerged vegetation..................... 499
Effect of vegetation on constitution of plankton........... ...... 500
Effect of vegetation on fish production..................-....25- Sol
EPPO AMINGATNE SUABOA dno09 000589 000000 Deon 0G 0n0Gs0 00000000006 502

Internal factors and plankton production .......................-.005- 502
Normal regimen of plankton production.....................---+-+-+--+- 503
No seasonal regularity in amplitude of production..................-. 504
Rank of different stations in production more stable................- 504
Desneesiofstabilityaimeditterenthlocaliticss-emeeeaaeee eee eeeere 505
lisithere anormal isequencesink production ae ea eeee ene eeateer erat 506
Direction of movement in mean monthly production............... 507
Predominant seasonal changes in direction.....................--. 507
Mheicyclichmovementiotsrecurrentapulsesmere rae reee eer eee oerertee 509
Necessity of brief interval of collection........................... 509
Suggestions of cyclic phenomena in data of other investigators..... 509
ISVS IN OWE KECOMIS,coadaeeocd0 cnogcodc000 ba00 0000 000000000 510

Xvil

PAGE
Affe ctedibysenvinonmentaletactors ries et eet ene ieee: 510
Approximation in time of pulses at different stations.............. 510
Normal regimen in our waters one of recurrent pulses of varying am-
lik SSH re yee aie cee a Neca wins ele vei ostons nese aerate lereseee elas: 511
Souncemancdumaintenancelotpotamoplanktones seen eeee eer 511
PLOblempStated naw nesae ace sy NR MR nN aie Noe oR eee 511
IRGIATOM Of SSSPAGS WUE. coo.0n b060 00050005 obu5 do ouUDdddcboadeano™ 512
IRGETOM Oi TimloMininy Sites. 5 od buacadcod0occud000 0000 0Gc0 000000000 513
IS arMMAAHOM Gt Omiver Gra coocoooclso cong cvan0c0cc00 nb00 0000 a0 514
Collectionsyandimethodteacnree cee Cee ee eee ene ancre: 515
Constituents of Quiver Creek plankton.......................25. 516
Comparison with plankton of river................... Teena ead 517
Quiver Creek a diluent of channel plankton......... ........... 518
Relative numbers of species in tributaries and river.............. 519
Ghremicaliconditionssssxqeho acne sc temas sass cae emerinesic acer e. 520
JE AUAITAH OM OE SOOM RING, gaoisccs coop code odyooueaeudodadooowds 521
Comparison of chemical conditions in Spoon and Illinois rivers... 521
Resources of Spoon River adequate for large plankton......... 522
Lack of time for breeding a cause of barrenness..............-. 523
Comparison of quantitative plankton production in Spoon and
WM OISORIV ENS eteyetstrs tate atcvervkee tee ze rie eeeccencieceiee. ee sienere actne 523
Bros mesulting trommleakarerandysilltan-mmereerieicelieeeee 523
Statistics of production by monthly averages of all collections... 525
Ratio~f production tes scrcnccae sac joes ate tos nade sees 526
Comparison of statistics of coincident catches................. 527
Cause of periods of relatively larger production in Spoon River. 528
Quantitative effect of access of tributary water formulated....... 529
Qualitative analysis of plankton of Spoon and Illinois rivers...... 530
COMBASE tin GoM PO OWIATOM. 5000005000000 00000000 0000000008 531
Relative development of different groups..................... 531
TEES Sarin Giactd ae ee TI O OCR EERO OR COWS CUD ACen Deca Oamioe 531
DiatOmMSs aye nsec na eae aise Oa Ae dae qeeeuee se aisles aisiaeas terete 532
IRJat AO OCG eronenaccigoed Bcoe aAoe CMa OIA OTIC cia sericea a arene 533
MARE RO SINE scons culo odduinivos cooa bnae CUDaDooobuee Roo COObOS 533.
WASH OICOLN Ot SHON IVR 5000 c600che0 08000000 b00090000 533
Gay PMO TEL sata aaa a ada UE tae it a Oca oI Ebon Oc Esai Apes 534
IROUAONEIS 6.48 8.5.qi- ecto alee emOaOmpn anes PodecoraD HOSA mor 534
FPTEO LOS TA Cass ars sees sissy yee eye a eee ET le SuSTe SV e aie tenors etaee a Saas eo 530
PMS EGER Vie me hse aed hee lave othe ae nt lcterel oredr aisle Iolo etal 530
CGomparisonkortotalmunmber otspecicsseerere ree teeter eerie 537
Companisonfoisseasonalmoutinen- eee eerie eerie 537
Contrasismneantumnalsplanktonneeen eee eee nee nreerear 538
Applicability of conclusions to other streams..................... 539
Effect of tributaries upon channel plankton....................... 539
Relation of backwaters to channel plankton......................... 540
Coniplexityzoithey prob lemper ners et eer eLearn 540
Imnpoundinesachonotiood-plainseereen eerie reine 541
Anmnomutrotimpoundedwateraeeer renee ae Geek 541

DuTranonroisimnpoundin Sepa merer errr er erie tere ctor 542

XVill

PAGE
INepresentativelchatacternotougdataleene erent eer eee eeeeeeeee 543
Predominantly higher production in backwaters................... 543
Causes of periods of low production in backwaters ................ 544
Summary of statistics of channel and backwater production........ 544

Incigenousiplaniktonjofachannelaeeseee eer ereee rere ee rer en Tre aes 545
Generalistimmainy, jcc tee saci ta ere eee un eee 2 ee 546
Total annual sproductiones ao saee saaee ace eace On ee a macene cee 547
At Plavainay iin cays shania saver en acshetacte tar!) crater eye see aN Gee ee 547
Ae mouth Of IVER sale uee voles a wiv nate nek ener Seen: 0. eee 548
WATENTIOM TiRONEN WEA (TO S(EBF5a00000000000000 0000 000000000000 0000 v00K 548
Total annual loss of organic matter from Illinois River.............. 549
Determination of total production as affected by leakage through silk
MEdcaso000d00000000000000000000000000 Do00D00 po00800000000000008 549
Volumetric determination by means of filter-paper catches.......... 549
Ciraracisie Oi Silke thn WNSSS CAWKENES 400 0000 00000000 40000000 eno 000008 550
Filter-paper catches not suited for volumetric work................ 540
Confirmation of my results by the work of Lohmann ............... 550
Methods of making filter-paper catches............-.......ee000-- 551
Statistical data of silk and filter-paper catches...................... 552
FRAEIOS ace lees bine GAR se ieee, cee eters sate a acvatte Auer e Searels ee 554
Seasonallichangeshinwratlostene heen rere e et Gore rece ore ecrereerr 555
Volumetric methods imperfect as a test of productivity.............. 556
Comparisoniwithyothembodilesioi waten saree eee eee eee eeeeenerneree 556
INCSONES OF COMNSIAIIS CME. 640¢600 0060 0090 0000 9000000000800000006 557
Comparison with» Danubex(Steuch)pereeeeeacee ee coer eee Er eeeee 557
Comparison with New England streams (Whipple).................. 557
Comparison withs2lbe(Schorlen) eases ecee eee ee eee eee 558
Comparison with Oder (Zimmer and Schreeder)...................... 558
Omission of comparisons with lakes................-2.0 eee eee eee 558
Does geographical position determine planktograph?................ 559
Comparison of maximum production.........................0.. sees 559
Statistical! datay nic, svmesse pevesysrsius aveieisiels = g/ele sae salts nea Ree 560
Relative productivity of Illinois waters............ ..........+..... 560
ocationofseasonalemaximanrre 4s eeree asec cen eee eee 561
ECONOMIC \CONSTAETATLONS Ae ele araes ciara te clos ei eae ele EOE 561
IllinoissRiversasiaysourcelofwealth see eeeeaaeeeaccon ee ieee eee 561
Walwe Sov Gowers ByaGl TECTEAMCIM. o.45.6560.6000500000005000'96000000 0000 0006 561
Are resources now utilized to advantage?...............- 00sec eee eee 562
Relationof planktonstownshereseeeeerreeisescicecrcekicr lier acer 563
INS foodsotsfish Sw eccicmc ascension saci ois Seite) eicieeer Tete keri meee 563
Importance of knowledge of plankton in scientific aquiculture........ 564
Comparison of annual product of fisheries and plankton............... 565
CSHAGISOICR GENES ban con0.00c00ge0ed 6540 coon code apa900Dne2 Gab 00000008 565
(Coynrssnenvelanee) ihe CEH ob 05 oc000000000009400000 b400n0 90 0Dua DODD GOOC 566
Annual wastage and fish production ................eeceeeseee cree 567
Suggestions for utilization of resources............-...-++- +++ -++-e- 567
COM HURON S oho'ncagc000 cons coved ooobsaGDGo900dONnODO0G Sed0c0n700 000C 569-574
IP AHUDS cone dsdeooso cdo dos bo0dd 4060008000000 6000 00000000 000000000000 575-618
[TT OORANIAEBY 50.00.5006 8000 0000 0000 906000000000 000000000000 2dd000000¢ 619-624.

1D GNA GRCODN Op IDL /IDS, 55 gad coosaneupose bod OG O0dG0000 0005 5000 625-628

Dr. Charles A. Kofoid, the writer of the accompanying report on the plankton of
the Illinois River, was appointed to the staff of the Illinois State Laboratory of Natural
History as Superintendent of the Illinois Biological Station, July 1, 1895, and con-
tinued in that relation until December 31, 1900. Elected Assistant Professor of
Histology and Embryology in the University of California during the summer of the
latter year, he received a virtual leave of absence from that University until the be-
ginning of the January following to enable him to complete the collation and tabu-
lation of the data of the Station studies, on which he was then engaged, and these
materials were sent to him at Berkeley, California, early in 1901. His paper was
thus mainly prepared after his formal connection with the State Laboratory had
ceased, and during his residence in a distant state.

Grateful acknowledgements are due to the University of California, and espe-
cially to the successive heads of its Department of Zodlogy, Professor Joseph Le Conte
and Professor William E. Ritter, for the privileges accorded in this connection. without
which this report would necessarily have been prepared, under embarrassing disad-
vantages, by another hand.

S. A. FORBES, ;
Director of Laboratory.
Urbana, IIl., October 10, 1903..

BULLETIN

OF THE

PEEIN@IS STATE LABORATORY

OF

NES TUIR IE, Toth TOI!

Ursana, ILuinots, U.S. A.

Wor Vil. NOVEMBER, 1903 ARTICLE II.

THE PLANKTON OF THE ILLINOIS RIVER, 1894-1899, WITH IN-
TRODUCTORY NOTES UPON THE HYDROGRAPHY OF THE ILLINOIS
RIVER AND ITS BASIN. PARTI. QUANTITATIVE INVESTIGATIONS AND

GENERAL RESULTS.

BY

€. A. KOFOID, PH.D:

—— i —e

fn,

Articte [i.— Plankton Studies. IV.1 The Plankton of the
Illinois River, 1894-1899, with Introductory Notes upon the Hydrog-
raphy of the Illinois River and its Basin. Part I. Quantitative
Investigations and General Results, By C. A. Kororp..

INTRODUCTION.

When the work of the Illinois Biological Station was be-
gun in 1894, it seemed to the Director desirable to determine
as far as possible the normal routine of aquatic life as a
necessary basis for the detection of problems for investiga-
tion and experiment, and as an indispensable background for
their adequate solution. Such an investigation demands not
only the discovery and specific determination of the biological
population, but involves also the study of life histories, seasonal
changes, and mutual dependencies of the assembled organisms
by quantitative and statistical methods, together with a study
of the environment and an analysis of its factors. The plank-
_ton presented itself as the most available and concrete assem-
blage of organisms to which this method of study could be ap-
plied, and it afforded, moreover, a problem not only of prime
scientific interest, but af&o of some important practical relation
to fishculture. A presentation of the most general results of
this investigation of the free microscopic fauna and flora, or
plankton, of this typical stream of the Mississippi Valley is the
object of the present paper.

Inasmuch as this is the first of a series of reports upon the
plankton of the Illinois River system, it has seemed advisable

1. The three preceding numbers of this series, all by the present writer, have
been published as articles in the Bulletin of the Illinois State Laboratory of Natural
History, Volume V., as follows :—

Article I. Plankton Studies. | 1. Methods and Apparatus in Use in Plankton In-
vestigations at the Biological Experiment Station of the University of Il]lingis.

Article V. Plankton Studies. II. On Pleodorina illinoisensis, a New Species
from the Plankton of the Illinois River.

Article 1X. Plankton Studies. III. On Platydorina, a New Genus of the Family
Volvocide, from the Plankton of the Illinois River.

96

to treat with considerable detail all those more general features
of the environment which pertain to the river as a whole, and
which must therefore be considered not only in the discussion
of the plankton of the river proper, but also in any investiga-
tion of the bottom-land lakes and marshes.

From the vantage-ground of the present development of
plankton methods and in the light of the experience gained in
the years that have passed, many deficiencies in the work will
be evident. To none are they more patent than to the writer.
Problems everywhere crowd for solution, and the desirability
of additional data and supplementary work will repeatedly ap-
pear. In a general survey such as this, many statements of a
more or less tentative character must be made which future in-
vestigation alone can confirm or invalidate. Indeed, one of the
principal values of pioneer exploratory work of this sort lies in
the fact that it suggests new fields of endeavor. For the solu-
tion of many of these allied problems considerable preliminary
work has already been done, but their full discussion falls be-
yond the scope of the present paper.

The magnitude and complexity of the task have increased.
with each succeeding year, but it is to be hoped that the con-
clusions here presented from the data accumulated during this
unique opportunity for continuous and Systematic observation
upon the minute life of a river, will lead to the advancement
of the science of limnology.

ACKNOWLEDGMENTS.

For more than a score of years Professor 8. A. Forbes has
been Director of the State Laboratory of Natural History and
State Entomologist of Ilnois. The confidence of the public
in his good judgment which this service has inspired has been —
shown by the people, through their legislature, in repeated ap-
propriations for the support of the Illinois Biological Station
founded by him in 1894, an institution whose work les mostly
in the field of pure, rather than applied, biological science. To
him, then, is due in a very true sense the opportunity of prose-

97

cuting through a series of years these investigations upon the
life of the Illinois River, a problem for whose solution private
enterprise and even the usual university facilities are quite in-
adequate. To him I wish also to make acknowledgment for
his valuable directions, suggestions, and encouragement
throughout the whole course of the work. To my colleagues
of the State Laboratory staff acknowledgments are due for co-
operation in manifold ways. The collections of the period
preceding July, 1895, were made by Professor Frank Smith
or under his direction. He also devised the “oblique-haul”
method of collection, and has rendered assistance by the identi-
fication of aquatic oligocheetes. A portion of the field work in
1894, 1895, and 1896, was performed by Mr. C. A. Hart and Mr.
Adolph Hempel. To the former I am indebted for clerical ser-
vices and for assistance with the aquatic insects and the mol-
lusks; to the latter, for some data concerning the rotifers and
the Protozoa. During the last seven months of our operations
the field work was faithfully attended to by Mr. Wallace Craig.
Acknowledgments are also due Mr. Miles Newberry, who from
the beginning to the end of our operations served, in summer’s
heat and winter’s cold, as field assistant in the work of col-
lection. His faithfulness and skill in dealing with the frequent
difficulties and the occasional dangers of the river situation
have added not a little to the success of our work. I am under
much obligation to Mr. R. EK. Richardson (of the class of 1901,
University of Illinois) for most efficient clerical assistance in
the laborious task of the counting work and in the compilation
and organization of the statistical data resulting therefrom.
From Captain J. A. Schulte, Mr. J. M. McHose, and the city
authorities of Havana the Station has received many courte-
sies. Hon.J.M. Ruggles and County Superintendent M. Bollan,
of Havana, have also rendered favors by way of information on
various points. To many other correspondents I am under
obligation for courtesies, and not the least to Mr. G. A. M. Lil-
jencrantz, of the office of U. 8. Army Engineer of Chicago, for
oft-repeated contributions of hydrographical data,

98

THE GEOLOGICAL AND HyproGRaPHic FEATURES OF THE
Inurnois River Basin.

These subjects have received elaborate treatment, in con-
nection with the problem of the disposal of the sewage of the
city of Chicago, by Cooley (’89 and’91); and by Leverett (96)
ina report to the U. 8. Geological Survey upon the “Water
Resources of Illinois.” The following discussion of those
physical features which are more or less directly related to the
jheme of this paper has been, to a considerable extent, com-
piled from these papers, with such supplementary data as
could be gleaned from the reports,of the U. S. Engineers and
from the observations and records made by the biological
station staff at Havana and at other points along the river.

In many respects the Illinois River may be regarded as a
typical stream of the prairie region of the North-Central
States; and its basin, in the glaciation of its surface, the level
character of the land, the fertility of the soil, the absence of
extensive forest areas, the amount of rainfall, the general
climatic conditions, and its central position, might well be
called a typical one for the central region of the Mississippi
Valley. On the other hand, in several very important respects
the river presents features and combinations of features that
are exceptional and even unique. Foremost among such
features is the very large amount of sewage received, an
amount largely increased by the opening of the Drainage
Canal in December, 1899, by which almost the entire sewage
of a metropolis of about two million inhabitants enters the
river. This, together with the large amount of organic refuse
from the distilleries and cattle-yards along the course of the
river, adds immensely to the fertility of its waters, especially
when the river islow. Again, the present river is a babe in a
giant’s bed. The channel and the bottom-lands of the present
stream lie in the bed of an ancient outlet of Lake Michigan
whose flood-plain constitutes the fertile “second bottom.” In
this channel of its predecessor the Illinois River is now rapidly
building up its flood-plain, the low gradient of the former oc-

99

cupant still persisting. The slight current, the frequent over-
flows, and the disproportionate extent of water areas in the
bottom-lands result from this somewhat unusual ancestry.

LOCATION.

The latitude of the Illinois River is approximately that
of the Tagus, the Tiber, the Kezil Irmak, the Oxus, the Yar-
kand, and the Pei-Ho. Its drainage basin lies between the par-
allels of 39° and 43° 15’ north latitude and extends from the
isotherm of 45° to that of 55°, a belt which, in Europe, includes
the areas drained by the Thames, the Seine, the Loire, the
Rhine, the Elbe, the Oder, the Vistula, and a considerable por-
tion of the basins of the Black and Caspian seas, and, in Asia,
the basin of the Hoang-Ho and that of the Aral Sea. The
position of Havana, Ill., near which place our plankton collec-
tions haye been made, as determined by Mr. G. 8S. Hawkins, of
the U. 8. Geological Survey, is 40° 17’ 37".19 north latitude and
90° 03’ 55".97 west longitude. The area tributary to the [h-
nois River at Havana lies between the isotherms of 50° and 55°,
and is therefore comparable with the more northerly parts of
the regions above enumerated.

GEOLOGICAL FEATURES OF THE ILLINOIS RIVER BASIN.

Illinois is the lowest of the North-Central States, the aver-
age elevation being but 632 feet according to Leverett’s compu-
tations from Rolfe’s survey. The range in altitude is from
1,257 feet, at Charles Mound on the Illinois-Wisconsin line, to
268.58 feet, low-water mark at Cairo. Low-water mark at the
mouth of the Illinois is 402.56 feet above mean-tide level at the
Gulf of Mexico according to the figures given by Cooley (91, p.
93), 404.7 feet according to Greenleaf (’87), and 402.76 feet
according to Rolfe, the different elevations given being based on
different surveys. The present bottom-lands from the mouth
of the river to La Salle range in elevation from 410 to 440 feet,
and bottom-lands slightly higher than these extend for some
miles up the Sangamon, and for a short distance along the

100

lower courses of other tributaries in the southern basin The
altitude of the river at low water at Havana is given by Rolfe
('94) as 429 feet, and data given by Cooley (’97, p. 60) indicate
an elevation of 422.96 feet above mean-tide level at the Gulf of
Mexico.* The fertile second bottoms, which are principally on
the eastern side of the river, lie from 30 to 75 feet above the first
bottoms, while the bluffs range in altitude from 450 to 800 feet,
the highest points being reached near Peoria, and near the mouth
in Calhoun county. The watersheds bounding the basin range in
height from 700 to 1,000 feet, but by far the greater part of the
area included has an elevation of 600 to 700 feet, being about the
average elevation for the state. The relief of the drainage
basin of the [hnois is thus quite insignificant. That part
which hes in southeastern Wisconsin is most diversified, while
that in the state proper, together with the Kankakee basin in
northwestern Indiana, is practically an unbroken plain.

In common with the greater part of the state the basin of
the Illinois is covered by glacial drift. West and south of a
line drawn through Amboy, Peoria, Shelbyville, and Mattoon,
which marks the location of the Shelbyville moraine, this de-
posit is known as the “older drift,” and is from 20 to 150 feet in
thickness. The drainage lines are here well developed, the
streams in many cases occupying preglacial channels; but to
the north and east of this moraine the glacial deposit known as
the “newer drift” overlies the older, their combined thickness
ranging from 50 to 300 feet. Within this latter region the
drainage is not so well developed as it is in the older region to
the west and south of the moraine, and the streams, with the
exception of the Illnois, do not follow preglacial drainage
lines. Aside from a few minor streams between Havana and
Peoria, the whole basin of the Illinois above our plankton
station lies within the area of this newer drift. It consists of
extensive plains of glacial till, separated by glacial ridges or

*« We seem to be reasonably certain that the elevation of the Illinois at its
mouth is 402.76 feet, and that at Beardstown it is 423 feet. We feel somewhat less
certain that at Peoria it is 436 feet, and at La Salle 440 feet. Beyond this we can only
approximate because the U.S. Engineers and Illinois Canal Commission differ so
widely.’—PROF.C. W. ROLFE, 27 etter, Nov. 12, 1901.

101

moraines which largely determine the position of tributary
streams. Extensive sand deposits are found in the basins of
the Kankakee and the Iroquois, and valley drift and alluvium
occur along the river and its principal tributaries. These
latter deposits along the Illinois River are very extensive, indi-
cating the size of the stream which formerly occupied the
valley and connected Lake Michigan with the Mississippi River.

This deposit of. valley drift reaches its greatest extent in
a strip extending down the river from Pekin a distance of 65
miles. It varies in width from 10 to 20 miles, attaining its
maximum a short distance north of Havana. It is a sandy
plain, in some localities of which the wind has produced veri-
table traveling sand-dunes, with characteristic fauna and flora.
The drainage basin of Quiver Creek lies mainly in this deposit,
while the basins of Kickapoo and Copperas creeks, south of
Peoria, lie in the older drift and consist of loess-covered till.

The basin of the Illinois thus lies in a typical prairie region
of the Mississippi Valley. To the north and east it is very flat,
but to the south and west it presents a more rolling surface.
The soil is a rich black loam one to four feet in thickness,
underlaid by boulder clay into which the streams have cut
their channels. The larger water courses are usually bordered
by strips of woodland. A very large part of the area drained
by the Illinois is under cultivation. During the last twenty
years the natural drainage has been supplemented by tile under-
drainage and by the dredging of open channels through large
stretches of flat country, the terminal water courses of a very
large proportion of the tributaries of the Illnois being thus
widened and extended, and the area of tillable land much in-
creased. The extension of these supplemental channels and
the removal of the turf by cultivation have undoubtedly a ten-
dency to facilitate the run-off of the rainfall and thus to in-
crease the suddenness and height of floods, and they also favor
the introduction of fragments of vegetation and particles of
loam and sand, thus increasing the amount of silt carried by
the waters of the river at times of flood.

102

THE ILLINOIS RIVER SYSTEM.

The length of the Illinois from its mouth to the place of its
formation by the junction of the Des Plaines and the Kankakee
is about 270 miles,* and if to this be added the length of the
Kankakee, the longest tributary, the total amounts to 505 miles.
This is about the length of the Seine, of the Rhone, and of the
Oder; of the Des Moines and of the Sacramento ; it is about one
half the length of the Rhine and of the Yellowstone, one third
that of the Danube, and over twice that of the Thames and the
Tiber. The distance, in a direct line, from the junction of the
Des Plaines and the Kankakee to the mouth of the Illinois is
214 miles. The increase in length due to the windings of the
stream is thus 61 miles or 28%, and the ratio of the development
of the streamis1: 1.28. From the mouth of the main stream to
the head waters of the Kankakee, in a direct line, is 315 miles.
Upon this basis the increase due to windings is 190 miles or
60%, and the ratio of development is 1: 1.6. The ratio of de-
velopment of the Connecticut River is 1 : 1.2, and that of the
Mississippi, as a whole, is 1 : 1.5, while from the mouth of the
Ohio to the Gulf itis 1: 2.0. Itis evident that the main stream
of the Illinois has an exceptionally direct course, though the
channel of the Kankakee is not of this character.

The area of the basin drained by the Illinois is approxi-
mately 29,000 square miles. This is more than twice the area
of the Hudson, and also of the Connecticut, and is comparable
with that of the Susquehanna, of the Potomac, of the Po, of the
Duero, of the Rhone, and of the Loire. It constitutes less than
one forty-third of the entire Mississippi basin. According to
Greenleaf (’85) the drainage basin of the Illinois comprises an
area of 29,013 square miles, 24,726 of which lie within the state,
1,080 in Wisconsin; and 3,207 in Indiana. About three sevenths
of the area of the whole state belong to the drainage basin of
the Illinois. The following list of tributaries with their respect-
ive areas is taken, with slight modification, from Cooley (789).

*The statement of the Standard Dictionary (p.2172) that the length of the IIli-
nois River is 350 miles is manifestly incorrect.

108

DRAINAGE BASIN OF THE ILLINOIS RIVER AND TRIBUTARIES.

Area to:

Junction
Morris
Seneca
Marseilles
Ottawa

“

Utica
or

Hennepin
ae

Henry

Chillicothe

Peoria

Pekin

Copperas Cr. Dam
Kingston
Copperas Cr. Dam

Havana
Havana
“er

Beardstown

La Grange Dam
Griggsville Landing
Montezuma

Kampsville Dam

Tributary Area foes Pee Bank
Das IPilenines INV ocooceaond an 1,392 1,392| 00.0 |R. B.
iain AOS RWG. 560ncebac08s 5,146 6,538 oo.o | L. B.
Mixa Salle sRiviete es. s.ce ans so- 218 6,756 Mo@ || Io 1s
Mizvoyal IRVINE Co eueas ao so soo8Or 540 7,296 @o7 |) Wo 13
INigiile Creeks, CEs So nasccdeone 63 75359 10.0 |R. B.
Waupecan Cr. and Hog Run.. 70 7,429 WoW || Wee 18).
Karekalpoo) (Greek. see se acl: 45 7,474 DDG) || Ro 1B
South Kickapoo Creek........ 24 7,498 DEF) |) We Io
To Mouth Fox River.......... 16 7,514 BRoit || Iso 18},
sRoOMViouthwhoxg Riviera. 4-161 15 7,529 OR i || Wy 183,
ONG VST Are ce creiciexsenve sasisie-c ce 2,700| 10,229 Bait || Ike Ish
Govelk Greeks. cee eile skies 100} 10,329 Aoi, || Wy, 18,
Clans INihiieeamemorecce mares 36] 10,365 M255 || IRe 1B
Wemilion IRtWeieogoe ss0ucoco00 1,317| 11,682 46.2 | L. B. |Peru
Pecumsaugan Cr. L. Verm. R. 165] 11,847 MoM | IRo Wo) %
Sporting Crees venoucocssaunreas 56] 11,903 52.9 |R. B.
ING PONGreelke os. asec cevesink Bale eS 7 7/03} || Ito 18k,
PANIBHOGIES: ae cv ac nia sc lannstociernerec FA| NBSXKN0)||s006 0000 IL, 18%
Burmeami@reek) f285.25 65.0.2 nee 480; 12,489 62.9 | R. B.
Coiiee Creek sccocascauens conn 24| 12,513 5.8 || Ib, 18.
GCleamGrceks etnies cease 52| 12,565 WhoG || leo 18,
Senachewinle Greeky =e ees. 77| 12,642 73.8 |R. B.
Sanayy Creeks aces cu aousonccoss 147| 12,789 D5 oF \\ Wo 18s
Cron Cireells (Q7ESD)oocceeca500c 88} 12,877 81.0 | R. B.
GrowsGreek (east) ic acces 226| . 13,103 S30), || Is 18},
Senachewine Creek........... 132] 13,235 90.4 |R.B
IRi@lallewarel Citselie, GE, co0e code uc 198} 13,433 93.8 | L. B.
West SIOOS Gogo odsoesosecrnd AG) VAN) |loooc acce R. B.
IXI@RAOOO) CREOE Gcasaonwede oodo BuO} WAGso)|| Wii || Ie 18,
Lio (Geel iooe paca anata ae 42| 13,831| 114.9] L. B.
IMizKolingiiy IRMEP55c0u06600 0066 KQU7), USO t2V© || Ibe 18
Tanmerisa Cee. ossecesoaudec Bis WENO avo cccc IR 18.
Cop DEAS Greek Goaconsccenonc 151). 15,254| 134.0] R. B.
IDUGK CiGSs Baas aes cane aoe Ifo} 15.364] 138.1 | R. B.
Plankton Station..........]...... 15,364) 149.5 |......
Quiver Crees, cone gceovaceadse 220) 15,584 1409.9 | L. B.
SPOON IQViVSiesasamacwosu season 1,870] 17,454) 151.6/R. B.
Otter and Wilson Creeks ..... MAO) WH Sol) W607 || Ro 18.
SaneAinoin INE 5 seco adso end 5,670] 23.264] 174.1 | L. B.
Owigaie CraGen ae acoso meee KO) DB AML | IF/o7/ VIR. IB
Crookeal Cire@lk woos ogee dong cue 1,385) 24,829) 188.3 |R.B.
IindiantGreeks S25. so bee ck. AQ, AGE UiIG|| UwOERo/A || ls Iss
MICIXGES INMGitsogoGo pced adpoos M72) BSS |) BOS 7 || Ro 18
Mauvais Terres Creek ........ DY5|| DEAK || AC). || Ib, 18),
WWIESTRST OP OWE i tota cise ace eeac ee AG) = 2Q2EQAL ocov csc R. B.
Idi Seimelyoveles Gooucasasooacs NOO|ue2 ONS) 22 Ova neem
WESE SJ OOCateagquucemocr ora nee AS AAC co co00000 R. B.
A\pyolle Cirteclks, GE, coco aaoncoue S25) Zow/Bi || BB507/ || Wo 18s
W. Slope to Macoupin Cr. .... AS AYTTO|cocasces R. B. |.
Nac oupine Creekerse tee dace 985| 27,761] 248.6] L. B.
OfterlGreek yes lined nce 85| 27,846] 256.4 | L. B.
\WWiGSE SI Oa" so owoneesomancueac (OQ) DEH ||aocacooe Rew E:
ASTI SIO DOr rycen cn eat ccen ee De} AVIA |eooo0006 Wy 183,

Mouth at Camden

104

It will be noted that according to these estimates the area
is only 27,914 square miles; also that our plankton station, lo-
cated about two miles above the mouth of Spoon River and
slightly above that of Quiver Creek, is just within the lower
half of the basin. The water passing this point is derived from
an area of 16,250 square miles (15,363 according to Cooley ), or
59% of the total basin, no account being taken of additions to
the stream by the pumping works at Bridgeport or by the
Drainage Canal.

A glance at the map (PI. I.) shows that the basin of the
Illinois River extends diagonally across the center of the
state from the southwest to the northeast as a broad belt one
hundred miles in width. The head-water region is spread out
in a Y-shaped area which embraces the southwestern portion
of Lake Michigan. The northern arm of the Y is formed by
the basin of the Des Plaines, which extends northward into
Wisconsin for a distance of 50 miles. It is separated from
Lake Michigan by a narrow strip of territory 3 to 22 miles in
width which is tributary to the Lake. The eastern arm is the
more extensive basin of the Kankakee, which extends for a
distance of over 90 miles into Indiana.

The river does not take its course through the middle of
the basin but hes to the westward, being 60 to 80 miles
from the southeastern watershed and but 20 to 40 miles from the
northwestern. In the last 50 miles of the course the western
watershed is within 10 miles of the stream. Such a deflection
of the main stream toward one side of its basin is not infre-
quent, and has been attributed in many cases to the influence
of the rotation of the earth. Russell (98) says: “Thus, in
the northern hemisphere the tendency of the earth’s rotation
is to cause the streams, no matter what the direction of flow,
to corrade their right more than their left banks. * * *
There is thus a tendency, due to the earth’s rotation, for them
to excavate their right more than their left banks, and to mi-
grate to the right of their initial courses. This tendency is
slight, but all the time operative.” Streams flowing south-

105

ward in the northern hemisphere thus tend to shift toward the
western watersheds of their basins. The position of the Illh-
nois River in its basin seems to afford an illustration of this
application of Ferrel’s law to the flow of rivers. A reference
to the contour maps of the state which Leverett (’96) gives,
shows that the bed of the ancient stream which the Illinois
River and its bottom-lands now occupy lies toward the western
side of the flood-plain of the stream ; in other words, from
Hennepin to the Mississippi the second bottoms are of much
greater width upon the eastern than upon the western side of
the river.

From its origin, fifty miles southwest of Chicago, the [h-
nois pursues a course almost due west for a distance of sixty
miles, to a pointa few miles above Hennepin, where it turns
abruptly toward the left, and flows sonthwest by south in quite
a direct line fora distance of 165 miles (205, by river) to its
union with the Mississippi, 25 miles above St. Louis.

The tributaries of the Illinois River are distributed in a
somewhat unusual manner. Dividing the river into three
regions, the upper, middle, and lower, terminating respectively
at Ottawa, at our plankton station, and at the mouth, we find
a very unequal distribution of tributary areas. The upper
river, although but 12% of the total length, drains 37% of the
basin owing to the fact that it receives three large tributaries,
—the Kankakee, the Des Plaines, and the Fox,—besides a con-
siderable number of smaller streams. The middle river, on the
other hand, constitutes 43% of the total length but drains only
18% of the basin. This is due to the fact that aside from the
Vermilion and the Mackinaw there is no tributary of impor-
tance in the 117 miles of its course. These two tributaries have
basins of 1,517 and 1,217 square miles respectively and rank in
area as seventh and eighth in the list of tributaries. The
lower river constitutes about 45% of the total length, and
drains a corresponding per cent. of the total basin, since it re-
ceives the Spoon and Sangamon rivers and, in addition, a num-
ber of creeks of considerable size. The location of the plank-

106

~

ton station at the lower end of the middle section of the river
is fortunate in that it has enabled us to make collections in
water that is typical of the stream as a whole. No large trib-
utary is near enough to disturb the balance, and the greater
part of the water of the stream at the place of collection has
been moving in the channel for some time. There is, conse-
quently, abundant opportunity for a thorough mingling of the
waters derived from the various tributaries and for the breed-
‘ing of the plankton. The conditions are thus favorable for a
uniform distribution and development of the plankton in the
river at the place where our collections are made.

THE RIVER BOTTOMS.

As before stated, the present river channel, at least from
the bend near Hennepin to its mouth, lies in the bed of a stream
which formerly connected Lake Michigan with the Mississippi
River. The channel excavated by this ancient water-course is
far in excess of the demands of the present river, and it has
filled up by alluvial deposits, which constitute the bottom-lands
of to-day. This ancient channel varies in width from one and a
half to six miles, and borings made near Havana in the bottom-
lands of the present river, ten feet above low water, reveal a
deposit of alluvial soil twelve to eighteen feet in thickness
which hes above alternating beds of sand and fine clay. The
depth to which these beds extend is not known. Wells in the
bottom-lands are seldom deeper than fifty feet and usually do
not exceed twenty feet, water-bearing strata of sand being
found at varying levels between these limits. At Cedar Lake,
sixteen miles north of Havana, the pipe of a driven well was
checked at a depth of fifty-two feet,—forty feet below low water
and 389 feet above sea level,—apparently by rock, and the water
drawn from this depth is heavily charged with salts of iron, be-
ing similar to that from the shales of adjacent coal regions.
Alternating beds of sand, gravel, and clay similar to those found
beneath the alluvium in the bottom-lands were encountered in
a prospect-boring for coal at Mason City, twenty miles south-

107

east of Havana. The elevation at this place is 169 feet greater
than at Havana and these complex drift deposits are of corre-
spondingly greater thickness, the underlying rock floor being
found at an elevation above the sea of 396 feet, approximately
the level of the rock floor at Havana.

The flood-plain of the older river lies from 30 to 50 feet
above that of the present stream and varies in width from 8 to 20
miles, reaching its maximum a short distance above Havana, and
being widest upon the eastern side of the river. The bluffs rise
from 30-to 300 feet above the present flood-plain, the minimum
height representing only the first bluff, or that of the present
bottoms, the bluff of the second bottoms being found further
inland. The greater heights are reached where the first and
second bluffs coincide, as is frequently the case upon the west-
ern side of the river. The height of the flood-plain of the
Illinois River ranges from four to sixteen feet, varying with
the local conditions, the highest levels being found where
tributary streams cross the bottom-lands. The detritus which
they carry is deposited in large quantities in the impounded
and quieter waters of the bottoms, and builds up the banks,
especially below the region traversed by the tributary streams.
This is very apparent at Havana, where the banks of Spoon
River rise about sixteen feet above low water. The bottom-
lands below this tributary are submerged only at maximum
floods, while those above consist in large part of marshy tracts
six to eight feet above low-water level.

The total area of the bottom-lands from Utica to the
mouth of the river, a distance of 227 miles, is estimated by
Cooley (91, p. 61) to be 704.3 square miles. The average
width is 3.1, of which .6 of a mile is estimated to be marsh or
water. The middle region, extending 59.5 miles,—from Cop-
peras Creek dam (16.8 miles above Havana) to La Grange dam
(42.7 miles below Havana),—has an average width of 4.3 miles
and a total area of 256.9 square miles, of which 20.60 are water
and 28 marsh. Of the 75 square miles shown in the map of the
field of operations of the Biological Station (PI. II.) 56:5 belong

108

to the bottom-lands, of which about 17 square miles have been
cleared of the forests and placed under cultivation, 7 represent
river and lakes at low-water stage, 10 are permanent marshes,
and the remaining 22.5 are covered by forests, and lie at so low
a level as to be subject to frequent overflow. It is difficult to
distinguish between marsh and woodland in those areas
covered by low growths of willow (Salix nigra) or sparsely
wooded with willow-trees of considerable size. As their low
elevation renders them subject to overflow on slight rises of
the river, and as the vegetation is usually of a semiaquatic
nature they are on our map in large part included in areas
designated as marsh. As the elevation increases, maples
(Acer dasycarpum) appear among the willows, then the green
ashes (Fraxinus viridis), while in the higher bottoms the elms
(Ulmus americana) form the major part of the forest, with
maples, box-elders (Negundo aceroides), syeamore (Platanus occi-
dentalis), pecans (Carya oliveformis), oaks (Quercus palustris), and
clusters of cottonwoods (Populus monilifera) interspersed. The
marshes and lagoons, especially along the lower part of the
river, are often fringed with dense and impassable thickets
of button-bush (Cephalanthus occidentalis) and buckbrush ([or-
esteria acuminata).

Cooley (’91) gives the average height of the banks of the
Illinois above low-water level as 10 feet for the region between
Copperas Creek and Havana and 11 feet from Havana to the
mouth of the Sangamon River. The range in height for the ~
same distance is 7 to 12 and 9 to 12 feet respectively. The
greater height below Havana is doubtless due to the deposits
contributed by Spoon River. The dam at La Grange, com-
pleted October 10, 1889, has raised the water about two feet at
Havana, so that the actual height of the banks above the water
at its lowest stage, under present conditions, averages less than
8 feet. The immediate banks are usually higher than the ad-
jacent bottom-lands. This is true of the tributary streams also,
and is especially well marked in the case of Spoon River,
which carries large amounts of sediment at times of flood. It

109

has built for itself an elevated ridge across the bottom-lands,
fifteen feet above the low-water mark, through which it pur-
sues its tortuous course, flowing thirteen miles (See Pl. II.) to
reach the Illinois, which is only five miles from the point
where the Spoon enters the bottom-lands. The rapidity with
which the alluvium is deposited at times is illustrated by the
fact that the floods of 1898 left on the banks of the Illinois at
the mouth of Spoon River a layer of earth nine inches in
thickness. Nevertheless, we find an unusually large area of the
bottom-lands occupied by lagoons or bayous, locally known as
lakes, by marshes, and by bodies of water of an ephemeral
character. Some of these, as, for example, Thompson’s Lake
(Pl. II.), retain at all times their connection with the river,
and receive their water supply wholly or in large part from it.
Others, as Quiver and Matanzas lakes, retain their connection
with the river, but are fed to a greater or less degree by
streams and springs. They respond to changes in the river
level and are subject to invasion by the river at times of rising
water. During falling or stationary water, except at times
of overflow, these lakes are filled with the clear water de-
rived from their drainage basins, which stands in sharp con-
trast to the turbid waters of the river. Such spring-fed lakes
are not uncommon in the bottom-lands along the eastern side of
the river from Pekin to its mouth. They derive their water
supply from the sand deposits of the second bottoms, at whose
margin they usually he. Other tracts of the bottoms, lying at
about the level of low water or losing their connection with
the river before low-water mark is reached, become permanent
marshes, as in the case of Flag Lake (PI. II.). In some in-
stances where the body of water left by the overflow les some
distance above low-water level the characteristics of a marsh
are not established, owing to the seepage and evaporation of
the water and to consequent drying and hardening of the bed,
and we have simply an ephemeral lagoon, as in the case of
Phelps Lake.

110

THE RIVER.

As previously stated, the course of the Illinois as compared
with that of other streams of the Mississippi basin is remark-
ably direct. The present stream has not as yet developed in its
bottom-lands—the bed of the ancient stream—a meandering
course like that of the neighboring Mississippi. The position
of its channel in the bottom-lands is often determined largely
by the deposits of its tributaries, those made by the streams
from the east, as the Mackinaw and the Sangamon, forcing the
river towards the western bluff, while those from its western
confluents, as Spoon River and Crooked Creek, crowd it against
the eastern bluff. The width of the river at low water gradu-
ally increases from 536 feet at Peru to 1,040 feet at its entrance
to the Mississippi. The expanse in Peoria Lake is over a mile
in width, and further down, in Havana Lake, it is about 2,500
feet. aS
The undeveloped condition of the flood-plain of the Illinois
River and the consequent large areas of the marshes, lagoons,
and lakes, affect the plankton of the river most fundamentally.
In the first place the flood-plain serves, to an unusual extent,
as an impounding area in which the flood-waters are stored, the
barriers, natural and artificial, in the bottom-lands combining
with the low gradient to delay the run-off. This delay is still
further prolonged in most years by high water in the Missis-
sippi caused by the run-off from districts of more northerly lat-
itudes and higher altitudes and thus occurring after the spring
run-off in the basin of the Illinois. In a few instances the
backwaters from the floods of the Mississippi have been known
to flow up the Illinois for a distance of one hundred miles,
and the slope of the stream is such that the impounding
effect might, under suitable conditions, extend even farther.
The result of this combination of factors is to increase to a
marked degree the volume of water, and to add greatly to the
diversity of the environment at the time of the maximum de-
velopment of spring plankton. It thus profoundly affects both
the total product of plankton and its diversification.

111

In low water stages the flood-plain has less influence upon
the quantity of plankton present in the river, for the contribu-
tions from the lagoons and marshes are at a minimum at that
season, constituting but a small part of the total discharge of
the river. On the other hand, as the river falls and the flood-
plain emerges the local environments of the relict bodies of
water become more pronounced, and local developments of the
plankton more varied. The great variety of forms found in the
summer plankton is doubtless due in large part to the contri-
butions from this diversified environment.

Four dams have been placed in the river for the purpose of
alding navigation, the State of Illinois building those at Henry
and Copperas Creek, and the United States Government subse-
quently erecting the othertwo. The appended table gives their
location, date of construction, length of pool, elevation of water,
and the estimated increase in the volume of water in the part
of the river included in their respective pools. The data in-
cluded in the table have been in part compiled from the vari-
ous reports of Captain Marshall in the Annual Reports of the
Chief of Engineers, U.S. A., for 1890-94, and in part furnished
through the courtesy of Mr. G. A. M. Liljencrantz, Assistant
Engineer at the Chicago office, and Mr. E. J. Ward, of the [h-
nois and Michigan Canal.

The effect of the dams upon the volume of water in the
river is much greater at low stages than when the river is out
of its banks, the increase in volume resulting from them rane-
ing from eighty to one hundred and twenty-five per cent. The
increase due to the dam at Copperas Creek is less than that from
the other dams because of the deep reach of water from Lacon to
Chillicothe, and the considerable expanse under normal condi-
tions in Peoria Lake, both above the dam in question. As a
part of the biological environment the dams are of great im-
portance, for they check the current, delay the run-off, especial-
ly at low water, facilitate the deposition of silt, and double
the volume of water at low-water stages. All of these factors
tend to increase the production of plankton and are most
effective at low-water stages.

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113

From Peoria to Pekin and again from Copperas Creek
dam to Havana there are narrower reaches whose average
widths fall to 604 and 603 feet respectively. The depth of the
river at natural low water varies from .8 of a foot upon some
of the bars to more than 14 feet in the deepest channels. The
average depth from Copperas Creek to Havana is about 9 feet
and the average cross-section 2,801 square feet. Between
Havana and the LaGrange dam the river becomes more shoal
again, as is usual below the mouths of the larger tributaries.

According to figures given by Cooley the dam at LaGrange
raises the level of the river at Havana 2.4 feet. During 1894,
a low-water year, no records of the river-gage were kept at
Havana, but at the time of the exceptionally low water of
1895 the gage-reading (see Pl. VIII.) repeatedly fell below the
level assigned by the engineers to this point in the pool of the
dam. From January 12 to February 22 the gage ranged from
2.4 to 2.2, standing the greater part of the time at the latter
reading. Again, from June 10 to July 16 it stood below 2.4,
reaching the minimum reading 1.7 on June 23. On August 10
and from the 14th to the 23d it stood below 2.4, and so also on
September 3 and from October 4 till November 7. During the
year the gage read less than 2.4 feet on 111 days; 2.3 on 41
days, 2.2 on 46, 2.1 on 17, and 2.0 to 1.7 on 7 days. During
1896 the gage fell to 2.4 on but a single day, July 19. In 1897
the gage read 2.4, or below, on 84 days—from August 9 till
October 31. It stood at 2.4 on 3 days, at 2.3 0n 8 days, at 2.2
on 2 days, at 2.1 on 3 days, at 2.0 on 32 days, at 1.9 on 23 days,
at 1.6 on 11 days, and at 1.7 on 7 days. In 1898 the lowest
point reached was 2.5 The dam at LaGrange is estimated to
raise the water 2 feet on the lower gage at Copperas Creek
dam, but during 1897 the readings at this place during the pe-
riod of lowest water very nearly coincided with those at
Havana (see Pl. VII. and X.). The coincidence of the readings
would indicate that the gages at the two places have not been
correlated, since under the conditions the gage at Havana
should read somewhat higher than that of Copperas Creek,

114

The records during periods of low water both at Havana and
Copperas Creek thus indicate that the effect of the dam at La-

Grange is to raise the water in the upper end of the basin
~ somewhat less than 2 feet—about 1.7 feet at Havana, according
to the Havana gage. This gage was established in 1875 by Mr.
R. A. Brown,a U. 8. Army Engineer, and is based on the low-
water record of 1873.

The fall in the Illinois River, owing to the lack of devel-
opment of the relief of its basin, is but slight. The difference
between the elevation of its highest watershed and the low-
water level at its mouth is only about 600 feet, or an average
fall of 1.2 feet per mile of the total course. The Illinois
proper, from the union of the Kankakee and Des Plaines to the
mouth, has, according to Cooley (91, App. I.), a total fall of
81.7 feet, or an average of .267 feet per mile. Of this fall 50.7
feet occur between the mouth of the Kankakee and the head
of the pool of the Henry dam at Utica in a distance of 42.6
miles. From Utica to the mouth, a distance of 227 miles, the
fall is but 31 feet, or an average of .137 of a foot per mile.
According to Rolfe the altitude of the low-water level at
LaSalle, three miles below Utica, is 440 feet, while at the
mouth of the Illinois it is 402 feet, thus affording a total fall
between these places of 38 feet and an average of .167 of a foot
per mile. The elevations given by Professor Rolfe are based
upon Ilinois and Michigan-Canal levels, while those given by
Cooley are derived from later surveys. Accepting either figures
the fall in the main stream from Utica to the mouth is but
slight, exceptionally small, indeed, in comparison with the gradi-
ent of other rivers of the Mississippi system. For example, the
Mississippi at Cairo has a slope of .666 of a foot per mile, almost
five times that of the Illinois, while from Cairo to the Gulf of
Mexico,a distance of 1,097 miles by river, it has, according to the
most recent surveys, an average slope of .24 of a foot per mile—
about twice that of the Illinois from Utica to the mouth.

115

CURRENT.

The effect of this low gradient is seen in the slight current
found in the Illinois, a current so insignificant that Mississippi
River steamboat men are wont to refer contemptuously to the
Illinois River as a “frog pond.” The current is further im-
peded, especially when the water level is below eight feet, by
the presence of the four dams, which at low water convert the
river into a series of slack-water pools.

DISCHARGE OBSERVATIONS ON ILLINOIS RIVER AT LAGRANGE LOCK, 1887-1890.
(Gage referred to low water of 1879; Price current meter used in 1888-89.)

Cape Mean 1 Mean Time required (days)

Date ies) velocity (feet) | velocity (miles) to move from Utica

per second per hour - to mouth, 227 miles
Low water, 1887*...| 0.00 0.600 0.409 23.14
August I, 1887 ....| 0.20 0.600 0.409 23.14
December 21, 1888] 1.98 1.329 0.906 10.44
December 20, 1888] 2.00 1.277 _ 0.871 10.86
December 31, 1888] 2.95 1.539 1.049 9.02
February 4, 1889..| 4.33 1.758 1.198 7.90
May 20, 1889...... 5.40 1.942 1.324 7.14
/Nyouill toh, WEXs0)5 oon ae 5.01 1.852 1.263 7.49
March 30, 1889....| 5.85 2.053 1.400 6.76
March 25, 1889....] 6.72 2.258 1.540 6.14
May 30, 1889...... 16.98 2.011 1.371 6.90
March 8, 1889....., 7.65 2.554 1.741 5-43
April 22, 1889..... TS 2.406 1.640 5-77
March 11, 1889....| 8.36 2.572 1.754 5.39
Tielhy is, tke) Goces 8.37 1.857 1.266 7.47
UMS O, UWEslopoouase 10.00 2.520 1.718 5.51
July 9, 1889 ....... 10.33 2.053 1.400 6.76
January 18, 1890 ..!12.80 2.547 1.737 5.45

*Computed. +Backwater from the Mississippi River.

As shown in the above table, the mean velocity per second
of the current at LaGrange, forty-three miles below Havana, has
been determined by the U.S. Army Engineers (see Marshall ’90,
p. 2443) to range from .409 of a mile per hour at low water to
1.754 miles at 12.8 foot stage—1.8 feet above bank height at that
point. The velocity, in miles, per hour and the time required to
move from Utica to the mouth at this rate are given in the
table, having been computed from the data in the second col-
umn, quoted from Captain Marshall’s Report. It will be noted
that in a general way the velocity of the current increases as
the river rises. This increase is, however, modified by the rel-
ative heights of the water in different parts of the stream ; thus

116

backwater from the Mississippi River or from a tributary may
cause the river to rise and at the same time check the current
above to some extent. Such modifications are often, however,
localand temporary, and soon give way to the rush of the current.

Mr. C. A. Abrams, a steamboat man of many years’ experi-
ence upon the Illinois River, writes me that the current is as
much asthree miles an hour at high water and on a rising river,
while at low water it amounts to “nothing” except on the
bars and in the narrower and shoaler parts of the stream such
as those near Havana.

Capt. J. A. Schulte, of Havana, Ill., whose experience in
steamboating on the Illinois River, especially near Havana, is
extensive, has kindly sent me data which indicate that at high
water the current from Copperas Creek down to Havana is about
2.5 miles per hour, and at low water about 1.28 miles. He
further states that he has observed that the current above
Havana is strongest when the river is bank-full and slackens
somewhat when the river overflows, while below Havana the
current is strongest at times of overflow. It is probable that
the elevated bottom-lands above the mouth of Spoon River
cause this difference.

A shghtly greater rate than the mean quoted from the U.
S. Engineers’ Report is indicated in mid-channel by a few in-
adequate tests which we have made at the plankton station, near
Havana, by means of a vertical float reaching within a foot of
the bottom and projecting but a short distance above the sur-
face of the water. A test made September 29, 1897,—when the
river had been standing at the lowest levels reached since the
dam at LaGrange was built (1.7—2.05 above low-water mark on
gage) for forty-eight days and had not fluctuated during the
week preceding,—showed a current of .720 of a mile per hour.
Steamboat men say that, owing to the proximity of the Spoon
River bar, the current is as rapid at low water at this point as
at any place on the river. A similar test made June 22, 1898,
when the river was at 10.7 feet and was falling at the rate of 0.2
of a foot per day, showed a current of 1,033 miles per hour. At

117

high water (16 feet), tests made about half a mile below the
mouth of Spoon River with a steam launch indicate a current
at that point of about 3 miles perhour. The figures quoted from
the report of the Engineers give the mean velocity for the whole
stream at the place of observation, while our tests were made
in mid-channel and refer to that point alone. The results of
our own tests and those of the Engineers both indicate that the
current at low water is but one fourth as rapid as at times of
overflow. The current in the bottom-lands at time of overflow
is much slower than it is in the channel, being retarded by the
vegetation and by the natural and artificial irregularities of the
surface, such as the deposits of tributary streams, the embank-
ments of railroads, and the levees about cultivated lands. The
bottom-lands thus serve as impounding areas from which the
water, except at times of maximum flood, is slowly drawn off
through the main channel.

The rate at which the current moves down the stream is
not, however, an index of the rate at which the crest of a
flood traverses the same distance. For example, the crest of
the flood of May, 1892, as shown in the appended table, passed
from Morris to the mouth of the river in fifteen days, while the
current in the main channel, under these flood conditions,
would traverse this distance in four or five days—less than a
third of this time.

FLOOD MOVEMENT IN THE ILLINOIS RIVER.

Distance Rate
Place Dette Miles below Morris Miles per hour
WO TIS Here cavers were sis ar crate <\s May 6 rece sees
Copperas! Creekss.- eee 44 May 10 124.3 1.29
NGA GAN Gel sop. as :saavstere eony none May 16 183.7 0.41
Kanon onal. soodoocas06 6050 May 19 230.0 0.63
MIOWIEN sao emonaor en ona ames May 21* 259.2 0.61
*Estimated.

As stated on a previous page, the current at high waterranges
from two to three miles per hour, at which rate, as above shown,
water in the main channel would pass from Morris to the
mouth of the river in four or five days, This flood was sudden

118

and exceptionally high,—reaching 18.80 feet at Copperas Creek,
a height surpassed in recent years only by the flood of 1883
(19.25 feet),—and would thus cause a current at least as rapid
as the estimate above given.

This retardation of the flood is due, in partat least, to the
overflow of the bottom-lands, and it is much more pronounced
in the Illinois River than it is in ordinary streams owing to
the imperfect development of its flood-plain and the conse-
quent early inception of overflow stages on a rising river.

The current is an important factor in the environment of the
plankton. In the first place it largely determines the amount
of silt in suspension in the water, for upon its speed depends
not only the amount of material eroded from the banks and
carried on by the flood, but also the rate of deposition of the
silt delivered to it by the more rapid tributary streams.

The most important relation of the current to the plankton
lies in the fact that it is a large factor in determining the
length of time in which the plankton can breed, and thus
curtails or extends the possible number of generations of the
planktonts. The table on page 115 indicates that at the low-
water stage over twenty-three days elapse before the water
which enters the river at LaSalle, at the upper end of the pool
of the Henry dam, joins the Mississippi at Grafton. At the
stage of overflow the interval is reduced to less than five and
a half days, or about one fourth of the time at low water. It
is evident that the possible number of generations increases in
arithmetical progression as the current declines, while the
number of individuals may increase in geometrical progres-
sion. A concrete example will illustrate. A given organism
which multiplies by fission and in which a new generation ap-
pears each twenty-four hours will, at times of low water, reach
the twenty-third generation as it floats from LaSalle to the
mouth of the river, and the total possible number of individ-
uals of the last generation would be 8,388,608, while in the
more rapid current at the stage of overflow the number of gen-
erations could be but five and a half, and the number of indi-

is)

viduals only forty-eight. This rate of increase in individuals
is theoretically possible only for those organisms which repro-
duce by fission. In sexual and parthenogenetic reproduction
other factors enter to reduce the rate of increase and to render
the problem more complex, while life cycles, conditions of
the physical environment, competitors, and enemies further
modify and hmit the increase in numbers. Thus, in every in-
stance the struggle for existence sooner or later so checks the
rate of multiplication that the mathematical possibilities of in-
crease are never fully realized. In spite of these various modi-
fying conditions the fact is patent that the current is a very
important element in determining not only the amount of the
plankton, but also the relative numbers of its constituent or-
ganisms.

To a less degree the current curtails the development of
the plankton of the backwaters at times of overflow. in general
it is not so strong in the overflowed territory as it is in the main
channel, though local conditions in these regions sometimes pro-
duce quite as rapid a flow in limited areas. The slackened
current affording a longer time for breeding, the shallow water,
higher temperatures, and the larger amount of organic de-
bris combine to favor the development of the plankton in these
impounding areas, which, in turn, drain into the main channel
with the run-off of the flood.

The current in the Great-Lake system in many places
equals or exceeds that of the Illinois River. For example, the
St. Clair River at Port Huron moves at the rate of four miles per
hour; the Detroit River, at a rate of one to three miles per
hour; and the St. Mary’s, at.a rate of three quarters of a mile
to seven miles per hour. It is well known that currents pre-
vail in the open lakes, but there are no recorded measurements
of their flow. Thus, in certain aspects of its current the [h-
nois River does not markedly differ from the Great Lakes.
The impounded backwaters and the main stream at low-
water stages have but a slight flow, probably not in excess of
that in the open Lakes, while in the main channel at high

120

water the rate in the river does not differ greatly from that in
the contracted portions of Great-Lake systems. In the rate of
its current the conditions in the Illinois River thus approach
those of alake. In most lakes, however, in which currents may
be found whose velocity equals or exceeds that of the Lllinois,
the movement of the water does not involve to any like degree
its replacement by tributary waters. Thus, in the [llnois, even
at lowest water, the rate in the channel would necessitate a
renewal of the water every twenty-three days—a rapidity of
change which few lakes attain. This replacement of the
water becomes a most important phenomenon in the environ-
ment of the plankton of a river as contrasted with that of a
lake, contributing to its fluctuations, complicating the problem
of its maintenance, and ever tending to sweep it out of ex-
istence.

Biologically considered, the fundamental distinction be-
tween fluviatile and lacustrine waters hes in the more rapid
replacement and more recent origin, from springs and rain, of
the water of the stream as compared with that of the lake.

The attempt has been made by Schroeder (97) to give to
this relation of the plankton to the current a mathematical ex-
pression, a formulation which has been called Schroeder’s law.
Asa result of his plankton investigation upon the River Oder
and elsewhere the conclusion is reached that the volume of
plankton present in any stream is inversely proportional to the
rate of the current. It may well be that a comparison of the
plankton of certain slow and rapid streams, or of the same
stream under different conditions of discharge, will show con-
formity to this law of Schroedev’s, though no such conformity or
data for such comparison are as yetat hand. That any extended
investigation of the subject will afford the basis for an expression
so precise as to be couched in mathematical terms seems improb-
able in view of the many complex factors environing the plank-
ton. Furthermore, as will be shown later in the discussion of
the plankton of tributary streams of the Illinois River, the
biological significance of the current as related to the plankton

121

lies primarily in the length of time afforded for breeding. The
rate of the current is but one of the elements determining this
time. If this be true, the expression of this relation should
take another form, as, for example, the volume of plankton
present in any body of fresh water varies with the length of
time afforded for breeding.

THE DISCHARGE.

The total annual production of plankton in a given body of
water can be estimated only when the total discharge for that
timeis known. The seasonal] fluctuations of the discharge also
profoundly affect the local and seasonal distribution of the
plankton, and modify alike its quantity and its constituent or-
ganisms. For these reasons the consideration of this element
in the environment of the plankton is of prime importance.
The discussion of the subject naturally falls under two heads,
namely, the rainfall and the run-off.

The Rainfall——The political boundaries of Illinois do not
coincide with the watersheds of the Illinois River basin, though
almost half the area of the state les within this basin, which,
moreover, extends through more than two thirds the length of
the state, and is fairly typical of four fifths of its area. The
small portion of the basin (4,287 square miles) which les out-
side of the state does not present conditions of rainfall which
materially differ from those of parts of the basin within the
state. The northern part of Indiana, in which the Kankakee
basin lies, has a mean annual rainfall, according to Leverett
(97), of 35.49 inches, which is somewhat less than the average
(37.858 in.) for the whole State of Illinois; but since in [1h-
nois as in Indiana the rainfall in the northern part is less than
that in the southern part it is not improbable that the precipi-
tation in the Kankakee basin in Indiana is about the same as
that in corresponding latitudes of Illinois. Under these cir-
cumstances, the statistics of rainfall for the whole State of [-
linois may be taken to represent with considerable accuracy
the conditions within the basin of the Illinois River.

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123

The average rainfall for the State of Illinois for a period
of forty-nine years, from 1851 to 1899 inclusive, is 37.859 inches.
Leverett (96) gives a tabulation of the records of the U. S.
Weather Bureau from stations within the state and on its bor-
ders from 1851 to 1895 inclusive. The average for this period
of forty-five years, was 37.85 inches per year. The averages
for subsequent years, kindly furnished by Mr. M. E. Blystone,
of the U. 8. Weather Bureau, increase this amount by 0.008
inches.

The above diagram (Fig. A) shows the variations in the
rainfall in the period above mentioned. The irregularity in
the earlier years of observation may in part be due to the small
number of stations from which records are available. In 1895
‘records were made at ninety-seven points within or adjacent
to the state ; in 1885, at twenty-seven ; in 1875, at twenty ; in
1865, at sixteen; and in 1851, at but five. The range of the
annual averages is 24.8 inches, ranging from 54.1 inches in
1851 to 29.3 inches in 1894—a year of extreme drouth. Of the
forty-nine records twenty-four lie above and twenty-five below
the mean.

An examination of this diagram of the rainfall of IIli-
nois shows that the period covered by our plankton collec-
tions, 1894 to 1899 inclusive, was predominantly one of mini-
mum rainfall. The average for the six years is 35.5 inches, or
2.3 inches below the general average. It includes one year,
1894, when the rainfall was only 29.3 inches, the lowest on
record, while the remaining years with the single exception of
1898 are all more or less below the average. Omitting 1898, a
year of excessive rainfall, 46.6 inches, the average for the re-
maining years is only 33.2 inches, 4.4 inches below the general
average. The reduction of overflow stages of the river conse-
quent upon this lowered rainfall doubtless affected the plankton
by the restriction of the breeding areas, the concentration of
sewage, and the prolongation of the low-water period with its
slackened current. Our collections thus, as a whole, are repre-
sentative of a period of minimum rainfall and its attendant

124

low-water conditions. They are, however, fairly representative
of the whole range of rainfall and river conditions, including, as
they do, two years (1896 and 1897) which approximate the
average rainfall, and a year of minimum (1894) and one of
maximum (1898) rainfall.

The periodicity of the rainfall of Illinois and adjoining
states was noted by Leverett (96). There are alternating wet
and dry periods of eleven years which correspond somewhat
closely in duration to the sun-spot cycle as shown in Plate VI.
There is, however, in the sun-spot cycle no recorded alternation
of elevation and depression similar to that of the rainfall, the
maximum of sun-spot occurrences appearing at intervals of
eleven years while those of the rainfall appear in a twenty-
two-year cycle. In the diagram this alternation is brought
out by the horizontal lines, which represent the average
rainfall for periods of the eleven years included. The first
wet period within the time covered by the records of the
Weather Bureau lies about 1853-1863, the average being 38.5
inches—only 0.59 inch above the general average, though this
amount will be considerably increased if the period is shifted
back to include one or two preceding years. These earlier
records are, however, less reliable owing to the few places of
observation. A dry period from 1864 to 1874 falls 2.96 inches
below the general average, while the wet period of 1875 to 1885
rises 2.9 inches above it. The following dry period, 1886 to
1896, falls 3.05 inches below the general average, while the few
years of the current wet period already yield an average above
the general one. The average difference in rainfall between
the wet and dry periods is about 6 inches.

Our plankton collections are about equally divided between
the closing years of the last dry period and the opening years
of the current wet one.

A second cycle or rhythm in the rainfall has been discov-
ered by Sir Norman Lockyer and Dr. W. J. 8. Lockyer (00 and
01) as a result of their study of the temperature changes in the
sun, with their accompanying sun-spot phenomena, and the

125

rainfall in the region surrounding the Indian Ocean. They
have found that the mean solar temperature is followed by a
pulse of rainfall. These mean temperatures occur twice in
each sun-spot cycle of eleven years, at intervals varying from
four to seven years, and are accompanied by the crossing of
the iron and “unknown” lines in the solar spectrum, These
solar fluctuations in temperature produce atmospheric condi-
tions, especially over large continental and oceanic areas,
which result in rhythmic pulses of rainfall which have been
traced by these authors in the rainfall of India and the snow
upon the Himalayas, and in the rainfall of Batavia, Cape of
Good Hope, Mauritius, and Cordova. They have also correlated
them with the floods of the Nile and the famines in India. On
Plate VI. is a diagram taken from Lockyer (01) which shows
by curves the fluctuations of sun-spots (which in a general way
coincide with solar-temperature changes), and of the iron and
“unknown” lines. To this has been added the plot of the rain-
fall in Illinois and the hydrograph of the Illinois River. As
shown in the diagram the mean temperature (crossing of the
iron and “unknown” lines) occurs twice in each sun-spot cycle,
once on the rise in sun-spots (and temperature) (+ pulse), and
once on the fall (—pulse). The location of the rainfall pulses
of India and elsewhere accompanying these mean temperatures
is indicated upon the diagram.

A close correlation between these pulses of rainfall and
the fluctuations in rainfall in Illinois and in the hydrograph of
the Illinois River is at once apparent on inspection of the dia-
gram. The + pulses of 1892 and 1883, and the — pulse of 1876-77
are well defined, while that of 1888 is present though not so
pronounced.

Similar pulses of rainfall may also be detected at some-
what similar intervals in the rainfall of Illinois in the period
not covered by the Lockyers’ diagram, 1851-76. Thus + pulses
may be located in 1872, 1862,and 1851, and — pulses in 1865 and
1855 or 1858. Another — pulse is probably to be seen in the
heavy rainfall of of 1898, though according to the Lockyers’ dia-

126

gram no crossing of the iron and “unknown” lines had occurred
though normally to be expected. These unusual solar condi-
tions prevailing in 1897 to 1900 were accompanied by irregular-
ities in the rainfall in India, and may perhaps also be reflected
in the somewhat unusual irregularities in the rainfall records
and hydrograph in Illinois during this period. The data avail-
able for the discussion of the periodicity of rainfall are so lim-
ited that only tentative values can be given to any conclusions
upon the subject. The striking conformity of the Illinois data
to the Lockyers’ cycle will perhaps justify this discussion.

As might be expected, the variation in the rainfall for
any given point of observation may far exceed that of the
average for the whole state. Thus we find a record of 74.5
inches for Muscatine, Iowa, in 1851, while its lowest record is
23.6—a range of 50.9 inches. These extreme records are gen-
erally due to local rains of considerable magnitude, which are
often the cause of the sudden floods in the tributary streams
of the Illinois.

The seasonal distribution of the rainfall for Illinois is
shown in the following table taken from Leverett (’96).

Spring |Summer| Autumn | Winter | Annual | Cubic miles

JENEINES song blo opea000 10.2 11.2 9.0 7.7 38.1 34.0

The distribution by months, expressed in percentages of the
total, is as follows.

I | II Ill IV Vv VI |. VII | VIII) Ix x XI XII

6.2 | 67 7.0 8.2 | 10.4 | [2.2 | 9.9 | 8.6 9.0 8.5 7.1 6.0

The table shows a minimum in December with a gradual
increase to a maximum in June, from which the decline is
rapid, with only a slight interruption at the autumnal equinox.

The tables given above apply to the state as a whole. An
examination of the individual records shows that the south-
ern part of the state has a somewhat greater rainfall than the

127

northern part. This is due to the greater precipitation during
the winter months in the southern part, the rainfall during the
remainder of the year being practically the same in all parts
of the state.

The Run-off—Highty per cent. of the Illinois River water-
shed lies in two principal basins, each with peculiar climatic
and topographical conditions. These basins meet at Havana,
and consequently the conditions in the northern one constitute
a prominent feature in the environment of the plankton at
that point. As the two basins lie in different storm-tracks
their rain-floods do not always coincide. The southern basin
usually parts with its snow several days sooner in the spring,
and more promptly, than the northern, since its latitude is
more uniform, and, relatively, its floods are larger. The
climatic conditions of the southern basin are manifest at Ha-
vana principally in the backwater from floods in the lower
river, which check the current and delay the run-off from the
northern basin.

The subject of fluctuations in the volume of water in the
river is one of fundamental importance in our plankton work.
With rising water comes a decided increase in the current and
a rapid displacement of the sluggish waters teeming with mi-
nute life by a turbid flood to a large extent devoid of life.
With the overflow of the bottom-lands the subordinate
lagoons, lakes, and marshes are for the time being obliterated
from the landscape, and their peculiar fauna and flora mingled,
merged, and swept away with the flood. With the decline of
the flood, the unusual prolongation of which in the Illinois
River has been already alluded to, a great variety of conditions
of current, temperature, depth, light, and vegetation are
afforded, the most of which favor the development and diversi-
fication of the plankton. ‘The large amount of silt—composed
of a wide variety of substances, from an impalpable earthy
material to coarse sand and the comminuted debris of vegeta-
tion—introduced by flood water presents a most perplexing
problem in our quantitative plankton work. Aside from the

128

far-reaching effect that the turmoil of flood has upon the
quantity and the distribution of the plankton, there are intro-
duced other factors whose influence, though perhaps more
subtle, is of no less importance. Such factors are changes in
the chemical constituents dissolved in the water, in its temper-
ature, in its transparency, and in the relative proportions of
plant and animal life.

The run-off of the rainfall of the catchment-basin of ‘the
Illinois is influenced by a variety of conditions, all of which
are more or less variable. These are the amount and distribu-
tion of the rainfall, the slope, the perfection of drainage lines,
the geological structure, the amount of vegetation, and the
temperature. As has already been stated, the rainfall, amount-
ing on an average to 37.858 inches, is distributed with consider-
able uniformity—at least in the northern basin, with which we
are most concerned. Purely local excesses and deficiencies of
rainfall occurring within this area are rarely of sufficient pro-
portions or duration to affect profoundly the customary regi-
men of the stream as a whole.

According to Leverett (96) the slope of the stream beds of
the principal tributaries in the northern basin, the Des Plaines,
Kankakee, Fox, and Vermilion rivers, is on an average in their
lower courses several feet per mile, while in the lower two
hundred and twenty-five miles of the Illinois itself the slope is
only thirty feet or .13 foot per mile. In much of the state the
principal streams have an average slope of about two feet per
mile; and the small streams, of five to ten feet, excepting the
head waters. In the main, therefore, the slope of the stream
beds is such as to favor a very moderate run-off. The slope of
the general surface is also very moderate. It ranges from ten
to twenty feet per mile, being somewhat greater in the newer
drift, where moraines are more abundant, than it is in the
older drift of the southern basin. The steeper slopes of the
newer drift are, however, counterbalanced by the much in-
ferior development of drainage lines within its area. There are
large tracts of land at the head waters of the Vermilion and

129

Kankakee in which natural drainage channels have not as yet
been opened, a fact which has a tendency to further moderate
the run-off in the northern basin.

The newer drift which covers the northern basin presents
a great variation in its structure and consequent effect upon
drainage. In general it is less compact than the older drift and
offers greater opportunity for the storage of ground water,
especially wherever extensive deposits of sand and gravel
occur. Storage in such deposits tends to equalize the run-off
throughout the year.

The basins of the several tributaries present marked
peculiarities which influence their contributions to the flood
waters of the main stream. The basin of the Des Plaines
River is largely underlaid by impermeable rock upon which
the drift is twenty to one hundred feet in thickness. The
lower end of the watershed alone contains deposits capable of
affording considerable ground storage, while the upper end
abounds in lakes, bogs, and swamps, which also have a tendency
to retard and equalize the flow ofthe run-off. In spite of these
equalizing factors the floods of the Des Plaines assume large
proportions and, owing to the extent in latitude of the basin,
they are often prolonged. A considerable portion of the
flood water, under conditions prior to the construction of the
drainage canal, escaped over the Ogden dam and through the
Ogden-Wentworth ditch and the Chicago River to Lake Michi-
gan, following what seems to have been a former channel of
the Des Plaines. Cooley (’89) estimates that the discharge of
the normal extreme flood at the junction of the river with the
Kankakee is 12,000 cubic feet per second, and that this would
be increased to 20,000 if all the water from the basin sought
this outlet. This latter estimate is equivalent to the bank-full
capacity of the Illinois River at Copperas Creek dam, seventeen
miles above Havana. High-water level at the junction is 15.7
feet above low water. The flow at low water is insignificant,
amounting in 1887 to less than 16 cubic feet per second for a
period of five months. The variations in the Des Plaines thus

130

constitute a very important element in the fluctuations of the
main stream, and its contributions of detritus are extensive.
The basin of the Kankakee, occupying 5,146 square miles,
les in a single belt of latitude, extending 216 miles in an east
and west direction. About 700 square miles of the lower part
of the basin have a slope sufficient to afford a rapid run-off,and
of the remainder fully one half is swamp and marsh, the other
half being flat or slightly rolling, but capable of cultivation.
The drift, except in the lower portion, is of considerable depth,
and in much of the marshy region extensive deposits of sand
are found. The lower stream is also bordered by extensive
sand deposits, and these afford a storage basin for the waters
derived from the adjacent slopes. Cooley (’89) estimates the
mean of the extreme flood-discharges of the Kankakee at its
junction with the Des Plaines at 31,200 cubic feet per second,
and the mean of the extreme low-water discharges at 500 cubic
feet per second. Flood water at the mouth of the Kankakee
has been known to reach sixteen feet above low-water level.
Aside from the uniformity in latitude, the physical features of
the Kankakee basin, under present conditions, favor a gradual
run-off, with floods which rise slowly to a moderate height and
continue for a considerable period. Owing to the storage facil-
ities of the basin the stream maintains a relatively large flow
even in periods of prolonged drouth. The Kankakee is thus an
important factor in moderating the extremes of high and low ~
water in the Illinois. Its contributions of silt are but slight.
The northern part of the basin of the Fox River is similar to
that of the Des Plaines, and acts as a storage reservoir; but the
southern part, which is of greater extent, has steep slopes, and
the rapidity of the run-off is thereby heightened. Leverett (96)
states that its flood waters reach a level of fifteen feet above the
normal, and that the discharge, presumably at low water, is 526
cubic feet per second. Cooley (91) gives the discharge of the
Fox in the flood of February, 1887, as 13,680 cubic feet per sec-
ond. The conditions of its basin are such as to aggravate the
fluctuations and to increase the amount of silt in the hnois,

131

The Vermilion and Mackinaw rivers present common fea-
tures of drainage. They both drain till plains of compact drift
and have a comparatively rapid descent. The run-off is rapid,
and floods are sudden and of extreme proportions. Owing to
the absence of head-water marshes the flow in the period of low
water is very slight. The steep slope, the rapid run-off, and the
cultivation of practically the whole of their drainage basins
render the amount of sediment carried by their flood waters
very large.

The minor streams, such as Bureau, Clear, Copperas, and
Quiver creeks, and the rivulets which course down the bluffs
from the adjacent uplands, differ from the streams last described
only in the greater steepness of their slopes. This, added to
their proximity to the main stream, makes their run-off very
rapid. The clearing away of the forests and the cultivation of
the hillsides also add to the debris which they carry.

The varying contributions of these tributary streams com-
bine to produce the fluctuations manifested in the main stream
at the point where the plankton work of the Biological Station
has been done. There are also other factors influencing the
stage of the river at this point, notably the fluctuations of the
larger tributaries below, as Spoon River and the Sangamon.
Owing to the slight fall from Havana to the mouth of the river
—only 20.4 feet*—the stage of the Mississippi River may mate-
rially affect the gage-reading at Havana. High water in this
latter streams prolongs the floods in the Illinois, or even turns
the current up stream, as in 1844, when, as I am informed
by Hon. J. M. Ruggles, of Havana, the up-stream current came
within five miles of that place.

The Volume Discharged.—Streams in fertile regions of the
north-temperate zone usually discharge but little more than
one cubic foot per second per square mile of watershed. Thus
the mean discharge of the Great Lakes is about 14 cubic feet

*Based on Cooley’s figures in “ Lake and Gulf Waterway,’ Appendix I. Rolfe’s
survey makes it 29 feet (Rolfe, ’94, p. 133), though other data in his possession make
it 26.24 feet.

132

per square mile, while for some of the reservoir tributaries of
the upper Mississippi, which include regions of less rainfall, it
is estimated at about 0.75 cubic foot per mile.

There have been as yet no adequate measurements of the
flow of the Ilhnois River at its mouth, and no extended gagings
at any point on its course aside from the observations made by
the U. 8. Army Engineers at LaGrange, and a few isolated
records and estimates at other points.

The average flow of the river has been estimated by Cooley
(97) to be under rather than over one cubic foot per second
per square mile of watershed. Upon this basis it would be
somewhat less than 29,000 cubic feet feet per second, or 915,-
170,400,000 cubic feet or 6.2 cubic miles per year.

Measurements made in 1882 at Hannibal and at Grafton in
the Mississippi River above and below the mouth of the Illinois
indicate that the discharge of the Illinois River ranges from
11,000 to 80,000 cubie feet per second, with an average of. 30,-
000 cubic feet. This is equivalent to a maximum run-off of
nearly 3 second-feet per square mile, a minimum of 0.4, and an
average of 1.1. In 1882, one of the wet-year series, the river
was out of its banks during the greater part of the year owing
to the heavy rainfall which, throughout the state as a whole,
was 18 per cent. in excess of the average. A reduction of 18
per cent. from the average flow of 1882 leaves 24,600 cubic feet
per second, or 0.902 of a second-foot per square mile, as an esti--
mate of the mean annual flow of the Illinois River. Cooley’s
estimate (797) of the average run-off of the upper 15,250 square
miles of the basin, based upon the gage-readings at Copperas
Creek for eleven years (1879-1889), is 10,500 cubie feet per
second, or 0.688 second-foot per square mile. This is 25 per
cent. below the above-given estimate, based on Greenleat’s
measurements at the mouth of the stream. Accepting these
two estimates as approximately the average, and adopting the
calculation for the river at Copperas Creek as applicable to
Havana, eighteen miles below, we have the average run-off at
our plankton station approximately 0.688 second-foot per square

133

mile, or 10,570 cubic feet per second—a total, for the year, of
333,063,832,000 cubic feet, or 2.27 cubic miles. The run-off in
an ordinary year is equivalent toa trifle over eight inches of
rainfall in the whole watershed, or 21% of the total rainfall for
the year. Greenleaf (’85) states that the area of the entire
catchment-basin of the Mississippi is 1,240,039 square miles, and
that the average discharge per second is 675,000 cubic feet, or
only .b4 cubic foot per second per square mile. The Illinois,
with one forty-third of the catchment-basin, thus contributes
one twenty-third of the discharge. Greenleaf’s estimate of the
discharge of the Illinois, even when reduced to 0.908 second-
foot per square mile, places the stream in the category of the
St. Lawrence River, whose discharge is shghtly in excess of one
second-foot, rather than with the Mississippi River, whose total
discharge is but about half that amount. The average dis-
charge from the Illinois is thus somewhat less than that of the
Connecticut, of the Hudson, or of the Seine ; is about the same
as that of the Delaware and of the Elbe; but is much lessthan
that of the Loire and of the Po, and relatively less than that of
many European streams.

The maximum flood discharge of the Ihnois has been vari-
ously estimated. On the basis of normal basin ratios for streams
of like climatic conditions it should be equal to the two-thirds
power of the area (A%), which would be about 123,000 cubic
feet per second. The exceptional flood of May, 1892, the crest
of which at Kampsville had a height of 22.8 feet above low
water, was reported by the engineers of the Chicago Drainage
Comunission to have discharged only 94,760 cubic feet per second
at the mouth of the river. Cooley (97), basing his estimate
upon the discharge curves oi the Mississippi at Hannibal and
at Grafton, states that the maximum discharge seldom exceeds
70,000 to 80,000 cubic feet per second, and that a flood of 16 feet
—a height which ordinary floods rarely exceed—would approx-
imate only 55,000 cubic feet per second. The maximum dis-
charge is thus considerably below what is to be expected, and
the explanation lies in the delay in the run-off due to the im-

134

pounding action of the bottom-lands, a phenomenon which will
be discussed later. This discharge occurs most often in March

or April, or in June, and rarely, if ever, in the late summer or

fall, from July to December.

The minimum discharge of the Llinois is, for a stream of its
size, extremely small, indicating the impermeability of the
strata of its basin and the slight contribution of ground water
to its volume. According to Cooley (91) the discharge over
the dam at Copperas Creek for a period of low water continuing
for twenty days was less than 500 cubic feet per second, or 200
cubic feet less than the amount sent through the Illinois and
Michigan Canal by the operations of the Bridgeport pumping
works. In conclusion Cooley says: “It is probable that since
the Bridgeport pumps were erected, in 1883, over half the min-
imum discharge above Havana has come from Lake Michigan,
and one third of the minimum below the Sangamon. For the
purposes of calculation, the normal low-water volume is taken
at 600 cubic feet per second for the upper section of the river
and at 1,200 cubic feet for the lower section.” The minimum
discharge occurs most frequently in the late summer and
early fall—in August, September, and October,—and occasion-
ally in the early winter months.

THE REGIMEN OF THE ILLINOIS RIVER.

Leverett (96) gives the following as the usual regimen of
an Illinois stream:

“During the winter, when the ground is frozen and precip-
itation is comparatively light, the streams are low. In early
spring the thawing of the ground and the greater precipitation
lead to a spring freshet, when the streams are often bank-full,
or even overflowing. This freshet usually occurs in March or
early in April. For a few weeks after this freshet the streams
are at a moderate stage, slightly above the normal. This is
followed by the ‘June rise,’ occasioned by the great rainfall
which occurs in that month, when the streams often reach as
high a stage as in the spring freshet. After the June rise the

cel eT

135

streams usually drop to a low stage and remain low through
the heated term, evaporation and absorption being so great as
to dispose of nearly all the rainfall. In the autumn, about the
autumnal equinox or a little later, heavy rains occur, which
cause the streams to become swollen for a few days, or even
weeks, but which seldom cause them to overflow their banks.
In some years these seasonal variations are slight, and the
streams show but little change in volume, but such years are
exceptional. The rainfall is seldom sufficient to cause freshets
to last more than a few days. The moderate and low stages
are estimated to generally cover ten months of the year, and
occasionally eleven months.”

In the Annual Reports of the Chief of Engineers of the U.S.
Army for the years 1890 and following, Captain Marshall has
published the readings of the river gages located at the govern-
ment dams in the Illinois River. The readings at Copperas
Creek, 16.8 miles above Havana, begin in 1879, and those at
LaGrange, 42.7 miles below, in 1883. The dam at Copperas
Creek was completed in 1877 and the one at LaGrange in 1889.
On Plate VII. will be found hydrographs plotted from the daily
readings at the gages below these dams from 1879 and 1888, re-
spectively, to 1900. The heavy sinuous lines represent the
fluctuations of the river, referred in the plot to the low-water
level of 1879. The mean annual curve was plotted from the
mean monthly readings at the above-named localities from
1879 and 1883, respectively, to 1900. Deficiencies in the records
at the two points named have been supplied, by estimate, from
records at nearest point of observation, in a few cases from our
Havana records.

A comparison of the hydrographs of the gages at Copperas
Creek, Havana, and LaGrange reveals a close correspondence
in the fluctuations, and suggests that these main movements
are due to general rains or spring thaws coincident in the
greater part of the drainage basin. The differences are of a
minor character, and many of them are consequent upon local
conditions of rainfall. On closer inspection the records at Cop-

136

peras Creek and LaGrange exhibit certain general differences
which are not thus explained, but result from some more widely
operative cause. Asa rule the extremes of high and low water
are more pronounced at LaGrange than at Copperas Creek. This
is apparent in the hydrographs of 1883, 1893, and 1896-98. It is
also expressed in the tabulation (Tables I. and II.) of the ex-
tremes of high and low water at Copperas Creek for twenty-one
years (1879-1899) and at LaGrange for seventeen years (1883—
1899). The average range between highest and lowest water
at Copperas Creek is 13.14 feet, at LaGrange 14.68 feet—an in-
crease of 1.54 feet or 11.5%. In like manner the average of
the total + and — movements per year of the river level at the
upper dam is 50.5 feet to 59.15 feet at the lower one—an in-
crease of 17.1% in the fluctuations of the stream at that point.
The greater fluctuations probably result from the fact that
in the lower basin, within which the lower dam lies, the rainfall
is greater, the drainage lines better developed, and the run-off
more rapid. The reservoir action of the Des Plaines, the Kan-
kakee, and the pumps at Bridgeport are also less effective in
regulating the flow of the stream at this point, owing to their
distance and to the reduction in their relative contributions.
The distance, by river, from Copperas Creek to Havana is’
16.8 miles; from Havana to LaGrange is 42.7 miles—a total of
59.5 miles. ‘The fall between the two dams is given by Cooley
(91) as 8.5 feet at natural low water. Our plankton station
thus lies in the upper and more evenly regulated portion of the.
LaGrange pool, and probably in the most stable portion of the
river between Utica and its mouth. The dam at LaGrange
is estimated by the engineers to raise the water 8 feet at
LaGrange, 2.4 feet at Havana, and 2 feet at Copperas Creek.
As has been stated on page 115, prolonged low water will lower
the level at Havana to 2 feet or even less. At such times the
river between the two dams is practically a slack-water pool,
which responds quickly to flood water from any source. Two
principal tributaries, Spoon River and the Sangamon, enter this
pool from opposite sides of the river, the former 4 mile above

137

Havana and the latter 22 miles below. During the summer
season, when local rains occur, it sometimes happens that a
storm is confined to the basin of a single tributary, especially
as the Sangamon and Spoon rivers he, according to Cooley
(91), in different storm-tracks. In such cases the effect may
be very evident at one gage, but be dissipated in large part be-
fore it reaches the other.

The progress down stream of floods which originate in the
upper valley varies with the abruptness and extent of the riseand
with the stage of water in the lower [lhnois. As stated on page
117, it took 15 days for the crest of a flood to pass from Morris
to the mouth of the Illnois, a distance of 259.2 miles. Compar-
isons of the gage-readings at Copperas Creek and LaGrange
show that the progress of the crest of the flood between the
two dams is subject to great variations in duration. In some
instances the culmination is reached upon the same day at both
dams; in rare instances it is reached at LaGrange several days
before it is at Copperas Creek, probably as a result of excessive
flood water from the Sangamon. In the majority of cases,
however, the maximum height is reached at the upper dam in
from 2 to 3, or even as high as 7, days before it is at the lower
dam. This delay is due to a variety of causes, of which one

of the principal ones is the impounding action of the
bottom-lands.

FLOODS AND THE IMPOUNDING ACTION OF THE BOTTOM-LANDS.

Owing to the slight development of its flood-plain, overflows
occur at early stages of the rising river. The appended table,
adapted from Cooley (791), gives data pertaining to bank height
and bank-full capacity of the river at various points along its
course.

It will be noted that the bank-full capacity at Kampsville
is 40,000 second-feet, only one third more than Greenleaf’s (’85)
estimate of the average discharge at that point. At Copperas
Creek, on the other hand, the more moderate estimates of
Cooley (91) place the average discharge at 10,500 cubic feet

138

per second, while the bank-full capacity is estimated at double
this amount. In either case complete overflow stages appear
more readily than they do in the majority of streams.

The impounding action of the bottom-lands, on the other
hand, begins with every rise of the river, for as the water rises
large amounts are drawn off from the main stream by the
adjacent lakes and bayous, many of which retain their connec-

BANK-FULL CAPACITY OF LOWER ILLINOIS RIVER.

Distance Bank Height Cubic feet

Locality | from Utica (feet) per Remarks
(miles) Av. Range second

tion according as river

Perce diner 6.2 10.4 8—13 18,000 —22,000 Measured in 1889. Varia-
| is rising or falling

Henry.. ... 33.2 9.4 Q—I11 | 20,000 —22,000|Very tentative estimates
| from dam and prison
Copperas Very tentative estimates
Creek | 92.7 13.7 I2—15 | 18,000—20,000] from dam and prison
Havana a 109.5 10 6
LaGrange . .| 152.2 11.5 8—I5___| 30,000 Measured in 1889

197.8 11.8 8—15 | 40,000 Estimated from measure-
ments in 1889

Kampsville..

tion with the river even at the lowest stage. In the vicinity
of Havana, for example (see Plate II.), Quiver, Thompson’s, and
Matanzas lakes respond at all times to fluctuations in the river.
Flag Lake is invaded at about the stage of 3 feet, and at 5 to 6
feet the water begins to overflow the bottom-lands between Flag
and Thompson’s lakes. It is not, however, until the river has
reached a stage*of 8 to 9 feet that the water enters Phelps Lake.
The wooded bottom-lands to the east of Flag Lake are not en-
tirely submerged until the gage reads 12 feet, while those below
Spoon River and adjacent to the main stream do not disappear
until the water has reached 16 feet. Thus the impounding
action of the bottoms is at its greatest as soon as the water
reaches the condition of complete overflow, though it begins
at the first stages of a rise above low water.

In his discussion of this subject Cooley (91), speaking of

139

the inadequacy of the stream for the prompt removal of flood
waters, says: “This lack of capacity, while it explains the widé
and deep overflows, by no means implies that any large pro-
portion of the volume moves down the valley for considerable
distances except in the river bed. The dense timber and the
vegetation in summer, the higher ground leading across from
the bluffs along every tributary, the occasional approach of
bluff, terrace, or ridge, the frequently returning sloughs from
interior ponds and lakes, all forbid this. The bottoms are
really storage grounds to impound the flood waters that arrive
faster than the channel can carry them away, and they prolong
the floods in some inverse ratio to the reduction of volume.”

Observations made in the course of field work during the
floods of 1896 to 1900 at Havana, lead me to suggest that there
may often be developed a fair current outside of the channel
of the main stream in such localities as Thompson’s, Flag,
Quiver, and Phelps lakes (Plate II.), where a considerable reach
of open territory lies in the general direction of the main cur-
rent. Even in the wooded districts the current may not be
wholly absent, though it is often very slight.

The duration of the overflow in various parts of the valley
illustrates the reservoir action of the bottom-lands. In the
period from 1883 to 1889 the river was out of its banks at Morris
60 days, or 8.5 days per year; at Copperas Creek, for 444 days, ©
or 63.5 days per year; at LaGrange, 526 days, or 75 days per year.
I quote from Cooley (’91) the following discussion of this subject:
“A better appreciation of the reservoir action, or equalizing
effect, of overflows may be obtained by a consideration of the
impounding area of the bottoms. An area of 704 square miles
submerged to a uniform depth of four feet—this isa flood height
of sixteen feet and not an unusual occurrence—represents 1.21
inches of water running off the entire watershed, and will sup-
ply the river at the rate of 110,000 cubic feet at the mouth for
8.26 days, or at half this volume, which is an approximation to
the true maximum discharge, for 16.52 days. An overflow of
eight feet, or a flood of twenty feet, which is an extraordinary
occurrence, represents 2,42 inches of water running off the

140

entire watershed, and will supply the river at the rate of 110,-
000 cubic feet for 16.52 days, or at half the volume for 33.04
days. * * * During flood stages the valley is a great lake
of, say, 700 square miles, into which flood waters from above
and from tributaries are precipitated, and from the lower end
of which they run out more at leisure and in reduced and
equalized volume.”

When we remember that even in the average year over
21%, or more than 8 inches, of rainfall escapes by way of
the river, that the greater portion of this run-off takes place at
times of flood, and that the overflows are greatly prolonged in
the lower river by the inadequacy of the channel to carry off
the excess of water and by the imperfect development of the
flood-plain consequent upon the past history of the valley, we
realize how important, and at the same time how unique, a fac-
tor is the retardation of the run-off in relation to our plankton
operations. 7

The past decade has witnessed the completion of a vast
amount of surface and under-drainage throughout large areas
in the watershed of the Ilhnois River. Extensive open ditches
have been dredged through localities where the slope or other
conditions do not favor the establishment and maintenance of
natural channels. These have been supplemented by miles
- upon miles of tile drains, thus bringing under constant cultiva-
tion hundreds of square miles of territory occupied in former
years by pond, marsh, or meadow of the original prairie. Even
in the rolling prairie the thousands of little ponds and marshes
which formed the head waters of the various tributaries of the
river have been blotted from the landscape by the tile drain.
In addition to this the natural lines of drainage have been sup-
plemented in a great many cases by under-drainage, in order to
facilitate the run-off of the rainfall and the ground water, and
thus bring the soil as soon as possible into condition for culti-
vation. This work of drainage is to a great extent completed
throughout a large part of the catchment area. The principal
exception is the basin of the Kankakee River, but the drainage
of even this has already been projected.

141

The outcome of this wide-spread interference with the
established condition of natural drainage has given ground for
the almost universal testimony that streams which in former
years held a continuous flow throughout the summer no longer
run in the dry season. The reservoirs at their head waters are
emptied and the supply of ground water is early exhausted by
the artificial drainage in their basin. There is also a consider-
able concurrence of opinion that, in the smaller. streams at
least, the floods come more suddenly and rise to greater heights
than they did in former years. The “wash” along the banks
and consequently the amount of silt carried in suspension by
the flood waters are thus increased.

The presence of under-drainage undoubtedly facilitates the
discharge of such water as reaches the drains, but this impetus
is in large part counteracted by the greatly increased power of
absorption of the soil when thus drained. Heavy rains upon a
soil already surcharged with moisture may lead to even a
greater run-off than the same rainfall upon the same territory
rendered porous and capable of absorbing and retaining, for a
short time at least, a large amount of moisture.

From many points of view the subject of the effect of drain-
age of the catchment-basin upon the flow of streams is one of
interest and importance. For its adequate discussion records
of a long series of years of the stages of tributary streams and
the river both before and after the installation of the drainage
system are needed. With a view to throwing some hght upon
the possible effect of drainage upon the floods in the main river,
and consequently upon the plankton, I have tabulated the
fluctuations (in excess of .25 foot in 24 hours) in the river level
at the lower gage at Copperas Creek for an earlier and a recent
period, each of five years. The earliest authenticrecords which
I have been able to secure begin with 1879. This antedates the
completion of a considerable portion of the artificial drainage
of the river basin. I have accordingly chosen the records of
1879-1883 inclusive for comparison with those of 1892-1896
inclusive. This choice is unfortunate in one respect, for the
earlier series lies in a period of heavy rainfall and the later in-

142

cludes two years of unusual drouth. The fact that the earlier
period is in a series of wet years and the later in one of dry
years will, it seems, tend to obliterate whatever contrast may
exist in the rate of the fluctuations. Thus the extent of the
fluctuations is much greater in the earlier period and the dura-
tion of high water is longer. The river was above the six-foot
level during 1,028 days in the first period, as against 709 in the
second; and.it was above ten feet, that is ata stage of overflow,
645 days in the earlier period, and only 297 in the later one.
The dam at LaGrange, completed in 1889, raises the water 2
feet on the lower gage at Copperas Creek at the low-water
stage. Its effect at the stages above cited is not, however,
according to Cooley, perceptible at the upper end of the pool.

The results of the tabulation do not reveal any alarming
changes in the flood habits of the river. There is, however, a
well-defined increase in the rate of movement in the later period
as compared with the earlier. The average daily movement
(above .25 foot) 1s in the first period .416 foot, in the second
period .492 foot,—an increase of 18%. The difference is still
more marked when the comparison is made in the rate of rise
alone. In the earlier period the rate of movement (in excess
of .25 foot) was .4848 foot per day; in the later period it was
.592 foot; an increase of 22%. The distribution of this increase
through the year is somewhat irregular, and, owing to the in-
sufficiency of the original data, is probably of slight significance.
The greatest increase occurs, however, in the months of May,
December, September, and March, all months in which floods
prevail, or at least occur occasionally.

As shown on previous pages the conformation of the valley
is such as to induce a prolongation of the floods. The records
and the hydrographs show that the decline from a rise is in
most cases much less rapid than the approach of the flood. We
find accordingly in the above table that the number of days of
decline (at a rate exceeding .25 foot per day) is considerably
less than those of rising waters, and that the rate of fall is also
less than the rate of rise, being only .3185 and .337 foot, respec-
tively, per day, in the two periods. The increase in the rate of

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144

fall is thus less than 6%. So far, then, as the table goes, it
indicates that there has been a moderate increase in the
rapidity with which floods rise and a slight increase in the rate
of their fall, as compared with the rate of their movements in
a corresponding period thirteen years ago.

It is impossible from data at hand to determine whether or
not the general drainage of the basin has shortened the period
of high water and extended that of low water with a consider-
able diminution of volume at low-water stage. The decade prior
to 1896 seems to have witnessed such a change, as hydrographs
on Plate VII.show. This diminution is the more marked when
allowance is made at low-water stages for the 2 feet which the
dam at LaGrange (completed October 12, 1889) is estimated to
raise the water on the lower gage at Copperas Creek. The fact
that the rainfall was deficient during this decade doubtless

MONTHLY MEANS OF GAGE-READINGS (IN FEET) BELOW COPPERAS CREEK DAM
1879-1899.

(Basis of reference, low water of 1873 and 1879.)

Year | Jan. | Feb.| Mar.'April|May | June} July | Aug.|Sept./Oct.| Nov.| Dec. ae
1879...| 2.76, 6.20] 8.66 10.80] 5.52) 2.66) 4.53] 2.09] .30|1.03] 2.19] 5.24) 4.33
1880...] 9.88] 9.83] 9.65|10.15]12.39] 9.90| 7.48] 2.83] 2.90|2.32] 1.69] 1.58) 6.72
1881...| 1.48] 7.88]/14.69'14.72/11.41] 9.01] 4.89] 2.04] 1.22/4.74]10.69]13.88] 8.05
1882...|12.47| 9.61/13.87|12.43|12.91/14.65|11.64| 6.10] 4.06/3.29] 4.22! 5.08] 9.19
1883...) 6.58/10.01]14.95]12.60/11.85/11.57| 9.43) 5.83] 1.94/2.91] 8.48] 9.63} 38.82
1884...| 6.58]12.23]13.54/13.55/10.57| 7.57] 6.41] 3.49] 2.82|7.89] 6.22) 6.91) 3.15
1885... .|13.12]10. 31/12. 33]13.69|11.12| 7.34] 4.90] 5.04] 6.06/6.68/10.30] 9.07) 9.16
1886, . .|12.28]12.67]13.24]12.85]12.37| 8.87] 2.85] 1.78] 2.24/3.13] 2.91] 2.67] 7.32
1887...| 4.29]13.05|12.48] 7.77] 3.86] 2.40] 1.62] 1.40] 1.83/2.38] 2.09] 3.49] 4.72
1888,..| 6.48] 7.47/12.87]11.75| 7.81/10.18] 8.31] 4.05! 1.86]1.91] 2.85) 2.59! 6.51
1889...| 4.52] 3.84] 7.18] 6.24) 3.88] 8.81] 8.80] 4.44] 1.30/2.47] 4.10] 6.03} 5.30
1890... 9.56] 9.31| 8.98]11.24|10.07|10.46| 7.86] 3.17| 2.66)3.16! 3.32] 3.52] 6.92
1891...| 3.67] 4.08] 8.00]11.94] 9.23) 6.85] 4.73] 3.13] 2.41|1.93| 2.47] 4.24] 5.22
1892...] 4.58] 5.53} 6.88/11.44/16.46/14.52/13.41| 7.14] 3.31/2.83] 2.90) 3.77) 7.74
1893...| 3.87] 7.69|14.90|12.60]13.74|/10.37) 4.93] 1.73] 1.67/2.42] 2.54) 3.33] 6.63
1894...| 3.92] 4.29] 9.24] 7.40] 7.29] 4.63] 2.32] 1.99] 4.43/2.96] 2.97] 3.41] 4.63
1895...| 3.30] 3.51| 6.28! 5.41| 3.68] 1.88] 3.17] 2.43] 3.42/1.93] 2.20] 6.16] 3.61
1896...|10.65] 9.23] 9.79| 7.66] 7.35] 7.73] 4.38] 7-70] 4.66/6.37| 6.10] 5.64] 7.26
1897.. .|II.39|11.04|14.09|13.34| 9.52] 5.71| 6.19] 2.36] 1.81]1.76| 2.42] 3.06] 6.86
1898. 10| 9.31/13.25|14.69/11.49|11.49] 5.50] 3.52] 4.29/4.28] 7.79] 6.92] 8.11
1899... 47| 7.28|13.07|11.24] 7.86] 7.58] 4.05] 2.71] 2.24/2.54| 3.64] 4.56) 6.27
Means

for 21

years! 6.90] 8.20|11.34|11.11| 9.59] 8.29] 6.06] 3.57! 2.82/3.271 4.38] 5.27! 6.74

145

MONTHLY MEANS OF GAGE-READINGS (IN FEET) BELOW LAGRANGE DAM

188 3-1899.
(Basis of reference, low water of 1879.)

Year | Jan. | Feb.| Mar.|April] May | June] July | Aug.|Sept.|Oct.| Nov.| Dec. vey
1883...| 7.41 11.36/16.71|12.77]12.18|/13.04/10.34| 5.62] 1.67)2.52] 6.89] 8.81] 9.11
1884...] 6.09/13.04/14.17)14.92|11.22| 8.66] 6.42] 4.04] 2.74|7.62] 6.01] 6.70} 8.47
1885... |14.17/12.06/13.84/14.20/12.48) 7.99] 6.40] 4.72] 5.18!5.69] 9.32] 8.15] 9.52
1886, . .|12.83/13.77|/14.24|13.79|12.77| 9.31| 2.79] 1.54) 1.68/2.53] 2.12] 2.32] 7.47
1887...| 3.70|12.71|13.64| 7.36] 3.75] 1.70] 0.72] 0.23] 0.24!0.79] 0.83] 2.21] 3.99
1888...| 6.25] 7.62) 9.87/12.01] 9.02/10.78] 8.61] 3.93] 1.21]0.95] 1.79] 2.05] 6.17
1889*..| 4.33] 3.59] 7-27] 5-78] 3.72] 9.48] 9.05] 4.00] 2.45)0.92] 3.75] 5.43] 4.98
1890... .|10.22| 9.41) 8.92/10.43] 9.39] 8.82] 6.83] 1.39] 1.11]1.58] 1.86] 1.92] 5.96
1891...| 2.21] 2.67| 6.06)10.13] 9.00] 5.18] 3.56, 2.16) 0.92/0.32) 1.23] 2.83) 3.86
1892...] 3.42! 4.84] 6.69 12.70]17.16|15.97|14.39] 5.84] 2.13!1.29] 1.69! 2.94) 7.42
1893...| 2.46] 8.31]15.44'13.74]15.87|12.00] 4.24] 0.68 0.34|1.28 1.09] 2.24) 6.45
1894...] 2.70] 4.19] 7.38] 6.28] 5.80) 3.24] 1.26] 0.57) 2.96/1.56] 1.73] 2.12] 3.30
1895...} 1.96] 2.70 4.98| 4.05] 2.32) 0.73] 1.96] 1.55] 2.74/0.86] 1.02] 4.99] 2.49
1896...|10.06) 8.64 8.92 6.61] 5.90] 7.09] 4.77] 7.59] 4.32/5.28] 5.20] 4.85] 6.60
1897. :|I1.50)10.95|14.50,15.49]10.28] 4.99] 5.65] 1.80] 0.98/0.86] 1.43] 1.93) 6.67
1898...| 4.55] 9.09/13. 15}/16.33]12.74/12.85] 5.44] 3.29] 3.96/3.57| 6.75] 6.40] 8.14
1899...| 7.87] 7.87|13.79|11.58] 8.92) 8.93] 3.94] 2.28] 1.08]1.23] 2.45] 3.19] 8.09
Means

for 17

years.| 6.57| 8.40|11.15!11.07] 9.56) 8.28] 5.67] 3.01] 2.11/2.28] 3.25] 4.07| 6.40

*Dam practically completed in November of this year.

accounts for much of this change. Records during a period of
abundant rainfall are necessary for an adequate discussion of
the problem.

The foregoing tables give the monthly means and monthly
and yearly averages at the two dams for the period above named.

In Tables I. and II. are to be found tabulations of the ex-
tremes of low and high water, the range of movement, and the
total of the + and — movements for each month in the periods
covered by the records at the two dams. The appended table
also gives some data pertaining to the major fluctuations at
Copperas Creek. The rainfall statistics refer to the state as a
whole and are taken from Leverett (’96).

From the data presented in the hydrographs and these
tabulations the variations and the average condition of the
Illinois River may be determined, and some estimate made of
the normal regimen of the stream. In general terms this is as
follows: There is in each year a period of high water—that is,

146

FLUCTUATIONS AT COPPERAS CREEK.

Per cent.
rainfall

Number of
rises exceed-
ing 3 feet in

ececee

Number of
culminations
of floods ex-
ceeding Io
feet above
low water...

Occurrences
of minimum
stages forthe
year

Occ urrences
of maximum
stage for the

Average num-
ber of days
when water
was more

than 8 feet
above low
Wat@luiarcmicn

Average num-
ber of days
when water
was less than
4 feet above

low water ..

Jan. | Feb. Mar./Apr. May|June| July/Aug.| Sep.| Oct.|Nov.|/Dec.
O37) O57) 7/0), 32/15/12 ©.0) 3.4) ©.6| 8.5] 7.0) 6.
ee So alee ek es | 3 |S
ABS | oO |S.) G |O FO |o}o |. | 3
fo) fo) fo) fo) fo) I 3 6 8 5 I I
3 B 5 © | 2 I Oo |©O1oO lo | © I
I1.1/ 15.8 24.8 23.9 20.1| 16.8] 7.9] 1.7| 0 1 Oe) er KOS
10.0] 3.8] oO fo) 3.6 4.8) 8.9 20.8) 23.2, 25.0 19.0] 15.0

Total

132.2

134.1

*Minimum levels reached in two different months in 1887 and in 1892, and in three

in 1897.

more than 8 feet above low water—whose duration has aver-
aged 132 days, ranging from 11 days in 1895 to 230 in 1883. The
average seasonal position of this period is from February to
June, inclusive, though portions of it have occurred in every
month of the year but September.
the autumnal rains in October or November and continues
throughout the winter, as in 1881 and 1889, though in some in-
stances this early autumnal rise is followed by a sharp and con-

In some eases it begins with

147

siderable decline. The rise of the flood may occur in any of
the succeeding months up to and including April. There is a
predominance of flood movement in January as compared with
February, there being more instances in the former month of
movements exceeding 3 feet and culminations of floods exceed-
ing 10 feet than there are in the latter. What is popularly
known as a “January thaw” is probably the occasion of this
predominance. The rise of the flood is often very rapid, as, for
example, in 1881, 1888, and 1895, the rise in 1883 being over 11
feet in 8 days. These rapid rises often occur after heavy pre-
cipitation in winter months when the conditions favor a very
rapid run-off. The initial stages of the flood are usually less
precipitous, as are also the final stages preceding the culmina-
tion, especially at overflow stages, when the flood capacity is
greatly increased by the impounding action of the flood-plain.
The flood curve is rarely an even one, such as that of 1887, since
fluctuations of more or less importance occur, as a rule, during
both the rise and fall. <A well-defined culmination is, however,
present, except in a few instances, such as in 1890, when three
about equal maxima appear.

The maximum of the flood occurs most frequently in the
latter part of March or the first part of April, though it may
appear as early as December, as in 1895, or as late as June, as
in 1889. Of the twenty-one maxima six have been in April,
five in March, three each in January and February, two in
May, and one each in December and June. The highest point
reached at Copperas Creek in 21 years was 19.25 feet in 1885.
The rises in excess of 10 feet above low water in the 21 years
have appeared nine times in April, six in June, five in March,
four in January, three each in December, February, and May,
and but once in November, while no flood has reached this limit
in the remaining four months. The decline of the flood is much
less rapid than its rise, and is often marked by secondary rises
which more or less delay the return of the low-water period.

The “June rise,” caused by the heavy rainfall of that month,
is masked by the averaging process in the mean hydrograph,

148

but appears occasionally (nine times in twenty-one years) in
the annual ones as a well-defined flood. In the majority of
years, however, it appears as a slight interruption in the decline
of the earlier spring flood. In a few cases these fluctuations
occur late in May or early in July. The fact that this June
rise is so little felt in the Illinois, while it is so prominent in
other streams of the state, is explained by the fact that it often
occurs within the period of overflow, when large accessions of
water produce relatively slight rises of river levels. A compar-
ison of the hydrographs of 1889 and 1892 will illustrate the
points in question, the June rise of the latter year appearing as
a slight fluctuation in the declining flood, while in the former
year it stands out as a well-marked rise, owing simply to the
previous low water.

As compared with Leverett’s normal regimen for an I]linois
stream, we find in the case of the Illinois River that the high-
water period exhibits a considerable range; that it extends over
a much longer time; and that the phenomenon of the June rise
is less pronounced,—all of which deviations may be explained
by the impounding action of the slightly developed flood-plain
of the Illnois.

Following the period of high water comes an equally pro-
nounced period of low water, extending through the summer
‘months until the late autumnal or winter rise. As shown by
the averages, this low-water period (below four feet) extends
from August to November, inclusive. It varies, however, with
the high-water period, appearing even in May, as it did in 1895,
and frequently continuing through the fall and winter till late
in February, as it did in 1891, 1893, and 1894. The average
time during which the water was below 4 feet for the 21 years at
Copperas Creek is 134.1 days, two days more than the high-
water period. This low-water stage is quite variable in its du-
ration, ranging from 260 days in 1895 to 5 in 1885. The low-
water period, which Leverett estimates as continuing at least
ten months in normal] Illinois streams, is thus much shortened
in the Illinois Riyer, The lowest levels of the year are reached

149

usually in September, the occurrence of minimum levels being
distributed among the months as follows: In the records at
Copperas Creek, eight occur in September, six in August, five
in October, three in July, and one each in November, December,
and June. The lowest level was recorded at Copperas Creek in
1879, when the low-water mark was established. It has not
again been reached, owing since 1889 to the dam at LaGrange.

The low-water period is often one of marked stability as
contrasted with other parts of the year, the total movement of
river levels falling to 0.10 foot per month in November, 1898,
and frequently amounting to less than one foot in September,
October, and November, while even this movement is probably
caused to a considerable extent by the operation of the locks
and by changes in the direction or force of the wind. The stage
of extreme low water is followed by a gradual but very slight rise
during the fall months, which cannot be attributed entirely to
ramfall since, as shown in the table on page 126, these are
months of lessened precipitation. This increase is well shown in
the hydrographs of 1893 and 1897. It seems more probable that
with the falling temperatures the loss by evaporation, both from
the river and its tributaries, is sufficiently lessened to account
for this slight rise in levels, amounting in most cases to about
one foot.

This low-water period is frequently interrupted by minor
fluctuations, some of which appear at or subsequent to the
autumnal equinox. These fluctuations are due to heavy sum-
mer rains, and usually appear suddenly and decline with almost
equal abruptness. They rarely rise to eight feet and are usually
below five; they thus do not cause overflows, and affect only
those bayous and lakes which maintain connections with the
river at low-water levels. Their duration is short also, being
but a week or ten days, rarely a fortnight. In 1896 there was
a repetition of such rises of more than usual prominence and
duration, giving a unique character to the hydrograph of that
year. The equinoctial period, marked by the slightly increased
rainfall of September, is not marked in the average hydrograph

150

by any increase. Indeed, the average level for this month at
Copperas Creek is only 2.82 feet, the lowest average for the
year. The rises attending this period appear but twelve times
in twenty-one years, are usually insignificant, and are often less
than two feet, owing doubtless to the greater capacity of the soil
for absorption at this season of the year.

The time not included in the high- and low-water periods.
as here defined amounts on the average to 96 days, a relatively
short time for the transition between these two extreme condi-
tions. This abruptness of the transition stages is to some ex-
tent apparent in the hydrographs.

On Tables I. and II. will be found tabulations of the total
movement, both + and —, of the river levels in each month in
the period covered by the records at the two dams. The
monthly and yearly averages of these data are also given. The
figures are to a certain extent an index of the relative stability,
both monthly and annual, of the river. The averaging process
has to some degree masked the differences in the several
months, as will be seen on a comparison of the mean monthly
movements with those for any single year, the latter exhibit-
ing at some times of the year much greater contrasts than the
means. Thus the greatest and least movements in 1897 are re-
spectively 10.37 feet in January and 0.40 in October, while the
corresponding limits in the means are 4.18 feet in July and 2.78
in November. The means indicate two periods; one of consid-
erable movement, corresponding to that of high water, and one
of less movement, representing the low-water stages. The
greatest movements occur in February and July, indicating the
rise and decline of the flood. The least movement is found in
November, a period of low water and freedom from sudden and
heavy rainfall. The several years exhibit quite a range in the
total amount of change in levels, the extremes in Copperas
Creek in twenty-one years being 68.70 feet in 1881 and 32.92 in
1894; at La Grange, in seventeen years, 85.36 feet in 1898 and
40.41 in 1887. The movement is thus somewhat greater and
more yariable at the lower dam, In general there is some cor-

151

relation between the average heights of the water for the year
and the total movement of levels, though this correlation 1s by
no means continuous or uniform, as will be seen, for example,
on comparison of the average heights and movements for 1895
and 1896 (3.61 and 7.26 feet; and 51.89 and 53.16 feet). The ab-
normally low water in 1895 was followed by an unusually early
rise in December. Had this rise occurred ten days later the
correlation of average heights and total movements would have
been more apparent in these years.

The range in movement of river levels between the highest
and lowest water of the year as shown in the tables varies at
Copperas Creek between 9.00 feet in 1889 and 17.70 in 1883, and
at LaGrange between 8.75 in 1894 and 20.52 in 1888, while the
extreme range for the period of record at each dam is 19.27 and
22.92 feet respectively. Somewhat greater fluctuations thus
occur at the lower dam.

The preceding discussion of the fluctuations in river levels
affords evidence for the extreme instability of the environment
of the plankton with which we are to deal. Indeed the only
really constant feature seems to be this very instability. The
mere presentation of the statistics of the fluctuations can give
but little hfe or color to the great modifications which these
changes produce in the physical conditions environing all the
aquatic life of the river. The great increase in area and vol-
ume (not far from one hundredfold) which occurs at high
water (Plate III.) affords an opportunity for a great increase in
the total production of the plankton, especially when the flood
period extends into the spring and early summer months, when
the maximum development of the plankton sometimes occurs.
The submerged flood-plain also affords the greatest variety of
conditions of depth, current, vegetation, bottom, light and
shade, temperature, and sewage, thus favoring the diversifica-
_ tion of the plankton locally-produced but carried away to some
extent into the channel by the receding floods.

A trip by boat across the submerged bottom-lands from the
Quiver shore to the western bluff (Pl. I. and III.) in the latter

152

part of May would be far more enlightening than any descrip-
tion that might be given. As we leave the sandy shore of
Quiver we traverse the clear, cold, and spring-fed water along
the eastern bank with its rapidly growing carpet of Cerato-
phyllum, and in a few rods note the increasing turbidity, rising
temperature, and richer plankton of the water which has moved
down from the more or less open and slightly submerged
bottom to the north (PI. II.). As we cross the muddy bank of
Quiver ridge and enter the main channel of the river we find
rougher water, caused by the wind which usually sweeps up or
down the stream with considerable force between the bordering
forests. The water also appears much more turbid by reason
of silt and plankton, and no trace of vegetation is to be seen
Save occasional masses of floating Ceratophyllum or isolated
plants of Lemna, Wolffia, or Spirodela. Huge masses of cattle-
yard refuse, veritable floating-gardens, may also at times be
seen moving down the channel or stranded in some eddy along
shore. As we plunge into the willow thicket on the western
shore we have to pick our way through the accumulated drift
lodged in the shoals or caught by the trunks of the trees or the
submerged underbrush. The surface of the water is one mat
of logs, brush, sticks, bark, and fragments of floating vegeta-
tion, with its interstices filled with Lemnacee dotted with the
black statoblasts of Plumatella. From this dark labyrinth we
emerge to the muddy but quiet waters of Seeb’s Lake with its
treacherous bottom of soft black ooze. We next enter a wider
stretch of more open territory with scattered willows and ma-
ples and a rank growth of semiaquatic vegetation, principally
Polygonums. The water is clearer and of a brownish tinge
(from the diatoms), while mats of alge adhere to the leaves
and stems of the emerging plants. A flock of startled water-
fowl leave their feeding grounds as we pass into the wide ex-
panse of Flag Lake. We push our way through patches of lily-

pads and beds of lotus, past the submerged domes of muskrat —
houses built of last year’s rushes, and thread our way, through
devious channels, among the fresh green flags and rushes just

153

emerging from the water. Open patches of water here and
there mark the areas occupied by the “moss” or Ceratophyllum,
as yet at some depth below the surface. The Lemnacee are
everywhere lodged in mats and windrows, and, amidst their
ereen, one occasionally catches sight of a bright cluster of
Azolla. The water is clear and brownish save where our
movements stir the treacherous and mobile bottom. We now
enter a second time the partially wooded country, and cross
the submerged ridge to the sandy eastern shore of Thomp-
son’s Lake. This ridge is covered by submerged vegetation
which has as yet attained but little growth. The “breaks” of
the startled fish show that we have invaded favorite feeding
grounds. The waters are evidently moving towards the river,
and they bear the rich plankton of Thompson’s Lake, while
their turbidity is doubtless increased by the movements of the
tish. Schools of young fry can be seen feeding upon the
plankton in the warm and quiet waters. Thompson’s Lake,
the largest expanse of water in the neighborhood, is wont to be
rough in windy weather, but if the day be still we can see the
rich aquatic vegetation which fringes its margin and lies in
scattered masses toward its southern end. Its waters seem
somewhat turbid, but more from plankton than from silt,
though the deep soft mud which forms much of its bottom is
easily stirred. The slender transparent limnetic young of the
gizzard-shad may be seen swimming near the surface. There
is a perceptible drift to the south in the open lake, though this
current is deflected by the elevated banks of Spoon River ( Pl.
II. ) towards the Illinois River, crossing the lower bottom-lands
above this region. If we push on through the fringing willows
at the south we find a series of open places locally known as
“nonds”. The warm still waters are turbid in places from the
movements of fish, and at times we see the compact schools
of young dogfish (Amia calva) and, if we are late enough in
the season, the myriads of young black, tadpole-like catfish
(Ameiurus), likewise in schools, while young carp ( Cyprinus
carpio) are everywhere. The new vegetation is already spring-

154

ing from the decaying and matted stems of the preceding sum-
mer. Turning back towards the river we pass through the
heavy timber where the still brown water, cool and clear, over-
lies the decaying leaves and vegetation of last season’s growth,
now coated with the flood deposits of the winter. Hmerging
again upon the river channel we may find a turbid yellow flood
pouring out from Spoon River, bringing down its load of drift
and earth, and marking its course down the stream as far as
the eye can see.

From an environment even more varied than this come
the different contributions to the plankton of the river in the
flood seasons. Every change in level modifies this environ-
ment by connecting or cutting off backwaters, shifting or check-
ing currents, disturbing vegetation and temperature in a man-
ner the very complexity of which beggars description.

Contrast with the extent and variety of conditions at flood
the limitations placed upon the stream at low water (PI. IV.
and V.). Instead of an unbroken expanse of four or more miles
we find now a stream only 500 feet in width (at Station E), while
the adjacent territory is dry land save where the sloughs,
marshes, and lakes remain as reservoirs. Quiver Lake is now
much reduced in width, and it may be choked with vegetation
except in a narrow channel where the clear water shows little
or no current. A half mile below we find the river water rush-
ing in a narrow “cut-off” across the ridge of black alluvium
into the lower end of the lake. The wooded banks which sep-
arate the river from Quiver and Seeb’s lakes are now crowded
with a rank growth of weeds and vines. The latter “lake” is re-
duced to a shallow stagnant arm of the river, whose warm turbid
waters are foul with dead mollusks, and whose reeking mud-
flats beneath the August sun shine green and red with a scum
of Euglena. As we pick our way through the tangle of rank
vegetation we come upon Flag Lake, now a sea of rushes. The
discharge from this marsh to the river ceased in the early sum-
mer, and its margins are even now dry, with gaping cracks.
Beyond the marsh we pass to the shore of Thompson’s Lake to

155

find its southern end choked with vegetation, though the greater
part to the north is open water. The woodland and open
ground to the south are now pastures and fields of waving corn
The only outlet to this large body of water, now somewhat re-
duced in area but warm, turbid, and rich in plankton, is a tor-
tuous slough six miles to the north. The discharge, however,
is in any case but slight, the lake being, indeed, not infrequently
the recipient of river water. Spoon River still pours a sluggish
but constant stream into the river, but save for a water-
bloom of livid green (Huglena) its waters yield but little plank-
ton. Thus, of all the wide area contributing to the plankton of
the channel at high water there now remain only Thompson’s
and Quiver lakes and Spoon River, each much diminished in
volume, but all diversified in character.

Returning now to the river itself we find a gently sloping
bank of black mud, baked and cracked by the sun’s heat, ex
tending towards the softer deposit at the water’s margin. A
low growth of grasses, sedges, and weeds springs up as the
water recedes. The river margin does not often have much
aquatic vegetation. In low-water years, such as 1894 and 1895,
a considerable fringe is formed along the shore, but this is
quickly cleaned out on the seining grounds, which occupy a
large part of the shore, as soon as the fishing season opens in
July. In years of normal high-water the vegetation rarely
gets much of a foothold along the shores, even at low-water
stages. Save for the few sandy banks where springs abound,
such as those below Havana along the eastern bluff, there is
little, at least in the LaGrange pool, to vary this monotony of
mud banks and fringing willows. The backwaters have been
reduced to the lakes, sloughs, bayous, and marshes (Pl. II.)
which abound everywhere in the bottom-lands. Many of these,
as, for example, Phelps and Flag lakes, have ceased in their re-
duced condition tocontribute tothe river. Others, like Thomp-
son’s Lake, maintain a connection with the river by means of
a long and tortuous bayou or slough through which the cur-
rent flows in or out as the relative levels of the two fluctuate.

156

This lake receives but little water from a few springs and
creeks along the bluffs, and like many others in the bottom-
lands serves only as a reservoir from which the water is slowly
drawn off as the river falls, but when once the lower stages are
reached its contributions cease. Still others, like Quiver and
Matanzas, maintain direct and open connection with the
river, and since they receive tributary streams they continue
to feed the river, but in reduced volume. Though the number
of tributary areas is thus much reduced at low-water stages,
the individual peculiarities of the tributary waters in the bot-
tom-lands become more pronounced. As each one loses its
connection with the general flood it becomes a separate unit of
environment, with its local differences in those factors which
determine the character of the plankton developing in its
waters. The resulting contributions may thus differ greatly in
amount and component organisms, and accordingly tend to
diversify the river plankton of low water to a degree even more
marked than that of high water.

With the confinement of the river waters to the channel
goes a marked condensation of the sewage, which, under condi-
tions of uninterrupted low water, leads at times to an excessive
development of the plankton, or, if the river is closed by ice, to
stagnation conditions. But few years, however, offer such op-
portunities; for, as a rule, in most low-water periods sudden
and heavy rains are wont to occur which flush the stream,
wash away the sewage and plankton-laden waters, and store
anew the reservoir lakes without causing any considerable
overflow. After each catastrophe of this sort the decline of the
flood affords a new and favorable opportunity for the develop-
ment of the plankton.

In this instability lies the great distinction between the
river and the lake as a unit of environment—for I believe we
are justified in applying this phrase to the conditions of fluvia-
tile life, though it must be admitted that the “fluviatile unit”
is an exceedingly complex one. As the discussion of the river
fluctuations indicated, there is a seasonal routine which the

157

cycle of seasonal fluctuations more or less approximates year
after year, and not a few of the important environing factors
are operative in much the same way upon by far the larger
part of the biological area. There is thus a common basis
upon which the other less constant factors produce their effect.
The best justification, however, for the use of the term lies in
the results of our work, which show a biological assemblage
adapted to this complex environment, and exhibiting in some
of its phases at least as much uniformity as the more stable
factors of its surroundings.

During 1894 and the early part of 1895 readings were re-
corded only at occasional intervals owing to the fact that the
Station was occupied but part of the time, its work being as yet
in the preliminary stage. From August to October, 1895, bi-
daily readings were made by Mr. Newberry at a gage located
by us at our field headquarters and based upon the government
gage on the protection at the wagon-bridge at Havana. From
October, 1895, to January, 1896, the readings were taken by
Mr. Hempel at the government gage, and since that time bi-
daily or daily readings have been taken under the direction of
the city authorities of Havana. These readings are given in
the tables which follow.

158

READINGS OF RIVER GAGE AT HAVANA, 1895.

(Plane of reference, low water of 1873.)

Jan. | Feb. | Mar. | April ||May | June] July
SEE Pe Sle el Sean na | nie
zVevenatonall Biacieacvalberorpete General Sooaan ieee of
sueversi oval] fereceter eal sealerorsts 4.85} 4.00] 2.80]......
AEB lees orl iokicunel adic Si BH OO| latices
rapecseavel eueimeacarelllesorenets| aes ener ASOD! sc, Seullls neta
Ea ee Ban a OAS ee Ah tea | ae
Said sonal leolava anal etrerdee A35|lsospeelloaaeudlloadcos
eral fae acta [Gee ASOS | eacesreral| evcssisve leer
Sia us| See evel hares Shere B£Cl|ooao0clloodoc0]) BoA)
Hance Stores a ane GE20| irae aomiline srr Ze 5
Sears herctaveys iamiorars BSG rates se ci|tocretseovel|everscor eee
Ron “lis sate une meat a ait Ne ye a
Meettscull Gesvtheis GSO |i soci ssi) oe Sd Or steels o|lereresevers
legal Aree lteeaiertnl ieee 0 ced ae DOOM Ge
sais Touevellteyave oxtforltNrateye tore BsS8llocdocal| Bai ccoode
A Al Retatise eter acIEae po 3125||| 2. Colman -
sere tera evesenceustel| Carerauar eel lerocenstene 3.00 1.860...
srameyscelltwalerute 52(0lladao col (suoooal besos clananioe
seseheas all aoevoealltens oil een ane Taso ee
Idee vl ltestsre ie tones bevel leaeeas are lyeueteraes a7Olee eee

Reece rexel levercicnnl lia octet BelOvaarhyer
Bee ens: 5.10 5-10]....e-Jeveee[eeeees
be coe | ne

eee ee

eoee ee

eee eee

Sept.| Oct. | Nov. | Dec.

Ao 6 7/5]| BsZ5)looooc
2.42) 2.55] 2.30] 3.15
6BY)| PolblAlaaco o> 3.20
5.12] 2.37] 2.30] 2.20
Bey 2o3Oloocndc 3-35
5.87| 2.27) 2.37) 3.35
5.80} 2.22} 2.45] 3.35
BoA] 2220) 2o8Gllooooc
5.00} 2.20] 2.65! 3.35
A 30) 2oAOcacccc 3.35
AMO oocda. 2.67) 3.05
3.77| 2.20] 2.70] 3.00
3/55) cers 2.70) 2.92
3.27| 2.20) 2.70) 2.85
3200 |seeaer Da \ocoo
3.47| 2.25] 2.70] 2.70
3. 62|) (2237) eeeee eee
3.52| 2.45] 2.70] 2.85
3-35} 2-37) 2.75) 5.20
312 haar 2.77| 7.60
2.92| 2.40) 2.75] 7.75
2.82} 2.35) 2.70] 8.45
DeifP| AoB5| Bo7/5}| Goe2
BLY) BoRElloooocc 9.55
2.62} 2.30] 2.80]10.30
2.72| 2.40] 2.90/11.00
BIO 2|bo00 0-0 2.85/11.50
BO 2QoSAicocacc II .92
padeoo 2.30, 2.85]/12.25
ister 2.25] 2.90/12.50
averstar 2.25|......|12.60

159

READINGS OF RIVER GAGE AT HAVANA, 1806.

(Plane of reference, low water of 1873.)

5-89] 5.48

S)
oO
a)
>
°
Z
=
2G | FOSTOONMDANRADARAOOROTAMAODO ARO TMAHOH! O
5 | FTFIMMOOOOOOOODOODOOO OOOO ininininininminin | oO
. | a
eo, | COMTAVHFONwWMMAH OH MHA +tNO ADDO NOMtHOM No)
w rerormwaa sp poppet ttt tte ttt ttt Ht HHH Ht SS ks
5 [3
DAIMOOO N+FtMNAH ONO +AHNINMA H GOO NRO INnMA O Goo | +
SN So Sra te eee ES EON SSIES SEROMA RANI IAN GXC9) BSNO) WADE] ONE)
2 MOMMNMMOMAMOMOOONNNAKRKRKRKRRKRKL.NOWOO0D0ODOUOMO vain | ~N
— wm
> NOOO NO NTH O ONINMH ONINAH MANO MNRH H00 Mm | in
ea | MwmoyttpspttttTTMMMMMAANAMtHHt+H¢HFMMOOONRNA | +
ee)
| TOMO FMMAAA HO OOO MOO IN1INSTAO ORINMH ONRinin (S)
2 eee eee ee eee cece NANKRKRNARRROOOCONO InMmmMM N
ee)
= FARO DANMO+TNODO+FNO DOO OtRONA +NMOW OHM] In
SI | NWNRODDOOOOO minininintt+iunMOO RKKRK.KKRocwod | 0
= r oO
pret | oR ROC nt Ot MMMGHMHHOOADQADO00HH N
al | NANA RARRA RRNA RRR ANA RA ROWOOO ARARN N
: S _
| CHAO =O Gers Noman ONO oe ne ale
s | SCODDDDDDD DD DAADDADAAAACMMMDADMMOMCON| oO
eet
. te
a Finn 1n0 O 0000 DO OHHH ODO ININMH OW H +O O (ee)
[xy PWWDWMMMMAMDMODM ADDAADDOODODNONMDMH AAAAD | ee
(S|
MI ANNNAKDKNHHHHOOOD ODO AAA KMMM MMO OO
Le Nn Nc Be le fiat
md BN OFMO DOO DOHA M+INO DOO MOH AMANO RO DOH
A SSR See ee NNANANANAAAAARMND

Mean 10.24

6.975

(Giana ANIGRISS aia Saroa os GO diols Gree CCR OR re Rela BE BERGA OO Tercera naar

READINGS OF RIVER GAGE AT HAVANA, 1807.

160

(Plane of reference, low water of 1873.)

Day | Jan. | Feb.
I | 4.5 |11.8
D || SO |wit 7
3 | ZO [Ui
4 | 8.0 |I1.5
5 | 8.6 ]11.4
6) 9.5 |I1.3
FZ |i@Oo3s WP
8 \10.8 |11.2
g |I1.2 |I1.1
IO |11.6 |I1.0
II |12.0 |10.9
12 |12.2 |10.7
13 |12.4 |10.6
14 |12.5 |10.4
I5 j12.6 |10.4
16 |12.6 |10.4
17 |12.6 ]10.5
18 |12.7 |10.7
Ig |12.7 |10.8
20 |12.9 |10.9
21 |12.9 {11.0
22 |12.9 |II.1
23 |12.9 |11.3
24 |12.6 |11.4
25 |12.6 |11.6
26 |12.6 |I1.7
27 \12.5 |11.6
28 |12.4 |11.7
720) Wo |loso0
30 |12.1 |.
31 |12.0 |.

Meanj11.28,11.13

April

= |
Urn
CON! |

=
N
WRU AN COO DO HWUND = NUINO HS ODO HS ON OO

II

| CROUNYS OVE DVO HONAWS HNHENAWOO COHN

June | July

NN DDDAUIMNAS HL HPHHAHPHHUINIMNIIMMN HNAAADAA
* NRBONF ONW BNW NOHNHS HAOOODONFLF DAWMO NFM AC

Aug.

Sept.

Al PEL AUN 1111 OD OD ON N ON N NNN NNN™
2 | A COO HW HOR NWEUNDO OW DONO ONWSNNWH HL

OOO OO ee NN NNN DN NWWWWWH LS

00 00 60 60 00 00 0000 CD DODDD0D9DO 0 OWbWWN DMNWHNAWO

NNNNNNNNNNNNNNNNNNNNN NY HHH HHH
> CODCDODODOOOOOHHHHOOOCOOOO OD MONNNNN

|
|

xe)
Pe MOR rc Oe eR |

RAWNNHHOO000 00000000009 HODCDODDDO

NNNNNNNNNNNNNNDNDD HHH HHH He RH ee

Zz,
{e}
s
\S)
a)
aQ

TREN NO HOMHWDD DO WMMMHD OMDDHDADHAAUUM
;

GO © © BG) Gd LD © BD Od WD WD WD WD WD Od WD Oo OW Od WW WWD WD WW WDD
VPNYONNKYNVNVDDNNwWHOWEEEENEHHHOOOOOONW

2 82)| 3.22

Grand Average mace cmichiscuacincicn ere eeon te euiateiciet a veveho et enor Cele eee rtns 6.903

161

READINGS OF RIVER GAGE AT HAVANA, 1808.

(Plane of reference, low water of 1873.)

June |} July | Aug. Sept.} Oct. | Nov. Dec.

]
Ex SOY DO, DOO PIO SH CAO DOO OH A Dt OVO 60 00 60 00 000010
S AERA SCOOCOOODDDOADDADOA COHN AMAMMAMMAMNN
[Ca SMa aL ta} tS) SES) Epi t=) Ln ce en oe ee PD
= DOANE SD MON 8 UN 60 UNO COO PH DAN int A 000.0 int |
& | POND ROOO Mint tHtHtMMMMAANAAAMEee
<= Fae TS SASF ARCA PN td Ped Fed fd et ut Pt 0 et Fs J Fmt end po nd fDi dP dda ed LV
u SET SRD O00 0 HO OH POON IN IN© NAO InN
g BS BSR ee OS) eS A nc on bt <P MIMO NI
= TN SNIPS SLAF Feat md) Bead SAB ed Dt Pm tet ad Pont m0 od J Jd a A ay TF ed et
=
8 | OPO tun OM OH inM Mo OO mo QA Mr OH MeN qs
BS | SSN NENNRANN NOCD ADADDAODOOOHH HHA
A ce Be oe oe Boe Ee |
Pa AAAAAAAAMONM+NOO TAN tOOM+N~DO KO QOON
po $96 69 69.69 09 69 ODEN ODEN SIN INININININININING OOSDOSS NNN
t
Pr 1 AM +INO RD DOHA M+INO Noo OHAM+UMNO NRO DOH
E TES N=) Va ERAT EN Ep sipee) Na) fenleNiat
if

. 8.015

Grand Average......

162

READINGS OF RIVER GAGE AT HAVANA, 1899.
(Plane of reference, low water of 1873.)

Day | Jan. Feb.| Mar.} April} May | June | July | Aug. | Sept.| Oct. | Nev. Dec.
|) O45 |] GO || WO.6 || 1.8 |) ©. |) S.7] AO} 3B 2.21 2.6] 3.5 | Aon
2 || oH || WoG) || WU.3; | 12.6 | ot || B&B | AO] 308] 2.2 |) 26] 3.6] 4.1
Z|) @at3 |} Fotd |) Wise) || 1.5 | O41 || BO |] SO |] 3.7 | 2.3] 2.6] 3.6] 4.0
AN) Oso) |) FoF |) 122 ||1.3) |) “SoS |! Oo | AO] 2.7 | 2.3] 2.6) 3.6 || 4.0
Bl 7ot |) 7oS |) 12.0 |) Wat | B25 | O.3) 227) 3.7 |] 2.31 2.6 || 3.8 | 4.0
|| 702 || Poth |) U2 || 12.0 | oR) Oo |) A034] 308) 253) 2.6] 3.8 || 4.6
FN Got N Wo8 || 1250) | 1A5© | B.A |) os | os) oS || 2.3 |] 20] 3.5 | 4.0
S750 | W082 || 12.0 | 12.0 || BO |] O23] 4.3 || 3.0 | 2a) 2.6] 3.4 | 2.8
Oi) 7S |) 7/08) || WoO |] WiC) || Fo] O24] 2.43) AO) 2.4.) 2.6) 3.4 | 4.8
10] 7.9, 7.1 | 13.1] 11.8 | 7.8] 9.2 4.2 Boo) I Bad || 2o7/ || - Boal || 4.6
mm | SO || Oo) |) WBou |) wi | Wo || Ooi Agi le Bos | Boh il Bo?! Bod | Ao
1 || Sak | Oats) |) 12.0 | TsO |) Woh |) Oo) Mot | Bo7 |) 2.5) 2.7] Bo || so
13} || @o® |) Way/ |) 1i3}o8} |] UNG |! God) BB) AL) Bo] 2.5] 2.3] 3.6 || Aoi
| Bo | OoO MN uBoi |) Wad) od || Goh |) Ae Bo | 2.4) || 3.0] 3.7 | 4.2
5 |] Bok | Ooh || UBow |) Uo | Fo || BO] Mow | 3.8) 2A Bo.% | 3.8 |] 4.2
KG || Bo% |} Oodh || WR. |} 153 | 7.4 |) Goh | AO} Bor Awll lo Boil 2.0) || 2.3
17 || Bo | Oo || URO© |) 1.2 | Wow SoA |] M53) |] Bs@Q |) Bodt || 3.2) Al.© || And
Vhs) |] 253} || Oot |) Wor |) WHO |] Foi! GO} a.O]}) 3.©]) 2d) 2.2] au | A.©
Fie) |] Sock || Foe) |) W353} || WHO | oO Wo7 |) dso || BO} 2.0) Boul dou | 4.7
BO) | SoS || Gaz |} UBodt || LOO || Foi Aols | Ac©. || AO) Bod || Boo 4.2] 4.8
DM || Boh || GoS || UR” || Wo.7 || 70% || 7%o2 |] 2.6 || 2o| 3.2) Bo.i | 4.3 | 4.9
BD | Bo7 || God |) UBasd || Wo | 7oO | YO] SFO] 2s] 22] B.u | 4.3 || 5-0
XB |! B.6) || Oot ! UBO || sa || Yoo] O.7! 5.©]} 2.8) Bou |) Boi 4.4 | 5.0
A || {oO |) Oo} || ws5 |) 10.3) | BO |} Oo) 27) Bod BO] 2.2] Aa || §.3
AS || Ga) || OO |) URazi 4] 1O.© | B.O] GO|) 42.8] 2.7 || BO] 3.2] a4 | 5.2
AS) || Bats) || o® |} 1354 || ©oO |} WA Sof || 40} Zod |] ZO] B.A] aoa | 5.3
PN o5) || Cos) |) WoW || Oo || Gos} || Soa |) 405) 2a |) 2.8] 3.5 | aoa || S24
As) |) Bos Oo || 30H || ©. G0 |) BoA] Ao 253) 207 |] 3.58) Ao |) 5-5
230) 352 lIloooe || Uo |! @aodh | 8.7 || AO | 4.2) 2.3) 2.7 1 3.8) A-2 || §.0
30 | 8.0 iA© |) ©.2 Bo.7 |) AsO |} Aoi BIB| AO| Foals 4.1 | 5.6
31 | 80 14.0 aaa 8.7 ats AO || 2B atone 3015 5.7

Mean] 7.99| 7.02. 13.05] 11.15 8.02] 7.8] 4.38| 3.20] 2.63 2.991 3.88] 4.74

GrandPAvecraceerene eee eee eee J Matha Ore ob adele Gene eI Cera eee 6.401

These gage-readings at Havana have been plotted in the
hydrographs of Plates VIII. to XIII. on a seale large enough to
show the minor fluctuations, and at the same time to serve as a
basis for the graphic representation of temperatures of the
water and the results of the quantitative study of the plank-
ton. The hydrographs for 1894 and 1895 are based upon the
records at Copperas Creek with such supplementary data as
our incomplete records at Havana provide. For convenience in
comparing the seasons in the several years the following tables
have been prepared from the same data, to show the monthly
and yearly means, extremes, range, and total movement.

3
3 61
8] 6.98

2.82] 3.22] 6.90
7.44] 6.59] 8.02

Av.

Yearly
July

3.41] 4.6
6.16

Nov.| Dec.
.20

2

.96 2.97

1.93
6.04 5.89) 5-4

2.01

JuomMoaop, | WEVATS JOomoaoW | Gawd

abrrwort

Se Se ee a | AAYAM wo
Jsomory f TBAT D esuvy | oaswuod

jsoysiA | VERMATS

OMAN | SH SSSA

YSOMO’T | ee ee

asuey | 22IASE

3
5
7
7
9
5
Extremes | Totals

2

3] 2.99] 3.88] 4-741 6.40

3.66] 4.44] 4.86

3.20] 2.6

163

8.

HAVANA, 1894-1899.

iio
5
(Plane of reference, low water of 1873.)

Y laiddags ga | SERVOS
SOUBI
o ySOMo/T | PAUVSLS PSEMIEAEL || Sea SES
S MSD tat
= | ORME QGA ATYNOAW 1) eee a2
YOY | Sd Ss 4x yu AOW | Sands
1 u
nemosaowm {= AeVod] g | CQSES MANES
+ WI cit Su Fs esurey Ssdsan
1
5 osuey | ‘ey ITs = j
B YW | faa 3 OMT | Ve eS
s jano'T | SGGcan| A Fe Sees
LALO LSA S I
conse IAS PETE eee ee
oor terse ee) cottse len TtOATOO
TSSSem| iE wNoMAAOW | Sagrada
JHOMPAOI |aGator) 8 Aaa) SS
& saucy | EIS # use Nes
= Tl ado¥ou @ amor | 2a ets
By | eee ea Set PCS | Old [ae etn Ne
a a te jsoy sig | SS eens
= LONnoen : AaASMos
yond I SNS ree
TRIS WemaaoW [dat odd
JHOTHOAOTN | rata fi u Saas ae OFTMNOR
eZ e DOMIQA 3 99URD | TASS
a 9SUCY | idaiarst ood Ss ary BATACS
| MEARHA| Y WSOMOT | GHtaod
s OMOT | Sr ASS| CO FRaE eee

ei mMmoagaraw
SEE | SSNSRS SOUTH | SAaSASS
OYA | ordosrs po oerO

(Plane of reference, low water of 1873.)
Mar.|April| May | June] July | Aug.|Sept.| Oct.

February

GAGE-READINGS AT COPPERAS CREEK, 1894-95, AND AT HAVANA, 1896-1899,

Jan. | Feb.

9-24
3.30} 3.51] 6.28
10.24] 8.83] 9.41] 7.
IT, 28/11.13/13.89]13.40
5-08] 5.94]12.99]14.00j)I1.
7.99| 7-02|13.O05|II.1£5

MONTHLY AND YEARLY AVERAGES OF READINGS OF RIVER GAGE AT
3-92| 4.29

January

Year
NOQAe rete.

HIGHEST AND LOWEST WATER, RANGE, AND TOTAL MOVEMENT, BY MONTHS, OF RIVER LEVELS FROM

USQOmarrs os «
io y Aa een
MOO Ore ry oe.
MOQO peers =

MSO Geer tei<i-.-

MOK KTS PUOMIAOW | ¥aomsosa
yromaaoyw | Aaa —s55555
3 CRO Sos

WSOMO'T | Fai Siew

sued | anon

ronNorna
JSOMO'T | Gas csar

September

json sig | 2OSS2S SOUTH | isda
'H | Feats

aaa OAS:
JPUOTMOAOT | aicd fareat

scree esuee | icictatc
Sontotrn
}SOMO/T UW) 00 F110 AT

August
5
8
8
8
6
2

yS9MO'T | Grid dare
perieb | Soo OS QAneSro
yoy sa | FACT OF 06 {SOUSA | AT 00 Fu
Eee EEE

1v9 Ivo 00 00
A Se aee PSI eB Sey

A glance at the general hydrograph (PI. VII.)

It is evident that the changes from year to year in the
conditions of the river environment are such that they must
be taken into consideration in any study of the fluctuations of

the plankton.

years present the same fluctuations, and both typical and aber-

shows that the years of our plankton work at Havana practi-
cally include the extremes of conditions in the river; no two

164

rant hydrographs are found. In the discussion which follows,
the average or “normal” conditions and figures pertaining
thereto are based upon the twenty-one years of record at Cop-
peras Creek, eighteen miles above Havana.

The year 1894 (Pl. VIII.) is typical in that the high- and
low-water periods are normally located as to season and also
in the presence of a March, June, and September rise. Both
the extreme and average heights for the year, 10.4 and 4.63
feet respectively, are, however, much below the general aver-
age (13.8 and 6.74 feet). The high-water period (above 8 feet)
is shortened to three weeks, and the overflow stage is thus al-
most eliminated. The concentration of the sewage in the nar-
row limits of the channel during the early summer favors the
greater development of the plankton. With the exception of
the September rise the extreme low water continued without
interruption for a period of eight months—till the last of Feb-
ruary, 1895. These are conditions which cause the drying up
of extensive backwater areas, and also the development of a
large amount of aquatic vegetation in those lakes and marshes
which remain—a circumstance which reduces their plankton,
and their contribution, if there be any, to the river. The auton-
omy of the river plankton is thus emphasized in such a year
as this, which may be briefly characterized as one of predom-
inant low water and unusually stable conditions.

In 1895 (Plate IX.), another low-water year, we find, on
the other hand, little that approaches the normal. There is, to
be sure, a diminutive March rise and a sharp but very brief
equinoctial one, with very low water in the autumnal period.
The abnormal features are the failure of overflow, the long low
stages,—almost ten months, with unusually low water in Feb-
ruary and June,—the July rise, and the December overflow.
The extreme low water of the year is apparent in the average,
3.61 feet, the lowest on record in twenty-one years. The low
water in the winter combined with ice produced a stagnation
fatal to the plankton, while the June minimum favored an un-
usually large development for that season. The July, Septem-
ber, and December rises flushed out the river. The low water

165

of this year, following that of the previous year and combined
with the absence of overflows with rise and current sufficient
to ft and carry away the vegetation, resulted in a very unus-
ual growth of the aquatic flora in the lakes and even along the
river margins. The conditions prevailing throughout the
greater part of the year thus continued to favor the autonomy
of the main stream noted in the previous year. In brief, the
year may be characterized as one of extreme low water, with
some minor and unusual fluctuations. The contrast with 1894
is best seen on comparison of the total movements of the two
years, viz., 39.98 and 51.75 feet respectively.

The year 1896 (Pl. X.) is one of still more unusual char-
acter, since it presents a series of bimonthly rises culminating
in step-like succession throughout the year. In none of these,
however, save the initial one, is more than a very moderate
stage of water reached. This results (Pl. VII.) in a reduction
of the normal March flood, the isolation of the June flood in
the hydrograph, and the submergence of the September rise
between the abnormal rises of August and October. The gen-
eral result of such a series of rises is to bring the average level
for the year up to 6.98 feet (7.26 at Copperas Creek), 0.71 feet
above the general average, though the rainfall for the year is
slightly below normal. The increased average height does not,
however, in this case carry with it the usual extension of the
flood period. The river was above ten feet for less than a
month and above eight feet only three months. The overflow
stage was thus shght, and in addition it occurred in the
first months of the year, during the winter minimum of the
plankton, while during the spring months, when the normal
overflow occurs, the river was practically confined to its banks.
The succession of minor floods and the shght increase in the
average level does, however, greatly extend the reservoir action
of the permanent backwaters. The.repeated floods also had
the effect of clearing out the vegetation in the river and lakes
where some current develops, as, for, example, in Quiver Lake.
This reduction in the amount of vegetation in the reservoir

166

waters 1S accompanied by a considerable increase in their
plankton.- This fact, combined with the increase in the vol-
ume of their contributions due to higher levels, augments the
relative importance of their share in the formation of the river
plankton, tending to increase its quantity and variety. On the
other hand, the repetition of floods, no less than eight of which
may be found in the hydrograph, flushes the river so often that
no concentration of sewage and marked maximum of plankton
occur. The unusual extent of these movements is apparent
when the total movement for the year, 50.7 feet, is compared
with the totals of other years having about the same average
height. For example, 1890 and 1897, with an average height
of 6.9 feet, have a total movement of only 44.2 and 36.56 feet
respectively. In brief, the year was one without extended
overflow, with lower water than usual at the normal flood sea-
son, with prolonged bank-full river and reservoir action of the
permanent backwaters, and with more than the usual turmoil,

In 1897 we find a hydrograph (Pl. XI.) which approaches
the mean closely in its main features, and exhibits all the ex-
pected movements excepting the equinoctial rise. The average
height for the year, 6.90 (6.86 at Copperas Creek), is also near
the general average (6.74). The year thus approximates the
normal. The high-water period is of 141 days’ duration, al-
most exactly the average (140), but it occurs somewhat earlier
in the year and attains 16 feet—a little more than the usual
height. The earlier decline renders more prominent the June
rise, and gives an early start to the extreme and uninterrupted
low water of the remaining five months of the year. The low-
water period (155. days) is normally located but is somewhat in
excess of the average (147), and it is also unusual in the fact
that the extreme low-water level (1.7 feet since the completion
of the dam at LaGrange) continued almost unchanged from
the middle of August till the first of November. This was fol-
lowed by the usual slight increase in water in the closing
months of the year. The total movement of the year (43.1
feet) is considerable in view of the average height (6.9 feet),

167

but this was less disastrous to the plankton than usual since it
was in the main due to the spring flood and not to minor
changes when the stream was within its banks. This freedom
from minor interruptions during the low-water period is some-
what unusual, and resulted in a concentration of sewage ap-
proaching stagnation and in a marked increase in the fall plank-
ton. The overflow period, in which the reservoir action of the
bottom-lands as a whole was operative, prevailed during the
first five months; the change to low water, during which the
reservoir action of the more permanent and diversified waters
was in force, took place very rapidly; while the low-water
stages, during which it is a minimum, were both pronounced
and prolonged. These circumstances combine to emphasize
in this year both the unity and the autonomy of the river. In
brief, 1897 was a year of normally located but pronounced high
and low water, of marked freedom from interruptions, and of
unusually favorable conditions for the unity and autonomy of
the plankton of the river and for the full development of its
normal seasonal cycle.

In 1898 (Pl. XII.) we find another year whose hydrograph
approaches the normal in its main features. There is a well-
defined period of high water followed by one of much inter-
rupted low stage. The spring flood is normally located, con-
tinues (above 8 feet) for 164 days, and culminates at 18 feet
on April second. The extension of the flood period for 24 days
beyond the normal is due largely to the “June” rise of unusual
proportions, which culminated in the last of May at 13.8 feet,
and covered a period of five or six weeks. The impounding
action of the bottom-lands as a whole is thus shifted forward
into the late spring and early summer, while the concentration .
of the overflow into the channel occurs in the early part of
May and again in June, and the conditions of rainfall, season,
and overflow combine to favor the production of a relatively
large amount of plankton at these times. The decline is rapid
in July to low-water stage, which continues but three weeks,
the lowest record being 2.5 feet. This is followed by a series

168

of minor rises, which flush the river at short intervals during
August and September, and a rise to bank height in November
—fluctuations which favor the reservoir action of the perma-
nent backwaters,and at the same time introduce much silt and
interrupt and diversify the plankton cycle. Of all the years of
our operations at Havana this was the one of highest average
level—8.02 feet (8.11 at Copperas Creek)—and greatest move-
ment (66.2 feet). The dilution of the sewage, the increased
current and silt, andthe flushings incident to such hydro-
graphical conditions tend under most circumstances to de-
crease the relative amount of the plankton, though doubtless
they also tend to increase the total production of the stream.
In brief, the year was a typical one of high water with much
delayed run-off and interrupted low-water period.

In 1899 (Pl. XIII.) we find another year conforming very
closely to the normal hydrograph in its main outlines. Weare
concerned only with the first three months, at the close of
which occurs the maximum (14 feet) of the spring flood. The
greater part of the rise occurs 111 a brief period at the close of
February, and the declining waters or more stable conditions
at other times reduce considerably the flushing and silt attend-
ing most winter floods, such, for example, as that of the pre-
ceding year. The decline in February also afforded a good op-
portunity for the reservoir action of the permanent backwaters
under midwinter conditions. Our collections of 1899 thus cover
a period of winter flood of more than usual stability.

The wide range of hydrographical conditions during the
six years of our plankton work at Havana have afforded a
unique and, up to this time, unexampled opportunity to follow
the effect of flood and drouth, of changing season, and of yearly
fluctuations upon the life in the waters of a stream, and to give
to the conclusions here reached the confirmation which repeti-
tion alone can bring.

TEMPERATURES.

The fluctuation in the temperature of the river water con-

stitutes for the plankton one of the most marked evidences of

169

the climatic changes of the recurring seasons. This factor in
the environment of the plankton is thus an ever changing one,
but at the same time it runs an annual cycle of the same gen-
eral character year after year with ever present minor varia-
tions of a seasonal or local origin. The extremes of tempera-
ture in bodies of water in this latitude are so divergent that
they afford the basis for marked seasonal changes in both the
constitution and the quantity of the plankton. Adaptations on
the part of the organisms of the plankton to definite tempera-
ture limits thus occur.

Records of the temperature of the air and of the surface
and the bottom water have been taken regularly at all stations
where quantitative plankton collections were made. These
are recorded in Table I. The temperatures were taken with a
Negretti-Zambra self-recording thermometer from 1894 till May
24,1898, after which time a Hick’s self-recording maximum-mini-
mum thermometer wasused. Under stable conditions no appre-
ciable variation was noted in the reading of the thermometers,
but at the times of sudden change, as in the mingling waters of
a rising flood, readings would sometimes vary as much as four
or five degrees at one location and level.

The temperature of the river water is influenced by a vari-
ety of causes in addition to the immediate action of solar heat.
The most prominent of these are the access of the tributary
water from streams, springs, and impounding backwaters. The
temperature of tributary streams, such as the Spoon River
(Table 1V.), is often, though not always, warmer in winter and
colder in summer by several degrees than that of the main
stream, as a result probably of the greater proportion of spring
water and the greater nearness of the same to its subterranean
source. A good illustration of this was to be seen along the
eastern shore of Quiver Lake, where at low-water stages springs
near the water’s margin kept up a continuous flow. The tem-
perature of the water in summer was 54°, while in winter it
fell only to 51°. The smaller tributary waters also respond
more quickly to fluctuations of temperature than does the river

170

itself. In hke manner the backwaters, which are usually much
shoaler than the river, are subject to greater changes, exhibit-
ing in warm days greater extremes of heat, as high, for example,
as 96° having been found in the margins of bottom-land ponds.
On the other hand, the flood waters in the forests and marshes,
where the vegetation protects the water from the direct rays of
the sun, remain at lower temperatures than those of more open
tracts. The lakes and bayous with aquatic vegetation also re-
main cooler in their deeper waters, as, for example, Thompson’s
Lake, where, among the Ceratophyllum, the temperature at
the surface on the fifteenth day of July was 88.2°, while only
six inches below, in the vegetation, it was 80°, the difference
being due to the protection from sun and wind which the veg-
etation afforded.

Another factor tending to modify the temperature is the
earth temperature, which in the very shallow waters of our
environment becomes relatively important in both summer and
winter. In the low temperature of winter this is heightened by
the fact that most of the bottom of the backwaters is strewn
with a mass of vegetation whose decay must produce some
heat. This probably accounts for the higher bottom tempera-
tures sometimes observed in winter (cf. Tables III. and VIIL.)
in Flag Lake, where such detritus was more abundant than in
the river, where but little is found. For example, on February
26, 1897, the bottom temperature in Flag Lake was 36°, while
in the river, with about the same surface temperature (382°) and
ereater depth, it was only 32.5°. This difference may also be
due to the effect of the current in the river in mingling more
quickly the surface and bottom waters and thus equalizing their
temperatures more rapidly.

The temperatures recorded in the [linois River, Spoon River,
and in Thompson’s, Quiver, Dogfish, Flag, and Phelps lakes are
to be found in Tables III.-IX. respectively, and they appear on
the plates with the hydrographs and plankton data of the re-
spective years and stations. The extreme range of temperature
observed by us in the river and its adjacent waters at Havana

171

was 32°-96°. The highest temperature recorded in the river
was 89°, on the afternoon of August 3, 1897, and again, at the
same time of day, July 26, 1898.

The diurnal range in temperature is considerable at times,
depending naturally upon that of the air. On August 3-5,1898,
in connection with a test of the diurnal movements of the
plankton and accompanying analysis of the gases dissolved in
the water, the temperatures recorded indicate in the surface
waters a range of 5.5°, with a maximum of 79.5° at 5:00 p. m.,
and a minimum of 74° at 2:00 a.m. The bottom water (depth
2.44 meters) showed a range of but 2°, from 74° at 8:00 a. m.
to 76° at 11:00 a.m. The air temperatures on the days in ques-
tion ranged from 88° at 5:00 p. m. to 58° at 5:00 a.m. A diur-
nal variation of 5.5° in surface waters and 2° in bottom waters
is thus indicated at this time. Other conditions will probably
show a slightly greater range.

MONTHLY AND YEARLY AVERAGES OF SURFACE TEMPERATURES, 1894-1899,
ILLINOIS RIVER.

>
Year | Jan. | Feb.| Mar./April] May |,June| July | Aug.|Sept.| Oct. | Nov.| Dec. a &

>
LOOM Meer ere erst lecoete ca |lescce ell <sereitvs [feos eis OPERA 65 7758 Ne ble Be) loocn ae
isi Sasoullscoae Dea see, 8 soo H80) (7) (On GUD AIKD.G |B7/oly lloooc 00
1896... .|32-75|33.7 |39-52/64.54|72.7 |74.7 |80.7 |82 [65.75/56 [44 [33.6 [56.66
(07a aad lapor 32.25|43-8 |60 [66.3 |75 |81.02/80.9 |77.07/65.1 |45.7 33-02) Bait
1898..../32-7 |32-12/43.3 |53.32/65.8 |78.8 (82.87/80. 56/71 .87/54.37/41 .42'32.98/55 .84
1899... ./32.9 |32.6 Sor) Bere teara | esis alllsventts ol feebrs cifeeretferse tense eo retaeallerehercieellieosiotote:
Monthly
average|32.78/32-73/40.45|60. 4668 27/77. 75|81 -03/81 - 49/74 - 21157-55143 -00 35 22157 .08*

*Average of monthly averages.

The temperature records are too isolated to plot complete
thermographs of the river and its backwaters, though they do
give a very fair idea of the seasonal fluctuations, especially in
the later years, when they were more evenly distributed, and
in the midsummer, when they were more numerous. ‘They were
usually taken between 7:00 a.m. and 5:00 p. m., and may be
regarded as day temperatures. A comparison of the records in
Table IIL., the plottings (Pl. VIII.—XIII.), and the above table,
giving the monthly averages of surface temperatures of our
records, shows the following seasonal routine in the river:

172

During the months of January and February there is a
period of minimum temperature approaching 32°, averaging
32.75°, and rarely exceeding 34°. The constancy of the tem-
perature at this season is probably due in large part to the
equalizing effect of the ice which normally covers the stream,
and especially its backwaters, at this season of the year. Dur-
ing the early part of March the temperature rises, but the rate
becomes more rapid in the last part of the month. The up-
ward movement reaches 40° or 50°, in early springs, such as
1898, attaining the latter temperature. The average for the
month rises to 40.45° and the fluctuations increase in extent.
The rapid rise continues through April, attaining 60°—70°, and
averaging 60.46°. The records for this month are somewhat
meager for any comparisons. In May the season of maximum
temperature is approached and occasionally reached, as in 1896,
the average temperature from somewhat scanty records being
then 68.27°. This month is one not only of marked rise but
also of considerable fluctuation. The period of maximum tem-
perature is in full swing in June, and continues through July
and August and well over into September. The average rises
from 77.75° in June to 81.49° in August, and falls to 74.21° in
September owing to the decline which begins in the latter part
of this month. This period of maximum summer heat 1s fairly
well defined in the thermograph and continues at or near 80°
approximately three months, from the middle of June to the
middle or latter part of September. It is a time of consider-
able fluctuation, most of the movements being within 10°,
though the range for August in the five years of record was
from 74.8° to 89°. These fluctuations combined with the di-
urnal changes and the wind are effective in producing a con-
siderable vertical circulation of the water.

Following the summer maximum comes the fall decline,
which begins late in September and is practically completed
in November. The greater part of the change takes place in
October, the average decline in that month being 16.76°, while
that in November is 14.55°. In some years, as 1897, the de- —

173

cline is a gradual one; in others, as 1895 and 1898, it is subject
to some irregularities. With December the winter minimum
returns, but with less persistence than in the months which
follow, flood waters at this season bringing their higher tem-
peratures. .

The annual temperature cycle thus falls into four periods:
one of minimum and quite constant temperatures, including
December, January, and February, and a varying portion of
March ; one of maximum and more fluctuating temperature,
approaching 80° and extending, with some interruptions, from
the early part of June till about the middle of September; and,
separating these, the two shorter intervals of change. The
period of increase in temperature, which is also one of rapid
change and increase of the plankton, includes the latter part
of March and the months of Apriland May. The period of de-
cline, which is sometimes more abrupt than the spring rise, as
in 1895, 1897, and 1898, extends from the latter part of Septem-
ber until the end of November. This is also a period of change
and of frequent but not universal diminution in the plankton.
The average temperature for the years, as expressed approxi-
mately in the table, is 57.08°. This point is passed about the
middle of April and again about the middle of October with
considerable regularity. Since, however, these dates both lie
in periods of rapid change, the average temperatures are of
much less duration than the more extreme ones. The existence
of these well-defined periods of maximum, minimum, increase.
and decline of temperatures affords the basis for corresponding
seasonal changes in the minute life of the water as fundamental
and extensive as those which affect the plant and animal life of
terrestrial and aerial environment. This subject of the rela-
tion between temperature and organisms of the plankton will
be fully discussed in connection with the statistical study of
their seasonal distribution.

A comparison of the thermographs (Pl, VIII.—XIII.) of the
different years and an inspection of the table on page 171,
reveal but few significant annual differences. The spring rise

174

in temperature was somewhat delayed in 1896 and again in
1899, and the summer maximum was less pronounced in 1895
and 1897, though in compensation the summer heat was pro-
longed into September in these years. The spring rise in 1896
and the autumn declines in 1895 and 1898 are rather more
abrupt than usual. These annual differences extend and cur-
tail the plankton periods characteristic of the seasons, or
render their changes more abrupt.

The difference between surface and bottom temperatures
is,as arule, but slight. It is perforce usually lacking during
the period of decline in the autumn, and at cther seasons
varies in amount with the air temperature, the wind, and other
attendant circumstances. So long as the temperature is above
the point of maximum density of water, 39.2°, the surface
waters are the warmer by an amount ranging from a fraction
of a degree to 5°, the latter occurring on still, hot days. With
air temperature falling below that of the water the surface and
bottom quickly come to have the same degree of heat. Below
39.2° the colder waters are at the surface, though at this season
of the year there is usually much less contrast at different
levels than in the warmer months.

Temperature fluctuations, following those of the season and
the day, occur in the waters of this region toa degree not realized
in the typical lake, whose deeper waters respond but slowly to
the surface changes, and thus exercise an equalizing effect.
Examples of this quick response are found in the unusually
high temperature (82.3°) in both top and bottom waters of the
river on May 18, 1896, while temperatures of five days later
showed a drop to 71.2° in both regions. A decrease equal in
suddenness and extent occurred in September, 1898. The
surface layers of water, quickly affected by temperature changes,
form relatively a very large part of the volume of the river and
its backwaters, and thus instability of temperature becomes an
important feature of the environment of the plankton of the
river as contrasted with that of the lake. Changes of the ex-
tent above noted must affect considerably both the movements
and the multiplication of the plankton organisms.

175

The temperature conditions here described are those as-
signed by Whipple (’98) to lakes of the temperate type and
third order, those whose bottom temperatures are seldom very
far from their surface temperatures, and in which there is con-
siderable vertical circulation at all seasons when the surface is
not frozen. Atno place in the region examined by us has a
depth been found sufficient to permit the occurrence of a
stratum of cold water at the bottom unaffected by the vertical
circulation and warming process in the surface regions, such,
for example, as has been found by Birge (97) in Wisconsin
lakes. This absence in ‘the river environment of the “thermo-
cline” and of summer and winter periods of stagnation in
lower levels, marks another point of contrast between the river
and some lakes as units of environment.

The temperature conditions in the bodies of water adja-
cent to the river do not differ to any considerable degree from
those here diseussed. The limited extent, greater amount of
vegetation, shallower waters, or greater access of spring water
in some of these will cause slight variations from the condi-
tions found in the river.

The ice conditions attending the winter minimum are of
profound biological significance, since they produce important
alterations in the winter routine. As a result of the presence
of an ice sheet on a body of water, the temperatures become
more constant, the mingling of waters due to winds ceases, the
usual processes of aeration are interrupted, and the propor-
tions and amounts of the gases dissolved in the water may be
very much altered, the degree of the change depending upon
conditions such as the completeness with which the surface is
sealed by the ice, the amount of sewage, the relative abundance
of plant and animal life, the duration of the ice, and the exist-
ence of currents. So far as our observations goat Havana, the
stage of stagnation attended by the destruction of the animal
life which is sometimes found in small lakes is rarely realized
in this environment. Several reasons may be assigned, the
principal one being being the instability of river levels in the

176

winter season, which prevents the: culmination of stagnation
conditions. Again many of the backwaters are rich in vegeta-
tion, and some of them are spring fed at the margins which
thus remain open even in the coldest weather. The river itself
rarely closes over entirely, air-holes remaining where the cur-
rent is rapid. Thus, below the mouth of Spoon River (PI. II.)
a large area was usually free from ice even when the river was
closed above this point. The currents due to tributary waters,
as in Quiver Lake, and to changes in level, as in all impound-
ing waters, also tend to prevent stagnation conditions. In
spite, however, of these favoring circumstances one catastrophe
of this nature did occur in the years of our work at Havana.
In the winter of 1894-95 prolonged low water and heavy ice
upon the river and lakes combined to render the conditions
unfavorable to life in the river, and to some extent in Quiver
Lake. Conditions in other localities at this time were not
observed. The practical extinction of the plankton and the
death of large numbers of fish attended this period of stagnation.

The duration of the ice at the various stations in the sev-
eral years is indicated at the bottom of the diagrams which
give the hydrographs and plankton data of the several stations
by black lines of a thickness proportional te the ice. The
occurrence of ice in the different years at Havana has varied
considerably. No records were made in 1894—95, but from other
sources, river stages and weather reports, it seems probable
that the river closed in the last days of December, and that
the ice continued until the rise of February 25, a period of
almost 60 days. In the winter of 1895-96 there was but little
ice, the river and backwaters being partially closed only for
the first fortnight in January. In 1896-97 the river did not
close until after the rise in the early part of January, the ice
remaining about one month, going out with the rise of Febru-
ary. The lakes, on the other hand, were closed toa large ex-
tent throughout December, and again, to varying extents, dur-
ing January and a part of February, the current due to high
water keeping portions free from ice at times.

177

In 1897-98 the lakes closed the last days of November
and opened again on December 12, freezing again December
17, and not clearing entirely until February 14. Rising water
continued from January 10, so that stagnation conditions did
not ensue. The river also closed partially early in December,
opening and closing again with the lakes. The first ice went
out with the rise on January 11. The river closed again Jan-
uary 27, and the ice went out February 9 and 10. Again on
February 21 ice was present, and for several days following.

In 1898-99 ice again formed early in December and par-
tially closed the river during the month, going out about the
27th and reappearing on the 380th. This went out gradually
January 17-24, and the river froze over again on the 26th and
remained closed fora month. Thin ice formed March 5, re-
maining only three days. The lakes closed early in December,
the ice never entirely disappearing until the middle of March.
Partial breaking up occurred at the times of breaking up of the
river ice. ‘These partial openings and the changes in level
were sufficient to prevent a period of stagnation.

OTHER METEOROLOGICAL FACTORS.

As indicated in Tables III.-IX., at each plankton collection
observations of the direction and force of the wind, with its
effect upon surface conditions and on the state of the sky, were
recorded. The relation of these factors to the plankton may
not seem intimate or apparent. They haye more bearing on
the subject of vertical movements of the plankton, data upon
which will be found in the study of the surface and bottom col-
lections made with each of the vertical collections which form
the basis of the present paper. The surface waters affected by
the intensity of the sunlight and the movements caused by the
wind form relatively so large a part of the environment of the
river plankton that these factors are much more widely opera-
tive here than in the lakes, where the surface stratum thus
affected is relatively small.

178

The wind conditions on the river and the lakes adjacent to
it—which are generally elongated in the direction of the main
stream (PI. II.)—are somewhat peculiar. Owing, it may be, to
the configuration of the river valley, or perhaps still more to
the bordering forest of the contiguous bottom-lands, the pre-
vailing direction of the wind is either up or down the river or
lake, especially during the summer season. The effect of an
up-stream wind is greatly to increase the disturbance of the
surface when wind and current are thus opposed. These winds,
when prolonged and violent, decidedly affect the levels of the
different parts of the lakes, and, for example, in Thompson’s
Lake (PI. II.) determine at low-water levels whether the lake
shall discharge its waters into the river or itself receive an
access of river water. Owing to the mobile condition of the
abundant bottom deposits, at low stages the winds also add
very much to the silt in suspension in the water, and thus hin-
der the penetration of hght.

The effect of varying sky conditions lies primarily in their re-
lation to the temperature of the water, but is due in a less degree
to the influence of light upon the multiplication of chlorophyll-
bearing organisms—the primal food supply of the plankton—
and upon the movements of these and other plankton organisms.
The abundant silt in suspension in waters of the river and most
of the adjacent lakes doubtless hinders the penetration of the
sunlight, but modifies to a much shghter extent its effect upon
temperatures. Wind and sky conditions combine to favor or
prevent the appearance of the “water-bloom.” This is a char-
acteristic green scum which coats the surface of the river, and
occasionally of the lakes, on still, warm days in midsummer.
On cloudy or windy days the minute organisms (Huglena, Chlam-
ydomonus, ete.) which form the bloom do not rise to the sur-
face. The conditions of wind and sky are thus important fac-
tors in the economy of limnetic life and, by reason of their rel- ~
atively greater effectiveness in the river and its adjacent
waters as contrasted with the typical lake, add to the elements
of instability in the fluviatile environment.

179

TURBIDITY.

Records of the turbidity were made (Tables ITI._IX.) in gen-
eral descriptive terms during the first two years of our work at
Havana. After April 29, 1896, the turbidity was tested by
means of a white plate of semi-porcelain, 10 cm. square. The
depth at which this square disappeared from view was recorded
in centimeters as a measurement of turbidity. Although the
method is somewhat primitive and subject to some variations
with the conditions of sky and daylight, it is still sufficiently
accurate for the purposes of the present paper. The disc
method has not as yet been correlated with the platinum-wire
method, the diaphanometer method, or the silica-standard
method of Whipple and Jackson (00), and comparisons with
these are consequently excluded.

As might be expected in the river environment, when floods
occur the turbidity is often extreme, and is exceedingly varia-
ble according to the locality and the river levels. (Cf. Tables
IiJ.IX.) The extreme range of our records extends from 1.3
cm., in a Spoon River flood, to 260 cm., in Quiver Lake, under
the ice.

In the river (Table III.) the great majority, about two
- thirds, of the records lie between 20 and 50 cm., while the ex-
treme range is from 2 cm., in the flood of May, 1897, to 115 ¢m.,
in the declining waters of July, 1896. The clearer waters ap-
pear, as a rule, with declining floods and stable low stages,
especially under the ice. With the inception of floods the most
turbid water is found, which gradually clears even while the
rise continues. The river varies in clearness according to the
instability of the river levels, as will be seen on comparison
of the turbidity in 1896 and 1897, the latter year being more
stable and having relatively fewer records of a marked turbidity.

The turbidity of the river is due to both plankton and silt,
the latter being as varied as the character of its tributaries,
with the added contamination from the cities along its banks.

In Spoon River (Table IV.) the extremes are even more
marked than in the main stream, varying from 1.8 cm., in flood

180

conditions, to 165 cm.at low water under the ice. The turbidity
here is almost entirely due to silt, that at flood being largely
composed of earth and clay, giving a black or yellow tinge to
the water. The amount of comminuted vegetable debris found
in the waters is considerable.

In Thompson’s Lake (Table VIII.) the turbidity is not so
frequently marked by the extremes seen in the other bodies of
water examined, the range being from 115 cm. in the declining
waters of May, 1896, to 6 cm. in invading floods, and again in
the late autumn of 1897, when high winds roiled the shallow
waters. As a general rule the turbidity of this lake is somewhat
less than that of the river, but as great or greater than that
of other backwaters. This turbidity is often due in part
to the heavy planktons occurring here, and also to the floccu-
lent debris loosened from vegetation and stirred up from the
mobile bottom by fish and the waves. Very little silt enters
the lake except at times of inundation, especially with back-
water from Spoon River. Owing to its origin the silt in this
locality is usually of finer, more flocculent material than that
found elsewhere.

In Quiver Lake (Table V.) the extremes are much more
marked than in any other locality, ranging from 3.5 cm.,
in flood water from the river, to 260 cm. on June 5, 1896, in clear
impounded water. In winter, under the ice, the bottom was vis-
ible on December 8, 1896, in 260 cm. of water. A great deal of
variation in turbidity occurs in this lake. In years of low water,
as 1894 and 1895, when vegetation is abundant, the turbidity 1s
very slight, the bottom being visible much of the time. In the
three succeeding years the lake was free from vegetation, and
the turbidity was considerably increased as a result largely of
the increase in the plankton. The sources of the silt in this
body of water are varied; occasional freshets in Quiver Creek,
which enters the upper end of the lake (Pl. II.), invading floods
from the river, and debris from vegetation and the bottom put
in suspension by the wind, current, or movements of fish,—all
contribute their share to the pollution of the otherwise clear
water of this lake.

181

In Dogfish Lake (Table VI.) the conditions are essentially

those of Quiver Lake, of which it is an arm. The principal
difference lies in the fact that flood water entering Quiver
Lake at low stages never moves as far up as our station in Dog-
fish Lake (Pl. II.). Floods from Quiver Creek also merely back
up the clear water in Dogfish Lake without themselves invad-
ing that territory. The only flood silt entering this region is,
consequently, that which comes with general inundations.

In Flag Lake (Table VII.) the conditions at inundation are
similar to those of other impounding backwaters. The great
amount of vegetation found here adds to both the vegetable
and the flocculent debris which roil the water whenever this is
disturbed by waves or the movements of fish. Turbidity, is
but rarely caused by plankton here, with the exception of the
few instances when diatoms or Oscillaria became very abun-
dant. The water is thus usually clear, the bottom being
commonly visible in the small spaces left free of vegetation,
even at a depth of 215 cm.

In Phelps Lake (Table IX.) the silt conditions are peculiar.
The high level at which the lake lies and the intervening
stretch of bottom-lands (PI. II.) combine to keep out all silt-
laden flood-waters except those that enter by a now abandoned
channel from Spoon River or from the main stream at times
of their maximum floods. At other times the silt consists prin-
cipally of particles of bark and dust from the adjacent forests, or
of fragments of loam from the bottom, which is here unusually
stable. The comparative freedom from vegetation removes a
large element common in the silt of the other lakes. The turbid-
ity, however, is very marked in this lake, falling in many cases
below 20 cm., and in the majority of instances is largely due to
the very abundant plankton characteristic of its waters during
the greater part of the summer. Movements of fish and water-
fowl add considerably to the silt in suspension in this lake at
some seasons of the year.

The color of the water has not been made a subject of
special inquiry. In general the turbidity gives it a grayish cast

182

that varies to yellowish or blackish tints with silt of clay or
loam origin. When diatoms are abundant a brownish tinge is
very evident, and with Oscil/aria rising in quantity, as it does
in some semi-stagnant waters in late summer, a blackish tint
becomes pronounced. In midsummer and early fall, when
water-blooms rise, we find varying tints of green according to
the kind and quantity of chlorophyll-bearing organisms present.

The turbidity, as above suggested, is due to a great
variety of factors, one of the most important of which is the
plankton itself. Indeed, under some conditions turbidity be-
comes a token by which the relative abundance of the plank-
ton may be estimated. The presence in our plankton of vast
numbers of the most minute planktonts, such as the flagel-
lates, renders this relation of plankton and turbidity more
prominent in our waters than it is in waters where such organ-
isms are less abundant.

The turbidity otherwise is due to non-living solid matter
in suspension. ‘This is brought in by tributary streams, and is
torn loose from the shores and bottom by the current of the
river, the movements of fish, the wash from steamboats, and
the constant sweeping of the river channel by fishermen’s
seines during the open season at stages when seining is possible
in this place. The dust from prairies and forests brought by
winds; the waste from factories, distilleries, glucose-works, and
cattle-yards; and the sewage ofa score of cities along the banks,
—all make additions to the burden of the water.

Microscopical examination of the plankton has revealed
the diverse character and origin of the silt which accompanies
it. Fine fragments of quartz, bits of mollusk shells, small
pieces of coal or ashes, minute particles of loam or clay, and
the fecal pellets of aquatic organisms—especially of mollusks
and of insect larvee—constitute the heavier element of the silt.
To this is added a variable but ever considerable quantity of
exceedingly fine sediment of earthy or clayey origin, some of
which remains long in suspension. The coarser and lighter
silt consists largely of comminuted vegetation, both terrestrial

——a

183

and aquatic, minute bits of leaves, stems, bark, and wood, with
the characteristic grain refuse from distilleries and glucose-
works and the offal from the cattle-yards at Pekin and Peoria.
At all seasons of the year and in all waters the scales of Lepi-
doptera and the pollen of coniferous trees are of common oc-
currence. Mingled with this material, especially when aquatic
vegetation is present, is a very light flocculent material con-
sisting, in part at least, of the zodgloee of bacteria. It isin the
midst of debris of this varied composition that the plankton
lives, and it is in collections consisting to a greater or less ex-
tent of silt material that the river plankton must be studied,
its species determined, and its individuals enumerated.

In collections made with the silk net the greater part of
the fine silt passes through the meshes with the water. In
filter-paper catches some of it adheres to the paper, and the
finer flood silts will even pass through hard-pressed filter paper
in small quantities. With silt of so varied a character it is
practically impossible to establish and continue any standard
of measurement or estimate which affords a satisfactory basis
for the determination of the relative amounts of silt and plank-
ton present in the collections. After considerable experience
in the examination of our collections I have endeavored to
estimate the amount of silt present in them as they appear
in the Rafter counting-cell. The distribution of the material
in the cell and the conditions of examination are such
as to favor a uniform standard of estimation. On the other
hand, the estimates are purely personal, without any volumet-
ric check, and are thus only comparable with each other. This
method seems to be the only solution at present available for
this perplexing problem. These estimates are given in Tables
IIL.-IX., together with computations, based thereon, of the
amount of both plankton and silt per cubic meter. These
figures form the basis of the diagrams in Plates VIII.—XIII. and
XXII-—XLII. As will be seen in the tables, the per cent. of silt
varies from a mere trace to almost the entire catch, changing
with the river conditions as previously stated.

184

A still more accurate determination of the total amount of
solids in suspension in the river, both silt and plankton, is
afforded by the catches made by the Berkefeld army filter,
data concerning which will be found in Table XV. This filter
removes all of the suspended solids and permits their complete
removal from its surface, but adds a small portion of its own
substance to the catch. After the first few catches with this
filter the wear becomes somewhat uniform and is thus dis-
tributed. On computing the loss from the filtering sur-
face by wear, and quadrupling this volume to allow for its less
compact condition, we find that it constitutes less than five
per cent. of the catches washed from its surface. The true
amount of solids is thus about five per cent. less than the
figures cited in the tables and in the following discussion.

The amount of water strained in making these catches was
usually 5 liters, while the tables give the computed amount
per cubic meter.

The amount of solids was measured by our usual method
of measuring plankton, that is, by condensation in a centrifuge.
In this treatment it usually attains the consistency of soft mud.
For the river the amount ranges from 148 cu. cm. (per cubic
meter), in declining water under the ice in December, to 5,416 eu.
em., in the incipient stages of the winter flood of February 28,
1899. The average amount of the weekly catches for 1898 is
592.2 cu.cm. per cubic meter, which for an average flow of
24,600 cubic feet of water per second (see page 132) means a
discharge of 14.57 cu. ft. of solids per second, or, 459,794,232
cubic feet (1,801,990 cubic meters) per year, or 16,472 cu. ft.
(46.64 cu. meters) per square mile of the catchment-basin of
the river.

The average amount, per cubic meter of water, of solids
taken at fortnightly intervals in 1898 in Quiver Lake was only
378 cu. cm., a fair index of the greater clearness of its waters.
In Thompson’s Lake similar collections average 557 cu. cm., in-
dicating waters somewhat clearer than the river. In Phelps
Lake the average amount is large, 1,572 cu. cm., due in no small

185

degree to the very abundant and minute plankton organisms.
In Spoon River the average of the monthly collections is 1,746
cu. cm., three times as much as the main stream carries. The
heavy floods and rapid current of this tributary are responsible
for this large amount of earthy solids in suspension.

In this matter of silt and turbidity the river as a unit of
environment stands in sharp contrast to the lake. Deposition
of solids and clear water are normal to the environment of the
lake, while solids in suspension and marked turbidity are the
rule with river waters. Owing to their varied occurrence these
elements, silt and turbidity, also add to the instability of
fluviatile, as contrasted with lacustrine, conditions.

Siltand turbidity are usually attendant upon floods, so that
their unmodified effect upon the plankton is not easily deter-
mined. Some inferences and observations regarding the rela-
tion of these factors to the economy of the plankton may, how-
ever, be made. The silt affects the plankton indirectly by
hastening the solution of nutrient substances from the organic
detritus that forms a considerable portion of the unstable de-
posits which accumulate in shoal and in sheltered parts of the
stream. It hinders the penetration of light, thus checking the
development of the chlorophyll-bearing organisms while favor-
ing the multiplication of bacteria and hastening the decay of
organic matter in suspension. It also seems probable that it
produces a deleterious effect upon the Hntomostraca by ad-
hering to the hairs which clothe their various appendages, thus
hampering their movements and causing them to sink to the
bottom. Accessions of flood water are frequently followed by
an increase in the relative number of moribund and dead
Entomostraca, especially of the Copepoda.

CHEMICAL CONDITIONS.

The food supply is the most fundamental feature in the
environment of the plankton. Its abundance or scarcity de-
termines to a large degree the growth and reproduction of or-
ganisms, and its fluctuations are important factors in deter-

186

mining the seasonal and local production of plankton. The
primary source of the food of the plankton lies in the water
and in the gases and inorganic salts dissolved therein, the oxy-
gen, the carbon dioxid, the nitrates, and the phosphates being
usually regarded as of prime importance to the growth of chlo-
rophyll-bearing organisms. The phytoplankton, which utilizes
these inorganic materials, then becomes itself the food for the
zooplankton. These inorganic substances, the primary food
supply, are thus indices of the capacity of the water for the
production of plankton.

With the inauguration of the work of the Biological Sta-
tion at Havana arrangements were made whereby collections
of water taken by the Station staff from the river and some
of the adjacent lakes were sent to the Chemical Department
of the University of Illinois, at Urbana, for analysis. In
1895 the Chemical Survey of the waters of the state was es-
tablished at the University under the direction of Prof. A. W.
Palmer, and in September of that year regular shipments for
analysis from the Illinois River and from Quiver Lake were
made at intervals of one week, and in January of the following
year Spoon River was added to the collection points. ‘These
collections were continued throughout the period of our oper-
ations at Havana. In September, 1897, collections were insti-
tuted in Thompson’s Lake, and from that time on the samples
for chemical analysis were taken at the same time and place
as the plankton and, like that, by the plankton pump. After
the date above named a fortnightly interval corresponding
to the plankton interval was made between collections in
Quiver Lake, though the weekly interval was continued in I[]li-
nois and Spoon rivers. August 16, 1896, a disastrous fire in the
chemistry building of the University destroyed many of the
records, and this fact accounts for the absence of data of the
analyses in the months of the year prior to the fire and for
some other gaps in the record. Special collections were made
during the last twenty months of our operations for the deter-
mination of the oxygen and carbon dioxid dissolved in surface

187

and bottom waters, but determinations of these dissolved gases
made by Professor Palmer immediately upon collection in the
field, yielded results which throw some doubt upon the value of
those made on samples which were shipped for analysis at the
laboratory of the Chemical Survey. Twenty-four to forty-eight
hours elapsed between the time of collection and that of anal-
ysis, and during this time changes no doubt took place in the
gases dissolved in the samples, so that the results of the analy-
ses give no trustworthy basis for a statement of the amount
of dissolved oxygen and carbon dioxid in the water at the time
of collection.

I am indebted to Professor Palmer not only for the data of
the chemical analyses which he has furnished me from the
records of the Chemical Survey, but also for many other cour-
tesies in Gonnection with this subject.

COMPARISON OF CHEMICAL CONDITIONS AND PLANKTON AT THE DIF-
FERENT STATIONS.

In Tables X.—XIII. will be found data from the chemical
analyses of the waters of Illinois and Spoon rivers and Quiver
and Thompson’s lakes, together with plankton data of the same
or contiguous dates. The most important of the determinations,
those of chlorine, oxygen consumed, free and albuminoid am-
monia, organic nitrogen, nitrates and nitrites, as well as the
plankton, are graphically shown in Plates X LIII.-L.

CHEMICAL ANALYSES OF WATER FROM PLANKTON STATIONS. AVERAGEs OF ALL ANALYSES.
PARTS PER MILLION.

| a | Residue on Evaporation > | Nitrogen 5
B\ 7; 7 Losson | |#|, 38 be Bale
1 Ignition = | Ammonia | 2 ¢ = 5 3)
ae rah da = S | as Sx | %=
Locality od ms I} is} 3 o | & ee SI
5 Be Bice enc o| Sa | Gos
ts) > = P| a] s S| | © Slo a”. b
= lal 2! él al slele Ele lela ae ip
FI ei io a eI ee il & o SG ee el ey
2/5 2) 2) SB] SlSaiel 2 & le |Sie By 3
a iS Qa 1) is) AlO;SO fj << iis 4|4 Cs e
Illinois River........| 188}367.5)304.1| 61.4 32.8] 25.1/21.6]/10.4| .86 46 1.03).147/1.58) 1.91 2.00
Spoon River ...... 137|522.3)167.1!274.3 41.9} 24.4) 3.8/14.1] .245 | .604 /1.292).039)1.01 388 -969
Quiver Lake .. 50/268 .9|248.2) 25.1 27.5] 25.6] 4.8] 5.9] .165 | .251 -61/.023| .66] 1.62 -62
Thompson’s Lake} 40/326.4/282.9! 44.6 36.5! 28.3'16.3]11.9! .422 | .546 | 1.05'.048| .64] 6.68 1.00

* Plankton and silt averages are for collections coincident with or contiguous to collections of
water samples.

The foregoing table gives the number of samples analyzed
from each locality and the averages of the different substances

188

determined for each. Since the samples were collected at in-
tervals throughout the year, the averages may be regarded as
presenting in succinct form the chemical characteristics of the
stations examined, and they may therefore serve as a basis for
a comparison of the relative fertility of the localities.

The residue upon evaporation, which comprises the solid
matters left upon evaporating the water and drying the residue,
includes both organic and inorganic substances. The inorganic
constituents are salts, and comprise mainly compounds of lime,
magnesia, soda, potash, iron and alumina with chlorine and with
carbonic, sulphuric, nitric, and silicic acids. In this residue lie
both the mineral constituents of the food of the phytoplank-
ton and the undecayed organic matter found in the water. Not
all of the constituents of the residue are equally utilized as
food by the phytoplankton, so that the quantity of the residue
gives a basis only fora very rough estimate of the fertility of
the different waters. Some significance, however, attaches to
the marked differences shown in the table.

The differencés in total residue in [lois and Spoon rivers
(867.5 and 522.3) and Quiver and Thompson’s lakes (268.9 and
326.4) show no particular correlation with those of the average
plankton production of these waters for corresponding periods
(1.91, 0.384, 1.62, and 6.68 cm. per m.°, as shown in Tables X.-
XIII.). The amounts and relative proportions of the dissolved
and suspended residue in these localities show some relation to
the plankton production. The residue in suspension is not, in
its present form at least, available for plant food. Its occurrence
in the four localities is almost directly correlated with the rela-
tive turbidity of the water Spoon River has from four to eleven
times as much suspended matter (274.3) as the other localities,
and this consists largely of clayey material with considerable
fine quartz, neither of which contributes any considerable
source of nutrition to the phytoplankton. The suspended ma-
terial in the other locations at times of flood partakes of the
character of that in Spoon River. At other times it contains
a considerable proportion of debris of plant or animal origin

189

including the plankton itself. The current of the river is doubt-
less responsible for the excess (61.4) which its waters carry
above that in the lakes (25.1 and 44.6). The greater amount
in Thompson’s Lake (44.6) may be due to two sources, its
greater dependence on the river for its water supply and the
greater disturbances in its waters due to fish and to waves.
The fact that the total catches of the plankton net (3.91, 1.35,
2.24, and 7.68) do not on the average more nearly approximate
in their ratios to each other the ratios of the chemical resi-
dues (61.4, 274.8, 25.1, and 44.6) is due to the great leakage
of the finer suspended particles through the silk, especially in
Spoon and Illinois river waters.

The residue in solution contains the available supply of
mineral salts for the phytoplankton as well as some organic
materials which become sources of plant food, and its distribu-
tion in the four localities is correlated with the plankton pro-
duction in the direction of the differences, though not in their
quantity. Thus Spoon River with the least dissolved residue
(167.1) has the least plankton production (.884), and Quiver
Lake has likewise less residue (248.2) and less plankton (1.62 )
than Thompson’s Lake (282.9 and 6.68). The Illinois River ex-
ceeds all of the localities in its dissolved residue (304.1), which
may be attributed to the fact that the water is “older,” afford-
ing greater time for solution, and that it is the recipient of
considerable sewage and industrial wastes which add to its
burden of substances in solution. The small amount in Spoon
River may be attributed to the fact that it is largely uncon-
taminated surface water of recent origin. The greater amounts
in the two lakes (248.2 and 282.9) are due in part at least to their
dependence upon the river, which in the case of Quiver Lake
is Shght during the summer season. In so far as the total res-
idue held in solution is an index of fertility, the data indicate
that the river itself carries the greatest store of food (304.1);
Thompson’s Lake, somewhat less (282.9); Quiver Lake, still less
(248.2): and Spoon River, least of all (167.1). On this basis and
in the hght of the production of Thompson’s Lake it would

190

seem that the river water might under more favorable condi-
tions develop a more abundant plankton. These favorable
conditions are to be found in the quiet backwaters of river-fed
lakes, where time for breeding is afforded.

The loss which the residues of total solids suffer upon igni-
tion (heating to redness) includes the organic matters which
are burned away and such constituents of the mineral matters
as are volatile or are decomposed by heat into volatile sub-
stances. In stream waters the suspended portion of this mate-
rial may be a rough index of the quantity of plankton and silt
of organic origin, all of which on decay add to the water sub-
stances available for plant food. From the data in the table it
may be ascertained that the four localities yield respectively,
in the order of the the table, 7.7, 17.5, 1.9, and 8.2 parts per
million of such material. The excess in Spoon River (17.7) is
doubtless due to silt of organic origin, while the plankton pre-
sumably forms a larger proportion in Thompson’s Lake and in
the Illinois River. The poverty alike of plankton and of silt in
Quiver Lake is reflected in the small amount (1.9) lost on igni-
tion in its waters. The loss, on ignition, of substances held in
solution shows no differences at all commensurate with the
relative production of plankton, though the trend of the differ-
ences is similar in three instances of the four.

The chlorine is contained in surface waters in combination
with various basic elements, but chiefly in the form of common
salt. Its principal source is animal matter, sewage, or drain-
age from refuse animal matter. In our river and lake waters
it is largely an index of their relative contamination with sew-
age from cities within the drainage basin. Since its combina-
tions are not utilized by plantsas foodinany considerable quan-
tity, at least as compared with other constituents of the sew-
age, such as the nitrates, the chlorine becomes the best crite-
rion of the amount of sewage andthus of the principal adventi-
tious fertilizer which the waters examined by us contain. The
differences in the four localities are striking and significant.
The average chlorine in the Ilhnois River (21.6) is more than

191

five times as great as that in Spoon River (3.8), while that in
Thompson’s Lake is more than three times the amount in
Quiver Lake. The large amount of chlorine in the Illinois
and in Thompson’s Lake—which draws its water supply mainly
from the river—is due to contamination by the sewage of Chi-
cago, Peoria, and other cities within the drainage basin. Quiver
Lake receives water from the river only during flood periods,
when the sewage is diluted, and at other seasons it contains
more nearly the chlorine of the uncontaminated prairie stream.
Its chlorine thus averages low (3.8). That of Spoon River runs
higher (4.8), in part because of backwater from the main stream
to the point of collection. The sewage systems discharging
into this stream are few and but slightly developed, and its
chlorine is correspondingly low. While it is true that the
chlorine is not a precise measure of the amount of sewage or
of the adventitious fertilizing material received by a stream, it
is nevertheless significant that ratios of chlorine and plankton
production not only trend in the same direction but are quanti-
tatively somewhat similar when lake is compared with lake and
stream with stream. Thus in Quiver and Thompson’s lakes
the ratio of their chlorine content is 1 to 3.4 while that of
the plankton production is 1 to 4.2. The corresponding ratios
in Spoon and Illinois rivers are 1 to 5.7 and 1 to 5. An increase
in chlorine due to sewage or animal wastes seems thus to be
accompanied by a proportionate increase in the plankton pro-
duced. It is safe to infer that it is one of the factors producing
the increase, but, as shown elsewhere in this paper, other fac-
tors, such as vegetation and current, are also potent in produc-
ing the contrasts in plankton production above noted.

The oxygen consumed in oxidizing the organic matters af-
fords an additional index of the quantity of these substances
present in the water, but since all kinds of organic matter are
not oxidized in the analysis it does not yield a criterion of
the total quantity of organic matter. A comparison of the
oxygen consumed in the four localities yields results very sim-
ilar to those obtained by a comparison of loss on ignition, ex-

192

cept in the case of Quiver Lake, where the oxygen consumed
(5.9) is proportionately very much lower than the loss on igni-
tion (27.5). The amount of oxygen consumed is greatest in
Spoon River (14.1), and may be attributed largely to the detri-
tus of organic origin which the stream carries, or to the prod-
ucts of its decay held in solution. It may also be due in part
to the organic material of the water-bloom (Huglena) which es-
capes the silk of the plankton net. There is, however, no in-
crease in the oxygen consumed in the season of the water-bloom
which can be considered commensurate with its development.

Nitrogen is an essential constituent of protoplasm and of
many of its products. It is taken up by plants in the form of
nitrates and free ammonia, and there is increasing evidence
that it may be utilized, especially by the lower plants, in more
complex combinations, such as the amido-compounds. Since
the other principal constituents of protoplasm—carbon, hydro-
gen, and oxygen—are present in inexhaustible quantity in the
air, water, and carbon dioxid, and since the nitrogen available
for plant food is practically limited to that contained in the
above-named compounds, the nitrogen in combination in any
given body of water becomes par excellence an index of its fer-
tility. These compounds exist in living plants and animals, in
their wastes, and in the products of their decay. They enter
stream and lake waters in various ways: in the debris of veg-
etable and animal origin washed into the stream, especially by
flood waters ; in leachings from such matters drawn from the
soil in seepage and spring waters ; and, especially (in the I1h-
nois River) in the sewage and industrial wastes of Chicago,
Peoria, and other cities within the drainage basin. In the lake
and stream waters these nitrogenous compounds are found in
solution in the water, in the sediment and debris of organic or-
igin in suspension, in the zo0- and phytoplankton, and in the
macroscopic aquatic plants and in the larger animals—such as
fish, mollusks, insects, and crustaceans. The chemical anal-
yses show only those nitrogenous compounds in solution, in
silt, and in plankton, while that stored in the larger plants and

193

animals is not determined. Since the silt is undergoing decay,
and since the individuals of the plankton are short-lived and
rapidly release their nitrogenous compounds into the water by
waste and decay, the determinations of nitrogen in its various
forms in the analyses represent both the present fertility and
that in immediate prospect. The contributions from the ma-
croscopic plants and animals not included in the samples
analyzed constitute an undetermined element in the sum total
of the nitrogenous matter available for the sustenance of the
phytoplankton. The relative amounts of nitrogen in the several
stages of decomposition are shown in the determinations of
total organic nitrogen, of nitrogen as albuminoid and free am-
monia, and of nitrites and nitrates.

The total organic nitrogen includes all nitrogen that is in
combination with carbon (together with other elements) in the
tissues of living plants and animals and in many of the waste
products of the latter. It is also present in organic matter in
the early stages of decay, and is accordingly found in organic
debris and sewage of stream and lake waters. It is accord-
’ ingly an index of the quantity of organic matter which in its
present form is not available for plant food (with the possible
exception of certain amido-compounds) but is destined to be-
come available by decay. It thus indicates the potential fer-
tility of the water. The differences in the amount of total
organic nitrogen present in the four localities are not in each
case correlated with the actual plankton production. Spoon
River, which contains the least plankton, has the greatest
amount (1.292) of organic nitrogen. The absence of any ex-
cessive contamination by sewage in this stream combined with
the paucity in plankton, makes it apparent that this mat-
ter is probably in the organic detritus of the silt, which is pres-
ent in an unusual amount in this stream. The close resem-
blance of the Illinois River and Thompson’s Lake in the matter
of total organic nitrogen (1.03 and and 1.05) is explained by the
dependence of the latter upon the river for its water supply,
and by the excess of sewage in the former and of plankton in

194

the latter. The small amount in Quiver Lake is attributable
to its greater independence of the river, to the paucity of its
plankton, and to the sandy nature of its drainage basin and
consequent share of spring water in its water supply. It is
noticeable that the large amount of submerged vegetation in
this lake does not contribute any great amount of organic
nitrogen to the water at any season of the year.

The nitrogen as albuminoid ammonia is included in the to-
tal organic nitrogen, and exhibits almost identical relative
amounts in the four localities, though actual quantities are
only half as great. It represents the nitrogenous materials
which have not undergone decomposition.

The nitrogen as “ free” ammonia represents the ammonia
contained in the water in free or saline condition. Itis a prod-
uct of the decomposition of organic matter in the first stages
of oxidation, and its quantity 1s an indication of the amount
of such matter present in the water in a partially decomposed
state. It is abundant where sewage occurs, and together with
the chlorine affords evidence of the degree of contamination.
The occurrences of free ammonia in the four localities (.86,
.245, .165, and .422) are not in most instances in the same ra-
tios as those of the chlorine (21.6, 3.8, 4.8, and 16.3) or of the
plankton (1.91, .384, 1.62, and 6.68). The excess (two to five
times as much) of decaying organic matter in the river as com-
pared with the other situations is apparent, and is doubtless due
to the concentration of sewage in its channel and to the more
recent access of the sewage there as compared with that in the
reservoir backwaters, as, for example, in Thompson’s Lake.
The early stages of decay are in consequence more active in
the river. The free ammonia is high in both the river (.86) and
Thompson’s Lake (.422) but lower in Spoon River (.245), where
the organic material in suspension is considerable, as indicated
by the loss on ignition, the albuminoid ammonia,and the organic
nitrogen and oxygen consumed. The decay of this matter and
the accompanying release of free ammonia has not been attained
as yet in a part at least of the silt in Spoon River to the same

195

degree that it has in the older river and lake waters. Its bur-
den of silt thus adds to the sources of fertility of the main
stream and of the reservoir backwaters at times of flood. The
small amount of free ammonia in Quiver Lake (.165) is corre-
lated with the small amounts of the substances above named
in its waters and the sandy nature of its drainage basin. The
differences in the two streams in the quantity of free ammonia
(.86 and .245) have the same trend as the differences in plank-
ton production (1.91 and .384), but they are not commensurate
quantitatively, owing apparently to the more recent origin of
the water in Spoon River. In the lakes the free ammonia (.165
and .422) and plankton (1.62 and 6.68) exhibit a similar trend
and a like absence of quantitative differences in the plankton
commensurate with the free ammonia available for support of
the plankton. The effect of the relative food supply is thus
apparent in the trend of the differences, and the operation of
other factors is suggested by the quantitative contrast. The
factors in Quiver Lake tending to reduce the plankton below
the amount that the food supply would make possible are to be
found in the passage of tributary waters through the lake and
in the excessive aquatic vegetation. It is noticeable that the
considerable amount of submerged vegetation in Quiver Lake
does not seem to effect any appreciable increase in the free
ammonia. The abundance of free ammonia in the Illinois
River would seem to afford a basis for a greater development
of the phytoplankton than it attains under the conditions in
that stream. The time for breeding which is afforded in the
’ backwaters is one factor involved in this contrast.

The nitrites constitute a second intermediate stage in the
oxidation of nitrogenous substances into inorganic products.
Their presence indicates organic matter in the final stages of
decay, and that decompositions due to the vital processes of
living organisms are under way. The nitrites exhibit a distri-
bution in the four localities which in the trend of the differ-
ences is similar to that of the free ammonia. The ratio of the
free ammonia in Spoon River to that in the Illinois is 1 to 3.4,

196

while that of the nitrite content of the two streams is | to 3.7.
The ratios in the two lakes, Quiver and Thompson’s, are 1 to
2.6 and 1 to 2.1 respectively. Spoon River and Quiver Lake are
thus poorerin nitrites than Illinois River and Thompson’s Lake.
The same contrasts are to be found in their production of
plankton, though the differences in the amounts produced are
greater than those in this source of fertility. The amount of
nitrites (.048) in Thompson’s Lake is quite low when the large
plankton production in this lake (6.68) is contrasted with the
much smaller amounts (1.91, .884, and 1.62) in the other local-
ities, where the nitrites are but a little less or even greater (.147,
.039, and .023). Hither the nitrites are an inadequate measure
of the potential fertility of the water, or the other waters named
might, in the environment of Thompson’s Lake, support a more
abundant plankton.

The nitrates are the final products of the oxidation of ni-
trogenous matters, in which the nitrogen returns to morganic
compounds and is once more in a form most available for util-
‘ization as food for the phytoplankton or other aquatic plants.
The quantity of these compounds is a prime index of the 1m-
mediate fertility of the water, and becomes a basis for future
growth of the phytoplankton and other aquatic plants. The
amounts of nitrates present in the waters of the four localities
are very different, and at first glance exhibit little correlation
either with the other forms of nitrogen present in the water or
with the quantity of plankton produced. It should be noted
in this connection that the nitrates, more completely perhaps
than any other form of nitrogen, are utilized by the chloro-
phyll-bearing organisms as food, and if taken up by the phyto-
plankton the nitrogen appears in the subsequent analysis as
organic nitrogen. If, however, the phytoplankton or the zod-
plankton feeding upon it is utilized by some macroscopic animal,
—as, for example, by Polyodon, or by the Unionide which cover
the river bottom in places,—it is removed from the field of
analysis, excepting only in such animal wastes as are returned
to the water by the feeding organism. If it is utilized by the

197

- grosser forms of submerged aquatic vegetation, it is likewise
effectually removed from the field of analysis until again
released by the decomposition of this vegetation. The nitro-
gen aS ammonia in organic compounds, or as nitrites, is either
entirely unavailable for plants or, with the probable exception
of the free ammonia and the amido-compounds, is less availa-
ble than the nitrates. These other forms consequently more
fully represent the potential fertility of the water than the ni-
trates do, for the latter indicate mainly the wnutilized portion
of the nitrogenous plant food immediately available. In the
light of the foregoing conditions more significance attaches to
the distribution of nitrates and plankton in the four localities.
The excess in the river (1.58) over that in the tributary waters
of Spoon River (1.01) and Quiver Lake (.66) may be due in part
to the greater age of the waters of the main stream and the
opportunity thus afforded for the completion of the processes
of decomposition of organic substances delivered to the main
stream by tributaries above the point of examination. When
the quantity of nitrates in the river is compared with the or-
ganic nitrogen, free ammonia, nitrites,and nitrates in Spoon
River or Quiver Lake, it becomes apparent that the tributary
waters of this stream still act as a diluent of the river water.
The source of this excess in the main stream is to be found in
the sewage and industrial wastes of Chicago and Peoria. The
unutilized nitrates are two and a half times as great in the
river (1.58) asin Thompson’s Lake (.64). In so far as the ni-
trates are concerned, both Spoon River and the [linois might
support a much more abundant plankton than they now pro-
duce (1.91 and .884) if the conditions permitted. Thompson’s
Lake, drawing its water from these sources, does maintain a
greater production (6.68) and exhibits a great reduction in the
amount of nitrates (.64), the unutilized residium being less
in this lake than in any of the other localities. The increase in
the amount of plankton in Thompson’s Lake over that in the
river (3.5 times as much)is roughly proportional to the decrease
in nitrates in the lake as compared with the river (.4 as much).

198

The similarity of the residual nitrates in the two lakes is strik-
ing (.66 and .64), and it bears no apparent relation to their
plankton production (1.62 and 6.68). The excess of other forms
of nitrogen in Thompson’s Lake (roughly twice that in Quiver)
would seem to indicate either that the decomposing nitroge-
nous substances are utilized before they reach the form of ni-
trates, or that they are abstracted from the water so promptly
that they do not accumulate above a certain residual minimum
which is apparent during the growing period of the phyto-
plankton and of the coarser forms of aquatic vegetation. (See
Plates XLIX. and L.) It is evident that the nitrates in the two
lakes (.66 and .64) cannot adequately represent the nitrogenous
resources of the two bodies of water; neither can they furnish any
reliable clue to their actual productiveness in plankton. Other
factors of the environment are equally or even more potent.
The number of analyses and of plankton catches is so great
(188 and 156 from Illinois River and 40 of each from Thomp-
son’s Lake), and they are so distributed through the year, that
the inference is justified that the nitrates shown by chemical
analysis in the water of a lake or stream, especially during the
growing period of vegetation, afford no reliable basis for judg-
ment as to its plankton production.

The sewage received by the Illinois River bears an impor-
tant relation to the chemical condition of its water and thus to
the plankton which it produces. No measurements are made
by boards of public works of the amount of sewage which mu-
nicipal systems discharge into the various streams which unite
to form the Illinois River. Two sources of information are,
however, available which throw some lhght on the extent of
sewage pollution arising from these sources. They are the
population of the cities in question and the pumpage of their
water-works. Municipal engineers are accustomed to estimate
the sewage discharged from a city with well-established sewage
and water systems as approximately equivalent to the pump-
age of the latter. I have accordingly prepared a table which
includes practically all of the cities provided with these works

199

in 1897, and states the pumpage in gallons per day, the popula-
tion, and pertinent data concerning the systems in discussion.
The population is that reported by the census of 1890, and the
figures for 1897 would show a considerable increase owing to
the rapid growth of the urban population in the vicinity of
Chicago during the past decade. The second part of the table
includes the smaller cities with water-works but without de-
veloped sewage systems. These do not contribute to the stream

POPULATION AND PUMPAGE IN CITIES WITH SEWAGE SYSTEMS.

City Population in 1890 Rae Remarks.
Lllinots
Aurora 19,688 1,338,570 |Combined sewage system
Chicago 849,850 520,275,109 |Population 1,099,850,from
which 250,000 was de-
ducted for area of City
draining directly into
Lake Michigan. Pump-
age is that at Bridgé-
port.
Elgin 17,823 1,143,488 |Combined sewage system
Hinsdale 1,584 124,000
Joliet 23,264 2,500,000 |Part separate, part com-
bined systems.
Kankakee 9,025 1,200,000
LaGrange 2,314 223,609 |Combined sewage system
La Salle 9,855 1,503,835
Lemont a 600,000 |Population not given in
1890 apart from that of
township.
Mendota 3,542 205,479 |Separate sewage system.
Ottawa 9,985 511,000 |Sewage system incompl’t.
Pekin 6,347 750,000 4
Peoria 41,024 5,000,000
Peru 5,550 216,183 |Sewage system incompl’t.
Pontiac 2,784 750,000 |Pumpage estimate re-
duced from 2,000,000
gal.
Streator 11,414 2,000,000
Utica 1,094 720,000 |Water supply from ar-
tesian wells.
Watseka 2,017 150,000 |Pumpage estimated.
Wheaton 1,622 70,000 |Sewage system incompl'’t.
Wisconsin
Waukesha 6,321 500,000 |Separate sewage system.
Indiana
La Porte 7,126 747,788
————— ————————————
Total 1,032,229 540,529,061 Reielliputapelye, ade 7

ft. per sec.

200

waters a volume of sewage equal to the pumpage, though their
imperfectly developed systems of drainage, combined with the
surface run-off, carry some sewage to the stream.

POPULATION AND PUMPAGE IN CITIES WITHOUT SEWAGE SYSTEMS.

Daily Pumpage

City Population in 1890 in gal. Remarks.
LIllinots
Batavia 3,543 2,500 1,500— 3,500 gallons.
Braidwood 4,641 5,500 1,000 — 10,000 ©
Chenoa 1,226 20,000
Delavan 1,176 50,000
Dundee 2,073 70,000
Earlville 1,058 25,500
Elmwood 1,548 19,000 7,000— 31,000 gallons,
E] Paso 1,353 27,500 25,000—30,000 “
Fairbury 2,324 71,500 53,000—90,000—“
Forrest 1,021 8,442
Geneva 1,692 40,000 Pumpage estimated.
Lacon 1,649 15,000
Lexington 1,187 60,000
Lockport 2,449 44,500
Minonk 2,316 109,689
Momence 1,635 250,000
Morris 3,653 54,795
Plano 1,825 31,500
Princeton 3,396 650,000
Spring Valley 3,837 55,000
Washington 1,301 100,000
Wenona 1,053 23,000 21,000—25,000 gallons.
West Chicago 1,506 20,000
a mpage, 2.8 cu. ft.
Total 47,562 1,753,426 Teo BOCe

The principal sources of the sewage contributed to the
Illinois River above Havana are Chicago, Peoria, and the
smaller cities within the drainage basin. The amounts
contributed by each are approximately 520,275,109, 5,000,000,
and 16,007,378 gallons respectively per day. The total amount
of 542,282,487 gallons per day or 838.7 cubic feet per second is
about 8 per cent. of the average flow of the river at Havana and
exceeds by 40 per cent. the estimated low-water flow at Cop-
peras Creek dam, eighteen miles above our plankton station.
In 1890 the population of the two larger cities and the total of
the remaining smaller ones was respectively 849,850, 41,024,
and 188,817, a total of 1,079,691, 250,009 having been deducted

201

from the population of Chicago, as before stated, because of the
fact that the drainage of certain districts did not enter the [h-
nois River. It is apparent that Chicago, with a population four
times and a pumpage twenty-five times as great as that of the
remaining territory, is the principal source of sewage, over-
shadowing all others by its magnitude.

The sewage of Chicago during the period of our operations
was mainly discharged into Chicago River, a tributary of Lake
Michigan. An area of 50.63 square miles lying within the city
limits and having in 1897, according to estimates kindly fur-
nished us by the engineering department of the Sanitary Dis-
trict,a population of 250,000 to 300,000, drains directly into Lake
Michigan. The water supply of Chicago is drawn directly from
the lake, and to decrease its pollution by sewage, pumping works
were established at Bridgeport which raised the fouled water of
Chicago River into the Illinois and Michigan Canal, which emp-
ties into the Illinois River at La Salle. At low-water stages the
pumpage of Bridgeport prevented the discharge of a considerable
amount of the sewage into the lake, reversing at times the direc-
tion of the current in the river. During floods the pumps were
powerless to prevent the discharge of large amounts of sewage
into the lake. Under the conditions prevailing during the years
of our operations a considerable portion of the sewage of Chicago
thus found its way into the Illinois River. This sewage included
a large amount of industrial wastes, especially from the Union
stock-yards and slaughter-houses connected therewith. The
average daily pumpage of the city water-works in 1897 in
Chicago was 265,530,910 gallons—an amount 50 per cent. less
than the pumpage at Bridgeport. The amount discharged into
the Illinois and Michigan Canal thus represents a somewhat di-
luted sewage as compared with that from other sources. Chemi-
cal examinations of the canal water indicate (see Palmer, ’97)
that the maximum period of decomposition of the sewage passed
before the water entered the river. The location of the crest
of this wave varied with the temperature, ranging from Lock-
port to Morris. Bacteriological determinations (see Jordan ’00)

202

also indicate a somewhat similar wave of bacterial develop-
ment, which is to be correlated with the wave of nitrification
detected by the chemical analyses. By the time the sewage of
Chicago entered the Illinois River at La Salle it was thus al-
ready in the advanced stages of decay and available for the sup-
port of the phytoplankton or other vegetation, if, indeed, it
was not already used to some extent by these agencies. The
progressive nitrification of the sewage in the canal is shown by
the average nitrates found by Palmer (96) at Lockport (.84),
Morris (1.44), and La Salle (2.51 parts per million). The average
at Havana, about one hundred miles below La Salle,in the same
year, was only 2.34 with the added amount from Peoria’s con-
tribution. At Kampsville, about 190 miles from La Salle, the
amount falls to 1.39. ;

The sewage of Chicago under conditions prior to the open-
ing of the drainage canal in 1899 thus enters largely into the
sources of fertility of the river water. It reaches the maximum
of decomposition before mingling with the channel waters at
La Salle, and is reinforced by the sewage and wastes of Peoria.
The products of decomposition ( nitrates ) continue in dimin-
ishing quantity, diluted by tributary streams—as, for example,
by Spoon River, where the average amount of nitrates (1.01)
is somewhat less than that of the river at that point (1.58, for
1894-99 )—and utilized by the developing phytoplankton and
other aquatic vegetation. Entering practically at the head-
waters of the Illinois, it becomes one of the most potent fac-
tors in the maintenance of the abundant plankton found in the
river and its backwaters.

The sewage of Peoria, as represented by the pumpage of the
water-works, is but a small fraction of the total amount re-
ceived, being less than one per cent. if industrial waters are
included. For two reasons its effect upon the plankton in the
river at Havana is proportionally much greater than the fig-
ures indicate. The firstis the proximity of Peoria, it being 55.7
miles above Havana. The maximum stages of decomposition
are usually passed, even in the coldest weather, before the sew-

203

age reaches our plankton station, so that its fertilizing effect
upon the water has been operative for some time. The second
reason lies in the fact that large industrial plants with private
water supplies—such as the distilleries and cattle-feeding yards
connected therewith and the glucose factory—discharge im-
mense amounts of organic wastes directly into the river. As
many as thirty thousand head of cattle are often on hand at
one time in these feeding-yards, and the refuse from the feed-
ing-pens is flushed into the stream or piled at the river’s edge
till a rising flood carries it away in huge floating islands. The
contributions from these sources at Peoria and Pekin are con-
siderable. The comminuted vegetable debris of the silt owes
its origin to this source in some degree, and it shares also in
producing a wave of bacterial development (Jordan, ‘00), of
putrefaction (Palmer, ’97), and of the rapidly developing plank-
ton organisms whose crest lies between Peoria and Havana.

The contributions of sewage from the smaller cities in the
drainage basin above Havana are relatively so small, so scat-
tered, and so mingled with tributary waters in many cases be-
fore they enter the river, that no localized effect upon the
plankton of the stream can be traced.

The direct conveyance into drainage channels of so large
an amount of animal wastes as occurs in sewage diverts from
the soil and adds to the water an unusual, and, owing to the
narrow confines of our streams, a proportionately great, source
of fertility. In these particulars, together with its unusual ex-
tent of impounding backwaters, its low gradient, and its im-
mediate access to markets, the Illinois River offers a magnifi-
cent field for the development of a scientific aquiculture.

CHEMICAL CONDITIONS AND PLANKTON PRODUCTION. :

A summary of the chemical conditions as related to the
production of plankton in the four localities, Illinois and Spoon
rivers and Quiver and Thompson’s lakes, yields some evidence
of correlation, and also some points of difference which indi-
cate the operation of other factors than nutrition in determin-
ing the production of plankton. The following table—giving

204

the sum total of the averages of the nitrogenous matters (free
ammonia, organic nitrogen, nitrites, and nitrates) and also the
average plankton production—sets forth in brief the relative
fertility and production of the four localities.

Sum of averages of
Locality. nitrogenous matters
—parts per million.

Average plankton—
cm.* per m.?

Illinois River........

3.617 1.91
Spoon River......... 2.586 384
Quiver Lake......... 1.456 1.62
Thompson’s Lake.... 2.160 6.68

There is more nitrogenous matter in the streams than in
the lakes, but also less plankton. Nutrition for the plankton
is present, but time for breeding, owing to the more recent or-
igin of stream waters, has not been afforded there, while in the
lakes, which have somewhat of a reservoir function, there is
time for growth of the plankton, and the store of food is de-
pleted as compared with that in the river. It is also evident
that there are unutilized stores of food in the rivers affording
a basis for further development of the plankton.

The Illinois River exhibits the greatest fertilty (total
nitrogenous matters 3,617), owing largely to sewage and in-
dustrial wastes. These matters cause the high chlorine (21.6)
and the large amount of free ammonia (.86) and organic nitro-
gen (1.03), while the abundant solids in solution (804.1) and the
nitrites (.147) and nitrates (1.58) show how large a part has
reached the last stage of decomposition. The unutilized prod-
ucts of decomposition are without exception in the data here
discussed greater in the waters of the channel than in the trib-
utary or impounded reservoir waters.

In Spoon River the solids in suspension are highest (274.3)
and those in solution least (167.1), a condition due to the re-
cent origin of its water and to the large amount of silt which
it carries. The organic origin of some of this silt is shown by
the large loss on ignition (41.9), the oxygen consumed (14.1), the
albuminoid ammonia (.604), and the total organic nitrogen

205

(1.292), all of which are in excess in its waters. The freedom
from sewage is evidenced by the low chlorine (3.8), while the
considerable amounts of free ammonia (.245), nitrites (.039),
and nitrates (1.01), indicate organic decomposition in progress
or completed. In the absence of any considerable contamina-
tion by sewage it seems probable that these substances have
their origin in the organic silt and the soil waters of the very
fertile catchment-basin of the stream. The water of Spoon
River, in so far as the nitrogenous substances (2.586) are con-
cerned, could support a much more abundant plankton than it
produces (.3884). Asin the case of the main stream, the ex-
planation of the slight production lies in the recent origin of
the tributary water. Impound Spoon River water in Thomp-
son’s Lake, and it produces an abundant plankton.

In food resources Quiver Lake is the poorest locality of the
four (1.456, total of nitrogenous substances), having 40 per cent,
of the amount of the nitrogenous substances in the [llnois, 56
per cent. of that in Spoon River, and 67 per cent. of that in
Thompson’s Lake. The suspended solids (268.9), the loss on
ignition (27.5),and the oxygen consumed (5.9), are least here as a
result of slight access of silt-laden waters. The chlorine is low
(4.8), and would be much lower if contaminations from river
water at overflow could be eliminated ; and corroborative evi-
dence of the shght contamination of the waters of this lake by
sewage is seen in the amounts of free (.165) and albuminoid
(.251) ammonia, of organic nitrogen (.61) and nitrites (.023), all
of which exhibit minimum averages in this lake. Organic mat-
ter in decay is less abundant here than in the other localities,
being, for example, about 50 per cent. less than in Thompson’s
Lake. The final products of decay, the nitrates, are greater
(.66) than the amounts of organic matter would lead us to ex-
pect, and are probably due in large part to soil waters from the
drainage basin. In the light of the production of Thompson’s
Lake (6.68) the small amount of plankton produced in Quiver
Lake (1.62) finds no adequate explanation in a reduction of 33
per cent. in the total nitrogenous substances. Flushing by tribu-

206

tary water and abundance of submerged non-rooted vegetation
are the more potent factors in the failure of the plankton de-
velopment in Quiver Lake.

In most particulars the averages of the analyses of water
from Thompson’s Lake approach those of the river water, from
which it draws its main supply. There are less solids in sus-
pension (282.9) than in the river as a result of sedimentation,
and less in solution (44.6)—probably the effect of the small
amount of creek water, or of the utilization by the plankton
and vegetation of substances held in solution. The loss on ig-
nition (36.5), oxygen consumed (11.9), albuminoid ammonia
(.546), and organic nitrogen (1.05), all run higher than in the
river as a result of the greater amount of plankton. The de-
creased amounts of free ammonia (.422) and of nitrites (.048)
as compared with those in the river (.86 and .147) would seem
to indicate less decomposition here, while the small amount of
nitrates (.64)—the least of all the averages—suggests utiliza-
tion of these matters by the plankton, which here reaches a
greater development than in any of the other localities under
present consideration.

SEASONAL CHANGES IN CHEMICAL CONDITIONS AND PLANKTON.

The data concerning these changes are given in Tables X—
XIII., and they are presented graphically in Plates X LIII.—
L. They afford evidence for the following general conclusions:

There is a major seasonal movement in the chemical con-
ditions which can be traced in the analyses for each year and
each locality. There are, in addition to this wide-spread and
recurrent cycle of changes, many abrupt and often considerable
fluctuations due to floods, while others are of minor importance
and apparently of local origin. The various nitrogenous sub-
stances to a considerable extent fluctuate together. The quan-
titative fluctuations in the plankton show no intimate and im-
mediate correlation with those of any substance determined in
the analyses: Certain relations of the plankton to the quantity
of nitrogenous substances are however indicated, but precise
quantitative correlations cannot be established. The operation

207

of other factors is evident, chemical conditions alone offering
no satisfactory clue to causes of many of the fluctuations in the
amount of plankton.

The cycle of seasonal fluctuations in chemical conditions
is best seen in years of more normal hydrograph, such as that
of 1898, and it is more regular in the backwaters, such as Quiv-
er and Thompson’s lakes, than it is in tributaries such as
Spoon River, or in the Illinois itself. In the streams the floods
produce irregularities which either do not enter the reservoir
backwaters or reach them only in diminished volume. The
varying degree of contamination by sewage in the different lo-
calities and in different seasons in the same locality adds an-
other element which diversifies the seasonal changes and makes
it more difficult to detect the common features which the fluc-
tuations exhibit in all the localities.

The cycle of seasonal fluctuations (see Pl. XLITI.—L.) in
the chemical conditions is, in the most general terms, an in-
crease in the nitrogenous compounds during the colder months
and a decrease during the warmer ones. The maximum period
usually appears in October and continues until the following
summer, declining in May and June to the summer minimum,
which in the following October and November rises again to
the winter maximum. This fluctuation is somewhat similar to
that found in soil waters. This coincidence suggests the oper-
ation of fundamentally similar causes back of the common phe-
nomenon.

These maximum and minimum pulses in the Illinois River
in 1896 (Pl. XLIII.) are most evident in the nitrates and free
ammonia, though traces of their influence can be detected in
the curve of the albuminoid ammonia. The suppression of this
spring flood and the recurrence of four minor but unusual
floods during the summer and fall are probably the cause of
the nonconformity of some of the substances to these pulses
and of the irregularity which they all exhibit in this year.

In 1897 (Pl. XLIV.) the curve of the nitrates again exhib-
its these pulses, but they are not apparent elsewhere unless it

208

be in the free ammonia. The prolonged and unbroken low
water from August to the end of the year, and the consequent
concentration of the sewage in the river and the marked de-
velopment of the water-bloom during this period, seem to have
obliterated the minimum pulse in all but the nitrates. The
marked rise in chlorine and free ammonia gives some idea of
the unusual degree of concentration of the sewage.

In 1898 and the first three months of 1899 (Pl. XLV.) these
pulses are much more evident, being traceable in the nitrates,
albuminoid ammonia, organic nitrogen, and oxygen consumed.
The marked depression of the free ammonia during the flood
season in a measure modifies its conformity to these pulses.

A relation of these maximum and minimum pulses to the
growth of the plankton is suggested by the chronology of the
chemical (especially that of nitrates) and the plankton curves.
The spring maximum of plankton production, which normally
occurs in the last of April and the first of May, comes toward
the close of a long period of high content of nitrogenous mat-
ters. Itis followed by or is coincident with the decline in
these substances. With the decline in plankton production in
late autumn the nitrogenous substances again increase (PI.
XLUI-XLV.). During the low water of 1897, when the mid-
summer minimum of nitrogenous substances was overshadowed
by the concentration of the sewage, we also find a marked in-
crease in plankton production as contrasted with that of cor-
responding seasons of 1896 and 1898. The warm season is pre-
sumably one of more rapid nitrification, the heat favoring the
more rapid decomposition of the organic matter in water, but
excepting instances of great sewage concentration, as in the
late summer of 1897, we do not find an increase or an accumu-
lation of the products of such decay in the water during the
warm season. Indeed, the opposite seems to be the tendency.
The explanation of this phenomenon lies, it seems, in the rapid
utilization of the nitrogenous products of decay by the nitro-
gen-consuming organisms of the water. In open water these
are the chlorophyll-bearing organisms of the plankton. In

209

lakes rich in vegetation the grosser forms of aquatic vegetation
draw heavily upon these resources. The accumulations of de-
cay in winter and the increased products of decomposition in
summer are all largely and promptly transformed again into
organized matter, leaving only an unutilized residual mini-
mum which represents an equilibrium of the processes of
erowth and decay in progress in summer waters. The seasonal
distribution of floods may also enter as a determining factor in
the problem.

The coincidence of the spring plankton maximum and the
decline of nitrogenous matters in the river water has its par-
allel in the decline of nitrates in soil waters with the pulse of
spring vegetation. In both cases the decline in nitrogenous
matters seems to be due to utilization by growing vegetation,
by chlorophyll-bearing organisms.

These maximum and minimum pulses of nitrogenous mat-
ters may also be traced in the analyses of samples from Spoon
River. In 1896-97 (Pl. XLVI.) the nitrates exhibit most clearly
the fluctuations in question. Traces of their presence can be
detected in the plottings of the organic nitrogen, albuminoid
and free ammonia, and oxygen consumed, though in all these
cases the effect of flood waters is also evident and cannot be
eliminated from the problem. Invasion of Illinois River water
is also apparent in October of the low-water period of 1897, be-
ing shown especially by the chlorine curve.

In 1898 and the first three months of 1899 both the cold
weather maxima and the warm weather minimum are more
sharply defined and appear in all the substances above enumer-
ated.

The plankton of Spoon River, with the exception of that
of the low-water period of 1897, is too insignificant to make
much of a showing even when plotted upon a scale tenfold
that used for other stations (see explanation of Pl. XLVI.);
nevertheless we still find here the same midsummer reduction
in nitrogenous substances which has just been explained as the
result of the utilization of such matters by the phytoplankton.

210

In spite of this seeming contradiction, I believe the explana-
tion still holds in the case of Spoon River. The minimum peri-
od occurs during the time of low water, when the principal
source of the flow in the stream is ground water which has
already been robbed of its nitrates to some extent by terrestrial
vegetation. Again, the plankton production of Spoon River,
judging from the development of the water-bloom (Huglena),
consists largely of chlorophyll-bearing organisms, which also
rob the water of its nitrogenous substances. The period of de-
velopment of the water-bloom covers the months of summer
and early autumn, thus coinciding with the period of depressed
nitrates. It is quite certain that the collections of the silk net
fail completely to represent the quantity of those minute or-
ganisms which compose the water-bloom, and thus give no
adequate clue to the amount of nitrogen-consuming organisms
present in these or other waters. The reduction in nitrates in this
stream during summer months is not, however, as great in
quantity as it is in the Illinois River (cf. Pl. XLV. and XLVI).
The excess of sewage in the latter creates a greater winter
maximum, thus permitting a greater range in reduction to the
residual minimum of midsummer, which is about the same
in both streams. But httle correlation between the chemical
conditions of Spoon River and its plankton production can be
established beyond the reduction in nitrates in the plank-~
ton maximum of the autumn of 1897 at a time of abnor-
mal low-water. Under normal conditions the plankton curve
(silk-net catches) exhibits no movement correlated with or
commensurate with the changes in chemical conditions. Flood
and current afford here no time sufficient for the expression of
the chemical factors.

In Quiver Lake the maximum and minimum periods ap-
pear with distinctness and affect all of the substances in ques-
tion. This is partly the result of the diminished effect of
floods in this reservoir area, and also of the delimitation of the
lake as a separate unit of environment with the cessation of
overflow. During the flood period (see Pl. III. and hydro-

211

graphs on Pl. XLVIII. and XLIX.)the lake receives in addition
to the drainage of its own catchment-basin some access of
flood waters from the bottom-lands above and from the adja-
cent river. The water along the eastern shore, even in flood
conditions, is “lake” rather than river water, as a comparison
of the plottings of the analyses of water from the two sources
clearly demonstrates. Our collections of plankton and water
samples were taken within or near this belt of lake water, in
which contamination by flood waters was not usually noticea-
ble. Compare in this connection the chlorine curve of the
river and lake (Pl. XLV. and XLIX.). To some slight extent,
then, the analyses pertain to two sources: to the waters of
overflow, largely belonging to the colder months and period of
the maximum of nitrogenous substances; and to the waters of
a spring-fed lake, delimited during the period of low water and
of the minimum of nitrogenous substances. The data at hand
do not cover low-water conditions during a “maximum” period,
which might give evidence of a seasonal cycle in chemical
conditions in this lake independent of the river overflow. From
conditions elsewhere it seems probable that such a cycle does
occur here also, though the overflow and probable contamina-
tion may serve here to heighten somewhat the contrast be-
tween the maximum and minimum periods of the seasonal
cycle.

In the autumn months of 1896 and 1897 covered by the
analyses, the rise in nitrates only is indicated (Pl. XLVIII.), the
summer minimum continuing through the low-water period
of autumn.

In 1898 and the first three months of 1899 (Pl. XLIX.) the
period of maximum, November to May, is well distinguished
from that of the minimum, May to November, and not only in
the nitrates but to some extent also in all of the other substan-
ces, appearing most clearly in the free and albuminoid ammonia
and the organic nitrogen.

As in the Illinois River, so here also the spring maximum
of the plankton (Pl. XLIX.) comes at the close of the period

212

of maximum of nitrogenous substances in the water and is fol-
lowed by a period of depression in these substances, and in this
case by a much more marked fall in the amount of plankton,
which does not again rise until the return of the nitrogenous
substances in the autumn. The unutilized minimum of nitrates
during the summer season is but a trifle less than that in the
river (cf. Pl. XLV. and XLIX.), but the fact that all the
other forms of nitrogenous matters are not only low but are
lower than in the river throws some light on the slight devel-
opment of the plankton here as compared with that in the
river during this period of the summer minimum of nitroge-
nous substances. While the small amount of plankton seems
inadequate to explain the marked reduction in the various ni-
trogenous substances, it may be that the more permanent veg-
etation, the submerged aquatic flora of this lake, is an import-
ant factor in the reducing process. In its seasonal production
the plankton of Quiver Lake shows a general correlation with
the movement of the chemical changes, though all of its fluc-
tuations are not commensurate with the fluctuations of the ni-
trogenous materials. The operation of other factors—such as
the submerged aquatic flora and replacement by tributary wa-
ters—must be called in to throw light on all the plankton
changes in this lake.

In Thompson’s Lake the seasonal cycle of periods of maxi-
mum and minimum amounts of nitrogenous matters is almost
as well defined as it is in Quiver Lake. The plottings of the
analyses (Pl. L.) from September, 1897, to March, 1899, include
two periods of winter maximum and one of summer minimum,
all of which are well defined, and affect not only the nitrates
butalso the organic nitrogen, the albuminoid and free ammonia,
and the oxygen consumed. The diminished effect of floods
and of unusual flushes of sewage in this reservoir backwater
is evident in the greater regularity of its seasonal curves of
nitrogenous substances as contrasted with those of the river.
Its close dependence upon the river for its water supply is
shown by the similarity of its chlorine curve to that of the

215

river. The rise in chlorine during the minimum period, July
to November, indicates the entrance into this lake of sewage-
laden waters of the river during this period, but it brings with
it no corresponding increase in the residual nitrogenous sub-
stances. The depression of the nitrates, and possibly of the other
forms of nitrogen, may be referred here as elsewhere to their
utilization by the phytoplankton and submerged vegetation of
the lake during their period of growth. Asin the Illinois River
and Quiver Lake, the spring maximum of the plankton appears
at the close of the maximum of nitrogenous substances and is
followed by their minimum period. The autumn maximum
appears, at least in 1897, somewhat before any marked in-
crease in the residual nitrates, though in both this year and
the following one it extends into the period of rising ni-
trates. A general correlation thus exists between the seasonal
production of plankton and the seasonal fluctuations of ni-
trogenous substances.

The seasonal fluctuation of the several nitrogenous substances
exhibits some interrelations with the changes in the plankton,
and especially with the accession of flood waters, and some
variations from the general maximum-minimum cycle above
discussed which call for brief notice.

The nitrates, the final products of decomposition, exhibit the
maximum-minimum cycle most clearly, as, for example, in Pl.
XLV.,XLIX., and L. The fluctuations which affect the other
substances appear here in diminished prominence, as may best
be seen by comparing the plottings of Spoon River (Pl. XLVI. and
XLVII.) with those of Thompson’s Lake (PI. L.). The close of
the maximum period of nitrates is usually later than that of
the free ammonia (PI. L.), and extends for a varying distance
into the period of growth of vegetation. This growth in our
latitude becomes marked in the last days of April and the first
of May, and continues, in some plants at least, until the frosts
of October. The nitrates do not reach minimum levels, how-
ever, (see Pl. XLV.—L.) until late in June. In like manner the
close of the minimum period is frequently delayed beyond the

214

limits of the growing period of vegetation into November or
even December. This seeming inertia in the seasonal move-
ment of the nitrates seems to be due on the one hand to the
gradual utilization of the accumulations of the winter and con-
tributions of the spring floods by the spring plankton ; and on
the other, to the slow accumulations of the autumn and to
utilization by the autumn plankton, which, as in Thompson’s
Lake in 1897, often attains a considerable development.

A somewhat intimate connection between the nitrates and
the plankton maxima can be detected in many instances in the
diagrams. When the plankton increases, the nitrates often
exhibit a depression, the extent of which, however, is not
always proportionate to the change in the plankton. This
absence of any constant ratio between the apparent changes in
these two factors indicates the operation of other factors, one
doubtless due to defects in the quantitative plankton method,
and another due to changes in the component organisms of the
plankton.

In the Ilhnois River in 1895-96 (Pl. XLII.) the plankton
maxima of April and October are accompanied by a marked fall
in nitrates; on the other hand, those of November, June, and
August appear with rising nitrates, the last two accompanying
floods. The depressions in nitrates in October, December, Feb-
ruary, June, July, and September are not in any case associ-
ated with a rise in the plankton, though often with the initial
stages of the flood. In 1897 (Pl. XLIV.) the April-May, July,
September, and October maxima are all associated with de-
pressions of the nitrates. The February and March depressions
of nitrates occur with floods, while in November and Decem-
ber no correlation is apparent. In 1898-99 (Pl. XLV.) the effect
of the May, June, and July maxima can scarcely be detected
in the nitrate curve, while those of December and March pro-
duce corresponding depressions. In this diagram neither plank-
ton nor nitrates show marked changes after July.

In Spoon River the development of plankton is apparently
so slight and the nitrates are relatively so abundant that no

215

correlation between the respective fluctuations is apparent in
the data except in the fall of 1897, when an unusual minimum
of nitrates appeared in conjunction with an unusual develop-
ment of plankton (Pl. XLVI.). Decrease in nitrates often at-
tends the initial stages of flood independently of plankton
development, as in December, 1896 (Pl. XLVI.). Some nitrate
increases, as in the autumn of 1896 (Pl. XLVI.), appear with
the crests of floods, especially those of the gradual type. Other
fluctuations in the nitrates—and they are often considerable—
show no correlation with available data

In Quiver Lake in 1898-99 (Pl. XLIX.) the plankton maxima
of April-May, June, and December all occur when nitrates de- .
crease. The tendency of nitrates to increase and then fall
again with the crest of the flood is apparent in January, March,
May, November, January, and March.

In Thompson’s Lake in 1897-99 (PI. L.) practically all of
the maxima are attended by a greater or less diminution of the
nitrates. This appears in October, November, December, April-
May, June, July, August,and December. The effect of floods
in decreasing the nitrates in their initial stages and subse-
quently increasing them is slightly indicated in January, Feb-
ruary, November, and February.

The nitrites exhibit a tendency in the Illinois River to ex-
cess during the low-water period of midsummer (PI. XLIII.-
XLYV.), averaging about .3 to .4 parts per million to .1 during
the remainder of the year. This excess was prolonged into
November in 1897 with the low-water period of that year. It
seems thus to attend the concentration of sewage in the river.
No constant correlation of movement between the nitrites and
plankton can be detected. In a few instances, however, plank-
ton maxima coincide with marked decrease in nitrites, as, for
example, in the river in September and October, 1897 (PI.
XLIV.), and the spring maximum precedes the rise in nitrites
in each year. The changes in the nitrites show no constant
correlation with those of other forms of nitrogen, though at

216

times they exhibit indications of a common movement with
the nitrates or the free ammonia.

In Spoon River (Pl. XLVI. and XLVII.) the summer rise
in nitrites is not apparent except in the low water of 1897.
The decay of organic matter is thus less active during this
season in tributary water than it is in the main stream. In
contrast with the summer, the winter exhibits somewhat more
nitrites, but these are not markedly different in amount from
those in the main stream at that season. The only correlation
between the nitrites and the plankton of this stream appears
in 1897 from May to December, when plankton maxima are
uniformly attended by decrease in nitrites. As elsewhere, they
present no constant relation to the fluctuations of other forms
of nitrogen.

In Quiver Lake (Pl. XLVIII. and XLIX.) the nitrites have
their maximum during the colder months and the flood period.
A marked depression of nitrites appears with the May maxi-
mum of the plankton in 1898 (Pl. XLVIIT.).

In Thompson’s Lake (PI. L.) the changes in the nitrites
are slight, irregular, and without apparent correlation either
with other nitrogenous substances or with the plankton. Like
the nitrates, the nitrites are not greatly and immediately
affected by the accession of flood waters, and they run lower
in the reservoir backwaters than in the main stream.

The albuminoid ammonia and the total organic nitrogen
fluctuate together so closely (see Pl. XLIX.) that it seems un-
necessary to distinguish between them in this discussion. The
seasonal fluctuations in these substances in the Illinois River
(Pl. XLII-XLV.) are not marked, as a result apparently of
the somewhat uniform accession of sewage. The dilution of
the sewage consequent upon overflow is to some extent offset
by the large accessions of these substances, which as silt and
leachings accompany flood waters. A slight increase attends
concentration in the low water of 1897 (Pl. XLIV.), and a
slight decrease comes with the period of overflow of the same
year, Similar movements are less evident in the other years

217

(Pl. XLUT. and XLV.). The effect of sudden floods, presuma-
bly those of tributaries but a short distance above Havana,
appears in February, 1896 (Pl. XLIII.), and in 1899 (Pl. XLV.)
as a twelve- and two-fold increase respectively, which is re-
markably abrupt and is followed in both cases by a quick but
somewhat more gradual return to the previous condition.

Owing to the complexity alike of the substances included
in these items of the analysis and of the plankton itself, no
uniform correlation of these factors can be discovered. ‘Two
different and in a certain sense opposite tendencies can be de-
tected in the relationship of the movements of the plankton to
those of the substances under discussion. During the winter
season and the period of excess of nitrates, plankton pulses are
attended by cncrease in the albununoid ammonia and organic
nitrogen. This appears in the Illinois with the pulses of April,
1896 (Pl. XLIII.), and December, 1898 (Pi. XLV.). During the
warmer months, when most of the plankton pulses occur, the
opposite tendency is seen in the movement of these substances.
They tend to decrease at times of plankton pulses, as may be
seen in August and October, 1896 (Pl. XLIII), in May, July,
September, and October, 1897 (Pl. XLIV.), and in June, 1898
(Pl. XLV.). With the pulses of December, 1895 (Pl. XLIII.),
and May, 1898 (Pl. XLV.), no marked effect in either direction
is apparent.

In Spoon River any seasonal movement of the albuminoid
ammonia and organic nitrogen is quite thoroughly masked by
the disturbances due to floods. In 1898 (Pl. XLVII.) these
substances are a trifle lower in the warmer months than in the
colder, a condition which may result from the prevalence of
floods in the latter season. In 1897 (Pl. XLVI.) they increase
during the warm season and period of low water attending a
development of the plankton unusual in the water of this
stream. .

The effect of flood upon the quantity of these substances
in the water of this stream is well defined, and seems to throw
hght upon the relation which flood waters bear to the plankton

218

of the main stream. Not all of the floods which flush this
tributary appear with corresponding prominence in the hydro-
graph of the main river, which is the one plotted upon all the
diagrams pertaining to Spoon River. In many instances they
coincide. All instances in the chemical diagrams (Pl. XLVI.
and XLVII.) of abrupt, steeple-like eminences in the curves of
albuminoid ammonia and organic nitrogen (and also of oxygen
consumed) are due to sudden floods, and appear most promi-
-nently when the date of collection of the water sample coin-
cides with the initial stages of the flood. This is well shown
in September, 1898 (Pl. XLVII.). Not all of the samples from
flood waters were collected at times which afford evidence for
the enriching effect of the initial stages of these tributary
flushes. The relative amount of these and other forms of
nitrogen which floods bring to the river is well shown in this
flood of September, 1898 (Table XI. and Pl. XLVII.). On
August 80 the amounts of albuminoid ammonia (.32) and
organic nitrogen (.6) are normal for that season of the year.
With the flood of the first week of September these amounts
increase more than tenfold (being 3.6 and 8.32 respectively ),
falling again a week later to the normal (.2 and 48). A large
part of this matter is in suspension. For exampie, in the flood
of May, 1898 (Pl. XLVII.), about 86 per cent. of the albuminoid
ammonia (2.32) and 90 per cent. of the organic nitrogen (5.46)
was in suspension.

It is not plankton, neither is it to any large extent sewage,
which the tributary floods of Spoon River bring to the Illinois
as organic nitrogen, but largely organic debris not yet decayed.
The sewage-laden river habitually carries much less of these
substances than these tributary flood waters laden with this
organic debris from fertile prairies. The latter thus become
very important agents in maintaining the fertility of the
river water. The effect of these periodic additions of nitroge-
nous substances by tributary floods upon the plankton of the
river will be discussed in another connection.

A decrease in these nitrogenous substances attends the two

219

plankton pulses of 1897 (Pl. XLVI.) in the warm months of
May and September, but the increases noted with the pulses of
plankton in the winter in the Illinois River are not apparent
in the case of the pulses of February and December in this
stream, though no decrease appears as in the summer months.

In Quiver Lake in 1898-99 (Pl. XLVIII.) a seasonal move-
ment in the albuminoid ammonia and the organic nitrogen is
evident, though it seems to accompany the access of sewage-
contaminated waters of overflow, as appears on comparison
with the chlorine curve. This seasonal movement is evident
as a depression of the curves during the warm and low-water
months, and as an elevation during the colder months of the
flood period. As in Illinois and Spoon rivers, the plankton
pulses in Quiver Lake of the warm period, in May and June, are
attended by a temporary decrease in these nitrogenous sub-
stances. A still more marked decrease in both albuminoid
ammonia and organic nitrogen attends the winter pulse of
plankton in February, 1899, while that of the preceding De-
cember appears with an upward movement of the organic
nitrogen and a downward one in the albuminoid ammonia.
The correlation between the movement of albuminoid am-
monia and organic nitrogen and of the plankton is thus in this
instance (predominantly, at least) similar to that noted else-
where in the warmer months. The very slight ripples in the
plankton curve in July, August,and September attend minor .
increases in these nitrogenous substances, a feature noted else-
where in colder months.

In Thompson’s Lake (PI. L.) the albuminoid ammonia, the
organic nitrogen, andthe plankton are all more abundant and ex-
hibit greater fluctuations than they do in Quiver Lake. These
conform in a general way to the tendencies noted in other
localities. The amounts present during the colder months,
October to May, are a trifle greater than in the intervening
warmer period. There is also a temporary decrease in those
nitrogenous matters attending plankton pulses in the warm
months, This appears with the pulses of June, July, and

220

August-September, 1898. A temporary increase appears with
plankton pulses in co/d months, as in December-January and
February, 1899. Some exceptions to these general tendencies
appear here asin Quiver Lake; such, for example, as that in
the low water of the autumn of 1897, when the great plankton
pulse of October-November attends an unusual wave of both
the albuminoid ammonia and the total organic nitrogen.
Temporary decrease in the former appears with the crest of
this plankton pulse, and again in the pulse of December, along
with an increase in organic nitrogen. The spring maximum of
April-May, 1898, comes witha rising wave of both substances,
whose crest coincides with the fall in the plankton.

It is evident from the data here presented that the fluctu-
ations in the volume of the plankton, as determined by the
methods employed by us, show some intricate correlations
with the changes in the quantity of albuminoid ammonia and
organic nitrogen. The massing together of all organic matters,
both living and dead, indigenous and adventitious, in the de-
termination of these two substances, and the composite nature
of the plankton itself, including both the synthetic phytoplank-
tonts, and the analytic zodplanktonts, alike combine to conceal
the relationship which exists between the succession of living
forms in the plankton and the flux of nitrogenous matters in
suspension and solution therein. Furthermore, the plankton
is not the only assemblage of organisms concerned in this flux
of matter; the bottom fauna, the fishes and other aquatic ver-
tebrates, and aquatic fauna of the grosser sort, all share in
effecting the changes here manifest.

We lack a common unit of measurement in terms of which
we can express the values alike of the chemical analyses and
of the volumetric and the statistical determinations of the
plankton. Precise comparisons, for example, of the changes in
the organic nitrogen with the cubic centimeters of plankton
and the number of diatoms cannot be made. The direction of
the changes in these several elements can, however, be noted,

221

and its interpretation, in many cases at least, becomes probable,
if not, indeed, certain.

In the first place it may be noted that the fluctuations of
the plankton are not paralleled by proportionately great move-
ments in the total nitrogenous substances in the water which
enter largely into their composition. For example, the spring
maximum of the plankton is accompanied by no such wave in
thesesubstances. Indeed,aslightrippleof depressionseemsto be
the only concomitant fluctuation. Hven granting a large mar-
gin because of the absence of a common unit of measurement,
it remains apparent that the fluctuations of the substances in
question and of the plankton are not proportional. A single
illustration, found in the spring maximum in Quiver Lake in
1898 (Pl. XLIX.), will suffice to make this point clear. The
following table, drawn from Table XIII., gives the amounts of
plankton and of the several forms of nitrogen present before

QUIVER LAKE.

Date Free Albuminoid

Organic Fone aL
1898 Ammonia | Ammonia Nitrogen Nitrites | Nitrates | Plankton
Nora W@ss5806 046 ; 44 1.01 033 .65 103
WEN SeG5 ceetoo .092 32 82 .022 35 42.14
Mia 70 ip oaetie .05 48 .98 O15 Th ie i
Per cent. of Change.
April 19 to | i i
View eae. I LOOM Ie 2 lg = 8875 || = +3991

(April 19), during (May 3), and after (May 11) the plankton
wave, and the extent of the change, in per cent., of the amount
present on the 19th which each exhibits. The plankton rises
from 1.03 em.’ per m.* to 42.14, falling subsequently to 4.70 and
1.97. This is an increase of 3991 per cent. No one of the ni-
trogenous substances in the table exhibits a change exceeding
100 per cent.,and the average change is only 45 percent. In
this case the change in plankton is eighty-eight times as great
as that in the average of all forms of nitrogen, assuming, of
course, that the units of measurement are comparable,

222

Three causes may be assigned in explanation of the absence
of proportional correlation in the flux of these nitrogenous sub-
stances and of the plankton, all of which are operative, but in
varying effectiveness at different times and under different
conditions.

In the first place, the plankton itself constitutes but a part
of the total organic nitrogen; how small a one the data at
hand do not determine. Barring out error arising from the
death of the plankton and from the solution of the products
of its decay which might take place during the interval
between the collection and analysis of the sample, we find in
the relative amounts of albuminoid ammonia and total organic
nitrogen in solution and in suspension respectively some evi-
denceas to the possible limits of the proportionate amount which
the plankton and silt together form of the total nitrogenous
substances. The average amount (Table X.) of albuminoid
ammonia in solution and in suspension from July 6, 1897, to
March 28, 1899, is .855 and .131 parts per million respectively.
Plankton and silt together thus constitute about one third of
the total albuminoid ammonia in the Illinois River. The rela-
tive amounts of dissolved and suspended albuminoid ammoniaat
the weekly intervals of analysis fluctuate according to access of
flood waters and increase in the plankton. The former is the
more potent factor. Usually the amount in suspension is from
one third to one half that in solution, rarely equaling or surpas-
sing it, as in the flood of February, 1898, when it rose to .4 as
compared with .28in solution. The plankton pulse of April-May,
1898, accompanies a rise in total albuminoid ammonia from .4
to .6—an increase of 50 per cent. The increase les almost
entirely in the suspended form, which rises from a previous
level of .04 to .08, to .08 to .20, that is, it is more than doubled.
The volumetric increase in the plankton is, however, over
thirty-five-fold. Thus, under the most favorable conditions,
receding flood, little silt, and plankton maximum, the increase
in suspended albuminoid ammonia attending a thirty-five-fold
increase inthe plankton constitutes but 33 per cent. of the total

228

amount present. During the long-extended periods of plank-
ton minimum it is apparent that the plankton must constitute
a very much smaller part of the total amount of albuminoid
ammonia in the water.

That much of the albuminoid ammonia may be in the silt
is shown especially in the table (Table XI.) and diagrams (PI.
XLVI. and XLVII.) of Spoon River at times of flood. In such
waters there is practically no plankton—as will be shown else
where from the examination of our plankton collections in
that stream—although the amount of albuminoid ammonia is
often very great.

The average amounts of total organic nitrogen (Table X.)
in solution and in suspension during this same period are .69
and .34 parts per million respectively. The latter (.84), which
represents plankton and silt, thus constitutes about one third
of the total amount (1.03) of organic nitrogen in the water.
The proportion of this fraction which the plankton may consti-
tute under the most favorable conditions may be inferred from the
increase in the suspended organic nitrogen which attends the
spring pulse of 1898(Pl. XL.). This rises from a previous level
of .12—.16 parts per million to .24-.64, the latter with the de-
cline of the plankton, and at its maximum (.64) it constitutes
46 per cent. of the total amount of organic nitrogen in the
water. On May 8, when the plankton is at its maximum, the -
suspended organic nitrogen is but .24, or .25 per cent. of the
total. During the periods of plankton minimum the propor-
tion which the plankton forms of the total organic nitrogen
must be very much less than at times of plankton maximum,
since the amount in suspension shows no decrease at all pro-
portional to the fall in the amount of plankton. Here also
floods are quite as potent as plankton in causing marked in-
crease in the amount of total organic nitrogen in suspension,
as will be seen on comparison of the curves of this matter with
the hydrographs on Plates XLITI.-L.

It is thus evident that the plankton does not form, even
under most favorable conditions, any large part of the total

224

organic nitrogen—certainly less than 50 per cent. and on the
average much less than 33 per cent., which figures represent
the total organic nitrogen, both plankton and silt, in suspen-
sion. The fluctuations of the organic nitrogen contained in
the plankton are thus masked by the predominance of the dis-
solved form, and by the undetermined quantity of nitrogen-
containing silt.

A second cause for the lack of proportional correlation
between the movement in these nitrogenous substances and
the plankton may lie in the utilization by the plankton itself
of some forms of nitrogen included within the range of sub-
stances reported in the analyses as albuminoid ammonia and
total organic nitrogen. For example, some organisms of the
phytoplankton may utilize as food such forms of organic nitro-
gen in solution in the water as the amido-compounds and the
humus acids. It may be that some of the animal wastes are
turned into the more highly organized nitrogen of the phyto-
plankton without passing through complete oxidation and a
return to the inorganic nitric acid and nitrates. If this be the
case the flux of nitrogenous matters may lie quite within the
range of substances here discussed, and the movements in
nitrogen incident to these changes will consequently produce
no pulses in the common curves of these substances. When,
however, the inorganic nitrogen enters largely into the ebb
and flow of the nitrogen of the plankton, the possibility of a
correlated movement of plankton and organic nitrogen be-
comes apparent, though proportionate pulses in the two remain
improbable so long as the organic but non-living nitrogen con-
tributes also to the flux of matter involved in the plankton
changes.

That the phytoplankton, as other low forms of vegetation,
may thus utilize organic nitrogen in some of its forms as food,
has been rendered probable by the experimental work of Loew
(96), Bokorny (97), Maxwell (96), and Zumstein (799). The
work of the latter is especially in point in this connection, since
his experiments deal directly with a genus, Huglena, which

225

furnishes a large part of our phytoplankton of midsummer and
the bulk ofthe water-bloom. The experiments of this author have
shown conclusively that this chlorophyll-bearing organism is
usually autotrophic (holophytic) in the light and in the ab-
sence of abundant organic nitrogenous matters in solution, and
under these conditions its chromatophores are a bright green.
When organic nitrogenous matters in solution are abundant
the organism becomes mixotrophic (half saprophytic) even in
the light, and its chromatophores may become paler. In the
dark it becomes colorless, and depends entirely (saprophytic)
upon the dissolved organic nitrogen for its growth and multi-
plication.

The waters of the Illinois River and its backwaters are
unusually turbid, thus excluding more than the usual amount
of light. The plankton of this environment is rich in species
and individuals of flagellates, alge, and diatoms, many of
which exhibit this tendency to become paler. This I have
noticed repeatedly in the examination of the living plankton,
and to some extent in material preserved in formalin-alcohol.
It has occurred in the several species of Huglena, viz., viridis,
sanguinea, deses, acus, spirogyra, and gracilis. I have noted it
also to a very marked degree in Chlamydomonas, Carteria,
Trachelomonas, and Lepocinclis. It has been less pronounced in
the Peridinide, in Mallomonas, and Dinobryon. Among the
diatoms the most striking instances occur among the typical lim-
netic forms, such as Synedra, Melosira, and Asterionella. Inthe
light of Zumstein’s results, and in view of the chemical data exhib-
iting an absence of proportional correlation between the move-
ments of the organic nitrogen and the fluctuations in the volume
of the plankton, and of the frequent occurrence in our waters of
colorless individuals of chlorophyll-bearing species, it seems
that we are justified in assuming that the flux of nitrogenous
matter involved in the plankton changes lies to some appreci-
able and as yet undetermined extent within the range of sub-
stances included within the dissolved and suspended nitroge-
nous matter of the water.

226

A third reason for the absence of proportional correlation
between the movements of the organic nitrogen and the fluc-
tuations of the plankton lies in the cumulative nature of the
latter as contrasted with the non-cumulative character of
changes in the chemical substances at whose expense it
increases. Growth and reproduction of organisms is funda-
mental in the plankton pulses, and there is nothing comparable
to either of these in the chemical changes of non-living
matter.

It remains only to discuss the correlations that do appear
between the albuminoid ammonia and total organic nitrogen,
on the one hand, and the plankton, on the other. The two
diverse tendencies noted in the preceding pages, the one for
the plankton pulses of warm months to coincide with a
decrease in these nitrogenous matters, and the other for the
pulses of cold months to coincide with an increase in these
substances, or at least in the organic nitrogen, will be fully
accounted for only when the changes in the different elements
included under these common designations, the dissolved por-
tion, the silt, and the plankton, shall be differentiated,and when
the changes in the different kinds of organic nitrogen shall be
separately unraveled, and, furthermore, when the fluctuations
of the synthetic (phytoplankton) and analytic (zoéplankton)
portions of the plankton can be separately expressed in terms
of acommon unit. It is evident that the available chemical
analyses and volumetric and statistical determinations of the
plankton do not afford such comprehensive data. The incom-
plete data at hand throw some light, however, upon the nature
of the correlation, and suggest the probable explanation for
the two divergent tendencies noted and the numerous excep-
tions thereto.

As has been previously shown, plankton pulses are usually
coincident, or nearly so, with an upward or a downward move-
ment in the nitrogenous substances, organic and inorganic.
The upward movements of the albuminoid ammonia and
organic nitrogen and the downward movement in the nitrates

227

occur most frequently when the diatoms are most rapidly mul-
tiplying. As will be shown later, these seasons occur in the
colder months, and often precede the summer pulses of plank-
ton whose crests are predominantly of the animal plankton.
The upward movement of the organic nitrogen and the down-
ward movement of nitrates is thus due in large part to the
synthetic action of these organisms. The major plankton
pulses, which are as a rule predominantly animal in their com-
position, usually occur in the warmer months With their cul-
mination there is always a great decrease in their food supply
(the phytoplankton) and analytic processes thus predominate,
and the decay of the products of animal metabolism results in
a decrease in the total organic nitrogen and leads to a recovery
of the nitrates. This interplay of the synthetic and analytic
processes of the phyto- and zodplankton, is, I believe, the basis
of the coincidence in the fluctuations of the plankton and of
the nitrogenous contents of the water. Further reference will
be made to the subject, and data illustrating it will be cited in
connection with the discussion of the seasonal changes of the
plankton.

The seasonal changes in free ammonia seem to be due to
the effect of floods and temperature upon the processes of
decay, and reveal but minor correlations with plankton
changes. A marked increase with rising flood waters is appar-
ent in Spoon River (Pl. XLVI. and XLVII.) and occasionally
in the Illinois, as, for example, in February, 1896 (Pl. XLIII.).
Prolonged high water, on the other hand, tends to lower the
free ammonia (Pl. XLIV.). The stagnation in the sewage-
laden river when it is covered with ice at low-water stages
appears in the elevenfold increase in free ammonia under the
ice in December, 1897 (Pl. XLIV.). The fluctuations are also
much more marked in the rivers (Pl. XLIJI—XLVIL.) than in
the lakes (Pl. XLVIII.-L.), owing to the diminished and
equalized effects of flood and sewage in the reservoir back-
waters. There are repeated instances where the plankton
pulses coincide with decreases in the free ammonia followed

228

by a recovery upon the decline of the plankton. Illustrations
of this may be seen in the April-May pulse in Thompson’s Lake
(Pl. L.), where a decline of fifty per cent. accompanies a nine-
fold increase in the plankton. The April pulse of 1896 in the
Thnois (Pl. XLII.) coincides with a still more pronounced
decline in the free ammonia. Upward movement of both
plankton and free ammonia appears occasionally, as in the
Illinois in September, 1897 (Pl. XLIV.), though a downward
movement of the free ammonia attends the plankton pulse of
the subsequent month. The free ammonia thus exhibits some
evidence that it enters into the flux of nitrogenous matter
involved in the rise and fall of the plankton. It decreases
when the synthetic activities predominate in the plankton,
and some, at least, of its increases coincide with periods of
predominantly animal (analytic) plankton.

The changes in the oxygen consumed coincide very nearly
with those in the organic nitrogen and albuminoid ammonia
both in direction and amount, and thus bear much the same
relation to the plankton changes.

The changes in the chlorine are of especial interest, not be-
cause of their direct relation to the plankton, but on account of
the fact that they indicate, perhaps better than any other ele-
ment in the analysis, the relative contamination by and con-
centration of the sewage in the different localities at different
seasons of the year.

In the Illinois River (Pl. XLITI.—XLV.) the chlorine usually
fluctuates in a direction opposite to that of the hydrograph,
running low during high water and rising with the return of
low water. Some exceptions appear, as in the rising flood of
December, 1895, and the declining flood of June, 1896, the
former apparently due to the flushing of sewers by initial flood
water, and the latter to an irregularity for which no natural
cause appears. The marked irregularity of the chlorine in the
Illinois, indicating a corresponding instability in access of sew-
age, with its additions of matter helpful or deleterious to the
plankton, adds to the environment of the potamoplankton a

229

further factor of uncertainty not present, to alike degree at
least, in the reservoir waters of the lake.

That natural waters in this locality are not subject to the
presence of chlorine (sewage) in such excess or in such fluctu-
ating amounts appears on contrast of the chlorine curves of
Spoon River (Pl. XLVI. and XLVII.) with those of the Illinois
(Pl. XLITT—XLV.). In the former, barring a few instances of
apparent contamination by river water (October, 1897, January
and February, 1899), the chlorine runs uniformly low through-
out the year, dropping but a trifle with rising floods.

In Quiver Lake (Pl. XLVIII. and XLIX.) the chlorine
similarly runs low during the period of individuality of the
lake, that is, of low water. The increase in chlorine comes
only at times of invasion of flood water from the river or the
bottom-lands above, as, for example, in November and Deceme
ber, 1898 (Pl. XLIX.). The periods of fertilization of this lake
by sewage thus depend upon floods, and occur at times of
greatest dilution.

In Thompson’s Lake (PI. lL.) the chlorine (sewage) content
exhibits the same general tendencies found in the river, from
which its water supply is derived. The chlorine content runs
high during low water and drops with the rise of the flood.
The abrupt and numerous fluctuations of the chlorine of the
river do not, however, appear in the lake, being diminished and
equalized by its greater permanency. Even under these favor-
able conditions it is difficult to find any constant or well-
defined correlation between the chlorine pulses and those of the
plankton. It may be that the fertilizing elements of the sew-
age which the chlorine is regarded as representing have already
been exhausted, so that the chlorine curve no longer represents
a commensurate fluctuation in the fertility. In a few cases, as,
for example, in December, 1897, and in January and September,
1898 (Pl. L.), a slight correlation in the chlorine and plankton
curves appears, though the only relation between the two may
he in the effect of changing river levels upon both, a declining

230

flood (as in September) concentrating the sewage and at the
same time favoring the development of the plankton.

That the sewage of Chicago is quite thoroughly rotted out
before it enters the Illinois at La Salle, and that the contribu-
tions from Peoria are also well advanced in decay before they
reach Havana have been demonstrated by the chemical and
bacteriological examinations made at the instigation of the
Sanitary District of Chicago apropos to the opening of the
drainage canal. The full results of this work have not as yet
been published, but from the data published by Prof. A. W.
Palmer (97) from the analyses of the Chemical Survey and
from the preliminary report of Jordan (00) upon the bac-
teriological examination it is evident that the nitrogenous
matters of the Chicago sewage were in process of rapid oxida-
tion in the upper reaches of the Illinois and Michigan canal
near Lockport; that this process was largely completed before
the canal waters entered the river at La Salle; and that the Pe-
oria pulse of sewage is, during the summer months at least, well
decayed before it reaches Havana, though in colder weather,
when decay is less rapid, the sewage is not so well oxidized and
the bacteria are more abundant than during the summer at
this point. The following table, which has been made up from
the averages in Palmer, 97, exhibits to some extent these facts
in tabular form. The increase in nitrates and decrease in free
ammonia unite in indicating the extent to which decay has
progressed.

: Total | Total Albu- | Total

i | tess residue jloss on| Chlo- eee minoid| Organ-| Ni- Ni-
Station. Chicano. |°2 evap-| igni- | rine |“ 75,'°]Ammo-| ic Ni- | trites | trates

£°-| oration. | tion nia. | trogen
Lockport...............22.-- 29 438.6 20.5 24. 092 417 84 .019 95
IMONniSs eebeessecsecoseeess 57 359.4 23.4 29.7 | 3.55 709 1.44 149 1.72
La Salle. ...... peers 95 372.3 23.03 19.6 971 612 1.26 255 2.51
1 SXe(0) et: eee eee ee eeeacts 158 376.7 21. 41.8 252 -516 1.06 +209 2.59
Havaianas 199 355.3 21.2 15.4 63 455 1.06 135 2.35
Kampsville® ............... 288 352.1 22.4 13.4 -261 -508 1.17 062 1.39

*Average July 23—Dec. 29, 1896.

The influence of the sewage of Peoria upon conditions at
Havana, owing to temperature changes, is not uniform

231

throughout the year, and it may be that some of the seasonal
fluctuations in the chemical substances which have been dis-
cussed in the preceding pages, and some of those in the plank-
ton also, depend in some measure upon this changing effect of
temperature upon the sewage.

The following table, taken from Jordan (’00), gives the
seasonal changes in numbers of colonies of bacteria from May

BACTERIOLOGICAL EXAMINATION OF ILLINOIS RIVER AT HAVANA.

. 1 8
Dae Chlorine. | Stage of | Temperature No. of colonies per cm’.
1899 (DISS JE I ce tin fal 9 :
lion) , water, C. Havana Pekin
May 30. 13.6 8.7 21 4,500 542,000
WHE “Ooasoae 13. 9.3 26 18,450 129,000
MS yercneecye 13.5 8.8 25 15,900 205,000
ADs 50000 12.1 7.5 26 2,500 225,000 (1)
Sse woe 14.9 5.2 25 4,500 2,030,000 (2)
hyeneSiocs cs. 14.7 4.7 26 2,400 52,000 (3)
Waa 23 4.1 26 7,300 1,435,000
TOR 36. 4.9 27 5,700 470,000 (4)
DON sees 31. 4.8 30 850 980,000 (5)
ANUS “Oadecor 27.5 4.1 26 1,550 985,000 (6)
Dako 34. 3 26 goo 10,000 (7)
_ 3O0..-.-- 39. 2.2 29 9,800 30,000 (8)
SepiwlOmn 40. 2.4 29 1,900 650,000 (9)
WA sais 46. 2.5 22 1,500 310,000 (10)
RO ies ies ars 35. 3.5 14 3,400 240,000 (11)
Decrees 49. R, 16 3,700 120,000 (12)
Octh Wan... 52. 3 14.5 2,500 500,000 (13)
ipteeeeeae 5O. 3.2 16. 6,600 430,000 (14)
Ons ares 58. 3.2 17 8,800
2D 65 Oe or 60.5 3 12 3,900 30,000 (15)
INI) Aeeene 63. 3.5 9 7,000 150,000 (16)
i eemors Bile Bu 10 3,300 30,000
Psp riae 47.5 4.4 II 128,000 1,650,000
OW erat 43. 4. 6 41,600 380,000 (17)
IDE WOSseare 35. 3.1 2 85,000 140,c00 (18)
AO ole care 233 4.8 I | 66,800 5,000
(1) June 21. (2) June 27. (3) July 6. (4) July He e ) July 25. (6) Aug. 8. (7)
Aug. 22. (8) Aug. 29. (9)S ee 5. (10) Sept. 12. (11) Sept. 18. (12) Sept. 26. (13)

Oct. 3. (14) Oct. Io. (15) Oct. 31. (16) Nov. 7. (17) Nov. 30. (18) Dee 5.

30, 1899, till the end of the year at Havana, and at Pekin,
thirty-two miles above. The decline from the larger numbers
in June to a fairly well-maintained minimum during midsum-
mer at Havana is very evident, as is also the rise as the tem-
perature lowersinthe autumn. Both the period of time andthe

232

reach of the river in which the bacterial action and attendant
decay of the sewage ensues, are lengthened as the temperature
falls, and we find in consequence an increase in the bacteria in
the river water passing Havana which approximates fortyfold.
The pulse in bacteria due to the sewage of Peoria which is
found at Pekin during the summer, reaches Havana also, thirty-
two miles below, as temperatures fall in the autumn.

The averages of the number of colonies of bacteria found
in the canal and river water at points from Bridgeport to Graf-
ton during the period of analyses given in the first table are to
be found in the following table, also taken from Jordan (00).

CHLORINE AND BACTERIA—DES PLAINES AND ILLINOIS RIVERS,
BRIDGEPORT TO GRAFTON.

0 SS Se SS SS SSS =

Distance from | g

f : : Chlorine (pts.. | Number of col-

Collecting Stations Brigecey per allo onies per cm.’
Bridgeport sianccveceriscunee eerie fo) 119.2 1,245,000
WockpOrty..:. wocsaee ee ens 29 117.4 650,000
joliet Raya ie i evevaleapie ste asyerausiicl aster asaanaptes 33 104.8 486,000
ONS ch, csays beciacaunterm eye ara ceatonoa eleven 57 68.1 439,000
Ottawa hs ceisc acess eae cata 81 58.5 27,400
Teal Salles sain savaiarcaebepeeneisrecees 95 46.1 16,300
LGTY aretinyo alcas eke, Srayeves eich evel perreleersie aC 123 44.2 11,200
Avieryvillein 26 teste seen chorivee 159 40.9 3,660

WiesleyiG@ityers acres sere nerree eee 165 40.9 758,000 °
Be Keli stare sveieravos ietslave cloretercre tretnte misters 175 38.4 492,600
Pawan: js ssvecikiasesdicrereicus Meters eatriorelmerstors 199 36.2 16,800
Beard stows rer.asnsevseie. sae teierclemietes 231 29.3 14,000
Kampsvyillleieecncan aeons screech 288 22.9 4,800
Graktonen nuys cetrescaonerwoe eeokee 319 18.3 10,200

The chlorine content at the several points also appears in
the table, and exhibits a steady decline from Chicago to the
Mississippi River with a brief pause at Peoria. This decline
expresses approximately the dilution which on an average the
sewage undergoes during the low-water period. The flood
season of the spring was not included in the period of analysis.
From Ottawa to the mouth of the Illinois, as indicated by the
chlorine, this dilution is about one third.

The decrease in number of bacteria, while it may not coin-
cide strictly with the completion of processes of decay still

233

gives in general a suggestive index to the extent to which
oxidation of the sewage has proceeded.

When the facts of both tables are taken into consideration
it becomes evident that the sewage of Chicago has been thor-
oughly decayed, and its fertilizing capacity presumably to some
considerable extent utilized in the development of the plank-
ton, before the water reaches Havana. The sewage of Peoria
likewise, during the summer months, is well oxidized by the
time the sluggish current of low water brings it to Havana,
thus adding new resources for the increase or rehabilitation of
the plankton. During the colder months the process of decay
is not so fully completed owing to the lowering of the temper-
ature and the increased current attending the higher water
which often prevails at that season. In the winter the initial
effect of the sewage upon the plankton may be witnessed, par-
tially at least, at Havana. At all seasons the plankton of the
channel waters passing Havana isthe resultant of two succeed-
ing pulses of fertilizing additions to the normal constituents of
stream waters. It represents during the warmer months pre-
dominantly the later phases of the cycles of organisms, which
multiply and succeed each other with considerable rapidity
after the enrichment of the water. In this important particu-
lar the plankton at this point in the stream differs from that
of the lake, where the whole sequence of changes may be
accomplished in one locality. The fact that a relatively small
proportion of the tributary waters enters the stream between
La Salle and Havana makes it possible for these chemical
changes to take place, and for the plankton cycles to run their
courses with less interruption and disturbance than in other
parts of the stream.

The enrichment of the Illinois River and its backwaters
by the sewage of Chicago and Peoria has been utilized thus to
some considerable extent before the waters reach Havana.
The chemical products of its oxidation have béen converted
into aquatic vegetation and phytoplankton, and some of the
latter in turn into zodplankton. The development of new

234

cycles of limnetic organisms at this middle reach of the river
comes accordingly to depend to a great extent, not upon
the primary contributions of the sewage, but upon secondary
or even later conversions of the nitrogenous matters originally
contributed. The decay of the vegetation of the backwaters
and bottom-lands, and the wastes and decay of the plankton
itself and of the other organisms dependent upon it, come to
be to a greater extent the immediate sources of support of the
locally developed plankton.

COMPLETE MINERAL ANALYSES.

Three complete mineral analyses of the water of the
Illinois River have been made by the Chemical Survey under
the direction of Professor Palmer, the samples for which were
collected by us at Havana. These appear in the accompany-
ing table.

ANALYSES OF MINERAL MATTERS CONTAINED IN SAMPLES COLLECTED FROM
ILLINOIS RIVER AT HAVANA, ILLINOIS. PARTS PER MILLION.

INow tand2,| Oct. 31 and | Junets,
| 1897 Nov. 1, 1898 1900
Teithiay visas yack eos teh sere agate cesar 0.0 trace 0.0
Potassium phosphate K3;PO,............ 0.0 2.4 0.0
Potassium nitrate KONO ay diteral eects 5.05 2.4 6.
Potassium nitrite TEIN @ ope alee 6.06 0.0 0.0
Potassium chloride Ki Cee aisnaeiae 3.72 4.4 2.2
Sodium chloride INaG@ien ete ene 100.85 44.2 21.4
Sodium sulphate INiabs Opener IZ 27.5 20.1
Ammonium sulphate (NAS Ose 6.21 10.2 DoF)
Magnesium sulphate IMIESOnc'o 000 co000% 31.02 33.4 35.5
Magnesium carbonate MgCO3........... 74.01 TRS 69.7
Calcium carbonate (CACO nea tontian deur 137-79 150.3 267.5
Iron carbonate SACO RS asco dsones 152 33 6.6
Alumina Allo O's BA anicsdemete 8.95 RoW Fo
Manganese oxide MiNOpocooosbocede 0.0 0.0 0.7
Silica SiOhe cna tamer 26.07 31.6 27.6
Mo balls Se eis s,acceieiw eyeseieraytncvane sts etemeeeertyoerets 420.65 385.7 466.5

The analysis in 1897 was made in a period of prolonged
low water, the effect of which appears in the large amount of
sodium chloride, indicating the concentration of sewage, while
the presence of potassium nitrite suggests the active decay of

235

sewage or the products of animal metabolism, such as might
occur with the abundant plankton of that autumn (PI. XIL.).
The analysis of 1898 was made toward the close of a con-
siderable rise, and it shows the effects of dilution of sewage in
the lessened sodium chloride. The analysis of 1900 was
made in a high-water period, and exhibits even a greater dilu-
tion of sewage, as shown in the chlorine and ammonia salts.
These analyses indicate an abundance of all the salts upon
which plant life depends for its growth, and. complete the
demonstration of a chemical basis for the development in
abundant phytoplankton.

COMPARISONS WITH OTHER STREAMS.

So far as I am aware this is the only instance in which
opportunity has been offered for a comparison of the chemical
conditions in stream waters and the plankton fluctuations coin-
cident with them. Steuer (01), who worked upon the plank-
ton of the Danube, near Vienna, in 1898-99, cites averages of
chemical analyses madein 1878. These analyses indicate that
the Danube at that time was barren in comparison with the
llinois River. The average organic. matter in solution as
shown by the oxygen consumed was only 5.6 parts per million
in the Danube to 43.4 (in 1898) in the Illinois River, while the
chlorine was but 2.4 to 12.40. The conditions of analysis differ,
so that the nitrogen content of the two streams cannot be
compared, though the indications are that the nitrogen com-
pounds are low in the Danube as compared with the Illinois
River. The silica and carbonates are also lower in the former
than in the latter stream. The poverty of the plankton of the
Danube which Steuer describes, seems thus to be correlated
with a deficient food supply, and the rich plankton of the Illi-
nois with a more abundant one.

In general terms, a chemical analysis of stream and lake
waters throws some light on the productive capacity of the
water. This appears in a comparison of the chemical condi-
tions and plankton production of Quiver and Thompson’s lakes.

236

With less nitrogen we may expect to find less plankton. The
contrast of Illinois and Spoon rivers shows the same tendency,
though the difference in the chemical conditions in the streams
is less than that in the lakes, while the contrast in plankton
production is much greater. Likewise in seasonal changes, the
greatest developments of the plankton—the spring maxima—
appear at the close of a period of high nitrogen content.

On the other hand, precise comparisons and correlations
cannot be maintained, in part because of the operation of other
factors,—such as temperature and vegetation,—and in part be-
cause of the fundamental difference between chemical and
biological phenomena. The fertility of a body of water must
be judged, not by chemical analyses only, but in conjunction
with other phenomena which condition growth and reproduc-
tion. It is also evident that isolated chemical analyses throw
as little light upon the fertility of a body of water as isolated
plankton examinations do upon its productiveness. The routine
of seasonal changes must be discovered in both before trust-
worthy data for estimation of fertility can be obtained.

VEGETATION.

The aquatic environment at Havana impresses the visiting
biologist who for the first time traverses its river, lakes, and
marshes, as one of exceedingly abundant vegetation, indeed al-
most tropic in its luxuriance. The aquatic flora of the ponds,
lakes, and streams of New England, of the Middle States, and of
the north central region is, as a rule, but sparse in comparison
with that which here constantly meets hiseyes. He will note
the entire absence of beds of Chara and patches of Nitella, and
will find the Potamogetons fewer both in species and numbers:
The shore-loving Juncacew, Cyperacee, and EHquisetums are also
less in evidence, for here the shore itself is a shifting region,
lacking the permanence which these plants demand. On the
other hand he will find acres upon acres of “moss,” as the fish-
ermen call it—a dense mat of mingled Ceratophyllum and Elodea
choking many of the lakes from shore to shore, and rendering

237

travel by boat a tedious and laborious process. Beds of lotus
(Nelumbo lutea) and patches of Azol/la will suggest warmer
climes, while the fields of rushes (Scirpus fluviatilis), and patch-
es of water-lilies (Nymphea reniformis), arrowleaf (Sagittaria
variabilis), and pickerel-weed (Pontederia cordata) will recall
familiar scenes in northern waters. The carpets of Lemnacee
will be surprising, and the gigantic growths of the semiaquatic
Polygonums will furnish evidence of the fertility of their en-
vironment.

Both the nature and the quantity of the vegetation varies
in the different localities whose plankton has been the subject
of investigation by us, and in the same locality the conditions
may change at different seasons and from year to year, low
water in the early summer favoring its growth, and summer
floods and fishermen’s seines uprooting and sweeping it away.

The following list includes only the most common and
most important members of the aquatic flora, with brief notes
on their habitat and frequency.

Ranunculus multifidus Pursh. Found occasionally in quiet
waters in shoal regions with soft alluvial bottom.

Caltha palustris L. Rare, along springy shores.

Nelumbo lutea Pers. Forming large patches in the more
open vegetation in the permanent backwaters on very soft allu-
vial bottom. Usually at some distance from shore and in quiet
waters.

Nymphea reniformis D.C. Common in the more open
regions of the permanent backwaters in quiet regions, and along
channels on alluvial bottom.

Cardamine rhomboidea D. C. Rare, along springy margins.

Cardamine hirsuta L. Occasional, along alluvial margins.

Nasturtium sessiliflorum Nutt. Rare, along wet sandy mar-
gins.

Nasturtium palustre D. ©. Common, in shallow water along
alluvial shores.

Proserpinaca palustris L. Rare, along shady shores perma-
nently fed by springs, |

238

Angelica atropurpurea L. Occasional, along margins.

Sium cicutefolium Gmelin. Occasional, in swamp margins
near bluffs on alluvial bottoms.

Cicuta maculata L. Common, in places with the preceding.

Cicuta bulbifera L. Occasional in margins of swamps.

Utricularia vulgaris L. Rare in quiet backwaters, in the
more open places with alluvial ooze and underlying sand and
springs.

Polygonum amphibium L. Common in shoal water, in
places, in the flooded bottoms and along margins of permanent
backwaters. Habitat usually dry at low water. Stems often
attaining a length of fifteen to twenty feet.

Ceratophyllum demersum L. Abundanteverywhere in shoal
and deeper waters, often above low-water levels, and at times
even encroaching upon channels where currents are main-
tained. It grows in patches and dense masses, sometimes
choking the smaller lakes from shore to shore. It occurs us-
ually on bottom of soft alluvium, which in some places forms
but a thin film above the hard sand beneath. It reaches the
surface in early summer, and grows throughout the warm sea-
son unless swept away by floods or seines. These agencies,
combined with wind and decay, remove much of the summer’s
erowth in the autumn. Large areas of bottom growth survive
the accidents of the colder season and, together with the de-
tached terminal buds, provide for the rapid recovery of the
water meadows of Ceratophyllum in the following spring.
Though essentially an immersed floating plant, this species has
its lower stems fixed in the soft ooze of the bottom upon which
they rest, and it thus becomes almost as firmly “rooted” as
do the Potamogetons and similar plants. This species consti-
tutes the greater mass of the aquatic vegetation of the larger
impounding and permanent backwaters. It is known in local
parlance as “moss,” though this designation is not always con-
fined to this plant. No true aquatic mosses have been found
in this bottom-land region. This Ceratophyllum forms by far
the greater part of the aquatic vegetation in this locality.

239

Elodea canadensis Michx. Common on alluvial bottom with
Ceratophyllum, especially in quiet waters, but not reaching the
surface so generally. It is widely distributed and is next in
abundance to the preceding species, though forming a wry
much smaller proportion of the total vegetation.

Vallisnervia spiralis L. Rare; found only in channels with
currents, as at the mouth of Quiver Creek.

Pontederia cordata L. Common along open places, such as
the channels at the head of Quiver Lake and the outlet of Flag
Lake, on both alluvial and sandy bottoms.

Heteranthera graminea Vahl. Creeping along margins of
lakes and the river, usually on alluvium.

Juncus acuminatus Michx. Common in shoal water along
sandy shores.

Typha latifolia L. Occasional patches found in the swamps
and sloughs of the permanent backwaters.

Sparganium eurycarpum Engelm. Frequent in the margins
of lakes and sloughs along channels on sandy and alluvial bot-
toms.

Spirodela polyrrhiza Schleid. Everywhere in quiet waters,
forming in places dense mats upon the surface. Often drifted
by wind or current in great windrows along shore. Very com-
mon in open water, usually but not always on the surface.
Often taken in the plankton with other species of the family.

Lemna trisulca L. Locally abundant in the more open veg-
etation of the backwaters in quiet bays and nooks in both sur-
face and deeper waters. Not generally distributed, and less
abundant than other members of the family.

Lemna minor L. Associated with Spirodela but much less
abundant.

Wolffia columbiana Karsten. In surface and deeper waters
in both river and backwaters among vegetation and in open
water. Frequently taken in the plankton.

240

Wolffia braziliensis Weddell. With the preceding but less
abundant.*

Sagittaria variabilis Engelm. Abundant in shallow water
along margins of lakes and swamps and in protected nooks
along the river. On both alluvial and sandy bottoms, and often
forming well-defined belts of vegetation.

Triglochin palustris lu. Occasionally found in marshes on
alluvium.

Potamogeton natans L. Widely distributed along margins
of lakes, sloughs, and the river, in both quiet and flowing
water, often occupying the open spacesin the littoral vegetation
and among Ceratophyllum and Hlodea.

Potamogeton pusillus L. Rare, in open water of larger lakes.

_ Potamogeton pectinatus L. Rare, in lakes and in river near
channels where there is considerable current.

Naias flerilis var. robusta Morong. Frequent along shores
of lakes and river in shallow water on alluvium.

Dulichium spathaceum Pers. Occasionally found along allu-
vial shores of quiet backwaters.

Eleocharis palustris R. Br. Very common, forming patches
of considerable extent along low sandy shores and in the mar-
gins of swamps.

Eleocharis intermedia Schultes.. Occasional in the mar-
gins of lakes and swamps.

Eleocharis tenuis Schultes. In shallow water in margins
of swamps. Not common.

*According to some criteria all of our representatives of the Lemnacee might be
considered as part of the plankton. This is especially true of Wodfia, which is found
in open water at all levels. Wind and current have much to do with its distribution,
but, it has, nevertheless, a Jimnetic habit, comparable with that of many organisms of
the plankton. Its general distribution and its small size afford further reason for
regarding it as a part of the plankton of our locality. It was therefore not removed
before measurement of the plankton. There are but few instances in our collections
where it becomes a disturbing factor by reason of its predominance. The other
members of the family are much larger and are more irregular in their distribution,
and thus tend to distort the quantitative relations of the more typical plankton. For
these practical reasons it seemed best to remove all specimens of these species from
our catches before measurement.

241

Eleocharis acicularis R. Br. Common in shallow water on
alluvial and sandy bottoms.

Scirpus pungens Vahl. Common along sandy margins.

Scirpus lacustris L. Lake and swamp margins ; common
on both sandy and alluvial bottom.

Scirpus smithii Gray. Occasional along sandy shores.

Scirpus fluviatilis Gray. Very abundant in bottom-land
swamps on alluvial bottom. Forming great tracts, to the ex-
clusion of other plants, and contributing largely to the decay-
ing vegetation of the backwaters.

Scirpus atrovirens Muhl. Common, in marshy borders.

Rhynchospora alba Vahl. Rare, along sandy margins of
backwaters in shallow water.

Zizania aquatica L. Forming meadows of considerable ex-
tentin margins of lakes and more open swamps in the backwaters.

Equisetum limosum L. Sparingly present along springy
margins of sandy shores.

Azolla caroliniana Willd. This brilhant little cryptogam
is locally abundant in warm sheltered regions of the back-
waters in early summer. It is found principally in the dense
mats of drifted Spirodela, where it forms bright red rosettes,
the clusters sometimes forming an area several square feet in
extent. |

The filamentous alge, principally Spirogyra and Zygnema,
becomes very abundant in shallow waters in spring and early
summer as the bottom-lands emerge from the receding flood.
As the shores of the more permanent bodies of water are left
bare, there remains upon them, half supported by the semi-
aquatic vegetation, a thick felted mat of fading green, the
strength and consistency of which are sufficient to justify the
local name of “blanket moss.” Its rapid decay in warm shal-
low water contributes immediately to the support of the plank-
ton.

VEGETATION AT THE SEVERAL STATIONS.

Illinois River (Station E').—The following statements con-

cerning the vegetation of the river are based upon many obser-

242

vations about Havana, and upon the conditions observed during
a trip made in May, 1899, by the courtesy of the Illinois State
Fish Commission, upon the steamer “Reindeer,” from the mouth,
at Grafton, to Hennepin, 211 miles above. Asa rule, the river
is quite free from vegetation. There is, to be sure, in the upper
part of Peoria Lake, which is merely an expanse of the river
(Pl. 1.), an extensive area which is permanently occupied by
aquatic plants. A similar expansion known as Havana Lake
(Pl. II.) is also at times abundantly supplied with vegetation
in its shoaler and quieter portions. There are also springy
shores, usually of gravel or sand, located where the channel
encroaches upon a bluff upon which a permanent littoral veg-
etation is maintained regardless of river levels. Generally,
however, the water reaches the steep or sloping bank of black
alluvium without any fringe of green. There are scattered
Lemnacee—principally Spirodela polyrrhiza and Lemna minor,
with Wolffia braziliensis and columbiana—floating with the cur-
rent from spring till late in the fall. Patches of “moss” con-
sisting of Ceratophyllum demersum are also floated into the chan-
nel from flooded backwaters, or loosened by fishermen’s seines
and then carried by the current from backwaters or the shores
of the river into the channel. On some protected shores where
the current is slight the arrowleaf (Sagittaria variabilis) main-
tains a foothold—as on the eastshore, just above the “towhead”
(Pl. I.). A small patch of Potamogeton pectinatus also remains
year after year in the river in the rapid currents that rush
through Quiver cut-off (Pl. II.). Such instances of permanent
vegetation are, however, of rare occurrence, and form but insig-
nificant factors in the immediate environment of the river
plankton.

A temporary fringe of vegetation has appeared along the
river margins when relatively low-water stages prevailed in the
spring and were maintained without marked floods until sum-
mer, as in 1894 and 1895. This httoral growth is not composed,
however, of the permanent littoral flora, such as the arrowleaf,
the Polygonums, and the rushes, but is like that found in deeper

243

and more permanent backwaters. It consists, in the main, of
Ceratophyllum with some Naias and Klodea. Scattered sprays
of Potamogeton natans lie in the more open places, and the Lem-
nacee multiply in the more sheltered nooks, while the yellow-
flowered Heteranthera abounds at the water’s edge and creeps
out upon the black mud at the margin. This fringe of vegetation
continues until it is stranded on the shore by the recession of
the water, washed away by sudden floods which lift it from its
slight foothold upon the unstable bottom, or pulled out upon
shore or floated down stream by fishermen’s seines. Thus, of
the heavy fringe present in June, 1895, only a trace was left by
September of that year. In thefour years following, the river
levels were such that no vegetation of consequence appeared
along the shores of the river at any season of the year.

Even at the time of its maximum development this littoral
belt of vegetation did not often exceed ten meters in width. It
is thus a relatively small, as well as an inconstant, factor in the
environment of the plankton of the river itself. The current
carries the plankton-laden water through its tangled growth,
and sessile animals, such as Hydra and the Bryozoa, find in it
an abundant food supply. These and other organisms which
find a retreat in the shelter of the vegetation are from time to
time carried into the channel by the current and serve to diver-
sify the plankton. On still, warm days Hydra habitually aban-
dons its sessile mode of life and adopts a limnetic habit, often
attaching itself to the surface film of water.

Owing to the changes in levels and to other reasons above
cited the vegetation of the river, where it occurs, does not con-
tinue until autumn, and is absent during the ice blockade of
the winter. In this respect the river environment is in strong
contrast with that of most of the backwaters, in which the veg-
etation, though reduced, persists throughout this period. This
absence of winter vegetation in the river is one of the condi-
tions favoring the stagnation which sometimes occurs, as in 1895,
in the Ilhnois.

Spoon River (Station M).—Spoon River, throughout the

244

bottom-land region at least, is free from vegetation—a condi-
tion which prevails throughout the greater part of our prairie
streams.

Quiver Lake (Station C). Pl. XV.-XVII.—The vegetation is a
very important and much more constant factor in the environ-
ment of Quiver Lake than it is in that of theriver. In its max-
imum development reached in the summers of 1894 and 1895 it
fills (Pl. XV.) the lake from shore to shore with a closely matted
growth, the only open places being an interrupted and _ tor-
tuous channel through which the waters of Quiver Creek (PI.
II.) make their way to the river. The vegetation in the body of
the lake consists in the main of Ceratophyllum, with an admix-
ture of Hlodea and Potamogeton toward the margins. Along
the eastern shore, and toward the upper end of the lake where
springy shores and sandy bottom are to be found, the vegeta-
tion partakes more of the permanent littoral.character. Here
rushes, sedges, arrowleaf, and the aquatic Cruciferw and Um-
bellifere appear among the Potamogetons and other floating
plants. In the northern area, especially along its western shore,
where more alluvium is found, water-lilies, pickerel-weed, and
the lotus abound, and the Potamogetons are more abundant (PI.
XVII). The “wild celery” (Vallisneria spiralis) is sparingly pres-
ent in the channel of the eastern arm of the lake, while in the
tributary bottom-lands above are aquatic meadows of wild rice
and other water-loving grasses, rushes, and sedges.

In years of higher water (Pl. XVI.), such as the four follow-
ing 1895, the vegetation differs from that of low-water years
more in quantity than in kind. The main body of the lake and
a considerable portion of both arms are freed to a greater or
less extent from their vegetation, a border of varying width
remaining near the shores, and scattered clumps dotting the
lake here and there in the broad stretches of open water.

Dogfish Lake (Station L). Pl. XVUI.—This lake shares the
flora of Quiver Lake, of which it is but the northwestern arm.
Its vegetation is somewhat denser, having no channels travers-
ing its matted growth. A fringe of marsh flora along its north-

245

eastern border and the encroachments of the semiaquatic bot-
tom-land plants but slightly vary the uniformity of the vegeta-
tion, which at low-water stages fills the greater part of the lake.

In such lakes as Dogfish and Quiver the vegetation by
reason of its predominance exerts a profound influence upon
the quantity and the constitution of the plankton. Its fluctua-
tions in quantity with the change of the seasons and the inva-
sion of flood water are attended by marked readjustments of
the plankton.

Phelps Lake (Station F’), Pl. XXI.—Phelps Lake was prac-
tically free from vegetation throughout the period of our plank-
ton collections. The drying up of the lake in 1894 and its cul-
tivation in 1895 destroyed whatever foothold the aquatic veg-
etation had obtained. In the following years the ingress of the
aquatic flora become increasingly evident, though the alluvium
in the bed of the lake, hardened by the drouth, gave but scant
foothold to marsh-loving plants, especially to the perennial
species or to those with well-developed roots. Each spring saw
here a remarkable development of “blanket moss,” a mat of
algee, principally Spirogyra, Zygnema, and Cladophora. In the
period of midsummer stagnation a dark green film of Oscillaria
coated the bottom or rose to the surface in scattered masses.
The fringe of button-bush (Cephalanthus occidentalis) and
willows (Salix nigra and S. longifolia) at the edge of the sur-
rounding forest gave shelter to a few semiaquatic Composite and
rushes, and beyond these there were scattered clumps of Pota-
mogeton natans and Nais flexilis var. robusta, which found a
place even in the first year in which the water reentered the
lake. In 1899 the margin occupied by these plants had increased
in width, and arrowleaf and lotus were represented by a few
isolated plants, while the ubiquitous Ceratophyllum had made
its first appearance in the lake. Aside from the alge, the aquatic
flora formed but a small part of the environment of the plank-
ton in this body of water.

Thompson’s Lake (Station G). Pl. XX.—This lake combines
in one area almost the whole range in the development of the

‘

246

aquatic flora characteristic of the backwaters of the Ilhnois
River bottoms. The regions occupied by aquatic vegetation
(Pl. II.) are of considerable extent even at low-water stages,
and increase rapidly in area at higher river levels. The diver-
sity of the aquatic flora is most pronounced at the moderate
stages of water (38 to 6 feet above low water) which often pre-
vail after the decline of the spring flood during early summer.

A characteristic littoral flora is found along the firm san-
dy margin of the eastern side, and on afew points of similar
soil which project from the western bluffs to the lake. Jun-
cacee and the shore-loving grasses and sedges abound here, and
as the shores emerge the bottom-land Composite and Polygo-
nums encroach upon their domain. In other regions the
slope is more gradual and the shore line, as the water recedes,
moves over wide stretches of alluvial soil, often of slight con-
sistency, to a considerable depth. Here the vegetation is more
luxuriant, and Polygonum amphibiwm, the arrowleaf, and the
water-lily vie with the big river rush (Scirpus fluviatilis) for a
foothold in these regions, exposed only at lowest levels and
never baked hard by the midsummer’s drouth.

At higher levels is found a varied mixture of semiaquatic
and upland genera, such as Lippia, Bidens, and Polygonum, with
coarse grasses and sedges. Inside of this varied littoral zone is
found a permanent flora of almost equal diversity. Along
sandy shores we find a belt of more or less open vegetation con-
sisting largely of Potamogeton natans, Elodea, Nais, and a few
Juncacee, with scattered lilies and lotus. At the southern end
of the lake there is an area over a mile in length occupied
mainly by Scirpus lacustris, great beds of lotus and water-lily,
and mats of Lemnacee. A narrow belt with less of the Scirpus
is found along the alluvial margins of the western shore, and
scattered patches occupy the shoals that connect the northern
end of the lake with the swamps that he to the northward.

In the deeper waters Ceratophyllum takes possession in some
regions to the practical exclusion of all other species save a few
Potamogetons and some scattered Hlodea. The region in which

247

this species prevails lies in the southern third of the lake and
along its sides for a distance of several hundred feet from
shore, and again at the northern end for a distance of three
quarters of a mile from the outlet. During low-water years
scattered clumps of Ceratophyllum and Potamogeton were found
as far north as the middle of the lake. ‘Thus, at all seasons
about half of the lake—often two thirds of it—is open water
with scarcely a trace of fixed vegetation.

The seasonal changes in the vegetation of this lake are very
marked. In midwinter, during the ice blockade, which contin-
ues much longer upon the lakes than upon the river, the vege-
tation is not much in evidence. At low stages dead rushes
rise above the ice in a few places, but give little hint of the
great mass of broken and more or less comminuted vegetable
debris which covers the bottom in those portions with vegeta-
tion of a semi-littoral character. This debris is of great extent,
and in the absence of current and buoyancy is not carried away,
but remains to enrich the waters and the unstable ooze upon
which it hes. Most of the vegetation in this belt is dormant at
this period, little trace of green appearing on the half-buried
root-stalks and rhizomes of the perennial species belonging to
this zone. In the deeper water, on the other hand, a consider-
able quantity of Ceratophyllum, with some Hlodea, remains upon
the bottom throughout the winter, keeping its foliage beneath
theice. This isan important factor in preserving the equilib-
rium in the gaseous contents of the water, and thus in the main-
tenance of the winter plankton.

With the rise in temperature in spring the vegetation starts
into growth which the spring floods to a large degree conceal.
This growth and the decline in river levels combine to make
its appearance at the surface or its emergence above it some-
what sudden. The greatest growth takes place during the
months of May and June, and is in large part attained by the
close of the latter month. The changes subsequent to this pe-
riod which are incident to growth are but slight, and have but
little effect upon the “waterscape.”

248

Late summer and early autumn see the decay of much of
the more succulent vegetation, such as the water-liles and
lotus, the arrowleaf, the Potamogetons, and some of the Hlodea
and Ceratophyllum, while the emergent and more resistant
rushes, sedges, and grasses yield more slowly and later to the
accidents of flood and ice. and do not reach the late stages of
decay until the following spring.

The vegetation of Thompson’s Lake is subject to consid-
erable fluctuations, due to other than seasonal changes.
These are variations in river level, the seining of fishermen,
and the movements caused by flood, wind, and ice. The
changes in level, owing to the very gentle slope of most of
the shore of this lake, greatly contract the littoral zone as the
spring flood recedes, and restore more or less of it with each
recurrent rise—changes which facilitate the decay of whatever
vegetation of the submerged type develops in this zone. The
location of the lake with its long axis in the direction (S. W. to
N. E.) of the prevailing winds, gives a force to the waves suffi-
cient at times to tear isolated patches of “moss” from their
sight hold on the unstable bottom and drive them toward the
northern end of the lake. This is an important factor in keep-
ing the greater part of the lake free from vegetation.

The vegetation of Thompson’s Lake is thus a considerable
factor in the environment of the plankton. It furnishes a con-
siderable quantity of decaying organic matter in fall and spring,
both being periods of marked plankton development. At high
and moderate stages of water, when a gentle current passes
through the lake, its influence must be generally diffused. At,
low-water stages, when the current is cut off, its effect 1s much
more local. At such times no open channel is maintained
through the vegetation at the northern end of the lake (PI. IT.)
to the outlet, as in the case of Quiver Lake. The movements
in the lake attending change in level tend to mingle the plank-
ton of regions full of vegetation with that of the open lake or
vice versa, thus tending to diversification. There still remains
at all times a large tract of open water in which for considera-

249

ble periods of time the vegetation forms no appreciable part of
the environment of the plankton. It was in this region that
the most of our collections were made, and they may therefore
be regarded as in the main typical of vegetation-free waters
of our locality.

Flag Lake (Station K). Pl. X1X.—In vegetation this is the
richest by far of all the bodies of water examined by us. It 1s
the type of a permanent marsh, filled from shore to shore by a
rank growth of plants (Pl. XIX.), with little or no development
of channels or current, anda bottom of ooze with great quanti-
ties of decaying vegetation. The wide expanse of this marsh
(over 1,200 acres) and the varied character of its borders afford
opportunity for great diversity in its vegetation. Its margins
are not sharply defined, and the vegetation in such regions
varies greatly according to the locality, and in the same local-
ity according to the present and previous stages of water. Thus
in the autumn of low-water years the Composite, Polygonums,
and grasses of the dry and higher bottoms attain a rapid and
rank growth in regions where Sagittaria and Lemna held sway
in the spring. A greater part of this marsh is occupied by a
dense growth of the river rush (Scirpus fluviatilis ) to the exclu-
sion of almost all other aquatic species of any size. Here and
there irregular areas of considerable extent are filled with scat-
tered Scirpus, water-liies, and the lotus, together with great
quantities of the Lemnacew (Pl. XIX.). Near the center of the
marsh there existed throughout the years of our examination
two irregular spaces of open water of several acres in ex-
tent, more or less encroached upon by a surrounding belt of
Ceratophyllum. Whenever access was possible our collections
were made in these open places.

The vegetation of this marsh, by reason of its omnipres-
ence, its great volume, and its periods of growth and decay, isa
factor of great importance in the environment of its plankton.
The nourishment taken up by the submerged and more succu-
lent vegetation is released again by decay in the autumn, and
thus favors the development of the autumnal plankton. The

200

emergent vegetation, which reaches a great development here,
adds its contributions to the enrichment of the marsh waters
with the return of flood conditions and temperatures facilitat-
ing decay—conditions prevailing in the spring at the time of
plankton maximum. The growth of vegetation in the spring,
and the choking up of the lake which attends its transforma-
tion into a marsh seem, on the other hand, to introduce condi-
tions of nutrition and light inimical to the development of the
plankton.

PLANT ZONES.

The classification of the aquatic vegetation of our Jocality
and its divisions into definite zones or belts is made difficult by
the fluctuating character of the environment. The average
range in river level is almost fourteen feet, and with the changes
in level go advance, recession, or even obliteration of the
shore-line in a large part of the territory included in our field
of operations. Drouth and untimely flood also bring wide-
spread catastrophe to the aquatic vegetation. The depth, even
if it was constant, is insufficient to provide for any extreme
differentiation of plant zones, while its inconstancy obliterates
any which may gaina partial development. The greatest depths,
7-8 meters, occur temporarily in maximum floods in Spoon and
Ihnois rivers. The depth at such times over areas of vegeta-
tion in the backwaters rarely exceeds 5-6 meters, while during
the period of spring growth itis usually less than 3-4 meters and
in large areas less than one. The whole area of vegetation .
thus lies within the depth assigned by Magnin (’98) to the lit-
toral zone. Under these conditions the origin and mainte-
nance of permanent zones of vegetation is far less possible in
this fluviatile environment than it is in the more stable condi-
tions of the typical lake.

An attempt to classify our water meadows according to the
scheme adopted by Magnin (’93) for lakes in the Jura, and by
Pieters (94) for Lake St. Clair cannot succeed in our fluviatile
environment. The zone of deep and colder water character-

251

ized by Chara—called the Characetum—is entirely absent in our
locality. The zone characterized by pond weeds—Potamoge-
tonetum—may perhaps be found in the great areas of immersed
vegetation, principally Ceratophyllum, which occur in Quiver
and Thompson’s lakes. The few Potamogetons found in our
locality occur in this zone, though they are not confined to it.
The depths in which this zone is here found are much less than
in Lake St. Clair, in the lacustrine environment. The “Nu-
pharetum” may be represented in the lotus beds of Quiver,
Thompson’s, and Flag lakes; but these do not show a zonal
arrangement, and merge variously with littoral and Ceratophy!-
lum regions. The littoral zone, which, according to the authors
above quoted, extends from the shore line to a depth of 3 me-
ters, is confined in our waters to a much shoaler region, and, as
elsewhere, is characterized by Scirpus, the sedges, Polygonum
amphibium, Nymphea, and Potamogeton natans. Almost all of
Flag Lake, the northern and southern ends of 'Thompson’s Lake,
and the northern and eastern margins of Quiver Lake belong to
this zone.

A classification more applicable to our locality is that of
Pieters (’01), who recognizes in Lake Erie two regions,—one
including all submerged forms and those with floating leaves,
the other all the remaining species with emersed leaves
and growing with roots and parts of the stem in the water.”
These regions of immersed and emergent flora are often recogni-
zable in our locality. To the latter belong the greater part of
Flag Lake, a considerable portion of Quiver Lake along the
eastern and northern shore, and the two ends and the margin
of Thompson’s Lake ; to the former, the body of Quiver and
Dogfish lakes, a small area in Flag, and a large area at either
end of Thompson’s Lake. It is this zone which constitutes the
great plant factor in the environment of the plankton of our
waters, and it consists almost entirely of Ceratophyllum. The
effect of vegetation upon the production will be discussed in
another connection.

It is evident that our investigations afford a unique oppor-

252

tunity for examining the effect which vegetation (the word is
used in the sense of the coarse aquatic growth as distin-
euished from the microscopic phytoplankton) has upon the
quantity and kind of plankton in bodies of water the remain-
ing factors of whose environment are for the greater part com-
mon.

253
QUANTITATIVE INVESTIGATION OF THE PLANKTON.
GENERAL CONSIDERATIONS.

The purpose of this investigation was the determination,
by measurement, of the quantity of minute organisms develop-
ing in the water at intervals throughout the year, and by this
means to trace the seasonal fluctuations in production, and
the relation of quantitative changes to constant and fluctuat-
ing factors of the environment, to flood and drouth, to chemi-
cal conditions, to the ice blockade, and to vegetation; and to
contrast production in waters of the main and tributary
streams, In impounding backwaters and the channel, and in
bottom-land lakes and the main stream.

METHOD OF COLLECTION.

The method used in determining the quantity of plankton
was based upon that devised by Hensen (’87) and modified by
Apstein (796) for use in fresh water. The changes and modifi-
cations which were made to adapt the method to use in our
situation and to correct some of its errors have been described
in detail by me elsewhere (797); I shall, therefore, only briefly
refer to a few phases of the subject of special pertinence or
interest in this connection.

The changes in method during the progress of the work
are indicated in Tables IIJ.-IX. From June, 1894, to May 20,
1896, the plankton was collected by means of the silk net,
made after Apstein’s smaller model (see Apstein 796) of No.
20 silk bolting-cloth of Keller’s manufacture. This net was
drawn through the water at a uniform rate of one half meter
per second for a distance of thirty meters. As shown in the
tables referred to, most of the hauls were made by the ob-
lique-haul method devised by Prof. Frank Smith, in which the
net was drawn along an oblique rope from bottom to surface
across channel in the river, and across the current, where cur-
rent existed, at our other stations of collection, except in

254

a few instances when conditions of ice or vegetation necessi-
tated a temporary modification of the direction.

Collections subsequent to May 20, 1896, were made by
means of the plankton pump, a known volume of water being
strained through the silk net. The water strained was taken
in such a way as to represent a vertical column of equal di-
mensions from bottom to top. This was accomplished by low-
ering the inlet of the hose from the intake of the pump to the
bottom, or as near it as we could go without fouling the water
by disturbing the unstable deposits, and raising it to the sur-
face during the progress of the pumping. To secure a perfect
column it is necessary to begin raising the hose with the first
strokes that deliver water to the net, and to arrive at the sur-
face long enough before the required amount is pumped to
allow surface water to reach the net. With a fixed hose
length and a known capacity of pump, this is easily deter-
mined by experiment. ‘The volume strained varied with the
contents of the water. Asa rule, one fourth ofa cubic meter
was strained. When plankton was scanty and silt hght the
quantity was doubled, and occasionally in excessive plankton
or unusual silt but half this volume was strained. Variations
of minor importance in the methods here noted will be men-
tioned in connection with the discussion of the plankton at
the several stations. These variations are such as were ne-
cessitated by difficulty of access with collecting apparatus, or
by the exigencies of flood, ice, and current

PRESERVATION AND MEASUREMENT.

During the first three years the plankton was killed and
preserved in strong alcohol. In subsequent years 70 per cent.
aleohol to which formalin had been added to the grade of 2
per cent. was used, and proved to be a better preservative than
the strong alcohol.

The quantity of plankton present in the catch was deter-
mined by compression in a Purdy centrifuge for two minutes

\ 255

at the rate of 1,000 revolutions per minute, resulting in an appli-
cation of 1,420,484 dynes. All records and discussions in this
paper are based upon this method of measurement. It brings
about a considerable reduction in the volume of plankton as
compared with that recorded by the usual method of allowing
the plankton to settle in the Eggert color-tubes for twenty-four
or forty-eight hours and condense by gravity only. I have de-
termined the amount of this reduction in measurement of all
planktons collected by us up to June 6, 1896. There are two
hundred and forty-three of these catches, and they represent
the full seasonal and local range in quantity and quality, cov-
ering, as they do, a period of two years and all the localities
with which we have dealt. The actual quantity of plankton
handled in these tests ranges from .025 to 10.25 cubic centi-
meters (centrifuge measurement), and 143 of the 245 catches
he between .25 and 2. cubic centimeters.

The average decrease in volume when determined by the
centrifuge as compared with that by the gravity method in
these 243 cases was 49.5 per cent. As shown in the following
table, the decrease ranges from 8 per cent. to 76 per cent. In
21 cases itis just 50 per cent., in 111 cases it is below this,
and in 111 above.

TABLE SHOWING DISTRIBUTION ACCORDING TO PERCENTAGE OF DECREASE OF
243 CATCHES MEASURED BY GRAVITY AND CENTRIFUGE METHODS,

Per No. Per No. Per No. Per No. Per No.
cent. of cent. of cent. of cent. of cent. of
lost | catches lost catches} lost {catches} lost | catches lost | catches
76 I @ | A 52 4 42 3 2 B
7 I Gi, |e 51 5 41 2 31 I
74 2 Gonna as 50 21 40 4 29 5
71 I So) || © 49 8 39 I 27 I
69 I BS | 9 48 II 38 7 26 I
67 4 Sy || LO 47 10 37 5 25 I
66 4 56 5 46 7 36 4 22 I
65 3 55 12 45 9 35 4 21 I
64 5 54 7 44 6 34 4 13 I
63 3 53 II 43 9 33 I 8 I

256

The factors determining the decrease are the proportions
of silt and plankton and the character of each. When floccu-
lent debris is abundant, or when filamentous diatoms or alge,
Copepoda, or the Cladocera with long antenne are present in
numbers, the decrease upon centrifuging is greater. When the
silt is earthy or contains considerable quartz, and when the
plankton consists of Protozoa such as Synura, or Rotifera such
as Syncheta, or Cladocera such as Chydorus or Bosmina the de-
crease is less. The amount of plankton placed in the tubes of
the centrifuge also slightly affects the ratio of decrease in vol-
ume. For example, one of our largest planktons, measuring
11.15 cm. by the gravity method, fell but 8 per cent. when cen-
trifuged in a single tube. When divided among three tubes
the decrease became 14 per cent. This was a plankton largely
composed of Chydorus and Bosmina. Another large plankton,
measuring 11.85 cm. by the gravity method, fell to 7.6 em. upon
centrifuging in a single tube—a loss of 36 per cent. This con-
sisted very largely of Synura. As other large catches decreased
as much as 50, or even 60, per cent., it is clear that large vol-
umes do not necessarily yield only shght decreases.

The instances in which the decrease exceeded 70 per cent.
are 5in number. Of these, 3 contained Melosira or Fragillaria,
1 was rich in Oscillar/a, and 2 contained considerable floccu-
lent debris from aquatic vegetation. All of the 12 whose de-
crease was less than 30 per cent. occur in April and May, when
Chydorus and Bosmina are at their maximum and constitute
a large, if not the greater, part of the plankton. In a few in--
stances these catches which showed slight reduction in volume
contained /Tydra, insect larve, and other adventitious forms
from surrounding vegetation.

Both extremes contain numerous instances in which the
plankton catch is made up of typical plankton organisms, and
consequently the range in the decreases here recorded ts normal
for the range in planktons occurring in our waters throughout the
year. Itistherefore reasonable to assume that the centrifuged vol-
umes here reported for plankton in the Illinois must, on the average,

257

be doubled for comparison with volumes reported in similar regions
elsewhere and measured by the gravity method.

The silt in our catches and the predominance of rotifers at
times will tend, I believe, to render the decrease on centrifug-
ing somewhat less in the case of our planktons, on the average,
than that found in lake planktons where filamentous diatoms
and Copepoda abound more generally. Ward and Graybill (00)
find that the decrease ranges from 60 per cent. to 70 per cent.
and averages slightly less than two thirds. Juday (’97) finds
that the decrease amounts on the average to 80 per cent. Both
of these records deal only with a smal] number of midsummer
planktons, while our records cover the whole round of sea-
sonal changes. This may be an element which tends to
increase the range of the decrease shown in our results. The
gravity work in our experiments was done in tubes identical
in pattern with those used by Ward and Graybill (’00), and the
time for settling was the same. Juday (97) gives no account
of his gravity method.

The centrifuges which we have severally used are only
approximately of the same pattern, and they have not been
used in exactly the same way by any two of us.

We may compute the specific pressure in dynes per square
centimeter ata given distance from the axis of rotation accord-
(r2—re )

rea i]

ing to the formula °# : in which 6 is the density

J

of the contents of the tube; », the angular velocity in ra-
dians per second; 7 the distance in centimeters from the
axis of rotation to the bottom of the tube; and 1, the dis-
tance from the axis to the top of the fluid. For density I
have used the specific gravity of water, since the extractions
from the plankton considerably increase the specific gravity
the alcohol in varying degrees in which the plankton was
preserved.

of UM 3 : .
The formula for » is —5—. in which nv is the number of
revolutions per minute.

258

On this basis the pressure in dynes in our use of the centri-
fuge, where there were 1,000 revolutions per minute with dis-
. tances of 16.7, and 4.5 cm. to bottom of tube and top of liquid
respectively, was 1,420,484. Professor Ward writes me that
these distances 7 and 7; in the Bausch & Lomb machine he used
were 14 and 5 cm. respectively, which with a density of 1 and
80 turns of the crank, equaling 1,840 rotations of the axis (on
the manufacturer’s authority that the machine is geared to
give 23 rotations of the axis to one of the crank), gives 2,774,-
897 dynes. Mr. Juday (’97) states that the pressure in his cen-
trifuge was 391,680 dynes, but he writes me that the density
used was the difference between that of alcohol and dried
plankton, amounting to only .2 and .25. Reducing his ecaleu-
lations to our basis in so far only as the matter of density is
concerned, we find the dynes to be from 1,958,400 to 1,566,720.
A further difference between our methods lies in the fact that
in our use the pressure was exerted fwo minutes, and but one
minute in that of the other investigators.

The practical differences may not really be so great as the
figures indicate because of the asymptotic character of the
curve of reducing volume as the pressure continues or is in-
creased. It it desirable that some standard unit of measure-
ment be agreed upon for purposes of comparison.

The use of the centrifuge in the many measurements here
recorded has only confirmed the views expressed by me (’97)
regarding its utility, greater accuracy, and convenience for
volumetric plankton work. Material which has been properly
preserved has not suffered inthe compression. All of the enu-
meration work to be reported in the second part of this paper has
been done upon plankton which has been centrifuged at least
once and in some cases six times. I have not detected any
mutilation or distortion of the constituent organisms unless it
be of Leptodora hyalina, an elongated and delicate cladoceran,
and several other organisms of great delicacy of organization.
These are often crumpled as a result either of the compres-
sion or manipulation of the plankton, but the crumpling rarely

259

interferes with identification of the species or determination
of sex or breeding condition.

The statement made by me (’97, p. 20) that “this is, I be-
lieve, the first application of the centrifugal machine to quan-
titative plankton work” requires modification. In Kraemer’s
account of Samoan plankton (97) he describes a traveler’s
centrifuge for use on shipboard for measurement of plankton,
and I infer from his text that this machine was in use by
him in 1893-95 in Samoan waters, though I find no explicit
statement to that effect. If this be true, his use antedates
ours, which did not pass the experimental stage until January,
1896. In any case the measurements he publishes (’97) were
made by the centrifuge. The following statement made by
Ward and Graybill (’00), —“Juday (97) was apparently the first
to publish an account of the use of the centrifuge for this pur-
pose. Both Dr. Kofoid and I had, however, experimented indepen-
dently for more than a year before that, and had written to var-
ious investigators regarding the advantage of such aninstru-
ment,’—requires notice in this connection, since the question has
been raised by these writers as to the priority in publication of
the use of the centrifuge for plankton measurement, and the
facts are incorrectly given. The date of Juday’s paper is subse-
quent to May 28, 1897,* for the volume containing the. paper
contains the records of the field meeting of the Indiana Acad-
emy held on that date. The date of publication of my ac-
count of the centrifuge was March 10, 1897, and it was also
mentioned by Professor Forbes (96) in the biennial report of
our Station operations. This report was again issued January
24, 1897, in separate form, and distributed to plankton investi-
gators generally. The date of publication of Kraemer’s work
is “Ende Januar oder Anfang Februar 1897; genauer kénnen
wir das Datum leider nicht augeben,” according to informa-
tion received by me from the publishers Lipsius and Tischer,
of Kiel, Germany. The empty honor of first publication thus
probably belongs to us, and certainly not to Juday as Ward

*In a letter Mr. Juday informs me that his paper was published in August, 1897,

260

and Graybill state. The real credit for first centrifuging plank-
ton belongs evidently to Kraemer. In view of the statement
above quoted it may be well to add that our experimental use
of the centrifuge was begun in the autumn of 1896. It was at
once adopted, ard our plankton thus far collected was meas-
ured by it at that time. The measurements made are those
used in the present paper. Our experiments with and adop-
tion of the centrifuge were independent of and without knowl-
edge of similar work elsewhere.

SILT ESTIMATION

In Tables HIL-IX. the amount of the actual catch of
the plankton net will be found, and in subsequent columns the
estimated percentage of silt, and computed volumes of silt,
plankton, and total catch are given in cubic centimeters per
cubic meter of water. In all our discussions of the plankton
the amounts used are those of plankton only, unless otherwise
stated, that is, of the total catch less the estimated amount of silt,
and they are always quoted in terms of cubic centimeters per
cubic meter of water.

The determination of the amount of silt has been of ne-
cessity a matter of personal estimation, and involves a source of
error of uncertain extent. The estimates have been made large-
ly by myself, with some aid from Mr. Rh. E. Richardson, and no
effort has been spared to maintain a uniform standard of esti-
mation so as to distribute, as far as possible, the error incident
to the process. Accordingly the estimates were revised and cor-
related after the qualitative and numerical analysis of the col-
lections at Station EH, and they consequently rest upon a com-
parative basis upon the examination of the catch as it appears
in the Rafter cell.* In the case of the collections from the Illinois
River only, they have been controlledin some degree by the re-
sults of the numerical analysis. The estimates of silt were made

where there is much light flocculent debris, which occupies considerable space in the
Rafter cell but may be compressed considerably in the centrifuge.

261

without reference to, and in most cases prior to, the prepara-
tion of tables and plots of seasonal distribution. Estimates
made by others, not accustomed to judging the plankton, re-
veal a wide divergence in percentages, and independent esti-
mates which I have made of the same material on different oc-
casions show some divergence, though, as a rule, quite within
the probable error of plankton method. The silt estimation
does not, I believe, essentially vitiate any of the conclusions
drawn in this discussion of quantitative results, and in no way
enters into the qualitative analysis.

THE CLOGGING OF THE NET.

The collections made with the silk net drawn from the
bottom to the surface of the water in vertical or oblique hauls
are all diminished in volume to some extent by the resistance
of the silk to the rapid passage of the water. As a result of
this, the net pushes aside some of the water in the column which
it is supposed to traverse. As its meshes clog with the accu-
mulating catch the amount pushed aside is increased progres-
sively during the haul. The actual catch of the net is there-
fore only a portion of the total contents of the column of water,
whose length is that of the haul and diameter that of the
mouth of the net. The volume of plankton actually present
in this column can be computed if we can determine the factor
of correction. Hensen (’87 and 795) has sought by experiment
with filtered water to determine the mathematical formula
which will give this correction for a net of known silk and di-
mensions drawn at given velocities. This factor he calls
the “coefficient of the net.” Reighard (’94) attempted to de-
termine the coefficient of his net by using a miniature model
in water in which Lobelia seeds had been placed, but ultimately
adopted the formula of Hensen.

It was necessary that in our final computation of the volume
of plankton we should make some correction in all catches of
the drawn net for this loss due to the pushing aside of the
water. Since our net was constructed after the Hensen-Apstein
model it was possible to apply the mathematical method of

262

Hensen (795). This coefficient—computed for us by Instruc-
tor W. C. Brenke, of the University of Illinois—is 1.320 or
1.3038, according to the area of the silk in the bucket of the
net, for the velocity of one-half meter per second, which
we uniformly employed. Our net has an area of 81.72 square
centimeters in the opening; of 1,847.5 and 22.66 square cen-
timeters respectively in filtering cone and windows of the
bucket; and its coefficient is 1.82. With a disk of silk clamped
to the lower end of the net,—a method used prior to the adop-
tion of my detachable bucket,—the area of the silk of the buck-
et falls to 15.2 and the coefficient is accordingly reduced to
1.303. A second net frame which we used, with an opening
two millimeters less in diameter, has a coefficient of 1.318.
Apstein’s (96) net has an opening of 92 square centimeters, a
filtering cone of 1,730, and the silk of the bucket measures 62
square centimeters. The coefficient of his net is computed to
be 1.39.

Observations on the operation of.the net in the field
through the seasonal changes of the plankton led me to be-
lieve that a uniform coefficient, and, moreover, one founded
on the operation of the net in filtered water, would not ade-
quately correct the error, since it takes no account of the sea-
sonal changes in the quantity and kind of plankton, and does
not recognize the effect of the progressive clogging of the net
by the catch, or the change of the net with use.

Upon the adoption of the pumping method cf collection a
number of tests were made for the comparison of the amount
of plankton taken by the drawn net and that by the pump and
filtering net along parallel courses of thirty meters—our usual
haul. The results amply justified my belef that the coeffi-
cient fluctuates with the conditions above named as well ag
with the condition of the net. We therefore sought by this
empirical method to determine the coefficient under a variety
of conditions representative of our environment. These tests
were not carried beyond this point, since we had adopted the
pumping method for the later and major part of our work.

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263

In this method the question of coefficient is entirely eliminated.
The results of these tests are given in the preceding table.
The variation in the coefficient with different seasons, lo-

calities, and planktons is apparent upon the first glance at

the table. The greater straining capacity of a new net as com-
pared with one which had been used for some time may be seen
in the tests made June 16, and July 9, 11, and 21, 1896. The
new net—the silk in which had been shrunken by washing and
pressing several times prior to use—catches at least 50 per cent.

more than the old one which had done service since February 25.
The rise in the coefficientas the net progressively clogs

by plankton is demonstrated by the tests of October 14, 1899,

and July 27, 1897. The latter test is graphically presented in

the accompanying figure.

30

215) 20 15 10 3) O 7m.

Fic. B.—Catches of plankton made on 30-meter haul by drawn net and pump

The upper, continuous line represents the pump catch; the middle, dotted line the

catch of the net measured by the settling method; the lower, heavy line the same
measured by the centrifuge.

TABLE OF DETERMINATIONS OF COEFFICIENTS OF NETS BY EMPIRICAL METHOD.

Length Net |Haul

Gravity Method—24 hrs. Centrifuge

|
Date Locality, etc. of haul

t |Pump \Cectiicient

ao

Enumeration—1 m.° water

Plankton.

Coefficient

Coefficient

Net | Pump

Some silt. Syaura and Copepoda.

8
| ince niver | wom] 2] + | as | ns 2717 | ors | 2.808 | yon ua
Dec, 30] Illinois River Tle: | I | .160 | .760 4.375 | 119,150 2.041 | Much silt. Syaura, Synchata, and Copepoda,
ope a i 325 | .850 2.143 3.468 | Small amount of flocculent debris. Polymixic
fel) 2 235 | .900 3-333 5.819 | plankton. Many nauplii. Ltomostraca, Rhi-
4 | av. | .280] .-- 2.609 4. (340 | zopoda, Rotifera, diatoms,and Profophyta present,
June 16] Quiver Lake 30 m. ae ; eras ie ems Soe
5 | 4 | .410 | .900 1.667 2.971
5 | av. | .520 | .850 1.304 2.604
Se eS ae an Ee S _—————— oo
=e all fount of debris. Polym’
July9 | Matanzas Lake | 30m. | 4) 1 | .365 ie 3.562 | -180 | .540 | 3.000 4.347 Pen errs Rotifera, Rated Poe
ea 4] 1 | -550 1.225 2E100 2.084 Polymixic plankton. otifera, Entomostraca
July 11/Thompsons 4a oe m, Alea ters 848 gis | 27atezca, and Protophyta. u
3 4| 1 675 |1.125 25222 3.280 Entomostraca somewhat more abundant than jin
July 21/Thompson s Lake} 30 m. “ils ero eee ee 591 1.844 the preceding test. Plankton polymixic,
45 LG 2008 (235 : : yee 4-223 | Much silt and debris. Polymixic plank
AN 2 || Ae bose 175 | - qouo 1.375 4.062 : : Plankton. £7-
Aug.28| Illinois River gzom.| 4] av. | .200/.... 3 A Pe i. 1.222 ; 4 144 MOSEL AEE, syncheta, Protop yas
Ble || a AS aaa) eee eno 3.600
5) 1 | -275 | .250 : : .08 1,000 | 160,932 | 310,470 1.929 eae
5 3 SAID | agen 5 R aude Loe 1.968
30 m. 5 5 .170 sees +799 2.090
5| 7 | -260 Sci0g 682 aoe
5 | av. | .239 5680 934 2.000 | Very little debris. Polymixic plankton. Rotifera
Oct. 14|Thompson’s Lake — —| ——|— especially Syncheta, Protozoa, Entomostraca,
5 ; “400 250 4 a tae Protophyta, and diatoms. Largely small forms, —
15m.| 5] 6 | .200 areas ‘ : 425 1.720
By 3 |) tle) ceooe 694 | - 567 1.860
5 | av. | .163 | ...-- : .552 1.738
_—_——_ — oT oe | Ne ee
s 20 cm. below | 30m.| 5] I {1-375 |3.200 | 2.625 2,071,384 3.740
ae a suntace 15m. | 5 | 2 {1.800 | 24pe | 1 500 11,830,862 2.118 | yonotonic plankton. Principally Syacheta, a
a Reeaselow, igor | 5 | 4 [ncos0) |/..00) | euenctrs |e cam ager |) 503)702)| eer cried tea few Synura, nauplii, Brachionus, and Codonella,
8 surface 15m.}| 5| 4 | -900] ...- (THEY AG |i Sooo || poooss
oe =| lea [ie ee Ee Ee ee ee eee
1897 |
5 2 -425 168 1.706
Bm.) 5) || 3) I) +359 2.780
5 | av. | .388 2.114
5] 5 |} -55° 2.581
Iom.| 5] 6 680 2 ae
5 | av. | .615 2.508
|) i |) ola |] coec ence
15 m ©) |) a889 |i sone ee
x 5 ave B77 Sh | eters 3.299 Small SN EE debris, Polymixic
July 27/Thompson’s Lake 5 se hee ——— plankton. Leptodora, Cyclops, nauplii, Difiugia,
20m.| 5| 12] .650 | 33 oe and Flagellata.
a 5 | av. | .825 | 3.867
i 5 14 | .720 fe hea)
je 15 | -550 j 6.996
[si 5.208
5} 1 | .725 |2.050 tee cont
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gom.| 5] 7 | -950 Oe Weta 1.868 |
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5 | av 879 8.700 {| 203,712 4969 }

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264

The coefficient has been computed in each case on the ba-
sis of measurements by the gravity method, by the centrifuge,
and by enumeration of all the larger and quantitatively more
important constituents of the catch. An examination of the
table will indicate that the relation and direction of the dif-
ferences of the various coefficients do not materially differ by
the three methods. Theresults by the enumeration method
give the largest coefficient—probably as a result of the elimina-
tion of the silt factor in some instances, and possibly by reason
of the large margin of error involved in the method.

It is evident from the table that an average of a number
of catches, not only by the net but also with the pump, should
be used if empirical coefficients are to be established with ac-
curacy. It is probable that the low coefficients seen in a few
instances result from insufficient pump catches, or from some
error in paralleling the catches. Since the coefficient problem
was eliminated in our later work by the use of the pump, fur-
ther efforts to establish empirical coefficients were abandoned

for lack of time to carry on more elaborate tests.
Three alternatives were thus before us. First, to adopt
the coefficient computed according to Hensen’s formula, and
use this one factor, 1.32, for all catches irrespective of the age
of the net and of seasonal, local, quantitative, and qualitative
differences in the catch. This method Apstein (96) and other
Kuropean planktologists have adopted. Reighard (’94), Ward
(95), and Juday (97) have also followed this plan, but in each
case they were dealing only with catches taken in midsummer
from the same or similar bodies of water, and the resulting
error thus introduced was much less than would result from
the adoption of a uniform coefficient for our varied catches.
Furthermore, we had the evidence of the probable extent of
this errror which the pumping method afforded.

A second alternative was to ignore the coefficient question
entirely ; but this involves even greater distortion of the prob-
able seasonal and local fluctuations in the plankton.

A third method, and the one finally adopted, was that of

265

assigning an empirical coefficient to each catch. This coeffi-
cient was decided upon after analysis or inspection of the plank-
ton, and in view of its quantity and constituent organisms, the
amount and nature of the silt, and the age of the net, the basis
of estimation in each case being the coefficient test by the
pumping method whose conditions most nearly approached
those of the catch in question. These coefficients were decided
upon without knowledge of or reference to the effect which
they might have upon the theoretical questions arising from
the analysis of the quantitative results, and prior to the organ-
ization and analysis of the volumetric data.

Obviously this latter method involves both possible and
probable error in estimation of similarities and differences in the
catches examined and in maintaining throughout a uniform
standard. Nevertheless, for plankton catches as varied as those
with which we deal, it is probable that this method involves less
distortion of volumetric results than the omission of the coeffi-
cient factor or the adoption of a uniform factor for all catches
irrespective of the fluctuations in this factor as revealed by
our field tests. Accordingly all of the volumes of catches by the
drawn net, of plankton, silt, and total catch per cubic meter
recorded prior to May 20, 1896,in Tables III.-IX. have been
computed with this coefficient as one of the factors, the actual
factor employed being given in the tables in each case.

The results of my efforts (see Kofoid, 97a) to find an ade-
quate correction for the loss by leakage through the silk by the
use of hard-pressed filter paper and the Berkefeld army filter
will be discussed in another connection.

The volumetric data of the plankton at the seven stations
(see Pl. II.) at which periodical collections were made, name-
ly, the river channel (E), Spoon River (M), Quiver Lake (C),
Dogfish Lake (L), Flag Lake (K), Thompson’s Lake (G), and
Phelps Lake (F) will now be discussed, and the general ques-
tions arising from the investigation as a whole will then be
treated.

The chronological series of collections at these seven

266

stations included in this discussion number in all 6438, distrib-
uted as follows: Illinois River 235, Spoon River 386, Quiver
Lake 115, Dogfish Lake 48, Flag Lake 44, Thompson’s Lake 99,
and Phelps Lake 67.

ILLINOIS RIVER CHANNEL, STATION E.
(Table III.; Pl. 1, V., VII.—XIIL.)

DESCRIPTION OF LOCALITY OF COLLECTION.

The collections were made two and a quarter miles above
the city of Havana, a short distance above the outlet of Quiver
Lake (Pl. II.), at a point where the river was about 500 feet
in width at low water and about 600 feet from crest to
crest of the banks, which are here fringed by willows (Salix
nigra and S. longifolia) on both sides. The eastern shore is a nar-
row spit, 6 to 8 feet above low water, separating the river from
Quiver Lake. The western bank is higher, 8 to 10 feet, and is
covered by bottom-land forest. This is also a spit or “towhead”
between the river and Seeb’s Lake. At low water (PI. IV.) the
eastern bank is exposed asa gentle declivity of 25 to 40 feet,
while the western one is much wider—a belt, 50 to 75 feet in
width, of soft black mud with gaping cracks (PI. V.). A short
distance from the low-water shore-line the bank shelves some-
what abruptly to the bottom, which with the exception of a
slight ridge wear the center of the channel extends in an un-
broken level from side to side of the stream. The depth at low
water for a width of over 400 feet is 8 to 9 feet. ‘To the north-
ward the river deepens slightly, while towards the mouth
of Spoon River it shoals to 6 feet, and below it to less
than 5 feet. The banks are of black alluvium, hardened
in the upper levels by exposure at low water, but al-
‘ ways soft and treacherous near the low-water line. The bot-
tom in the channel is firm, being a compact bed of heavy blu-
ish mud mingled with sand and the shells of Unionide, which
form in many places continuous beds of large area.

A slight curve in the river above our plankton station shifts
the current at that point towards the eastern shore, but at the

267

point of collection the run of driftwood in the stream exhibited
no marked difference in current in the channel for an extent
of fully 400 feet. Approximately uniform conditions thus pre-
vail over a considerable extent of the river channel at this
point. At high water (Pl. III.) the banks are submerged, but
aside from increased rapidity and some lateral extension there
is no noticeable difference in the conditions of the current.

MODIFICATIONS OF METHODS AT THIs STATION.

Collections made by the oblique-haul method were always
taken on the western side of the stream, across the current
from a point in deep water; the surface end of the haul being
completed in shoaler water. At times of high water it was
necessary, both on account of the strength of the current
and the depth, to shift the apparatus still more towards the
shore, and, finally, in the flood of December, 1895, to abandon
the method and substitute temporarily a series of four to six
vertical hauls, amounting to about 30 meters—the usual dis-
tance of the oblique haul. These were made in midstream
from a floating or anchored boat, and were continued from De-
cember 27, 1895, to May 20, 1896. After the adoption of the
pumping method on the latter date the boat or launch was at
first allowed to drift with the current while the collection was
made. Owing to frequent difficulty caused by the drifting of
the boat into shallow water by the wind before the catch was
completed, we finally adopted the plan of anchoring the boat
or launch in or near the mid-channel while the collections were
being made.

During the winter season, owing to air-holes and weak
places caused by the irregular melting of the ice upon the low-
er surface, the ice on the river channel was rarely firm enough
to permit safe transit of our plankton outfit, whose total
weight was over 800 pounds. Steel runners were placed upon
the bottom of the boat, and by the aid of ice hooks it was. pos-
sible to run over or to break one’s way through thin or
rotten ice to the mid-channel station, where open stretches of

268

water were not infrequently found. In a few instances, owing
to roughness and rottenness of the ice, it was not possible to
reach the point up-stream where the collections were usually
made, and in such instances the catch was taken nearer Ha-
vana but always above the mouth of Spoon River (Pl. L.). Even
when the ice was running at the time of break-up, it was
possible by floating in rifts of the floes to secure a catch of
the channel plankton. Thus in all seasons our catches at this
station are typical of the channel plankton.

CHRONOLOGY OF COLLECTIONS.

As shown in Table III., the collections at this station cover
the period from June 12, 1894, to March 28, 1899, in which
time catches were made on 235 different days, 10, 50, 76, 34,
52, and 13, respectively, for the several years included. The
interval between collections in 1894 (Pl. VIII.) ranges from 14
to 34 days. In the first half of 1895 (Pl. IX.) they were few
and irregular, but four being taken, while in the second half of
that year 46 were taken at intervals of one to twelve days, the
interval varying with flood conditions, since an attempt was
made to follow closely the effect of changing river levels upon
the quantity of plankton. The December flood of this year
was followed at intervals not exceeding five days until Februa-
ry 10 of the following year (Pl. X.). From this time till April
24 the intervals average about seven days, in no case, however,
exceeding eleven. From this date till the end of August, 49 col-
lections were made at intervals of one to seven days, following
thus closely the fluctuations attendant upon the two recurrent
floods of that season (Pl. X.). The field station at Havana was
then closed, and until it was reopened in the following July
fortnightly or monthly trips were made to Havana for collec-
tions (Pl. XI.). From this time until the suspension of opera-
tions March 28, 1899, the collections—with the exception of a
few extras and two delays due to sickness—were made at regu-
lar weekly intervals (Pl. XII., XIII.). Thus, in one or another
of the years in question all months but October, November,

269

February, March, and April have been covered by collections
at intervals of five days or less, and from July 14, 1897, to March
28, 1899, a period of nearly twenty-one months, the series of
regular weekly collections is almost unbroken. The following
table gives the distribution of the collections by months in the
several years.

DISTRIBUTION OF COLLECTIONS BY MONTHS.

Ver | SIS} a) ale) a) Ss) ela d ere s

Slelz(slSlSiSi4ialoialale
1894 DNB I 2 I I I | 10
1895 I 2 I A TO Eh Fy ai] |) So
1896 QO Al Sil Si] oOo] Biwi wa) 2) Qi wi Bl 7
1897 2 ie es ea ee Sn Se meeal Se Selle dale 3A
TOQGMESH | elie Oued Ay AW Bog A bi Sige
1899 Bale 4a: nd: 13
Total | 17 | 15 | 15 | 12 | 15 | 16] 30 | 35 | 27 | 17 | 16 } 20 |235

The distribution by months is such that a fair basis is
formed for the determination of the seasonal fluctuations,
since every month is represented by a considerable number of
collections. The larger numbers in the summer months re-
sult from the fact that the field station was always open dur-
ing this season. . The total number, 235, is more than twice
that made at any other station in our field of operations, and
affords the most complete and longest series in our collections.
It is fitting that in this our most variable station the interval
between collections should be least. The total period covered
by our collections here is a little over fifty-seven months, and
the average interval between collections 7.4 days. I know of
no series of quantitative plankton collections, in any waters, of
equal range or time, variety of season, and brevity of interval.

THE LOCAL DISTRIBUTION OF THE PLANKTON AND ITS RELATION TO THE LIMIT
OF ERROR IN THE METHOD.

The investigator of plankton problems is constantly con-
fronted by the question of the extent of the error resulting

270

from the assumption that a collection at a single place is rep-
resentative of a larger area—an assumption necessary if any
wide significance is to attach to the analysis of plankton data.
It has been a matter of observation that the quantities of plank-
ton taken at different places in a body of water, or even within
very narrow limits, are not equal in volume under similar
methods of collection. Thus, Apstein (96) in eighty catches in
German lakes finds the average deviation from the means
to be 5.52 per cent. when the plankton is computed per square
meter of surface. Of the eighty catches 68 or 85 per cent. ex-
hibit a departure of less than 10 per cent. from the mean, and
only four have a departure in excess of 15 per cent. These de-
partures are derived from averages of comparable collections
on various dates and in several different lakes in groups of only
two to five, evidently from mid-lake waters, and hardly afford suf-
ficient data for an analysis of the conditions of distribution in
any given lake or inatypical lake, since on account of their small
number they do not throw any light onthe effect of shore, tribu- -
tary waters, vegetation, currents, or other factors of the environ-
ment. They indicate, however, the probable error of +5.52 per
cent. in mid-lake collections, and seem hardly sufficient to sub-
stantiate fully the more general conclusion that “das Plankton
sehr gleichmassig in einern Seebecken vertheilt ist.” Reighard
(94) finds in the case of twenty-nine hauls that his results
“agree very well with that of Apstein.” Of his twenty-nine
hauls, 26, or 90 per cent., have a “percentage of difference from
the average” which is less than 20. These percentages yield,
I find, an average of 9.7 per cent. to Apstein’s 5.52 per cent.
Reighard does not, however, compute his “percentage of dif-
ference from the average” in thesame manner as Apstein deter-
mines the “Abweichung von Mittel,” the former using the vol-
ume of each catch as the basis for the determination of the per-
centage of difference from the average, while the latter
employs the average of the two or more catches for this base.
Obviously this slightly increases one half of Reighard’s percent-
ages and decreases the other half, though it does not materi-

271

ally affect the average of all of them. Apstein’s method of
stating the + error in terms of departure from the mean is, it
seems to me, to be preferred to the “percentages of difference”
which Reighard uses.

In all instances but one Reighard averages but two collec-
tions, made at some one of fourteen points of collection in Lake
St. Clair. His percentages of difference, therefore, refer only
to these individual points of collection and not to the lake as a
whole. His collections were all made within an interval of ten
days, and it is probable that the results can be used to deter-
mine the departure from the mean in the lake as a whole.
This he has not done, though he concludes from these percent-
ages of differences of the pairs of collections that “the plankton is
distributed over Lake St. Clair with great uniformity.” In the
case of Apstein’s data the sets of collections are scattered over
several seasons and represent a number of lakes, and range in
number from two to five in each test.

It is obvious that conclusions as to the uniformity of distri-
bution of the plankton in the lake as a whole should be based
upon a comparison of all catches with their average, and are
best expressed in terms of departure from their mean, employ-
ing the mean as a base and expressing the deviation in percent-
ages whose average will constitute the mathematical expres-
sion of the variation in distribution or the + error of the method.
For reasons above stated, this method cannot be applied to Ap-
stein’s data as a whole, though it is the one he uses for indi-
vidual lakes or tests.

Applying this method to the data of Reighard’s (’94, p. 33)
table, asin the accompanying tabulation, I find that the aver-
age departure from the mean is +31.8 per cent., with a range of
+111.5 to—57.5,—a total of 169 per cent,—on the basis of the
amount of plankton per square meter of surface ;and +28.8 with
a range of +91.3to —-55.4,—a total of 146.7 per cent.,— ona basis of
plankton per cubic meter of water—a deviation much greater
than that expressed by Reighard’s method. This deviation
is much greater than that found by Apstein (’96), and it re-

272

sults in large part, doubtless, from the greater number of
catches averaged, and from the fact that they represent a num-
ber of more widely separated points in a larger body of water,

DISTRIBUTION OF PLANKTON IN LAKE ST. CLAIR.

Plankton per sq. m. of surface Plankton per m.° of water

rea rete ve Volume in Departure from Volume in {Departure from

cm. mean in per ct. cm.* mean In per ct.
IIQ 5.00 F< KG) —29.4 1.44 —55.4
Il 5.00 13.38 +31.3 2.68 —17.0
IIIQ 5.54 15.27 +49.9 2.76 —14.6
III 5.54 21.55 111.5 3.89 20.4
IVQ 2.50 5.02 —50.7 2.01 = 37 8
IV 2SO) 5.02 = 5On 2.01 = 37/3
VQ 5.26 14.40 +41.2 2.74 —I15.2
V 5.26 19.04 +86.8 3.62 +12.1
VIe 4.70 10.03 +-7.2 2.29 ae ZOR
VI 4.70 14.69 +44.2 3.08 —4.7
VIIa 1.17 4.32 = 57/05 3.69 +14.2
VII 1.17 4.32 S575 3.69 +14.2
VIIIQ 4.44 II.99 +17.1 2.70 —16.4
VIII 4.44 13.36 +31.1 3.01 —6.8
IXQ 4.28 10.88 +6.8 2.54 Pi 3}
IX 4.28 10.22 +0.3 2.39 —26.0
XQ 1.50 6.23 —38.8 4.15 +28..5
x 1.50 6.23 —38.8 4.15 28.5
XIIIQ Deal 10.59 +3.9 4.79 +48 .3
XIII Ph Pik 8.76 —14.0 3.97 =|22.0
XIVaQ 2.89 10.41 +2.2 3.60 +11.4
XIV 2.89 9.56 —6.2 3.31 $2.5
XVQ 5-17 9.2 —8.8 1.80 —44.2
XV 5.17 12.50 5-22, 2.42 2501
XVIQ 4.55 8.65 —I15.1 1.90 Al 2
XVI 4.55 10.61 +4.1 2EBB —27.8
XVIIIQ 1.27 7.09 —30.4 5.58 +72.8
XVIIIQ, | 1.27 6.13 —39.8 4.83 +49.5
XVIII 1.27 7.85 —22.9 6.18 +o91.3
Ay. 10.19 +31.8 BEB) +28.8

Range -FIII.5 to —57.5 + 91.3 to —55.4

in which currents, vegetation, shore, and bottom are important
factors environing its plankton.

This large variation in the distribution of the plankton in
lakes naturally raises the question whether there is in the
channel of a running stream, for example the Illinois River, a
plankton whose uniformity of distribution is such that a collec-
tion made ata given place and time may be considered as a fair

273

sample of the contents of the water in contiguous parts of the
stream, or of the plankton present in the water passing a given
point of the stream for any considerable length of time. Will
not the conditions pertaining to fluviatile life cause such local
variations in the plankton and such changes in it from day to
day that chronological series of isolated collections will reveal
only erratic and meaningless fluctuations, without significance
for the analysis of the factors of the environment and incapa-
ble of revealing an orderly regimen of aquatic life? In other
words, is the river a unit of environment sufficiently compact
to yield, by the plankton method, data of scientific value com-
parable with those derived from other bodies of water, types of
which we find in the sea and the lakes ?

As contrasted with the lake, the river as a unit of environ-
ment presents a constant and excessive predominance of the
longitudinal over the transverse axis. This feature, combined
with the fact that in a river the relative shore development is
much greater than it is inthe lake, makes it necessary to discuss
the longitudinal and transverse distribution of the plankton in
the stream separately.

LONGITUDINAL DISTRIBUTION.

With a view to testing this question ofthe local longitudinal
distribution of the plankton in the Illinois River, I made a series
of ten catches in immediate succession from a boat anchored
at our usual station in mid-channel on October 29, 1896. This
was at a time of a considerable autumnal development of Sy-
nura and Syncheta, and the quantity of plankton present (see
Table III.) was sufficient (Pl. X.) to allow room for considera-
ble fluctuation and to minimize the error attributable to meas-
urement.

In the following table the volume of the centrifuged plank-
ton per m.3 and the deviations from the mean in volume and in
percentages of the mean are given.

The similarity in the amounts of these successive catches
is Shown in the fact that the average departure from the mean
catch is only +3.58 per cent. and the total range of the limits of

departure only 14.1 per cent.

274

I know of no test of similar ex-

tent elsewhere with which this may be compared, but its range
is well within the limits of the records of repeated catches in

TEN CONSECUTIVE CATCHES FROM ANCHORED BOAT.

Vol. of catch :

Departure from average

DEPARTURES FROM

No. in cm.§ per m.” jin wolunae | In percentage
I 3.20 + .07 =o
2 3.24 oP ill +3.4
3 3.04 — .09 2)
4 3.40 = 27 +8 6
5 3.06 — .07 —2.3
6 3.20 EO, 2.2
7 2.94 = 410 Bab
8 3.20 + .07 +2.2
9 2.04 — .19 mle
10 3.10 OS Ts
Average 3.13 —+— 112 +3.58
Greatest + SP off +8.6
Greatest — — +19 Ten

IN GERMAN LAKES BY APSTEIN (96, pp. 56-57).

MEAN CATCH COMPUTED FROM HAULS FROM EQUAL DEPTH

Ap- No. | Average catch | Average depar- | Limits of depar-| Total
stein’s of i : ture from mean | tures of percent- | range of

No. hauls in cm." in per cent. ages. departure
23, b-d 3 4.66 DBD — 3.4 to+ 3 6.4
26 a-c 3 5.5 6.1 — 9.1 “ + 9.1 18.2
27 a-e 5 4.1 7.8 —14.6 “ +15.9 30.5
28 a,b 2 4.5 I1.1 —I1.1 “ +I! 2202)
30 a,b 2 9.12 1.3 = Jin 8 Se 33} 2.6
32 a-c 3 13.2 4.3 — 5.3 “+ 6.1 11.4
33 a,b 2 26.3 6.4 —- 6.7 “ + 6.7 13.3
33 dye 2 15.5 BoP — 3.2 “ + 3.2 6.4
34 a,b 2 17. 8.8 — 8.8 “ + 8.8 17.6
37 a-c 3 2.43 8.6 — 7.4 “ +13.2 20.6
41 a,b 2 1.5 13.3 —13.3 “ +13.3 26.7
43 a-c 3 1.93 19.5 —17.1 “ —29.5 46.6
46 a,b 2 2. Oo. Oo. Oo.
65 a,e 2 3-3 Tell = 99 SO Se Toll 15.4
73 a,b 12 2.5 Oo. Oo. O.
45 a,b 2 1.2 8.3 — 8.3% + 8.3 16.7
47 b,c 2 I. Oo. Oo. Oo.
63 a,g 2 1.23 23) =- 2.5 “ + 255 5.
68 a,b 2 0.1 O. Oo. Oo.
69 a,b 2 --0.1 O. O. O.
70 a,b 2 0.16 oO. O. Oo.
24 a-c 3 I. O. oO. oo
83 a-c 3 1.13 3.8 — 2.7“ + 6.1 8.8

275

smaller number in waters of European lakes. For example,
Apstein (96) records 23 instances of hauls on the same date
from equal depths and evidently in every case within distances
between catches /ess than that represented in the extremes of
our test. The number of hauls did not, however, in any of his
tests exseed four. I have compiled or computed from Apstein’s
table (pp. 56-57) the average and limits of departure from the
mean in these 23 cases. In 12 of the 23 the average de-
parture exceeds +3.58 per cent.—the average departure in
our test, in which there were from two and a half to five times
the number of hauls. In 10 of the 11 instances in which the
departure from the mean in Apstein’s records falls below +3.58,
only two hauls were averaged. The total range of the limits of
departure also exceeds that found in our test in 8 of the 23 cases.

In the light of Apstein’s results and considering the larger
number of catches averaged in our test, and also the considera-
ble length of the channel that it covers, it seems beyond rea-
sonable doubt that single catches of the plankton inthe channel
of the Illinois at our station of collection afford as trustworthy
a basis for the analysis of plankton problems as do similar
catches made in a lake. The margin of error thus introduced
is no greater, if indeed so great, as that appearing in investiga-
tions in such waters.

Since these catches were made from an anchored boat, the
water from which the plankton was taken was distributed over
a considerable length of the stream. The test was made between
7:30 and 9:30 a.m. The river stood at 5.1 ft. above low water
and was falling rapidly, so that the current was noted at the
time as unusually swift, probably approaching two miles an
hour in mid-channel at this point. At this rate the collections
represent plankton taken at ten intervals from a body of water
about three miles in length. This areal distribution is compar-
able with, if it does not exceed, the limits of widest distribu-
tion of catches in Apstein’s tests, but it is much less than that
of Reighard’s, which lay within an area of about ten by thirty
miles.

276

A series of ten consecutive hauls made on the afternoon of
August 21, 1896, from a floating boat between the bend in the
river above the plankton station and the towhead below it (PI.
II.) throws some lght on the questions of local distribution and
of variation in catches from a limited area. Owing to the wind
it was not possible to float with the current, and the apparatus
also served to impede the boat. The river stood at 7.1 ft. above
low water and was falling slowly, so that the current was not
so strong as when the ten were made from the anchored boat.
The test occupied about eighty minutes, and the boat drifted
about a mile, so that the body of water actually passing it,
from which the plankton was taken, was less than half a mile
in length. Considerable dislodged vegetation and some cattle-
yard debris were floating at the time, causing more than
the usual inequality in the distribution of the silt which
these elements introduce into the plankton. The catches
ranged in centrifuged volume from .4 to .575 cm.3, averag-
ing .48, and showing an average of divergence of + 11.2 per cent.
from the mean, with limits of +19.9 and --16.6—a total of 36.5
per cent. The divergence in this test is greater than that
from the anchored boat, owing in part to the floating debris,
and in part, probably, to the fact that the wind drifted the boat
across fully three quarters of the channel.

These divergences, both in average and limits, fall within
the figures of parallel catches in lake waters quoted above from
Apstein (96) and computed from Reighard (94). The fact
that the range of variation on the whole is greater than the
average run of Apstein’s results is doubtless due in part to the
larger number of catches included in my test.

These two tests thus indicate that the plankton of the
main channel waters of the Illinois at the point where our col-
lections are made, is distributed quite as evenly as that in lakes
thus far examined from this point of view, and in consequence
single collections may be utilized for the study of plankton
problems with no greater error for the potamoplankton than for
the limnoplankton. The divergence from the mean will upon

277

the average, in all probability, fall within +10 per cent.

Our chronological series of collections affords a few instan-
ces of catches under somewhat stable conditions of river levels
and temperature, and at intervals so short that they may be
utilized as tests of local distribution within certain larger limits
of error, since the utilization of such data introduces the er-
rors resulting from changes of chemical conditions due to rot-
ting of sewage, and from growth, reproduction, and destruction
of the plankton in the interim between collections. The follow-
ing tabulated instances (p. 278) from Table III. and Plates X.
and XI. may be cited as throwing light on this question of local
distribution along the length of the stream.

The fourteen groups of collections were selected with refer-
ence to stability of conditions, therefore in falling or low water
and in periods of relatively even temperatures. Inspection
of the tables and plates above referred to will show that the
selection has not been made so as to eliminate wide varia-
tions, and it may therefore be regarded as fairly typical. The
periods included, range from 2 to 15 days in extent, and
upon estimated rates of current the several tests include plank-
tons taken at intervals in reaches of channel water from 24 to
252 miles in length. The average departures from the mean,
range from +0 to +29.8, and yieldagrand average of 14.1. In
view of greater number of catches averaged and extended
time element involved, these results compare very favorably
with those derived from Reighard’s data and Apstein’s results.
The probable error resulting from variations in the longitu-
dinal distribution under stable conditions seems to be less than
+15 per cent.

An inspection of Table III. and Plates X.-XIII. will show
that in the case of invading flood waters the departures from
the mean of catches at similar intervals would be considerably .
greater than the averages above computed. Also, thatin case
of plankton pulses in stable conditions—for example in Sep-
tember and October, 1897—collections at weekly intervals may
exhibit departures in excess of +50 per cent. Itis evident, how-

LOCAL DISTRIBUTION

278

OF PLANKTON

IN RIVER AS SHOWN BY CHRONOLOGICAL

Esti- |
mated | mated

No. of | rate of | range

group | cur- in
rent

| Esti-

5 3715, || iets)
6 6 115
{
7 BW Bh)
l
8 2.5 252 ,
9 2 720 :
5
10 2 720 {
(
II I 24 {
12 I 48 {
13 075 108
i
14 6 | 43.4 4
Av. | |

oe
Aug.
2 5 36

CATCHES.
[Be reieea eget al De- Av. | T'lrge
| Temp. | Stage Catch | parture depart.| of limit
Date (F.) at of per from |inper | in per
bott’m | river m.? mean in| ct. of | ct. of
per cent |mean | mean
1895 i
July 29 | 75-5 | 5.3 “47 | 1-223
wa 8 | WS |) Azo 74 —22.3 | =22-3] 44.6
Aug. 5 | 79. 3.13 -95 (o)
BN oS. 2.63 .95 oO 2 @
Aug. 12} 82.5 | 2.40 5.94 =—1.2
«75 83.2 | 2.38 | 6.08 | -er72 ==) 2) zea
Aug. a 78.5 2.35 7.87 tes
Zo) 79: Zo) 4.32 19,8
“ 29] 80 2.58 3.92 —26. | =24-3) 74.5
BM Wao 2.65 5.08 4.1
Sept.5 ! 72.5 | 5.70 1.48 +22.3
G TPs 6.85 1.16 + 4.1
Go || op 5.88 .86 —28.9 |+17-6| 51.2
CO | 725° |) Dosis 1.48 La
cea TOT ile 4.25 1.06 —12.4
Sept.12] 78. 3.90 2.92 +27
BWA W503 || BoB | Bod) — |) yg
BO Wha |, 3029 1.91 =17, +29.8| 91.3
GSS | oS) |p bol) I —aas.3
20) aor 3.20 1.98 —13.9
Sept. 23} 76.5 | 2.75 1.37, | +15.1
HW) 25 7202 |) Boek) 05 —11.8 |+10.4| 26.9
GB 9 7B. 3.23 1.14 = 2
1896
Jan. 6 | 32.2 | 12.20 51 —42.7
8) |) 321) | 190 1.21 +36
“to | 32.3 | 11.40 1.02 Hie G 25 78.7
“ 13 | 32.4 | 10.80 83 = 16.7
Jan. 15 a 10.40 ue —j0.2
2 OMG Ze 9.50 1.81 7
G0) oI WB 8,60 2.36 ALR +10.8]| 26.8
2%) || BVl8} || Wall 2.18 4 ©,9
Mar. 9] 37.1 | 10.20 4.96 Gi OT
GT S59 || C70) 5.08 = 8.8 || 6.6 15.9
GDA) EOo7/ 8.80 5.80 SETORS
Apr. 2 71.8 | 6.90 | 17.07 Oe |.
r Be 67.5 | 6.90 | 16.91 ieee 0.5 I
Apr. 2 70. 7-10 9-93 28.1
May ; 68.8 | 7.10 5.00 ae == 20) Kil 5 On
Aug. 15 | 78. 7-40 2.32 JL ia
«8 | 78. | 7-50 | 2.72 | 418.8 | i128] 38.4
Go || 9f3 7.10 1.84 =sTOLO
Aug. 26 | 77 6.50 1.44 = 77
eo 2 \\ 7A 0800) |) 0 rs68) aston 7/5720 lee
i | [=14.1[ 37-4

279

ever, that in all tests extending over many days other factors
than variation in local distribution come in to modify the re-
sults.

LONGITUDINAL DISTRIBUTION FROM THE MOUTH TO HENNEPIN.

By courtesy of the Illinois State Fisk Commission I made
on May 18-21, 1899, a trip on their steamer “Reindeer” from
the mouth of the Illinois to Hennepin, about 205 miles from
the mouth, making ichthyological collections for the State
Survey. Incidentally plankton collections were also taken
continuously from a short distance above the mouth to Henne-
pin—in all, 21 collections. Of these, 19 will be utilized in the
following comparison, the first being omitted because of uncer-
tainty as to the distance, and one other because of loss of the
collection. The catch was made by means of a 14 in. iron pipe
carried from the guards of the boat to a depth of 18in. below
the surface of the water. The intake was redueed to ? in. and
turned toward the prow of the vessel, so that, while moving, a
continuous stream of water was discharged into the plankton
net, immersed in a barrel on deck. In this fashion a con-
tinuous stream from the level of the intake was filtered. The
contents of the net were removed approximately every ten
miles of transit, and its clogging to the point of resistance pre-
vented by shaking it down whenever necessary, thus minimiz-
ing, in part at least, this source of error. The following table
gives the data concerning these catches and the measurements
and silt estimations,* together with my computations of the de-
partures of the total catches from their mean and of the esti-
mated planktons.

The distances between points of collection were not deter-
mined with great accuracy, since we had no log, and maps give
no clue to the not infrequently tortuous steamboat channels.
The distances are therefore approximations based on the expe-
rience of the pilot and engineer in charge of the boat.

*By the generous permission of Professor Forbes, centrifuge measurements and

silt estimations have been kindly furnished tome by Mr. R. E. Richardson, who is
preparing for publication in this Bulletin 4 detailed report upon these collections.

| wel Vol. in cm.3 Departure from
| : 21 SO 18.3 of catch mean in per cent.
No. | Location Time = | OWS el
‘ A = eis 8 FV ok! | To- Total Dawns
| | 22 ton Silt | tal catch ton
1 |1m.above ,Hardin..... 5:45-6:45 p. m. 10; 72 | 60 |; .18 26 44 — 85 — 75
2 |Kampsville Dam......... 6:45-7:45p. m. 08 | 71 | 80 | .23 | .91 | 1.14 — 61 — 68
3 j1m.aboveC.A. bridge| 4:30-5:45 a. m. -08 | 69 | 90 | lost
4 |Florence.. 6:00-7:05 a. m. 03168111099) 5027s Disa IN 2534 — 21 — 97
5 \Mauvaise Terres ‘Cr’k| 7:10-8:10 a. m. -04 | 68 | 98 | .05 |2.36 | 2.41 — 18 — 93
6liNMeredosiane == 8:10-9:15 a. m 04 | 69 | 95 | 11 12.15 | 2.26 = 2B} — 85
4 \Wa Grange ........ ....... 10:00-11:00 a. m .04 97 | .07 |2.21 | 2.28 — 24 — 90
8 |Beardstown ...... .-... 11:00-12:00 a. m 04 88 | .22 |1.61 | 1.83 — 38 — 69
9 |Browning. 0 .-...: 2:45-3:45 p. m .05 95 11 {2.15 | 2.26 — 23 — 85
10 |Holmes IEE SSIES Roa 3:45-4:45 p, m .05 10 /1.80 .20 | 2.00 — 32 +153
TUL, SIAN EOE nese cease ceecas 6:15-7:30 p. m 05 80 53 |2.13 | 2.66 = 0) — 25
12. |Liverpool. ..... 4:20-5:20 a. m 04 |67.5| 50 2.12 |2.12 | 4.24 + 44 +199
13 |2 m. above Copperas”
Creeley ke ees 5:25-6:30 a. m 04 1 68 | 80 '1.32 15.29 | 6.61 +125 + 86
14 Mackinaw ‘Creek. 7:10-8:20 a. m 05 { 67 | 70 |1.47 |3.42 | 4.89 66 +107
15 |6m.above Pekin._..._| 8:40-9:45 a. m, 06 | 67 | 90 95 | 8.59 | 9.54 +224
é J 9:50-10:10 a. m o
16 |7 m.above Peoria... | 12-12:40 p. m 08] 67 | 60 |2.19 |3.29 | 5.48 + 86 +209
17 |Chillicothe Park...._.... 12:50-1:50 p. m 12} 66 | 15 | .92 16 1.08 — 63 + 30
18 |1m. below Lacon .......! 2:30-3:40 p.m 15| 66 | 20 | .88 22 | 1.10 162 + 27
1O/a||Elerirayet nee ae TO | 4:00-4:55 p. m 20| 66 | 88 | .12 | .90 | 1.02] — 61 =
20 |Hennepin -................ 5:20-6:30 p. m 20} 66 | 95 | .12 |2.20 | 2.32 — 21 — 8
Average | 71 2.23 | 2.94 +57 | E89

An inspection of the data of this table at first gives little
comfort to one desiring to establish even an approximate uni-
formity in the distribution of the plankton along the length of
the stream. The average departure from the mean is +57 per
cent. in the case of the total catch and +89 per cent. in the esti-
mated plankton, with ranges respectively from --85 to +224,
a total of 309 per cent., and from --97 to +209, a total of 306 per
cent. This is greatly in excess of the figures above given from
the work of Reighard and of Apstein, and as a whole the data
are So aberrant as apparently to disqualify them for scientific use.

If, however, we take into consideration the conditions un-
der which the collections were made, the aberrancy of this se-
ries loses its force. In addition to the errors introduced by the
slight clogging of the net and the uncertainty as to the precise
distance, there is an error of undetermined proportions caused
by the vertical movement of the planktonts and consequent
possibility of uneven distribution at the 1$-in. level between
4:30 a. m. and 7:40 p. m.—the extremes of our time of collection.

Furthermore, an examination of the planktographs in the
river and its backwaters for 1896 and 1898 (Pl. X., XIL,
XXVIII, XXIX.,XXXI., XX XIII.) —in which years the collec-

281

tions were sufficiently frequent to trace the movement in plank-
ton production—shows that this season of the year is wont to
be a period of rapid change in plankton content. Thus, in the
river in 1896 on May 13-18 the plankton fell from 3.56 to .86, or 76
per cent., in stable hydrographic conditions. A similar phenome-
non may be involved in the fluctuations in plankton content
found in this transit of the river. The time intervening between
the first and last collections was a little over two days. T’o this
must be added the consideration that the collections represent
a strip more than 200 miles in length, since we were traveling
against the current, and, furthermore, that we have to deal
with the volumetric changes in plankton content, as it passes
down stream, due to growth and decay.

Allof these influences areapparently butslightin comparison
with the effect of certain environmental factors which are local-
ly dominant within certain sections of the river. Wecandistin-
guish on the days of collection four sections or minor units of en-
vironment dominated by different factors. The frst three col-
lections made in the lower river lie in a region of comparatively
clear water free from flood invasion. Unfortunately the third
collection was lost, but the remaining two exhibit a departure
in the case of the estimated plankton of +12 percent. and of +44
per cent. in the total catches. The next six collections, covering
a stretch of 60 miles, from Florence to Browning, were all taken
in a section of the river invaded by flood water of recent origin
and poor in plankton, as was evident from the increased tur-
bidity, the large amount of drift floating, and the discharge
from tributary streams—principally on the right bank. In such
conditions the amount of plankton (estimated) is small, and its
variations form proportionately large percentages of its mean,
the average departure being +51 per cent., with a range from
—T79to +127—a total of 206 per cent. ‘If, however, simply the
total catch is taken, the average departure is+5 per cent., witha
range of —18to +8—a total of 26 percent. In view of the extent
of the river included in this section—60 miles—and the uneven
distribution of the flood contributions, it is not surprising that

282

we should find such irregularity in the (estimated) plankton.

We now come to the section of the river dominated by the
Peoria-Pekin pulse of sewage, including 70 miles of channel—
from Holmes Landing to Peoria. The flood waters are still in
evidence, but in reduced volume, and there is marked increase
in the plankton content. The average departure from the mean
plankton is +32 per cent., with arange of —64 to +48—a total of
112 per cent. In the case of the total catches the average de-
parture from the mean is +36 per cent., with a range of —60
and +89—a total of 149 per cent.

The upper section of the river, above Peoria, a stretch of
40 miles, was less disturbed by flood conditions, there being
only slight local invasions. This region is within the sphere
of influence of Chicago sewage, and not receiving any large
tributaries, we might expect but do not find conditions some-
what equalized here. The average departure from the mean
plankton is +76, with a range of —76 to +80 per cent.—a total of
156 per cent. The average departure of the total catch is +34
per cent., with a range of —27 to +66 per cent.—a total of 93 per
cent. These departures will be much reduced if we break this
section into an upper and lower region of two collections each,
the percentages falling from +34 to +2 and +0 for plankton,
and to +1 and +39 per cent. for the total catch for the two
sections, each of which represents 20 miles approximately.

The average departures from the mean plankton in the
four sections are respectively +12,+51,+382, and +76 per cent.,
yielding a grand average of —43 per cent.; while the corre-
sponding average departures for the total catches are +44, +5,
+36, and +34, with a grand average of +29.7 per cent. These
four subordinate units of environment represent longitudinal
extensions of 20, 60, 70, and 40 miles. The area included in
Reighard’s Lake St. Clair collections has a length of 32 miles
and a maximum width of 54, and the average departure from
their mean (computed by similar methods for all localities ) is +
98.8 per cent. Similar methods of computation thus yield for
Lake St. Clair and these sections of the Illinois River almost
an identical + error of distribution.

283

In the light of these volumetric data the conclusion is pat-
ent that plankton data from fluviatile environment contain on
the average a distribution error which approximates that in
plankton data from limnetic areas of similar extent selected
with reference to unity of environment as determined by local
factors.

It should be noted in this connection that the conditions
prevailing when this plankton traverse of the [nois River was
made, were most adverse to an equalized plankton in the fol-
lowing particulars. It was at a time of rapid seasonal change
in plankton during the decline of the vernal pulse, and it was at
a time of intercalation of flood water of local and recent ori-
gin, whose poverty in plankton is brought into contrast with
the larger content of the run-off of impounded backwaters else-
-where. Finally, the river stage, which was 9 feet at Kamps-
ville and 6.9 at La Grange, was such that the equalizing effect
of general overflow on plankton content in impounded back-
waters had ceased and local differences were emphasized, while
at the same time their discharge continued in considerable
volume. All of these factors, the last two of which are more impor-
tant in the river than in the lake, tend to diversify the plankton
content in the river at this season. It is reasonable to suppose
that under other conditions—such as general overflow, the
more stable features which attend falling levels above or below
9-7 feet, or in prolonged low water—we should find the uni-
formity of distribution of the plankton more pronounced than
it was on May 18-21, 1599, barring, however, the effect caused
by sewage contamination, which at all stages and seasons is
the most potent factor in the environment of the plankton of
the Illinois River.

TRANSVERSE DISTRIBUTION AND RELATION OF SHORE TO PLANKTON.

The shore is a factor of great importance in the aquatic
environment. It is here that land and water come into most
intimate relation; seepage and drainage waters enter here;
vegetation gains its foothold, affects the gaseous contents of

284

the water, and contributes by its decay to the nutrition of
aquatic organisms; rise and fall of temperature are more pro-
found here in shoal surface waters; light. pervades more com-
pletely; and currents are less rapid. It is in many respects a
less stable region than the central waters which it bounds, and
it may, indeed, be regarded as a separate unit of environment,
in contrast with mid-lake or channel waters.

The effect of the shore-line upon the distribution of the
plankton in the lake has not entered into the data referred to
in the previous section, for in the investigations of both Ap-
stein (96) and Reighard (’94) along-shore collections were not
made, and, moreover, the shore-line is less important relatively
in the lake as compared with the stream. For example, the
absolute development of the shore-line in Lake St. Clair—de-
termined by the method of Seligo (’90) (—shore-line divided by
square root of area) is given by Reighard (’94) as 9.23. In the
Ilhnois River at high water, from Utica to the mouth it is ap-
proximately 17.1, and at low water 78.3, omitting all the con-
necting lakes and bayous, computing the area on the basis of
the average of the low-water widths given on page 110, and ig-
noring sinuosities exceeding that of the channel. The relative
development (absolute development divided by absolute devel-
opment in a circle in which 7=1) in Lake St. Clair is 2.607,
in the Illinois River at highest water, 4.83, and at low water,
22.1. These figures serve to show in a general way the exceed-
ing importance of the shore-line in the environment of the po-
tamoplankton. Owing to the great sinuosities of the shore-
hne as rising waters invade the bottom-land, these figures are
probably very much smaller than actual measurement would
make them. Itis probable that the relative shore develop-
ment in the Illinois is ten times that of Lake St. Clair, and fif-
teen times that cf most lakes.

Added to the diversifying action and predominance of the
shore-line in the river, there is the tendency of its tributary
waters, especially of the smaller lateral feeders, to follow their
shore for some distance. The absence of great sinuosity in the

285

Illinois as compared with other streams, as shown by the
slight ratio of development of the stream (see p. 102), tends to
prevent the rapid mingling of channel and marginal waters,
and thus gives cumulative effect to their differential charac-
ters.

In order to trace the quantitative effect of the shore and
determine the variation in transverse distribution, I made two
series of ten collections each along a transverse line, the first
at our usual plankton station and the second below the mouth
of Spoon River (see Pl. II.). The results of the first-named
test, made August 26, 1896, are given in the following table, to-
gether with conditions of distance from shore, depth, tempera-
tures, and turbidity. The river at this time stood at 6.5 feet
above low water, and had a width at the station of 150 meters.

PLANKTON IN CROSS-SECTION OF RIVER AT STATION E.

e DB @ | Tempera- Centrifuge Enumeration Omitting Omitting
S| Bool ze ture > method method Nos. 1,9, 10] Nos. 1, 8, 9, 10
Sealevaily = GR
OM ON stuillae > amass aa tees YS
ale ie gc2 a | ae De- | Per m.3 |Under 1sq. m.
. - c 1 1: So ar og ina eT eat eS aaa GE
2 18 2) Bo lewis He Bolton i.| ture ND, OF Hine Ie Wie:
o 133] © |¢ Sole ae LOU eeror DEUS | saan pate Dar
S$ § = || ace | tom [Org ee AGEN HOLS D2 aaee Vol-| ture | Vol- ture
a a m.3 | in a in E| |e | me) in
| per ct per ct per ct
1 10 1.68 82 17 33 2.00 | +27.5 143,800 +31.8 3.36
2 37.5 3.96 73 77 .33 1.34 | —14.5 110,000 + 0.8 {1.34 |—22.1 G SY —25.2
3 75 4.88 77.5 v7 45 1.34 | —14.5 95,600 —12.4 }1.34 |—22.1 6.54 | — 7.9
4 85 4.88 77.5 vw 45 lesy) || =" si? 110,200 + 1.0 |1.52 |—11.6 7.42 | + 4.5
5 95 4.27 17.5 au 45 1.44 | — 8.6 109,600 + 0.5 |1.44 |—16.3 6.15 | +13.4
6 105 4.04 71.5 | 77 42 2.36 | +50.5 93,100 —14.7 |2.36 |+37.2 9.53 | +34.2
7 115 | 3.18 77.5 771 40 2.40 | +53.1 112,500 + 3.1 |2.40 |-+39.5 7.63 | + 7.5
8 125 1.68 17.5 17.5 -40 1.64 | + 4.8 110,300 + 1.1 1.64 |— 4.7 [2.76]
9 135 1.22 77.75| 77.5) .38 1.04 | —33.9 109,900 ie Se {1.27}
10 146 0.56 77.75| 77.6| .30 -60 | —61.7 96,200 —11.8 [ .34]
Average | ney || S=enal aeyeD |sera fisal| Sano] wo || sane

The collections were made with the pump, one fourth of a
cubic meter of water taken from bottom to surface being
strained in each catch.

The variation in the catches is much greater in the cross-
section than in limited longitudinal tests, in accord with the
greater contrast in environmental conditions. The marked
decline near the western shore may be due to the marginal
belt of vegetation then present along that side of the river, and

286

the increase in the initial collection at the east shore is caused
in part by the greater abundance of Wolffia drifted there by
the prevailing wind. It is obvious that for comparison with
lake collections these shore catches should be excluded, for the
former are rarely taken so near shore. Furthermore, all our
chronological series on which this paper is based were taken in
mid-channel, far from the shore belt, and in excluding those
marginal collections but one sixth to one third of the total
width of the stream isremoved from the test. After all al-
lowances are made, it is obvious that quantitative differences
in the plankton are much greater in a single transverse trav-
erse of the stream than they were found to be in a longitudi-
nal test extending over approximately thirty times the width
of the stream. Indeed, it is to be expected that differences
arising from the effect of the shores and of tributary waters
would be carried by the current far down the stream. On the
basis of volume per m.* the probable error of distribution is
+ 27.23, with a range of —61.7 to +53.1, and a total between
limits of 114.89—all within these limits of variation in Reig-
hard’s data from Lake St. Clair, but exceeding somewhat the
more limited data of Apstein. If we omit the three inshore
collections, Nos. 1, 9, and 10, the probable error of distribution
falls still lower,— to +21.9 per cent., with a range of —22.1 to
+ 39.5, a total of 61.6 per cent. between limits.

If we take the amount of plankton under one square me-
ter as the basis of comparison the results will be much more di-
vergent, owing to the greater relative difference in depth in
my locations and to the introduction of variation due to verti-
cal distribution of the plankton. In Apstein’s tests the great-
est departure from the mean depth in no case exceeds 10 per
cent., and with but four exceptions his 31 tests are in water
from 15 to 45 meters in depth, where differences in depth are
of less importance than in shoaler water. In Reighard’s se-
ries the greatest departure from the mean depth is 66.9 per cent.,
the range being from 1.17to5.54meters. In my test the range
is from .56 to 4.88 m., the greatest departure being $1.5 per cent.,

287

and my inshore collections were all probably very much nearer
the shore than any of his were made. It is therefore legiti-
mate to omit these inshore collections in comparisons based
on amounts under one square meter. Accordingly, if we omit
Nos. 1, 8, 9, and 10, the probable error of distribution becomes
+ 15.4 per cent., with a range of —25.2 to +84.2, a total of
59.4 per cent. between limits. This is far within the hmits of
error which Reighard’s St. Clair data yield. Since his catches
include two at depths of 1.17 m., we may include all of my
catches except No. 10, in which case the probable error of dis-
tribution rises to +38 per cent., with a range of —77.1 to
+ 71.7, a total of 148.8 per cent., Reighard’s data yielding on
this same basis of computation +31.8 per cent., —57.5 to
+111.5, and 169 per cent. The greater average + error of
distribution in my river test when these lateral collections are
included is manifestly an expression of the effect of shore—an
element not so pronounced in Reighard’s tests. On this basis
the limits and total range still remain less in the river test
than in the lake.

From the data of transverse distribution in the Illinois
River it isapparently demonstrated that, on the whole, the dis-
tribution is no more variable than it is in Lake St. Clair; and
if we eliminate marginal collections and consider only channel
waters, that is the middle two-thirds beyond 20 meters from
shore, the variation falls considerably within the margin of er-
ror found in the lake, being in the six centrally located col-
lections +15.4 per cent. on computations per square meter of
surface, and +24 per cent. for the same on the basis of plank-
ton per cubic meter.

The variation was also tested by counting the planktonts
in the catch, with the resulting error in distribution of +7.8
per cent. for all ten catches, with limits of —14.7 and +31.8—a
total of 46.5 per cent.

The cross-section made below the mouth of Spoon River
September 30, 1897, contains ten collections made at equal dis-
tances, about 12 meters apart, and the first and last this same

288

distance from the east and west shores respectively. As will be
seen in Plate XI., this was made after nine weeks of uninter-
rupted low water, when the river had been standing at 2 ft.
for some time. The catches were made between 2 and 4
o'clock p.m. There was no vegetation in the river at this
point in this season, though both Havana Lake and Quiver
Chute, to the north (PI. II.), contained a small amount. The
discharge from Quiver Creek and Lake makes its way along
the eastern margin of the river, while that of Spoon River un-
der these hydrographic conditions hugs the western shore. The
effect is seen in the turbidity records, the clearer water be-
ing on the eastern side and the more turbid on the western.

The following table gives the data of collection. ‘There
was almost no silt in the catch, and the silt estimates are
therefore omitted.

PLANKTON IN CROSS-SECTION OF ILLINOIS RIVER BELOW MOUTH OF SPOON RIVER.

D
Num-| Temperature are Plankton per Plankton under Sea ee cen aaa
penet (F.) Depth | depth m.3, in cm. 1sq. meter (omitting Nos. land 2)
FEU ns =a in m. Ba | iss ea PST ee || | a
5. Suz | Bot idise | Vo [Pepattirs, [vor] DePets [Perms | Usderd
ESS om visible | ume in per cent. ume) in per cent. Sqn
1 15 76 -66 335 2.40 —60 1.58 —83
2 71.5 70 1.06 33 3.88 —35 4.11 —57
3 70.5 70 1.42 35 5.40 —10 7.67 —20 —20 —32
4 70.5 70 1.58 30 6.32, + 5 9.99 + 4 7 —12
5 70.3 70 1.58 31 5.60 —7 8.85 — 8 —17 —22,
6 70.5 70 1.68 25 7.64 +27 12.84 +34 +14 +14
7 705 70 1.83 25 8.20 +37 15 00) +56 +22 +33
8 70.5 70 1.88 22 7.40 +23 13.91 +45 +10 +23
SQ | el 70.5 | 1.83 .20 6.84 | +14 12.52 +30 aL) 441
10 71.2 71 1.72 Bis) 6.28 +5 9.55 —1 — 6 —15
Average | 6.00 |:22.3 | 9.60 | eae || sel || se207

The results of this test are confirmatory of the thesis here
maintained, namely, that the distribution of the plankton in a
stream does not differ in the main from that thus far observed
in lakes in the matter of variations in the plankton content
(volumetric) in different localities. The average + depar-
tures from the mean volume, computed per m.’ and under 1
sq. m., in these ten catches are 22.38 and 33.8 respectively, as
‘compared with 31.8 and 28.8 for Lake St. Clair and 5.52 for
the German lakes examined by Apstein.

289

The hydrographic conditions and the location of the test
in the stream are responsible for a large percentage of this va-
riation. ‘Though the low-water levels cut off and reduce the
diversifying action of impounding backwaters, the slight cur-
rent minimizes the equalization due to mingling by the flow
of the water in the channel, and, most of all, the location of
the test just below the outlets of Quiver Lake and Spoon Riv-
er (Pl. II.) involves the full effect of the diluent action of
their relatively poorer waters. In Spoon River, on the day of
the test, 3.12 cm.’ of plankton per m.* of water was found
(Table IV.), while in Quiver Lake on October 1 there was only
.O7 cm. per m.* (Table V.). The discharge from Quiver Lake
is reinforced by the seepage from springs along the eastern
shore,and these diluents are probably the cause, to some extent,
of the low plankton content in the two collections nearest
the eastern shore—2.4 and 3.88 cm.’ to an average of 6. for the
ten collections. The effect of Spoon River isseen in the much
smaller decline in the inshore collection on that side of the
river. Combined with the diluent action of these plankton-
poor tributaries may also be the effect of shoal water and the
horizontal stratification of the plankton.

If we eliminate from the test the two collections made in
the marginal belt of spring-fed waters, 24 meters wide along
the eastern shore, the +departures from the mean fall from
+22.3 and +33.8 to +12.1 and +20.2. These latter figures
more truthfully represent the variation in distribution of
plankton in channel waters including four fifths of the width of
the stream—a lateral extension far beyond the range in that —
direction of the mid-channel collections of our chronological
series which form the basis of the conclusions of the present
paper.

The data concerning the local distribution of the plankton
in the Illinois River in longitudinal and transverse directions
presented in the preceding pages may be summarized as fol-
lows: The average + departure from the mean longitudinal
distribution in consecutive catches at the same point in the

290

stream is 3.58 per cent; from a floating boat, 11.2 per cent.; at
intervals of 1—7 days for periods of 2 to 5 days in the more
stable hydrographic conditions, 14.1 per cent.; and in the
stream as a whole for 200 miles of its course, 57 (total
catch) or 89 per cent. (plankton estimated). If, however, we
break up the 200 miles into four sections representing sub-
ordinate units of environment, each dominated by some local
factor, the + departures from the mean are 12, 51, 32, and 76
per cent. respectively for estimated plankton (i. e. after silt
deduction), or 44, 5, 86, and 34 per cent. for the total catches,
the averages for the two methods being + 48 and + 29.7 per
cent.

The average departure from the mean catch in two trans-
verse series of 10 catches each is + 27.2 or + 22.3 on the basis
of plankton content perm. If we eliminate the shallow-wa-
ter shore collections, the departures fall to + 21.9 and +12.1,
or on the basis of volumes under | sq. m.,to + 15.4 and + 20.2.
The departure from the mean number of planktonts is only +
7.8 for the whole cross-section.

These results are in the main within the + error of distri-
bution of the plankton in lakes arrived at by similar methods
of computation. The plankton method may therefore be applied
to the quantitative investigation of the life of a stream as legitimately
as to that of a lake. The laws of the horizontal distribution of the
plankton are in this respect essentially the same in both types of
aquatic environment.

Whether or not a fundamental source of error as large as
this—probably the greatest of all the errors in the method as
we have used it—vitiates the utilization of such data for scien-
tific conclusions must be to some extent a matter of opinion.
The extent to which it renders conclusions tentative must de-
pend upon the distribution of the error, the extent of the data,
and the method of their utilization. Personally I may say that
close study of the at first sight aberrant data upon which
this paper is founded, has led me to attach less significance to
this source of error than I was at first inclined to do. Readers

291

of the paper will, I believe, find that in the main the conclu-
sions arrived at rest on a body of confirmatory data so large as
to counterbalance to some extent the probability of vitiating
error from this source. The distribution of the error is, more-
over, continuous throughout the whole series of data, with,
however, some probability of variation with the stability of the
hydrographic conditions. Finally, the conclusions to be drawn
in subsequent pages rest upon data which to a large extent
rise above the level of the error resulting from the irregularity
of distribution.

PLANKTON PRODUCTION.
1894

(Table II., Pl. VIIL.)

Ten collections were made by the oblique-haul method in
this year between June 12 and December 15. The volumes of
plankton, silt, and total catch per cubic meter average 2.49, .28,
‘and 2.77 em.’ respectively. The maximum catch, 10.18 cm.’ per
m.* (plankton, 9.67; silt, .51) was taken Aug. 15, and the min-
imum, .25 em.’ (plankton, .10; silt, .15), on Nov. 11. The series of
ten catches form a somewhat regular curve, rising during July
and August, and declining, most rapidly in September, toa
minimum in October-December.

A comparison of the record of 1894 (Pl. VIII.) with that of
other years (Pl. [X.-XII.), as shown in the accompanying table
of averages (p. 292), and with the conditions of temperature and
hydrograph, will serve to throw light on the significance of the
plankton volumes of this first year of our collections.

As shown on pages 168 and 164, this wasa year of normally
located high and low water, with March, May, and September
rises all so reduced as almost to eliminate overflow stages and
to prolong low-water stages, resulting in the low average height
of 4.63 ft. above low water. Our collections all fall in the sta-
ble period, broken only by the September rise. They therefore
afford no data on the spring maximum of plankton production,

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293

revealing only a single midsummer pulse, culminating in the
August maximum in a period of maximum heat and lowest water.

In the light of collections of later years in this and other
localities it seems probable that collections at more frequent
intervals would have yielded a curve of greater irregularity,
with other fluctuations than the single one apparent in the
present record.

It seems probable from the records of 1896 (Pl. X.) and
1898 (Pl. XII.) that the small average (0.74) in June is due to
the fact that the dates of collection fallin a period of decline
from an April-May pulse, hastened by the rise in May and per-
haps reduced in volume by the relatively small contributions
of impounded backwaters resulting from the depression of the
spring flood. It may also be that the collection of June 29 ex-
hibits the flushing, depleting effect of the rise of the preceding
ten days. It will be noted that the collection of June 12 lies
about four weeks after the crest of the May rise—a location
which is attended in 1896, 1897, and 1898 (Pl. X.—XII.) by a
decline to a minimum after a pulse of plankton development.

The hydrographic conditions of July in 1894—decline of
flood to low-water levels—are approximately realized with va-
rying stages of river and rates of decline in all the other years
but 1895 (Pl. [X.-XII.). In 1894 they attend a tenfold in-
crease in the plankton during this month. The movement of
production is in the same direction approximately in July in
1896, 1897, and 1898, though its development is less in 1896 and
1898, and data are lacking for its progress in 1897. In 1894,
and to a varying extent in other years, this rise attends among
other factors the restriction of contributions from impounding
backwaters and the differentiation of what might be called
channel plankton proper. The July production in 1894 aver-
ages 5.12 cm.’ per m.*—the largest, with the exception of that
for 1895, of any year, and a fact to be correlated with the un-
usually stable conditions then prevalent.

In August of this year the single collection forms the apex
of the season’s production, reaching 9.67 cm.° per m.*—an

294

amount not surpassed for this month in any subsequent year.
It may also be correlated with the continuance of stable con-
ditions. The nearest approach to this amount is found in 1897
(9.45 em.’, Table III.), likewise in stable conditions. It is notim-
possible that there is more than one culmination in the months
of June and July, collections being at too great intervals to
suggest the direction of the movement in production.

The flood of September attends a decline of the plankton
to a minimum of .34 on the 17th in the fluctuations in level on
the crest of the flood (Pl. VIII.). Similardirection of movement
in production may be traced in 1895, 1896, and 1898. This
decline in production attends the beginning of theautumnal de-
cline in temperature, 10°-15° of which occur within this month.

The hydrographic conditions during the remainder of the
year are exceedingly stable, there being a gradual rise of only
.O ft. from the middle of October until the middle of December.
Beyond the insignificant rise in the October catch no movement
in production is evident. A comparison of these scanty data
with the curves of production in these months in 1895 and 1897,
both with low-water autumns, makes it evident that collections
in 1894 were too infrequent to serve as a basis for any conclu-
sions as to the average autumnal production in this year, and
raises the query as to whether considerable fluctuations of
pulse-like character might not have run their course in the in-
tervals between our collections. The higher averages in Octo-
ber-December in other years supports this suggestion. It is
evident that the monthly interval of plankton collection is too
infrequent to afford usable or significant data.

The average of the ten collections in 1894 is 2.49 em.’, and
that of the seven monthly averages 2.53 cm.* Thisis larger than
the averages for a similar period in 1896 and 1898 (.99 and 1.09
respectively), both years of disturbed autumnal hydrograph. It
is much less than that of the last seven months of 1895 (7.15).
If, however, the exceptionally large collections of June-July
be omitted in this year, its average (of monthly means) falls
to 2.05. In the main, the hydrographic conditions in 1894 and

295

1895 in the last five months are somewhat alike, and their
plankton production is somewhat similar (cf. Pl. VIII. and X.).
In 1897, however, the uninterrupted and prolonged low water
yields a much larger production of plankton (3.56 for the last
seven months).

Though incomplete, the evidence in a general way indi-
cates that 1894, in the period included in the collections, was
a year of abundant plankton production, approximating 2.5
¢m.* per m.° of water.

1895.
(Table III.; Pl. 1X., XLII, LI.)

Of the 50 collections of this year but 4 were made in the first
six months. This was particularly unfortunate, for the spring
was one of exceptionally low water, and the collections are so in-
frequent as to give only the faintest clue to the curve of plank-
ton production in this important period. All of the collections
were made by the oblique-haul or repeated vertical-haul method.
Omitting the very unusual catch of June 19, the mean volumes
of plankton, silt, and total catch per cubic meter are respective-
ly 2.12, 1.88,and4.01cem.* As an average, the proportion of silt
in the catches isthus quite low—a fact explained by the absence
of considerable floods during the period of most frequent col-
lections.

As is shown on pages 164 and 165, this wasa year of unusu-
ally low water, the mean annual stage of the river being 3.61 ft.
The spring rise did not bring the river to much more than min-
imum bank height, and there was no June rise. Aside from a
few minor meteoric rises to less than 6 ft. in July and Septem-
ber the low-water period was unbroken until the December
flood culminating at 12.6 ft. at the close of the year A glance
at Plate [X. will indicate that the collections suffice to trace
the production during the last six months,—a low-water period
with minor rises,—and to follow somewhat closely the effect of
these hydrographic changes upon the volume of the plankton.

The isolated collection of Feb. 23, made beneath 37 cm. of
ice at the close of a period (PI. [X.) of ice blockade of approx-

296

imately two months’ duration, reveals an almost complete ex-
termination of the plankton, the amount given in the table,. 01
cm.’, being only an expression for an amount beyond the reach
of our methods of measurement. As shown in Plates VIII.
and [X., there was prolonged and quite stable low water from
Oct. 15, 1894, till the flood of the last week of February of the
following year which carried away the ice. The concentration
of sewage under such conditions was shown by the stench of
the water, by the departure of fish into tributary backwaters,
and by the death of many not escaping. Unfortunately no
chemical analyses of river water at this season are now availa-
ble, and the chemical conditions can only be inferred from
those in later years at times of briefer ice blockade, higher
water, and presumably less contamination. For example, in
January, 1898, following the low water of 1897, we find under
ice of three weeks’ duration (PI. XI., XII., and XLIV., XLV.)
great excess of freeammonia and chlorine, and high albuminoid
ammonia, organic nitrogen, and oxygen consumed—all, in-
dices of contamination. The ice sheet upon a contaminated
stream must also profoundly affect the equilibrium of oxygen
and carbon dioxide dissolved in the water, and thus directly
influence the life of all constituents ofthe plankton. It is there-
fore not surprising that these unusual conditions should ex-
terminate all but the most resistant members of the plankton.
The catch consisted almost entirely of flocculent debris (zo-
ogleee?) with a few minute filaments of bluish green alga of
uncertain affinities, while the usual plankton was represented —
by only 43 individuals, representing 14 + species, as follows.

Protozoa:
Diffugia sp. (deformed?).......... 1
IG DISHTIS S05 WEG. co 554o8oc5¥ es. 3am
Carchesium lachmanni, head....... 1
Cilhate, indeterminate... ......... if

RCH OZOR1 ie eee epee lee Sonne Meenas 1

297

Rotifera:
' Brachionus dorcas, female......... Il
J BOLO OP UO CNIS: NEVI 5556 4600 9
Polyarthra platyptera, female...... 2
Polyarthra platyptera, female with
CO CR Feta a 1
Indeterminate rotifer sp........... l

Entomostraca:
Cyclops bicuspidatus, female, young,

dead or moribund..... 1

Cirlofos, WOUMG 26 6s66o0s0e0e0000 2
Colas, Wena... ose sb6osoosuer 4
Canthocamptus, nauplil............ 4
CRYCOPUS GUOOUSIS 6 00 6646646500 606 1

Miscellaneous:

Iniinarlocl @ coe Ne eee Serer aie) aiccres es: 1

DAR DUG he Os Hoe be ee On RE Ce 2
Indeterminate re tasers 7

AO Gallien atc ade 43

In towings made at the time of the quantitative collec-
tions Mr. Hempel found an individual each of Pterodina patina
and Notholca acuminata,

The list includes representatives of the prominent winter
planktonts excluding alge and diatoms. The effect of the
sewage contamination is observed in the reduced numbers
both of individuals and species, in the moribund condition of
Difflugia, Carchesium, Epistylis, Brachionus, and Cyclops, and
in the fact that apparently the only breeding forms, with the
exception of the Cyclops, were the ubiquitous and perennial
Polyarthra and the muck-loving Canthocamptus, and possibly
the slime-dwelling Rotifer tardus.

This incident affords a striking illustration of the catas-
trophic effect of the ice blockade upon the life of sewage-fed
streams in whose waters the products of decay are concen-
trated by the exclusion of the air by the ice sheet.

The absence of collections in March prevents any tracing

298

of the initial stages of the rise in vernal production imdicated
in later years, especially in 1896 and 1898.

The two April collections average 3.18 cm.’—about 87 per
cent. below the mean for this month in the three subsequent
years. An inspection of the vernal plankton curves for this
and subsequent years at this and other stations (Pl. [X.-XII.,
XXVI.-XXXIV., XXX VI.-XLII.) reveals the presence of a ver-
nal volumetric pulse* of plankton, which, as a rule, marks the
maximum period of production in the year, and follows imme-
diately upon the vernal rise in temperature.

In 1895 our collections were too infrequent to detect the
location and extent of this vernal pulse. In other years, as
seen in the plates to which reference is made above, the best-
defined vernal pulses appear in the closing days of April and
the first week of May. From the character of the best delineat-
ed vernal pulses—e. g. those of 1896 and 1898 (Pl. X. and XII.)
—it is probable that the apex or crest of the pulse is narrow,
that is, the maximum development lasts but a few days. If
this be the case, our two collections in April may miss entirely
the period of culmination. The second collection, upon the
29th, would appear to be located at the probable season (tem-
perature?) to detect the maximum development. If this be the
case the vernal development of 1895 is much reduced, and might
be correlated with the suppression of overflow stages and con-
sequent reduction of contributions from the impounded back-
waters. ‘l'wo facts lead me to think that two well-developed ~
vernal maxima may have been present in 1895. First, a com-
parison of the vernal pulses of 1896 (Pl. X.) and 1898 (Pl. XIT.)
indicates that the pulse of the former year culminates about

*[ use the term plankton “pulse” to designate the phenomenon of a periodic in-
crease of the plankton volumetrically, as a whole, from a minimum to a maximum,
followed by a decline to another minimum, the rise and fall being more or less
gradual, and the data forming when plotted a more or less symmetrical curve, re-
sembling that known as the “probability of error’ curve. A typical example of this
phenomenon and resulting curve is seen in the case of the April-May plankton of
1898 (Pl. XII.).

The term may also be applied to a periodic increase in individual members of the
plankton similar in its graphic delineation to that of volumetric changes. The
pulses will be designated by the months in which the major part of their course is run.

299

April 24 and that of the latter about May 3. The temperature
curves of 1896 pass 60° about sixteen days before they reach
that point in 1898. This may be the cause of the earlier cul-
mination of the vernal pulse in 1896. Now in 1895 there is a
suggestion in the temperature curve of an early spring, and the
suggestion is borne out by the records of the U. 8. Weather
Bureau for central [linois. The normal mean temperature
for Illinois as a whole in April is 51.8°. In 1896 it was 54.8°.
In this case we might expect to find an earlier vernal pulse
culminating, as in 1896, before the end of April, so that our col-
lection of the 29th would fall upon its decline rather than upon
its apex. I use the term vernal maxima advisedly, for I am
inclined to the view that the period from April 29 to June 19
witnessed a remarkable development of the plankton. The
reasons for this view are found, first, in the fact that the catch
of June 19 contains many Moina micrura, numerous males and
epphippial females being among them, whose presence suggests
the close of a period of rapid multiplication by parthenogenesis.
The catch of June 19, though large, may thus represent the
decline of a still larger population. In the second place, the
qualitative collections made witha tow-net in the river in the in-
terim between the quantitative collections of April 29 and June
19 indicate an exceedingly abundant plankton rich in Moina.

From the available data in 1895 and the course of the ver-
nal production in other years it may be inferred with some de-
eree of possibility, if not indeed of probability, that the vernal
production in this year was accelerated by the early spring,
and that a pulse appeared prior to April 29, and that this was
followed in May-June by another pulse of much larger propor-
tions and longer duration, a part of which (probably the decline)
is detected in catches of June 19 and July 6. Of the occurrence
of this latter and larger pulse there is little doubt, though the
data are not available for its location and delineation.

The unusual and prolonged low water of these spring
months thus seems to result in a marked increase in the plank-
ton content. The causes which lead to this are not far to seek.

300

The decreased volume of water causes a relative concentration
of the sewage and consequent increase in fertility of the chan-
nel water over that of the usual high water of this season.
Lower levels insure more rapid rise in temperature, and the
slackened current affords more time for the breeding of the
plankton. The occurrence of Moina micrura, a lover of foul
water, 1s in itself an index of the character of the stream in
this low-water spring. The contributions of the impounded
backwaters to the stream during this April-June period (see
Pl. [X.), owing to the small areas submerged, are reduced in
volume so that both the relative and actual share which they
have in the formation of the channel plankton is probably less
than in years of normal spring flood. Nevertheless, as seen in
Plate XX XVI., such waters as Thompson’s Lake tend by their
run-off to enrich and increase the channel plankton.

The month of July (Pl. IX.) witnesses the rapid decline of
the second vernal pulse from 29.68 cm.’ on the 6th to6.8 on
the 28d and .83 on the 29th—a fall of 98 per cent. in 23 days.
The last stages in this decline were hastened by the rise of 3
ft. in the third week of July, the flushing and destructive action
of the flood waters continuing until the close of the month.

In this and subsequent years I shall call attention—when-
ever the interval between collections is brief enough to afford
adequate data—to the phenomenon of recurrent pulses of
plankton production. I am led to make this emphasis by ob-
serving in the numerical analysis of these catches recur-
rent pulses in most if not all of the more abundant species,
pulses, moreover, which exhibit a degree of concurrence in
many species which I believe to be expressed in the faintly
traceable volumetric pulses which run like waves, erratic in
amplitude but more regular in interval, through the seeming
vagaries of the volumetric data. I shall therefore treat the
volumetric data from this point of view, endeavoring to discoy-
er evidence of cyclic production wherever it exists, and seek-
ing to correlate this phenomenon with the more patent fac-
tors of the environment.

301

Considering, then, the data from July to the end of the
year in 1895 (Pl. IX.), we find that the month closes at a min-
imum of .33 cm.*—the end ofa pulse of uncertain limits and the
beginning of the next, which culminates in the third week of
August. This August pulse is followed by one of less ampl-
tude and duration, culminating about three weeks later, by
one of shght amplitude in October, culminating at an interval
of about four weeks , by one of greater amplitude in November,
after an interval of about five weeks, and by one in December, al-
so of considerable amplitude, at an interval of about four weeks.

The fluctuations of some of the component groups of organ-
isms are shown in Plate LI., and considerable correspondence
inthe volumetricand statistical pulses will be apparent on com-
parison.

The August pulse has a duration of 39 days,—from July 29
to Sept. 9,—and a maximum amplitude of 7.63 cm.’ on August
24. The mean of the pulse,* that is the line upon which the
center of gravity of the polygon formed by connecting the ordi-
nants hes, falls upon August 22. This pulse occurs in a period
of somewhat stable low water, and its decline from the maxi-
mum of 7.65 reaches 2.07 on Sept. 4 and occurs without the
assistance of flood waters. On Sept. 5 a sudden minor flood,
due to local rains, flushes the stream and completes the deple-
tion of the plankton to .69 on the 7th. The August average for
1895, 4.03 cm.’, is higher than that of any other year excepting
1894, in which but a single collection was taken, which may
not be representative of the whole month. Freedom from ris-
ing flood waters in 1895 is doubtless one cause conducing to
this high average of production. The enriching effect of the
minor flood which culminated in the closing days of July may
also contribute to this end. The absence of rises in May and
June would also tend to increase the contributions of organic
material to the stream by this July flood as compared with

*The mean was computed by multiplying the volume of each catch in the pulse
(ordinant) by the number of days from preceding minimum to date of collection
(abscissa) and dividing the sums of the products by the sum of the catches in the
pulse, the quotient being the abscissa of the mean.

302

floods which followed normal spring rises. The correspond-
ence of the August pulse of plankton with a heat wave of 10°
amplitude is well shown in Plate IX. Similar correspondences
may be detected in some instances elsewhere in the plankton
and temperature curves, but neither the completeness of our
temperature data nor the corroborative evidence is sufficient to
lend much support to a causal nexus between the phenomena.

The September pulse has a duration of 25 days,—from Sept.
7 to Oct. 2,—and a maximum amplitude of 3.25 cm. on the 14th.
Its mean falls on the 17th, 26 days after that of the August
pulse. This isa month of considerable hydrographic disturb-
ance, the rises of the 6th, 17th, and 27th causing almost twice
as much movement (8.75 ft.) in river levels (see Table I.) as is
found in other years of our operations. These accessions of
flood water in each instance attend a fall in temperature of 5°
to 8°, though that on the 27th is combined with normal autum-
nal decline. None of the three is sufficient to cause overflow,
and each is of but few days’ duration. Their effect upon plank-
ton production is, however, considerable. In the first place,
the immediate result of the invasion of flood water is an in-
stant decline in the plankton, as shown by the change from
2.07 on the 4th to .69 on the 7th, the flood in this case acceler-
ating and perhaps continuing the normal decline of the August
pulse. So also the little rise of the 17th checks the rising curve
of production, the fall being from 3.25 cm.’ on the 14th to .89 cm.
on the 18th. The rise of the 27th evidently occurs towards the
minimum of a declining plankton pulse, and the fall from —
1.03 cm.? on the 25th to .37 cm.’ on Oct. 2 is of less extent. The
location of these floods in the pulse is such that if my conjec-
tures as to their reducing effect be true they cause a shifting
of the apex of the curve and of the location of the mean to the
left of their probable position had not the floods occurred. In
technical phraseology the mode of the curve of this pulse ex-
hibits left-handed skewness. In the second place, the general
effect of these recurrent rises is a reduction in total production
the extent of which can only be conjectured. It seems proba-

303

ble that the rise of the 17th is responsible for the suppression
of a rising pulse whose culmination had not yet been reached.
The slight recovery in the following week is indicative of the
upward tendency in production thus interrupted. That con-
tinued low water in this month may attend great plankton
production is seen in the records of 1897, when the monthly
average (see table on page 292) is 8.83 cm.’ to 1.52 em.’ in 1895,
On the other hand, in 1896 and 1898 the disturbed conditions,
with higher water and more current, are accompanied by
much reduced production, averaging only .38 and .69 cm.’

The last week in September witnesses the first stages of
marked decline in temperature from the well-sustained summer
heat of 75°-85°. The decline reaches 68° at the end of the
month. This phenomenon combined with the last flood to ac-
celerate and complete the decline of the September pulse
which had already appeared prior to the last flood.

The October pulse has a duration of 29 days,—from the 2d
to the 380th,—_and a maximum amplitude of .76 em.’ on the
11th and 15th, following a rise in nitrates and attending in-
creased sewage contamination (PI. XLIII.), Its mean falls on
the 18th, 31 days after that of the preceding pulse. This isa
month of stable low water approaching minimum levels, the
total movement in the pulse period at Havana being only 1.03
ft. The temperature in this period falls from 61° to 45°, and
this taken in connection with the fall of 11.5° in the preceding
week brings to bear upon the plankton production of this
month the cumulative effect of a decline of 27.5° and the results
of the low temperature of 45°. The consequence is that the
summer planktonts are killed off or reduced in numbers, and
the winter planktonts have not as yet had time or temperature
to reach any considerable development. The plankton produc-
tion is therefore low ; so low, indeed, that its pulse-like char-
acter is largely a matter of conjecture in the volumetric data
(ef. statistical data on Pl. LI.). Phenomena of like character
are to be detected at corresponding periods of autumnal decline
in temperature in September-October, 1896 ; in October-Novem-

304

ber, 1897; and in October, 1898. The effect of this autumnal
decline of temperature may also be traced in monthly averages
of production in the table on page 292. Rapid decline in tem-
perature is thus immediately followed by rapid decline in pro-
duction in the channel plankton. Such correlation in decline
of temperature and plankton cannot, however, be found as a
general phenomenon in the bottom-land lakes (cf. Pl. XX X.-
XLII.) and a causal nexus between the two declines must there-
fore be of limited operation and at the best highly conjectural.
The operation of other factors than that of direct temperature
is probable.

The monthly mean of production for October in 1895 is .67
cm.*, approaching that of 1894 (.61) and 1898 (.24). In 1896
and 1897 it is much higher (1.11 and 5.95 respectively), an
earlier decline of temperature in 1896 (Pl. X.) and a later one
in 1897 seeming to shift accordingly the attending decline in
plankton, so that the September (.38) and November (1.) aver-
ages respectively more nearly represent the October averages
of 1895.

The November pulse has a duration of 35 days,—from Oct.
30 to Dec. 4,—with a maximum amplitude of 4.37 cm.’ on Nov.
27. Its mean falls on the 22d, 36 days after that of the pre-
ceding pulse. Thisis also a month of continued stable low
water, with a slight rise of .75 ft., due to the checking of evap-
oration and to autumnal rains. Thetotal movement is only .99
ft. at Havana. Temperatures during the first three weeks are
somewhat stable for this season of the year, exhibiting a range
of only 5.8°—from 48.5° to 43.2°. The last week, however, ex-
hibits a fall of 10.2°, to minimum winter temperatures and the
beginning of the ice blockade. Under these stable conditions
the plankton production in November rises to a level approach-
ing that of midsummer of the current year, its apex (4.37) fall-
ing 44 per cent. short of the August apex (7.63), and its aver-
age (3.02) 25 per cent. short of the August average (4.03).
Both volumetric (Pl. IX.) and statistical data (Pl. LI.) demon-
strate the rapid multiplication of the plankton in these stable

305

conditions, and the result is a pulse of considerable amplitude,
moreover, one not attained in any other year in channel plank-
ton ; a fact whose significance is apparent when we find (PI.
VIII.—XII.) that no other year combines to the same extent
stability of hydrographic and thermal factors. The relative
production in different years (see table on p. 292) bears upon
the point in question, the monthly mean (3.02) being from 150
to 3 times as great as that reported for other years. The chem-
ical conditions attending this remarkable plankton production
(Pl. XLIII.) are those following increased sewage contamina-
tion, namely, a rise in nitrates, free ammonia, and chlorine.
The December pulse has a duration of 21 days,—from De-
cember 4 to 25, the limits being taken from the statistical data
(Pl. LI.), which are based only on catches at intervals of 5 to 7
days. Its maximum amplitude (2.60) occurs on the 20th, and
its mean falls on the 16th, 24 days after that of the preceding
pulse. The first 18 days of the month are relatively stable,
with a movement in levels of only 1.05 ft. and stable minimunr
temperatures under the ice sheet. During this period a slight-
ly developed pulse begins its course (ef. also Pl. LI.), but its
apex does not rise much above the level of previous produc-
tion. It is noteworthy that this takes place beneath the ice
sheet which covered the upper river during the fortnight pre-
ceding the flood. Itis in this month that the contamination
noted in November reaches its maximum (PI. XLIII.), at least
as shown by nitrates and free ammonia. The chemical condi-
tions thus favor a continuance of the productive activity of
the previous month. On the 19th heavy general rains started
a flood of unusual magnitude which continued to rise, culmina-
ting at 12.6 ft. at the end of the month. This raised the temper-
ature about 9°, brought in an immense load of silt, flushed out
the plankton, and increased the rate of the current so as to
greatly reduce the time for breeding. The first two days of
rising water did not materially change the quantity of plank-
ton per m.°, indicating a considerable rise in production had not
the flood occurred. By the 25th, however, the flood waters had

306

swept away all but a vestige of the rich plankton of the earlier
weeks. The amount remaining was so small that its quantita-
tive changes were swamped in the errors of the volumetric
method and silt estimation. The large amount of silt carried
in this and subsequent floods of the winter is due to the fact
that bottom-lands and fields covered with a rich vegetation were
now submerged for the first time in two years (Pl. VII.), and
vast quantities of debris from this region and tributary streams
now entered channel waters.

In comparison with other years December in 1895 is, in
spite of its fortnight of flood, the most productive December
recorded (see table on p. 292), averaging 1.14 cm’ to .76 in 1896,
.56 in 1897, and .99 in 1898. It shares the large development
of the preceding month, and with it presents the most marked
late autumnal development in channel waters, though falling
far below the production of some of the permanent backwaters
in thisand other years in this season. The unusually stable
hydrographié conditions in the river doubtless contribute in
large measure to this exceptional development. That low tem-
peratures alone do not prevent the development of a large win-
ter plankton is apparent from this December development of
2.6 cm.’ per m.* and 11.1 cm.’ per square meter at temperatures
but little above 82°.

The year 1895 as a whole may be summed up as one of mid-
winter stagnation followed by excessive spring and early sum-
mer development of the channel plankton, of midsummer and
equinoctial floods, which check development at that season, of
stable autumnal conditions and exceptional production in late
autumn, and of catastrophic reduction by flood to a minimum.
As a whole the year was one of exceptionally heavy production
when expressed in terms of plankton per cubic meter. This is —
seen in the high average—3.22 cm.’ of all catches, 5.31 cm.’ of
monthly averages. When total production is considered it may
be that the decreased volume of water at the time of the maxi-
mum in the low water of June will at least counterbalance the
excess per cubic meter, and that the total production will not

307

exceed, if indeed equal, that of years of more normal hydro-
raph.
aa 1896.
(Tables IlI., X.; Pl. X., LI.)

There were 76 collections made in this year, of which 69
are prior to Sept. land are, moreover, atintervals brief enough
to enable us to trace the curve of plankton production with
some degree of accuracy. In the last four months the fort-
nightly interval is too great to permit more than conjecture as
to the probable course of the plankton curve.

The collections prior to May 22 were all the result of com-
bining 4 to 9 repeated vertical hauls of the net. Subsequent to
that date they were made with the plankton pump. This, as is
shown on page 165, was a year marked by recurrent floods,
which bring the average height for the year up to 6.98 ft. ina
year of less than average rainfall. This is almost twice the
average height (3.61) of the preceding year. Since the flood
did not in most cases reach bank height, the overflows were
not extensive and did not occur during periods of large plank-
ton production (Pl. X.). The distribution of the collections
with reference to the floodsis such that we have again in this
year the opportunity to test the effect of the access of flood wa-
ter upon the curve of plankton production at all seasons of the
year but the autumn months. Inthis year the vernal rise in
temperature occurred abruptly in the middle of April, and
the autumn decline began quite early but progressed slowly.
Summer temperatures were also lowered somewhat by access
of flood water.

The plankton of January, February, and March (Pl. X.)
forms so small a portion of the total catches that its quantita-
tive changes are swamped by the probable error of silt estima-
tion, and are apparently of such slight extent that their signifi-
cance cannot be detected. The amount of silt carried is very
large, doubling or trebling in quantity on rising floods, and
reaching a maximum of 14.77 cm.’ per m.’ on the crest of the
March freshet. No recurrent pulses appear in the volumetric

308

data, though the statistical data (Pl. LI.) indicate the recur-
rence of three such pulses in this period.

The volumetric production is very small throughout this
whole period, rising above an estimated amount of .01 cm.? per
m.* in only 7 of the 18 catches; and not exceeding .13 in any of
them. This results in monthly averages of .01, .02, and .07 re-
spectively for the three months (see table on p. 292). These are
lower than those of any other years excepting only that afforded
by thesingle collection of February, 1895. The cause of this slight
production is, I beheve, the high water and increased current
resulting therefrom, which does not afford to the channel plank-
ton the time requisite for breeding a more abundant plankton. —
Some corroboration of this view may be found in the fact that
the February collections in the high water of 1897(Pl. XI.) lke-
wise yielded minute quantities of plankton (average .04 cm.* per
m.*), while the channel waters of 1898 (Pl. XII.) in January
and the early part of February, and of January—March, 1899
(Pl. XIII.), produced at stages below that of overflow (8 ft.) a
more abundant plankton—.07 to 1.15 cm.’ per m.? of water.
High water with accompanying rapid current is thus deleteri-
ous to plankton production in channel waters, in midwinter at
least. It is noteworthy that this minimum production occurs
in the presence of nitrates in great excess, in fact in quantities
larger than those recorded at any other period of our records.
(ef. Pl. XLUI.—XLV.). It is not therefore for lack of nitrates
and other products of decay that the plankton fails to develop.

The data of the collections in the latter part of March in-
dicate a rising production as levels fall and temperature rises.
The direction of movement is upward, though the quantity at-
tained in this month is not great.

The interval of collections and the quantities of plankton
obtained from March to September enable us to trace with some
probability the course of the recurrent plankton pulses of this
season.

The April pulse has a duration of 32 days,—from March 30
to May 1,—with a maximum amplitude of 9.39 cm.’ on the 24th.

309

Its mean falls onthe 23d. Thisis the vernal pulse, often the lar-
gest of the year, this distinction being attained in 1896. It rises
in 25 days from a minimum of .13 cm.’ on March 30 to a max-
imum of 9.39 on the 24th—an average daily increase of .37
em.’ This pulse, as elsewhere, follows immediately upon the
vernal rise in temperature, which in this spring reaches 72° on
the day of the maximum of the pulse and passes from 46° to 66° a
week prior to it. The maximum thus lies a fortnight after the
most rapid vernal rise in temperature begins. It attends a sharp
decline in nitrates and free ammonia, and its maximum coin-
cides (Pl. XLII.) with that in the organic nitrogen. It also
occurs in a period of apparently stable hydrographic condi-
tions, the total movement in April in this year being only 1.4
ft. less than in any other year. This stability 1s more appar-
ent than real. The decline of the March flood (Pl. X.) was
checked, and slight rises resulted from spring rains which
brought large quantities of silt into the stream, so that move-
ment in river levels is not in this instance a sufficient index of
hydrographic stability. The result was apparently the sup-
pression to some extent of the vernal pulse (cf. on this point
1896 and 1898, Pl. X.and XII.). The amplitude of this vernal
pulse (9.39) is less than that of 1898 (85.68)—the only other
year in which our collections are frequent enough to lo-
cate and delineate this pulse with sufficient accuracy.
This may be due to the operation of one or more of the
following factors. First, to the spring rains above referred
to, at the time of the apparent maximum of the pulse, which
flush it out and dilute it, and to some extent destroy the
plankton. In the second place, there was no general overflow
at this season, and plankton bred in the less current-swept,
impounded backwaters is not entering the channel to the
usual extent at this period of the year (cf. Pl. X. and XII.).
Again, the periods of standstills in levels and those of rise
check the outflow from impounding areas or turn channel
water into the bottom-lands, conditions which obtained in 19
of the 30 days in April. Lastly, there is some possibility that

310

the days of maximum production were not touched in our col-
lections. The meteoric character of the vernal pulse of 1898
in channel waters (Pl. XII.) is indicative of such a possibility.
If a greater production than that recorded did occur, it prob-
ably fell between the 17th and 24th—a period of non-interfer-
ence by flood and of rising production.

The location of the apparent maximum in this year is sig-
nificant. This was an early spring, the average of the surface
temperatures in April in 1896 (see p. 171) being from 4° to® 11°
higher than that in any other April represented in our records.
The temperature of 70° degrees is attained almost a full month
earlier in 1896 than in 1898 (cf. Pl. X.and XII.). The maximum
production was recorded in 1898 on May 8; in 1896, on April
24, nine days earlier, and it may have antedated even this.
Early spring thus affects the life in water much as it does
that upon land. Vegetation bursts into leaf and insects mul-
tiply in field and forest in proportion to vernal rise in tempera-
ture; so in lakes and streams, in like response, thealge multiply
with meteoric rapidity, and the animal planktonts dependent
on them follow in their wake. In 1896 the early vernal rise
in temperature deflects the maximum of the vernal pulse to
an earlier date by virtue of this response on the part of aquatic
hfe to the environing factor.

The average production in April in 1896 (5.67) exceeds
that in any other year of our records, in large part, it seems,
because of the early spring and the deflection into that month
of the maximum production, which in other years passed un-
detected or fell in the following month in consequence of la-
ter vernal rise in temperature, as in 1898.

The May pulse has a duration of 31 days,—from the Ist to
June 1,—with a maximum amplitude of 3.56 cm.’ on the 13th.
Its mean falls on the 15th, 22 days after that of the preceding
pulse. There is in this month considerable hydrographic dis-
turbance—a total movement of 7.5 ft., consisting of a fall of
3.1 ft. followed by a rise of 4.4. The maximum production oc-

ec urs during the decline in the earler weeks, which is practi-

311

cally the run-off of the April rains which checked the fall of
the March flood (Pl. X.). This is also a period of rising tem-
perature, a rise of 12° (to 82°) attending the decline of river
levels and the rising plankton production. The rising plank-
ton pulse is, however, flushed out by the entrance of flood
waters in the closing fortnight of the month. The plankton
falls at once from 3.56 cm.? on the 18th to .86 on the 18th with
the first stages of the flood, and the fluctuations during the
period of rise are erratic, suggestions of recovery and decline
appearing in the data. These vagaries may be due to the dis-
tribution of local storms, which contributed largely to this
somewhat slow rise in river levels. The general effect of the
flood seems to be to depress the production and thus to deflect
the apex or node and the mean of the curve of production to
the left, that is, to an earlier date. The flushing effect of the
floods of May, 1596, is apparently greater than that in 1898, as
shown by the plankton production. The flood of 1896 did not
exceed bank height. Its diluent action is thus concentrated in
channel waters. In 1898 the floods occur in overflow stages
and are thus diffused over a large area.

The chemical conditions show but little relation to plank-
ton movement in this month. The maximum production fol-
lows immediately upon a rise in nitrates, nitrites, and free am-
monia, and coincides with a slight decline in the two first
named. The decline in production during the rising flood
takes place along with considerable increase in nitrates and
nitrites.

The average production in May, 1896 (1.80 cm.*), is less
than that of the following years (see table on p. 292), since it
does not contain the vernal maximum, and also because it is
reduced by flood action.

The June pulse is not well differentiated in the volumetric
data, and its delimitation here becomes largely a matter of
conjecture though it stands out more clearly in the statistic-
al results (Pl. LI.). If we follow the latter the pulse termi-
nates, at least so far as the chlorophyll-bearing organisms are

312

concerned, in the last week of June. If, on the other hand,
we delimit the pulse here as heretofore by minimum volumes,
we shall find its later limit to be July 6, giving it a total duration
from June 1, of 35 days. Its greatest amplitude, 1.68 cm.’, oc-
curs on the 11th, and its mean on the 14th—29 days after that
of the preceding pulse. With the exception of the first three
days this was a month of continuously falling river levels.
The large proportion of silt in the catches and the fluctuations
in the temperatures in the first ten days of the month suggest
flood water of recent origin. Nevertheless, the maximum pro-
duction of the pulse appears at the close of this disturbed peri-
od,a shght decline with little subsequent fluctuation in pro-
duction marking the remainder of the pulse.

The average production in June, 1896 (.72 cm.*) is low in
comparison with that of 1898 (3.96), the only other year in
which the June production is sufficiently represented in our
records. In both of these years there was rapid and prolonged
decline from previous flood, but in 1896 the proportion cf con-
tributions from impounded backwaters was much less than in
1898. Greater time for breeding plankton is thus afforded as
a whole in 1898, and greater production follows. The maxi-
mum production coincides with the maximum of nitrates
(Pl. XLITI.), though it attends a depression in nitrites and free
ammonia. The general low production of this month occurs
in the presence of an unusual quantity of nitrates, so that one
at least of the important elements for production was not
lacking.

The July pulse has a duration of 19 days,—from the 6th to
the 25th,—with a maximum amplitude of 2.24 em’. on the 20th.
Its mean also falls on the 20th—86 days after that of the pre-
ceding pulse. This isa month of considerable hydrographic
disturbance, the total movement in levels being 7.7 ft.—a fall
from 5.2 to 2.5 followed by an interrupted rise to 7.3. The
pulse lies in the middle of this period and falls under the in-
fluence of both fall and rise. During the period of decline
the recovery of the plankton from its minimum of .26 on July 6

313

progresses irregularly to a slight maximum of 2.24 on the
20th during a very rapid rise caused by a Spoon River flood
(Pl. Il.) which, while not invading the stream above its mouth
to any great extent, held back the water from the upper river.
The greater part of the rise in the latter part of the month was
due to the access of water below the plankton station or in re-
mote headwaters, and is thus a reflection of the rise in the lower
river or distant tributaries. The freedom from silt apparent
in the catches bears testimony to this fact. The pulse reaches
its culmination and declines in this rising flood.

The average production for July in 1896 (1.44 em.*) is less
than that in any other year save 1898, and that, too, in what
seem to be favorable hydrographic conditions. The sharp de- ~
cline in nitrates (Pl. XLIII.) from 2.8 to .4 parts per million
may be a factor in the small production.

The August pulse has a duration of 27 days,—from July 25

“to August 21,— with a maximum amplitude of 3.90 cm.’ on
July 30. Its mean falls on the 5th, 16 days after that of the
preceding pulse. This was predominantly a month of falling
levels. The culmination of the rise at 8.6 in the first six days
is followed by a steady decline reaching 5.8 on the 31st, broken
only by the slight interruption in the middle of the month.
The total movement is 3.7 ft., and the total at Copperas Creek
(4.60) is somewhat above the average (4.06). The disastrous
effect of the local floods at the culmination of the rise which
flushed out the rising plankton pulse is apparent in the de-
cline from 3.90 cm.? on July 30 to .40 on Aug. 1, and in the in-
troduction and continuance of a considerable volume of silt.
The rapid recovery of the plankton is seen in the rise from
a minimum of .26, .48, and .32 on Aug. 3-5, to 1.08, 2.40, and
2.60 on Aug. 6-8. These data suggest the intercalation of
barren flood waters of recent and local origin in the course of
channel waters bearing a much more abundant plankton, and
the apparent result is a cleft in the otherwise somewhat sym-
metrical curve of production of this August pulse. It also re-
sults in an apparent shifting of the node and means of the

314

curve to the left, giving a left-handed skewness to the curve.
Aside from this depression due to flood there is a general de-
cline in production as levels fall, the pulse closing on the 21st
with a minimum of .28cm.? This dechne in production is at-
tended by a steady rise in nitrates, organic nitrogen, and free
ammonia (Pl. XLIII.), and thus in the presence of increasing
nutriment, as well as growing hydrographic stability—that is
lower river levels. The two summitsof production in this pulse
coincide with temperature pulses. The plankton and tempera-
ture pulses are alike set off by flood waters, and the causal
nexus may lie between plankton and flood rather than between
plankton and temperature. The location of the flood also has
the effect of lowering the average production of the month to
1.12 cm.'—the lowest average on record, excepting only 1898
(.91), also a year of much disturbance.

From this point the remaining collections of 1896 are too
infrequent to delineate or even to suggest recurrent volumetric
pulses. They are also insufficient to adequately trace the results
of hydrographic changes. Diminished production at the time
of rapid decline of temperature is apparent late in September.
Increased production follows declining flood and stable tem-
peratures and a downward movement of nitrates (Pl. XLII.)
in October, and the phenomenon is apparently again repeated
in December, though the volumes do not equal those of the
preceding year.

As a whole, 1896 was a year of but slight plankton produc-
tion, averaging only 1.16 (average of all catches) or 1.05 (aver-
age of monthly averages) cm.* per m.* This is only a half or
a third that of other years in our records (see table on p. 292).
The silt, on the other hand, is more abundant than in any other
year, averaging 2.55 cm.’ per m.° to .28, .72, 1.91, and 2.11 re-
spectively for 1894, 1895, 1897, and 1898. The total movement
in levels for this year at Copperas Creek is 53.16 ft., an excess of
that in all other years but 1898 of 4 to over 40 per cent. (Ta-
ble I.). From this fact,and from the evidence accumulated in
the detailed discussion, it is apparent that the oft-recurrent

315

floods of this year are responsible in large degree not only for
the increased silt but also for the reduced production of plank-
ton. The floods of this year were not only more numerous,
but they were also more effective as reducing factors, since they
rarely reached stages of considerable overflow, So long as the
flood does not exceed bank height its flushing action is concen-
trated in channel waters, and impounded backwaters do not
contribute so largely to channel plankton, nor are they so im-
mediately connected with the channel on account of the bank
development along the stream. The floods of 1896 were of
such a character that they continually flushed the channel
without at any time, except midwinter, forming any large body
of impounded water in which the plankton had time to reach
any marked development. Although there was a plankton in
the backwaters—e. g. Thompson’s and Phelps lakes—which was
more abundant than that in the channel (see Pl. XX XVII. and
XL.), contributions from such areas to the channel plankton
are relatively small owing to their slight connection with the
stream in this year.

As shown in Table X., the average amount of nitrates in
1896 is 2.34 parts per million; in 1897, 1.66; and in 1898, only.81.
The smallest production of plankton observed in the years cov-
ered by our data has thus taken place in water richest in ni-
trates. Other forms of nitrogen than the nitrates vary in the
same general direction with these. It seems probable that ni-
trates, or available nitrogen generally if not, indeed, nutrition
as a whole, are less dominant in determining plankton produc-
tion in our waters than other environing factors, as, for exam-
ple, in this instance, hydrographic conditions, or, more specitic-
ally, current in its relation to time for breeding.

1897.

(HablesplDIe erly XI Ven WeTe)

There were 34 collections in this year, of which 6 were
madeat intervals of abouta month from Februaryto July, and
the remainder at approximately weekly intervals, or less, during

316

the remainder of the year. All of the collections were made
with the plankton pump. This was a year of high winter floods,
a normal March rise, a belated June rise, but prolonged low
water throughout late summer and autumn. The collections
afford a good opportunity to observe the result of prolonged
low water and a late autumn. ;

From February to July the collections are too infrequent
to enable us to trace the curve of plankton production or de-
tect any cyclic movement. Of the two collections in February
the first was made under the ice sheet and yielded little plank-
ton or silt. The second, made while the ice was going out,
contained much more silt—the result of the rising flood. Both
were very poor in plankton (.03 and .05 respectively), but
neither showed the least evidence of stagnation conditions such
as obtained in 1895. This was due to the larger volume of wa-
ter and the swifter current and greater dilution of sewage, as
well as to the briefer ice blockade and the direct connection of
channel waters with the vegetation-rich bottom-land lakes and
forests when the ice was full of air-holes, so that the equilibrium
of gases in the water did not undergo so violent a disturbance
as in 1895.

In the March collection there is evidence of the increas-
ing production as vernal temperatures approach. The col-
lections of April and May were both made on the decline of
the March flood, and both le at temperatures between 60°
and 70°. This spring presented ideal conditions for a very
large plankton production, namely, uninterrupted decline, with ~
run-off of impounded backwaters in which the plankton had
had abundant time to breed. Neither of our vernal collections
shows any large production, though that of April hes in the
period in which the vernal maximum may be expected. It is
not improbable that a maximum occurred but was not detected.
The June collection lies in the midst of turbulent flood waters,
as the great proportion of silt (26.33 cm.’ per m.°) indicates.

From this point until the close of our operations in March,
1899, the weekly interval of collection was adopted, and the

317

data accordingly afford opportunity to trace the cyclic move-
ment in production in this period.

The July pulse has a duration of 32 days,—from June 28 to
July 30.—with a maximum amplitude of 8.16 cm.* per m.* on
the 14th. Its mean falls on the 20th. This was a month of
falling river levels with slight interruptions by local rains, of
rising temperature and of falling nitrates, but of increasing
sewage contamination (Pl. XLIV.) as shown by the rising chlo-
rine and oxygen consumed. The pulse presents a very sud-

‘den drop in production from 6.40 cm.* on the 16th to .92 cm.’ on

the 21st, followed by an immediate recovery to 6.91 on the
23d. I amataloss fora satisfactory explanation of this fluc-
tuation. There is no change in levels at Havana (see page
160) which suggests flood, though there is a slight increase in
turbidity (Table III.) and was a rise of .1 ft. at Copperas
Creek on the 20th which does not appear in the Havana gage
readings. The chemical analysis of the sample taken on the
21st (Table X.and Pl. XLIV.) contains evidence of some dis-
turbance in conditions. There isa sharp decline in nitrates,
nitrites, and oxygen consumed, with a check in the rising
chlorine, while free and albuminoid ammonia and total or-
ganic nitrogen move upwards. Had the oxygen consumed
risen and the free ammonia fallen, all indices would point to-
ward access of recent storm water carrying silt into the stream
and locally diluting the plankton, though not materially af-
fecting the hydrograph. In any event the fluctuation in pro-
duction is correlated with a localized disturbance in chemical
conditions suggesting in some particulars restricted access of
recent storm waters.

The average production for this month (4.69) is higher
than in any other year excepting 1894 and 1895, due it seems
to the somewhat stable conditions of continued decline in ley-
els, with slight overflow sufficiently prolonged (3 weeks at 6 ft.)
to afford time for breeding plankton in the waters of overflow,
though apparently similar floods in 1896 resulted in much light-
er production (Pl. X.). The main difference in hydrographic

318

conditions between the summer floods of 1896 and those of 1897
hes in the fact that in the latter year a great spring flood
preceded the summer floods. This, it seems, might occasion
the difference in summer production apparent on comparison
of these two years. The slowly receding spring overflow of
1897 seeded the submerged territory with cysts, spores, and rest-
ing stages of the planktonts which afford the basis for rapid
production upon the next flood invasion. In 1896 the summer
floods follow a period of two years in which there had been no
prolonged overflow in a period of marked plankton production.
The overflowed lands were thus not recently seeded, and pro-
duction was longer in gaining headway in 1896 and did not at-
tain the same amplitude.

It is to be noted that this pulse arises in declining nitrates
and falls away as the temperature rises.

The August pulse does not reveal itself plainly in the vol-
umetric data, though it stands out more clearly in the statis-
tical curves (Pl. LII.), Adopting these as a clue to its limits,
the pulse has a duration of 25 days—from the 30th of July to
Aug. 24. The volumetric data would apparently terminate it
on the 17th and limit it to 18 days. Its greatest amplitude is
2.02 cm.® per m.’, attained on both the 3d and 10th. Accepting
the shorter interval, the mean falls on the 10th, 21 days after
that of the former pulse, while with the longer interval it is on
the 14th—24 days after the preceding mean. This is a month
of remarkably uniform production, the departure from the
mean in no case exceeding 26 per cent. It is accompanied by
stable hydrographic conditions, the total movement being 2.2
ft., most of which occurred in the first week. After a heat
pulse in the first week the temperature conditions were also
stable, while in the chemical conditions there is but slight
change. The chlorine increases as the sewage contamination
rises with decline in levels. The absence of any marked max-
imum in this month is evidently due to the fact that the ani-
mal plankton which forms the greater part of the volumetric
pulses has not greatly fluctuated as a whole. The occasion for

319

this-may be detected in the slight wave of the chlorophyll-
bearing organisms (PI. LII.), which in comparison with the
wave of July and September is indeed diminutive. There is,
however, nothing in the chemical data to explain this suppres-
sion of the pulse of the chlorophyll-bearing organisms.

The average production for this month as a whole, 3.65
em.’, is large, though not so great as that of 1894 (9.67) or 1895
(4.03), both, like 1897, with stable conditions. It is, however,
ereatly in excess of the production in 1896 (1.12) and 1898 (.91),
when August floods flushed out the stream.

The September pulse, on the other hand, is very well de-
fined. It has a duration of 35 (28) days,—from Aug. 17 (24?)
to Sept. 21,—and a maximum amplitude of 19.80 cm.’ per m.*
on the 14th. Its mean falls on the 9th (10th), 30 (27) days
after that of the preceding pulse. As a whole, this is a month
of great stability. The total movement of the hydrograph is
only .4 ft—the smallest monthly movement recorded at Ha-
vana during the years of our operations, and but rarely sur-
passed in many years at Copperas Creek (Table I.). Most of
this movement—Sept. 3-10—was due to the flash-boards placed
upon the LaGrange dam. The chemical conditions also are
in the main remarkably uniform, the only aberrant movement
being the constant upward tendency of the chlorine (Pl. LIL.)—
an index of the increasing proportion of sewage in the stream.
There is, however, no proportional increase in the various forms
of nitrogen, though they all exhibit a shght upward movement.
The temperature is sustained at summer heat (80°+) till the
middle of the month, dropping 10° in the third week.

The plankton, however, exhibits considerable fluctuation,
rising to a maximum of 19.80 cm*. per m.? on the 14th, and fall-
ing again to 3. on the 21st, at the rate of 2.4 cm.’ per day. This
is the maximum record for this year, though, it may be, not
equaling the undetected vernal maximum. It is also the lar-
gest volume recorded inany year after the first week in July.
Contributing causes for this exceptional development are to be
found in the stable conditions and concentration of fertilizing

320

materials attending low water. This is the month of greatest
production in 1897, and also the one of lowest unutilized ni-
trates, the latter not exceeding 1 part per million during the
month. It isin the rising chlorine (Pl. XLIV.) that we have
a suggestion of the degree to which sewage has made contribu-
tion to the stream. The unutilized nitrates do not of course
afford a measure of its quantity.

The October pulse has a duration of 42 days,—from Sept. 21
to Nov. 2,—with a maximum amplitude of 12.92 cm.* per m.’ on
the 5th. Its mean also falls on the 5th, 26 (25) days after that
of the preceding pulse. This extended volumetric pulse is found
to include within its limits two of the pulses of chlorophyll-
bearing organisms (cf. Pl. LII.),one culminating Sept. 29 and
the other Oct. 19. The month was one of continued hydro-
graphic stability. The total movement in levels was only .d ft.,
due mainly to the check in evaporation resulting from decline
in temperatures. The temperatures in this month average
about 64.5°, which is 6° to 8° higher than the average in other
years of our records. The difference between the extremes is
only 17° as compared with 23° in 1896 and 27° in 1898. The
autumnal decline in this year has come later and progressed
less rapidly, at least till the last ten days of the month (Pl. XL),
than is usuallythecase. Thecurve of the October, as well as
that of the September, pulse is delimited on either side by
declines in temperature.

The chemical conditions in this month (Pl. XLIV.) are less
stable than in September. The nitrates and nitrites move in-
versely with the plankton,and both chlorine and free ammonia
ascend rapidly to unusual heights, suggesting the presence of
sewage in which decay had not yet progressed as far aS was
wont during warmer weather. This is doubtless the result of
the Peoria sewage pulse, which as winter approaches extends
down stream toward Havana, and under the stable low-water
conditions of 1897 appears in exaggerated form.

In view of the stable conditions, excessive fertilization by
sewage, and abnormally high temperatures, it is not surprising

321

that the production in this year exhibits a monthly average
(5.95 em.*) 5 to 25 times (see table on p. 292) that foundin the
same month in other years.

The decline at the close of this pulse to .06 cm.’ on Noy. 2
reaches the lowest point recorded after the midwinter-flood con-
ditions of the previous February. This decline is abrupt and
complete, and is followed by a recovery in production of ap-
parently normal proportions. The prime cause may he in the
cyclic growth and reproduction of the planktonts in which an
“internal” factor may be dominant, or it may be due to the
operation of one or more external factors in the environment
or to the combined action of internal and external factors.
What external factors can be cited to “explain” this abrupt
decline in production in the midst of these apparently stable
conditions? In the first place, the minimum record (.06 cim.’)
was made when the autumnal decline had reached 54° (a little
below the yearly average), and after a decline of 25°+ from
the summer heat of 80°-+. The cumulative effect of this
change in temperature is suggested, and similar declines in pro-
duction during or towards the close of the autumnal decline in
temperature in other years may be cited in corroboration of this
conjecture. The recovery in production in this year in the face of
the cumulative effect of further decline may not weaken the force
of this conjecture, since it occurs at a time of change in the con-
stituent organisms of the plankton. This minimum of produc-
tion is, then, a period of readjustment between summer and
winter conditions. Again, in the chemical conditions the
pulse of the nitrites (Pl. XLIV.) and chlorine, and the steady
rise in free ammonia may indicate conditions which compelled
a readjustment of the fluviatile population and resulted ina
temporary decline in production. It is not, however, a simple
matter to find corroborative instances in the records. It may
be that we have in this marked decline at the close of this
pulse an instance of combination of the internal (cyclic) factor
on the part of the constituent organisms and several depress-
ing agencies in the environment, whose united effect is this
almost complete but temporary suppression in production.

322

The November pulse has a duration of 21 days,—from Nov.
2 to 23,—with a maximum amplitude of 1.86 cm.’ per m.? on
the 15th. Its mean falls on the 16th, 42 days after that of the
preceding pulse. The limit between this and the December
pulse is not well defined in the volumetric data, and any treat-
ment from the cyclic standpoint seems arbitrary. The end of
the pulse might as well be regarded as Dec. 7, in which case its
duration is 35 days and its mean falls on the 21st, 47 days after
the preceding one. The conditions during this month are not
so stable as during September and October. The autumn rains,
though shght, cause a movement in levels of 2.1 ft. and intro-
duce considerable silt into the stream. These are insufficient
to flush out the river or to materially reduce the sewage con-
tamination. There is some decline in chlorine (Pl. XLIV.) and
considerable in nitrites, but the free ammonia continues to rise
rapidly, indicating much organic material in process of decay.
The nitrates also show much increase. The temperature de-
cline to the winter minimum is completed. The production
rises, however, in these conditions from .06 to 1.86, and continues
ata fair volume for this time of the year throughout the last
half of the month, bringing the monthly average up to 1. cm.’
per m.*—an amount surpassed only by the heavy production of
1895 (3.02 cm.’ Seetable on p. 292). This is also a year of sta-
ble November hydrograph. It may be noted that the maximum
accompanies a pulse of nitrates and a check in the falling tem-
perature , and that the decline on Dec. 7 attends a drop to ne
minimum beneath the forming ice.

The December pulse has a duration of 21 days,—from the
7th to the 28th,—with its greatest amplitude of 1.22 cm.* per m.?
on the 14th, and its mean on the 16th—80 (25) days after that
of the preceding one. This is likewise a month of stable hydro-
graphic conditions, the total movement in levels being only 1.1
ft. The ice-sheet covered the river during most of the month
(Pl. XI.), with a slight break with rising levels in the second
week. This closing of the river conduced to stagnation, as is
shown by the chemical conditions (Pl. XLIV.). The free am-

323

monia rose from a normal of less than 1 part per million in
October to 5.6 on the 28th—the maximum record for all the
analyses (Table X.). This is attended by shght increase in the
oxygen consumed and the albuminoid ammonia as well as in
the total organic nitrogen, all of which betoken the approach
of stagnation. This is reflected in the fall of the plankton pro-
duction to .03 em.’ per m.* on the 28th. The extermination of
the plankton did not approach that of Feb. 23, 1895, though
there was a marked decrease in the number of planktonts ex-
cepting only in stagnation ciliates. Temperatures during this
month were at the winter minimum of approximately 32°, with
only a slight increase to 86° with the rise of the second week.
The plankton of this December in average production (.56
em.*) falls below that of all other years with the exception of
the inadequately represented 1894. This relative falling off
results, it seems, from the near approach of stagnation, due to
sewage which the stable low water permitted under the ice-
sheet.

As a whole, 1897 was a year of heavy plankton production
when measurements are stated in plankton per cubic meter
(3.69 cm.’ if all collections are averaged ; 3.27 cm’., mean of
monthly averages). If, however, we consider the slackened
current and reduced volume of the discharge of the stream, it
is evident that the total production may not be greatly, if at
all, increased during the low-water period of high plankton
content. The vernal production, judging from results in simi-
lar conditions in 1898, was possibly very large. It is evident
on comparison, that our isolated vernal catches do not ade-
quately represent the vernal production, and, furthermore, that
the vernal maximum may have exceeded that of the low-
water period in plankton content. Fuller representation in
this period would doubtless have raised the yearly average.
The high water, rapid current, and large discharge at this period
combine to make the production in these conditions relatively
very great, as compared, for example, with that of 1896, when
the impounding action of the reservoir backwaters was slight,

324

current and discharge reduced, and plankton content below the
normal. The effect of prolonged low water, with its attendant
stability, is shown in increased plankton content, and in the
increased contamination by sewage, which under the ice results
ultimately in stagnation and great reduction of production.

1898.
(Tables III., X.; Pl. XLV., LII.)'

As shown on page 167, this is a year of normally located
spring floods of considerable amplitude followed by a disturbed
summer and a considerable autumnal rise. It accordingly af-
fords our best opportunity for tracing the vernal movement of
production in flood conditions, and also another chance to note
the effect of floods at times of reduced flow of the stream.
Both vernal and autumnal changes in temperature came on
eradually, and chemical conditions were free from catastrophic
fluctuations. The collections of this year number 52, all at
weekly intervals excepting only in January, when the regular
interval is shghtly varied. They are without exception pump
collections. The interval between collections is so brief that
the cyche movement can be traced, as a rule, and this point
of view will continue to control the discussion, though in this
year the suppression of production by floods increases the ele-
ment of conjecture in this method of treatment.

The January pulse has a duration of 28 days,—from Dec.
28 to Jan. 25,—with a maximum amplitude of .81 em.’ per m.’
on the 21st. Its mean falls on the 22d, 37 days after that of
the preceding pulse, This isa period of stagnation followed
by a small flood which carried off the ice-sheet. A fall in tem-
perature immediately closed the river again, and levels fell only
to continue again an interrupted rise during the last fortnight,
carrying the imperfect ice-sheet with it, but not breaking it up
and carrying it out (Pl. XI. and XII.). This second rise removed
the stagnation conditions in the third week, producing a sharp
decline in chlorine and free ammonia (Pl. XLV.) toward a nor-
mal status. There is also a fall in the several forms of organic

325

nitrogen and a rise in nitrates and in the oxygen consumed,result
ing from the introduction of storm waters and silt. The temper-
atures remain at or near the winter minimum, rising slightly
with access of storm water. The total movement in levels is 6
ft., but the rise is so gradual that a considerable development of
the winter plankton appears. This brings the monthly aver-
age up to .45 cm.’ per m.*, an amount over twice that record-
ed in 1899 and forty-five-fold greater than that in the flood
of 1896. The occasion for the greater production in this
year is, it seems, the greater enrichment of the waters (though
not in nitrates), the lower levels, and the shghter current, the
latter affording time for breeding even upon the slowly rising
flood. The same or even less rate of rise at higher levels—e. g.
1899—would be attended by a more rapid current with lessened
time for production.

The February pulse hasa duration of 35 days,—from Jan.
25 to March 1,—with a maximum amplitude of .67 cm.’ per m.*
on the 3d. Its mean les on the 7th, 16 days after that of the
preceding pulse. This is a month of almost continual rise,
there being only a shght cessation in the first week. The total
movement in levels is 5.1 ft., of which the greater part is above
bank height, and leads to extensive overflow. The large
amounts of silt carried (Pl. XII.) testify to the extent of the
overflow and the access of flood waters of recent origin. These
result in a contmued reduction in free ammonia and chlorine,
both of which reach approximately normal levels at the close
of the month. Nitrates rise with access of flood waters, and
the nitrites continue to decline, while the oxygen consumed
and organic nitrogen rise with the increase of silt. Tempera-
tures remain at the winter minimum throughout the month,
and an imperfect and disintegrating ice-sheet covers the stream
during a part of the month. The effect of the rising levels,
access of recent flood waters, increased current and great vol-
ume of silt is seen in the falling off of the plankton content
to a minimum of .02 cm*. per m.’ on March 1. The incipient
pulse of production of an amplitude exceptional for this season

326

is thus washed out, and the apex and mean of the pulse are
shifted to the left. Flood conditions thus check the winter
production and reduce the monthly average to .27 cm.” per _m.*
This occurs in the presence of an increasing abundance of
nitrates (Pl. XLV.). This monthly average is much higher
than that of 1896 (.02) under somewhat similar conditions.
The levels and amount of movement are about the same in
both years (cf. Pl. X. and XII.), but antecedent conditions dif-
fer. In 1896 there is six weeks of flood before February, but
in 1898 the flood begins but a fortnight before. The cumula-
tive effect of its flushing action is thus less developed in 1898,
and production is greater under similar immediate conditions.
[t is, however, but one third as great as that of February, 1899,
a month of falling levels.

The March pulse has a duration of 28 (42) days,—from the
Ist to the 29th (or Apr. 12),—with a maximum amplitude of .77
em.’ per m.° on the 22d. Its mean falls on the 22d (or 26th),
43 (or 47) days after that of the preceding pulse, Levels de-
cline in the first week of March, but thereafter rise rapidly and
continuously toa maximum of 18 ft. on Apr. 2—a point not
surpassed during our operations. The total movement in Mareh
is 7.5 ft., and the result is complete overflow following the in-
troduction of vast amounts of flood water of recent origin. As
a result of this, chlorine and free ammonia reach a flood mini-
mum, and the nitrates decline, the excess since previous heavy
rains having been leached out from the water-shed. Other
forms of nitrogen decline or remain stable, and the oxygen
consumed falls as silt declines. Owing to the great expanse of
the stream, tributary waters enter more into impounding back-
waters and drop their burden of silt there, so that channel
waters are now much freer from it than in the earlier stages
of the rise. Temperatures begin the vernal ascent, passing
from the winter minimum to 50°. In keeping with this and in
the presence of rising flood and rapid current the plankton pro-
duction begins its vernal increase, attaining an average of only
.33 cm.” per m.*—about the same level of production as that in

327

1897 (.38) and 1899 (.28),and much more than that in the more
stable conditions but lower levels of 1896. Our collections in
1896 and 1898 (cf. Pl. X. and XII.) are frequent enough to af-
ford a basis of comparison of the two years. The very small
production in the former year (.07) as compared with the five-
fold greater product (.33) of the latter may find its explanation
in the earlier rise in temperature in 1898. In this year the
average temperature of surface water is 43.3° ; in 1896, only
39.9°. In 1898, 40° is passed on the 10th; and in 1896, on the 28d.

The two summits on March 22 (.77) and Apr. 5 (.53) are due
to the separation by a fortnight of the rotiferan and entomos-
tracan maxima. The later limit, Apr. 12, may therefore be
regarded as the probable end of this volumetric pulse, and it
might therefore be designated as the March-April pulse. It is
noticeable that the decline in this pulse follows, at a week’s
interval, upon a check in the rising temperature (Pl. XII.).
On April 22 the temperature (see Table III.) is 51°; a week
and a fortnight later it is respectively 49.5° and 48.3°. It rises
to 52° on the week following. The plankton production de-
clines from .77 cm.’ on March 22 to .43,.53, and .13 respectively
in the three weeks following. The fluctuations in production
during the month seem to show a very close interrelation be-
tween production and temperature at this degree of heat and
season of the year.

The April-May pulse has a duration of 49 days,—from Apr.
12 to May 31,—with a maximum amplitude of 35.68 cm.’ per m.'
on May 3. Its mean falls on May 5, 44 (40) days after that of
the preceding pulse. The monthsof April and May are both
months of very high water, the level falling below 4 ft. on but
four days in the latter month. Thisstage of the river, exceed-
ing bank height, results in wide-spread overflow and fullest
communication between channel and backwaters. The total
movement in April and May was 6.7 and 5.9 ft. respectively.
The month of April, with the exception of the first day only
(see page 161), witnessing a rapid and unbroken decline from
18 to 11.4 ft., the decline continuing till May 15, when an early

328

“ June rise” set in, which culminated at 13.8 in the last week
of May. The high levels, the rapid fall, and the subsequent rise
are all associated with strong current and rapid replacement in
channel waters. The early vernal rise in temperature noted
in March did not continue with like rapidity. The rise from
33° to 51° occurred in 21 days, while that from 49.5° to 73°
takes 49 days. In 1898, 70° is attained on May 19, while in 1896
it is reached 27 days earlier. The result of this delay in the
vernal rise is seen 1n the shifting of the vernal maximum from
April into May in 1898.

The chemical conditions throughout this period are re-
markably uniform. The great plankton wave of the 3d is ac-
companied by but the slightest ripple in the nitrogenous matter
in the stream, a slight drop in the nitrates and rise in the free
ammonia being the only attendant phenomenon (Pl. XLV.).

The average production in April, 4.4 em.’ per m.?, is slightly
below that of the two years preceding (5.67 and 5.11) as a result
of the delay in the vernal rise and consequent shifting in the
vernal maximum, and the May average (11.30) is for the same
reasons much in excess of that in these earlier years (1.30 and
5.62).

The maximum of this vernal pulse (3 5.68 cm.*) is the lar-
gest plankton content noted by usin channel waters. The con-
ditions which environ this pulse are therefore of more than
passing interest, since they must be potent factors in determin-
ing production. Since the cyclic character of plankton produc-
tion 1s apparent throughout the greater part of our records, we
are not here concerned with those factors which operate to pro-
duce this serves of recurring waves of production, but only with
those whose influence is potent in bringing about the unusual
amplitude of this vernal pulse.

In general we may group the important environing factors
under the heads of chemical, thermal, and hydrographic condi-
tions. From all that has been said in previous pages regarding
chemical conditions it is not probable that they are immediate-
ly the occasion of this great development. An analysis of the

329

conditions prevalent during this pulse (Pl. XLV.) does not re-
veal anything pecwliar to this season. The nitrogenous sub-
stances are neither greater nor less than at other times when
production was ata minimum. It is only evident that there
is an overplus of these substances in which all correlation be-
tween chemical and plankton contents of the stream is lost.
The shght quantitative rise in nitrates (.75 to 1.1 parts per mil-
lion) a week prior to the culmination of the plankton pulse
(Pl. XLV.) may contribute to the increase, but similar rises in
nitrates elsewhere are not followed by lke results. We may
therefore dismiss chemical factors—in so far as our data reveal
them—as affording only the basis of nutrition, but neither re-
vealing nor explaining their meteoric utilization in this remark-
able pulse of growth and reproduction of the plankton
organisms.

The thermal factor peculiar to this season of the vernal
pulse is the vernal rise in temperature. This pulse in produc-
tion follows immediately upon it, rising with it and culminat-
ing shortly before summer heat is reached. The vigor and ra-
pidity with which growth and reproduction ensue in the aquatic
world is comparable with that which we see in field and wood
at this same season of the year. On the very days in which this
plankton pulse culminates, the bursting buds are releasing leaf
and flower in growth unsurpassed for rapidity during the whole
year. The animal world, notably the insects, also begin their
rapid multipheation at this period. The same fundamental
causes, whatever these may be, underlie these responses of or-
ganisms to the vernal rise in temperature both on land and
inthe water. The prolongation and gradual ascent of the vernal
pulse in 1898 may have made its cumulative effect much greater,
and thus increased the amplitude of the vernal pulse beyond
that of years of more sudden approach of spring.

The hydrographic conditions in 1898 thus conduce to the
presence in channel waters of an unusually abundant plankton at
this season. Reference to Plates, XXIX., XXXIX., and XLII.
will show that the backwaters have a greater plankton con-

330)

tent than the channel, Quiver, Thompson’s, and Phelp’s lakes
showing respectively 42.14, 51.389, and 76:17 cm.’ per m.’ of
plankton. The first two collections were taken on the same
day as that in the channel; the last, two weeks later. On May
3 the river was 11.1 ft. above low water, and thus above bank
height in almost all localities. Flood water had invaded the
bottom-lands in the middle of February, two and a half months
before, and the invasion had continued for a month and a half
before the run-off of the impounded flood commenced. Time
for breeding a plankton had thus elapsed, and hundreds of
pools, ponds, lakes, and swamps which had dried up in the
drouth of the previous fall afforded a proline seed-bed of rest-
ing stages of plankton organisms to populate the impounded
and submerging waters. The slight current, shoal and warm
waters, and abundance of organic debris in these impounding
regions contribute also to the great development of plankton
which the rapid decline in levels draws off into the channel to
mingle with and enrich the plankton content of its waters.
The proportion of impounded water entering the channel at
times of such rapid decline from the high levels of April, 1898,
is avery large part of the run-off, and predominates over waters
of tributary streams which contain but little plankton (see
Pl. XXIV.).

The conjunction of the vernal rise in temperature and
the run-off of the impounded flood from reservoir backwaters
in which the plankton has had time to breed are thus dominant
factors in determining the amplitude of this unusual vernal
pulse of plankton in channel waters.

The effect of the flood of the last part of May upon plank-
ton production is apparently slight. The decline from the
maximum of 35.68 cm.’ on the 3d was well under way, reaching
10.31 on the 10th, and 5.22 on the 17th with the first entrance
of flood waters. The remainder of the decline forms a very
regular curve in which no break due to flood waters—such,
for example, as that of August, 1896 (Pl. X.)—can be traced,
This is not due to the presence of an abundant plankton in the

331

waters of tributary streams such as Spoon River, the paucity of
whose plankton content (.023 cm.’) may be seen in Table IV. and
Plate XXIV. It is the result of the relatively greater volume
of impounded backwaters into which, by reason of the ease of
entrance in overflow stages, the flood waters of tributaries in
part make their way. Their diluent action is thus less than at
lower levels, and owing to river levels their contributions go
into backwaters quite as much as into the channel. Thus, at
such levels Spoon River flood water invades the Thompson’s
Lake region to the north and rushes southward through the
bottoms about Phelps Lake (PI. II.). At levels only a trifle be-
low that of this flood all of the storm waters are carried with-
in the banks of Spoon River and enter the channel directly.
Conditions such as these at the mouths of tributaries tend to
render floods which occur during overflow stages less destruc-
tive to the channel plankton.

The June pulse has a duration of 35 days,—from May 31 to
July 5—with a maximum amplitude of 6.99 cm.* per m.* on
June 14. The mean also falls on the 14th, 40 days after that
of the preceding pulse. Thisis a month of falling levels, the
“June rise” (p. 161) declining from 13.6 to 9.6 ft. above low water
—a total movement of 4 ft. The decline was checked thrice by
silt-bearing flood waters of slight proportions, the results of
which are seen in the increased silt content of the catches. The
chemical conditions are relatively stable, the only marked
changes being the usual summer rise in nitrites and chlorine
(Pl. XLV.). The nitrates fall somewhat, while the other forms
of nitrogen remain somewhat uniform, exhibiting no move-
ment in correlation with, or proportionate to, that in the plank-
ton production. Temperatures exhibit an upward pulse whose
apex coincides with that of plankton production. Flood waters
may contribute to the depressions which delimit this heat wave.
The average production for this month (see table on p.292) 3.96
cm.* per m.* is larger than that found in any other year save
1895, when abnormally low water prevailed. It exceeds that

302

of 1896, our year of fullest observation, by over fivefold. These
two years are much alike in that both (cf. Pl. X. andXII.) have .
continuously falling levels from a “June rise” just culminated,
with similar rates of decline and much the same flood duration.
They differ in the fact that the level of 1898 is on the average
4.2 feet above that of 1896. Higher levels with increased res-
ervoir action of backwaters thus seem to conduce to greater
production in this instance.

The contrast in the amplitude of the April-May and the
June pulses (Pl. XII.) is very striking, the former being five-
fold greater than the latter. Both occur on declining floods at
almost identical levels (11.1 and 11.9 ft.). The principal differ-
ences in environmental conditions lie, first in the higher tem-
peratures (by 20°) in June, and, again, in the duration of the
flood on whose decline the pulse appears. The April-May pulse
appears at a level which had been exceeded by ten weeks of
overflow, while that of the June pulse had been exceeded by
only four. Greater time for breeding is thus afforded in the first
instance. Iam inclined to think that the main factor in this
decreased production is to be found in the fundamental mid-
summer decrease apparent in most years and localities in our
quantitative catches by the silk net. . To this decrease summer
heat may be one of the contributing factors.

From this point onward in our records the variations in
amplitude of the fluctuations in plankton production are but
slight, andit may seem from the volumetric point of view of
little importance. Since, however, they may continue to illus-_
trate what I have called the cyclic movement in plankton pro-
duction | shall endeavor to trace the recurrent pulses wherever
they can be found in the data.

The July pulse has a duration of 21 days,—from the 5th to
the 26th,—with a maximum amplitude of .88 cm.’ per m.* on the
19th. Its mean falls on the 18th, 34 days after that of the pre-
ceding pulse. This is a month of most pronounced fall in river
levels. The distance between the extremes (9.4 and 2.5 ft.)
and the rate of decline (.25 ft. per day) are unequaled in any

339

other month of our plankton operations. It is a decline from
overflow exceeding bank height to the midsummer minimum
within four weeks. This sweeping change in river levels in-
volves great hydrographic modifications and accompanying
disturbance in the equilibrium between the plankton and its
movement. It brings about a reduction of the reservoir action
of the backwaters to a minimum. Such waters as Phelps and
Flag lakes (Pl. II.) speedily lose all connection with the river,
’ and the greatly reduced contributions enter from those which
maintain permanent connection with the stream, for example,
from Thompson’s Lake. The inflow of water from tributary
streams thus comes to form more and more the principal source
of channel waters as levels decline. These tributary waters are
mostly of recent origin, from rains or springs, and have not had
time as yet to breed a plankton of much volume. I believe this
growing preponderance of tributary waters to be one of the
factors responsible for the slight amplitude of this July pulse.

Along with this there comes also a further decline in
nitrates (Pl. XLV.) and a slight increase in free ammonia and
chlorine indicating a greater proportion of sewage. The heat
pulse of the last fortnight in July is not attended by any simi-
lar movement in plankton production.

The August pulse has a duration of 28 days,—from July 26
to Aug. 23,—with a maximum amplitude of 1.62 cm.’ per m.’
on the 2d. Its mean falls on the 9th, 22 days after that of the
preceding pulse. In this month there begins a series of small
rises in the river which flush the stream repeatedly at inter-
vals of one to two weeks until October. Two of these fall
within the period of this pulse, result in its suppression, and
shift its apex and mean to the left. The total movement in
levels inthis month is 8.2 ft—a distance not equaled in any
other August of our records. The result is seen in the low av-
erage of production (.91 cm.*), which is but one fourth to one
tenth that in other years save only 1896 (1.12)—also a year of
much hydrographic disturbance.

J04

The nitrates are at a minimum (PI. XLV.) during this
month, and the sewage contamination is shown by the high
nitrites and increase in chlorine and freeammonia. The move-
ment in these substances is correlated with that in the river
levels rather than that of the plankton. The maximum ampli-
tude of this pulse follows at an interval not exceeding a week
the heat pulse of the last part of July, and its slight decline co-
incides with a period of lowered temperatures.

The September pulse has a duration of 42 days,—from Aug.
23 to Oct. 4,—with a maximum amplitude of .95 cm.* per m.? on
the 20th. Its mean falls on the 12th, 34 days after that of the
preceding pulse. The movement in levels in the month of Sep-
tember is 5.9 ft., and no less than five small rises appear in the
records during this pulse (see page 161). The result is a con-
siderable fluctuation in nitrites, chlorine, and free ammonia,—
all of which tend to run high at this season—and a depres-
sion of the plankton to a continued low level of production, .69
em.’ per m.° being the monthly average. The production in
other and more stable years is from two- to thirteen-fold great-
er. In 1896 alone, a year of even greater September disturb-
ances, does the production fall below that of 1898. The net
decline in temperature is about ten degrees, and the production
at the decline of this pulse is lower than that in other instan-
ces, save one, since the preceding April. The cold wave in the
middle of the month (PI. XII.) with a temporary decline of 20°
coincides with a slight decline in production.

The October pulse has a duration of 35 days,—from October
4 to Nov. 8,—with a maximum amplitude of .42 ¢m.* per m.* on
the 18th. The mean falls on the 20th, 88 days after that of
the preceding pulse. This was a month of more stable hydro-
graphic conditions, though the flood at its close brings up the.
total movement to 3.7 ft. Considerable movement in chemical
conditions also occurs, as this is the beginning of the period of
readjustment to lowered temperatures. The nitrates rise slow-
ly, the nitrites fall to the winter minimum, and the chlorine
and free ammonia fall and rise with river levels. It is in this

339

month that the greater part of the autumnal decline in temper-
ature occurs, the total reduction being 27°, at the rate of about
1° per day. This, with the other environmental changes above
noted, necessitates considerable readjustment on the part of
the plankton to the new conditions. We find here as in corre-
sponding conditions in other years a decline to a minimum pro-
duction, which in 1898 lowers the monthly average to .24 em.*
per m.’, the least recorded for this month in any year (see table
on p. 292). The average temperature of surface waters in October,
1898, is about 56.4°—about the average, and 8° less than in 1897,
when production was much higher (5.95 ¢m.°). It is 2° higher than
in 1895, when production was double (.57) that in 1898. I at-
tribute this least production in 1898 in part to the unstable con-
ditions in the month prior, and in part to the cumulative effect
of the rapid decline in temperatures, which exceeds by 30 per
cent., or more, that in other years of our records. The rapidity
even more than the extent of the change seems to be the po-
tent factor in depressing production. It is significant that this
most complete suppression of plankton production occurs at
this season of greatest change in environmental conditions.
The November pulse has a duration of 35 days,—trom Nov.
8 to Dec. 13,—with a maximum production of 1.26 cm.’ on Dee.
6. Its mean falls on Dec. 2, 43 days after that of the preceding
pulse. This was a month of continued rise to a maximum of
8.7 ft. on the 25th, after which the river fell. The total move-
ment was 3.1 ft. This autumn flood brought with it from bot-
tom-lands and prairies a load of silt composed largely of the
summer’s growth of vegetation, as well as the accumulated ref-
use from industrial establishments on the banks of the stream
above our location. The silt thus reaches the unusual amount
of 22.18 cm.’ per m.’ on Noy. 22. The chlorine and free ammonia
decline with the dilution of the sewage caused by flood, the ni-
trates continue their autumnal rise, and other forms of nitro-
gen remain rather constant. The net temperature decline is
only 10°, reaching, however, almost the winter minimum. There
is no rapid decline in temperature, and the hydrographic

336

changes are also relatively gradual with the exception only of
the rise on the 17th. There is under these conditions a gradual,
though slight, rise in production, which with the establishment
of winter temperatures and decline in levels culminates at 1.26
em.* on Dec. 6. Increase in stability even in winter conditions
thus tends to increase production.

This November pulse drops suddenly in the silt-laden
waters of the slight rise in river level on Dec. 11 to a minimum
of .01 on the 13th. The completeness of this decline is doubt-
less due to the fact that this collection was made in storm
waters of recent local origin due to local rains. Flood waters
of slight extent were thus intercalated in the stream, and if
there was a normal decline in production accelerated it to
this extent ; or it may be that the flood is solely responsible for
the separation of the November and December pulses. The
cyclic movement elsewhere renders this also a matter of con-
jecture.

The December pulse has a duration of 28 days,—from Dee. 13
to Jan. 10,—with a maximum of 1.98 cm.’ per m.* on Dec. 20. Its
mean falls on the 22d, 20 days after that of the preceding pulse.
This isa month of falling river levels with the exception of the
rise of .4 ft. on the llth. The total movement is 3.4ft. Since,
however, all but 0.4 ft. of this is downward movement, the en-
vironmental stability is greater than the extent of the move-
ment indicates. Temperatures under the thin ice-sheet that
formed in the first week change less than 2°, and throughout
the period of the pulse the several forms of nitrogen (Pl. XLV.)
vary but little. The chlorine, free ammonia, and oxygen con-
sumed, however, rise steadily as levels fall, to fall again as the
river levels rise at the close of the month. This increase is again
an index of the approach of stagnation under the cover of the
ice-sheet and with the advance of the Peoria sewage pulse down
stream as winter comes on. Stagnation is not reached, how-
ever, andin the relatively stable conditions of this period of
the plankton reaches a level of production (1.98) not before
attained since the close of the June pulse (Pl. XII.). It may be

337

significant that the nitrates fall during this period of increased
production (Table X.) to half the content in November. The
average production in this month (.99) isin excess of that in all
previous years excepting 1895, when stable conditions of longer
prior duration were prevalent. The relation of stability in en-
vironmental conditions to increase in plankton production is
thus confirmed by the data of this month.

As a whole, 1898 was a yea of relatively heht Aalon
production, averaging 2.13 cm.* per m.’ (mean of all collections),
or 2.08 (mean of monthly averages). This is all the more
apparent when we note (PI. XII.) that production falls below 2
em.’ in all but eight weeks of the year and below 1| in all but
fourteen. The only large production is found in April—June,
and the unusual extent of this brings up the yearly average.
The well-defined vernal pulse under peculiarly favorable hydro-
eraphic conditions, and the suppression of production by the
flushing effect of repeated floods are the prominent features of
the year’s record. The effect of stability of environmental
factors in increasing production, and of instability in suppress-
ing itisapparent. The cyclic movement of production is also
to be traced throughout the year.

1899.
(Tables III., X.; Pl. XIII., XLV., LII.)

Collections at weekly intervals were made in this year
through the month of March. The 13 collections afford an op-
portunity of tracing the effect of the interrupted ice blockade
which continued during the first two months in semi-flood con-
ditions, and of noting the effect of the early maximum spring
rise upon production.

The January pulse has a duration of 21 days,—from the 10th
to the 3lst,— with a maximum amplitude of .5 cm.’ per m.* on
the 17th. Its mean falls on the 18th, 27 days after that of the
preceding pulse. ‘This is a month of gradual though consider-
able change in levels, the total movement being 3.5 ft. The
eradual character of the rise permits the development of a

338

slight pulse of production which, however, declines with the
culmination of the rise and increase in current attendant
thereon. The nitrites rise again (Pl. XLV.) to twofold the
quantity present in December, when plankton production was
fourfold as great as in the present month. The movement of
free ammonia and oxygen consumed suggests varying degrees
of sewage decay, while the chlorine falls with flood dilution.
The ice blockade continues till the close of the month, but gives
way with rising temperatures and the culmination of the flood
on the 24th. The average production for the month (.18 cm.’)
is much less than that of January, 1898 (.45), when the direc-
tion and extent of movement in levels were very similar, but the
levels lower by 2.5 ft. on the average, and hence the current less
rapid. Less time for breeding is thus afforded in 1899, and
production is less than in 1898.

The February pulse has a duration of 28 days,—from Jan.
31 to Feb. 28,—with a maximum amplitude of 1.92 em.’ per
m.* on the 21st. Its mean falls on the 20th, 33 days after that
of the preceding pulse. During the first three weeks of this
month there is a steady decline in levels under an ice-sheet of
unusual thickness (31 em.), which was carried out by the sud-
den rise from a level of 5.5 ft. to one of 10.2 ft. in the last week.
The temperature beneath the ice remains at the winter mini-
mum of 32°+ with a variation of lessthan1°. Chemical con-
ditions (Pl. XLV.) are subject to abrupt and great change with
the rising flood of the last week. This is due in large part to
the sudden increase in industrial refuse from the accumulations.
on the banks above previous water levels at Peoria and Pekin.
These are carried into the stream by the flood and cause the
fivefold increase in oxygen consumed and the rise in albumi-
noid ammonia and organic nitrogen. Prior to this flood there
had been a rise in nitrates, and on the 21st the chlorine, nitrites,
organic nitrogen, and free ammonia all exhibit a very marked
upward movement suggestive of the approach of stagnation
conditions. Stagnation is not reached, however, owing to the
higher levels, to the break in the ice inthe blockade late in Jan-

339

uary, and to the repeated flushing of the stream in the preced-
ing autumn. The plankton was not therefore diminished by
the change in chemical conditions which had progressed up to
the time of the sudden rise on the 28d. The average produc-
tion for the month (.81 cm.’) is the largest recorded in any
year. Production reaches on the 21st the unparalleled midwin-
ter level of 1.92 cm.*—an amount in excess of any production
in July-November of the preceding year. This is due, it
seems, to the stable conditions attending the decline of the
January rise, to the high levels which permitted some access of
plankton from backwater breeding grounds, and to the freedom
from stagnation. The near approach of this condition is, how-
ever, revealed by the direction of the changes in chemical con-
ditions, but its arrival was prevented by the almost equally
catastrophic invasion of the sudden flood of the 23d, which re-
duced the plankton content to a minimum of .07 cm.’ on the
28th. Plankton production of this volume at approximately
freezing point, equaling that at the summer maximum in July,
is a Striking instance of the adaptation of the plankton to the
extremes of temperature.

The March pulse has a duration of 28+ days,—from Feb. 28
to Mar. 28+-,—with a maximum amplitude of. 54 cm.’ per m.’ on
the 7th. Its mean falls on the 12th, 20 days after that of the
preceding pulse. In the first week the rise of the last of Feb-
ruary ceased at 13 ft., affording overflow of all but the highest
bottoms. Levels continued to fluctuate between 13 and 14 ft.
during the remainder of the month, so that we have here a
month of sustained overflow with repeated additions of storm
water. The sewage and organic materials carried into the
stream with the first access of flood waters decline rapidly dur-
ing the month, as is seen (Pl. XLV.) in the rapid and consider-
able decline of chlorine, oxygen consumed, free ammonia, and
organic nitrogen. Temperatures rise but 5° during the month,
and the average for the month is from 5° to 10° lower than that
in other years. The reduction in production with the initial flood
and the thrice-repeated influx of storm water, combined with

340

late spring and high levels with rapid current, result in but
slight plankton production in channel waters. The pulse is
barely perceptible, and its amplitude is very slight. The
monthly average is but .28 cm.*, a production somewhat less
than that in 1898 (.33) and 1897 (.38), though exceeding that
of 1896 (.07).

In comparison with other seasons these three months of
1899 exhibit a greater production, reaching even tenfold, and
this result is correlated with the freedom from stagnation and
the gradual change in river levels in the first two months.

COMPARISON WITH TRIBUTARIES AND BACKWATERS.

STATION M, SPOON RIVER.

(Tables IV., XI., XIV.; PI. I. IL, XIV., XXII., XXIV., XLVI., XLVII.)

ENVIRONMENTAL CONDITIONS.

This is a tributary on the right bank, draining 1,870 square
miles of fertile prairie, and entering the Illinois about a mile
and a half below our plankton station (Pl. I. and II.). No
large cities lie in its water-shed, so that its pollution by sewage
is not excessive. Its waters therefore represent the normal
run-off of the central water-shed, and ave typical of the tributa-
ry waters received by the Illinois below La Salle. A study of
plankton content and chemical conditions will accordingly
throw light upon the relations existing between channel and
normal tributary streams in general in the matter of plankton
production.

Our station at which collections were made in Spoon
River was located immediately below the abandoned trestle of
the Chicago, Peoria, and St. Louis Railroad (Pl. XIV. ), less than
forty rods from the mouth of the stream. A blockade formed
by a raft of driftwood prevented further progress up stream
during a part of the time, and in the winter the ice which
formed and continued in the tributary when at times the main
stream was open, made approach, even to the bridge, difficult.

Owing, however, to the current, our collections, with one

341

or two possible exceptions, were all made in tributary water,
though the chosen location could not always be reached.
These exceptions were at times of backwater from the Illinois.

Spoon River has near its mouth a width of 75-100 ft., and
a depth below low-water mark in the Illinois of 10-14 ft. It
runs between almost vertical banks of alluvium (PI. XIV.), and
has a hard gravelly bottom full of sunken logs which form
treacherous snags at low water. The current at the point of
collection at low water may be scarcely perceptible, while at
times of sudden flood, due to local storms in its water-shed, it is
so strong that a boat enters it with difficulty. At such times
its load of silt and drift is very great. During the heated term,
and especially when the heat pulses occur and there is little
wind to ruffle the surface, the green water-bloom on this stream
is remarkable, exceeding—possibly because of protection from
wind—that of the main stream in lividness and density.

The turbidity of this stream (see Table IV. and p. 179) is
ereater than in any other locality and serves as a general index
of its silt content. It is, for example, in 1898, 51 cm. (average
of disc readings), while in the Illinois River in that year the
average is 40 cm.

COLLECTIONS.

All collections were made with the plankton pump. Ex-
amination of the plankton of this stream was begun in August,
1896, and continued at a fortnightly interval until December of
that year, and thereafter until the close of operations in March,
1899, at approximately a monthly interval. From the charac-
ter of the curves of plankton production in the Illinois
River we may infer that collections at this long interval in
Spoon River will fail to give us any adequate or accurate delin-
eation of the movement in production in this stream. Further-
more,in the summer season at least, the plankton of Spoon River
is composed largely of those small planktonts—such, for exam-
ple, as Huglena and Trachelomonas—which almost wholly escape
through the meshes of the silk net. A comparison of the plank-
ton of the two streams on volumetric data derived from the

342

catches of the silk net is to some extent misleading, owing to
the relatively greater proportion which the escaping planktonts
form of the production in the tributary stream. Another factor
which prevents an equally accurate volumetric determination
of the plankton of the two streams is the presence in Spoon
River of a much greater proportion of silt. For example, in 1896
and 1898 the estimated ratios of silt and plankton in the average
of the catches (Table IV.) is .007 to .349 and .029 to .796. In 1897,
when low water and slight current and some probable invasion
of channel waters increased the plankton production, the ratios
are 1.257 to 1.178. The ratios of the first-named years are more
nearly normal for this tributary, and in such ratios it is quite
probable that the error in silt estimation to some undetermined
degree tends to prevent any precise determination of the actual
plankton production. Nevertheless, after a very wide margin
is allowed for probable error in the data, the comparison of
production in the two streams is instructive and significant, for
it is the direction of change or contrast in production which is
of greatest consequence, and this may be found even in the
presence of a large but distributed error.

It should be noted that the plankton ordinants in the
Spoon River plates (X XII.—XXIV.) are plotted on a scale ten
times that of all other stations in order to give an appreciable
height to the plankton portion of the entry.

PLANKTON PRODUCTION.
1896.
(Table IV.; Pl. XXII., XLVI.)

For purposes of comparison I introduce at this point a
table which gives in terms of monthly averages of plankton
in cm.’ per m.’ the relative production in the seven locali-
ties examined by us. ‘The number of collections entering
into each average is stated, and the grand average of all collec-
tions and of the monthly averages are given for each station.

In 1896, nine collections were made in Spoon River in
August-December, the average being only .007 cm.’ per m.°

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348

(Table IV.), with a maximum of .032 on August 25. The
amounts reported are all very small, and the significance of
their differences is questionable. The following correlations
with environmental conditions may be noted. There is little
plankton (.004) in the turbid (8 em.) flood water of August 18 ;
there is more (.032) in the clearer water (380 cm.) of August 25.
The production following the rapid decline of temperature in
September falls to a minimum (.002) as it does in the channel
waters (.53 and .23), and like the latter rises again (.008) late
in October, after a month of somewhat stable temperatures
(Pl. XXII). The December production (.002 and .001), how-
ever, Shows no rise corresponding to that in the main stream.

The average production in Spoon River for the five months
in 1896 in which collections were made there is only .0O7 cm.
per m.*, while that in the main stream is 97 times as great, the
production there exceeding that in the tributary from 4-fold to
380-fold in each month (see table between pp. 342 and 343).
Spoon River water is thus throughout this season a diluent of
the channel plankton.

The chemical conditions during this period reveal unutil-
ized nitrates averaging 1.2 parts per million in Spoon River to
1.15 in the Ilhnois. Other forms of nitrogen are somewhat
more abundant in the main stream. ‘There is, however, plenty
of food for the plankton in the tributary, and other causes than
poverty of nutrition must be cited to explain its paucity of
plankton.

1897.

(Tables IV., XI.; Pl. XXVIIJI., XLVI)

There are 13 collections in this year, at intervals of two
to six weeks. They average 1.257 cm.’ per m.*, and havea
maximum of 7.296 on September 11. The conditions attending
the unusual plankton production in Illinois River channel
waters in this year affect Spoon River also in much the same
manner. The vernal overflow mingled impounded backwaters

o44

to some extent with the channel water of Spoon River, and the
prolonged drouth of the autumn cut down the run-off and re-
duced the stream to a series of slack-water pools, in which,
owing to the reduction in current, there was time enough for
an abundant plankton to develop.

The explanation of the contrast between the plankton con-
tent of this stream on February 3 (.002) and 26 (.092) is to
be found in the hydrographic conditions. The tributary shares
the rise in production seen in channel waters (.03 to .05). The
rising flood of the 26th forces the impounded backwaters away
from the channel, and in their downward movement some of
them get into Spoon River channel in the overflowed bottom-
lands above the point at which our collection was made.
Thompson’s Lake waters contained considerable plankton (.39)
at this season, and it seems probable that some of its richer
waters may have entered and (PI. II.) enriched Spoon River
channel plankton at this stage of river. Under such circum-
stances we find the tributary with a richer plankton (.092) than
the storm-filled channel (.05)—an exceptional occurrence in the
history of the two streams. The very slight production (.007)
on March 22 is due to the fact that Spoon River itself at this
time was rising rapidly, turbid (2 cm.) with silt, and invading
rather than receiving contributions from the impounded back-
waters through which it rushed to the channel. The collection
of April 27 was also in flood waters (turbidity 5 em., silt 4.75
em.*), which are in part responsible for the check in the flood
decline at that time (Pl. XXIII.). This held back contribu-
tions from connecting and impounded backwaters, and the
plankton content is low (.048), while that in the main stream
(5.11) shows no such flood reduction. In the collection of May 25
(.44) we find the tributary waters as well as the main channel
exhibiting a vernal rise in production, though its amplitude is
13-fold greater in the latter. The lower river level (8 ft.) then
prevalent precludes the possibility of any considerable contri-
butions from impounding areas, though accessions in small yvol-
ume are not improbable, On June 28 the silt-laden storm-water

345

in the Illinois River channel (turbidity, 2 cm., silt, 26.33 em.°)
contains but .27 cm.’ per m.* of plankton, but the vernal pro-
duction in the tributary does not suffer so marked a decline,
remaining at .25 em.’, so that its diluent action on this occasion
was slight. As in the main stream, so also in the tributary
there is a dropin production in August (.056) toabouta fourth
that in June-July.

From this time throughout the remainder of the year the
production in Spoon River is considerable, exceeding that in
the main stream, however, only in the last two months of the
year. The production rises on Aug. 26 to 1.248 and on Sept. 11
to the unprecedented record of 7.296 em.*, while that in the
main stream is only 2.77 on Aug. 24, and on Sept. 7 and 14 is
8.47 and 19.80 respectively, On the 2lstand 29th of September
production in the Illinois falls again to 3.00 and 4.04 cm.’ re-
spectively, while in Spoon River on the 30th it is only 2.96,
production in the tributary thus remaining below that in the
channel throughout this period. The low chlorine in Spoon
River at this time (38 to 4 parts per million. See Table XI.)
as compared with the main stream (21-50 parts) indicates
that the Spoon River water is not contaminated by channel
water, and that we are dealing with an indigenous plankton.
None of our collections falls in the period in October (PI.
XLVI.) in which chlorine in Spoon River rises temporarily.
The three collections of November-December, 1.351, 1.99, and
.599 cm.*, are respectively 22.5, 1.6, and 20 times as great as the
production in the main stream at the same time. The month-
ly averages for this period are 1. and .56 for the Illinois, and
1.671 and .599 cm.’ for Spoon River, so that the excess in the
latter is apparently not more than 50 per cent. Under these
conditions the tributary stream enriches the plankton of the
channel instead of diluting it, but its discharge is shght.

Hydrographic, thermal, and ice conditions are similar in
the two streams, and we find the main difference in the chem-
ical conditions. Aside from evidences of sewage contamina-
tion in the last weeks of October, the Spoon River records

346

(Pl. XLVI, Table XI.) show somewhat uniform conditions in
strong contrast with the instability in these particulars in the
Illinois. With greater stability Spoon River apparently pro-
duces a more abundant plankton in this low-water autumn.

The exceptional production in this autumn stands in
strong contrast with the poverty of this tributary in the same
months in 1896 and 1898. As seen in the table between pp.
342 and 348, the maximum monthly production in the low
water of 1897, as recorded in monthly averages, is from 285 to
to 5,180 times greater than that in any month in this season in
the other two years. A comparison of the data in Table XI.
for the three years in question and of their plottings on Plates
XLVI. and XLVI. will show the great similarity in the chem-
ical conditions which accompanies this remarkable inequality
in production. The accompanying table summarizes the data
concerning nitrogenous contents of the water and the plank-
ton.

NITROGENOUS SUBSTANCES AND PLANKTON, 1896-1898.

MONTHLY AVERA GES—PARTS PER MILLION.

November December
ge,/28| 2 y, Ba |e. / 26) 2 2 5
W ts | foo] 2 2 ss |Loss || Gao | & g s
So Aalee A eo ee | a A A
TOOO cee eee .065 | .84 1013) ||) 1165) Saas" |) Yor 52 | .008 | 1.3 .002
TOO J sarees sey eet 052 | .76 | .008 .56/1.671 | .022| .68 | .005 | .63 | 599
1SOS aie wees 026 | .37 .009 .58| .oor | .084} .89 | .o15 | .33 Rolo)

Other factors than these chemical conditions are thus re-
sponsible for the great differences in production in these three
years. Low water, shght or imperceptible current, and conse-
quent time for breeding in the latter part of 1897 are the most
probable factors in causing the high production of that sea- -
son, while in other years the recent origin of the tributary wa-
ter, from rains or springs, precludes any considerable produc-
tion in water otherwise capable of supporting an abundant
plankton, as is shown by the production in 1897.

As a whole, Spoon River plankton in 1897 reflects the same

347

relation to environmental factors that was found in the case
of the Illinois. This is seen in the increased winter produc-
tion, in the vernal rise, in the decline after the vernal pulse,
and in the unusual autumnal development. The tributary
stream, with but four exceptions, was acting as a diluent of
channel plankton at each examination of its plankton content.
These four exceptions—on Feb. 26, Nov. 2 and 30, and Dec. 28—
are due in the first instance to channel flood, and in the last
three cases to exceptionally low water in the tributary and less
stable chemical conditionsin the channel. In the four years in
which Spoon River was examined they are the only exceptions
to the general rule that these tributary waters are dilu-
ents of the channel plankton. The average production for 1897
(1.257 em.*) is 180 times that recorded in the last half of 1896,
and 45 times that for 1898—as a result of the low-water con-
ditions discussed above.

1898-1899.
(Tables IV., XI.; Pl. XXIV., XLVIL)

There are 14 collections at intervals of four or five weeks
in the 15 months included in this period, and they fairly rep-
resent the contributions of this tributary ina year of consider-
able flood and repeated access of storm water. In 1898 there
is but a trace of plankton in the January (.017) and February
(.016) collections, while that in the March collection (.124) isthe
maximum for the year. At this time the spring flood is nearly
at its height (16.5 ft.), and the waters of Spoon River are in quite
free connection with the general overflow that spreads over
the surrounding bottom-lands. On the day of the Spoon River
collection there was .43 cm.* of plankton in the Illinois and .79
the week prior in Thompson’s Lake, three miles above Spoon
River (Pl. Il.). There is thus three and a _ half times as much
plankton in the main stream and six times as much in Thomp-
son’s Lake. With its maximum burden of plankton, the trib-
utary is still a diluent, and its plankton content at this time is
probably in large part derived from the run-off of the contigu-

348

ous impounding backwaters. No Spoon River collection falls
in the week of the vernal maximum (see Pl. XII.), but the col-
lections of May (.023), June (.096), and July (.036), all exhibit
a considerable rise above the usual level of production, and all,
moreover, were made during the run-off of the spring flood and
receive slight contributions from impounded waters. It is n
the direction of the movement in production that the tributary
and mainstream are alikeatthisseason. In the amplitude of the
curve of production the difference is very great, production be-
ing respectively 491-, 41-, and 16-fold greater in the latter in
the three months named.

Throughout the remainder of the year 1898 plankton pro-
duction in Spoon River is at a minimum, there being but the
merest trace of living organisms in the catch. None of these
catches was taken in rising flood water (Pl. XXIV.), though
they all show the results of the flushing action of the frequent
floods which wash out with rapid current whatever plankton
may have developed in the tributary, and at the same time ai-
ford little opportunity for its replenishment. The relative ab-
sence of backwater feeders in the tributary stream at this
stage of river levels serves also to emphasize the poverty in
production of the tributary.

The average for 1898 (.029 cm. per m.?) is exceeded over
73-fold by the yearly average of the Llinois (2.13). The tribu-
tary waters are at all times—at least in so far as the data go—
diluents of the channel plankton, reaching their lowest ratio,
.124 to .88, in March, when they share most in impounded back-
waters of the main stream, and at the same time are at the max-
imum of their own reservoir action.

This meager production occurs in waters almost as rich in
nitrates (av., .67 parts per million) as the main stream (.809),
and, save on rising floods (Pl. XLVII.), in normal chemical con- —
ditions. The potent environmental factor is rather to be found
in the recent origin of the tributary waters than in any availa-
ble chemical data.

In the three months’ collections of 1899 we find that the low

349

level of production continues under the ice, which remains on
the stream for about three months (Pl. XXIV.). There is con-
siderable fluctuation (Pl. XLVII.) in the organic nitrogen, free
ammonia, and oxygen consumed, most if not all of which are
traceable to the access of storm waters rather than to any con-
siderable degree of stagnation. The catches are all full of silt,
though the turbidity of the stream is not great under the ice in
January and February. The silt at such times is mainly com-
minuted vegetation brought in by the storm waters. There is
a slight rise in the plankton production in March (.026), when
the river stands at 12.9 ft. and the plankton-rich waters of
Thompson’s Lake (see Table V.) are brought into connection
shghtly with Spoon River by overflow.

During these three months the production in the tributary
is but a small fraction—never more than a tenth—of that in
the main stream. It continues to be a diluent of the channel
plankton.

SUMMARY.

The average plankton in all of the Spoon River collections
is .465 cm.’ per m.* of water. In the Illinoisit is 2.19, or over
4.7 times as much. If we omit the low-water period, Aug. 26
to the end of 1897, and compare only the remaining collections
between Aug. 18, 1896, and the close of operations, the ratio of
production in the two streams becomes .044 to 2.19, or 1 to 50.
As has been repeatedly pointed out in the preceding discussion,
this contrast in production is not explainable on any difference
im available chemical data. The tributary waters are fertile
enough to yield a large production. The explanation is rather
to be sought in the hydrographic conditions, in the recent ori-
gin, from rains or springs, of the tributary water, and in the more
rapid current, and consequently the less time for breeding a
plankton in the tributary environment. That this is the proba-
ble explanation is borne out by the large production in the only
period of prolonged low water in the tributary in the fall of
1897, when time for the growth of the plankton was afforded
in the slack waters of the tributary.

350)

The immediate effect of the access of the tributary waters
of the stream 1s as a whole diluent upon the plankton content
of the Ilhnois. A mixture of equal volumes of each would re-
sult in a reduction in the Illinois to 1.33 cm.’ per m. from 2.19
—a falling off of 39 per cent., or even of 49 per cent. if we omit
the low-water period of 1897. If we consider the areas of the
drainage basins as an index of the relative volumes of water
carried by the two streams, and determine the effect of Spoon
River contributions, we find the net result, based on the aver-
ages of our collections, to be a decline in plankton content in
the Illinois from 2.19 em.’ per m.* to 2.00—a decline of 9 per
cent. Ifthe low-water period of 1897 is omitted, the decline
is even greater, namely, from 2.19 to 1.96—a fall of 11 per cent.
in the plankton content as an immediate result of the contri-
butions of this tributary. Spoon River thus exerts in the econ-
omy of the [llnois an immediate diluent function upon its pro-
duction, which, qualitatively, is approximately 10 per cent.

STATION C, QUIVER LAKE.

(Tables V., XLII. ; Pl. IL, 1V., XV.-XVIL, XXV.-XXIX., XLVIIL, XLIX.)

ENVIRONMENTAL CONDITIONS.

This lake lies on the right bank of the Illinois (PI. IT.), ex-
tending parallel to the river for a distance of three miles, in-
cluding Quiver Chute. This is the lower end of the lake, which
is separated from the Illinois River only by a low mud bank
submerged at levels of 4 ft. and crossed just below our plankton
station in the main stream by two “cut-offs” which bring a va-
rying volume of river water into the chute, the amount de-
pending upon the relative levels on the two sides of the spit.
The close connection of the lake and river makes the former
responsive to all changes in level in the latter at all stages of
water. This lower spit extends northward as a low bank 5 to
40 rods in width and generally less than 6 to 8 feet above low-
water mark, lying between the lake and river. This is covered
with low willows and, to the northward, with heavy forest (PI.

301

IV., XV., XVI.). The northern end of the lake is Y-shaped,
and the western arm is known locally as Dogfish Lake.

The lake from Quiver Creek to its mouth near Spoon River
is about 3 miles long, and does not exceed a quarter of a mile
in width at any point. The lake proper, that is, above the
chutes and excluding the western arm, contains at low water
about 230 acres (93 hectares), but approaches 500 acres if these
contiguous bodies of water be included. As levelsrise, its area
increases rapidly, and at 6 to 8 ft. the demarcation between
river and lake is obliterated, and extensive areas to the north-
ward (PI. II.) come into connection with it, while at higher
levels it quite loses its identity as a separate area (PI. III.) ex-
cept as the tree tops and its clearer waters serve to differentiate
it from contiguous channel waters. Its depth at low water
(river levels about 2 ft. above low water of 1873) is throughout
most of its area less than 2 ft., and in the deepest parts, at the
narrows above the chutes, it does not exceed 4 ft.

The bottom is of hard sand and bluish clay covered gener-
ally by a soft alluvial ooze of | to 2 or more feet in depth. Its
eastern bank is a sloping sandy bluff (Pl. XV.), which abounds
in clear springs of cold water, occurring the whole length of
the lake and contributing nota little to its water supply. The
western bank is of black alluvium, and the ooze along its mar-
gin of considerable depth. The eastern arm of the lake receives
Quiver Creek, a tributary draining 220 sq. miles of sandy upland
and “second bottom.”

The vegetation, described on page 244, in low-water condi-
tions frequently chokes the channel, which extends from the
mouth of Quiver Creek in a tortuous course through the vege-
tation along the western shore of the eastern arm towards the
point between this and Dogfish Lake, and thence in an equally
crooked and shifting course towards the mouth.

It was in this channel in low water, and in its neighbor-
hood at times of high water, that our plankton station was lo-
cated (Pl. II). It is simply a shifting path through the vegeta-
tion, and is not generally marked by deeper waters than adja-

302

cent regions. It was only a few meters in width, and in 1894
and 1895 it was frequently necessary to clear it of encroaching
vegetation in order to make feasible the 30-meter oblique haul.
In high water and generally in years subsequent to 1895 it was
only necessary to avoid with drawn net or pump the clumps of
Ceratophyllum which still dotted the bottom in this neighbor-
hood. The point of collection thus lay at all seasons towards
the narrowing end of the lake and in the path of the current
maintained by Quiver Creek and the marginal springs. At
times of high water it was in the direct path of the downward
current of impounded backwaters thrust towards the channel
by the encroaching eastern bluff (PI. IT.).

At times of flood the invading river waters extend for some
distance, even to the middle of the lake, crowding the clearer
lake waters to the eastern side. When the western bank was
not submerged the backwaters entering by way of the chutes
sometimes reached the plankton station. Our collections were
always made in evident lake water unless otherwise stated
(Table V.).

The access of creek and spring water, the extensive areas
of dense vegetation, and the shoal waters, which at all levels
form the greater part of the area of this lake, all combine to
make the temperature conditions subject to great local varia-
tion, and to diversify the fauna and flora indigenous or adven-
titious in the plankton of this body of water.

COLLECTIONS.

Our chronological series in this lake includes 115 collections,
extending from June 6, 1894, to March 28, 1899. The collec-
tions in the several years number 14, 13, 31, 24, 26, and 7 re-
spectively. Their distribution by months is shown in the table
between pages 342 and 343. In the earlier years the interval of
collection was somewhat irregular, though with 6 exceptions
every month is represented. From July, 1897, collections were
made at least every fortnight and on the same day as at the
other stations. The oblique-haul method was used—with a few

3909

exceptions of repeated vertical hauls (Table V.) in the winter
flood of 1895-96—from the beginning till May 22, 1896. After
this date all collections were made with the pump.

This lake is a type of some other bottom-land waters, spring-
fed and rich in vegetation, and our collections suffice to show
the relation which these bear to production in the adjacent
channel waters. They alsoserve for comparison of production
with that in other backwaters less rich in vegetation, and since
the quantity of vegetation in Quiver Lake varied from year to
year they also throw some light on the effect of vegetation up-
on plankton production in a single area.

PLANKTON PRODUCTION.

1894.
(Table V., Pl. XXV.)

The 14 collections in this year average 1.08 cm.’ per m.’ to
2.49 em.’ in the Ilhnois. The maximum (3.50) falls on Septem-
ber 6. There isa striking resemblance in the planktograph of
Quiver Lake for this year (Pl. XXV.) and that of the adjacent
channel (Pl. VIII). The amplitude is generally less in the form-
er, but the direction of movement is the samein both. The
June production (monthly average) is low in both Quiver Lake
(.23) andthe Illinois (.74); it rises in July (2.20 and 5.12); and
it declines in September (2.12 and 1.36) toa minimum of .80 and
84, from which it recovers slightly in October (.95 and .61) to
fall again in November (.02 and .10) and December (.03 and
10). The only exception to this parallelism in the movement
in production is seen in August, when in Quiver Lake produc-
tion drops to .74 but attains a seasonal maximum of 9.67 in the
river. Aside from the fact that this is the season of greatest
predominance of vegetation in the lake, owing both to growth
and to low river levels, there seems to be nothing in the en-
vironmental conditions to be correlated with this contrast.

While as a whole for this year the contributions of Quiver
Lake (1.08 cm.’ per m.*), as shown by our data, only result in

304

an immediate dilution of the channel plankton of the Illinois,
there is a season when its plankton content exceeds that of the
river. The average of the collections in September-Novem-
ber in Quiver Lake exceed by 70 per cent. the average of those
in the Illinois. This is the season when some autumnal decay
of vegetation takes place, and this vegetation-rich lake has a
larger plankton production than the river waters which it
thus enriches.

1895.
(Table V.; Pl. XXVI. XLVIIL)

There are 13 collections in this year, with an average of .78
cm.’ per m.*° as compared with 3.22 in the Illinois. The maxi-
mum of 4.57 occurs on April 29, being but 1.26, or 22 per cent.
less than the corresponding vernal maximum in the adjacent,
but—owing to river levels in this season—non-contiguous, river.

The similarity ia the movement of production between this
lake and the river noted in the previous year can be traced in
1895 in but two instances,—in the rise to the vernal maximum
and in the increased production in December (cf. Pl. XX VI. and
IX.). Outside of these periods there is no resemblance between
the planktographs of the two waters. From July to November
inclusive the low level of production is broken only by two
pulses, both of which attend a rise in river levels with increase
in the impounding function of the lake. These changes in level
shift the loosely attached vegetation, and are often followed
by death and decay of masses of aquatic growths. The slight.
rise in the last week in August (Pl. XX VI.) caused an invasion
of muddy river water into the lower end of the lake. Decay of
the vegetation and death of many fish, clams, and other ani-
mals ensued in the invaded area. The flood early in Septem-
ber (Pl. XXVI.) came largely from up-river rainfall, and the
lake waters, enriched by invasion, were impounded with result-
ing increase in the plankton. It was not apparent that either
of the large collections were made in invading waters, and I
infer that the plankton was indigenous and not adventitious,

300

though the invasion resulted in the enrichment of the lake by
the decay of vegetation and dead animals. It may also have
“seeded” the lake with organisms whose subsequent multipli-
cation caused these temporary increases in production. These
same floods are attended by depressions in production in the
main stream, so that these two pulses in Quiver Lake lie in
these depressions, intercalated between summits of the curve
of production in channel water (cf. Pl. IX. and XXVI.). The
inference is suggested that the run-off of this plankton-breeding
impounded water of Quiver Lake and similar reservoirs else-
where may have contributed to the increased production in
channel waters following the flood.

The plankton content of Quiver Lake water on July 26
(.71) and Sept. 6 (1.57) thus exceeds that in the river on July 23
and Sept, 6 (.68 and .99), and its contributions to the stream, if
any were made, serve to enrich the channel plankton. In three
other cases the lake production exceeds that of the river; on
Feb. 23 (lake, .03, river, .01), April 9 (1.42 and .52), and Dee. 28
(.29 and .01). In the first instance there was stagnation under
the long continued ice-sheet in both river and lake, as wasshown
by the great mortality of fish in the latter. The plankton, how-
ever, did not reach the degree of extermination in lake water that
it did in the channel, since there was less sewage, more veg-
etation, and access of spring water. In the April instance
the silt burden of the channel waters (4.67 cm.’, Pl. IX.)
is much greater than that in the lake (1.43), and suggests the
intercalation of storm water in the former, resulting in the
slight rise in levels (Pl. IX.) and the lessened plankton content
of the channel waters as compared with those of the less dis-
turbed lake. The great contrast on December 28 is also due
to the flushing action of the great winter flood which depleted
the channel plankton but increased the impounding function,
and therefore breeding capacity and productivity, of the lake.
Each of the three instances of greater production in lake than
in river waters occurs with rising river levels, when the rising
river checks the relative outflow from the lake or otherwise

306

increases its impounding function. Whatever run-off from lake
to channel occurs under such conditions will result in a slight
enrichment of the plankton content of the channel waters
with which the tributary mingles. At all other seasons of this
year our collections indicate that the immediate result of the
access of Quiver Lake waters to the river is a reduction in
plankton content of the main stream, on an average for the
year for equal volumes of tributary and channel waters, of 38
per cent.; or if the relative volumes of each based on areas of
drainage basins are considered, the plankton content of the
channel is reduced to 3.19 cm.’ per m.’—a decline of about 1
per cent.

This was a year of maximum development of vegetation
in Quiver Lake. The low water of this and the preceding year
and the absence of floods adequate to flush the lake of its
loosely attached vegetation permitted an unusual and enor-
mous growth of Ceratophyllum and other aquatic plants, which
choked the lake from shore to shore and from Quiver Creek far
down the chute towards its mouth (Pl. XV.). The very slight
plankton production in its waters during the summer is due, I
believe, to this predominance of vegetation. The rise in pro-
duction when river levels rose in July and September (PI.
XXVI.) attends, among other factors favorable to production
already discussed, a reduction in the relative abundance of
vegetation.

1896.
(Table V., Pl. XXVIL.)

There are 31 collections in this year, with an average of
2.59 cm.> per m.* as compared with 1.16 in the Illinois. The
maximum of 16.76 cm.’ occurs on April 24, exceeding by 7.37
cm.’, or 78 per cent., the production in the adjacent river on
that day.

The similarity in the movement of plankton production in
Quiver Lake and the Illinois noted as generally present in 1894
and but slightly so in 1895 is quite apparent throughout this

307

year, as will be seen on a comparison of Plates X. and X XVII.
With a few exceptions which will be noted in the subsequent
discussion, the trend of the production is similar in the two bodies
of water to a most striking degree month by month throughout
the year.

With rising temperatures in February-March, production
in the lakeattains the unusual level of 1.75-1.85 cm.* per m.’,
an amount not equaled at this season in this lake in any other
year, and exceeding by 88- and 26-fold the production in the
adjacent flood-swept stream (see table between pp. 342 and 343).
This greater production in the lake is due, it seems, to the fact
that Quiver Lake collections in these months represent the im-
pounded backwaters of the eastern bottom-lands forced through
the lake by the configuration of the eastern bluff (Pl. II.). Slight
current and time for breeding permit in them a production not
possible in the silt-laden rapidly flowing channel waters with
which at our plankton station (PI. II.) they are contiguous
during prevalent levels. The larger production in this year
may be attributed to the enrichment of the water by the great
mass of organic debris accumulated on the now submerged bot-
tom-lands during the two preceding years of low water.

The vernal pulses in the two waters coincide in the posi-
tion of their limits and maxima though not in amplitude at
any time, as will be seen on comparing Tables III. and V. and
Plates X.and XX VII. The vernal development in the lake pro-
ceeds more rapidly, appears earlier, and attains a greater am-
plitude than it does in the river. Thus, on April 10 and 17 there
is present in Quiver Lake 3.29 and 16.32 cm.’ of plankton per
m.° to 1.68 and 4.45 in the river. The rate of increase is 4.7 times
as rapid in the lake, and attains on the 17th a volume 3.7 times
as great as that inthe river. The maximum (16.76) is almost
twice that in the river (9.39). The large development (16.32) on
the 17th indicates that the true maximum probably occurred a
few days earlier in the lake than in the river. A partial ex-
planation of this phenomenon, and also of the earlier and more
rapid rise in production, may be found in the somewhat higher

308

temperatures in the shoaler and clearer impounded waters
which are drained off through Quiver Lake. The temperatures
of surface waters in the lake from February up to the time of
the maximum are from 1° to 15° higher than in the river, as
will be seen on comparison of the thermographs on Plates X.
and XX VII.

The May pulse in Quiver Lake attains 8.14 cm.’,—more than
twice the amplitude of that in the river, 3.56,—while the aver-
age production for the month in the lake (2.99) exhibits a sim-
ilar ratio to that of the river (1.30). The very sudden decline
from 8.14 on the 8th to .51 on the 16th attends a decline of
about 2 ft. in river levels at.a stage which cuts off the lake from
large impounding areas to the north, and also, at this season of
the year, brings the submerged flora to the surface.. These two
factors combine in effecting this sudden drop in production in
the lake before it appears in the stream (cf. Pl. X. and XXVIL.).

The flood which wipes out the rising June pulse in the river
(Pl. X.) increases the impounding area and relative occupation
of the lake water by vegetation and permits a pulse of some
amplitude (2.60) to develop in the lake, while only a belated
and slight development appears in the contiguous river. As
levels fall in July and impounding areas are again cut off and
vegetation anew occupies a relatively larger proportion of the
lake, production declines to so slight an amplitude that a July
pulse can hardly be traced (Pl. XXVII.), and the average
monthly production in the lake falls to a fifth of that in the
stream, whose plankton content it had in previous months of
the year exceeded.

With the rise of the August flood, production again assumes
a pulse-like character, lagging throughout its development a
few days behind that in the adjacent stream (cf. Pl. X. and
XXVII.), and lacking in the lake the cleft in the apex of the
curve caused in the river production by the flushing action of
local floods.

The seven collections during the remainder of the year ex-
hibit a similar direction of movement in production in every

309

instance but two, Oct. 14 and 29. In the first of these, silt-laden
flood waters in the river, but not in the lake, interrupt the par-
allelism. In the second instance the production of the lake de-
clines and that of the river rises—again as a result of the prior
flood conditions, as will appear on a comparison of the sequele
of the June and August floods in the two bodies of water. In
these, as also in the October flood, there are indications that the
rising plankton pulse common to both is temporarily suppressed
in the river and continues undisturbed and reaches an earlier
culmination in the lake, but only a delayed one of shght ampli-
tude in the stream.

The average production in the lake in the last four months
of the year exceeds that in the river by 52 per cent. and in five
of the seven collections.

The comparison of production in Quiver Lake and the IIli-
nois River in 1896 is very instructive in several important par-
ticulars. In the first place, both the relative and absolute pro-
ductivity of the lake has increased, rising from 1.08 and .78
em.” in 1894 and 1895 to 2.59, an increase of two- to three-fold.
The ratio of productivity in the lake to that in the river in 1894
was | to 2.3; in 1895, 1 to 4.1; while in 1896 it falls to 1 to .45. The
low average in the river is, as has been shown, the result of the
repeated flushing by storm waters. The increase in the lake is
due to the higher levels and increased impounding function,
and to the actual and relative decrease in its vegetation. The
combined result of the operation of these factors is thatin this
year the lake waters cease to be diluents of the channel plank-
ton and become sources of enrichment. Considering the areas
of their respective drainage basins, and basing calculations on
the yearly averages, the net result of the contributions of Quiv-
er Lake is a rise in the plankton content of channel waters
from 1.16 cm.’ per m.* to 1.18—an increase of a little less than
2 per cent.

Not only was the average production in the lake (2.59)
sreater than that in the stream (1.16), but individual collec-
tions upon coincident or approximate dates exhibit the same

360

relation in 22 out of 31 instances, and 4 of the 9 exceptions fall
in the period of low water in July, during predominance of veg-
etation in the lake. The monthly averages in the lake also
exceed those in the stream in all months but July and Sep-
tember. Higher levels, increased impounding function, and
decrease in vegetation thus favor plankton production in Quiv-
er Lake, and tend to raise it from a diluent to a source of imme-
diate enrichment. :

In this connection it should be noted that the increased
production of this year (2.59) still falls below that of the river
in 1894 and 1897, and, as seen in the table on p. 292, below the
general average of the river production (2.71); and also that the
higher river levels of this year tend to lower the proportion
which the tributary spring and creek waters form of the total
volume of Quiver Lake. —

A second significant fact brought out by the comparison is
rendered patent by the frequency in this year of the coilections
in Quiver Lake. The weekly interval from April to Septem-
ber (Table V.) makes it possible to trace somewhat fully the
movement of production, and demonstrates in Quiver Lake a
pulse-like movement in production similar to that previously de-
scribed in the Illinois River, and one, moreover, which exhibits a
very striking coincidence of developmental succession. A superpo-
sition of Plate XXVII. upon Plate X. will make this demon-
stration apparent. ‘There are exceptions, but these, as shown
in the preceding discussion, are in most, if not all, instances to
be correlated with local environmental factors confined to one
or the other body of water. The return to parallelism with
the cessation of the peculiar factor incident to the interruption
serves still further to emphasize the significance of this simi-
larity. The key to the parallelism must le in fundamental
factors common to the plankton of both areas or to their envi-
ronment,

361
1897.

(Tables V., XIII.; Pl. XXVIII., XLVIII.)

There are 24 collections in this year, with an average of
0.88 cm.* per m.’ as compared with 3.69 in the river, and a max-
imum of 13.38 on April 27—more than twofold the production
in the river (5.11) on that day.

The collections of the first six months of this year are so
infrequent that the course of production is but slightly indicat-
ed. In February the production in the impounded waters of the
winter flood in Quiver Lake (.19) is nearly fivefold that in the
current-swept channel (.04), while in March there is little differ-
ence (.34 and .38) in their plankton content. The collection of
April 27 probably falls near the presumably common vernal max-
imum and in the midst of the decline of the spring flood. Since
Quiver Lake at the stage of river (11.6 ft.) then prevalent
contains the run-off of the impounded backwaters to the north,
it is not surprising that its plankton content (13.38) is more
than double that of the river (5.11). The similarity in the
movement of production thus far seen in this year is interrupted
on May 25 by the decline in the lake to 1.29, while the river
rises to 5.62. The decline in the lake may be attributed to the
great reduction in impounding area due to the decline in levels
to 8 ft., and to the gain in proportion in the lake of the contri-
butions of creek and spring water and of the area occupied by
the now rapidly appearing vegetation. The silt-bearing flood
of June in the river yields less (.27) than the lake waters (1.26)
impounded by the rise of the river.

In the last six months of the year the collections are of
sufficient frequency to enable us to trace somewhat the move-
ment in production. This period is marked by a great depres-
sion in plankton content as compared with that of the same
season in the previous year, the average for each being 1.06 and
.23. The parallelism in the movement of production can still
be traced in the slight tendency in Quiver Lake to increased
production in July, September, and November at times of pulses

362

in the channel plankton. The amplitude attained in the lake
is, however, but slight.

The explanation of this marked decrease in production in
this year as compared with that of 1896 lies, I believe, in the
hydrographic conditions of the two years. In 1896 (Pl. XX VIL.)
the average height of the river for the period August-Decem-
ber is 5.89 ft., while in 1897 it is only 2.47 ft. The impounding
action of the lake was at its minimum, and there was present
in it in these months of 1897 only abouta third the quantity of
water that it contained in the corresponding season of 1896,
and this consequently gave to vegetation in 1897 a relatively
greater predominance in the lake, and also made possible a
more frequent renewal of lake water by the contributions from
the creek and tributary springs, thus cutting down the time for
breeding. Both of these factors tend to limit plankton produc-
tion. We find, accordingly, that the lake produces on an av-
erage from August to December but .1 cm.’ per m.’ to 4.0 in the
adjacent river, that is, only a fortieth of the plankton content
of the stream. The contrast between the lake and the river in
this year is heightened by the fact that owing to low water and
increased fertilization by sewage the production in the river is
much greater than usual.

A comparison of Plates XI. and XXVIII. will reveal the
fact that in only 5 instances out of 24 in 1897 does Quiver Lake
contain more plankton than the river. Theseinstances in Feb-
ruary and April attend impounding action of the lake when it
is not differentiated from overflowed bottom-lands as a separ-
ate unit of environment, while those of June 28 and July 21
are caused by the flushing of channel waters by floods from
which the lake is exempt.

As a whole for this year, the net result of the contributions
from Quiver Lake is a dilution of the channel plankton with
which it mingles. Basing calculations upon the yearly aver-
ages and areas of the drainage basins, the quantitative effect
would be a decline in the plankton content of channel waters
from 3.69 to 3.65, or a loss of 1.1 per cent.

363

The lake waters in October-December contain (Table XIIL.,
Pl]. XLVIII.) but a fraction—from a third to a tenth—of the
nitrogenous matter that is found in the channel. ‘This is an
index of the relative poverty of Quiver Lake waters when
isolated as a separate unit of environment and dependent
upon creek and spring waters, mainly of seepage origin, for its
supply. This relative poverty, combined with the factors be-
fore discussed, les at the basis of the relatively small plankton
production in this body of water in this year.

1898.
(Tables V., XIII.; Pl. XXIX., XLIX.)

There are 26 collections in this year at fortnightly inter-
vals, with an average of 2.44 em.* as compared with 2.13 in the
river, and a maximum of 42.14 on May 3 coincidently with the
vernal maximum in the channel (PI. XII.), which, however,
falls 6.46 em.*, or 15 per cent., short of that in the lake.

The parallelism in the movement of production noted to
a varying extent in prior years may be traced also in 1898. The
most striking coincidence is the agreement in the location and
relative development of the vernal pulse, and further resem-
blance may be seen in the June pulse and the December rise
in production. The small quantities of plankton in the lake at
other seasons and the fortnightly interval of collection render
the correspondences less obvious though perhaps not less sig-
nificant.

During the low water of January and in the subsequent
flood (Pl. XXIX.) there is little plankton in the lake (.02) as
compared with the river (.45—see table between pp. 342 and 843),
though an increase with a rise in levels and development of
the reservoir function of the lake might have been expected.
There is, therefore, no January-February rise in the lake cor-
responding to that in the river unless the increase from .003
Jan. 11 to .04 Jan. 25 be held to be significant. The February
flood, which depletes the plankton of the channel, is accom-
panied by arise to .58 on the 22d in the lake coincidently with

364

a shght but not equal rise (.10) in channel production. The
March pulse in the river, with a maximum amplitude of .77 on
the 22d, is attended by almost equal production in the lake (.67).

The vernal pulse rises with like abruptness at both stations,
increasing from April 1 to May 3 from 1.03 to 42.14 in the
lake, and from 1.12 to 35.68 in the river. The decline of this
pulse is much more abrupt in the lake, falling from 42.14 on the
3d to 4.7 on the 11th—a decrease of 89 per cent. in 8 days, while
the decline in the stream is from 35.68 to 10.31, or 71 per cent.,
in 7 days. The more abrupt change in the lake plankton is due
to the fact that the decline in levels of 1. ft. in the interim be-
tween the two collections compared, is at the critical point ap-
proaching bank height, when the bottom-lands to the north of
Quiver Lake-are beginning to emerge and cut off and divert
some of the run-off of the impounded backwaters which at higher
levels make their way to the channel through Quiver Lake (PI. II.).

There is a very shght July pulse in the lake on the 19th
coincident with the July maximum in the river. Inthe early
part of August there is another maximum in the river, but no
parallel developement in the lake, owing possibly to the low
water then attained and the resulting dominance of vegetation
and tributary waters—conditions not incident to these levels
in like degree in channel waters. The rise at the close of August
and again in September, and the low level and slight change in
production in October found in channel waters are all to be
traced coincidently, or approximately so, in the less complete
records of the lake production.

The silt-laden flood waters which cause rising levels in No-
vember deplete the channel plankton (.25), increase the im-
pounding function of the lake, and lead to greater production
(.73) in the latter. There are coincident culminations in river-
and lake on Dec. 6, but the interval of collection in the lake
does not permit comparison in case of the river maximum of
Dec. 20. The large December production (1.74), six to eleven
times that of July (.16), August (.22), September (.33), or Oc-
tober (.23) is noteworthy.

365

There is thus a striking similarity in production in the
river and lake in 1898, not only in the larger movements, such
as the vernal pulse, the low level of midsummer, and the De-
cember rise, but also in the minor details which differentiate
movements at shorter intervals, suggesting in some cases, and
demonstrating in others, the presence of coincident recurrent
pulses of production with approximately similar locations but,
it may often be, with more widely differing amplitudes.

A part of this similarity is doubtless due to the fact that in
1898 for fully five months of the year, when the river was at
8 ft. or above, the lake was not, superficially at least, differen-
tiated from the general bottom-land environment, and there-
fore shares more extensively the course of production elsewhere
than it does when its emerging boundaries delimit it as a sep-
arate unit of environment. The similarity is not, however, con-
fined to this period of aquatic continuity, but appears also in
the season of delimitation, when local factors are relatively
more potent. It is also true that even in the period of conti-
nuity the environmental factors peculiar to the lake continue,
though submerged or invaded,—as, for example, the chemical
conditions, which even in flood periods exhibit a certain auton-
omy in the lake, as will be seen on comparison of Plates XLV.
and XLIX.,—to exercise some differentiating influence, which,
in the presence of the apparent tendency towards similarity of
movement in production, still produces modifications sufficient
to stamp the seasonal planktograph with a characteristic facies,
thus differentiating it from other localities.

The average production for the year is 2.44 cm.? per m.* as
compared with 2.13 in the river, so that as a whole in this year
the outflow from this lake enriches the channel plankton. On
the basis of yearly averages and drainage areas the net result
is an increase from 2.13 to 2.14, arise of lessthan .5 per cent. A
more detailed analysis of the data reveals the fact that in 7 of
the 12 months, in January, April, and June—October, the river ex-
ceeds the lake in production. As will be seen on Pl. XXIX., the
remaining months are those of high river levels, when the im-

366

pounding action of the lake is most operative and its localiza-
tion least pronounced. The largest production, in May and
June, occurs when on declining flood the flow of impounded
bottom-land waters from the north is greatest through the lake.

If we omit from both records the months of May and June,
we find that the averages of the remaining monthly averages
(see table between pp. 342 and 343) are.91 and .50 respec-
tively for the river andthe lake. Thus for ten months of the
year the plankton content of the latter is but five ninths of that
of channel waters, and during this period the immediate result
of the access of the run-off from Quiver Lake will be a dilution
and diminution of the plankton content of channel waters, due,
it seems, to the relatively more recent origin, from storm and
seepage waters, of these tributary contributions, and to the
greater prevalence of vegetation in the lake. Another factor
operative in the diminished production of the lake is relative
poverty in nitrogenous substances. For example, the average
nitrates (cf. Tables X.and XIII.) for the year in river and lake
are respectively .809 and .68; the nitrites, .121 and .029; the or-
ganic nitrogen, .92 and .569; the albuminoid ammonia, .431 and
.275; and the free ammonia, .95 and .138. The unutilized ni-
trogenous substances in the lake are, however, of sufficient pro-
portions to indicate the possibility of the support of a larger
volume of plankton if greater time for breeding were allowed.

1899.
MANES We, Ske DL SOX, SILIDX,)

The 7 collections in January-March average .67 cm.’ per
m.* as compared with .41 inthe river. Asin the previous year,
the direction of movement in production is similar in the two
regions. For example, the January pulse in both culminates
on the 17th and that of February on the 14th and the 21st, while
the March production is at low levels in both, and the apex of
the pulse is not apparent in the lake records. The invasion of
some channel flood water with the March rise and its speedy
elimination may be traced in the chemical records (Pl. XLIX.)

1

367

The production in the lake during this period is greater
than that in the river at all times of coincident examination
excepting March 14 (.14 and .35). The average production in
the lake (.67 cm.*) is 63 per cent. greater than that in the river
(.41 cm.*). This percentage of increased production is a meas-
ure, or an index, of the impounding or reservoir action of the
lake under the hydrographic conditions of these months. The
immediate result of the access of Quiver Lake waters to the
channel will be a rise in its plankton content from .41 cm.’ per
m. to .414—an increase of | per cent.

The summary of the interrelations of production in this
lake and the river will be made in conjunction with that of Dog-
fish Lake, which is only an arm of Quiver Lake.

DOGFISH LAKE.
(RADIO WIS Pl, SAVAUIL, YORK, XOOXTIO)

ENVIRONMENTAL CONDITIONS,

This so-called lake is only the westerm arm of Quiver Lake
(Pl. I1.), separated from the eastern by Quiver Point, a low
marshy spit covered with rushes and willows and lying but a
few feet above low-water mark. It is of elliptical form, about
three quarters of a mile long and one third of a mile wide,
contains about 150 acres at low water, and as levels rise it ex-
tends northward and eastward over the low bottoms towards
Mud Lake and Cartwright Slough, but it is only at highest
levels that very much of a current makes its way down through
this lake. As levels rise above 8 ft. the intervening ridge sep-
arating this lake from the river is gradually submerged, and
channel waters invade more or less of the lake. It affords the
natural channel for the run-off of the backwaters impounded
in several square miles of bottom-land marsh and forest
through the swale (Pl. I.) which extends towards Mud Lake.

Its shores are everywhere low and marshy, of black alluvi-
um, and a soft black ooze of similar origin covers the bottom of
the entire lake. In only a limited area towards the east-

368

ern side can a substratum of harder sandy clay be reached be-
neath two or more feet of this deposit. With the exception of
a narrow fringe along the eastern side, the vegetation lacks the
lies, rushes, sedges, and other emergent plants which charac-
terize the eastern shore and northern end of Quiver Lake proper
(Pl. XVII.). It consists (Pl. XVIII.) almost exclusively of Cer-
atophyllum, Elodea, and Potamogetons, which, in the low water
of 1895, represented in the plate, filled the lake from center to
periphery. Irregular openings in this dense growth appear oc-
casionally in the area, and are modified by the shifting of the
lightly attached vegetation, by wind, and by flood water.

Except at high water and during the rapid run-off of im-
pounded backwaters no appreciable current traverses this area.
It receives no immediate contributions of spring or creek water
along its margins, but depends entirely upon backwater from
Quiver Lake or flood invasions for its supply.

The examination of the plankton content of its waters ac-
cordingly affords an opportunity to test the effect of this im-
pounding factor, and also serves to throw some further hght on
the effect of vegetation on plankton development in impounded
waters.

COLLECTIONS.

The collections in this lake cover a period of two years—
from April 29, 1895, to June 28, 1897 (Table VI.). They num-
ber 48, and are distributed in much the same manner as those
in Quiver Lake in the same period. The collections of 1895 and
those of 1896 through May 8 were all made by the oblique-haul
method with the single exception of that in the flood of Feb.
27, which was one of repeated vertical hauls. The collection
of May 19, 1896, was made in the midst of rapidly growing veg-
etation by dipping from surface waters, which then afforded no
area suitable for an oblique haul. The oblique hauls were made
for the most part near the center of the lake in a channel freed
from vegetation a day prior to the collection. From May 21,
1897, all collections were made by the plankton pump in open
stretches of water amid the vegetation.

369

In 1895 the lake was choked with vegetation which the
winter flood largely removed and the recurrent floods of the
following year reduced somewhat in extent, while higher levels
lowered its relative occupation of lake waters.

PLANKTON PRODUCTION.
1895.
(Table VI., Pl. XXX.)

There were 12 collections in this year, from April to De-
cember, averaging 3.25 cm.* per m.° The average of the
monthly averages (see table between pp. 342 and 348) is 3.3
em.* to .74 and 6.65—similar averages for the same period in
Quiver Lake and the Illinois River. The maximum collection
was made Dec. 19—a very unusual date for such production.

A superposition of the planktographs of the river and
Quiver and Dogfish lakes for this year brings out some in-
structive similarities and differences in the movement of pro-
duction. The vernal pulse of April 29, in so far as the data
reveal it, is quite similar in all three localities, reaching its
ereatest development in Dogfish Lake (8.20), where im-
pounding action is greatest, and being greater in the river (5.88)
than in Quiver Lake (4.57), where, owing to low levels, the
proportion of water of recent creek or spring origin is greater
than in the channel of the adjacent river.

The June-July pulse may be found in all three localities,
but it is belated and much smaller in the lake waters. This
pulse in Dogfish Lake (4.59 cm.’ per m.*) is less than a sixth of
that in the river (30.42), where, in the semi-stagnant sewage-
polluted channel waters of unusually low levels, Moima and
other Cladocera caused the unusual production. Between the
April and June-July pulses the river levels fell 2 ft., to mini-
mum stages (Pl. XXX.), so that the proportion of creek and
spring water in Quiver Lake is probably more than doubled at
the later date. This may account in large part for the very
low production in Quiver Lake (.02) on July 8, while on July 5

370

the contiguous but impounded and current-free waters of Dog-
fish Lake contain 229 times as much plankton.

The increased production following the September flood is
apparent in all three localities, but reaches its highest level
(4.65) in Dogfish Lake, the region where the impounding factor
is greatest, while the least increase and quickest decline is in
Quiver Lake, where tributary waters of recent origin are in
greatest proportion. The low production in October is com-
mon to the three localities, reaching a slightly lower level in
the lakes (.13 and .52) than in the river (.57). The consider-
able increase in production in November-December attains the
highest level in Dogfish Lake (5.01 and 10.57), exceeding by 100-
and 17-fold that in Quiver Lake (.05 and .63), and that in the
river (4.37 and 2.60) by 1.2- and 4-fold. Here also the effect of
the quieter impounding waters of Dogfish Lake is apparent in
this relatively greater development. The large plankton content
on Dec. 19 (10.57) seems to be due to a combination of several
favoring environmental factors. This collection was made
after a steady but slight rise lasting for over five weeks, fol-
lowed by ten days of gentle decline in levels and contracting
margins of the lake. The steady rise to levels which intro-
duced no run-off currents through the lake established the 1m-
pounding function to its fullest, and invaded a considerable
stretch of margins rich in dead and decaying vegetation. There
is also at this season of the year less growth and more decay of
the Hlodea and Ceratophyllum which abound in the lake. The
collection was taken when the December flood had just be-
gun to rise (about 2.6 feet) and with the combined action
of wind and waves which attended the storm then raging had
torn loose the vegetation and dislodged many of the smaller
Crustacea and insect larvee which find shelter in it. There
were at the time 572 Allorchestes per m.? adventitious in the
plankton. A part of this large production is thus adventitious .
owing to disturbed hydrographic conditions. Nevertheless,
there still remains after such contributions are deducted a con-
siderable plankton of normal constitution (mainly Cladocera),

371

in amount certainly much in excess of the production at that
time in Quiver Lake (.63) or the river (1.74). This large pro-
duction in this locality is then, it seems, to be attributed to im-
pounding and decaying vegetation combined with accession of
adventitious planktonts.

The average monthly production (3.3) in this lake is on the
whole less than half that in the river (6.65) for the same period,
and it exceeds by over fourfold that in Quiver Lake (.74), through
which all its run-off passes to reach the river. Since the com-
parison of the two lakes is based on coincident collections, these
amounts may serve as a quantitative statement of the effect of
the environmental differences. As vegetation is much the same
in both lakes the difference in production must be attributed to
some other factor presenting a difference which may be corre-
lated with that in production. Such a factor is found in the
impounding action, which is at a maximum in Dogfish Lake
and is relatively much less in Quiver Lake at the point of our
collections, where creek and spring water of recent origin cause
a more rapid displacement of the contents of the lake and car-
ry away the products of decay of vegetation before the plank-
ton can reach the degree of development that it does in the
more stable waters of Dogfish Lake.

The run-off from this lake in this year would thus tend to
enrich Quiver Lake, though not on an average of sufficient pro-
duction to enrich the river even if it could reach it without
mingling with that of Quiver Lake. However, owing to the fact
that this lake receives no tributary creek or spring water, and
except at high levels has no bottom-land current through it, we
must infer that its run-off is confined—excepting only at stages
of general overflow—almost wholly to stages of falling water.
During rising levels and in fairly stable conditions its contribu-
tions to Quiver Lake, and thus to the river, are practically nz/.

1896.
(Table VI., Pl. XXX1.)

There are 80 collections in this year, with a distribution

302

similar to that of the collections in Quiver Lake for this year,
the only exception to the coincidence of collections, actual or
approximate, being on December 29, when on account of rotten-
ness of the ice it was not possible to get the collecting outfit to
the station.

The maximum production occurs in the vernal pulse in the
last fortnight of April, culminating at 20.35 cm.’ per m.° on the
17th, though production is also large on the 24th (19.5). In Quiy-
er Lake this maximum is on the 24th (16.76), though production
is also large on the 17th (16.32). The maximum in channel
waters (9.39) is also on the 24th. These differences in the time
of the maxima may, I believe, be correlated directly with the
thermal factor. For example, in both Quiver and Dogtish lakes
the production is large and almost equal on the 17th and 24th,
but is greater in Dogfish Lake on the 17th and in Quiver Lake
on the 24th. This lag in the maximum is correlated with the
fact that surface temperatures in Quiver Lake on the J 7th and
24th are respectively 3° and .8° lower than they are in Dogfish
Lake. On the 17th the latter is 8° warmer than the river. After
all allowances are made for the time of day at which tempera-
ture records are taken, it isstill evident that the shallower waters
of Dogfish Lake would warm up more quickly than the spring-
fed waters of Quiver Lake or the deeper channel waters, and
we have found that the thermal increase favors the earlier rise
in plankton production.

The coincidence of the dates of collection makes possible
a precise comparison of the production in the two lakes, and ©
facilitates the comparison with that of the river. A superposi-
tion of the planktographs of Dogfish and Quiver lakes and the
river (Pl. XXXI., XXVII., and X.) for this year emphasizes far
better than any description the most striking similarity at the
three stations of the movement of plankton production as shown
by the direction of the differences in plankton content in suc-
cessive collections. The correlation between jproduction in
Quiver Lake and the river in this year—discussed in detail on
pages 357-360—is paralleled in every important detail by the

BY 3)

sequence of the changes in Dogfish Lake. Indeed, the corre-
lation is, if anything, even closer, since the amplitude of the
plankton pulses is greater in Dogfish Lake than in Quiver Lake,
and the changes are here—as, for example, in August—the
more readily followed and compared with those of the river.
Since I have already compared in detail the production in
Quiver Lake and the river I shall not repeat the comparison of
these similar data from Dogfish, for the correlations are essen-
tially the same in both cases, and it will suffice simply to empha-
size the similarity of the course of production in the three local-
ities.

The similarity between the production in the two lakes is,
however, even greater than that between either of them and
the river. This results from the greater similarity of the envi-
ronmental factors inthe two lakes, with which the river con-
trasts in matters of sewage and current. The similarity of en-
vironmental factors hes in the amount and kind of vegetation,
the depth, the character of bottom and shores—excepting the
eastern margin of Quiver, the impounding function (modified,
however, in the case of Quiver Lake by the access of creek and
spring water), and the freedom from sewage. Under these cir-
cumstances it 1s not surprising that the details of the course of
production as well as its ensemble are so strikingly alike in the
two lakes.

To be specific, the similarity in details of the course of pro-
duction in Quiver and Dogfish lakes hes in the fact that in the
31 coincident collections in these waters the plankton content
rises or falls in both at the same time in 28 out of the total num-
ber. The amplitude of the change is rarely equivalent, but its
direction is identical—referring, of course, to the fact of its being
an increase or decrease, and not to the particular angle which
the lines forming a planktograph might take. The 8 exceptions
to this similarity in the direction of movement in production
are shown in the following table, and may without exception be
correlated with differences in the environment.

In this table the plankton contents of the two adjacent col-

at4

lections determining the direction of the change in production
are given under the date of the later collection, and the posi-
tion of the entries also indicates the direction of the change.

VARIATIONS IN THE MOVEMENT OF PRODUCTION IN DOGFISH AND QUIVER LAKES, 1896.

Apr. 24 | May 8 |May 16-19] May 21-22) July 3 | Aug. 15 | Aug. 29 | Sept. 16

20.35 to 13.39 to 18.40 18.40 to 1.58 11.25 1.18 3.06

IDO BIDS WEIR. seacsses 19.50 13.06 | 13.06 to 36 | 1.14 to | 3.88to | .75 to | 1.18 to
16.76 8.14 8.14 to 99 .68 to 4.36 to 1.60 to .72, to

Quiver Lake.......... 16.32 to 4.24 to 51 51 to 49 3.42 72, 5)

In almost every case these exceptions to the precise simi-
larity of movement in production in the two lakes can be cor-
related directly with some disturbing environmental factor
potent in one and not equally so in the other, that is, to local
disturbance in the environmental similarity, as follows: The
exception on April 24 is due to the earlier appearance of the
summit of the vernal pulse of production in Dogfish Lake, and
this in turn is correlated with the greater proportion of shoal
waters in Dogfish and the greater access of spring water in
Quiver, both factors favoring the more rapid and complete
warming up of Dogfish waters. As has been repeatedly
pointed out, the thermal rise deflects towards itself the vernal
rise in production.

Conditions on May 8, when Quiver Lake production doubles
and that in Dogfish Lake falls shghtly, are to be explained by
the different effect which the hydrographic changes have at the
two stations. At stages existing at the first of the month
(7 ft.) there is not sufficient overflow to carry any considera-
ble current of warm backwaters to the southward down through
the lake to the river. The content is largely of local impound-
. ing. The slight rise at that time (Pl XXXI.) would therefore
tend to increase the local reservoir action, and creek and
spring waters would most naturally be impounded along the
usual line of their run-off, in which our Quiver Lake station
lies (PIL. II.), while the plankton-rich backwaters of Dogfish
Lake are held back, hence the low production in Quiver Lake

379

on the 2d (4.24) and the larger one in Dogfish (13.39). On the
Sth conditions are changed ; the decline in levels (.6 ft.) has in-
creased the run-off, and the recent contributions of tributary wa-
ter have brought down into Quiver Lake an increased proportion
of plankton-rich impounded backwaters which increase the con-
tent at that point to 8.14 cm.*, this being, however, still below
that of contributing and declining Dogfish Lake (13.59 to 13.06).

On May 16-19 the collections were not quite coincident,
but, such as they are, they form another exception to the simi-
larity of movement in the two lakes. In Quiver on the 16th the
decline of levels brings the proportion of tributary waters at
that point into greater prominence, while on the 19th in Dog-
fish the impounding function is greatly increased by the inter
vening rise in levels (1 ft.). Examination of the collections
also shows that the maximum of 18.4 em.’ in Dogfish Lake on
the 19th is caused primarily by an extraordinary pulse, or possi-
bly a local “swarm”, of Melosira with some Cladocera, whose
apex and location the date of collection approximates.

On the 21st the plankton content in the same locality fell
to .36 cm.*—a decline of 98 per cent. in 2 days. On the 21st and
22d a quantitative survey of the local distribution of the plank-
ton in the whole area of Quiver and Dogfish lakes was made,
with the result that no development commensurate with that
on the 19th at this point was anywhere detected. Sincea sim-
ilar sudden declineis to be seen in Flag Lakeinthis same week, I
am inclined to the view that we are dealing here witha complex
biological phenonenon in which the reproductive cycles of the
organisms as well as external factors—such as possible tempo-
rary decline of food supply, or encroachment of emerging veg-
etation—are involved. This sudden decline is earlier and less
marked in Quiver Lake than in Dogfish, possibly because of in-
creasing differential environment, and thus occasions this tem-
porary dislocation of the similarity in the movement of produc-
tion on May 16-19, and again on May 21-22.

On July 3 we again find lower levels reached and accom-
panying decline in production in Quiver Lake when tributary

316

waters rise in proportion. The readjustment which this ne-
cessitates so modifies production that its movement differs,
though the difference is slight and consequently the less sig-
nificant.

On Aug. 15 and 29 we deal again with a phenomenon simi-
lar to that of May 21, namely, a pulse of large production in
Dogfish Lake with an accompanying one of lesser amplitude
in Quiver. The pulse in Dogfish was again later, apparently,
in reaching its culmination (on the 15th) than that in Quiver
(on the 7th), and its decline (93 per cent.) on the 22d more
complete than that which Quiver attains (63 per cent.) on that
date from its maximum (4.36) on the 7th. The conditions in
Quiver Lake are further complicated by the fact that on the
15th river water was just beginning a temporary invasion at
the point of collection (see hydrograph, Pl. XXXI.). Save for
this invasion the similarity of movement might perhaps have
been preserved on the 15th. The abrupt and extreme decline
in Dogfish Lake on the 22d, however, with the resulting inter-
ruption of the similarity of movement on the 29th, is in some
way related to the excessive development of the 15th, which
may bring into operation again the factors above suggested in
connection with the like phenomenon in May. It seems not
improbable that the sharper localization in Dogfish Lake due
to absence of current and tributary waters and the presence of
these factors in Quiver tends to intensify environmental in-
fluences or inherent tendencies of the plankton in the one area,
and to minimize some if not all of them in the other, and that
this differentiating influence of these purely local factors is
fundamentally the cause of the dislocations and disturbances
of the otherwise similar movement in production in the two
lakes. These exceptions seem, however, to emphasize the es-
sential similarity in the production in the two areas, a similar-
ity founded on the common factors of the environment shared
equally by both, and on the identity, in the main, of the con-
stituent organisms of the plankton.

The general hydrographic conditions of this year affect

307

profoundly the plankton production in this lake and in Quiver
also. Although the average height for this year (6.975 ft.) is
almost the same as in 1897 (6.903 ft.), the distribution of high
water is such that the impounding function is exercised not
only during the winter months, when production is low, but,
owing to the recurrent floods, it is in operation to an unusual
extent during the period from June to October, when produc-
tion is wont, as a rule, to run low in these waters. ‘Thus levels
(Pl. XXXI.) are above 6 ft. fully half of this time and are at all
times above 4 ft. with the exception of 10 days in July. Not only
does this increase the impounding function of these waters, but it
decreases the relative occupation by vegetation in addition
to reducing its actual extent by uprooting and removal. It
also decreases the proportion which creek and spring waters
form of the total content of the area, or impounds them long
enough for the plankton to breed therein.

The distribution of high water is such in this year that it
affords an opportunity for increased production in the lake.
In comparison with 1895, when production averaged 3.25 cm.
_ per m.* from April to the end of the year, we have 5.01 in 1896
for the year as a whole. The average height of the river in
1895 was 3.61 ft. (p. 163), in 1896, 6.98—an increase of 3.37 ft.,
or the equivalent of almost doubling the volume of water in
the lake. So not only is the amount per cubic meter greatly
increased, but the total run-off of plankton into the channel 1 is
multiplied by some undetermined factor.

The net result of the hydrographic conditions of 1896 in
Dogfish Lake is therefore an increase in its impounding func-
tion at a time of large production (5.01),and its discharge
tends to raise the plankton content alike of Quiver Lake (2.59)
and the river (1.16), but data are lacking which might enable
us to compute its quantitative effect upon the plankton con-
tent of either.

Not only is the average production of Dogfish Lake greater
than that of Quiver, but individual collections here exceed coin-
cident ones there with the exceptions only of those on May 21

318

and 22 and Aug. 15, when phenomenal declines appeared in
Dogtish lake. In a similar way its production exceeds that in
the river in every case but one, that of May 21. Thus produc-
tion is prevalently higher here than in Quiver Lake and the
river, to which it contributes its run-off, as a result of the im-
pounding factor and, in this year, of the relative absence of veg-
etation also. The impounding permits the growth of the plank-
ton to utilize the nutriment derived from decay of vegetation
and other sources before it is carried out of the lake.

1897.
(Table VI., Pl. XXXII.)

There are but 6 collections here in 1897, in the first six
months of the year, at approximately a monthly interval. The
average production for this period is 2.23 cm.’ per m.’*, with a
maximum of 8.18 on Apr. 27. Since the collections are coin-
cident in the river, Quiver Lake, and this lake, a comparison
of production is facilitated. The similarity noted in the previ-
ous year may be traced here also, and the relationship of the
three areas remains in the main unchanged during this half of
1897. Briefly, there is low production in all three under the
ice in midwinter, with a slight increase in all in March, a ver-
nal pulse in April followed by a decline in production in May
in the lakes but not in the river, while in June the flood reduces
the plankton content in the river but changes that in the lakes
but little. The collections throughout the period show greater
production in the lakes (Dogfish, 2.28, Quiver, 2.77) than in the
river (average, 1.91) with the exception of the May collection
(Dogfish, 1.94, Quiver, 1.29, river, 5.62). This drop in plankton
content in the lakes below that of the stream occurs at the
time of greatest increase in vegetation and rapid drop in levels,
which increases the relative occupation by vegetation-—a factor
from which the river is relatively free. The flood of June,
flushing the stream, obscures the relationships of production at
that season. In all collections but those of May and Feb. 26
Dogfish Lake contains a more abundant plankton that Quiver

309

by from 25 to 100 per cent. This is apparently due to the pre-
ponderance of the impounding factor in the former.

Thus in this season also the similarity in the movement of
production noted in the previous year can be traced, and the
excess of production in Dogfish over Quiver continues in the
main. Its run-off therefore serves in this period to enrich the
plankton alike of Quiver Lake and the river. This is correlated
with the high levels and consequent increase in the impounding
factor and the relative diminution of vegetation in this area.

GENERAL SUMMARY,

RELATIONS OF PRODUCTION IN DOGFISH AND QUIVER LAKES TO THAT IN THE ILLINOIS RIVER.

The analysis of the data of production in these two lakes
leads to the following conclusions.

Plankton production is in a large degree a function of the
time allowed for the breeding of the plankton. Thus at times
of high water, when both lakes are filled principally with the
impounded backwaters of overflow, production is greater,
other things being equal, than at low water, when a greater
proportion of water of the lake (Quiver) is of recent origin
from tributary creeks and springs. So, also, areas such as Dog-
fish Lake, in which by reason of absence of tributaries and
springy shores the impounding function is greater, show a great-
er plankton content than similar areas (Quiver) where by reason
of access of tributary water the impounding function is de-
creased.

Vegetation of the character of that found in these lakes
seems to exercise an inimical effect upon plankton production.
Thus the season of dominant vegetation is generally one of low
production in these lakes. Also during this period, as levels fall
and occupation of the lake by vegetation becomes relatively
greater, production generally declines, and, conversely, produc-
tion rises when levels rise. Years of greater dominance of veg-
etation, other things being equal, are wont to exhibit a decline
in production, and, conversely, with lessened vegetation pro-
duction rises.

380

These factors, combined with changes in production in the
river, vary the relation which these lakes bear to production in
channel waters. In general, in times of low water and domi-
nance of vegetation the outflow from these lakes isa diluent of
channel plankton, but during the run-off of impounded back-
waters or in years of higher levels and less vegetation it serves
to enrich channel waters.

The river and the two lakes exhibit in common a very
marked similarity in the seasonal movement in production.
The recurrent pulses, which may be traced whenever collections
are of sufficient frequency, coincide closely in their location
but exhibit considerable local differences in their amplitude.
This similarity is greatest when local environmental factors,
such as vegetation and tributary waters in the lakes and sewage
contamination and recent flood water in the river, are least op-
erative, and is diminished or obscured as these factors come
more into action. The diversity, as shown in the differing am-
plitudes of the pulses of production and in the divergences and
interruptions in their rise and decline, can generally be traced
to the preponderance of some local factor or factors above
named.

The similarity in the seasonal movement of production is
allthe more marked when the striking differences of the three
localities in question are considered and the general instability
of the whole environment is borne in mind. The changes in
the plankton content of the river,—turbid and fouled by sewage,
traversed continuously by a considerable current, and scoured
repeatedly by flood,—of Quiver Lake,—with gentle current,clear
spring-fed waters, and greater or less, but always considerable,
vegetation,—and of Dogfish Lake,—with tranquil, almost cur-
rentless waters, without access of tributary contributions, and
also with considerable vegetation,—all exhibit a harmony that
compels us to admit the potency of those general factors of the
environment common to all—their climatic and geographical
surroundings, which determine the amount and distribution of
the light and heat, and the chemical constituents of the medi-

381

um in which the plankton grows. The similarity in the move-
ment of production must also be correlated with the fact that
these common environmental factors are responded to in the
three localities by a plankton composed of identical or closely re-
lated species in varying proportions. It is in the main the re-
sult of the response of similar organisms to the common fac-
tors of an environment, factors, moreover, of fundamental sig-
nificance.

FLAG LAKE.
(Table VII.; Pl. XIX., XXXIII., XXXIV.)
ENVIRONMENTAL CONDITIONS.

This is the local name for a marsh in the western bottom-
lands opposite the location of our plankton station in the river
(Pl. II.). Together with its outlet, Flag Lake Slough, it ex-
tends parallel to the river from north to south a distance
of about 43 miles, and is generally less than ? of a mile in width.
It has no precise boundaries, since the fringe of willows which
borders it, save for 2 miles along its northwestern margin where
it joms Thompson’s Lake, merges gradually with the marsh on
the one hand and the bottom-land forest on the other. It con-
tains about 24 square miles of permanent marsh, of which but
a small area toward the lower end was free from vegetation.
The depth depends upon the stage of the river or the extent of
the run-off of the impounded water. Its bottom, if we may dig-
nify the treacherous ooze from which the vegetation springs by
this name, is generally, if not entirely, several feet above low-
water mark in the river. In the autumn of 1897, during the
prolonged low water of that season, the lake dried up anda
road was opened across it to Thompson’s Lake. Generally, how-
ever, it retains sufficient water to tide over ordinary periods of
low levels. .

The hydrographic conditions are such as to make this
marsh exempt from all current save at times of most general
overflow. Owing to the somewhat elevated banks along Flag

382

Lake Slough and along the west bank of the river, no access of
river water is possible from the north or east until bank height
is exceeded by the flood. At all levels below this, water enters
the lake by the slough, which forms its outlet, or backs in from
Seeb’s Lake (Pl. IT.). Another line of access is the low margin
to the northwest between it and Thompson’s Lake. The rank
growth of living or dead vegetation which at all times fills this
region, effectually blocks any localized current here, and no
channel has opened in this region. Probably much of the water,
as indicated by the distribution of drift, enters the lake from
its southern end. The same reasons which prevent access of
water from the north also tend to restrict the flow through this
area at times of general overflow, and the fact that Thompson’s
Lake (Pl. II.) affords for backwaters impounded to the north a
channel where resistance is much less than in the shoal, forest-
begirt, and rush-filled Flag Lake, tends also to divert the mov-
ing backwaters to that region. Consequently, Flag Lake is in
the main an impounding area whence the impounded water
is drawn off as levels decline, but which is not generally trav-
ersed by the waters of general overflow as are Quiver and
Thompson’s lakes. It is thus one of the most strongly localized
of all plankton stations, and the unity of its environment is
more continuously maintained than that of any of the localities
thus far examined.

Its vegetation has been described on pages 249-250, and it
will suffice in this connection to call attention to the predom-
inance of the emergent and succulent types in its waters, and
to the fact that little, if any, of it is ever carried away by flood
or currents as it is from Quiver and Dogfish Lakes. This is a
large factor in maintaining the local fertility of this area.

This is a favorite haunt of migrating water-fowl! in fall
and spring, and contains breeding grounds of the few summer
residents. It isalso much resorted to by the German carp, now
one of the most abundant fish in the Illinois. Fish enter the
lake in numbers when levels rise, but leave again before low
water in the slough (Pl. II.) prevents their departure. Evi-

383

dences of the destructive work of the carp are seen in their ac-
tivity in uprooting great patches of Sagittaria. Such condi-
tions were prevalent shortly after the August flood of 1896 (PI.
XXXIITI.), when the combined action of the change in levels
and the invasion of fish destroyed not a little of the vegetation.

COLLECTIONS.

Systematic examination of the plankton in this area was
begun Oct. 17, 1895, and continued until Aug. 16, 1897. Six
summer collections were made in 1898 for the purpose of de-
tecting Trochosphera.

Owing to the surroundings of this region access to it ex-
cept during high water was a matter of much time and con-
siderable difficulty. Absence of roads and bridges made ap-
proach by conveyance impracticable, and save at maximum
overflow the elevation of the surrounding bottoms or the abun-
dant vegetation prevented the entrance of the steam launch.
The drift in the slough (Pl. Il.) and the matted, and in many
places impenetrable, growth of Scirpus fluviatilis rendered ac-
cess to the small areas of open water an arduous task. At low
stages the only means of obtaining a collection was to wade
out through the morass to a suitable place. The difficulties of
approach in winter were even greater, when ice and the emer-
gent vegetation combined to interfere with rapid transit of any
considerable load. For these reasons this station, though one of
much local biological interest, was early dropped from Our list.

These same difficulties have enforced some variation in
the methods of collection (Table VII.) and in the locality at
which collections were made. In the autumn of 1895 they
were made by dipping water in scattered areas in the vege-
tation and in advance of the roiling of the water caused by
wading. On Feb. 28, 1896, a measured quantity of water from
successive levels was taken amid the standing but submerged
vegetation with a pump. Other collections prior to May 28,
1895, were made by the oblique-haul method and thereafter by
the plankton pump.

384

In the autumn of 1895 collections were made in the north-
ern arm of the area marked as open water on Plate II., and
occupied at that time by a considerable amount of submerged
and floating vegetation, largely of Nymphea. During high
water, when landmarks were submerged, this location was ap-
proximated as nearly as possible, but in the following spring
the location of the plankton station was shifted to the lower
arm of this open area (PI. II.), and as the vegetation emerged
and blocked access the station was moved to the head of the
slough in effluent waters. These changes in method and loca-
tion impair somewhat the value of this series of collections for
comparisons inter se, but they still serve to throw important
and significant light upon the relationship of such marshes and
of their vegetation to plankton production in their own con-
fines and in the channel waters to which they may contribute.

There are 38 collections, extending continuously over 22
months in 1895-1897, with an interval of collection in the -
greater part of 1896 sufficiently short to enable us to follow the
course of production. The scattered collections of the remain-
der of the period and the six additional collections in 1898
throw but little hght upon the movement in production,
though they are of interest for comparison with other locali-
ties.

PLANKTON PRODUCTION.
1895.
(Table VII., Pl. XX XIII.)

There are but four collections in this year, in October—De-
cember, averaging 20.45 em.* per m.* and having a maximum of
57.76 on Oct. 17, and declining to 6.38 on Dec. 19. This period
was one of no marked changes in the hydrographic conditions.
The lowered temperature and autumn rains had checked evap-
oration and brought about a slight increase in the volume of
water, as shown by the increase in depth from .25 to.45m. The
lake was choked with decaying vegetation, the product of two

385

season’s growth without a flood exceeding 7 ft. Even the rise
to 5.2 ft. Dec. 19 was only beginning to affect the conditions
within the lake. In October the succulent vegetation, such as
Nymphea, Nelumbo, and Sagittaria, was undergoing rapid decay,
which was checked by falling temperatures, and we find plank-
ton production declining (from 57.76 to 6.88), and the decline
accelerated on Dec. 28 (3.26) with the invasion of flood waters.
This large production, unsurpassed at any other station (cf. PI.
XXXIII. with Pl. IX., XXVi., XXX., and XXXVLI.), is to be cor-
related with the excess of decaying vegetation in this locality
resulting both from the abundance and character of the vegeta-
tion and its freedom from flushing by current due to access of
tributary waters. The maximum in October is due almost
wholly to Synura ubella, which declines in the later collections
in which the Cladocera and later the Copepoda appear in in-
creasing numbers. Throughout this period there was no run-
off until flood levels were reached late in December, and even
then, owing to reasons above cited, the run-off from the area is
relatively slight. There was consequently no direct enrichment
of the channel waters from this area. Unfortunately, no chem-
ical analyses of water from this area are available, and the
chemical basis for an estimate of the relative fertility of this
marsh is lacking. The data of production illustrate the great
fertility of waters impounded where decaying organic matter
abounds. Both the impounding factor and the local enrich-
ment factor are apparently at a maximum potency here at this
season, and production is correspondingly great.:

1896.
(Table VII., P!. XXXIIL)

There are 27 collections in this year, with an average of
13.83 cm.’ per m.’, and a maximum of 203.52 on May 2. The
weekly interval of collection in April-June enables us to follow
the course of production with some detail, but the fortnightly,
or longer, interval prevalent during the most of the remainder

385

of the year reduces greatly the value of the data for such pur-
poses or for comparison with other localities.

The hydrographic conditions are such in 1896 that this lake
maintains, throughout, a connection with the river. This is
owing to the relative absence and brief duration of low levels,
the run-off not being completed before a new invasion occurs
as a result of a recurrent flood. Since falling levels prevail
during more than two thirds of the year, a run-off from the
lake continues during this portion of the time at least. The
lake is therefore in this year a factor in the determination of
production in channel waters, whose continuity is broken only
when levels are such that no waters are draining off from the
lake or passing through it during general overflow—which 1s the
case in less than one fourth of the time. The average produc-
tion in the lake for 1896 (13.83) is almost twelvefold greater than
that in the stream (1.16), and the monthly averages also (see
table between pp. 342 and 343) are from 24 to 218 times greater,
while individual collections in the lake in all but three in-
stances exceed coincident or approximate ones in the river. The
exception on July 30 occurred, when the invasion of flood water
was followed, as is usually the case in midsummer in vegetation-
rich backwaters, by a semi-stagnation with great development
of Oscillaria, and the formation of considerable gas with a strong
odor of HS beneath the felt of Oscil/aria which covers the bot-
tom. Under these presumably abnormal conditions the plank-
ton content reached a lower level in the lake (1.62) than in
the river (3.90), and this was at a time of influx rather than
outflow of water. With the above exceptions the lake at all ob-
served seasons contains a richer plankton than the channel,
which its run-off directly enters,and under similar hydrographic
conditions we are justified in predicting at other times a similar
relationship, though the exact ratio of production would proba-
bly vary according as the vegetation by its growth or decay
affected the fertility of the water.

In the absence of any satisfactory basis for determining
the amount of the run-off from this lake, a quantitative expres-

387

sion of its effect in increasing the plankton of the channel can-
not be given. Similar marshy regions are found, along the course
of the river elsewhere, especially above higher bottoms which
have been built up across the flood-plain by tributaries such as
Spoon River, and such areas presumably share with Flag Lake
this contributory function in the maintenance of channel
plankton.

In the discussion of production in Quiver and Dogfish lakes
I have called attention to the similarity in the movement in
production, these two lakes and in the river. In Flag Lake,
we are dealing with a very different environment ; bottom,
shores, vegetation, hydrographic relations, especially in the
matter of tributary waters, are all diverse. Indeed, the lake it-
self includes several distinct typesof environment. It is inter-
esting to note that in so distinct a unit of environment as this
marsh we find so large a degree of similarity in the movement
of production as can be traced between its seasonal plankto-
graph and that of the river and of the lakesthus far examined.
It should, however, be stated that the similarity is less precise
here and is more evident in 1896 than in other years, though
this is probably in part due to the absence of sufficiently fre-
quent collections.

The degree of similarity may be seen in the following com-
parisons. In 17 of the 27 possible comparisons between pro-
duction in Quiver and Flag lakes (Pl. XX VII. and X XXIII.)
the direction of the change in production coincides. Most of
the 10 exceptions are due to slight differences in the location of
apices of pulses, or occur at times of lowest water, that is, of most
pronounced local differentiation—-as, for example, at the drop
in levelsin May and againinJuly. Thesame number oi excep-
tions similarly located occurs when production in Dogfish Lake
(Pl. XX XI.) is compared with thatin Flag Lake (Pl. XX XIIL.),
and there are 11 exceptions in the possible 27 in the case of
the river (cf. Pl. X. and XXXIII.).

In general terms, the similarity consists in the rise in pro-
duction, probably obscured in Flag Lake by an overestimation

388

of silt on March 80—with increase in temperatures in January—
April, culminating in a vernal pulse in April-May, which in
Flag Lake reaches a much higher level (203.52) than elsewhere,
culminates later by 7 to 14 days and is not divided into two
apices as in the other three localities, but in duration covers
the period of two pulses elsewhere. It is further seen in the
May-June and August pulses and in the fairly well sustained
correspondence in direction of the changes in the September—
December period. The most marked disagreement appears
with the declines in stage of the river in May and July, when
local environmental factors are most potent, and when, also,
vegetation is at the height of its relative occupancy of the
lakes in question.

One of the most striking features in the production of this
lake, and one not without parallels elsewhere in our records
(Pl. XXIX., XXXI.), is the very sudden decline in plankton
content after the vernal pulse, namely, from 203.52 cm.’ per m.
on May 2 to 47.7 on the 9th—a decline of 77 per cent. in 7 days.
On the 15th it reached the low level of .72, a decline of 98 per
cent. in 6 days or of 99.6 in 13 days. The attendant hydro-
graphic conditions are not without significance. This pulse
(Pl. XX XIII.) attains its growth between March 30 (1.02) and
May 2 (203.52), in which period the net drop in levels in
channel waters is only from 8.1 to 6.9 ft. and the total move-
ment only 1.7 ft., while in this protected backwater the fluctu-
ations are probably somewhat lessened, as will be seen in the
fact that the depth in the lake changes only .5 ft. to 1.2 ft. in
the channel. The pulse thus rises in stable conditions.

The decline of the pulse takes place between May 2 and 23
from 203.52 cm.’ per m.’ to .12. In this time levels fall from 7.1
to 4.9 (see p. 159) on the 17th and rise again to 7.2 on the 23d.
The decline in production from the 15th (.72) to the 23d (.12)
is so small a part of the total that its significance in the present
connection is slight, and the rise in levels has probably not had
time to materially affect the lake. The hydrographic influences
potent in the decline in production have been operative prior

389

to this rise, and consist in a fall of 2.2 ft. in channel waters
though the depth at the station of collection changes only 1.6
ft.—equivalent to a reduction in volume of 25 per cent. at the
point of collection and 30-40 per cent. in the lake as a whole.
It thus involves a considerable and rapid run-off of the rich
plankton developed in these impounded waters. This factor
alone is, however, quite insufficient to account for the total loss
in plankton content in this period. Another factor which is
correlated with this reduction in the plankton content is the
increasing occupancy of the lake by vegetation. The decline
in levels hastens the emergence of the emergent forms and in-
creases the relative occupancy by submerged and floating spe-
cies, while the vernal growth in all during these three weeks in
May, more than any other factor, transforms the broad expanse
of open water into a vegetation-clogged marsh in which but few
stretches of open water are visible. This phase of the growth
of the grosser forms of the aquatic flora robs the water of some
of its store of nutriment and cuts off the free access of ight—
both of which might interfere with the growth of the competing
phytoplankton. Limnetic diatoms such as Asterionlla and Melo-
sira are the principal synthetic organisms building up this re-
markable pulse, and the Cladocera, principally Bosmina and Chy-
dorus, appear 1n numbers with itsculmination. The composition
of the plankton favors the inference that a temporary exhaus-
tion of the food of the phytoplankton and zoéplankton alike con-
tributes to the sudden reduction in plankton content, while the
additional and perhaps related factor of reproductive cycles may
also have a large causal relation to the phenomenon.

1897.
(Table VII., Pl. XXXIV.)

There are but 7 collections in this year, at approximately
monthly intervals in January-July. Collections were suspend-
ed on July 16, when decline in levels made access even to the
foot of the lake by boat impossible. With the further decline
(Pl. XI.) in river levels the run-off from the lake soon ceased,

390

and by the middle of September the water had practically dis-
appeared within its boundaries.

The 7 collections average 4.59 cm.’ per m.’—about double
the average production in the adjacent river, and in Quiver,
and Dogfish lakes on coincident dates. Individual collections
also exhibit in every case a greater plankton content in the
lake than in the river. This area in this season thus contrib-
utes to the enrichment of the channel waters, which its run-off
enters, and its contributions exceed those of the lakes on the
eastern side of the river. This higher production in this local-
ity is, I believe, a corollary of the greater impounding function
of Flag Lake, resulting from its freedom from tributary waters
of recent origin, from its somewhat sheltered location—which
checks the downward movement through its area of the gener-
al currents of overflow, and from the enrichment of its 1m-
pounded waters during this period by the decay of the abun-
dant vegetation of the previous season, which, for the reasons
just mentioned, is not extensively carried away by flood wa-
ters.

The fact that production appears to be so much less in 1897
(4.59 cm.’ per m.*) than in the corresponding months of 1896
(11.21) may be due to several factors ; to the greater dilution
in the greater volume of overflow (cf. Pl. XX XIII. and XXXIV.)
in the winter and spring floods of the latter year, to the greater
abundance in 1896 of decaying organic matter accumulated by
the vegetation of two preceding low-water seasons, and, possi-
bly, in a measure, to the infrequency of collections in 1897 and
the probable omission of the maxima of pulses of production
which would tend to raise the average.

The similarity in the movement of production in this and
other localities will appear at once on comparison of Pl. XXXIV.
with Pl. XI., XXVIII, and XXXII. The coincidence in the
direction of the changes is precise in all of the 7 instances in
the case of the river, in all but one for Quiver Lake, and in all
but two in the case of Dogfish Lake. This is a period of max-
imum overflow, when the individuality of these several locali-

391

ties is submerged by the flood. It will be noted that the ex-
ceptions he at the close of this period, when low water brings
local factors into prominence. It is at this time also that the
differences in the amplitude of production are most in evidence.

1898.
(Table VII., Pl. XXXIV.)

Six collections made at the outlet of Flag Lake in this
year in July-September for the purpose of detecting Tiocho-
sphera are introduced int» !:ble VIL., since they throw some
additional ight on productio. +e _. The four collections in
July exhibit a very low level of plankton content, the highest
being .62 cm.’ per m.’, and the level is not raised in the single
August collection. However, with the run-off of the slight
rises of August and September we find a rise to 15.54. At this
time water of overflow was making its way from across the
bottoms at the southern end of Thompson’s Lake through the
marshy swale into the foot of Flag, and thence out to the river.

The similarity in the movement of production here and
in other stations is seen in the general low level of production
in July and the shght rise towards the end of the month. A de-
cline early in August can also be traced, followed by a rise in
the next month (cf. Pl. XXXIV., XII. and XXIX.).

With the exception of the collection on September 6, the
collections of this year indicate that the effluent of Flag Lake
is a diluent of channel plankton. This may result from the
low levels and consequent dominance of the vegetation in the
lake at this time of low production there.

SUMMARY.

The. data discussed in the preceding pages lead to the fol-
lowing conclusions concerning Flag Lake.

The average production of plankton in this lake, or, more
properly speaking, marsh (11.46 cm.’ per m.’, or 9.23 on the
basis of monthly averages), exceeds that in the river (2.19 or
2.71). This greater fertility appears not only in the averages

392

but in general throughout most of the seasonal changes. Its
run-off therefore serves generally to enrich the channel waters.

The greater production is due to the decay of the abun-
dant vegetation which the lake contains, to the absence of trib-
utary water of recent origin, to the relative freedom from the
general current of overflow which largely takes the line of less
resistance through Thompson’s Lake (PI. II.), and, conseq uent-
ly, to the greater time afforded for breeding an abundant plank-
ton in this impounding area.

The dominance of the abundant vegetation is inimical to
large plankton production. Other things being equal, plankton
production is greater when the relative occupancy of the water
by vegetation is decreased.

The movement in plankton production in this area is in
the main similar to that in the river and in Quiver and Dog-
fish lakes. Pulses of production tend to coincide, though their
amplitude may differ widely in the several localities. This sim-
larity is least when local environmental factors such as vege-
tation, stagnation, or local exhaustion of the food supply are
most potent. Itis greatest when these are least, that is, during
high water.

STATION G, THOMPSON'S LAKE.
(Table VIII., Pl. Il, XX., XXXV.—XKXXIX., L.)

ENVIRONMENTAL CONDITIONS.

This body of water les in the bottom-lands on the right
bank of the Illinois, above Spoon River, midway between the
bluff and the main stream. It trends in a northerly and then
a northeasterly direction, following somewhat the curve of
the Illinois. It is about five miles in length at low water, with
a width in three fourths of the distance of about two thirds of
a mile, while the northern end is less than one third of a mile
in width. At this stage it contains about 1,400 acres. As levels
rise, its margins spread rapidly—owing to the slight gradient
of the shores—northward to Grass and Slim Lakes, westward,
through Mud Lake, towards the bluff, to the south, towards

393

Spoon River, while its connection with Flag Lake is early es-
tablished over the low sandy bank which lies between them.
At stages above six feet the “cut road” (Pl. IL.) and the marshy
swale above it fill, and connection with Flag Lake at its lower
end and with the river is established. Its area is about
doubled by the time the river reaches bank height and general
overflow ensues.

The lake is of somewhat uniform depth in the middle half,
but shoals toward either end. In prolonged low water, when
the slough at the northern end is practically cut off from the
lake, extensive mud-flats are exposed in the northern area, and
a portion of the southern end for about half a mile is also left
bare except when prolonged and heavy winds drive the water
towards one or the other end of the lake. The depth at lowest
river levels in the central region, which includes about two
thirds of the total area, is 3 ft. Laterally the water does not
shoal until within 10 rods of the shore. There is thus a large
area (about two square miles) of water with uniform condi-
tions in this particular.

With slight exception the bottom is of the softest alluvial
mud, several feet in depth, overlying a sandy blue clay. The
shores along the southern, western, northern, and northeastern
margins are also of soft alluvium and of a marshy character.
The eastern shore, for most of its extent, and hmited stretches
along the western one, together with the spit which makes out
into the lake on that side, are of sand and of a firmer consist-
ency.

All of the shores are bordered by a belt of vegetation,
which has been described on page 246.

This lake is the largest of the reservoir backwaters exam-
ined by us, and is one of the permanent type, resembling in all
important particulars except that of submergence in times of
general overflow and its reservoir relation to the river a typ-
ical lake of an alluvial prairie country. Its position in the
bottom-lands brings it into intimate connection with the river,
the source of most of its water supply, while at times of flood

394

its position is such that the backwaters from the bottom-lands
up-stream sweep through it and out to the river through the
“eut road,” being deflected by the alluvial deposits of Spoon
River (Pl. Il.). Its relation to the river is a peculiar one in
that its outlet, or slough, lies at its up-stream end. At stages
above six feet the current enters through this slough, and the
run-off takes place at the lower end through the cut road.
Below this level all the run-off must take place through the
slough. The direction of the movement in the run-off of the
lake is thus reversed as river levels pass this stage. There are
no tributary waters of consequence which enter the lake, though
a small rill and a few springs enter along the western margin.
The main supply is drawn directly from channel waters through
the slough, and when levels are stationary there is no in-
terchange in either direction. The current sets in or out, at
stages below 6 ft., according as the river rises or falls. The re-
sult of this condition is that during the higher levels back-
waters of overflow and the river water entering by the slough
are impounded and drawn off slowly at the lower end of the
lake. At stages below 6 ft. a run-off occurs only in the falling
stages and in relatively smaller volume through the narrow
and tortuous slough. The impounding function is accordingly
more highly developed at lower levels, while at lowest levels all
interchange ceases.

This close and intimate dependence of this lake upon the
river for its water supply in so far destroys the unity and inde-
pendence of the lake as a separate unit of environment, and
tends to eliminate the differences in plankton production be-
tween it and channel waters. This tendency is counterbal-
anced to a considerable degree by the large size of the lake and
consequent increase in the time occupied in transit during over-
flow, and by the impounding, at lower levels, of entering river
water at the upper end of the lake, where it deposits its silt and
soon permits the development of the lake plankton in its area.
Here, as elsewhere, local factors are most potent at lower levels.

The effect of the greater size of this lake is thus to equal-

395

ize environmental fluctuations and to obviate their catastrophic
results, which may be seen in their maximum violence in
channel waters, and in a lesser degree in the lakes thus far ex-
amined,

COLLECTIONS.

This station was opened June 7,1894, and collections were
continued until the close of operations on March 28, 1899. In
all, 99 collections were taken, distributed in the several years
as follows: 5, 14, 27, 18, 25, and 7, with but few exceptions at
approximately a monthly or fortnightly interval. It was only
in the spring and summer of 1896, when an interval of 7-10
days was adopted, that the interval is brief enough to enable
us to trace the movement in production with any degree of
fullness. At other seasons the data are suggestive, but not
conclusive, of its course. The relatively smaller number of
collections made at this important station is due to its distance
from our center of operations, the round trip from Havana to
the lower station in low-water conditions exceeding 25 miles.
The difficulties of access were greatly increased when at low
water it was necessary to make the trip from the outlet of the
slough by rowboat, and to drag or push this over the soft mud
and through the dense vegetation at the upper end of the lake,
and when, in winter, at low water, the boat and outfit had to
be dragged across the frozen bottom-lands.

The locations at which collections have been made are
principally the two marked on the map (PI. II.). The lower
one was used exclusively in 1894 and 1895, and thereafter
when access to the lake was had through the cut road. The
location off Sand Point, at the upper end, was used when the
lake was entered by way of the slough. Both were in the open
central region, well out in the vegetation-free area, though in
1895 and 1896 the lower station was encroached upon some-
what by shifting masses of Ceratophyllum. In a few instances,
owing to high southwest winds and the dragging of the waves
in the shallow lake, it was not possible to maintain an anchor-

396

age in the unstable bottom, and refuge was had under the lee
shore, but still in usual depths and open water. In several in- ©
stances in overflow stages, when the ice was too heavy to break
and too light to carry our load, it was necessary to make the
collection near the margin of the lake in effluent waters. These
variations in the location of the point of collection imtroduce
no error of consequence into the series, judging by the results
of an examination of the local distribution of the plankton in
this lake, the details of which cannot be given in the present
paper. .

With the exception of the single pump collection on Feb-
ruary 28, 1896, all collections prior to May 20 of that year were
made by the oblique-haul method, and thereafter by the plank-
ton pump.

This lake is a type of the larger reservoir backwaters, such
as Meredosia Lake, Clear Lake, and others found in the bottom-
lands of the Illinois and maintaining a constant connection
with that stream. An examination of its plankton content
will therefore serve to throw light on the relation which lakes
of this type bear to plankton production in channel waters.

PLANKTON PRODUCTION.
1894.
(Table VIII., Pl. XXXV.)

There are but 5 collections in this year, from June to De-
cember, at an interval of a month or more, with an average
production of 8.89 cm.’ per m.*° and a maximum of 24.92 on
June 7.

An inspection of the hydrograph (Pl. XXXV.) of this year
reveals the fact that only the first two collections were taken
under conditions which permitted any run-off from the lake to
the river, and both of them at times—that is, in falling levels
below 6 ft.—when the run-off was largely, if not wholly, through
the tortuous slough at the up-stream end of the lake. The pro-
duction in the lake (24.92 and 10.74) at these times was 33- to

397

4-fold that in the river (.74 and 2.39),so that the run-off at this
season enriches channel plankton. With the exception of the
August collection the plankton content in the other three col-
lections in the lake exceeds that in the stream. The low con-
tent in August (1.08) occurs at a time of lowest water, when
vegetation by reason both of river stage and the season is at its
maximum occupancy of the lake. At other times the effect of
the reservoir function of the lake is seen in the relatively great-
er production in its waters.

The scattered data of this year are insufficient as a basis
for any conclusions as to the correspondence in the movement
of production in this and other waters.

1895.
(Table VIII., Pl. XXXVI.)

There are 14 collections in this year, between April 10 and
the end of the year, averaging 9.67 cm.’ per m.*, and with a
maximum of 61.44 on May 1—an amplitude nearly 11-fold that
of this pulse in the channel.

The average production (9.67) is 3-fold greater than that
of the river in this year (3.22), and the monthly averages (see
table between pp. 3842 and 343) are in 5 of the 9 months from 1.6-
to 12-fold greater in the lake than in the river. In the remain-
ing four months, June, July, August, and December, the ratios
are respectively 30.42, 9.33, 4.03, and 1.14 (river), to 9.42, 4.83,
3.09, and 1.00. The lower production in June-August occurs at
atime when, with the exception of three weeks, levels were low
and vegetation atits maximum occupancy of the lake, and when,
moreover, the current was greatly slackened in the river, and
channel plankton in the richly fertilized waters had more than
the usual time to breed, while the less production in the lake
in December is, owing to the distribution of collections, more
apparent than real.

In the matter of individual collections on coincident or
approximate dates the lake shows a greater piankton content
in 9 out of the 14 instances, and of the 9 there are 5 in which

398

hydrographic conditions favor a run-off of this richer plankton
of the lake into channel waters. There are two instances in
which run-off occurs when lake waters are poorer than the
channel, but they are both at low levels and during slow de-
cline, so that the discharge and resulting diluent effect is but
shght. Considering the average production, the times when
run-off occurred, and the hydrographic conditions when the lake
waters contained less than the channel, it is probable that even
in this year Thompson’s Lake, owing to its reservoir function,
served predominantly to enrich the channel plankton. Though
this relation predominated, the total contribution of the lake
to the stream in this year was but slight owing to the hydro-
graphic conditions. In the April-December period covered by
our collections, the stage of river never exceeded 6 ft. until the
December flood. There was, therefore, never any general cur-
rent of overflow passing through the lake and carrying the im-
pounded waters out from the southern end (PI. II.) into the
riverand thus discharging a considerable volume of plankton-rich
water into the channel—a condition possible in both rising and
falling levels above 6 ft. At the levels below this point which
prevailed throughout this period, influx and efflux both can take
place only through the slough at the northern end, so that con-
tributions to the stream from the lake occur only during falling
levels, and, moreover, owing to the tortuous course and clogged
condition of the outlet, the volume discharged at these lower
levels is very much less than at higher ones, across the broad
outlet at the other end of the lake. Falling levels occurred in
less than one half of the time in April-December, so that the
contributions of the lake to the river were not only slight in
volume but limited in duration and discontinuous.

Collections were too infrequent to trace the movement in
production with fullness or certainty. There are, however, a
few suggestions of a similarity in the course of production here
and elsewhere. The direction of the changes in the course of
production in this lake and in the river in coincident or ap-
proximate collections is the same in 9 out-of the possible 13 in-

399

stances (cf. Pl. IX. and XX XVI.);in the case of Quiver Lake the
agreements number 7 out of a possible 12 (ef. Pl. XX VI. and
XXXVI.);in the production in Dogfish Lake the correspondence
is found in 9 out of a possible 12 (cf. Pl. XXX. and XXXVI.);
while in Flag Lake there are 2 out of 3 (ef. Pl. XX XIII. and
NOX IL).

The agreement is lessened in this year, it seems, by the hy-
drographic conditions. The low water affords less opportunity
for a mingling of the waters of the stream and its backwaters,
and also serves to bring out the local environments at each of
the stations. Thus Thompson’s Lake has but little connection
with other backwaters at any time during the year, and ingress
or egress of channel waters was but very slight during six months
of the twelve in this year. Vegetation also gained more ex-
tended possession of this lake in this year than in other seasons
of our operations. Low water also tends to make the channel
plankton more directly affected by its peculiar factors, such as
sewage. It is noticeable that the agreement in production is
most marked between Thompson’s and Dogfish lakes, both back-
waters of somewhat similar character in respect to tributary
waters, relation to the channel, and vegetation.

The most marked differences between production in this
lake and the channel appear in the respective amplitudes of
the pulses of production in April-May and June-July. In the
lake the rising vernal pulse attains the exceptional volume of
28.2 on April 10 to.52 in the river on the 9th, a difference which
may in part be due to the earher warming up of the shoal-
er lake waters. The maximum (61.44) in the lake is 12- fold
that observed in the stream. The June-July production in the
river, on the other hand, is 3- to 5- fold that in the lake, the
contrast being due on the one hand, it seems, to the temporary
exhaustion either of the chemical substances utilized by the
plankton or of the reproductive capacities of the planktonts of
the lake waters, and, on the other, to the increased sewage con-
tamination in the stream as a result of low levels. The direc-
tion of the changes in production, however, remains the same in

400

both localities (ef. Pl. IX. and XXXVI.) im the face of these
contrasts in amplitude.

1896.

(Table VIII., Pl. XXXVIL.)

There were 27 collections in this year, at monthly inter-
vals until April, and then every 5-1] days until the end of Au-
gust, and thereafter every fortnight. The average production
in this year is 9 cm.* per m.’, with a maximum at the vernal
pulse on May 2 of 48.99 em.’

The hydrographic conditions of this year are such as to
bring Thompson’s Lake into intimate connection with chan-
nel waters. The average height of the river for the year, 6.98
ft., is sufficient to maintain a run-off from the southern end of
the lake to the river, submerging the bottom-lands between to
the depth of a foot. Indeed a run-off of varying depths was
maintained for 241 days, in which stages exceeded 6 ft. This
was due to the recurrence of 6 floods, so distributed as to keep
the lake discharging through the southern outlet for 241 days
with only 5 interruptions between May and December. Of the
125 days in which water did not flow through the lake from the
northern to the southern end, there were 29 of rising water in
which no discharge to the river occurred, 28 of stationary
levels in which the movement of the water, if any, was declin-
ing, and 68 of falling water, in which the lake discharged
through the slough at the northern end. Thus, during 309 days
of the year this lake was discharging to the channel, waters
which had been impounded for a varying length of time within
its boundaries. The importance of this impounding area is
best shown by rough calculations which show that the run-off
of a single foot from the lake proper, not including the expand-
ing areas which join it with every rise in levels, will fill the
channel of the river at Havana to a depth of 8 ft. (low-water
stage) for about three miles. In 1896 the total depth of the
run-off for the year computed on a single discharge after each

401

rise 1s 26.9 feet—sufficient to fill the channel for 81 miles.
When we add to this the consideration that at levels above 6
ft. water is continually passing through the lake with brief im-
pounding, the length of channel filled by the run-off of this
area must be considerably extended.

The relationship of plankton production in this lake to the
plankton content in channel waters in this year may be in-
ferred from the yearly averages. Thompson’s Lake contained
9 cm.’ per m.* to 1.16 em.* in the river. The net result would
therefore be an enrichment of the channel plankton in a
ratio dependent upon the relative volumes of the mingling
waters. No quantitative statement of. this ratio is possible in
the absence of data as to the run-off of Thompson’s Lake. Not
only is the net result an increase in the channel plankton, but
the monthly averages (see table between pp. 342 and 343) and
the coincident or approximate individual collections (Tables
IL. and, VIII.) in every instance exhibit a higher plankton con-
tent in this lake than in channel waters. The monthly aver-
ages range from 2 to 251 times greater in Thompson’s Lake
than in the river—ratios within which most, if not all, of those
of individual collections fall. The data all indicate that this
impounded water of the lake breeds a plankton whose run-off, -
without exception throughout this year, enriched channel waters.

The effect of invading and plankton-poor river waters upon
the plankton content of the lake is not conclusively apparent
in the data, since we have also to deal with the phenomenon
of pulse-like changes in plankton content which are combined
with other factors in affecting the movements in production.
It may be significant of the diluent action of invading river
water that plankton content falls in the lake with the first en-
trance of the May-June, the July-August, the October, and the
November floods (Pl. XX XVII.). The recovery in production
follows promptly in each case with the impounding of the en-
tering waters. Since, however, declines in content, as in June,
July,and August, occur also when flood waters are not enter-
ing, we cannot conclude that the decline upon this entrance is

402

due solely and unequivocally to the diluent action of the in-
vading waters, though their share in the phenomenon seems
probable.

I have previously called attention to the similarity in the
movement in production in the several localities wherever col-
lections were of frequency sufficient to permit the tracing of —
the fluctuations in production. The course of production in
Thompson’s Lake in 1896 forms no exception to this similarity,
though the parallelism is less precise than itis in some other in-
stances. Thus the plankton content rises or falls together in
Thompson’s Lake and the Illinois River in 18 out of 26 instances
of coincident. or approximate collections; in Thompson’s and
Dogfish lakes in 18 out of 26 instances ; in Thompson’s and Flag
lakes in 16 out of 25 cases; and in Thompson’s and Quiver lakes
in 12 out of 25. The direction of the change thus agrees in a total
of 64 out of 104 possible instances in the data. This isa some-
what greater proportion of instances in agreement than chance
would demand, and its significance is enhanced by the fact that
the agreement with Thompson’s Lake is greatest (64 and 69
per cent.) in the case of Flag and Dogfish lakes—impounding
bodies similar to Thompson’s Lake—and of the river (also 64 per
cent.), which is in a measure and especially in this year a sum-
mation of impounded backwaters. Quiver Lake, on the other
hand, where tributary waters increase the local differentiation,
has an agreement in only 12 outof 25 instances. In like manner
months of high water, such as August, when local differences are
to some extent submerged, exhibit greater agreement than
months of low water, whentheyare emphasized. Thusin August
(average river gage, 7.42 ft.) 92 per cent. of the changes in produc-
tion are inagreement, while in July (average river gage, 4.55 ft. )
only 58 per cent. exhibit thisrelation. Again, since the above
comparisons are based on coincidence of changes in production it
results that shght chronological dislocations of otherwise similar
movements in production indicate a greater disagreement than
really exists. This is especially true of the vernal pulses of April—
June, where as a whole only 58 per cent. of the coincident or

403

approximate collections show this agreement. A comparison
ot Plates X., XXVII., and XXXI. with XXXVII., will show
that much of this disagreement is due to shght variations in the
positions of the apices of the several pulses in the different
localities. In each locality we can trace three diminishing
pulses in this period, pulses, moreover, which have much in
common, barring variations in amplitude and time of culmi-
nation. Their similarity is greater than the 58 per cent. of agree-
ment would seem to indicate.

The most marked difference between the production in the
river and in Thompson’s Lake, as has been shown, lies in the
amplitude of the pulses, which in the river never attain the
height that they do in the lake. A part of this contrast is due
to the fact that pulses of production are sometimes flushed out
by floods in the channel while they continue to a normal cul-
mination in lake waters, as, for example, the vernal pulse which
culminates in the lake May 2. Similarly, in the flood of the last
of Mayand July the plankton content is suddenly depleted in the
channel waters, while the rising pulse continues to a later and
much higher culmination in the lake.

1897.
(Lable VIII., XIII.; Pl. XXXVIII., L.)

There are 18 collections in this year,at monthly intervals
till July, and thereafter approximately every fortnight. The
average annual production this year, 10.48 cm.’ per m.’ is the
largest recorded for this body of water, and is due to the exces-
sive development in the low-water period, August-November,
which reached an amplitude (35.35) over threefold that de-
tected in the vernal pulse (10.38). (Pl. XX XVIII.)

The hydrographic conditions are very different from those
of the previous year, and change profoundly the relationship
of the lake and river. As will be seen on Plate XX XVIII., the
river levels were above 6 ft. from the beginning of the year
until June 6, and thereafter from the 25th until July 15, a total
of 175 days in which the lake received water through the

404

slough at the northern end, impounded it for some time, and
maintained a run-off at the southern end (PI. IL.) of its plank-
ton-rich waters. ‘There are in addition 35 days in June, July,
and August in which falling levels below 6 ft. afforded an op-
portunity for a run-off through the slough at the northern end.
Of the remaining 155 days, 10 are of rising levels below 6 ft.,
when the lake receives water from the river but does not dis-
charge any into it, and 145 belong to the low-water period of
the last 5 months, in which there was little interchange be-
tween lake and river though the run-off continued in diminish-
ing volume for a few days after stable levels were reached,
early in August. About August 16 the channel discharge was
so slight as not to float a rowboat in the narrow channel at the
northern end of the lake, and connection with the river was
not reestablished as the river rose in October-November until
the level of 2.8 ft. was reached, Nov. 10. The shght fluctuations
during the remainder of the year practically amount only to
the reception of .4 ft. of water by the lake. For the last five
months of the year—months of heavy plankton production in
lake. waters—there was no run-off to the river.

On the average the lake produced this year 10.43 em.’ per
m.*, about 3-fold that in channel waters (3.69 cm.*) and the net
result of the run-off would be, it seems, an enrichment of chan-
nel waters. The actual enrichment is, however, much less
than these averages indicate. An examination of the monthly
averages (see table between pp. 342 and 343) reveals the fact
that the excessive production in the lake, when the plankton
content rises to 5- to 16-fold that in the channel, appears in
the low-water period when no run-off occurs. During the first
7 months, in which there is an almost continual run-off, the
production in lake waters is but 1.5- to 2-fold that in the chan-
nel except in February and June, when flood waters in the
latter increase the ratio to 1 to 7 and 18 respectively. The in-
sufficiency of the collections in this period leaves in doubt
the amplitude of the vernal pulse. The April and May collec-
tions indicate only a low level of production as compared with

405

that in other years, and this also tends to lower the relative
productiveness in the lake. It is evident that the seasonal dis-
tribution of the period of flood waters and the resulting im-
pounding function of the lake affect greatly its contributions
to channel plankton. In this year flood waters are largely
confined to the colder and less productive season, when the
run-off contains little plankton and its contributions are small,
while in 1897 recurrent floods throughout the year afforded a
run-off in seasons of larger production, and this tended to
ereatly increase the enrichment of channel waters in that year
as compared with 1897.

Plankton content in 1897 in Thompson’s Lake was in ex-
cess of that in the river in the case of coincident or approxi-
mate collections in 16 of the 18 instances, the two exceptions
appearing in July and September, when pulses in channel plank-
ton rise above the recorded production in the lake as a result
of some undetermined factor.

The similarity in the course of plankton production here
and elsewhere is most marked in the first part of the year,
and decreases in the time of low water. Thus, on comparison
of the planktographs of Thompson’s Lake (Pl. XX XVIII.) and
the Illinois River (Pl. XI.) we find 14 out of 18 changes in the
course of production coincident in the two regions, the four ex-
ceptions occurring in May (1), July (2), and September (1).
The environmental differences between Thompson’s Lake and
the river are much less than between this lake and Quiver, and
we find a corresponding disagreement in their planktographs,
only 10 out of 18 changes being in the same direction, and six
of the ten are in the period of high water, when local differen-
ces are submerged. In the cases of Flag and Dogfish lakes col-
lections extend only to July, with agreement in 5 cases in each
out of a possible 7 and 6 respectively. In the year as a whole
and including all the above localities we find 34 agreements to
15 exceptions, in January—June the ratio being 8 to 21 for 4 lo-
ealities, and in July-December, in low water conditions, 12 to 13
for from 2 to 3 localities. The effect of the common elements

406

of the environment which high water introduces, in unifying the
course of plankton production in their several areas, and of low
water in diversifying it, is well demonstrated by these compar-
isons.

In the planktographs of Thompson’s Lake and the Illinois
River there is a striking general agreement in the low vernal
production and the increased and unusual autumnal production.
There are also some indications of a pulse-like character of the
planktograph in the lake, though the collections are too infre-
quent to demonstrate it.

1898.
(Table VIII., XII.; Pl. XXXIX., L.)

There were 25 collections in this year, at fortnightly inter-
vals, with an average of 5.71 cm.’ per m.* to 2.13 cm.’ in channel
waters. The net result of the run-off from Thompson’s lake in
this year is thus an enrichment of the plankton of channel
waters. This is true for all of the monthly averages (see table
between pp. 342 and 343) with the exception of April, and this
exception is due solely to the distribution of collections on the
rising vernal pulse, and is more apparent than real (cf. Pl. XIU.
and XXXIX.). The relative plankton content in the two areas,
as will be seen on a comparison of the planktographs, is not
subject to great variations in this year aside from January,
when the ratio of the lake to the river is 1 to 17, and, as above
noted, in April, when the ratio apparently falls to 1 to.6. With
these exceptions, it ranges in the first six months from 1 to 2-3
and in the last six from 1 to 3-5. These figures express quanti-
tatively the striking similarity in the planktographs of the two
areas, which may also be recognized at once in the plates (XII.
and XX XIX.) in the low winter production, in the meteoric ver-
nal pulse followed by a minor one in June, and in a low level of
production during the remainder of the year with fluctuations
within rather narrow limits.

The cause of this close resemblance lies in the hydro-
graphic conditions, which throughout this year favor constant

407

interchange between lake and river. The average height for
this year is 8.02 ft., the highest during our years of record.
From Jan. 22 to July 15 river levels were above 6 ft., anda
constant inflow of impounded water from bottom-lands above
the lake, or through the slough when overflow ceased, continued
with impounding in the lake and subsequent discharge from its
southern end to the channel. The same conditions again
prevailed from Oct. 30 till the end of the year, with an inter-
ruption of 6 days in December. During the remaining parts of
the year there was a constant wavering in levels which fa-
vored frequent—in fact, no less than 21—reversals in the direc-
tion of flow in the slough connecting the lake with the river.
During the 134 days of low water there were 56 of falling levels
in which the lake was discharging its plankton-laden water
through the slough to the river, making a total of 287 in which
it contributes to channel plankton to 78 in which, owing to low
levels, it merely receives an inflow from the river. Moreover,
the periods of greatest plankton production in the lake, during
the vernal pulse, occur at times when the run-off from the lake
is at its height, so that in this year all the hydrographic factors
combine with the distribution of the plankton production to
render this reservoir lake a feeder of the channel plankton.
Though the differences in the plankton content are such that the
actual enrichment per cubic meter may be less than in other
years, the total run-off of plankton into the channel must com-
pare favorably with that in any other year of our operations.
The comparison of coincident collections shows in all cases
but three, a greater plankton content in the lake than in
river. The first of these is on April 5, at the height of the
spring flood, when a considerable current sweeps through
Thompson’s Lake and shortens the period of impounding, and
thus reduces the time for the development of the plankton.
The second instance is on June 21, on the decline of the acces-
sory vernal pulse, which reaches a lower level in the lake
(2.47) than in the river (2.88). This is one phase of a not un-
common phenomenon in the plankton pulses of the backwaters,

408

They have greater amplitudes, but are frequently followed by
more sudden and complete declines. Thus, in this case the
apex of the pulse is at 18.39 and 6.99 cm.’ respectively in the
lake and river on June 7 and 14, while the decline has reached
2.47 and 2.88 on the 21st in the two localities—a fall of 86 and
59 per cent. respectively. The third instance occurs on Aug. 16
(lake, .45, river; .61), when a large silt content in Thompson’s
Lake, due to roiling of the water by heavy wind, obscures the
actual quantity of the plankton.

The similarity in the direction of the changes in plankton
content in Thompson’s Lake and the other localities continues
in this year even to a greater degree than formerly, owing in
part at least to the hydrographic conditions above noted and
to the more complete and uniform records. In the case of
Thompson’s Lake and the river there are 21 agreements in the
direction of the changes to 4 exceptions, and in the records of
Quiver Lake 22 to 3 in the possible 25. This is so far in excess
of the degree of agreement demanded by chance that we may
look with confidence for an efficient cause in the common fac-
tors of the environment, in the similar reproductive cycles of
the constituents of the plankton found in common in the sev-
eral localities, and in the uniformity in the reactions of at
least a predominant portion of the total plankton assemblage
to the factors of the environment.

The river levels average 8.01 ft. for the year and stood
above 6 ft. for 8 months of the 12. The high water increases the
area of the “open water,” and causes a retreat of the shore-line
and bottom, and a decrease in the relative occupancy of the
bodies of water in question by the spheres of influence of the
immediate environment. Thus the local differentiating char-
acters of the several environments are in general progressively
less potent as the open water increases in extent. The loca-
tions of the 7 exceptions to the similarity in the direction of
the movement in production are significant. All of them he
in the last five months, in the period of low water, and 2in the
lowest water in August, when local influences are more potent,

409
1899.

(Table VII1., XII.; Pl. XXXIX., L.)

There are 7 collections at fortnightly intervals in the first
3 months of the year, with an average of 1.21 cm.’ perm.’ to .41
in channel waters. With the exception of four days in Febru-
ary, river levels were above 6 ft. throughout the period, and con-
sequently the lake was continually receiving water at the north-
ern end and discharging at the southern, and contributing
throughout the whole time, in this way or through the slough,
to channel waters. The average result is an enrichment of the
plankton of channel waters. The monthly averages (see table
between pp. 342 and 343) in January and February in the lake
exceed those in the channel by 9- and 2-fold respectively, while
those of March, in highest flood waters, are respectively .28
and .21 cm.*, owing, as will be seen on a comparison of Plates
XIII. and XX XIX., to the distribution of the dates rather than
to an actual smaller production. A comparison of all coinci-
dent collections in lake and river exhibits likewise a larger
plankton content in every instance in lake waters. The lake
thus tends continually during this period to enrich by its run-
off the plankton content of channel waters.

The similarity in the movement in production noted in
1898 is interrupted in these winter months by dislocations of
the apices of the slight pulses of production, due in part to the
flushing action of sudden floods and its unequal distribution in
channel and backwaters. Of 7 possible agreements in the di-
rection of movement in production there are but 3 realized in
the case of both the river and Quiver Lake. A comparison of
the three plates (XIII, XXIX., and XXXIX.) will, however,
show that all, in common, exhibit evidences of a January and
a February pulse and a common March decline.

SUMMARY.

The grand average of all the Thompson’s Lake collections
shows a plankton content of 7.94 cm.* per m.° in comparison with

410

2.19 cm.’ for channel waters. The relative fertility of each is
perhaps better expressed by the average of the monthly aver-
ages, 8.26 and 2.71 respectively. The run-off of the impounded
lake waters would thus tend to enrich the plankton content of
the channel in some ratio dependent upon the relative vol-
umes and plankton contents of the mingling waters. We have
also seen that the enriching function of the contributions of this
lake is continuous throughout a large part of the year, with a
few interruptions dependent upon cessation of run-off in rising
levels in low-water periods, and, rarely, to a lower plankton
content in lake waters, due generally to increase of plankton
in channel waters as the current slackens in low river stages.

The following comparison of the averages of the monthly
averages for the years of our operations, taken from the table
between pages 342 and 348, is instructive in indicating the vary-
ing relation of production in lake and channel waters.

COMPARISON OF MONTHLY PRODUCTION IN THOMPSON'S LAKE AND ILLINOIS RIVER.

DS a \ Eg a & ' ob)
(S 3 a = A n o a Tm oo
s/E/2/E) 2) 8/5] lex) o|ezeaes
g~ 3) () :
ice emia 1 |[C &
Illinois River.. 213 3| .27] 4.59] 6.08] 7.22 4.23) 3.88 2.56] 1.70 88| -71| 2.71
Thomp. Lake..|3.79 | 1.27] 2.96]14.49)29.59|10.66) 4.74] 6.19] 5.37|10.64 639] 3.08] 8.26
IREIIO cooovcssec 1:18 | 1:5 | x:tel 1:3 | 4:5 [021-5] r:t.1[/ 421.6) 1:2 | 1:6 | 1:7 | 1:4 | 133
Average height
of river in ft..17.77 | 7.89!12.34!10.02! 9.18! 6.19! 4.36! 2.26! 3.78! 3.44! 4.26! 4.97

The average height of the river for the years represented
in the several monthly grand averages is also given in the above
table, and exhibits some relations to the relative plankton pro-
duction in Thompson’s Lake and the Illinois River, which,
however, are so combined with other factors—such as seasonal
temperature changes, the period of dominance of vegetation,
and qualitative seasonal changes in the plankton itself—as not
to be readily analyzed. We find in January—May a period of
high levels and low temperatures, of flood invasion everywhere—
but most potent in channel waters, a period in which production
in thelake is from 3-to 18-foldthatin the river and averages 8.4,

41]

This is the time of greatest contrast, and also the time of
highest levels (averaging 9.44 ft.) and therefore of continuous
and largest run-off. It is also the season of largest plankton
production, averaging 10.42 cm.’ per m.’,—8.4 times that in
channel waters,—and is accordingly the period of greatest en-
richment of the channel plankton by the run-off from the lake.
The factors operative in producing this result are the high
levels, with resulting increase in the impounded waters of the
lake at a season of rising temperatures favorable to plankton
production and to the enrichment of the waters by decay of
the vegetation of the previous year’s growth.

In June-September we have a period of falling levels,
maximum temperatures, lowest water, and growth predominat-
ing over decay in the aquatic vegetation, which is relatively
more abundant in the lake than in the river. It is therefore
the season of greatest predominance of local environmental
factors, and of run-off reduced to minimum volume and fre-
quently interrupted. It is also the season of least plankton
production, averaging 6.74 cm.’ per m.’—only 1.54-fold that in
channel waters. The midsummer season is therefore one of
least enrichment of channel plankton, as a result of both the
decreased and interrupted run-off and the decrease in the relative
production in the lake. This latter feature results both from
the decline in production in the lake and the low-water condi-
tions in the river, where increased fertilization by sewage and
slackened current tend to raise its level of production at this
season. Other factors tending to bring about the conditions of
production prevalent in this season are possibly the greater
relative exhaustion of the fertility in lake waters during the mid-
summer and low water, as indicated in our chemical analyses
by the generally lower level of the various forms of nitrogen in
the lake than in the river. (Cf. on this point Plates XLV. and
L.) This greater relative exhaustion maybe attributed in part
only to reduced interchange of river and lake waters at low levels
and consequent reduction in influx of sewage fromthe channel,
and tothe utilization of some of the constituents which support

412

the phytoplankton by the rapidly growing aquatic vegetation.
These factors are not, however, potent enough to overcome’ the
effect of impounding and consequent time for breeding which
prevail in the lake more than in the river, and thus to lower
the plankton production in the lake below that in the channel.

In October-December we find another season marked by
rising water but not high levels, in fact, averaging only 4.22
ft.—a level insufficient to provide for any current through the
lake or any considerable discharge in periods of decline. It is
thus a season of shght and interrupted run-off. It is, however,
a period of increased production, reaching 10.64 in October,
declining to 3.08 in December, with an average of 6.70—a trifle
below that of the midsummer period. Its relation to channel
production changes decidedly, rising from a ratio of 1 to 1.54
in midsummer to | to 5. This five-fold greater plankton con-
tent in Thompson’s Lake makes whatever run-off occurs of con-
siderable enriching effect upon channel plankton, though pre-
vailing low levels and large proportion of rising levels tend to
reduce the actual volume contributed in this season. The fac-
tors operative in increasing the ,elative production in lake
waters in this season are the influx of sewage-laden river
water, and the decay of some of the succulent vegetation of
the lake and its re-submerged margins at a season of plank-
ton pulses of an amplitude increasing by virtue of other fac-
tors, internal or external. Rising levels also bring about an
increase in current in the channel, while marked changes
in the bacteriological and chemical condition of channel,
waters attend this and the fall in temperature. The com-
bined effect of these factors, as shown by a comparison of the
records of 1897 (Pl. XI.)—when low levels continued and the
autumnal decline in temperature was late—with those of other
years, 1s to depress production in channel waters more than it
fallsin the lake. This fact, together with the increase in the
impounding function of the latter as levels rise, suffices to
bring about the increased relative production in lake waters in
the closing months of the year.

413

Thompson’s Lake and presumably other bottom-land wa-
ters of similar character, by virtue of their impounding fune-
tion, are reservoirs in which flood waters are stored for a great-
er or less time, permitting the development: in general at all
seasons of the year of a plankton exceeding in volume from
1+--fold to 18- fold that coincidentally developed in channel
waters of the adjacent river. The run-off from this and like
areas elsewhere thus serves to enrich and maintain. the river
plankton proper. The slightly developed flood-plain of the Illi-
nois and the consequent considerable area of such bottom-land
waters—which equalize the floods, prolong the run-off, and favor
the production of an abundant plankton in the impounded areas
—hbecome, accordingly, factors of great importance in causing
the richness, abundance, variety, and long continuance of the
unusual plankton production of the [llinois River. .

The similarity in the course of plankton production in
Thompson’s Lake and elsewhere in our field of operations is
shown in the following tabular summary, which gives the num-
ber of instances of agreement and disagreement in the direc-
tion of the changes in production in the four localities.

SIMILARITY IN DIRECTION OF CHANGE IN PRODUCTION IN THOMPSON’S LAKE
: AND AT OTHER STATIONS.

= - Sie ID Soe [a

Be Awe] fe Ave! fe Pel Se Awa] Me Axe
MOO GE t ciel 9 4 7 5 9 3 2 I 27 1373
MO@QOwie rs series <i 18 8 12 13 18 16 6 38
MOO/Pi ss cs seats 14 4 if) 8 5 I 5 2 34 15°
Tol a gold ween 21 4 22. Sieh Nevers cee rveeenel[eetrcmecee liner 43 Uf
MOOO ME ais eres = 3 4 3 AE hee scnrerall every alee oeterens alltees acaa|| © 8
plots ces ss 63 || aa 54 33 32 | 12 a3 | ae || ga | Bn”

This gives a grand total of 174 instances of similar direc-
tion of change in production out of a possible 255, or 68 per cent.,
for the 5 years included. It is noticeable that the years differ
considerably in the degree: of agreement detected, the latter
years of fuller records exhibiting fullest agreement. They are

414

also years of higher water, of greater uniformity of environment
—because of greater extent of open water, of greater interchange |
of water in overflow stages, and therefore of greater agreement
in the course of plankton production. The similarity in the
course of plankton production in different bodies of water is in
a large measure a function of the similarity of their environ-
ment and the resemblance of their planktons in the matter of
constituent organisms.

STATION F, PHELPS LAKE.
(Table IX.; Pl. XXI., XL..-XLIL)

ENVIRONMENTAL CONDITIONS.

This body of water les on the western side of the river about
a mile below the city of Havana, in the elevated bottom-lands
below the mouth of Spoon River. It trends northeast and
southwest for a distance of seven eighths of a mile, has a width
of 400-699 feet, and a total area of 50-60 acres. Its bottom lies
about 6.5 feet above low-water mark, and the greatest depth re-
corded in it at high water at the point of collection was only
10 ft. It is but slightly deeper toward the lower end. Its out-
let is by a tortuous slough choked with driftwood, which runs
for two fifths of a mile ina southerly direction to the river.
The elevation of the bottom of this slough at its entrance to _
the river is 8-9 ft. above low-water mark, so that all run-off
from the river drained hy this slough ceases when it drains to
this level, and it is not reinvaded by floods below this elevation.
When the river falls below the level of the outlet and the lake
drains as fully as the outlet permits, there still remain about
1.5 ft. of water from whick no further run-off occurs. The vol-
ume is then slowly reduced by evaporation or increased by sum-
mer rains.

The lake is not fed by springs or tributaries of any sort be-
yond seepage from the level alluvial bottoms in which it hes,
and which nowhere in the vicinity rise more than 10 feet above
its bottom and generally very much less than this distance. At
river stages of 11 ft. and above, backwater from Spoon River

415

makes its way through a now abandoned channel to the lake
and thence out to the river through the slough. Below this
level, the current of the gentle run-off of the great tract of adja-
cent impounded backwaters with which this lake has then but
a slight connection is the only movement in the area.

The surrounding bottoms are heavily wooded for a narrow
margin along the lake, though the forest gives way to cultivated
fields on both sides within a short distance. Its bottoms and
shores are of a rich black alluvium, which in low-water seasons
such as 1895 becomes the soil of a cultivated field.

The vegetation of this area is unique among our plankton
stations in its character and relation to the plankton. In 1894
there was little vegetation present, and whatever aquatic
growth had gained a foothold was eradicated by the dry au-
tumn and by the cultivation of the soil in 1895. In 1896-1899
the occupation of the lake by water was more continuous, and
Potamogetons, Naias,and even Nelumbo, gained a slight foothold
along the margins. The principal vegetation was a dense mat
of filamentous green alge, such as Spirogyra and Zygnema,
which covered the margins for a considerable distance into the
lake. During the heated term of midsummer a dense felt of
Oscillaria covered the bottom of the lake everywhere at times.
These algze were present during most of the summer, though
most abundant in spring, and by their continuous and prompt
decay they release into the lake waters a volume of nitrogenous
and other substances which are utilized by the phytoplankton.
The cumulative action of the longer-lived aquatic phanerogams
in withdrawing from the lake large stores of food which are
again released in the ensuing autumn or spring by the decay of
the season’s growth, is thus quite absent from this body of wa-
ter. The rapidly growing and rapidly decaying alge permit a
repeated flux of nitrogenous and other substances utilized by
the plankton as food in the course of a single season. This fac-
tor, combined with the complete impounding function of this
lake below river levels of 8 to 9 feet and the absence of tributary
and spring water, is, I believe, the secret of the unusual plank-
ton production in this area.

416

The absence of coarse vegetation, the sheltered situation
inariftin a dense forest, and the shallowness of the whole
lake during much of the summer, permit an unusual range of
diurnal temperature-changes falling but a few degrees short of
the diurnal range in the air. The records (Table IX.) fre-
quently contain readings of 90° to 95° in the summer season.
This lake swarmed with the fry of various native fishes and the
introduced German carp, all of which make great inroads upon
the vernal plankton. It was also the favorite haunt of many
fish-loving water-fowl. This abundant animal life served in
turn to enrich the lake waters with its nitrogenous wastes, at
once available for utilization by the phytoplankton. There are
thus many chains of food relations in this lake, in most of
which, if not, indeed, in all, the plankton forms many links.

COLLECTIONS.

There is a total of 67 collections from this lake ; 1 only in
1894, 29 in 1896, 9 in 1897, 22 in 1898, and 6 in 1899.

The single collection in 1894 was made by the oblique-haul
method. The absence of collections in 1895 is accounted for
by the fact that there was no water in the lake in that year.
In 1896-1899 collections were made in various ways according
to the conditions of access to the lake and the depth of the
water. Owing to rafts of driftwood, access at any season
through the slough is prevented. At high flood-levels, when
ice did not prevent, it was possible to enter the lake by boat
with our plankton pump and usual collecting apparatus. At
all other seasons access by boat was impossible, and apparatus
had to be carried across fields and through dense under-
brush to the lake, and collections made by wading out into the
lake or from a staging carried out from the shore for some dis-
tance over the water. ‘There are accordingly but 9 pump col-
lections. The remaining 57 were all made by dipping water
from the surface and pouring it through the plankton net.
Most of the collections represent, therefore, surface waters, but
owing to the exceedingly shoal water they are, nevertheless, in

417

the main representative of the plankton of the lake. Of the 67
collections, 32 were taken from water which in the deepest part
of the neighborhood of collections was less than 14 inches.
Owing to the roiling of the water caused by our movements, it
was necessary to dip from considerable areas in order to secure
the desired volume for straining.

Since a separate report on these collections is being pre-
pared I shall only deal in this connection with those aspects of
the data most intimately connected with the phenomena of
the channel plankton.

PLANKTON PRODUCTION.
1894.
(Table 1X.)

A single collection on June 8 yields a volume of 24.17 cm.°
per m.*, an amount 7-fold that of the same season in 1896, al-
most equaled in 1897, and more than doubled in 1898.

1896.
(Table 1X., Pl. XL.)

There are 29 collections in this year, extending from Jan.
8 to Nov. 17—when only a few scattered pools remained. This
is the most fully represented year of our series in this lake.
The yearly average is 13.17 cm.’ per m.*, with a vernal maxi-
mum of 54.80 on Apr. 16, and an autumnal one of 51.60 on Oct.
15. This is the earliest vernal pulse recorded in our work, and
should be correlated with the early rise in temperature in these
shoal and protected waters. Thus, in Phelps Lake on Apr. 16
the surface temperature was 77° and the average for April 68.4°
to 71° (Apr. 17) and 62.6° (average) in Quiver Lake, and to 66.3°
(Apr. 17) and 63.2° in the Ilhnois River. This lake was thus
apparently 5° to 6° warmer on the average than these other
localities, and the vernal pulse is accordingly accelerated.

Owing to the elevations of the lake and its outlet, run-off
from this area into channel waters practically ceases when
river levels fall below 8 ft. In 1896 there were but 114 days of

418

stages above 8 ft., 90 from Jan. 1 to Mar. 30, and 14 and 10 re-
spectively in the floods of May-June, and August. Of the 114
days there were 28 of levels above 10 ft., when, owing to run-off
from Spoon River, a current passes through the lake to the
river regardless, as a rule, of rising or falling water. In addi-
tion there were 43 days of falling water when a run-off might
be expected, making a total of only 71 days in this year in
which there was any run-off to channel waters from this lake.
The remaining 43 days of levels above 8 ft. were times of sta-
tionary (20) or rising (23) water, when discharge from Phelps
Lake was diminished or cut off.

Of the 71 days of discharge, 61 fall in the winter, in Janua-
ry—March, and 5 each in Juneand August, at times of depres-
sion in production (Pl. XL.). Nevertheless, the plankton con-
tent in Phelps Lake at all of these times greatly exceeds that in
channel waters. The ratio of Illinois River and Phelps Lake
plankton in Jannary is | to 189,in February, | to 607, in March,
1 to 274, in the June flood, | to 4,and in the August rise, | to 7.
These latter ratios are somewhat exceeded by those of the ay-
erage production for the year, 1.16 to 13.17 cm.’, or 1 to 11.
During the months of little or no discharge, April-December,
production in the lake as shown in monthly averages is 4- to
1600-fold greater in Phelps than in the Illinois, the latter figure
being reached in November and the other months averaging
only 11-fold.

Thus, this lake contributed to the enrichment of channel
plankton for a relatively brief part of the year, and at all times
produced a plankton greatly in excess of that in channel wa-
ters. The sharp contrast between the poverty of channel wa-
ters and the wealth of this lake is due to the impounding fune-
tion in the latter, and to the repeated flushings by storm waters
of recent origin in the former. Full time for the normal utili-
zation of the resources for growth of the plankton is permitted
in the lake but not realized in the constantly replaced river
water.

This is the only year in which collections were made in

419

Phelps Lake at weekly intervals for any length of time. Such
intervals extend from the end of March to the last of August,
and since similar series were made elsewhere we have an excep-
tional basis for comparison of the course of production in the
several localities.

A comparison of the planktographs of the river and Phelps
Lake (Pl. X. and XL.) reveals certain general similarities.
These are expressed in the three major fluctuations of the year,
the vernal, midsummer, and autumnal rises in production, which,
in the main, have coincident limits, but very divergent ampli-
tudes, in the two bodies of water. The absence of the sudden _
diluent action of flood waters is noticeable in Phelps Lake rec-
ords, though declines in plankton content coincide with the
flood invasions of both June and August. The absence of col-
lections in September in Phelps Lake at the time of the decline
in plankton content between the midsummer and autumnal
rises is due tothe very low stage of water in the lake, per-
mitting no collection. Replenishment by autumn rains is
followed by the large development in October (51.6 cm.’).

Not only is this general similarity between the movement
in plankton production in Phelps Lake and the Illinois River
traceable in 1896, but there is a more detailed agreement in the
changes in the direction of movement in production in coinci-
dent or approximate collections. This is most clearly seen in
the months of April to August, when collections are of sufficient
frequency to trace with some certainty the course of produc-
tion. During these five months there are 16 agreements in the
direction of the change out of a possible 20—a total of 80 per
cent.—between Phelps Lake and the [linois River. In the year
as a whole the agreements number 19, or 68 per cent., out of a
possible 28. Two of the exceptions in April-May are due to the
dislocation of the vernal pulses in consequence of the higher
temperatures in the lake above noted. When we take into con-
sideration the marked differences in the local environment of
the plankton in these two localities and the considerable inde-
pendence of this lake as contrasted with other reservoir lakes,

420

such as Thompson’s and Quiver, this marked degree of resem-
blance is the more striking.

A comparison of the course of production in Phelps Lake
(Pl. XL.) and Thompson’s Lake (Pl. XX XVII.) in 1896 reveals
14 agreements out of a possible 25, or 56 per cent. Of the 11
disagreements 3 fallin the period of few collections in the au-
tumn months, when Phelps Lake was reduced to shallow pools,
and 4 occur during the vernal pulse of April-May. A compar-
ison of the planktographs and thermographs of the two lakes
shows that in Phelps Lake the temperature is from 2° to 8°
higher than in Thompson’s Lake for a period of six weeks dur-
ing the rise of the vernal pulse. Hence this culminates earlier
by a fortnight in the former, and in consequence a dislocation
of the course of production in the two lakes occurs in this peri-
od. The two planktographs are, however, strikingly alike in
the fact that in the interval between March 31 and June 1
there are three pulses of regularly decreasing amplitude in
both lakes. The similarity is thus greater than the percentage
indicates.

A comparison of the course of production in Phelps and
Quiver lakes (Pl. XL. and XX VII.) reveals 15 agreements out
of a possible 28, or 54 per cent.—but little more than chance de-
mands. In this case the environmental differences are greater,
the effect of spring water, vegetation, and flood invasion inter-
fering in Quiver Lake with the course of production.

A comparison with Dogfish Lake, where the disturbing fac-
tors of spring water and flood invasion are less immediate in
their action, reveals a slightly greater degree of similarity—16
out of 28, or 57 per cent.

In the case of Flag Lake the agreement is still less, being
only 11 out of 24, or 46 per cent. It is a noticeable fact that:
the disagreements are most numerous in Quiver, Dogfish, and
Flag lakes, all of which are rich in vegetation, and these disa-
greements occur in greatest proportion during the months of
May—August, when with changing river stages the proportional
occupation of these lakes by vegetation fluctuates greatly—

421

a variable factor from which Phelps Lake is to a large extent
exempt. The degree of agreements, as a whole, in production
between Phelps Lake and other localities is seen in a total
of 84 instances out of a possible 141, or 60 per cent.

1897.
(Table IX., Pl. XLI.)

There are only 9 collections in this year, at approximately
monthly intervals with the exception of the last collections,
when the interval was somewhat reduced. Collections cease in
August, when the water entirely disappeared from the lake.
The average plankton content for the year is 10 cm.* per m.*,
the lowest annual average in which summer collections are in-
cluded in this lake. The vernal pulse was not detected, if pres-
ent, and the maximum record, 29.94 cm.’, was on Aug. 26, the
date of the last collection.

The hydrographic conditions were such (Pl. XLI.) that a
current from the flooded bottom-lands about Spoon River
passed through the lake uninterruptedly from Jan. 7 to May 13,
and the run-off of impounded waters continued until the 25th,
a total of 139 days. Throughout the period covered by our
few collections they indicate that the plankton content of this
area exceeded that in channel waters by from 1.6- to 11-fold
with the single exception of Apr. 27, when the lake had 4.26
em.’ to 5.11 in the channel. During the 139 days of run-off
the production in the lake scarcely exceeds 5- fold that in the
channel, but when discharge ceases the content rises to 10- to
11-fold that in the river—a phenomenon which illustrates the
equalizing effect of general overflow on the one hand, and the
effect of impounding in increasing production on the other.

The run-off from this lake in 1897 thus predominantly
served to enrich channel plankton. The fact that produc-
tion in Phelps Lake falls below that of the channel on Apr. 27,
when a vernal pulse might be expected of an amplitude greater
in backwaters than in channel,—as indeed it is in Thompson’s
(Pl. XXXVIII.), Quiver (Pl. XXVIII.), Dogfish (XXXII.), and

422

Flag (X XXIV.) lakes by 50 to 150 per cent.,—is to be attributed
to the diluent effect of invading flood-waters from Spoon River,
whose plankton content on Apr. 27 was only .05 cm.’ per m.*
The entrance of these flood waters, indicated by the check in
the decline of the hydrograph (Pl. XLI.), was noticeable at the
station on the day of collection, and is the cause of the increased
turbidity in Phelps Lake on that day (Table IX.).

The similarity in the movement of production in Phelps
Lake in 1897 to that in the other bodies of water examined by
us, is very close. In the case of the Illinois River, 8 out 9 pos-
sible instances, or 89 per cent., are in agreement ; in Thomp-
son’s Lake 7 out of 9, or 78 per cent.; in Flag Lake all in-
stances are in-agreement; in Quiver Lake 6 out of 9, or 67 per
cent.; and in Dogfish Lake 4 out of 6, or 67 per cent. As a whole,
32 out of 40, or 80 per cent., of the changes in the direction of
production in Phelps Lake accompany similar changes in di-
rection in these other localities. All of the 8 exceptions to this
agreement occur at levels below 8 ft., when local environments
are more potent, and 5 of the 8 are found in Quiver and Dogfish
lakes, where vegetation and access of tributary waters become
proportionately more or less potent as levels fall or rise in May
to August, when the 5 exceptions occur.

This unusual degree of agreement in 1897 must be attrib-
uted in large part to the hydrographic conditions in the period
of comparison. For almost 5 months of the year levels were
above 8ft., when fluctuations have relatively but a slight effect
on the various environments. Above this level the several lo-
calities are more or less submerged in the general overflow, and
all share alike in the wide stretches of open water in which some
current exists, and the commingling to an increasing extent,
as levels rise, equalizes and obliterates local differences in pro-
duction. The first 4 collections of this year were made under
such conditions, and agree without exception in the course of
production. The remaining 5 were taken at stages below 8 ft.,
in the very midst of the season of local diversification, and the
proportion of agreements falls from 100 to 60 per cent., and is

425

greatest in the most differentiated localities, Quiver and Dog-
fish lakes. It might also have been expected in Flag Lake (PI.
XXXIV.) if examination had continued there beyond the mid-
dle of July. It would seem, accordingly, that similarity in the
course of plankton production in different localities is to a
large extent a function of the community of environmental
factors, and possibly also of the similarity of the constituent
organisms.

1898.
(Table IX., Pl. XLIL)

There are 22 collections in this year, at fortnightly inter-
vals, in March—December. The average production for the year
is the unsurpassed amount of 44.08 cm.’ per m.*, with a maxi-
mum, also unsurpassed in our records, of 224.48 on Aug. 25. An
unusually high level of production is also maintainedfrom Aug.
9 to Dec. 13, averaging 63.54 cm.’, and falling below 30 in but
two instances.

Water re-entered Phelps Lake with the flood of February,
river stages passing 8 ft. on the 12th and 10 ft. on the 20th.
From this latter date until June 28, with the exception of 4
days in May, levels continued above 10 ft., so that a continued
current of overflow from the bottom-lands to the north passed
through the lake to the river. Declining river stages continued
from June 28, passing 8 ft. July 9, thus permitting a run-off for
a total of 138 days from the lake to the river in the period of
spring and summer floods. To this must be added 7 days of de-
clining levels above 8 ft. in the November-December rise, mak-
ing a total of 145 days of contributions to channel waters from
this lake. This is the most extended period of contribution in
the years of our operations, and is a result of the unusually
high and prolonged floods which brought the average height of
the river up to 8.02 ft., almost bank height, for the year.

The plankton content of Phelps Lake waters in the 10 col-
lections made during the period of discharge above noted, is in
excess of that in the channel in 7instances by from 1.4- to 15- fold

424

and averages 7.3. In three instances, March 3 and 1, (.01 and
.02), March 29 (.20 and .43), and April 26 (10.72 and 15.81) the
lake contains less than the river. All of these instances fall at
times of high levels, exceeding 11 ft., when Spoon River floods
invade thisterritory, and this deficiency in Phelps Lake is doubt-
less due to their diluent effect. Since our station for collections
was located in the upper end of the lake (PI. II.), the full effect
of the flood would be detected at this point, but would be di-
minished by mingling with the lake waters and the adjacent
impounded backwaters before it joined the channel. The first
of these exceptions, on March 3, isnot accompanied by increased
turbidity (.45) inthe lake (Table IX.), but the other two, March
29 and April 26, are attended by a marked rise in turbidity (.05
and .16). During this period of maximum spring flood in March
and April, owing doubtless to this diluent action of Spoon River,
the run-off from this area, as indicated by plankton content at
the upper end of the lake, dilutes, or but slightly enriches, the
channel plankton. This appears in the monthy averages (table
following p. 842), which for March are .33 em.’ for the river and
but .25 for the lake. In April they are 4.4 and 5.6 respectively.
In later months, during the declines of the spring flood, and
owing to absence of the flushing action of Spoon River floods
and to the rise in impounding function with decline in levels
and delimitation of the lake, we find a rapid rise in the relative
plankton content in lake waters. The production in coincident
collections is greater in the lake than in the river by 3- to 15-
fold, and the monthly averages for lake and river respectively
rise to 40.44 cm.® per m.’ and 11.30 in May; to 27.67 and 3.96 in
June; and to 6.97 and .58 in July; that is, the production is
from 3+- to 12- fold greater at this season in the lake than in
the river. During the run-off in these months this lake and its
contributing adjacent bottom-lands serve to increase, in
some unknown ratio dependent on their relative volumes,
the plankton content of the channel waters with which they
mingle.

Although the frequency of the plankton collections is in-

425

sufficient to trace with accuracy the course of production in
Phelps Lake in this year, they yield many suggestions of recur-
rent pulses of production similar in duration, though of greater
amplitude, to those more clearly defined in channel waters. A
comparison of Plates XII. and XLII. will indicate the presence
of pulses of production in both localities, culminating in the ma-
jority of instances at approximately monthly intervals. There
are eight such culminations in Phelps Lake visible in the rec-
ords of March—December, culminating in March, May, June,
July, August, September, November, and December. In spite
of the disparity in the records in this lake and the river, the
similarity in the location of the pulses in the two localities is
apparent in all of the above months but August and November
—both of which are months of unusual hydrographic disturb-
ances in channel waters.

A detailed comparison in the movement in production in
this lake and the adjacent river shows agreement in the direc-
tion of movement in 14 out of 21 possible instances,or 67 percent.,
5 of the 7 exceptions falling in the hydrographic disturbances in
August-September and November. Inthe case of Quiver and
Thompson’s lakesthe problem of comparison is made difficult be-
cause the fortnightly collections in Phelps Lake and these local-
ities are not upon coincident, butalternate, weeks, and makes the
the similarity or difference probable rather than precise. A
comparison shows 16 agreements out of a possible 20, or 80 per
cent., in the case of Thompson’s Lake, and 17 out of 20, or 85 per
cent., in the case of Quiver Lake. Both of these lakes are af-
fected by hydrographic changes at lower levels which do not
disturb Phelps Lake, and we find that 6 of the 7 exceptions oc-
cur in the period of floods at low levels. As a whole the move-
ments in production in the lake in 1898 agree with those else-
where in 47 out of 61 possible instances, or in 77 per cent. Jn
view of the fact that the records cover also the low-water period
this is a notable degree of agreement, and is to be attributed
to the unusually high average level for the year and to the
equalizing effect of high water. This factor is not, however, in

426

immediate operation during the last half of the year in so far
as Phelps Lake is concerned, and other factors common to the
whole environment or inherent in the common plankton must
be responsible for the similarity in this period.

1899.
(Table IX., Pl. XLII.)

There are but6 collections in this year,—in January—March,
at fortnightly intervals. The hydrographic conditions are such
that the lake is cut off from the river for 34 days during the 3
months, and of the remaining time there were only 32 days of
stages above 10 ft.in which currents passed through the lake to
the river, and 7 of falling stages at levels below 10 and above 8
ft., when the run-off continued, making a total of 59 days of
contribution to channel waters. These times of contribution
in January and March (Pl. XLII.) are also times of high plank-
ton production for that season of the year. Thus the plank-
ton content in Phelps Lake on Jan. 24 is 8.47 cm.’ per m.’ to .03
in channel waters. The run-off from the lake at that time
is thus 286-fold richer in plankton than the water it joins.
Again, in March, it is 3- to 9-fold greater. The monthly aver-
ages of production are (see table following p. 342) from 6- to
26-fold greater in the lake than in the river. This lake thus
serves, even in winter conditions and under a thick and long-
persisting coat of ice, as a rich breeding ground for plankton
whose run-off enriches the channel plankton. This is due to
its impounding function, which results in high production, as,
for example, during the decline of the January flood (Pl. XLIL.).
Proof of this is seen in the sudden decline in production (from
9.3 cm.* on Feb. 7 to .1 on the 21st) when flood waters from
Spoon River were scouring out the lake beneath the ice.

The movement in production in these months in Phelps
Lake bears little resemblance to that elsewhere, agreeing with
changes in channel production (Pl. XIII.) in only 1 out of 6
possible instances, and in 8 and 2 respectively out of 6 in the
case of Quiver and Thompson’s lakes. This exceptional disa-

427

greement may perhaps be due to the changes elsewhere, inci-
dent to rising winter floods.

SUMMARY.

Phelps Lake is the richest in plankton of all the localities
examined by us, averaging 19.65 cm. per m.*, the mean of all
collections, or 22.35 cm.*, the mean of the monthly averages.
This is 8- fold the production in the river and more than twice
that in any other impounding area examined. We find, how-
ever, that the lake does not contribute to the river at levels be-
low 8 ft., and is therefore cut off for a considerable part of the
time. In the years 1894-1899 inclusive, the days of run-off
were 14, 0, 71, 139, 145, and 86 days respectively, or an average
of 76 days. Asarule the plankton content of the lake waters
during periods of run-off exceeds that in the channel in varying
degrees, and the lake by virtue of the impounding function
serves to increase the plankton content of channel waters. The
exceptions fall mainly at levels above 10 ft., when the diluent
action of Spoon River floods affects the production in the lake.
The high records of production which indicate the great rela-
tive and absolute fertility of this body of water are in the main
found during summer and autumn months, when there is no
discharge and the impounding function is at its maximum.
This is confirmatory evidence of the effect of impounding when
the disturbing factor of tributary water is absent and coarse
vegetation is of little extent. Owing to its small area, its early
separation from the channel, and its relation to Spoon River at
high levels, the total contributions from this area are relatively
small as compared with those from Thompson’s and Flag lakes,
and at times from Quiver Lake, and its relative fertilty during
months of run-off, as compared with these localities, is wont to
rise above their level of production, especially at stages be-
tween 8 and 10 ft., when run-off is shght and impounding
function dominant. Illustrations of this will be found in the
monthly averages of 1897 and 1898 in April-June, the sea-
son of greatest’ run-off, when 4 of the 6 monthly averages

428

are considerably larger in Phelps Lake than in the other lo-
calities.

The course of production in this lake, as has been shown,
is predominantly like that in the other localities. It frequent-
ly has similarly located pulses, though their amplitude, es-
pecially in late summer and autumn, is often much great-
er than elsewhere. Moreover, in the majority of instances the
direction of the changes in production in coincident or approx-
imate collections is also similar to that elsewhere. In a total
of 260 possible instances there is agreement in 169, or 65 per
cent. This excess of agreement over the demands of chance,
combined with its recurrence in successive years and its occur-
rence in the case of different localities, is confirmatory of the
view that it is the result of the operation of common factors
of the environment. The predominance of the disagreements
at times of greatest local differentiation or disturbance, as in
low water in summer or in rising floods, lends further support
to the suggestion.

GENERAL COMPARISONS OF YEARS AND STATIONS.

It is my purpose to summarize in the following pages the
results set forth in detail with respect to the individual locali-
ties in the several years, and tomake the comparisons and draw
the conclusions which follow from such a summary regarding
the relative production in these different years and localities
and the factors operative in modifying production.

The following table gives for the various localities the yearly
averages of plankton, silt, and total catch, and the number of
collections in each year.

Av. of

IG of all eollecnions

No. of z

Station Year collections ees Plankton] Silt | Total
1894 10 283 De) oS. || 2977
Suen 7 18 fo) .gI 3.22 .72 | 3.94
iilinoiss River. ..---c- 1800 6 ee 1.16 | 2.55 | 3.71
1897 34 3.28 3.69 | 1.91 | 5.60
1898 52 2.03 2.13 | 2.11 | 4.24
1899 13 42 41 94 | 1.35
Grandiawererern terete 2.71% 2.19f | 1.79 |.3.98

Totaleasciccck: 235
1896 9 oor .007 349 36
: 1897 13 .983 257 io iZ7B || BodlB
SOOMRNIVET serial t-i- 1808 iI "029 “029 796 83
1899 3 OI .O1L |2.216 | 2.23
Gran dyavA vy lees ees 256 465 .939 | 1.41

otallenmare scr 36
“a 1894 14 .90 163 |] Wolly | Bowe
105 13 65 78 .70 | 1.48
2 I 31 2.19 2.50 549) || 2.70)
Oumivier Walken. .....:. ce 24 GS "38 62 | 1.50
1898 26 1.06 2.44 .40 | 2.85
1899 7 .66 .67 .43 | 1.11
GraiMnGleNyoscosonllaccoac00000s 1.75 1.70 .§2 || Be@2

Motall nero, ccs 115
1895 12 3.30 3.25 | 2.15 | 5.40
Dogfish Lake........ 1896 30 3.99 5.01 Si || 5.50
1897 6 2.65 228 22 | 2.45
Grandlavster sss tisoercetnac en: 3.16 4.22 .88 | 5.10

Motalliescereiscreraee 48
1895 4 238 20245 3.45 25.99
189 27 31 13.83 | 1.45 |15.2
Flag Lake wlelele ccs cece 1897 7 5.34 4.50 .69 5.28
1898 6 5.31 2.83 | 4.30 | 7.13
GCiaincleNGonesuel popes ome oe 9.23 11.46. | 1.90 |13.36

MotalllSerrcrret 44
aid 1894 5 8.89 8.89 | 2.23 |I1.12
1895 14 13.31 9.67 | 1.44 {11.11
; 1896 27 6.67 9.00 422) ||| Q)522
OOH DSOR'S Lels@oc oe 1897 18 10.41 10.43 | 1.28 |11.71
1898 25 5.06 5-71 -79 | 6.50
1899 7 1.15 1.21 03 |) 1.83}
ERAINGIEN 5 o0666|\s000 00900000 8.26 7.94 .86 | 8.79

dhotale teensy ae 96
1894 I 24.17 24.17 |trace |24.17
1896 29 14.74 13.17 “77 |13.94
PhelpsWake......... 1897 9 9.15 10.00 .54 |10.53
1898 22 37-34 36.31 | 7.76 |44.08
| 1899 6 3-74 3-74 29 | 4.03
GIRINGIEK Zaeogeal leneomececaaE 22.35 19.65 | 2.95 |22.60

Motal tie sre yve 67

*Grand average of all monthly averages, not of annual averages.

{Grand average of all collections, not of annual averages.

430
1894,
(CNS Wi, SORE SOO, )

Only three stations were established in this year: the [lh-
nois River Station, with 10 collections ; Quiver Lake, with 14 ;
and Thompson’s Lake, with 5. The appended table gives the
production in monthly averages of plankton per m.’ for the
seasons covered by the collections.

PLANKTON PRODUCTION IN 1894.*

Mean of

Station June July | Aug. | Sept. | Oct. | Nov. Dec. monthly
averages

Illinois River... |—| .74/+, 5.12!-+|9.67|—|1.36/—| .61 .10 210 !—| 2.53
Quiver Lake...|—] .23 Ar 2.20|—| .74|-+/2.12/--| .95 |—|.02 |=] -03 i QO
Thomp. Lake..!+|24.92!+ 10.74/—|1.08/+.6 qgo|..].....]..].... —| 1.29 +| 8.89

*The minus sign signifies below average and the plus sign above.

It is evident from comparisons with records in years of fre-
quent collections, for example, in 1898, that the interval of col-
lection is too great in 1894 to give a satisfactory basis for a dis-
cussion of production. As far as they go the data indicate a
level of production below the average of our records. In the
river and in Quiver and Thompson’s lakes the monthly aver-
ages in 1894 are below the general averages for the respective
months in 5 out of 7, 4 out of 7, and 2 out of 5 months respec-
tively, a total of 11 out of 19. The mean of the monthly aver-
ages in 1894 for the river, 2.53 cm.’ per m.°, is 7 per cent. below
the mean of all monthly averages in 1894-1899, and that of
Quiver Lake is 49 per cent. below its mean. Thompson’s Lake,
on the other hand, with 8.89 cm.°*, presents an excess of 8 per
cent.

The low level of production in the river and Quiver Lake
is attributable to the absence of overflow in June with its ac-
companiment of run-off of impounded and plankton-rich wa-
ters, to flushing action of the repeated rises in September, and
to the relative dominance of coarse vegetation in the lake and,
to some extent, in the river. The larger production in Thomp-
son’s Lake is attributable to freedom from the flushing action
of floods in the prevalent low water and to the relatively stable

431

hydrographic conditions. It is noticeable that production in
the river is on the average 7- fold greater in July-August
(Pl. VIII.), during stable low water, when current is slackened
and impounding most prolonged, than in June and September,
when high levels and flushing by floods occur.

The low level of production in the river in October—Decem-
ber is exceptional. Similar hydrographic conditions in 1897
Pl. XI.) yield a 5- to 10- fold greater production. It is not im-
probable that the monthly collections of 1894 may be interca-
lated in the depressions between plankton pulses of greater vol-
ume, and thus inadequately represent the real production. Pro-
duction in Quiver Lake in the months represented in our rec-
ords in 1894 exceeded that in channel waters only in September-
October, when a slight run-off occurred, and that in Thomp-
son’s Lakein June, July, September, and December, but a run-
off of any consequence occurred only in June and for a week
each in July and September. Apparently the channel plank-
ton in this year was largely independent and indigenous in
origin, deriving but lttle enrichment from impounding back-
waters, and not infrequently diluted by their contributions.

1895.

(Pl IX. XXVL, XXX., XXXII, XXXVI.)

To the river, represented by 50 collections, Quiver Lake,
by 13,and Thompson’s Lake, by 14, there are added this year,
Dogfish Lake, represented by 12, and Flag Lake, by 4 collections
in late autumn—a total of 93. The table on page 482 gives the
monthly distribution of production in the several localities,
and indicates their relation to the general averages.

This is a year of lowest levels, averaging only 3.61 ft. above
low water, and also one of high plankton content. On the basis
of means of monthly averages, the average content in the river,
5.91 cm.* per m.’, is the largest recorded, exceeding the average
of all monthly averages, 2.71, by 118 per cent., and being sec-
ond in the list if we base comparisons on the average of all col-
lections. This high content in river waters must be attributed

432

to stable hydrographic conditions, abrupt changes being limited

to less than 8 weeks in the year (Pl. IX.), and to low water

and consequent slackening in the channel with increase of time
PLANKTON PRODUCTION IN 1895.*

Station Feb. Apr. May | June July Aug.

INNING IRIE .s 506000 000060005000 —| 0.01|-=| 3.18). “[F/30- 42|+] 9.33/+] 4.03

OMIVEP ILENE, 4000008 0000 00b00006 —| 0.03 —| 3.00]..|.....].. —| 0.37|/—| 0.21

IDYeyn|N IAC. 5006000000 0aceoscolfoolloaces S.AGI\o allogooe I! 6, “12|-+ 2.99|--| 1.11
Blapo wakes « cnsciice eae eo toed lene ollie ons

Thompson’s Lake................ Ae | eee +28. 20|-+|6r .44|— ‘9. 42i+ “4.831- — 3.09

Mean of

Station Sept. Oct. Nov. Dec. monthly

Averages

INOS IRIE coos bb ogoccoga0da0s —| 1.52 |—| 0.57 |+] 3.02 |+] 1.14 |+] 5.91

Ouiver Make fern deen uae eiee +] 0.94 |—| 0.13 |—| 0.05 |—| 0.46 |—| 0.65

IOxoetnSly LARC 500600000 0000800000 =| 3.15 |=] 0.52 |--] 5.01 ISG) 5.32) |) ange

lag Males. ccs ccetimac meee Ie ue reve +) 57.76 |-+| 14.40 |+| 4.82 |-+] 25.66

shhompsonislakeneeeeeer renee —| 3.58 —| 3.15 I—| 5.07 !—| 1.00 |) 13.31

*The minus sign signifies below average and the plus sign above.

for the breeding of the plankton. The larger amounts of plank-
ton were found only during stable conditions, and floods inva-
riably depleted the volume of the plankton. These periods of
stable conditions occur in summer and late autumn, and we
find the plankton content at such times 38- to 30- fold that in
contiguous flood conditions. In the river the monthly produc-
tion exceeds the monthly average for our records in 5 out of
the 9 months represented, the exceptions being February, when
stagnation under the ice prevailed, April, a vernal period of
low water without overflow, September, a month of repeated
floods, and October, when an unusually early decline in temper-
ature occurs.

The stable conditions which attend low water thus favor
the increase in the plankton content per m.*, though by reason
of the lower levels and slackened current the total volume pro-
duced in the stream asa whole must be greatly diminished by
such hydrographic conditions.

The results of this low-water year upon production in Quiy-
er Lake (Pl. XXX.) are as a whole diametrically opposite to
those in the river. Here in the lake, production falls below

433

the average, the mean of the monthly averages (.65 em.*) being
63 per cent. below that of all monthly averages of Quiver Lake,
and but a ninth of the production in adjacent channel waters.
The cause of this very marked contrast is to be found in the
relative dominance of tributary waters of recent origin and of
coarse aquatic vegetation in the lake,—a dominance increas-
ing as levels fall,—and accordingly we find in this year of low-
est levels the least annual production (see table on p. 429).
Production is not only low on the average but also lower than
the average in every month of record save September, when it
rises 22 percent. above the mean content for that month. This
is a month of higher river levels,and asimilar tendency to in-
creased production isto be found in the August flood (PI.XXVI.).

In Dogfish Lake, production in this year averages for the
8 months represented 3.5 cm.* per m.’—44 per cent. less than that
in the adjacent channel waters and 408 per cent. more than that
in Quiver Lake. Thisis 4 per cent. more than the average
monthly content, and 18 per cent. less than production in the
same months of the following year. The deficiency below
channel production may be attributed to the effect of vegeta-
tion, and the excess over that in the contiguous waters of
Quiver Lake to the absence of access of tributary waters of re-
cent origin. Production is above the average for 4 of the 8
months, the exceptions being April, June, August, and October.
The absence of overflow is apparently the cause of the suppres-
sion of the vernal pulses in April and June, and the dominance
of vegetation may be responsible for the low production in
August and October, both low-water months. The months of
plankton content exceeding the monthly average are 4; July
and September—months of flood, and consequently of impound-
ing and greater extent of vegetation-free water—and Novem-
ber and December—times of lessened growth on the part of the
aquatic vegetation, of rising levels, and of some decay of organic
matters from the summer’s growth.

Causes of like nature are the basis for the large production
in Flag Lake in the late autumn months, when in October-No

434
vember the production is 10- to 3- fold the average, and in De-
cember 9 per cent. above the mean for that month.

In Thompson’s Lake the mean of the monthly averages,
13.31 cm.* per m,* is 61 per cent. in excess of the mean of all
the months of our records, though but 3 of the 9 months repre-
sented in the records of 1895 are above the average. The first
two of these, April and May, owe their predominance to a ver-
nal pulse of unusual volume, andthe small number of collections
gives these months abnormally high averages, while the large
production in July may be attributed to the enrichment of the
lake in this year by an invasion of plankton-rich river water
from the channel (Pl. XXXVI.). The deficiency shown in the
records of the remaining 6 months, falling from 10 to 70 per
cent. below the averages of our records for these months, finds
its possible explanation in the relatively greater dominance of
vegetation in the lake in this season, due to two successive
years of low water and the prevailing low levels. Collections
in this year were, moreover, taken near the margin of the veg-
etation belt of the lake.

Production in this, the second, year of low water, and the
lowest in our term of operations in all the backwater plankton
stations but Quiver Lake, is above the average in the year as a
whole, though falling below it in 57 per cent. of the time rep-
resented, ,

The apparent suppression of the vernal pulse in the river
and in Quiver and Dogfish lakes may be attributed to the ab-
sence of spring overflow and the consequent elimination of vast
impounding and breeding areas normally present at this season,
and also to the direct delivery of tributary water to the chan-
nel and increased relative diluent action of the slight April rise
(Pl. IX.) in both the river and Quiver Lake. The low levels
also serve to bring the vegetation of the two lakes named into
early dominance, and the relative occupancy is also increased
by the second year of low water and no removal of the accumu-
lated growth by flood action. Thompson’s Lake, on the other
hand, owing to its great extent of open water, is less affected

435

by the low levels, the cutting off of breeding backwaters, and
the relative occupancy by vegetation, and consequently a ver-
nal pulse of unusual dimensions reaches a culmination in its
area.

The June-July pulse of the river, abnormal in its location
and relative size and apparently without equivalent elsewhere,
is due to the unusual development of a stagnation plankton in
the sewage-laden river in a period when rising temperatures
hasten the decay of its unusual load of organic matter.

The causes above enumerated render this the year of great-
est fertility, in so far as our records reveal production, in the
river and in Thompson’s and Flag lakes,the next tothe greatest
in Dogfish Lake, and the least in Quiver Lake.

The low levels preclude any extensive impounding of flood
waters and, moreover, the period of run-off is of shght extent.
The rise in plankton content (PI. LX.) in the river following
the April, July, and September floods is suggestive of the effect
of impounding, the plankton content (cf. Pl. XX VI., XXX., and
XXXVI.) being generally greater in the discharging backwaters
examined than in the recipient channel during these run-ofts.
At all other seasons in our records for this year there is scant
opportunity for enrichment by tributary backwaters, and but
little suggestion of it.

1896.
(Pl. X., XXIL, XXVIII, XXXI., XXXII, XXXVII., XL.)

This is the most fully represented year in our series in the
number of stations examined. There are 76 collections in the
Ihnois, 9 in Spoon River, and 31, 30, 27, 27, and 29 respectively
in Quiver, Dogfish, Flag, Thompson’s, and Phelps lakes—a total
of 229. It was a year of higher levels, averaging 6.98 ft. above
low water,—almost twice the record of the preceding year,—and
witnessed a series of recurrent floods approaching or surpassing
bank height of the stream.

The accompanying table gives a summary of the data of
production.

436

PLANKTON PRODUCTION IN 1806.*

Station Jan. | Feb. | March | Apr. | May June | July
Mlinoise Rivera =) ‘o1|=|/ 0.02/=|f0107 |=) 5.67|=) 1.30|—' o.72||= aaa.
Spoon Riven ic. as. abinecluts|e ia leal Salle aene| Mal een lh Paes ege elle ese | Rr
Qwiyer LAKE. acccconsucs —-| .03/-+} 1.75]/+] 1.85 |-+]12.12/—| 2.99/+| 1.26/— 0.30
Doings LAK. 5500000060 +] .53/-F] 2.04)-+] 3.43|}—|15.11/+| 9.63/+] 2.64]— 0.91
IBN ILAVKCo ocacc00 cossc =] .29'+| 3.06/-+) 1.02 |+]17.72/-+|51.93|—| 2.13|— 3.33
Thompson’s Lake....... —-| 2.51/--| 2.58]+|10.26|+]16.94|—|23.11]—| 4.92|-— 2.73
JPNNOS WAKCGsocsob00+008 =! 1.89/+112. 14|-+l19.20'+125.44!—-|12.96|—! 2.90!-+ 9.03

Mean of

Station. Aug. Sept. Oct. Nov. Dec. | monthly
averages

DUNS IRTGERS 550050 000- Se oa CRE. 76 |=] | 2.65
SYOOOM IRIE 56060000000 —| ©€.018/—| 0.005/+-] .005/—| .005/—| .002/—| 0.007
Owwiiver LARC i 5660000000 Se 2c j=) QoS Re] 21 Fel oA |EHiO.62 [HE] 2.19
Dogfish Lake...... soe ce\ar| 220! | UoGs Ae) 5253 ||) 320 |=\2.20 JAF) 3.09
Blagghake smote. +] 3-74 |—| 2.09 |—] 5.67 |-| 4.37 |-|4.40 |—| 8.3:
Thompson’s Lake....... —| 4-74 |—| 4.20 |—| 2.81 |—| 2.66 | —/2.56 |—| 6.67
PINE OS ILAVKG5000 00000006 =| S40 |looll coaoac ae ZOU Sal UO seeee] al 14.74

*The minus sign signifies below average and the plus sign above.

While in 1895 production in the channel waters was both
absolutely and relatively high, yielding the highest monthly
mean (5.91 cm.) in our records, and exceeding production in
the adjacent backwaters in 15 out of 27 monthly averages avail-
able for comparison (see table on p. 432), in 1896 we find the op-
posite extreme in production in these particulars.

In the first place, the mean production as seen in the mean
of the monthly averages, 1.05 cm.’ per m.*, or, in average of all
collections, 1.16 cm.’ (see table on p. 429), is the least observed
in our years of record. This is 61 or 47 per cent., according
as we base computations upon means of monthly averages or of:
all collections, below the mean production in the JIinois. This
ensues from the catastrophic effect of recurrent floods which
periodically flushed the channel (Pl. X.), sweeping away the
plankton-rich contents of the stream and replacing them with
barren silt-laden flood waters of recent origin. There are 6
major and 5 minor flood culminations in this year, and most of
them are marked by abruptness in rise, a factor which added to
their destructive effects. The total movement in river levels
in 1896 is only 45.7 ft. (see table p. 163), while that in 1895 is

437

ol.9 ft. It is not so much the extent of movement in levels as it
is distribution which produces this depression in production.
Repetition of floods at relatively brief intervals is the cause of
low production in channel waters in 1896.

Not only is the mean production in the river below normal,
but all of the monthly averages are likewise from 97 to 35 per
cent. below their averages except those of April and December,
which are 23 and 7 per cent. above. Hydrographic conditions in
these two months of higher production are such as to favor in-
crease in plankton, since in both cases there is a period of 6-8
weeks of slowly declining levels with little or no interruption
in which a more abundant plankton becomes established.

The relation of production in the channel and the back-
waters in 1896 is also very different from that in 1895. While
in 1895, owing to low levels in general and to the prolongation
of rising levels, the backwaters were contributing but a slight
and interrupted run-off to the channel, and production, as shown
in monthly averages, was in the case of backwaters examined
predominantly lower than in the channel, we find in 1896, owing
to higher levels, that there is more impounding, and, owing to
the slow declines, a larger continuance of it and more run-off
to the channel. There are, for example, 157 days of falling
levels above 6 ft. distributed through 10 months, while impound-
ing and run-off continues for 90 days more at lower levels and
in decreased volume. Not only are backwaters thus contribut-
ing to the channel for a much longer period in 1896, but their
plankton content is predominantly higher than that in the
channel. An examination of the relative production (see table
on p. 436) reveals but 3 out of the 58 monthly averages of pro-
duction in backwaters, excluding Spoon River, which are less
than coincident production in the channel. These are for Dogtish
and Quiver lakes in July, and forthelatter mm September—both
months of lowest water, and consequent predominance of creek
and spring water in Quiver and of vegetation in both lakes.
This relatively greater production in the backwaters is not due
to increased absolute production as compared with 1895 except

438

in the case of Quiver and Dogfish lakes (2.59 and 5.01 em.*) when
we find for these lakes the highest mean annual production in
our years of records. In the case of Flag, Thompson’s, and
Phelps lakes the annual mean falls below the average on the
basis of monthly averages, though the average of all collections
in Flag and Thompson’s lakes is above the general average in
these lakes (see table on p. 429). The former basis of compari-
son is the better one, since it equalizes to some extent the ine-
quality in the distribution of collections. The plankton content
in backwaters in this year of recurrent floods is thus increased
in some instances and but slightly reduced in others, with the
net result of predominantly higher plankton content than in
the current-swept channel, and a much greater total production.

The effect of the run-off of the impounded backwaters _
upon channel plankton may be seen in the river planktograph
for 1896 (Pl. X.), where the March, June, August, October, and
November floods in each case reduce the plankton as they rise,
and are attended by a noticeable increase as levels fall again.
That other factors are involved may be seen in the rise in
plankton attending the rising flood of August, and in the de-
clines following the increases in plankton content in the midst
of rapid run-off in apparently favorable hydrographic condi-
tions in nearly every instance above cited.

The effect of the midwinter flood following two years of
low water, which permitted the accumulation in bottom-land
forests, marshes,and backwaters of a great amount of vegetation,
may be traced in the /avge production in winter and early spring.
In the table on page 436 it will be noted that in the months of
February—April production is above the average in every- back-
water in each month except in Dogfish Lake in April. More-
over, the largest records for this season of the year were ob-
tained in this year in Dogfish, Flag, and Phelps lakes in all
three months and in Quiver and Thompson’s lakes in the first
two, that is, in a total of 18 out of the 15 monthly averages.
During the remainder of the year, from May to December,
production in the backwaters generally falls below the average

439

production for those months in the several localities. Out of the
51 monthly averages in this period (see table on p. 436) 37 are
below the mean, and of the 14 above, 9 occur in Dogfish and
Quiver lakes, where reduction in vegetation increases the pro-
duction. The cause of this sharp contrast in the relative pro-
duction in the two parts of the year, is to be found in the hy-
drographic conditions which affect the nutrition of the plank-
ton. The rank vegetation which filled the forests, marshes,
and margins of the lakes during the two years of low water
was submerged by December flood, and by this early submer-
gence and subsequent decay increased the production in winter
months. This early consumption of the products of decay and
the relatively early run-off of the spring flood combined to
make vernal production relatively low in 1896. A comparison
of the planktographs of the 6 localities (see plates named at
the head of this section) will indicate the suppression of the
April-May, or vernal, pulse in every locality but Phelps Lake.
No plausible explanation for its occurrence here when it is not
found elsewhere is apparent. Subsequent floods by their brief
duration and frequent repetition tend to impoverish the back-
waters by the removal of vegetation and organic debris, and by
the run-off of nutrition in solution or suspension and of the de-
veloping plankton. In more stable conditions or floods of longer
duration, when the backwaters are impounded for longer times,
—largely by the restraining action of high water in the Missis-
sipp1,—decay is longer continued, and there is more opportunity
for the utilization of its products by a plankton not removed
quickly by the rapid run-off of the flood.

A comparison of the different regions even in this one year
bears out this inference. Spoon River, scoured by repeated
floods and swept by constant and relatively rapid current, con-
tains only an insignificant amount (.007 cm.’ per m.°) of plank-
ton. Quiver and Dogfish lakes, rid to some extent of the accu-
mulated growing vegetation and enriched by dead vegetation
in their submerged borders, yield in this year the largest an-
nual mean of monthly averages (2.19 and 3.99) in our records,

440)

In these lakes at levels prevalent in this year the impounding
or reservoir function is at its height. The higher levels reduce
the relative proportion of creek and spring water, and the ab-
sence of extreme high water cuts off to large extent the cur-
rent of general overflow through the lakes. Accordingly, pro-
duction here in the year as a whole exceeds the mean of all
monthly averages by 25 (Quiver) and 26 (Dogfish) per cent.,
and exceeds the mean of the respective monthly averages in 8
and 7 of the 12 months. In the case of Thompson’s Lake, on the
other hand, the hydrographic conditions are such that its pre-
dominantly reservoir function is interfered with as each recur-
rent flood passes the level of 6 ft. and starts the current of
channel water in at the northern, and out at the southern, end
of the lake (Pl. II.). Accordingly production in this lake falls
below the average of all monthly averages by 24 per cent., and
the individual monthly means are likewise deficient in 9 of the
12 cases.

In Flag Lake the production (8.31 or 13.88 em.’ per m.*) is
10 per cent. below the mean of all monthly averages, or 21 per
cent. above that of all collections, and exceeds the means of the
monthly averages in 6 of the 12 months. The accumulated
vegetation in and about this lake, and the moderate levels
which develop the reservoir function of the area without per-
mitting any current of overflow through it tend to keep up the
level of production. It is in considerable excess of that in sub-
sequent years, but falls below that of the exceptional condi- .
tions of the preceding autumn, discussed on page 385.

The moderate levels free Phelps Lake from currents of
overflow and increase its impounding function, and we find
here, accordingly, the largest production recorded in any of the
backwaters in this year. The fact that the production (14.74
cm. per m.°) falls 84 per cent. below the mean of all monthly
averages for the lake and is deficientin 6 of the 12 months, may
perhaps be due in part to the fact that in the previous year the
lake had been a cultivated corn field and had not therefore been
seeded by the spores and winter eggs of planktonts left on the

441

drying up of the Jake. In September the lake did temporarily
dry up only to be re-entered by the October flood, in which an
unusual plankton (51.6 cm.’) at once developed.

1897.
(Pl. XL, XXIIL, XXVIII., XXXII, XXXIV., XXXVIIL, XLI. )

This year is represented by 34 collections in the Illinois,
and 13 in Spoon River, and by 24, 6, 7, 18, and 9, in Quiver,
Dogfish, Flag, Thompson’s, and Phelps lakes. It was a year of
protracted winter and spring flood, a late June rise, and pro-
longed low water in summer and autumn. The data of compar-
ative production are given in the accompanying table.

PLANKTON PRODUCTION IN 1897.*

Station | Feb. | March | April | May | June | July
|

Illinois River........ Sl meos +) .38 |+) 5.11 |—| 5.62 [= 27 | + 4.69
Spoony River... +| .047|—|] .007/-+}| .048}+/] .440;+ BEOW sallocococ
Quiver Wake. ........ || -Igo |—| .34 )+)13.38 |—| 1.29 |] 1.26 | + 89
Dogfish Lake ....... |= 15 |—| .48 | —| 3.18 |—] 1.94 !—| 2.48 |..]......
Hine A = 67 |=} £2 1S) 8.88 | Sio.Gn |+ hy AB Wane
Thompson’s Lake... |—, .27 |—| .65 | —j10.38 |—| 7.88 ;—| 3.59 }—| 3.31
whelpsywakel. i... — .19 [az 1.44 -| 4.26 | —|22.58 |- 42 |+] 9.49
| | Mean of
Station Aug. Sept. Oct. Nov. Dec monthly
| averages
Illinois River........ =| 3-05 aq} ©268) |aF/ 5-05 |S] t¢9 |=, 290 ar) ges
SPOODMNIVER....- «--\- | O57? || SF Goi |) ccllosacoc \f Fea 559| +] 1.225
Oniver ake ......... — 21 |— I =| of. |S) cp ha! soon) all aa
Dingiisin ILAKG. epoca lee spoese lan hecorcre lial eee | dollecccod | Siete: —| 2.65
IMG ILE OR a seen Pell resect eave | Searenckesul ee | eee sspears cransiariyiees | aici —| 5.34
Thompson’s Lake ... +)19.40 +]1o.o1 | +/35.35 |-+]16.67 | +, 6.98 |+)10.41
Phelps Lake.......4, S125 700 | Sale cease se n. |e [oveeee | ees | -| 9-15

*The minus sign signifies below average and the plus sign above.

The infrequency of collections in January-June and the
suspension of work in Dogfish, Flag, and Phelps lakes before the
year ended, render general comparisons with other years of less
value because of insufficient data.

The annual channel production, 3.28 cm.’ per m.’,—the mean
of monthly averages,—or 3.69, the average of all collections, is
21 or 68 per cent, respectively above the means, and 6 of the 11

442

months represented also exhibit a plankton content above the
average. The causes of this large production are to be found
mainly in the prolonged low water, slackened current, and sew-
age contamination of the last half of the year. No large ver-
nal pulse appears in the records of the river or its backwaters.
It was either intercalated between collections, and thus escaped
detection, or the early winter flood, as in the previous year, by
its washing away sources of nutrition prior to the season
and temperature of greatest plankton development, tended to
depress production below normal at this season. It was to be
expected, however, that a large plankton development took
place in the stable conditions attending the three months of
declining levels which followed (Pl. XI.) the crest of the spring
flood. If such a development took place it would tend to raise
still higher the level of production established by our records
for this year.

The relation which the backwaters bear to channel produc-
tion in 1897 is correlated with the hydrographic conditions. In
January-June, a period of continued high water, the plankton
content in the backwaters exceeds that in the channel in 22 of
the 30 monthly averages (see table on p. 441), or, omitting Spoon
River, which does not properly belong in the category of back-
waters, in 21 out of 25.

This was a period of extensive and long-continued impound-
ing and of high levels, and, in the last three months (PI. XI.),
of rapid decline and therefore of speedy run-off and rapid cur-
rent in channel waters, factors which favor the breeding of the
plankton in the reservoir regions and cut down the time for its
development in the channel, in which barren tributary waters
of recent origin and plankton-rich backwaters impounded in the
more or less current-free areas for a greater or less length of
time, depending upon the direction and rate of change in river
levels, are mingled in varying proportions.

In the low-water period, July-December, stability of hydro-
graphic conditions continues throughout, while the extreme
low levels maintained for so long a time make the channel wa-

445

ters very largely independent of backwaters and tributaries by
reason of cutting off of communication in some cases and ces-
sation of run-off in others. Along with this independence goes
increased fertility by virtue of greater relative contamination
by sewage and longer time for breeding by reason of the slack-
ened current. Asa result, production in channel waters reach-
es in July-November, 1897, a level unsurpassed in our records,
rising above the monthly means of all years (see table fol-
lowing page 342) 11 per cent. in July, 245 per cent. in Sep-
tember, 250 per cent. in October, and 14 per cent. in Novem-
ber, but falling behind by 6 per cent. in August. As a result of
this increased development of plankton in the channel the pro-
duction in backwaters becomes relatively less with respect to
the channel production than in times of high water. Thus in
July-December, backwater plankton exceeds that in the chan-
nel in only 10 out of 19 monthly averages, or, omitting Spoon
River, in 8 out of 15—a marked change from the excess in the
preceding six months, 21 out of 25.

This is the only season in all our records in which the plank-
ton content of Spoon River rises above the barren level of .1
em. per m.’, or less. The production now rises to a level ap-
proximating, and in November—December exceeding, that in
the channel asa result of the practical absence of current and
consequent increase in the reservoir function of the stream.

The course of production this year in the various backwa-
ters is in most instances strikingly similar to that in the chan-
nel in its major outlines. Thus in all of them (Pl. XXVIIL,
XXXII, XXXIV., XXXVITII., and XLI.) production rises grad-
ually from the midwinter minimum to an unusually low ver-
nal pulse in April-May and declines again in June-July. At
this point collections were suspended in Dogfish and Flag lakes.
Production in channel waters rises again in August and con-
tinues at high levels till November, and in like manner and
with even greater amplitude in Thompson’s Lake (Pl. XXX-
VIII.), while a similar movement is initiated in Phelps Lake
(Pl. XLI.), only to be stopped by the drying up of the lake in

444

September. Quiver Lake, however (Pl. XXVIII.), pursues a
different course, production there dropping to a level rarely
exceeding .6 cm.’ for the remainder of the year. This results
from the greater relative volume of spring and creek water in
this lake. The discharge from Quiver Creek and the marginal
springs continued with relatively much less diminution through
the autumnal drouth than that from Spoon River, with the
result of making this lake far less productive of plankton at
this season than Spoon River (ef. Pl. XXIII. and XXVIIL.).

1898.
(Pl. XIL., XXIV., XXIX., XXXIV., XXXIX., XLIT.)

This year is represented by 52 collections in the [lhnois
and 11 in Spoon River, and by 26, 6, 25, and 22 respectively in
Quiver, Flag, Thompson’s, and Phelps lakes. It was a year of
normally located and fully developed spring floods, followed
by low water in summer much disturbed by minor floods, with
a subsequent autumnal rise of unusual proportions. This re-
sulted in the highest average river levels in our years of opera-
tion, 8.02 ft.—a level almost equaling bank height.

The accompanying table gives the data of comparative
production of the different localities in this year.

PLANKTON PRODUCTION IN 1808.*

Station Jan. Feb. | March April | May | June | July
MUG IW Eeo | Sel oAlS ar .27 |+| .33 |—| 4.40]/+ 11. 3° —| 3.96 |—| .58
Spoon River;-++) .017 .O16|-+] .124]..]..... =) 025) .096| =| .036
QuiverLake|—| .02 |—| .31 |—| .74 j=] .53)-+- 16. 27 mn Bey =| i
I) eye Dey iS eallone Pei anneal ercecinisc kaglsolots o.ni| ddl loan. ||folo Ho909a || o0|aoe. as —| .36
Thomp. L..|-+] 7.22 |—| .64 |—| .70 | — 2.44 25. 94 10.13 | —| 2.08
RA SICALC || wall aoson leobroce ce (2) Sa 2) 563i |e. | =| ocr

| Mean of

Station Aug. | Sept. Oct. Nov. Dec. monthly

| averages

Illinois River....... — Yor |=)" -69) |= 24 |= 25 a .99 | —| 2.03
Spoon River........ | — 002} —] .002] — OoL1}—] .OOr .OO1}; —| .02
Quiver Lake....... — 52 1) 538) pa OB SE. 073} + is 74 -+-] 1.969
lam lealkeran crm. > 08) WARM oGAU | callaocoae =llo6a000 —| 5.31
Thompson’s Lake.. | —| 2.63 |—] 2.66 |; —| 1.25 | —| 1.17 |—+- 3.8 —| 5.06
helps lakers. +1139-85 | 147-25 __ [+41a2. Bt jlaelbley esi2i- 26 +137 .34

* The minus ‘sign signifies below average and the ee sign above.

445

The average production in the Illinois for the year is 2.038
em.* per m.*, or 2.13 em.’ if the average of all collections is taken.
instead of the mean of monthly averages. This is 25 per cent.
below the mean of monthly averages, or 3 per cent. below
that of all collections. This depression in production is due to
the disturbed and irregular hydrographic conditions which
throughout most of the year left insufficient time for the plank-
ton to breed. .

As shown by the + and — signs in the table, production in
channel waters is below the average in 7 of the 12 months, and
4 of the 7 deficiencies fall continuously in the disturbed period
of August-November. The decline below the average produc-
tion in this disturbed period ranges from 72 to 86 per cent. The
other 3 months of deficient production are April, June, and Ju-
ly—4, 45, and 86 per cent. below their averages. The April defi-
cit is due to the delay in the vernal pulse, while those of June
and July are due, possibly, to the after effects of the high ver-
nal pulse of May. Production in excess of the average is found
in January-March, during the unusually slow rise of the spring
flood, in which the catastrophic effect alike of the sudden
and higher floods and of stagnation under ice in low water is
eliminated. Production is also high, by 86 per cent. in May, as
a result of the delayed culmination of the vernal pulse —the
largest one, moreover, found in our records in channel waters.
It isalso high by 40 per cent. in December, when declining levels
(Pl. XII.) afford the stability necessary for the breeding of the
plankton.

Production in Spoon River, as might be expected in a year
of much flood water, falls to a barren level exceeding .1 cm.’ in
but a single instance, in March (.124), when waters of general
overflow mingle with those of the tributary to a considerable
extent.

Production in the backwaters in 1898 again bears a striking
resemblance, throughout, to the course it presents in the chan-.
nel. The higher levels conduce to greater unity in the envi-
ronment, and to greater interchange between many localities,

446

and the plankton accordingly foliows similar lines of develop-
ment. This is noticeably prominent in the planktographs of
the river and Quiver and Thompson’s lakes, as will be seen by
a comparison of Plates XII., XXIX., and XXXIX. The princi-
pal features of the common course of production are the coinci-
dence of the May and June pulses, the subsequent low level of
development throughout the summer and early autumn, and
the December rise. These three bodies of water were submerged
in the common flood of overflow in February—June, and the
succeeding minor flushes of summer and autumn caused re-
current ingress and egress of water from and to the channel.
The similarity in the course of production in these three local-
ities and the lessened differences in the amplitude of produc-
tion in this year are in no small measure the consequence of
this equalizing action of this interchange due to floods.

Phelps Lake (Pl. XLII.) is the only one of our backwaters
which diverges from this marked agreement, and its divergen-
ces are increased by its intimate connection with Spoon River
during high levels and its isolation during the remainder of
the year.

The vernal pulse of this year is noticeable for its amplitude,
its meteroric appearance and disappearance, and its coinci-
dence in different localities. It follows a prolonged period of
extreme overflow, and a very gradual and somewhat tardy rise
in vernal temperatures. It appears, moreover, at levels of 10-
11 ft., just when great stretches of bottom-lands are contribut-
ing their last run-off to the channel. The submergence of the
bottom-lands did not occur until late in February in this year,
so that the period of vernal increase in the plankton was not
preceded by a long interval of flood, as in 1896 and 1897, which
might carry away in suspension or solution those organic sub-
stances in the vast amount of vegetable detritus which covered
the bottom-land as a result of the low water of the preceding
autumn, and which may have been utilized by the plankton in
this extraordinary vernal development as a result of the juxta-
position of flood and vernal growing season.

447

The comparison of backwater and channel production in
1898 is in some contrast with that in 1897. In 1897, omitting
Spoon River, production in backwaters exceeded that in the
channel in 29 of 40 monthly averages, or in 73 per cent., while
in 1898 the excess occurs only in 26 of 37, or in 67 per cent.
The excess, moreover, is frequently of less amplitude in the lat-
ter year, as is seen in the relation of the means of the monthly
averages of backwaters and channel in the two years. Thus in
1897 production in Thompson’s Lake (10.41) was 217 per cent.
in excess of that in the channel (3.28), while in 1898 (5.06 and
2.03) the excess was only 149 per cent. In Phelps Lake, on the
other hand, production rose to the unparalleled height of 37.34,
the mean of the monthly averages, 67 per cent. above the mean
of all monthly averages, and fourfold that in the previous year,
when the last 4 months were cut off by the drying up of the lake.

Production in Quiver Lake in this year is 1.96 cm.*, mean
of monthly averages, or 2.44, average of all collections—12 per
cent. and 44 per cent. above the mean respectively of all years.
This larger production is due to the excessive production in the
vernal pulses in May and June and to the high levels of pro-
duction in November and December, rising 138, 78, 217, and 176
per cent. above the average respectively for these months. The
hydrographic conditions in these months in Quiver Lake are
favorable to increased production. The May and June pulses
are at levels (11 ft.) when impounded run-off from slightly
submerged bottom-lands to the north was rapidly draining to
the channel through the lake. In November and December
there was at least double the usual volume of water in the lake,
due to a 34 per cent. increase in river levels, with a considera-
ble reduction in the proportion of tributary water and increase
in the impounding function. In the remaining 8 months of
the year, then, average production is 79 per cent. below the
general average for those months in Quiver Lake. This very
considerable depression in production falls in the main in the
period of greatest hydrographic disturbance. This body of
water, owing to its frequent invasion by channel waters and to

448

its own influx of tributary water from Quiver Creek, is the most
hable of all the backwaters examined by us to hydrographic
disturbance. It is therefore not surprising that in this year of
extreme disturbance we should find marked depression for a
long period in this lake. The total movement in levels in 1898
is 67.2 ft. (see table p. 163), 44 per cent. above the average. Of
this, 50.8 ft. fall in the 8 months of depressed production, that
is, 76 per cent. of the movement occurs in 67 per cent. of the
time. To this relative excess of fluctuation in levels, and proba-
bly to large access of local flood and spring water, we must at-
tribute the low production in Quiver Lake in these months.

Thompson’s Lake has an average production of 5.06 cm’,
or, if all collections are averaged, 5.71 cm.’*, 39 and 28 per cent.
below the respective averages for all years (see table, p. 429).
Not only is the general average below normal, but all of the —
monthly averages, save only those of January (7.22) and De-
cember (3.58), are likewise deficient by from 2 to 88 per cent.
The large January production is the largest plankton content
in this month in any year or locality, and accompanies an
invasion and impounding of sewage-laden river waters in the
lake (cf. Pl: XLV. and L.).

The cause of the low production throughout the remainder
of the year is again to be found in the hydrographic conditions.
During 8 months of the year (at levelsabove 6 ft., see Pl. XX XIX.)
the lake is swept by a gentle current entering at the northern
end and discharging to the channel at the lower. There is,
thus, in this year more than the usual run-off, not only of or-
ganic matters in solution and suspension; received with the
waters of ingress, but also those developed in its impounded
waters or about its shores. This tends to impoverish the
waters, and interferes with the accumulation and flux of or-
ganic matter in the plankton which manifested itself in such
amplitude in the low water of the preceding year (Pl. XXX-
VIII). Toa much less extent than in Quiver Lake is the de-
pressing effect of flood waters seen in the broader expanse of
this body of water. While in the former the production in

449

months of flood disturbance falls 79 per cent. below the mean
for that season, we find in the 10 months of depression in
- Thompson’s Lake a falling off of only 46 per cent. The differ-
ence is due to the greater proportion of creek and spring water
of recent origin in the former, and to the greater reservoir ca-
pacity and consequent longer impounding, as a rule, of the
sewage-laden channel waters which predominate in the latter
backwater.

Production in Phelps Lake is 37.34 em.’ per m.’, or, 1f all
collections are averaged, 36.31—67 or 84 per cent: above the
means for all years. In keeping with these facts we find that
the monthly averages equal or exceed the means for their
months in 7 of the 10 months of record, the greatest excess 0c-
curring during the period of complete isolation of the lake.

1899.
(Pl. XIIL, XXIV., XXIX., XXXIX., XLIL.)

This year is represented by 13 collections in the [lhnois
and 3 in Spoon River, and by 7 each in Quiver and Thompson’s
lakes and 6 in Phelps Lake, all in the first three months of the
year. This was a period of a slow rise of the river in January
to bank height, with an equally slow decline in the next month
followed by an abrupt and well-sustained March flood. The
data of comparative production are brought together in the
following table.

PLANKTON PRODUCTION IN 1899.

Mean of

Station Jan. Feb. | March | monthly

averages

MINITMOISMINI Ve Lee ens eine cins nse cerns —| .18 |-+] .81 |---| .28 |-F] .42*
‘S/DOOM. ININ/GICS nos pee ee einen aCe areca i—| .005|—| .oo1;—| .026|/—| .orI
Quiver LARC. Soeosoneemsoeaacedacderaes +! .77 |+] 1.05 |—| .15 ;+] .66
Siktomipsonis ake 2.0.0.6. 0 .0t ence se —| 1.64 |+] 1.59 |—| .21 | —| 1.15
Pingllos ILAKSCe paseo en en ceeccn ctor tates 4.69 Nes 4.70 | —| 1.82 | —] 3.74

*The + and — signs for this column refer to the relation of these averages to the
mean of all January-March collections; otherwise they are used as heretofore.

The average production in these winter months in the river
is .42 cm.’ per m.*, or, if all collections are averaged, .41 cm.°

450

This is the largest production for this period of the year in our
records, exceeding the average, .24 cm.*, by 75 per cent. and ap-
proximating or exceeding the monthly average in each instance.
The cause is to be found in the relatively stable conditions at a
level sufficient to prevent sewage stagnation beneath the ice-
sheet which covered the stream prior to the March flood.

Spoon River continued to discharge barren waters (av. .011
em.*), while the backwaters, with the exception of Quiver and
Thompson’s lakes in March, produced a more abundant plank-
ton than the channel. Quiver Lake produces .66 cm.’,—an ex-
cess of 20 per cent. above the usual production for this season,—
and in the first two months has 2- to 3- fold the usual plankton
content as a result of the moderate levels which make the lake
a reservoir without greatly increasing its current. When, how-
ever, the general current of overflow passes through it with the
March flood, production drops to one fifth of the mean for that
month. In Thompson’s Lake the mean production is 1.15 em.’,
56 per cent. below the mean production for these months. It
also falls below in January and March, when hydrographic con-
ditions are such (Pl. XX XIX.) that channel water is diverted
through it, and rises above the mean by 25 per cent. in Febru-
ary, when the run-off is diminished by falling levels. In Phelps
Lake the mean production, 3.74 em.’, is 23 per cent. below the
mean for these months. This lowered production, which also
falls below the mean in the last two months, is due, in part at
least, to the invasion of Spoon River water with the higher
levels.

The various years of our operations may be briefly charac-
terized as follows.

1894. A year of low water and fairly stable hydrographic
conditions, with nearly average production in channel and open
backwaters and deficiency in the vegetation-rich Quiver Lake
in the months of our records.

1895. <A year of continued and butslightly interrupted low
water, with stagnation destroying the winter plankton and
tending to abnormal production in early summer in channel

451

waters. Production is deficient in vegetation-rich backwaters
(Quiver Lake) and in excess in open reservoir lakes (Thomp-
son’s Lake).

1896. A year of recurrent floods of moderate height and
greatly diminished production in channel waters. The repeated
summer invasions of the vegetation-rich backwaters by flood
destroyed and removed much of the season’s growth, and we
find this the year of greatest plankton production in these areas
(Quiver, Dogfish, and Flag lakes). The more open waters, poor
in vegetation (Thompson’s and Phelps lakes), have vernal
pulses of considerable magnitude, but as summer and autumn
production is not up to the average there is as a whole a defi-
ciency in these areas.

1897. A year of prolonged winter-spring flood, followed
by continued and abnormally low water in the last 5 months
of the year. The early flood apparently reduces production
everywhere, while the prolonged low levels lead to abnormally
high production in the channel and in vegetation-poor back-
waters (Phelps and Thompson’s lakes). In Quiver Lake the
relative dominance of vegetation and tributary waters of recent
origin is so increased that production falls to alow level. Even
tributary streams (Spoon River) so decline in run-off in the
low-water period that an abundant plankton develops in their
waters.

1898. A year of normally located spring floods, followed
by repeated minor flushes in summer and autumn. There
is a meteoric but normally located vernal pulse, with a low
level of production throughout the remainder of the year in
the channel and in backwaters intimately connected with it
(Quiver and Thompson’s lakes), and an abnormally high and
well-sustained level of production in backwaters isolated from
flood contact and free from vegetation (Phelps Lake).

The different localities may be briefly characterized as fol-
lows.

Illinois River. Channel waters contain a plankton which
in constituent organisms, character of the course of production,

452

and relation to environmental factors shows marked similari-
ties to that found in the backwaters. The river is, however,
more immediately and directly subject to ihe effect of floods,
sewage, and stagnation, and exhibits less uniformity and regu-
larity in its planktographs. High water and repeated floods
are wont to depress its production, while stable conditions such
as prevail more fully in falling levels and low waters often lead
to increase in production. The run-off of impounded backwa-
ters where plankton breeds, which attends falling levels, and
the concentration of sewage in low water likewise conduce to
increased production.

Spoon River. This is always plankton-poor save at lowest
levels, when the slackened current renders the stream an im-
pounding area. At high levels in spring impounded backwaters
of the bottom-lands join it and tend slightly to increase its
plankton content. It is immediately and predominantly a dil-
uent of channel plankton.

Quiver Lake. Thisis an area subject to great vicissitudes
of production by virtue of the variety of environmental factors
operative and their changing efficiency with fluctuations in
river levels. Influx of creek and spring water of recent origin
and relative dominance of vegetation are increased at low lev-
els, and production falls. Backwaters from the channel in
floods below 6-8 ft. increase its impounding function, and de-
crease current, proportion of tributary water, and relative oc-
cupancy by vegetation, and production rises. In floods of higher
levels the general current of overfiow from submerged lands
up-stream courses through the lake, and local factors are great-
ly reduced in their effect. As a whole it is the least productive
of all the backwaters examined, but like the others has a rich
plankton when it is filled with impounded backwaters, espe-
cially at the season of the vernal pulse.

Dogfish Lake. This resembles Quiver Lake in many fea-
tures, but is freer from immediate access of tributary water and
invasion of channel waters at lower levels. It has accordingly
a higher and better sustained level of production.

453

Flag Lake. This, like Quiver Lake, is an area of great con-
trasts in production, resulting from its varying occupancy by
vegetation as levels rise and fall and from the changes in nutri-
tion available for the plankton attendant upon its growth and
decay. In so far as the data go they indicate a production sev-
eral fold greater than that attained in Quiver and Dogfish lakes.

Thompson’s Lake. In this area, by virtue of its considera-
ble size and freedom from immediate access of tributary water
of much volume, the fluctuations of the hydrographic, and to
some extent of the other, factors of the environment are ina
measure equalized. Production is therefore less disturbed than
in the backwaters previously named, pursuing what may be
called a more normal course, and is accordingly greater than
theirs,—excepting perhaps that of Flag Lake in seasons of high
water,—being three-fold that in the channel, from which its
main water supply is directly drawn. Owing to this intimate
connection with the river and freedom from dominating local
influences the planktograph of this lake is more like that of the
river than are those of other localities. Comparative freedom
from vegetation, highly developed impounding function, free-
dom from access of tributary water of recent origin, and close
connection with channel waters rich in organic matter, all com-
bine to cause the high production found in this area.

Phelps Lake. In this area production reaches the highest
level found in any of our localities. Jt exceeds that in the chan-
nel eightfold, and that in the most productive backwaters else-
where examined by us by two and one-half- fold to threefold.
Ingress of flood water from Spoon River depresses production
at high levels. At lower levels the freedom from vegetation
of the coarser, more cumulative, and permanent sort, the abun-
dance of alge whose decay releases nutrition for the summer
plankton, and the absence of tributary creek or spring wa-
ters, all favor the high production found in this area. Per-
haps most potent of all factors is the isolation of the lake at
high levels and consequent retention within its boundaries of

454

the organic substances in solution and suspension in its waters,
substances which in the other localities run off with the de-
clining flood. During last stages of low water in Phelps Lake
there is usually some dying off of the fish and other aquatic
animals, possibly as a result of extreme temperatures, and the
lake becomes a favorite resort for fish-feeding water-fowl. The
organic substances thus released for immediate solution in the
water and utilization by the phytoplankton may be of sufficient
quantity to materially increase production at these low levels.
It may be that the more complete access of light in these very
shoal waters and the condensation caused by evaporation and
seepage as the lake dries up are contributory to the increased
plankton content, but none of these factors seems adequate to
explain the excessively large production found in the summer
and autumn in the shallow pools which form the remnant of
the lake.

RELATION OF ENVIRONMENTAL FACTORS TO PLANKTON PRODUCTION.

The detailed discussion of the course of plankton produc-
tion as defined by volumetric data found in the preceding sec-
tion of this paper, has afforded many specific instances of the
relationship existing between the movement in production and
a number of factors in the environment. Prominent among
these are hydrographic conditions, temperature, light, chemic-
al conditions, vegetation, and the reproductive pee of the
constituent organisms of the plankton.

It is my purpose in the following pages to summarize, with
a few references to specific illustrations, the conclusions as to
general tendencies and the effect of these various factors upon
the course of production in the river and its backwaters.

HYDROGRAPHIC CONDITIONS AND PLANKTON PRODUCTION.

This is a comprehensive designation for a great variety
of major and minor influences which continually impinge upon
the plankton as a result of its environment in water. In the
case of the plankton of the Illinois River and its backwaters it

455

is the unique factor which more than any other differentiates
it from lake plankton. Toa less degree it seems to differentiate
this aquatic environment from other streams, as a result
largely of the imperfectly developed flood-plain, and conse-
quent unusual proportion of reservoir backwaters.

it is, moreover, an exceedingly variable factor, operating
with almost constant change in each locality, and from season
to season inthe same locality. Itisthis element of fluctuation
and the resulting chaos in the movements of production which
particularly characterize the river as a unit of environment,
and ina large measure differentiate itfrom the more stable
lake. The changes depend primarily upon the unequal distri-
bution of the rainfall and its run-off and the consequent fluctu-
ations in levels with attendant changes in area, depth, condi-
tions of ingress and egress of water in any given area, current,
and age of the water.

The effect of the area of the body of water upon its plank-
ton production in our situation is so masked by combination
with other factors that the available data are inconclusive.
Our largest vegetation-poor backwater, Thompson’s Lake, pro-
duces less (8.26 cm.*) than the smaller one, Phelps Lake (22.35
em.’). On the other hand, the largest vegetation-rich area, Flag
Lake, produces 9.23 cm.’—considerably more than the smaller
Quiver and Dogfish lakes, 1.75 and 3.16 cm.*—and these differ-
ences are, moreover, in all probability to be attributed to other
factors than mere area.

The relative development of the shore-line isa corollary of
the form of the body of the water, and is thus related to its
area. In the case of the river, the development of the shore-
line, as shown on page 284, is 78.3—a disproportionately large
element in the environment of the plankton.

This factor of area has been introduced here in order to
emphasize the fact that mere size in itself has apparently little
to do with plankton production. Plankton is present in small
as well as large bodies of water, with, of course, an increasing
proportion of littoral influences as areas contract. Within

456

our environment the submergence of all the localities, large
and small alike, in the major floods, tends to obliterate areal
differences, and to unify their plankton and to give them all
much the same initial start in the season’s course of production.
This is noticeable in the marked similarity in the vernal plank-
tographs of the several localities in years of high water. The
areal differences in later months and lower river stages are,
however, very considerable (cf. Pl. XX. and XXI.). Thus in
Thompson’s Lake there is a broad expanse of open water sev-
eral square miles in extent, while in the last stages of Phelps
Lake there are only a few pools, a fewacresin extent (PI. XXT.).
Under similar climatic conditions production in both runs
high, higher in fact than in other localities, and the same plank-
tonts are dominant, though in varying proportions in the two.
In general the plankton content per cubic meter runs very much
higher in Phelps Lake, the smaller body of water. There is no
evidence that the smaller size has anything at all to do with
this larger production, but this instance suffices to show that a
typical plankton with large production may be found in small
areas. On the other hand, Quiver and Dogfish lakes, next in
size to Phelps Lake, are the least productive of the backwaters.
Thus, area in itself tends apparently neither to deter nor to pro-
mote production.

The effect of depth, in all of its relations, upon plankton
production is manifestly not demonstrated in our data, since all -
of our collections have been made in shoal water of less than
10 meters in depth. Our deepest waters are Spoon and Illinois
rivers, where spring and flood water of recent origin tend to
depress production, and the shoaler waters are found in the
backwater reservoirs where impounding favors larger plankton
content. The significance attaching to the fact that our lar-
gest plankton production (224 em.’ per m.’ on August 24, 1898)
is found in Phelps Lake, the shoalest of all our localities, and in
depths no greater than 20 centimeters, is a matter of conjec-
ture, since many other factors are also involved. The highest
production in this lake was, as a rule, found during the periods

457

of shoaler waters, from 50 to 20 em. Flag Lake also, in the shoal
waters of the autumn of 1895, yielded a large production; and
Thompson's Lake, in the low water of the autumn of 1897, gave
the largest production on record for that season of the year in
that body of water. The vernal pulses, noted for their large
production, usually fall at the time of the run-off of large areas
of slightly submerged bottom-lands, Shoalness, then, does not
prevent large production. Indeed, there are some important
reasons why shoal waters should, other things being equal,
produce more plankton. Light pervades the water more com-
pletely, aeration by wind and waves preserves the gaseous equi-
lbrium more perfectly than in deeper waters, and upon sedi-
mentation the suspended organic matters in the water are not
removed from the immediate proximinity of the growing phy-
toplankton. Their decay and solution renders them imme-
diately available, while in deep waters only the slow process of
diffusion, in the absence of vertical currents dependent upon
temperature or hydrographic changes, brings them within the
field of surface-dwelling plankton.

It is well established that the plankton is relatively more
abundant in the surface than in the deeper waters of the ocean.
The researches of Reighard (794), Birge (95), and Ward (95)
show conclusively that the surface waters of our larger lakes
contain the greater part of the plankton. Thus, Reighard (94)
finds in Lake St. Clair from 1.2 to 37.2 times as much plankton
in the surface stratum of 1.5 meters in depth as in the remain-
ing bottom layer in depths of 2.2 to 8.4 meters. Birge (795)
finds 50 per cent., or more, of the Crustacea of the plankton in
the upper 3 to 4 meters, and over 90 per cent. in the upper 9
meters in depths of 18 meters, and Ward (795) reports 64 per
cent. of the plankton in the upper 2 meters.

Of our total 640 collections, 389 were made in water over 2
meters in depth. In the Illinois there were 208 such out of 235; in
Spoon River, 34 out of 35; in Quiver Lake, 60 out of 115; in Dog-
fish Lake, 27 out of 48; in Flag Lake, 8 out of 44; in Thompson’s
Lake, 48 out of 96; and in Phelps Lake, only 4 out of 67. Thus

458

about 40 per cent. of our collections were made in water less
than 2 meters in depth and at all river stages, and at all sea-
sons of the year a considerable proportion of the Illinois and
its backwaters has a depth not exceeding this limit. Moreover,
less than 12 per cent. of our collections are in 5 or more meters
of water, and these are confined almost entirely to the two
streams. Our collections as a whole are therefore within the
limit of depth of the surface stratum, which in deeper wa-
ters contains by far the greater proportion of the plankton.
This feature of our environment has a tendency to imcrease
the plankton content per cubic meter and to lower it when
production is stated in volumes per square meter of surface.
Thus, if we compare production in the [linois River in August
with that of Lake Michigan, as given by Ward (795), we find
that in quantity per m.* of water the river (3.88) exceeds that
of Lake Michigan. The average of Ward’s August collections
is 3.69 cm.* per m.* by the gravity method, or 1.23 cm.’ if we
reduce it to centrifuge basis (see Ward ’00). Production in
our environment in this month (see table following p. 342)
in all localities but Spoon River and Quiver Lake is from 1.5
to 47 times greater per cubic meter than in Lake Michigan ;
but if the average per sq. meter of surface be taken as a basis,
Lake Michigan exceeds the most fertile of our localities at this
season. The amount per sq. m. in Lake Michigan I find on
computation to be 37.98 cm.’ estimated centrifuge measure-
ment, while in the Illinois at average August river-levels
(4 ft.) it is about 15 em.*, in Thompson’s Lake only 9.29, and
in Phelps Lake approximately 14 cm.’

The age of the water is, other things being equal, one of the
most vital of all the hydrographic factors environing the plank-
ton. Rain and spring water of recent origin entering the river
or its backwaters in tributary floods or by seepage from under-
ground storage beds, is practically barren of plankton. This
same water impounded in the reservoir backwaters, seeded by
the spores and resting eggs of the planktonts deposited on the
submerged territory on the recession of antecedent floods, and

459

mingled more or less with the residual and plankton-rich wa-
ters of reservoir lakes and sloughs, soon develops an abundant
plankton ; or, retained in the channel and mingled with plank-
ton-bearing waters from a thousand sources, it develops a phyto-
and then zoo-plankton as soon as the requisite time for breeding
haselapsed. Illustrations which demonstrate the operation of
this hydrographic factor permeate all of the data of the variable
environment with which we are dealing. Attention has been
called repeatedly in the detailed discussion of the movement in
production to specific instances of the barrenness of flood waters
of recent origin which invade plankton-rich areas. By dilution
and replacement they lower plankton content in channel
waters pre-eminently and to a less extent in backwaters, where
their diluent action is less pervading and replacement less com-
plete. The most perfect illustration of this will be found in the
August flood of 1896 (Pl. X.).

Tributary streams such as Spoon River, whose waters are
of recent origin, contain but little plankton. Quiver Lake falls
in production as spring and creek waters preponderate in its
area at low-water stages, while the phenomenally rich waters
of Phelps Lake are poverty-stricken only so long as Spoon Riy-
er floods maintain a current through the lake.

The time requisite for the development of the plankton in
such waters of recent origin must necessarily vary with the at-
tendant circumstances, such as climatic conditions, previous
state of the plankton, and the proportions of the mingling wa-
ters. The volumetric pulses of plankton are frequently so
located as to suggest the agency of floods in determining, to
some extent at least, their location and amplitude. The apices
of these pulses are found at varying intervals after the pre-
ceding depression occasioned by invasion of water of recent
origin. Thus the August pulse in 1896 in channel waters makes
full recovery in a week from the scouring effect of the flood
(P]. X.). In the backwaters this same flood (Pl. XX VII., XXXI.,
and XXXVII.) was attended by a rising pulse which culmi-
nated after an interval of 2 to 3 weeks. Ina general way, 10-20

460

days suffice in most cases for production to recover from the dis-
aster of, or respond to the stimulus of, the flood. It is evident, how-
ever, that this matter is greatly complicated with the rythmic,
pulse-like character of the movement in plankton production.

In passing, attention should be called to the fact that re-
covery from the flood is not merely replacement by up-stream
waters rich in plankton, as might be concluded regarding chan-
nel waters. It takes place also in the impounded backwaters
under conditions of absolute independence of channel, as in
Phelps, Dogfish, and Flag lakes. In these cases it is an indig-
enous development in impounded flood waters, and, by infer-
ence, there must be a process of like import in channel waters
and areas more or less intimately connected therewith.

This necessity of some lapse of time before accessions of
tributary flood and spring waters can produce a plankton of
any considerable volume makes all important the impounding
function of the backwaters of the Illinois River. They act not
only as storage reservoirs whence the floods are drawn off in
reduced and equalized volume, but they serve also as nurseries,
where under favorable conditions the flood waters are seeded
with planktonts whose progeny utilize the organic materials
in suspension and solution in the invading flood or derived from
the invaded territory. The plankton thus developed, or the
product of its decay, is carried away by the run-off of the flood
into channel waters unless utilized by the larger and more per-
manent residents of the backwaters as food, or sequestrated in
some land-locked pool or lake as levels fall.

Intimately connected with the age of the water are the as-
sociated factors of current and rate of renewal. In and of itself
alone, current has little demonstrable influence upon plankton
production, but conjoined with other factors it becomes potent
for ill. Thus, in narrow confines, as within the banks of a
stream, by its mechanical action it fills the water with silt,
which diminishes access of light and thus tends to decrease
photosynthesis by the phytoplankton. The silt likewise, as
has been pointed out on page 185, seems by adherence to im-

461

pede the movements of the Hntomostraca, and perhaps also of
the fotifera, and thus to exercise a deleterious effect upon
them. The excess of moribund and dead individuals of these
groups in flood waters is evidence of the destructive character
of the silt-laden current.

When the existence of a current ina body of water involves
the run-off of its contents and their replacement by water of
more recent origin, the result tends to lower production, and
the proportions of the depressing influence will rise with the
rate of the current and the contraction of the volume, or with
rapidity of replacement, in the main in proportion as they
shorten the time for breeding of the plankton. Illustrations
of this tendency appear in contrasting our various localities.
In Spoon River, where current is rapid and renewal with re-
cent water complete and frequent, production (.256) continues
im minimum quantity and rises only when current slackens.
In the Illinois River the current is perhaps as a rule less rapid
than in Spoon River, replacement because of* connecting back-
waters less complete and frequent, and the replacing water has
a greater proportion of older water by virtue of the longer wa-
ter-course and the greater development of contributory im-
pounding backwaters. Production is accordingly greater (2.71)
in the larger stream. In Quiver Lake conditions in these par-
ticulars are extremely varied. As the lake emerges from the
general overflow the extent and rate of the current declines,
but the proportion of creek and spring water of recent origin
is increased with resulting depression in production. When by
reason of backwater from the channel at low levels the current
is reversed, the run-off checked, and the flood and tributary
waters are impounded,—as in the summer floods of 1896,—pro-
duction rises. Current with attendant run-off and renewal of
water in this lake constitutes one of the important factors in
lowering its production (1.75) below that of the other backwaters.

In Dogfish Lake the factor of current and renewal by recent
water is largely eliminated, and production (3.16) exceeds that
in the contiguous waters of Quiver Lake.

462

In Flag Lake a current is only slightly present in high
water and during the run-off of impounded floods. It is per-
haps less noticeable here than at any other station examined,
owing to the sheltered location and freedom from tributary re-
lations. Renewal is therefore least rapid and production ac-
cordingly high (9.23).

In Thompson’s Lake, owing to freedom from tributaries, to
the large volume of the lake, and to the relatively small and
frequently interrupted run-off, renewal is relatively infrequent
and incomplete. Moreover, the water which replenishes the
lake is drawn from the channel, and has a considerable propor-
tion of old and plankton-rich contributions from impounding
areas up-stream. Production is accordingly high in this area
(8.26).

In Phelps Lake, current, other than that of run-off of con-
tained waters, is absent at levels below 10 ft., above which Spoon
River flood waters of recent origin find their way through the
lake and depress production. At other seasons current is in-
considerable and soon ceases, and replacement no longer occurs.
Impounding and production (22.35) are at their maximum
here.

The net effect of the continued run-off and renewal of the
water in a stream or lake upon the fertility of the locality will
depend largely upon the inflow and discharge of nitrogenous
and other food materials or living organisms developed at their
expense. It is evident from the chemical data contained in
this paper that a vast amount of organic matter is continually
carried away from the drainage basin of the Illinois, and that
the amount in the streams is usually greater than that in the
backwaters. In general, production is less where this impovy-
erishing process is facilitated by continuous and relatively rapid
replacement (Spoon River, Quiver Lake, and the Illinois), is
greater where the rate of renewal and total run-off is less (Dog-
fish, Flag, and Thompson’s lakes), and is greatest when and
where impounding is most complete (Phelps Lake at low wa-
ter) and the organic matter in suspension and solution is re-

463

tained within the lake and augmented by the synthetic activi-
ties of the phytoplankton and other vegetation.

The fluctuations in hydrographic conditions consequent upon
changes to river levels constitute the one pre-eminent factor
peculiar in the fluviatile environment in the extent to which it
is developed and to which it influences and controls the course
of plankton production. These fluctuations operate by bring-
ing about changes in area, depth, and volume, in current, in age
of the water, in rate of renewal and period of impounding, in
relative proportions of tributary and impounded water, in
chemical contents and sewage contamination, in relative dom-
inance of vegetation, and in the interrelations of channel with
backwaters and of the backwaters with each other. Illustra-
tions of each and all of these results have been cited in the de-
tailed discussion of the course of plankton production in the
channel and the various backwaters. It will therefore suffice
in the present connection to cite briefly certain prominent fea-
tures, and to deal particularly only with some of the general
phases of the problem not readily followed through the maze of
details of the previous discussion.

The rise in levels results usually from access of tributa-
ry flood waters in local or up-stream territory, and rarely from
backwater due to entrance of storm water in lower reaches of
the river only. These flood rises occur in both high and low
river stages, though they are more frequent and of shorter du-
ration at lower levels, since in the much contracted volume of
the stream at such stages slight increases in the run-off which
would scarcely cause a ripple in the hydrograph in overflow
stages, now cause considerable change.

The river channel itself is most immediately affected by
this access of flood waters of recent origin, since tributaries,
with few exceptions, discharge directly into the channel, and
even when these courses across the bottom-lands are submerged
in general overflow the tributary current is always maintained,
in part at least, along its old path.

The result of this invasion is always a dilution of the plank-

464

ton-rich channel water, or its partial replacement by the plank-
ton-poor and silt-laden flood. Typical illustrations of its action
appear in the planktograph of 1896.

The rising stages of the flood are the most disastrous. They
carry the heaviest burden of silt, are formed of the most recent
water, and usually, because of their sudden inroads, most com-
pletely replace the previous channel contents. The December
flood of 1895 is a typical illustration. Rising suddenly from
low levels (8 ft.) to overflow stage (12.6 ft.) in 12 days, it de-
pletes the channel plankton from 2.6 cm? in the initial stages
of the flood on the 20th (PI. IX.) to .08 on the 25th, if not, in-
deed, earlier. Not only does it thus depress plankton content
in channel waters but, with a less catastrophic completeness,
that also in the backwaters. Thus in Thompson’s Lake the
plankton falls from 1.87 cm.’ on the 19th to .13 on the 28th,
in Quiver and Dogfish lakes, from .63 and 10.57 to .29 and
.06, and in Flag Lake, from 6.38 to 3.26. The effectiveness of
the depletion is greatest where overflow currents are best es-
tablished, as in Thompson’s and Dogfish lakes, and least where
the currents are slight and impounding greatest, as in Flag
Lake.

With the culmination of the flood the proportions of in-
coming storm water of recent origin decline rapidly, the effects
of the run-off of impounded backwaters begin to appear, and
recovery in production, other things being equal, marks this
stage of the flood. Typical illustrations will be found in the
June and August floods of 1896 (Pl. X.) and in the June flood
of 1897 (Pl. XJ.) and 1898 (PI. XII.).

The results of flood in the backwaters are similar to those
in the channel wherever currents of overflow are established
and replacement of the plankton-rich contents of the lake by
flood waters ensues, as has just been shown. Usually there are
accessory bottom-lands, not swept by current, where a part of
the original lake waters are retained, and where plankton
breeds abundantly. As a result of this, the recovery from the
depletion by flood—and this is usually not so complete as in

465

the channel—is more prompt and attains a greater amplitude.
A comparison of after effects of the June flood in 1896 in the
river (Pl. X.) and in Quiver (Pl. XXVII.), Dogfish (Pl. XXXI.),
Flag (Pl. XXXIII.), and Thompson’s (Pl. XX XVII.) lakes will
conclusively demonstrate these conditions. While the recoy-
ery from flood effects in the river is delayed till about June 10,
in the various backwaters it occurs from a week to 10 days
earlier.

It is evident from the pulse-like character of the movement
in plankton production, to which attention has been called re-
peatedly in the detailed discussion, that the recovery from flood
conditions is complicated with this phenomenon. Flood con-
ditions in backwaters, by influx of waters laden with organic
detritus, and by destruction, submergence, and decay of vegeta-
tion, tend to accelerate the appearance and, it may be, increase
the amplitude, of the pulses. When, however, the invading
waters have lttle plankton and largely replace the previous
contents, they tend to delay and depress the pulses, and, as in
the case of the May-June and August pulses, the flood may even
obliterate the apex of a normally developing plankton pulse.
Flood conditions thus affect these pulses profoundly, but they
do not seem to be fundamentally their cause.

Periods of declining river stages stand in sharp contrast
with rising levels. It is for the plankton a period in which re-
construction and growth are possible. The decreased propor-
tion of recent water and the prolongation.of impounding in
backwaters, characterize this as a time of relatively stable con-
ditions as contrasted with the chaos caused by the rising flood.

In a general way there is some correlation between the to-
tal annual movement in river levels and the average plankton
content per cubic meter of water. In the table on page 466
the available data are tabulated for the channel plankton.

The arbitrary division by years results in one misleading
presentation of the data. The December flood of 1895 (12.6 ft.)
occurred in the last days of the year, while its effects continue
beyond that limit. If we subtract the 9.8 ft. of this rise from

466

the total movement (51.9) of 1895 and add it to that of 1896
(45.7), the resulting figures (42.1 and 55.5) will more nearly
characterize the hydrographic conditions in which our plank-
ton collections were made. After making allowances for the

AVERAGE CHANNEL PLANKTON AND ACCOMPANYING MOVEMENT IN RIVER LEVELS.

Total movement in river| Plankton per m.*

Mean levels—in feet —in cm.’ *
TOO Aa so sysraisveueswis ovstevoremera caerary aout enone 32.9 2.53
POQG 5 sate Peencact aonero io chavalee en enetene oemnaster 51.9 (42.1) 5.96
T8QG 1.) RAS ic eae hc tee ee eee 45.7 (55.5)t 1.05
TSO 7 As ayoskee cea eat shel Le eS 44.8 3.28
WSOS Rie. sy arose ee oe eee 67.2 2.03
*Mean of monthly averages. TAfter transferring December rise to 1896.

fact that our plankton averages imperfectly represent the
actual production, it is still apparent that plankton production
(per m.*) is inversely proportional, in a varying ratio, to the
extent of the total movement in river levels.

In not a few of the years (PI. VII.) the hydrograph falls
into two periods dominated respectively by high- and by low-
water conditions. ‘This is seen typically in 1897, and with less
contrast in 1594, 1895, and 1898, while in 1896 the recurrent
floods obliterate almost all traces of such a division. In their
totality these two hydrographic extremes present strong con-
trasts which must bear important relations to the plankton
production. They are, moreover, so involved with other fac-
tors that no simple analysis of their results seems possible. For
example, the high-water period is predominantly, as a rule, of
low temperature, considerable ice, dilution of sewage, decreased
hght, increased access of recent water, increased current, de-
creased occupancy by, and lessened growth of, aquatic vegeta-
tion, and of greatly increased area and intimate and free con-
nection with reservoir backwaters. The low-water period, on the
other hand, is one of higher temperatures, no ice, concentration
of sewage, increased light,reduced volume of tributary water,—
which itself is of less recent origin than at high water,—slack-
ened current, greater domination by, and growth of, aquatic
vegetation, and of greatly contracted area and restricted con-

467

nections with and contributions from the remaining backwaters.
The complications arising from the combination of these vari-
ous factors in varying degrees and the seasonal shifting of the
two periods in the several years, render any sweeping general-
izations impossible.

The following table gives in parallel columns the monthly
means of plankton per m.°* and of river stages in feet above low-
water mark.

PLANKTON PRODUCTION AND RIVER LEVELS.

January | February March April May June
a ' i} ' ' ' 1
Co) o a) o M o od o ad o aes! oO wd
See ss ies es \ss ls |e ss) s | gs
a |e a |p, On |e A | a mn | A BD | &
SCAN PRN eee Revco oescene rors ll ees lNG. cess ee [Pay cveseateel| snentecrene [tavereseue afore. at shell vaielenens 4.63 74
MGOS| (tse Boil cet pawewbllaoedes Boll] Botlooccaclloooocs 1.88] 30.42
1896] 10.24) .o1] 8.83] .02) 9.41 07| 7.28) 5.67) 6.58} 1.30] 7.38 72
ieidy/loooeae II.13] .04} 13.89 .38] 13.40) 5.11] 9.41] 5.62] 5.54 27
1898] 5.08] .45| 5.94] .27) 12.99] .33] 14.00] 4.40] 11.55] 11.30] 11.53] 3.96
1899] 7.99] .18] 7.02] .81] 13.05 2748) | aiod craves Slo 0 ally orem eral acme Pil Goo ne aa eee
Mean| 7.77| .21| 7.29] .23') 12.34 .27| 10.02] 4.59] 9.18] 6.08] 6.19] 7.22

July August Sept Oct. Nov | Dec Ann’! Mean

o 1] 2 “4 wo | Oo | oO | 2 4 0 av
© Ee] og ES) PIES SES) SiS see) ace

ee 2 | oe ees he lao | a la
2.32 5.12] 1.99 9-67] 4.43] 1.36|2.96] .61/2.97] .10 3.41 10} 4.63] 2.53
3-17| 9-33] 2.43] 4.03] 3.42] 1.52) 1.93] .57/2.20/3.02, 6.16] 1.14] 3.61] 5.91
4.55] 1.44] 7.42] 1.12) 4.62] .38)/6.04]1.11]5.89] .02 5.48} .76] 6.98] 1.05
6.05] 4.69] 2.29] 3.65] 2.01| 8.83] 2.01] 5.95) 2.82 1.00! R927) .56| 6.90] 3.51
5.70 .58] 3.66 -91| 4.44} .69]/ 4.86] .24|7.44 25| 6.59 .99| 8.02] 2.03
50.0.0.0\ pace cel Neererea ener oo BS Sb o.a| |e a8 seca Nab Bell imeeyCl esta, clal Neerata i inal Mm nee nL 7
4.36] 4.23) 3.56] 3.88) 3.82/2.56) 3.56 1.70! 4.26 88, 4.97 SVAG| Rumcmtord Po Ait

An inspection of the table shows at once the complexity of
the problem, and yields the following generalizations.

In January-February, a period of sustained minimum tem-
peratures, high levels are attended by a small, and low levels
by a larger, plankton content, with the exception of stagnation
conditions in February, 1895. This contrast results from the

468

recent origin of the flood waters of these months, from the di-
lution of sewage and increased rapidity of run-off, and from the
reduction in time of impounding under these hydrographic con-
ditions.

March-May isa period of rising temperatures, maximum
flood levels, and increasing plankton production. The data, in
so far as they go, indicate that high levels tend to increase pro-
duction and low levels to decrease it, in some instances at
least. These months witness the maximum and the initial de-
cline of the spring flood, as a rule, and the greatest volume and
principal run-off of flood waters whose impounding has been
more or less prolonged. The proportion of impounded water is
greater in higher than in lower levels, and we find, accordingly,
production increased in the former and decreased in the latter,
as a general rule. It is noticeable that levels in May slightly
exceeding bank height, as in 1897 and 1898, yield much greater
production (5.62 and 11.50) than levels not attended by overflow,
as in 1896, when production falls to 1.30 at a level of 6.58 ft.

The data of the June period are somewhat aberrant, in part
as a result of insufficient data in some years, as 1895, and in
part because of the relatively great irregularity of hydrographic
conditions in this month in different years. The high produc-
tion (30.42 cm.°) in low levels (1.88 ft.) in 1895 attends sewage
concentration. The data for the remaining years conform in
the main to the conclusions concerning production in the three
prior months, namely, that high levels favor and low levels
depress production, and for the same reasons above cited. A
comparison of production in 1896 and 1898 in June yields con-
firmatory evidence on this point.

With July begins the low-water period proper, which con-
tinues during the remainder of the year. Levels do not rise, in
the means of the monthly averages, above 5 ft. in this period.
The relation which existed between production and high water
in March—June is reversed in the period of July-November. An
inspection of the table shows that in 20 of the 25 months in-
cluded in the table in this period this reversed relation obtains;

469

that is, levels above the average are accompanied by a fall in
production to an amount below the average, and those below, by
arise in production above the average. Thus, in this period
higher levels depress production and lower levels tend to in-
crease it. Two of the 5 apparent exceptions are in October and
November, 1894, when insufficient data are available, and one
is in July 1897, when the customary vernal conditions (PI. XI.)
encroach upon the low-water period.

The cause of this changed relationship of levels and produc-
tion in these months of predominantly low water is to be found
in the relation which summer rises in levels bear to the im-
pounding function of the backwaters. These summer rises are
rarely above bank height. They flush the channel, are not ex-
tensively impounded in the backwaters, run off quickly, and
accordingly depress production. The months of lower average
levels are more stable, and, owing to slackened current, a more
abundant plankton breeds, other things being equal, than in
the more rapid current in the summer months of higher levels.

The relations in December between production and levels
are again reversed. Indeed, suggestions of this réversal appear
in November. In this month minimum temperatures are again
reached and higher levels prevail, and production now is higher
in the years of high levels and falls below the monthly mean
in every year of low levels. The cause of this relation does not
seem to le in hydrographic conditions. It may possibly be in-
volved in the changed sewage and bacterial content of the
channel that accompany the increased current and the decline
in temperatures. The submergence of the summer’s growth of
vegetation in the margin of the river and its connecting back-
waters in years of higher levels may also be a contributory
factor.

We thus find that in channel waters higher levels favor
production only when they increase the impounding function
and by long duration afford time for production and run-off of
the plankton, and when they make available additional sources
of nutrition. They depress production when they first appear,

470

and when they are of short duration and merely flush the chan-
nel, as is predominantly the case during the low-water period.
Lower levels depress production when they introduce stagna-
tion conditions—as in the winter under the ice, and when they
cut off contributory backwaters or otherwise reduce the run-
off of impounded waters of long standing. They increase pro-
duction when they lend stability to hydrographic conditions,
increase the relative fertilization (sewage) of the stream, and
by slackened current afford time for breeding.

In general terms, production in the backwaters exhibits
relations to levels similar to those we have described for chan-
nel waters so long as the backwaters retain an intimate con-
nection with the channel, that is, generally during high water,
and for longest periods when, as in Thompson’s Lake, the con-
nection with the channel is most intimate. The diversification,
as levels fall, of the several regions examined by us, renders
generalizations impossible with respect to all of the backwaters,
since one or another local factor sooner or later comes in to
modify conditions. Moreover, some of the backwaters, as
Phelps Lake, are cut off from the channel early and are not
affected by changes in river levels, and, in general, the effect
of the changes in channel levels, especially the minor ones, is
reduced, equalized, or even obliterated, before it reaches the
backwaters.

The season at which the initial stages of the major flood of
the year occurs, affects the subsequent production. Thus in
1896 and 1897 floods begin early in the year. The result is
the carrying away in the run-off of great quantities of organic
matter in suspension (Table X.) before they have had time to
decay and yield up in solution their nitrogenous and other con-
stituents for the support of the plankton. Temperatures are
low in these months, decay is not rapid, and the plankton is
not produced in large quantities. The result is that the stream
is locally impoverished by this early run-off of matters in sus-
pension and to some extent in solution. In 1898, on the other
hand, the flood does not reach overflow stages till late in Feb-

47]

ruary and is continued well into the early summer. Thus,
while in 1896 and 1897 the vernal pulses of plankton production
(9.39 and 5.62) are not large, in 1898 the production in this
season rises to 35.68. Late high water, with decay and solution
of organic substances increased by higher temperatures, occurs
at the season of rapid plankton increase, and food matters
which run off in the winter floods are here utilized and increase
the amplitude of the plankton pulse. Winter floods thus tend
to locally impoverish the plankton, and spring floods to in-
crease it.

Enough has been said to indicate the supreme importance
of hydrographic conditions in the fluviatile environment in de-
termining the amplitude of plankton production and in differ-
entiating local.areas in our environment. It is the prime fac-
tor which distinguishes the fluviatile from the lacustrine envi-
ronment, stamping the former with an instability as character-
istic of the river as stability is of the lake,

TEMPERATURE AND PLANKTON PRODUCTION,

On pages 168-177 will be found a discussion of the temper-
ature conditions at the various plankton stations and their gen-
eral relations to the larger phases of plankton production. In
the present connection the more detailed comparison will be
made.

To facilitate this comparison of production and tempera-
ture conditions I have prepared the accompanying table (see
p. 472), which gives the monthly means of production and of sur-
face temperatures recorded at the times of collection in the
river.

This table in conjunction with the one following page 342
suggests the codperation of temperature in controlling in a large
way the seasonal fluctuations in production. In general, in the
colder months less plankton is produced than in warmer months.
Thus in the river the mean production in the 5 months below
45° is but little more than 9 per cent. of that in the 7 months
above this temperature, in Phelps Lake, only 40 per cent., and

472

PLANKTON PRODUCTION AND TEMPERATURE.

January February March | April | May | June
a cl
> a |x a | a a} a | x a | a |
SES eS eis | Blea) 2 | se
| Ay ae Ay fH Ay al Ay ial Ay cal Ay
1 of] |e otras Peconic [ee eater! acct anes ebro actes| Svea <a) ol [aster ae ete lee Gite .0 0.0 oo 80.25] 0.74
HEOVS||o 165 6 |looooe 32h OHO ecorcclleewenens 8 Bip tollgmesmelecs co 80. 30.42
1896|32.75| 0.01] 33.7 | 0.02] 39.52} 0.07] 64.54] 5.67] 72.7 1.30] 74.7 | 0.72
UW oocoo looocc 2.25] 0.04] 43 0.38] 60. 5.11} 66.3 | 5.62! 75. 0.27
1898/32.7 | 0.45] 32.12] 0.27) 43.3 | 0.33] 53.32] 4.40] 65.8 | 11.30] 78.8 | 3.96

1899132.9 | 0.18] 32.6 | 0.81] 35.2 | 0.28]......

July | August | September October | November | December
py | Ge | ta a. | ey |) a | ow a, | ey |
SCS a bas SE aise | aba | & | se
& | A a Ay sa Ay sal | Ay sa a ic Au
1894|82.25| 5.12] 83.5 | 9.67| 77.5 | 1.36] 58. 0.61) 41 0.10} 39 0.10
1895/79. | 9-33] 80.51) 4.03) 78.87) 1.52) 54.26) 0.57) 42.5 | 3.02| 37.5 | 1.14
1896|80.7 | 1.44) 82. 1.12] 65.75] 0.38] 56. I.11| 44 0.02] 33. 0.76
1897/81 .02| 4.69] 80.9 | 3.65] 77.07] 8.83] 65.1 | 5.95] 45.7 | 1.00] 33.02| 0.56
nee 82.87| 0.58] 80.56} 0.91] 71.87] 0.69 54-37) 0.24) 41.42] 0.25] 32.98} 0.99
UXN)ooc00lfooocnlloaoccnllacqdocloosa0cllocobcolaonnn0 so000blloocadcllooccan|\n0c000)000000

in Thompson’s Lake, 29 per cent. The difference would be in-
creased if the aberrant data of the late autumn of 1897 were
removed from the records. Low temperatures thus tend to
depress production in both channel and backwaters, and high
temperatures to increase it.

The minimum production of the year occurs in the river,
and with few exceptions in the backwaters, in January-Febru-
ary, the two months of minimum temperature. With the
period of rising temperatures in March—May there comes gen-
erally at all of the stations a rapid rise in plankton production,
culminating in the vernal pulse in the last days of April or the
first of May at about 60°-70°. The effect of this is seen in the
generally high average production in April and May in both
channel and backwaters. With the establishment of the sum-
mer period of maximum temperatures, which includes the
months of June-September with the exception of a few days

473

of rising and falling temperatures at the beginning and close
of the season, there comes, as a rule, a decline in production
from that of the vernal season. In channel waters this amounts
to 16 per cent. of vernal production, or, omitting the single
aberrant datum of June 1895, to 44 per cent. In the backwa-
ters, owing to the combination with various local factors, such
as tributary waters and vegetation, the change from vernal pro-
duction in midsummer varies greatly in different localities.
Thus, in Quiver Lake, where vegetation and the proportion of
tributary waters is increased in summer, the decline in that
season amounts to 87 per cent., while in Dogfish Lake, where veg-
etation alone is the main disturbing factor, the decline is 74 per
cent. of the vernal production, as seen in the April-May aver-
ages. In Flag Lake, where also vegetation enters as a disturb-
ing factor, the decline is 80 per cent. In Thompson’s Lake, where
disturbing local factors are less in evidence, it is but 69 per cent.
In Phelps Lake, in contrast with all the other localities, pro-
duction during the period of maximum heat exceeds that in the -
vernal season by 68 per cent. Thus the period of maximum
heat in most localities attends a depression in production, but
the exception in Phelps Lake is so striking as to preclude any
conclusion that summer heat is necessarily inimical to large
production, or that it is of necessity the most potent of the co-
operating factors. The omission of the averages for August
and September in 1898 from the Phelps Lake data would make
the average production in the period of maximum heat 33 per
cent. below that of the vernal months, and bring this locality
into agreement with the other stations as to the depressing
effect of summer heat in plankton production. It should be
emphasized in this connection that these conclusions apply to
catches of the silk net only, that the summer temperatures of
our waters approximate 80° on the average and frequently rise
above it,and that temperature is only one of the factorsinvolved.

Following the period of maximum summer heat is that of
decline in October-November—including also a part of Sep-
tember, or even December in some seasons—to the winter min-

474

imum. In general, this is a period of declining plankton in
channel waters, where production in these two months falls 71
per cent. below that in the preceding four months of maximum
heat, and in Quiver Lake, where it falls 48 percent. below. On
the other hand, in the rest of the backwaters there is a slight in-
crease in these two months as compared with the production in
the period of maximum heat. In Dogfish, Flag, Thompson’s
and Phelps lakes the October-November increase in percent-
ages over the average summer production in each of these sev-
eral localities is 33, 362, 26, and 11 per cent. respectively. In
view of these divergent tendencies in production under similar
temperature conditions it is evident that other factors are
operative, or at least more potent, in controlling autumnal pro-
duction. The October production is as a rule higher than that
of November, and suggests a tendency towards an autumnal
pulse comparable with the vernal pulse but of lesser amplitude.
The vernal pulse occurs in rising temperatures of 60°—70°, and
_ this autumnal one in falling temperatures of 60°—50°.

The month of December does not on the average quite at-
tain the minimum winter temperature, though in some years,
as in 1897 and 1898, it approached closely to it. Neither does
the plankton production drop to so low a level on the average
or in individual years in channel waters as during the two
colder months which follow. In general the same relation ex-
ists in the backwaters, though exceptions occur—principally in
Thompson’s Lake.

Thus, in a large way, temperature plays an important part
in controlling plankton production. Additional proof of its
potency is to be found in the correlations between production
and exceptional divergences from the normal course of tem-
perature changes, such, for example, as early or late vernal
rise or autumnal decline.

The accompanying table (p. 475), kindly furnished by Mr.
W.G. Burns, Section Director for [llinois of the U. 8. Weather
Bureau, gives the vernal air temperatures for 1896-1898, and
permits a comparison with the course of plankton production.

475

MONTHLY MEANS OF VERNAL TEMPERATURES FOR ILLINOIS AND OF PLANKTON
PRODUCTION—CM.? PER M’.

1896 1897 1898
Temper- Temper- Temper-
ature |Plankton| ature |Plankton} ature | Plankton
(Fahr.) (Fahr.) (Fahr.)
North section... 31.9 34.4 39.0
Central section. 36.4 41.1 44.4
March. |South’rnsection| 40.6 .O7 46.8 38 48.7 33
State, average. . 35.6 390.5 43.4
N@ma Go cdogos 37.6 | 37.6 37.6
North section..; 55.3 | 47.2 46.9
Central section 59.9 | 51.3 50.5
April ..|South’rn section; 63.6 | 5.67 55.0 5.11 53.0 4.40
State, average. 59.0 | 50.4 49.6
NOM aco ome 00 51.8 | Tl ots 51.8
North section.. 67.2 57-5 59.1
Central section. 70.6 59.7 63.0
May...|South’rn section] 71.7 1.30 62.1 5.62 66.8 II.30
State, average.. 69.5 59.3 62.2
IN@ dell soono6. 61.8 61.8 61.8

The most notable instances of correlation between deflec-
tions of temperature and plankton production are to be seen in
the early spring of 1896 and the late autumn of 1897. These
correlations have already been noted in connection with the
discussion of production in the river and the several back-
waters. The mean temperatures of the air here given corrob-
orate our conclusions based on the relatively scanty data of
water temperatures delineated in the thermographs of the plates
accompanying this paper. Thus, the spring of 1896 was 2° be-
low normal in the state as a whole in March, but was 7.2°
above normal in April, and 9.4° above the mean for 1898. Mean
plankton production is also higher in April in 1896 than in any
other year. Indeed, in this month the descending scale of mean
temperatures in 1896-1898 is accompanied by a similar scale
of decreasing mean production of plankton, and, as kas been
noted in the discussions of the course of production in the
river and backwaters, the vernal pulse of 1896 is from 10-14
days earlier than in 1898, when, as this table of mean tempera-
tures shows, the April mean of air temperatures was 9°-10°
below that of 1896.

476

So also in 1897, the means of our records of water tempera-
tures for September, October, and November of that year are
2.9°, 7.6°, and 2.7° above the average of the monthly means for
all years. This maintenance of high temperatures into the pe-
riod of normal autumnal decline is apparently one of the fac-
tors tending to make production in these months of this year
greatly exceed that of the same season in other years. In chan-
nel waters in these months of 1897 (see table following p. 342)
production is from 138 to 250 per cent. above the mean of all
years, and often 10- to 20-fold that in other years. In’ Thompson’s
Lake the excess in 1897 is even greater, ranging from 87 to 238
per cent. of the mean of all years, and from 1.6 to 28 times that
in the same months in other years. The higher temperatures
do not suffice, however, in the case of Quiver Lake, to overcome
the other factors tending to depress production there in these
months, and we must conclude that, although all-pervading
and potent, temperature is nevertheless not always pre-emi-
nent among the environing factors of the plankton.

We thus find that in a general way, in conjunction with
other factors, rising temperatures tend to increase, and falling
to decrease, plankton production, and that in the same locality
the warmer months generally yield more plankton than the
colder ones. On the other hand, minimum temperatures when
once established are not of themselves inimical to a considera-
ble plankton production. Evidence of this is ‘to be found in
the not infrequently increased production in December over
that of several months preceding. This is perhaps most notice-
able in the records of 1898. Thus in channel waters the am-
plitude of the December pulse (PI. XII.) exceeds that of all
other months since the last of June, and the December maxi-
mum in Phelps Lake (43.14) exceeds in amplitude all other pro-
duction in our records for 1898 in all other localities save only the
single apex of the vernal pulse (51.39) in Thompson’s Lake. It
is, however, only about one fifth of the August maximum
(224.48, Pl. XLII.) in Phelps Lake itself, so that the depressing
effect of lower temperatures is still apparent if we limit com-
parisons to a single locality.

477

The effect of the autumnal decline, and, in general, of low-
ered temperatures, in depressing production is apparent in not
a few instances in our records. It can be seen in the October-
November thermographs and curves of plankton production
of channel waters in 1894-1898, and inthose of Quiver Lake for
the same years; is much less apparent in Thompson’s Lake,
especially in 1897, even when temperatures have fallen; and
is often but feebly developed in Dogfish and Flag lakes in
1895-1897, while in Phelps Lake in 1896 and 1898 there are
pulses of considerable magnitude (51.6, and 99.86) in this period
of decline of temperature. The minima demarking these
pulses are, however, of less than the usual amplitude. This
depressing effect is thus traceable in all localities, but is bet-
ter developed in stream than in lake waters, appearing most
clearly in the channel and Quiver Lake, where, at this season of
the year, tributary waters are present in considerable propor-
tion.

Our water temperatures and the records of the United
States Weather Bureau at Havana and elsewhere in our lo-
cality reveal many instances of heat pulses at various seasons
of the year. There is little regularity in their duration or
amplitude. When plotted from the means of the tri-daily
readings of the air temperatures at Havana they do not ex-
hibit delimitations as well defined as those, for example, of a
fully observed plankton pulse. Their amplitude, except in
winter months, rarely exceeds 20° between extremes, and their
duration is usually less than a fortnight between minima. That
these fluctuations affect the course of plankton production can-
not be doubted. A detailed comparison of the course of produc-
tion in 1896 and the thermograph of that year will show that,
predominantly, rises of temperature attend or precede rising pro-
duction, while declines in heat are often correlated with de-
creased production. This may be largely coincidence, or, in
some cases, the common effect of cooler, barren flood-waters,
especially in the case of the records of channel production. A
close comparison, however, of the planktograph in Phelps

478

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479

Lake—where flood factors are largely excluded—and the ther-
mograph (air) for 1896 will serve to suggest the possibility of a
causal nexus between the two phenomena of fluctuations in
heat and some of the movements in plankton production. The
many exceptions to any close correlation emphasize, however,
the fact that heat is only one of the many factors involved in
the problem, and also indicate the necessity for much fuller
plankton data, with closer interval and the proper quantitative
representation of the minute forms now lost by leakage through
the silk, for any adequate discussion of the problem. The
present data serve only to suggest the problem for investiga-
tion.

The effect of the ice-sheet upon the course of plankton pro-
duction is apparent ina number of instances in our records.
The most noticeable case was the extermination of the plank-
tonin the channel in February, 1895, by the ice-sheet of two
months’ duration; but this catastrophe was not repeated else-
where in our records in this or other years. Indeed, owing to
the fact that the period of the ice blockade is usually one of
lower levels and more stable conditions, we find generally that
production under the ice, even at minimum temperatures,
rises above prior or subsequent levels. An inspection of the
plates, especially those of 1898, will show repeated instances of
this phenomenon in both channel and backwaters. One of the
most striking phenomena in all our records is this winter pro-
duction under the ice-sheet in 1898-1899, a production which
in the river attained an amplitude in December (.99) not
equaled since June, and in February (.81) one surpassed only
by the August (.91) and December means. In Quiver Lake
likewise, the December (1.74), January (.77), and February
(1.05) means are all considerably in excess of the June-Novem-
ber production, the-average of the winter months (1.19) being
over threefold greater than that of the warmer months (.33)
named. In Thompson’s Lake also the midwinter production
in this season was large, reaching an average of 1.94 for the
winter months above named, and only 1.96 for the five preceding

480

months, while the amplitude of the December and January
pulses was surpassed but once from June to December. Con-
ditions under the ice at minimum temperatures were thus in
these years and localities quite as favorabie to the quantita-
tive development of the plankton as were the conditions prev-
alent in summer and autumn.

As a whole, then, temperature changes bear an important
relation to the course of plankton production, but at times they
are not more potent than other factors. An abundant plankton
may develop at any temperature within the normal seasonal
range provided other factors favor it, but generally the ampl-
tude is less in lower or in falling temperatures, and greater in
higher or in rising ones.

The relations here discussed between the volume of plank-
ton and temperature depend primarily upon adaptations of
particular species to temperature—a subject which will be dis-
cussed in another connection.

LIGHT AND PLANKTON PRODUCTION.

There are at hand no adequate data on this subject, and it
is, moreover, complicated with the thermal and other forms of
solar energy and with the problem of turbidity in the water
itself. No detailed comparison is afforded by the data, espe-
cially since the more minute forms are not adequately repre-
sented by the catches of the silk net, and it is largely these
synthetic organisms, chlorophyll-bearing alge and flagellates,
which are most dependent upon light for their growth and re-
production. Our data alike of light and plankton are thus
deficient. Nevertheless, in the chain of relations, the catch of
the silk net—largely of animal plankton—is, at most, but a
few links removed from these synthetic organisms, and it must
therefore in some measure reflect their quantitative fluctua-
tions. Our data suggest a few inferences concerning the rela-
tion of light and plankton production.

The period of greatest illumination les between March 20
and September 22, and owing to the proximity of these dates

48]

to the ends of the months it will be possible, for the purpose of
utilizing our data in monthly totals and means, to divide the
year into two periods, April-September and October—March, of
greater and less illumination respectively. The contrast in
iUluminationis further heightened by the fact—derived from the
following table of cloudy days—that the number (at Havana,
159) of cloudy days between the vernal and autumnal equi-
noxes is only about one half that (311) between the autumnal
and vernal. On the average, the season of greatest light is also
the season of greatest production. Thus, in the channel waters
average monthly production in April-September (4.76) is seven-
fold that in October—March (.67), and in the backwaters, such
as Quiver, Thompson’s, and Phelps lakes, it is respectively 5-,
2.2-, and A. 6-fold greater. The records of individual years in
all of the localities will be found to exhibit a similar relation-
ship. We may infer, accordingly, that the increased light be-
tween the vernal and autumnal equinoxes tends to increase
production, and that the decreased amount in the remainder of
the year tends to lower it. It operates, of course, in conjunc-
tion with other factors, and our records contain not a few in-
stances where production in the period of less illumination ex-
ceeds that in the period of greater hight. For example, on
December 20, 1898, in the minimum illumination of the year
and under an ice-sheet 21 em. thick, which still further reduced
the light, the plankton production in Thompson’s Lake reached
an amplitude (2.58) exceeding that on June 21 (2.47) in the
same lake in maximum illumination, an amplitude, moreover, sur-
passed but once from June to October. Other factors are thus, at
times, at least, more potent than light in controlling production.
A phenomenon of like import exists in the conditions of
illumination and production in Quiver and Thompson’s lakes.
Both lakes are of approximately the same depth, but the
former, especially in low-water conditions, has remarkably clear
water, the bottom being generally visible, while the latter is
always more turbid, and lght penetrates the water far less
completely. Nevertheless, the lake, with most illumination,

482

yields least plankton. The factors of vegetation of the coarser
sort and of tributary waters serve here to modify and overbal-
ance light as a controlling factor in production.

From the data of the U. S. Weather Bureau at Springfield,
Mr. W. G. Burns, Section Director, has kindly furnished me the
records of the number of cloudy days per month in 1894-1899
observed at Peoria, Havana, and Springfield. These are given
in the accompanying table. The records for Havana have also
been plotted on Plates VIII.—XIII. in the uppermost row of
squares.

NUMBER OF CLOUDY DAYS.

Sel eale SSI siBl2i<
A SSIS El al ole igialalelel
© 2S | a S&S Ss | e}s] w/e Elolo]|ois
al & ols <q Ele] sis 2 BV |e

Er oo Saal

es — |
1894 } 13| 13, 8] 12] Io} 5) of 7] 9) 9} 14} 15/133] 5
1895 | 11} 7! 11] 13] 2) of 7] 4| 4] 4] 15) 18}105] 1
Sjprinigtield eee eeesere ae eo | ey OS FS] a Ey B29) 6
Ksioy/ || UG) Tl Bo] 7) Al TO) Gl Al xu) All wal anin27|) 3
1898 | 12| 12 16) 13] 11] 5] 3 8! 10) 15] | 12/126] 1
1899 | 16 14) 21) 12) 17) 7] 13) 7 6} 8] 16) 1o\147| 6
Total | 82] 73] 92] 75] 62] 45] 44) 30| 42| 47! 84] 91/767)...
1894 | 7 8 7| 6| 4} of of 3] 3] 6] 10} 7| 61] 1
TSQ50| Ol 3) 10) Vola Al yA 3s 42s ere as
ISEMIEYA : htig gadloon poae an 1896 | 7) © 4) 3) 5) 6] 4) 2{ 11) 3) 10) 9! 70) 2
1897 | 10|‘10| 17] 13] 6! 6! o| 4, 2] 4} 12) 15) 99] 6
1898 | II] Io 11 6) 8) 4) 3) 8) 2) 16) 5 Zions
1899 | 7| 6| 16 4) 5) 3) 5| 3) 3] 6] 10] 7| 75] 4

Total | 48) 43) 65) 41] 3t} 23) 16) 23] 25] 37] 60| 58!470
1894 | 11] 9] 6} 8] of of 3) 5] 8 6} 12} 11] 88) 1
1895 | 10] 8] ro] 8] 4} 5) 6) 5] 4| 2] 18] I9} go] 2
Peoria eee cee 1896 | 17) 10} 8] 3) 6) 8) 6} 2) ro) 10) 16) 14l1I0) 4
1897 | 13] 14] 18) 16] 5] 6) 1] 4| 3] 3) 15] IolII7] 5
1898 | 15] 14! 14] ro] 13) 6) 2] 8) 4) 16] 11 13'126] 6
1899 | 12] 12) 16] 10} 8] 2) 5] 5] 6| 6) 13] 11/106; 3
Total! 78! 6 | 72! 55' 45! 27| 23! 201 35! 43! 851 78.6461...

The variations in the relative cloudiness in the three local-
ities in many months and in the total number of cloudy days
in the several years in the three localities render any correla-
tion with production largely conjectural and close comparisons

Ver Wart ewes (nhnArt

\

J ein OF onites wh
W wrTeuws> mea 4 ac

483° ov Can. corer

impossible. That the reduction in light due to clouds does in
a measure affect production might be inferred from the August
—October records in 1896 and 1898. In the two years named,
cloudy days and production in August are 2 and 8, and 1.12 and
.91 cm.* per m.* respectively ; in September they are 11 and 2,
and .38 and .69; and in October 3 and 16, and 1.11 and .24. Hy-
drographic conditions are not remarkably different in the two
years, and while their differences in this respect are doubtless
potent, causing differences in production, it still seems prob-
able that the fluctuations in light are also operative. In any
event in these three months the mean production runs higher
in the year of fewer cloudy days and lower in the year of less
sunshine. Similar relations will be found to exist generally
in the production of the backwaters for these months (see
table following p. 342). The statistical data of the synthetic
organisms to be discussed in Part II. of this paper still further
serve to demonstrate the correlation of light and plankton pro-
duction. The necessity of hght for the process of photosynthe-
sis on the part of the phytoplankton places this factor at the
very beginning of the chain of relations whose later links are
the larger animals of the zodplankton which constitute the
greater proportion of the volume of the catch of the silk net—
the basis of the present discussion.

VEGETATION AND PLANKTON PRODUCTION.

It is evident that our investigations afford a unique oppor-
tunity of determining the effect of vegetation (the word being
here used to refer to the coarser aquatic growth as distin-
guished from the microscopic phytoplankton) upon the course
of plankton production with reference to both its volume and
constitution.

The conclusions to be drawn from our observations with
reference to volumetric production, already suggested in the
detailed discussion of production, will be summarized and dis-
cussed here, though some of the data upon which they rest lie
outside the scope of the present paper.

484

1. Other things being equal, bodies of fresh water free
from vegetation (submerged macro-flora) produce more plank-
ton than those rich in such vegetation.* Thus, the amount of
plankton produced (as indicated by the averages of all of our
collections in the several localities examined) in our open
waters is from two to eleven times as great as it is in our lakes
closed by vegetation. As shown in the table on page 429, the
average planktons in Thompson’s and Phelps lakes are 7.94 and
and 19.65 cm.’ per m.’ respectively, while in Quiver and Dogfish
lakes the quantity is only 1.70 and 4.22. Flag Lake, with an
average of 11.46 cm.’, is an interesting exception to this con-
trast, which will be discussed in another connection. The con-
trast is even more striking if the averages of the monthly
averages for all the years are made the basis of comparison, as
in the following table and diagram. i

ae
COMPARISON OF PLANKTON PRODUCTION IN VAR OISHE SINE POOR AND np (0
VEGETATION-RICH waters. N

f

Vegetation-pogt * Sena
Month : D - fish SOT DSO Tits) | ae Ratio
Quiver Lake) “72,2 cake (Phelps Lake

Janwany.eas aa. serrdeeo meine 2, 53 3-79 3.29 1:9
IAEA Aue conto sold .67 Ifo 1K) 1.27 5.68 1:4
Marche eee eee aT 1.96 2.96 5.68 1:3
Aprilisciiivneirccincereseeae 7.26 10.50 14.49 11.77 1:1.5
May 6.85 5-79 29.59 25.33 1:4
ute Pi cceacc aie 1.25 1.75 10.66 II.40 1:7
hye cis avererarnsc coisre tints : 78 1.95 4.74 8.50 1:5
AUC USE erasers hte 77 2.51 6.19 58.12 1:20
Septemberereseeeeeeree Mi 2.39 5.37 47.25 ky,
Octoberanise. ceases. .69 3.05 10.64 “27.68 1:10
INoyemberseeeeeeeeene 23 2.64 6.39 41.57 1:17
Decemberseeeeeeeee ree 63 3.76 3.08 2 .96 1:6
Gr’d av. of monthly av.. 7/8 3.16 8.26 22.35 1:6

On this basis, the waters full of aquatic vegetation pro-
duce throughout the whole year less plankton than waters
free from such growths. Relatively few exceptions to this rela-

* This relation of vegetation to the plankton may be formulated as follows:
The amount of plankton produced by bodies of fresh water is, other things being

equal, in some inverse ratio proportional to the amount of its gross aquatic Vee
tion of the submerged sort.

PE IAPAA IAN AMES Darr tS Mh

ae
ae
ee
Aan
ae
ane
Ie
| *

Phelps Lake,-----

Quiver Lake,

Fic. D.—Seasonal distribution of plankton production in vegetation-poor and
vegetation-rich waters, based on the averages of the monthly averages for all years
of collection.
tion will be found in the individual collections recorded in
Tables V. and IX. and VI. and VIL., or in the monthly averages
of the table following page 342. This striking contrast is still
more enhanced by the statement of the monthly ratios of pro-
ductivity in waters rich and poor in vegetation. These range
from | to 1.5 in April to 1 to 20 in August. The fluctuations
in the ratio are of themselves very significant. During the
period from February to July inclusive the ratio is at its lowest,
ranging from 1 to 1.5 to 1 to 7. Excepting only the month of
July, this is the period of high water, in which the vegetation,
if present, occupies a much smaller proportion of the volume
of the lake, and is therefore to a proportionate degree restricted
in its effect upon the plankton. Under such flood conditions
these several localities are more or less merged in the general

486

overflowed district, and are to a varying degree traversed by
waters from the bottom-lands above and adjacent to them, and
the purely local factors of their environment, such as vegeta-
tion, thus become less potent. Again, it is not until the latter
part of this period that the vegetation attains the development
which continues throughout the remainder of the summer.
The relative barrenness (in plankton) of the vegetation-rich
waters is thus least striking when the vegetation is least in
evidence.

During the period from August to November inclusive the
ratios are very much higher, rising to 1 to 16 or 20. This is the
low-water period, when the vegetation in the vegetation-rich
lakes isat its maximum development both in quantity and in
the relative volume of the lake occupied by it. It is also at
such times that these several bodies of water are more distinct
units of environment, with their local factors no longer merged
by flood conditions. The relative barrenness of the vegetation-
rich waters is thus greatest when the vegetation is at its maxi-
mum development and is most emphasized as a factor in the
environment. The conclusion from this comparison of the mean
production of plankton in vegetation-rich and in vegetation-poor
waters in our locality is thus inevitable that vegetation (in the
usual sense of the word) is inimical to the development of an
abundant plankton. It may also be said that the contrast
would be considerably heightened if it were possible to elimi-
nate from all the collections on which this comparison is based
the adventitious organisms—such as small insect larvee, mol-
lusks, oligochetes, Hydra, etc., which form a considerable vol-
ume of many of our catches in the vegetation-rich waters.

On the other hand, it must be maintained that the vegeta-
tion is only one of the factors concerned in the phenomenon pre-
sented by this contrast. It is quite probable that other fac-
tors, especially the current, tributary waters, and the chemic-
al constituents of the water, affect the problemin hand. Dur-
ing high water both Thompson’s Lake and the Dogfish-Quiver
region are traversed by a considerable current from the bottom-

487

lands above. The elevated deposits of Spoon River and the
consequent crowding of the channel of the river to the east
bluff at Havana force all of the water of overflow (at stages
below about 16 feet) to seek the main channel. The configura-
tion of the low-lying bottoms above is ‘such (see Pl. II.) that
the lakes in question form natural channels for the movement
of a large body of impounded water. This movement is well
marked at stages above eight feet. So far as I am able to judge
from field observations, the current conditions in Thompson’s
Lake and the Dogfish-Quiver area are not greatly different.
The current continues in both lakes as levels fall to six feet, at
which level Thompson’s Lake loses its connection with the
river through the “cut road” (PI. II.), and movements in it
at lower levels are confined to those due to ingress and egress
of water through the slough, and are consequently inconsider-
able. On the other hand, Quiver Lake continues to be traversed
by the discharge from Quiver Creek, and our collections were
usually made in the channel in the vegetation. In Dogtish
Lake at low stages there ‘is no current traversing the lake.
Phelps Lake lies at so high a level that only the floods exceed-
ing eleven feet bring it into connection with the general cur-
rent of overflow, which in this case generally comes from
Spoon River. Below this level the only movement in its water
is the gentle one due to the receding flood. So far, then, as
the current is concerned, itis a common though not equally
distributed factor at high-water stages in all areas compared,
while at low water it is an important feature in the environ-
ment in Quiver Lake but is practically absent in the other
three localities. This fact undoubtedly accounts in part for the
barrenness of the waters of Quiver Lake (1.53 cm.’ per m.’, or
only .55 for the average of low-water periods—1. e. below 5 ft.)
as compared with those of Dogfish (4.22), Thompson’s (8.13) and
Phelps (19.44) lakes. This current does not, however, traverse
or appreciably affect the waters of Dogfish Lake, and their bar-
renness still remains for contrast with the productiveness of the
vegetation-poor waters of Thompson’s and Phelps lakes.

488

Data are not available for a full comparison of the chemic-
al constituents of all the waters here under consideration.
No data whatever are available for Dogfish and Phelps lakes,
and only sanitary analyses for Quiver and Thompson’s lakes.
These shed no light on the relative amounts of phosphates and
carbon dioxid in the water, both important elements in the
growth of plants. On the other hand, data for a comparison
of the ammonia and the nitrates are found in Tables XII. and
XIII. and Plates XLVIII. and XLIX. The nitrates, in so far
as they are concerned,—as shown in the accompanying table,

CHEMICAL ANALYSES, SEPTEMBER, 1897, TO MARCH, 1899.
AVERAGES OF ALL ANALYSES—PARTS PER MILLION.

Thompson’s Lake |Quiver Lake

Free am montaycy aa syne acreprtanmiess clociemievosen oars biztie Se .422 .199
AN ooaMbNONGl AieNNNONE, 5500090000090 00050000000 vA .546 .293
INIEGIGES AOR os rep cteaceeserey suet ee ACI) eRe ree .048 .023
INET ACES Hasta cranes ete rede cua cute ghee See ese sta ott ora .640 .708

which gives the averages for coincident periods of examination
in 1897-1899,—offer no solution for the marked contrast in
plankton production which the waters in question exhibit, for
the amounts present differ but shghtly in the two lakes. The
plottings in Plates XLVIII. and XLIX. show that the nitrates
run low during the period from June 1 to October 1, which is
approximately that of the maximum development of vegeta-
tion. The averages for this period are .244 and .222 respect-
ively for Thompson’s and Quiver lakes in 1898. This is almost
identical in the two lakes, and may represent an unutilized
minimum of nitrates, the utilized portion supporting predomi-
nantly the phytoplankton in Thompson’s Lake and the gross
vegetation in Quiver Lake. During the remainder of the year
the contrast between the two lakes in the matter of nitrates is
more marked, the average being .923 and .684 respectively. So
far as any contrast appears in the matter of nitrates the waters
of Quiver Lake are, if anything, a trifle richer than those of
Thompson’s Lake.

489

It is different, however, in the matter of nitrites, which are
about twice as abundant in Thompson’s Lake as in Quiver, and
the same ratio also holds approximately for the free and al-
buminoid ammonia. These are all substances indicating or-
ganic matters in the process of decay, or available for decay
and thus for plant nutrition. These data show clearly that in
these particulars the waters of Thompson’s Lake are much
richer than those of Quiver, and this difference is undoubtedly
one of the factors on which the contrast in plankton produc-
tion depends. The more abundant plankton of the former
lake may itself be one of the sources contributing to the or-
ganic decay here indicated.

This contrast in the chemical constituents in part at least
follows from the sources from which the waters in the two
lakes are derived. River water impounded from receding
floods and more or less charged with sewage and industrial
wastes constitutes the principal source of the water in Thomp-
son’s Lake. Spring and creek waters replace this very
slowly, and every rise in the river introduces a new supply
of richly fertilized water which at levels above six feet trav-
erses the whole lake. Quiver Lake is subject to like invasions,
but its more abundant supply of creek and spring water coun-
teracts their influence to some extent and soon replaces their
contributions.

A consideration of these other factors, current and chem-
ical constituents, makes it probable that they also are efficient
in causing the contrast in plankton productivity in the two
lakes. How much of this contrast is due to vegetation and
how much to their agency is a matter upon which conclusive
evidence is needed. Experiment in the field may yield con-
clusions that will be final.

Some evidence corroborative of my contention that the
vegetation of Quiver Lake is inimical to the development of
its plankton is afforded from two sources; (1) the examination
of Matanzas Lake, and (2) the comparison of the plankton pro-
duction of Quiver Lakein years of abundant and scant vegetation.

490

Matanzas Lake (PI. Il.) more than any other body of water
in our field of operations resembles Quiver Lake in the various
factors of its environment, only upon a somewhat smaller scale.
Like Quiver Lake it has free communication with the river at
all levels, is subject to the same conditions of invasion and
submergence, has an eastern sandy and springy shore with lit-
toral vegetation, a western one of alluvium, and, between, a
bottom changing from sand to mud. The depth and bottom
configuration are very similar, and there is a supply of creek
and spring water roughly proportionate to the size of the lake.
The two lakes are thus strikingly alike save only in the matter
of vegetation. The vegetation in Matanzas Lake is confined
to a narrow belt of the littoral zone along the greater part of
the eastern margin and to a little Ceratophyllum adjacent to it
and fringing the western shore in places. Less than 5 per cent.
of its area is thus occupied. Quiver Lake, on the other hand,
has at all times a more abundant flora, which even in the years
of its least development holds possession of not less than 30
per cent. of its area. Under these circumstances a comparison
of the production of the two lakes should throw some lght
upon the effect of vegetation upon the development of the
plankton.

No chronological series of collections has been’made by
us in Matanzas Lake. A few isolated collections have indicated
that it is rich in plankton, and two thorough tests of the local
distribution of the plankton, made in 1896, afford a basis for
comparison with Quiver Lake at that time. Fifteen collections
with the plankton pump were made in various parts of Matan-
zas Lake on July 9, and twenty-five, similarly distributed, on
August 14. The averages of the plankton per m.* of water in
these collections and the amounts found in Dogfish and Quiver
lakes on the days following (July 10 and August 15) are given
in the accompanying table (p. 491). Averages for the months
of July and August in the several years are also given for Quiv-
er and Dogfish lakes.

The production of plankton in Matanzas Lake on the dates

491

PLANKTON PRODUCTION IN MATANZAS LAKE COMPARED WITH THAT IN
QUIVER AND DOGFISH LAKES,

Date Matanzas Lake | Quiver Lake | Dogfish Lake
Bees lo bite ve es
RRR omen ee rg era
VS EU te ise cece EE ee
ee) ae an
Ree em onoml aca Aig ui) errr
ene re Mn nes <5 9 Yoana
Bee ee ge 2st

of collection above indicated is approximately twice that of
Quiver and Dogfish lakes, where vegetation was at that time
somewhat more abundant. In 1896 Quiver Lake was freer from
vegetation than at any other time in the period of our opera-
tions, and the contrast between the production of the two
lakes appears greater if we consider other years or the average
for all collections in the months named. On the latter basis
the ratio rises to 3 to 1 for July and 8 to 1 for August in the
comparison of Matanzas and Quiver lakes. In the case of Dog-
fish Lake the contrast is less striking, but still evident. Ma-
tanzas Lake, similar in its environment to Quiver Lake save in
the matter of vegetation, thus produces a more abundant plank-
ton, and we may infer that the vegetation of the latter is in-
imical to the development of plankton in its waters.

A second line of evidence bearing upon the question under
discussion is to be found in the production in Quiver Lake itself
under different conditions of vegetation. In 1894, and still
more in 1895, owing to low water in early summer, vegetation
was very abundant in Quiver Lake. The growth of Cerato-
phyllum and Elodea choked its waters from shore to shore and
from bottom to surface except in a narrow poorly defined chan-

492

nel found in the lower end of the lake. This part of the lake
is Shown in Plates XV. and XVI., which portray the conditions
as they appeared in 1894 and 1896 respectively. The upper end
of the lake and its western arm, Dogfish Lake, are shown in
Plates XVII. and XVIII, the latter having been photographed
in 1896, when the center of the lake was not so full of “moss”
as during the preceding year. The repeated floods of 1896
swept the lake of much of its vegetation, and during the three
following summers it never recovered the abundant flora which
it presented in 1895. In 1897 and 1898 there was also much
less vegetation than in 1895, though somewhat more than in
1896. The plankton production, as shown in Table V. and
graphically presented in Plates XXV.-XXIX., does not uni-
formly rise and fall as the vegetation decreases or increases.
The phenomenon of its fluctuations involves many other fac-
tors, among which the effect of vegetation may perhaps be de-
tected. The average production for the years of vegetation,
1.08 and .78 cm.’ per m.° of water, is surpassed in 1896 (2.59)
and 1898 (2.44) but notin 1897 (.88). The marked increase in 1896
over the production of 1895 parallels the great change in vege-
tation, and is also accompanied by higher water, theaverage for
the year being over three feet above that of 1895. This differ-
ence in levels also tended to decrease the relative extent of the
vegetation in 1896. In Dogfish Lake also the contrast in vege-
tation in the two years, 1895 and 1896, is well marked, and the
average plankton production rises from 3.25 to 5.01 em.’ per m.°
The omission of winter collections in 1895 makes the contrast
less striking. Allowing for this, it is probable that the plank-
ton production is practically doubled in the year of decreased
vegetation. This is approximately the ratio of increase in
Quiver Lake in 1896 and 1898. Other causes, such as current
and chemical conditions, doubtless share in producing this
change in the plankton, but it seems highly probable that the
reduction in vegetation caused a considerable part of this
doubling in the plankton production. A comparison of the
plankton production of the same body of water (Quiver and

» \ ha AA \
\) J Geet,
iy ‘ 493

Dogfish lakes) in different years thus shows that more plank-
ton is produced in years of little, than in years of much, vege-
tation, and tends to confirm the view that abundant submerged
vegetation is inimical to the production of plankton.

An inspection of the planktographs in Plates VIII.-XIII.
and XX V.-XLII. shows the frequent occurrence of an autumn
maximum, often well defined. In the planktographs of Quiver
and Dogfish lakes, this autumn maximum is usually depressed
or missing. The spring maximum occurs, as a rule, while
the lake is full of water from the general overflow, and it is
therefore not purely a local phenomenon. The midsummer
and autumn plankton, on the other hand, is entirely a local
product, and the depression of the autumn maximum must
be due to local influences. in 1896, in both Quiver and Dogfish
lakes the autumn maximum occurs in two or three sharply
marked prominences, that of October 14 (3.52 and 6.60) being
a Melosira-Syncheta assemblage, typical for the autumn season.
This was a year in which there was little vegetation and high
(for autumn) water, the vegetation being, consequently, at a
minimum as a factor environing the plankton. In other years
this autumn maximum (see Tables VI. and VII.) is less evident.
In 1894 the apparent maximum on September 5-6 is almost
wholly due to the development of Oscillaria at a time of local
stagnation consequent upon backwater. In 1895 there was in
Quiver Lake a maximum on September 6 (1.57), due in part to au-
tumnal plankton and in part to adventitious organisms. Dogfish
Lake exhibits a somewhat larger maximum (4.65) on Septem-
ber 17, which is mainly normal in its components. The No-
vember-December maximum of 1895 in this lake is wholly due
to adventitious organisms, and may be disregarded in this con-
nection. At their best, these maxima in vegetation-rich years
are but one half to one third the magnitude of those of 1896, a
vegetation-poor year. In Quiver Lake in 1897 and 1898 the
autumn maximum is again depressed almost beyond discern-
ing. Although vegetation was not abundant in the lake in
these two years, the period of the autumn maximum was one

494

of prolonged low water in both years, so that whatever vegeta-
tion was present occupied relatively a large proportion of the
area and volume of the lake, especially as contrasted with the
conditions in 1896. The available data thus indicate that veg-
etation is inimical to the production of plankton, as shown not
only in the general averages but also in these maxima, which
may be regarded as the expression par excellence of the produc-
tive capacity of the lake.

There still remains for consideration, with reference to the
effect of vegetation upon plankton production, the result of
our examination of Flag Lake. As before stated, this is a
marsh choked with a rank semiaquatic growth whose extent,
abundance, and relative occupation of the area of the lake
equals or exceeds that in any other body of. water examined by
us. If our thesis that vegetation is inimical to the production
of plankton be true, we might expect to find here, of all places,
barren waters. ‘This is not, however, the case; for,as shown in
the table of comparison of plankton production on page 429,
Flag Lake is very productive (11.46 cm.’ per m.’), being ex-
ceeded only by Phelps Lake (19.65).

The only indication that vegetation is in the least inimical
to the plankton in the lake is suggested in Plate XX XIII. The
amount of plankton present from May 15 to October 1, the
growing period of vegetation, is only 2.87 cm.’ per m.*, while
in spring and late autumn (April 1 to May 15 and October 1 to
December 80) it is 32.89. In Phelps Lake, which, save for vege-
tation, is much like Flag Lake, the plankton during the period
of dominance of vegetation in 1896 averages 7.64, and in 1898 |
52.43 em.’, 38 to 18 times as much as in the vegetation-rich
waters of Flag Lake.

In the character of the vegetation in Flag Lake hes, I be-
lieve, the explanation of its fertility in plankton. Two kinds
are predominant, neither of which is present in like abundance
in Quiver Lake. These are (1) succulent vegetation, such as
Sagittaria, Pontederia, Nymphea, and Nelumbo, which die down
and undergo considerable decay in the early fall, and (2) the

495

emergent vegetation, principally Scirpus, which, on account of
its growth and structure, does not reach an advanced stage of
decay until ice and winter floods have broken it down. With
rising spring temperature it yields to decay and releases a great
store of nitrogen which the phytoplankton can utilize. Both
of these types of vegetation are rooted in the humus and allu-
vial deposits of the lake,and both are to some degree emergent.
They thus draw their supply of food (dissolved salts and gases)
largely from soil waters and the air, and less from the supply
in solution in the water of the lake. The submerged and non-
rooting vegetation (Ceratophyllum and Elodea) is not abundant
in Flag Lake, so that the food supply in the lake waters is not
drawn upon to any great extent by the aquatic vegetation, and
it thus becomes available for the phytoplankton, which, in
turn, supports’the zoéplankton. The products of decay of the
succulent and emergent vegetation, on the other hand, are in
large part released directly into the lake waters, and at times
(fall and spring) when the plankton reaches its greatest devel-
opment in this region. Owing to its character and to the pro-
tected situation of the lake the vegetation is never swept away
by floods, nor is the lake traversed by any marked current as
are both Thompson’s and Quiver lakes. The fertilizing effect
of the decaying vegetation is thus more localized in this region
than in the other bodies of water examined by us.

The data from Flag Lake thus throw light upon the effect
of emergent and rooted vegetation—which is typically of the
httoral type—upon the plankton. They indicate that this kind
of vegetation favors the development of the plankton by add-
ing to the food materials in the water, while at the same time
it does not to a large degree compete with the phytoplankton
in the consumption of the food thus released by its decay.

In 1896 a series of examinations of the local distribution
of the plankton in Quiver, Matanzas, and Thompson’s lakes was
made by the pumping method, and since the collections were
made in the areas of vegetation as well as in the open water
they might also be examined to determine, if possible, the effect

496

of vegetation on the distribution of the plankton. Only the quan-
titative data are at present available, and the results are con-
flicting. In some cases the plankton is greater in the vegeta-
tion than in the adjacent open water; in others the reverse is
true. These examinations were made at times of unstable
river levels, and the movements of water consequent thereupon
make any satisfactory analysis difficult. The general conclu-
sion that lakes full of vegetation (Quiver) are everywhere
poor in plankton, while those relatively free from it (Thomp-
son’s and Matanzas) support generally a more abundant plank-
ton is in all cases upheld by these examinations.

This poverty of the plankton in vegetation-rich lakes was
one of the surprises of our. investigations, and, so far as I have
been able to ascertain, it contradicts the general expectation
among observers of aquatic fe. It has its parallel in the pau-
city of life in tropical forests and among the pines and red-
woods of the Sierras. It is fundamentally a problem of nutri-
tion, and inheres in the utilization of the available food supply

_by a single type, or a few types, of plants which do not them-
selves in turn afford support for an abundant or varied animal
life.

Wherever the depth of the water, the currents, the winds,
or other factors, prevent the development of a submerged
aquatic flora, the nutrient materials for plant growth—the oxy-
gen, the carbon dioxid, the nitrates, phosphates, sulphates, and
carbonates dissolved in the water—are utilized by the phyto-
plankton, which, in turn, supports the zoédplankton. The en-
tire production of such a lake takes the form of plankton and,
in turn, of those larger species, insect larvee, mollusks, and fish,
which are directly or indirectly supported by it. When, on the
other hand, the conditions are such that a submerged non-
rooted aquatic flora obtains possession of a lake,—as, for exam-
ple, Ceratophyllum and Elodea in Quiver Lake,—these nutrient
materials are appropriated by it to the great reduction, even
practical exclusion, of the phytoplankton. In the struggle
which must ensue between the phytoplankton and the sub-

497

merged aquatic flora for the possession of a body of water
capable of supporting either, the greater duration and perma-
nence of the larger plants which constitute the submerged
flora must in the long run inure to the advantage of the latter,
hence they predominate over the phytoplankton wherever
other conditions favor their appearance. This coarse sub-
merged vegetation cannot in its living condition be utilized by
the minute organisms of the zodplankton, and only such as
feed upon it in decay can find sustenance in the vegetation-rich
lake. The absence of an abundant phytoplankton and of the
greater part of the zodplankton may thus be accounted for in
waters rich in submerged and non-rooted vegetation. The
total production of such a body of water consists mainly of a
large amount of coarse aquatic vegetation, which but few ani-
mals can utilize in its living condition as food, and a much re-
duced plankton, largely of animal constituents, together with
such larger and often attached species as find food in these
elements.

Some light on the relation of vegetation and plankton to
certain of the chemical constituents of the food of the aquatic
flora can be gained from a comparison of Plates XLV., XLIX.,
and L., and Tables X., XII., and XIII., which show the results
of analyses in 1898. The appended table also gives the average

AVERAGE OF ALL ANALYSES—PARTS PER MILLION.

Station Free Ammonia Nitrates

June 1 to Octo-| Remainder jJune 1 to Octo-| Remainder

| ber I, 1898 of year ber 1, 1898 of year
|
Thompson’s Lake...... .154 457 244 684
@uiver Lakes... 25.2... | .024 199 R222 923
Illinois River........... 566 786 .297 1.036

amounts of free ammonia and nitrates in Illinois River and in
Quiver and Thompson’s lakes in the period from June 1 to Oc-
tober | and in the remainder of the year—two periods which
approximately represent the times of maximum and minimum
of chlorophyll-bearing organisms.

498

A comparison of these two lakes indicates more nitrates in
Quiver than in Thompson’s (.68 to .53 parts per million)—a
phenomenon which may be explained by the proximity of the
former to the river and the greater invasion by its richer (.81) wa-
ters. In the matter of free ammonia Thompson’s Lake is much
the richer (.352 to .138 parts per million), though it falls con-
siderably below the river (.95) in this particular. The striking
feature of the diagrams and tables is the marked reduction in ~
nitrates and free ammonia during the period of growth, from
June 1 to October 1, in both lakes as contrasted with that of
quiescence, from October 1 to June 1. The former period is
one of higher temperature and less flood water, thus favoring
the process of decay and the concentration of its products. The
marked decrease in both the free ammonia and nitrates during
this period may be explained by the utilization of these prod-
ucts of decay by the chlorophyll-bearing organisms, which
presumably are much in excess of those of the colder period.
In Thompson’s Lake the phytoplankton would be the principal
consumer, while in Quiver Lake submerged vegetation assumes
this role. The uniformityin the nitrates throughout this period,
and the reduction to a similar amount (about .2 parts per mil-
lion) in both lakes are significant of some sort of an equi-
hbrium between the supply furnished by decay and its utiliza-
tion in the growth of plants. This phenomenon of reduction
of nitrates to a summer equilibrium is to some extent manifest
in the analysis of soil waters (see Palmer, ’97), and may in like
manner be attributed to utilization of the nitrates by vegetation.

At first thought the volume of submerged vegetation seems
large in comparison with that of the phytoplankton, which it
replaces; but when the permanence and persistence of the con-
stituent cells of Ceratophyllum are contrasted with the many
generations of the alge and diatoms of the plankton which
arise during a season’s growth, the difference is less evident.
Furthermore, a much greater proportion of the cells of the
phytoplankton contribute directly to the growth of the animal
hfe of the lake.

499

The submerged vegetation—such as that found in Quiver
Lake—affects the conditions of nutrition in other ways than
those above indicated. The absence of roots and the slight
hold which its lowermost stems can obtain upon the soft bot-
tom facilitate its removal by floods and seines, and the nutri-
ment stored in its tissues is thus taken from the lake, and its
waters are impoverished to that extent. Again, both Cerato-
phylum and Elodea are perennial, continuing beneath the ice
from year to year and never wholly yielding to decay. The ht-
toral vegetation of Flag Lake, with its large annual growth and
well-marked periods of decay in autumn and spring, contrib-
utes more generously to the enrichment of the water. Thus,
while robbing the water of its food material, the submerged
vegetation often fails to make equivalent returns.

The submerged vegetation also interferes with the free
operation of certain other factors which affect the plankton of
open water. It shuts out the sunlight, and effectually modi-
fies the temperature thereby. Thus, on a midsummer day the
water in Thompson’s Lake rarely shows a difference of more
than three degrees (Fahr.) between surface and bottom in
two meters of water. In the vegetation, on the other hand,
the temperature contrast is much greater and within much
narrower limits. On July 15, 1897, when surface waters were
at 88.2°, the temperature was but 80° at 15 cm. below. The
diurnal range of temperature is thus much less in vegetation
than in open waters. The growing portion of the submerged
vegetation is usually at or near the surface, while the deeper
portions are older and often moribund. This vegetation thereby
enjoys the full benefit of the sunlight, so essential to the growth
of chlorophyll-bearing plants, while its occupation of the water
—especially at the surface—shuts out the light to a consid-
erable degree from the more open deeper waters, and in this
way adds another effective barrier to the growth of the phyto-
plankton in surrounding water.

The dense growths of the Ceratophyllum also interfere -with
the movements of the water,and thus tend to establish and

500

maintain local units of environment within a body of water.
Lakes full of vegetation, like Quiver Lake, exhibit greater
variations in the local distribution of the plankton than are
found in open ones, such as Thompson’s Lake. Greater differ-
ences in the component organisms also appear. The vegeta-
tion thus acts as a barrier, isolating differing assemblages of
organisms. Thus, in Quiver Lake in one instance local aggre-
gations or swarms of Volvox, of Copepoda, of Oscillaria, and of
Melosira were detected in the examination of the local dis-
tribution of its plankton. To this isolation by the vegetation
may also be attributed the considerable irregularity in the sea-
sonal fluctuations of the amount of plankton, which is some-
what more evident in the planktographs of Flag Lake (PI.
XXXII. and XXXIV.) and Dogfish Lake (Pl. XXX.-XXXII.)
than in those of other stations. Such fluctuations, for ex-
ample, as those in May, 1896, in Flag Lake, when the plankton
fell from 203.52 em.’ to 0.72 in 18 days, or the fluctuations in
Dogfish Lake in 1895, which do not seem to be correlated with
any fluctuating feature of the environment, may be referred in
part to the isolation resulting from vegetation and the modifi-
cations of food supply and reproduction consequent upon it.
The maximum-minimum contrast in Flag Lake was due to an
excessive local development of Bosmina followed by its sudden
disappearance. The cycle of changes in the succession of life
are thus accentuated, and run a more rapid course in the midst
of vegetation than they do in the larger unit of environment,
the open water, where minor differences are quickly merged by
the turmoil of current and waves.

The plankton catches made in vegetation-rich lakes usually
contain a larger proportion of littoral and bottom-loving spe-
cies than those from open water. There are the khizopoda—
often those with the heavier shells—the attached diatoms, cili-
ates, and rotifers, together with many bdelloid and Ploiman
rotifers not found in open water, the aquatic insects, both
adult and larval, the oligochetes, the smaller mollusks, Hyalella,
and Hydra. They materially increase the volume of the

501

catches recorded in the tables, and show in the plates of the
plankton of Quiver, Dogfish, and Flag lakes. The sessile or-
ganisms above named, with the Bryozoa, which often occur on
Ceratophyllum, avail themselves of the plankton as food. Hydra,
especially, increases when the plankton is more abundant. In
Quiver Lake on May 8, 1896, Hydra was taken in plankton at
the rate of over five thousand per m.’ of water. These organ-
isms which find a substratum and shelter on the aquatic veg-
etation must have some important effect on the plankton, and
their presence is doubtless one of the minor factors in the
suppression of the plankton in lakes rich in submerged vege-
tation.

The economic aspects of the question of vegetation in
bodies of water arise from the relation which it bears to the
production of marketable fish. Quiver and Thompson’s lakes
are both seined by local fishermen, and their relative produc-
tivity as fishing grounds may be expressed in the market value
of the leaseholds of the fishing privilege. Quiver Lake is so
blocked with vegetation that clearing it for seining is at times
an expensive operation, and this has a tendency to lower its
market value. Thompson’s Lake, on the other hand, is less
accessible, and some clearing out of the littoral belt of vege-
tation is always necessary before seining, the operating ex-
penses being thus somewhat increased. For years the lease-
hold of Quiver Lake has been purchased for a merely nominal
sum, not exceeding $100, and it has often lacked a purchaser.
Thompson’s Lake, on the other hand, has been, in recent years at
least, an object of increasing value, and brings over ten times
this amount fora portion of the lake only. Thompson’s Lake
has an area of about 1,200 acres, while Quiver has only 230.
Their market values are thus out of proportion to their re-
spective areas. Capt. J. A. Schulte, of Havana, whose knowl-
- edge of the fishing industry in the Illinois River is extensive
and accurate, estimates that in the same area Thompson’s Lake
will produce five times as much fish as Quiver, and production
of fish thus stands in somewhat the same ratio as the average

502

plankton production (1.75 and 8.26 cm. per m.*). The produc-
tivity of the lake full of submerged vegetation, is, it seems, less
than that of one free from it, whether measured in cubic centi-
meters of plankton or returns for marketable fish.

The data here presented concerning the inimical effect of
submerged non-rooted vegetation upon the plankton suggest
an interesting subject for field or laboratory experiment. In-
deed, experimental proof is desirable for the generalization
here advanced. How far it will find support in the examina-
tion of other localities remains to be seen, for no investigation
bearing upon the question seems to have been made elsewhere.
It should be noted that it is not maintained that all vegetation
is inimical to the development of the plankton, but only such
as successfully competes with the phytoplankton for the availa-
ble plant food, and thus brings by its decay no additional
sources for plant nutrition into the water. These conditions
are approximately realized where the submerged non-rooted
type of vegetation prevails. Where, however, by reason of the
local conditions or the nature of the constituent plants, the
aquatic vegetation adds by its decay to the fertility of the
water owing to its utilization of sources of food in the soil
and the air not available to the phytoplankton, we may expect
to find the development of the plankton fostered by such vege-
tation. These conditions are realized wherever rooted, and
especially emergent, vegetation prevails and contributes by its
decay. to the enrichment of the water. A belt of littoral vege-
tation of this sort may thus be of considerable effect in main-
taining the plankton in a body of water.

INTERNAL FACTORS AND PLANKTON PRODUCTION.

Under this head attention will be called to certain phases
of plankton production with which in the present state of our
knowledge no environmental factors stand in apparent corre-
lation. From this point of view, which lays emphasis upon the
reacting organism rather than upon the stimulating environ-
ment, most of the relations and adaptations of the plankton to

008

environmental factors might be treated under this head. But
this has not been my method nor is it now my purpose to
adopt it. ,

The phenomena of growth and reproduction of the con-
stituent organisms of the plankton, on the other hand, owing
to our ignorance of their controlling factors, can at present be
treated only under this head. The volumetric data in them-
selves contain little evidence bearing directly upon the prob-
lem, but in the light of the statistical results the fluctuations
in the plankton become dependent upon fluctuations in the
rate of growth, and especially in that of the reproduction of its
constituent organisms. These fluctuations are often concur-
rent, or, at most, shortly consequent, in many species at the
same time and in several different localities, and give rise to
the coincident volumetric pulses to which attention has so
often been called in the preceding pages. Somewhat regular
alternations of growth and rest, of fission and spore formation,
or of parthenogenesis and sexual reproduction, are funda-
mentally the basis of the cyclic movement in production. The
amplitudes, and to some extent the location and duration of the
pulses, are plainly affected by the various factors of the envi-
ronment discussed in preceding pages—by light, temperature,
vegetation, tributary water, various hydrographic factors, and
by food supply, and, possibly, also, by chemical conditions not
directly concerned in nutrition, but the available data fail com-
pletely to afford any satisfactory environmental factor or group
of factors which stands in correlation, even remotely obvious,
with this cyclic movement in production. | therefore class
this periodic growth, these sexual cycles which cause volumetric
pulses, under the head of internal factors. The element of
periodicity in itself does not seem to be consequent upon any
known external factor.

NORMAL REGIMEN OF PLANKTON PRODUCTION.

The records of plankton production in the Illinois River,
its tributaries, and backwaters, contained in this paper raise

504

the question whether there is in this fluviatile environment a
normal regimen of production. Is there in the course of pro-
duction an orderly sequence, of any sort, of sufficient stability
and of sufficient frequency in occurrence in successive years to
justifiy its designation as a normal regimen?

A cursory inspection of the planktographs in the plates, of
the data in the plankton tables, and of the table of monthly
means following page 342 reveals at once an apparent state of
chaos that accords well with the instability of most of the en-
vironmental factors of the plankton, notably the hydrographic.
For example, the production in the same month in different
years or in the different localities examined by us is exceeding-
ly variable. Taking at random the month of August, we find
that the mean production for this month in the years of exam-
ination ranges in the channel from .91 to 9.67; in Spoon River
from .002 to .652; in Quiver Lake from .22 to 2.46; in Dogfish
Lake from 1.11 to 3.91; in Flag Lake from .03 to 3.74; in
Thompson’s Lake from 1.08 to 19.40; and in Phelps Lake from
8.80 to 139.85 cm.’ per m.*; and, furthermore, that the extreme
range in these means—.002 to 139.85— is found coincidentally
in the same year, 1898 (see table following p. 342). This does
not afford a very satisfactory basis for predicting the probable
August production in cubic centimeters of plankton in any of
these localities. It is evident that there is little regularity in
the actual amplitude of production in a given season and locality
in successive years.

If the problem be approached from the standpoint of rela-
tive production in different localities at the same time, or in
the same locality at different times, more semblance of order
is traceable, though not equally so in all localities or in all
months of the year. The relative rank of each locality in mean
monthly production, as seen in the table following page 342,
is tabulated below. For example, in the case of the Illinois
River in the total of 51 monthly means there were 5, 6, 16, 12,
4,10, and 1, instances when its production attained first to sev-
enth rank respectively among the seven or less localities repre-

505

RANK IN PLANKTON PRODUCTION.

oe : Thomp- c

Illinois | Spoon | Quiver | Dogfish Flag »P- | Phelps

Rank River River Lake Lake Lake sea Lake

it so gd bOOBaaode 5 fe) 4 2 4 13 28
20.000 SCOOT 6 I. 2 2 II 27 4
$i COO OOOO 16 I 14 sf) I 8 I
(64 SR OUBCReE 12 I 14 8 5 3 I
Bo.od6 crocs 4 12 15 2 2 fo) I
OMe oe isicinas 10 5 4 | fo) fo) oO I
Foot OOSEEE I 8 fo) fo) fo) fe) fe)
Gil Sooeeane 51 28 53 24 23 51 36
Average rank 3.9 5.6 4 308) 2.6 B aly

sented in the months concerned.’ An examination of this table
shows that in relative production (see table following p. 342)
the localities tend to arrange themselves in a sequence which
isrepresented by the average rank. Asshown in the above table,
this is as follows: Phelps Lake (1.5), Thompson’s Lake (2.),
Flag Lake (2.6), Dogfish Lake (3.8), Illinois River (3.9), Quiver
Lake (4.), Spoon River (5.6). This is essentially the sequence
in relative production represented by the averages of all collec-
tions and of the monthly ‘means (see table following p. 342),
except that Flag and Thompson’s lakes are transposed. From
the points of view either of average rank or of average produc-
tion the relations of production in the 7 localities examined by
us are, it appears, essentially similar. A considerable measure
of stability in this respect may therefore be expected.

If we inquire if these relations in production expressed in
terms of rank are equally constant for all localities and at all
seasons, we find that there are departures from the average in
all localities, and that different localities show different de-
grees of stability of relative production varying to some extent
with the season. This appears in a comparison of the ranks of
Phelps Lake and the Illinois River in the table above given.
In the case of Phelps Lake (average rank, 1.5) 32 of the 36
months rank first or second, while in the Illinois (average rank,
3.9) but 28 of the 51 rank third and fourth. Obviously the
divergences from the expected rank in production are greater

506

in the river than in Phelps Lake. A further inspection of the
table indicates that Phelps and Thompson’s lakes and Spoon
River exhibit the most stable relations in productive rank.
It is in these bodies of water that we have found environment-
al conditions most uniform. In Flag, Quiver, and Dogfish
lakes the divergences in rank are much greater, and it is in
these localities that conditions of high and low water and of
vegetation afford sharpest contrasts. In the Illinois River
itself, where hydrographic fluctuations are most immediately
effective, we find apparently the widest divergences in produc-
tive rank. Even in these instances of greatest divergence the
tendency towards a certain rank in production in each locality
is sufficiently evident to warrant the statement that in the
main the relative rank in production in the several localities
examined by us is well established and generally maintained.

Still more pertinent to the question of the existence of a
normal regimen in production is the question of sequence in
the course of production in successive years and in different
localities in the same year. Do the planktographs form curves
which may be superposed in successive years in the same lo-
cality or in different localities in the same year? A single
glance at the plates which accompany this paper will suffice
to reveal the chaotic complex of lines which such a superposi-
tion would produce. There is no such unity or similarity if
we base the comparisons on the actual volumetric production.
If, on the other hand, we disregard coincidence in amplitude of
the curve and consider mainly the direction of the changes, sim-
ilarity becomes increasingly apparent. It rarely approaches
to the condition of complete parallelism, however, owing to
the great variety in the amplitude of production in various
years and localities.

If the data in the table following page 342 be analyzed with
reference simply to the upward or downward movement in
mean production from month to month and year to year in the
various localities, we find certain tendencies appearing which
may afford a basis for predicting the probable course of pro-

507

duction to a shght degree in the localities examined and in the
region as a Whole. The following table exhibits the instances
of upward and downward movement in the monthly means for
each locality for each month of the year.

DIRECTION IN MOVEMENT OF MEAN MONTHLY PRODUCTION.

Station Jan. | Feb. Mar. Apr. May June! July | Aug.| Sept.| Oct. | Nov. | Dec.

¢ ie je le Je oe Jp le Je le le ke
6 26 e16 26 ald a6 al6 al6 a5 a6 aS o16
aPA Pia Pa PAPA HA pA PIA PA PA PIA DP
ininpeis TRA ccs Guess CLO Duaeell POD Omar! Sea) laa) nes ey ma ne ei ea
Spoon River-......... ...... Wo eccAll| Ayaecclll) Ths 79) The eO}y aL al 1 all Weo--AD) Deen! aly ale ol Wee} Yona Il
Omivier Wale ts --- ee 2._...1) 0:....41 1 3 Om 4 Poor i O23) 4] BBB 23) Shoal) Sone) ale hh
Dogfish Lake __............ iLO} aL.) =, 2] ae 2 ol Pyoccollf SL gerd] Dbeeroeall] a _all iE goal) ab all) @5 27}
I ey ee UE eee ee HL AON Th) On 24 0.d (0). ‘A 74. 0) W 74) als all) 2 al © cect) Aen) teal
Thompson’s Lake. Prorccill| Bll} U8} O 4 Aa Gh) Soc Accel) Ane Sasol) Shoei) Gal
Phelps Waike --._-...-....:--. TeelO}) Whee 1.2) Oo 3; ee 2 Sc (D) tl, . 2), eA ik 0 HL, tll] © .-2)) a0
ANGIZTU esteem eters greece mere p 0 Weeeec Ba aa ba} 6...16) 1.19 8 Al WS scod 14._..9 12...12 12...12 13. .7)13.....8]10...11

This table, combined with the plottings of the averages of
the monthly means at each station, shown in Fig. E (p. 508),
indicates the following course in production which predominates
in our records. Production falls in January, begins to rise in
February, continues to increase in March, but only to a slight
extent though more generally. In April the increase is prac-
tically universal and more extensive than in any other month
of the year. In May the increase continues in the majority of
instances (11 out of 19), and more frequently (63 per cent.)in the
backwaters than in tributaries (50 per cent.). In either June
or July there is a decline to a lower level of production in all
localities. There is, however, considerable diversity in this
matter in the several years and localities (partially as a result
of imperfect records). This appears in the ratios of downward
and upward movement in June (15 to 7) and in July (14 to 9).
In the months of August and September there is a tendency
towards a higher level of production in some ofthe backwaters,
though on the whole the instances of rising and falling produc-
tion are equal in number. In October and November produc-

Or
=>
CO

MAR.| APR.| MAY [JUNE [JULY

Ht

oe ————————

a eve

Fic. E.—Planktographs of all stations, plotted from averages of monthly
means.

509

tion again drops to a low level, and this movement appears in
60-70 per cent. of the instances in each month. In December
the decline in production is checked, and in a few cases the
upward tendency reappears, only to give way again in most
cases to the January minimum.

There is thus a general seasonal regimen apparent in the
totals of all localities, and an approximately parallel seasonal
routine for each of the localities, the degree of approximation
varying with the locality and the season. Butthis regimen can
be outlined only in the most general terms, and is everywhere
subject to divergences that frequently reduce it well nigh to a
semblance of chaos—a condition arising from the instability of
this aquatic environment.

The course of production above outlined considers only the
movement of the average monthly production, and consequently
deals only with the larger and more general seasonal move-
ments. It masks almost completely the minor fluctuations,
and especially obliterates all consideration of the phenomenon
of pulses discussed in the treatment of the course of produc-
tion in the several localities.

It is inthis matter of pulses, or,in other words, in the cyclic
movement in plankton production, thatthe nearest approach to
a normal regimen appears in our volumetric data. I have
shown that wherever our collections were made at intervals of
a week, or less, this movement is generally distinctly traceable.
In the backwaters, where collections were usually less frequent,
the cyclic character of planktographs is still apparent, even in
fortnightly collections. This phenomenon is therefore, it seems, —
a constant feature of the movement in plankton production in
our waters as it appears in the purely volumetric data. Sug-
gestions of the occurrence of a similar movement in the plank-
ton of other waters may be found occasionally in the data of
other investigators, but nowhere, to my knowledge, is there at
present a chronological series of collections of sufficient dura-
tion and brief enough interval of collection for comparison
with the data presented in this paper. The main basis for the

510

emphasis laid upon the subject in connection with my discus-
sion of the volumetric data will be found in the statistical data
of Part II. of this paper. In this connection it may be noted
that the statistical data of other investigators lend some sup-
port to the probability that this cyclic movement in the plank-
ton will be found to occur in other localities as well as in those
examined by us. Instances suggesting this occurrence may be
found in the statistical data cf Amberg (700), Steuer (’01), and
the more recent work of Cohn (03).

This cyclic movement consists in the repetition of rise and
decline in production—a repetition broken in our records only
by the imperfection of our data. Wherever collections are of
sufficient frequency it is possible to trace it—sometimes, how-
ever, only with the aid of statistical data—continuously through
all the vicissitudes of changing seasons, of summer heat and
winter’s ice, of the vernal rise and autumnal decline in tem-
perature, and of high and low water. Moreover, it appears in
all of our localities whenever collections have been made with
a weekly, or even fortnightly, interval.

These pulses vary in duration from 2 to 7 weeks, though
the majority occur in limits of 83 to 5. Their amplitudes vary
greatly, and are plainly influenced by various environmental
factors. Their limits are also frequently modified by these
factors, though the evidence is not clear that any of the envi-
ronmental factors we have discussed are correlated directly
with the cyclic movement itself.

In the discussion of production in the backwaters the uni-
versal approximation in time of these pulses in the various
localities, or even their precise coincidence in many instances,
was recorded. The cause of this tendency toward uniformity
in the direction of movement in production in these various
localities at the same time is not apparent from the data at
hand. Contributory to it are the facts of a plankton largely
composed of the same species of planktonts, of a connection
and commingling of waters in all of the localities in flood con-
ditions, and of the operation of environmental factors com-
mon to all of the localities.

511

The normal regimen is accordingly not delineated by a
planktograph of marked definiteness in its course, but is one
formed by a sequence of recurring pulses of approximately a
month’s duration and varying amplitudes, low in winter floods,
rising with the temperature to a vernal maximum of consider-
able magnitude, often, but not always, declining during the
summer months, frequently rising again in late summer or au-
tumn, and in some localities and years to an extent exceeding
that of the vernal season, and falling with autumn tempera-
tures but increasing in stable winter conditions after the min-
imum winter temperature is reached,—such is the general reg-
imen of plankton production in the [llnois River and its back-
waters.

If this cycle movement in production be characteristic of
the plankton generally, fresh water and even marine, it must
follow that scattered and irregular collections, or those at in-
tervals exceeding a week or at most a fortnight, may fail en-
tirely to give an adequate representation of the course of pro-
duction or relative fertility of a body of water. Chronological
series throughout the whole seasonal range of climatic condi-
tions and at close intervals—of one week or less—are neces-
sary for any accurate delineation of production and fertility
of water by the plankton method.

SOURCE AND MAINTENANCE OF THE POTAMOPLANKTON.

The existence of a very characteristic and abundant plank-
ton in the Illinois River at once raised the question as to its
source and maintenance. We find at Havana a stream which
year in and year out carries by a burden of life, microscopic as
to its individuals, to be sure, but in the aggregate a volume of
surprising extent. This stream of life exhibits a routine of
seasonal changes in constitution and quantity which neither
flood, the ice of winter, nor the drouth of summer wholly inter-
rupts. It recurs year after year with a regularity which stands
in strong contrast with the fluctuations of the environment.
Although the water in the stream is subject to continuous re-

512

newal,—the channel from Utica to the mouth discharging in
from 5 to 25 days, according to the rate of the current,—the
plankton is continuously maintained, and the seasonal routine
is run in the face of this continuous renewal of the water.
Furthermore, the plankton product of the stream is discharged
at the mouth of the river practically in its entirety, for the or-
ganisms of the plankton cannot maintain their place in the
stream against the current. The only organisms of the pota-
moplankton which remain, are those used as food by fishes and
other animals which are not carried away by the current, and
such as may be lodged—usually in encysted, and thus heavier,
condition—along the bottom or banks of the stream. At times
of flood the receding waters leave some of the plankton side-
tracked in the reservoir backwaters—in the lakes, lagoons,
bayous, and marshes of the bottom-lands. As river levels fall
it may be slowly drawn off into the channel of the stream, or
cut off from connection with the river. This continual dis-
charge of the plankton, never to return, makes the problem of
the maintenance of the potamoplankton, quantitatively at
least, very different from that of the maintenance of the plank-
ton in a lake.

Three suggestions arise in explanation of the perennial
character of the plankton of the river: (1) The plankton en-
ters with the tributary waters, in which case the problem is
only removed a step; (2) it is autonomous, developing in the
stream while the waters are in transit, in which case the solu-
tion liesin the river andits environment; or (8) thetwo elements,
contribution and autonomy, are combined, in which case the
share of each will appear on a comparison of the plankton of
the river and of its tributary streams and backwaters.

The water in the channel of the river comes from three
sources; from springs and seepage along the banks, from the
impounded backwaters of the bottom-lands, and from tributary
streams.

RELATION OF SEEPAGE WATERS.

The contribution from springs and from seepage are incon-

518

siderable in comparison with that from the other sources.
Wherever the river encroaches upon the blufts, as, for instance,
below Havana, seepage areas of some extent and springs of
some size are to be found. Such banks, however, in immediate
contact with the main stream itself, are of very limited extent.
Furthermore, their contributions to the plankton are relatively
still smaller. These springy banks abound in life—planarians,
amphipods, isopods, oligochetes, and rhizopods, mainly limic-
olous species, which rarely leave their habitat to enter the
river with the spring water. Such springy banks, exposed to
midsummer’s heat during low water, do at times teem with
species common in the plankton. For example, a bank of this
sort on the levee at Havana was covered with a brownish scum
composed principally of Synedra acus, a diatom abundant in
the plankton at cooler seasons of the year. The temperature
of spring waters along the bluffs in midsummer is about 60°.
Elsewhere in the warmer waters of this springy shore are to
be found patches of green and red scum, where Huglena viridis
and EH. sanguinea were abundant, both species being common in
the plankton at that time. Tiny rills of cool water traverse
the oozy bank and carry stray individuals of these various
species into the river, but their clear waters are poor in com-
parison with the brown water of the stream which they join,
turbid with plankton. Their contributions are thus insignifi-
cant in amount and, while adding a trifle to its diversity, their
main action is that of diluents of the potamoplankton.

RELATION OF TRIBUTARY STREAMS TO CHANNEL PLANKTON.

The relation of tributary streams to the potamoplankton in
the channel of the Illinois is a much simpler problem than that
presented by the backwaters. Their contributions enter the
river in well-defined channels, and the areas of their respective
basins are an index to the quantity of water they bring to the
river. Their share in the formation of the potamoplankton can
thus be more readily tested and estimated. Under conditions
prior to the opening of the Chicago drainage canal the river

b14

‘received at Utica, the upper end of the basin under considera-
tion in this paper, the drainage of 10,365 square miles of catch-
ment-basin, over one third of the total basin of the stream, to
which was added at La Salle, a few miles below, the water from
the Illinois and Michigan Canal containing the sewage from
the Chicago River. A large volume of water, richly fertilized,
is thus provided for the reception of tributary streams, no one
of which, with the exception of the Sangamon, has more than
one ninth of the drainage basin above the point of its union
with the river. The Sangamon has at its mouth a basin
one fourth as large as that of the river above. This presence
of a considerable initial volume and the distribution of tribu-
tary waters in relatively small streams at intervals along the
course are conditions which favor the mingling of the constit-
uent waters of the stream and tend to maintain the uniformity
of the plankton in the main channel.

The tributary waters, with a few minor exceptions, such as
Quiver Creek, enter the main channel directly. The elevated
deposits built up across the bottoms by their agency confine
their floods within their banks except during the maximum
stages of overflow, when they contribute directly to the back-
waters, but even under these conditions a strong current is still
maintained along their customary channels directly to the
main channel of the river. Their contributions are thus, as a
rule, carried directly to the river and mingle with it without
any period of impounding, and their effect upon the plankton
is direct and immediate.

Two tributaries, Spoon River and Quiver Creek, were availa-
ble for examination at Havana, in both of which collections
were made by us which throw considerable light upon the
character and quantity of their plankton contributions.

QUIVER CREEK.
In Quiver Creek we have a small tributary with a basin of

only 220 square miles, largely of alluvial second bottom with
more sand.and less heavy loam and clay than the adjacent

515

prairies. Its waters are discharged into the upper end of the
eastern arm of Quiver Lake, and are impounded for a varying
length of time before reaching the river. No channel defined
by the configuration of the bottom traverses the lake, and since
its area is relatively large in comparison with the discharge of
Quiver Creek, the tributary waters are subject to considerable
impounding when the lake is free from vegetation. When,
however, vegetation is abundant, a fairly well-defined channel,
through which the discharged waters make their way with per-
ceptible movement, is kept open through the matted growths.
The impounding period is thus reduced for the channel water
under such conditions.

Collections were made in Quiver Creek, near Topeka, I11.,
above McHarry’s mill-pond, from September 1, 1896, to April
20, 1897, at intervals of ten days, by Mr. W. R. Deverman, who
kindly volunteered this service for the Station. A tow-net of
No. 20 silk was used, but no exact quantitative method was
adopted, so that these collections are available only for quali-
tative comparisons.

The catch consisted largely of silt in the form of quartz
grains and coarsely comminuted vegetable debris, with rela-
tively few plankton organisms.

The several catches were uniformly diluted, and the plank-
ton organisms counted in a uniform fraction of a cubic centi-
meter of the dilution from each catch. The various species
detected and their monthly averages in numbers are given in
the appended table. The figures have but slight quantitative
value, though they will serve to illustrate in a general way the
composition of the plankton and its seasonal changes, and will
also afford a sufficient basis for a comparison of the constituent
organisms of the plankton of Quiver Creek, Quiver Lake, and
the river, though not for a comparison of their relative num-
bers per cubic meter in each of the three situations.

The plankton of Quiver Creek, as shown in the table, may
be characterized as largely tycholimnetic, that is, composed of
littoral species, shore-loving and bottom forms. This is seen

516

PLANKTON OF QUIVER CREEK, SEPTEMBER, 1896, TO APRIL, 1897.

Species.
Alge—totals..
Closterium acerosum.
lunula..
gracile
Oscillatoria Sp...
Unidentified ..
WiatOmssgtotalse
Amphora..
Cocconeis communis.
Cyclotella.......... .....--
Cynatopleura solea.
Diatoma vulgare...
Encyonewa.______...

Meridion circulare..
Navicula spp.......
Nitszchia sigmoides, _

Pleurosigma angulatum...

Surirella ovata
splendida.-
Synedra acus..
ulna.......
Unidentified...
Rhizopoda—totals...
Arcella angulosa.
discoides..___.
vulgaris. ......
Centropyxis aculeata
ecornis
Cyphoderia ampulla..
Difflugia acuminata..
acuminata bifida.
coustricta....
globulosa
Spee
Gromia s
Trinema enchelys
Mastigophora—totals...
Eudorina elegans... J
Phacus longicauda.........
Synura uvella_.__.............
Trachelomonas hispida -
Unidentified
Rotifera—totals___...
Cathy pna luna...
Colurus obtusus.
Conochilus sp.
Distyla spp.-_.......-
Mastigocerca sp...
Metopidia solidus.
Notholca jugosa......
Philodina megalotroch
Rotitey actinurus.

Unidentified.
Rotifer eggs
Entomostraca—totals ...
Cyclops serrulatus..
Nauplius.........-.....
Ostracod......-.....
Miscellaneous—totals..
Chironomus larva...
Unidentified insect.
Insect egg.__.....--.-
Unidentified egg..
Unidentified

Sept. Nov. | Dec. | Jan. | Feb.

Mar.

Apr. |Total

52

Total number of species........
Total number of individuals.

22

781 i 2

*Estimated.

tEgegs only.

19

61

_

ms
POE SROUNNNANENNOA

517

in the predominance of the diatoms, the Rhizopoda, and Chiron-
omus larve, and in the character of the few rotifers present.
It is also evidenced by the erratic distribution and often small
numbers of many of the species occurring in the creek waters.

There is little evidence in the data of marked seasonal
changes. The diminished number, both of species and individ-
uals, in the winter and spring months is due in part to the
flood conditions prevailing at that time. The disappearance
of the desmids in the colder months is apparent, as is also the
decline in the diatoms, the effect of which is heightened by the
greater proportion of dead and moribund individuals in the
winter months. There is also some shght evidence in the ta-
ble of a spring increase in March and April and of a late au-
tumn maximum in November. From conditions observed in
Spoon River and Quiver Lake during the summer months not
included in the period of our Quiver Creek collections it seems
probable that the plankton of this stream at that season of the
year is more diversified by the addition of flagellates and rotifers.
The flow of the stream is, however, much reduced at this sea-
son, and its contributions correspondingly small in quantity.

The inter-relations of this creek plankton are very patent.
The diatoms are the predominant members, having one third
of the species and nine tenths of the individuals. The rhizo-
pods include one fifth of all the species and almost two thirds
of the animal individuals. We have here a rich diatom flora
supporting a rhizopod fauna. The remainder of the species,
about one half, belongs to diverse groups and is numerically,
at least, an insignificant element in the plankton assemblage,
constituting but 4 per cent. of the total population.

A comparison of the plankton here delineated with that
of the river at the same seasons of the year leads to the follow-
ing conclusions :

1. The creek organisms all occur in the river plankton.

2. The facies of the river plankton is quite different from
that of the creek in that it has a greater abundance and variety
of organisms, a greater proportion of limnetic species, and a

518

much greater proportion of limnetic individuals, with a cor-
responding decrease in the relative numbers of the littoral in-
dividuals. This is very apparent throughout the whole season
covered by the collections. Thus in autumn months, when
Melosira, Synura, the ciliates, Syncheta, and various Brachi-
onide characterize the potamoplankton, we find them but
sparingly represented, or, as in the case of Syncheta and the
ciliates, wholly absent from the creek plankton. So, also,in the
winter months Brachionus dorcas and Cyclops bicuspidatus, so
characteristic of the river plankton, form no part of the popula-
tion of the creek. The perennial and abundant Polyartha
playtyptera was at no time found in the creek. That limnetic
species are not wholly absent from the creek is shown by the
presence of Melosira, Synura, Notholca jugosa, Eudorina, and
Trachelomonas, but their occurrences are isolated and their
numbers few. The creek is thus not a center of distribution
for such planktonts as these, their presence and numbers in
the river being practically independent of their appearance in
the tributary.

The abundance of diatoms in the creek waters suggests
that these may find centers of distribution here. Most of the
species, however, are quite as abundant in the river, with the
exception of the Surirellas. These are present in small num-
bers in the potamoplankton, and are often moribund.

3. The creek waters act as diluents of the potamoplank-
ton. The character of the Quiver Creek plankton and the
quantitative studies on Quiver Lake support this view.

The contribution of Quiver Creek to the potamoplankton
is thus largely of littoral species and of small quantity, and its
effect is that of a diluent of the potamoplankton.

The following table, which gives the relative number of
species in the plankton of Illinois and Spoon rivers and Quiver
Creek, demonstrates the small number of species found in the
creek, and the monotony of its composition as shown in the pre-
dominance of the Rhizopoda and the diatoms. The relative pau-
city of the Mastigophora in its fauna may be due in part to the

519

RELATIVE NUMBER OF SPECIES IN THE PLANKTON OF QUIVER CREEK AND SPOON
AND ILLINOIS RIVERS.

Quiver Spoon Illinois
Group Creek River River
PM ACetOCalSese aan onset evbae<cteiactien ani: 25 34 74
SOMO OV MKESES 5650000080 0000000000 6000 I 4 Il
Chlorophy.ceae rages eee aciere cncoeie a I Il 3°
Bacillaniaced ts mcaciaene cue ke wea 20 14 25
Comjpucal cnet een ae eee. B 5 iS)
PROOZOE =O giao dae bose Ocoee ae eene 18 63 154
IND Zopodacetsa. caters see eae tice 13 17 30
ISI@)VOAOE Re obodh loa eaoda DAA EC MET ees O fe) 4
MAST RODNOR coon ccce00o000 sn000nobee 5 28 62
Ciliatawienes fos tat ele ae Oo 16 55
SUCtonianeee fo) 2 5
HNotitera——totals) ooh;5 cessenorsisusinie weiiea wise ee II 44 107
PRU IZ Ot algee ee erste ae ee atone ccs eatsie di caraiac acter et: I I
BS dellordamep titer eerie ae oieao aks 3 4 6
IPUOIOOEWS 6 rd po do eon OC ee eon oO ee y | 39 95
Grustacea— totals) o..20.ceyss cscs ascent cent xc 2 13 49
Copepoda Nan sania e asin snineteletise See aie 6 I 5 17
Gladocerae ene Weert aNore Goa Oo 7 26
Ostracodane street sexteoeosiueare elon I I 3
Other! Grustaceal -josc/ecie. «asics cee lee fo) fo) 3
Wiscellaneous-—totals se eneeess seen. Vole 4 16 45
MtiSectwlanviceaare rita cme lice ieee I 5 6
Otherforms)-e cae se. oe ee emote 3 II 39
Wofiall IN@ SJOGOIES Sous seudoococscgnebo odes | 60 170 429

method and season of collection. The meager representation
of the Ciliata may be due to the absence of sewage contamina-
tion and hence of excessive bacterial development in the creek
waters. The food supply of many species is thus lacking. The
absence of a well-developed phytoplankton, aside from dia-
toms, and the fact that much of the vegetable debris of the
silt is only in the early stages of decay may account for the
small number of species of Rotifera and HEntomostraca, groups
which in part depend upon these sources of food either directly
or indirectly. The recent origin of the creek water from rain,
or springs and ground seepage, affords insufficient time for the
breeding, not only of these organisms which form the more dis-
tant links in the chain of food relations, but also for many of
the nearer ones, such as the alge, which subsequently do ap-

.

520

» pear in large numbers in the creek waters after they mingle
with those of the impounding bottom-lands or the slowly moy-
ing current of the main stream.

No chemical analyses have been made of the water in
Quiver Creek, but those made of samples taken at our plankton
station in Quiver Lake are in a measure applicable to the creek
itself, especially at low-water stages. In Table XIII. are data
derived from weekly analyses from September 24 to December
3, 1895, and fortnightly analyses from October 19, 1897, to
March 28, 1899, made by the Chemical Survey. A summary of
the averages will be found in the table on page 521. These
show a smaller amount of residue on evaporation in the lake
(268.9) than in the Illinois River (867.5), which may be due in
part to the deposition of suspended silt owing to the impound-
ing action of the lake and to the sandy nature of the catch-
ment-basin. The loss on ignition is somewhat less, and the
oxygen consumed very much less (5.9 to 10.4), in the lake than
in the river, indicating a smaller amount of organic matter
in the former. The small amount of chlorine (4.8 to 21.6) ex-
hibits the freedom of the iake from sewage contamination.
The albuminoid ammonia, representing undecomposed organic
matter, is also present in small quantity in the lake as com-
pared with the river (.25 to .48), while the free ammonia, indic-
ative of the first stages of decomposition, is still less (.165 to
.860). The nitrates, the final products of decomposition, are
not at all abundant in the lake (.66 to 1.58).

The lake waters, and by inference the tributary creek
waters also, are thus deficient, as compared with the river, in
organic matters and the products of their decay. These prod-
ucts are fundamental constituents in the nutrition of the phy-
toplankton, which in turn supports that part of the zodplank-
ton which does not depend upon the organic detritus in sus-
pension for food. The chemical condition of the water of
Quiver Creek is thus unfavorable to the development of a
plankton quantitatively as great as that of the river. Further-
more, its waters, poorer in the plankton itself, not only dilute

rn

521

the plankton of the river, but even diminish the productivity
of the river water by lowering the relative amount of its nutri-
ent constituents. ;

SPOON RIVER.

In Spoon River we have a typical tributary of the larger
type, from prairie country, with no unusual contamination by
sewage or industrial wastes, draining 1,870 square miles, a little
more than one tenth of the basin above its mouth, and dicharg-
ing directly into the main channel. :

A detailed discussion of the environmental conditions in
this stream and of its plankton production will be found on
pages 340-350. It will suffice in this connection to recall the
facts that the recent origin of the tributary waters, its greater
turbidity, and burden of silt, all militate against plankton pro-
duction in this tributary.

A consideration of the chemical conditions in Spoon River
and in the Illinois throws much light on the nutrition availa-
ble for the support of the plankton in tributary and channel
waters, a very important factor in the matter of plankton pro-
duction. In the following table the averages of all analyses
ip these two streams and in Quiver Lake are given.

CHEMICAL EXAMINATION OF WATER FROM THE ILLINOIS RIVER AT HAVANA, FROM
SPOON RIVER NEAR ITS MOUTH, AND FROM QUIVER LAKE—PARTS PER MILLION.*

Spoon Illinois Quiver
River | River Lake
Diesen SPEAR e758 |, 205%
Residue on tees 167.0 | 304-1 248.2
evaporation|Loss on | Total ........ 41.9 32.8 27) 0
ignition | Dissolved..... 24.4 25.1 25.6
Ciolloritnie’ esas seecnBaceeme cere rtne cries 3.8 21.6 4.8
Oxy ceniconsumed pean seats eee: woe 14.1 10.4 5-9
(@iiteewammioniaeeeee eee eee 124 86 165
| Albuminoid ammonia .... .60 48 £25
Nitrogen as{ Total organic............. 1.29 1.03 61
JMINAGEITE Sey ae genyctene tate oy ers -039 .147 .023
(ONitnatess te iste cece I.o1 1.58 .66

*Data from Tables X., XI., and XIII.

522

It is noticeable that Spoon River carries the largest amount
of matter in suspension, both absolutely and relatively, as
shown by the high total residue on evaporation (522.3 to 367.5
and 268.9) and by the smallest amount of the residue in solu-
tion (167.1 to 804.1 and 248.2). This is further shown by the
fact that the solids removed by the army filter in Spoon River
average 1,755 cubic centimeters per cubic meter to only 592 in
the same year in the Illinois. The large amount of organic
matter undecayed and undissolved, and therefore not available
for the support of the plankton, is partially indicated by the
high oxygen consumed (14.1 to 10.4 and 5.9), the high albumi-
noid ammonia (.60 to .48 and .25), and the high total organic
nitrogen (1.29 to 1.08 and .61), when considered in conjunction
with the small amount of residue in solution. On the other
hand, the waters of Spoon River are quite deficient in forms of
nitrogen more available for the phytoplankton, the free am-
monia (.24), nitrites (.039), and nitrates (1.01) being in each
case less than in the Illinois (.86, .147, and 1.58), while the
chlorine (3.8), an index of sewage contamination, is less than
a fifth of that in the channel (21.6).

Spoon River has therefore great resources, in so far as or-
ganic matters and the products of their decay are concerned,
for the support of the plankton. Not all of the matter is in
solution for immediate utilization, but there is still sufficient
for a large plankton development, time for which has not been
allowed in the tributary stream. The immediate effect of the
access of the contributions of Spoon River to the channel is,
in the average, a dilution of its inorganic nitrogen per m.° of
water, which is in some unknown measure made good by the
contributions of silt, in part of organic origin. The net result
is, of course, a large addition to the total resources of the chan-
nel waters available for the present and future development of
the plankton.

The amount of nitrogen in its several forms which Spoon
River carries is not small as rivers go, for this stream drains a
plain unsurpassed in fertility by any other part of the catch-

523

ment-basin of the Illinois. It also receives a moderate amount
of sewage from the cities of Lewistown and Canton, and the
drainage from a considerable number of towns. Its diluent
effect upon the plankton of the Illinois is thus not due to the
poverty of its own waters but rather to the excessive fertility
of the main stream, a fertility resulting from the sewage and
industrial wastes received by that stream from the cities of
Chicago and Peoria.

The contrast in fertility as indicated by the analyses tabu-
lated above is not as great as the differences in the plankton
production of the two streams. The ratio of nitrates which
perhaps most fully expresses their relative fertility is 1.01 to
1.58, while the ratio of the plankton production as expressed
in the average of the monthly means of the catches by the
silk-net method is 0.256 to 2.71. The failure of Spoon River to
develop a more abundant plankton is thus apparently due to
some other cause than the lack of nutritive elements in the
water for the support of the plankton. The development of a
considerable volume of plankton in it at times of low water
and slack current makes patent the probability that the lack of
time for breeding is at least one of the important factors in the
relative paucity of the plankton of this tributary stream.

QUANTITATIVE COMPARISON.

A comparison of the quantities of plankton taken by means
of the silk net in the two streams affords a fair contrast of
their relative productivity. Certain sources of error are, how-
ever, present in the data of comparison, and as they are not
equally distributed in the case of both streams they invalidate
to some undetermined extent precise comparisons. These
sources are the leakage of the plankton through the silk and
the presence of silt. The plankton escaping through the silk
is largely made up of the Mastigophora and small diatoms and
alge, and they are found alike in both streams. The presence
of a more abundant plankton in the Illinois and the somewhat
flocculent nature of much of its silt tend to induce more per-

524

fect filtration and to check shghtly the leakage of small
organisms through the silk. In Spoon River, on the other
hand, the plankton is scant and the silt mainly of tine loam
and clay in suspension, so that the silk net rarely clogs and
the escape of small planktonts is but slightly impeded. This
loss by leakage is far more significant in the case of Spoon
River than it is in the Illinois, for the escaping plankton con-
stitutes a relatively larger proportion of Spoon River’s total
product than an equally large or even greater loss would form
of the total product of the [lhnois. Again, the quantity of
silt is both relatively and absolutely much greater in the waters
of Spoon River than it is in the Illinois, and it is of a different
nature. This greatly increases the difficulty of maintaining
any uniformity of standard in the estimation of the silt con-
tent of the plankton catches in the two streams. These sources
of error, although considerable, do not, however, invalidate the
conclusions here drawn regarding the relative productivity of
the two streams. They are still patent within any reasonable
limit of error.

The plankton of Spoon River is very much less than that
of the Illinois. The average amount present in a cubic meter
of water in Spoon River, as shown by the average of the
amounts in thirty-six collections made between August 18, 1896,
and March 7, 1899, is .465 cubic centimeters. This average
amount is reduced to 0.191 cubic centimeters if the two collec-
tions of September 11 and 30, 1897, are omitted. This average is
still more reduced if we omit the collections from the last of
August, 1897, to the close of the year—a period of exceptional
and prolonged low water. ‘The omission of these four months
lowers the average to 0.044 cm. per m.* of water, an amount
which more truly represents the normal contributions of the
tributary to the main stream in years of rainfall normal both
in quantity and distribution.

The average plankton content of a cubic meter of Ilhnois
River water, as shown by the average of 235 collections made
between June 12, 1894, and March 28, 1899, is 2.19 cubic centi-

525

COMPARISON OF MONTHLY MEANS OF PLANKTON PRODUCTION IN ILLINOIS
AND SPOON RIVERS, BASED ON ALL CATCHES.*

January | February March April May June

Near Ee ec ei es meen) Sean

(a4 a fa = jas a a4 a eo é a4 S

ue (eo) ss (o) ie ° —> (o) 228 > wis °

= ° = [e) = lo} = fo} = fe) = fo}

Ls Q, l= jor Le jor Ler Q. L—! Q. Lo OQ.

op) Nn n Nn 0) n
AGA” | [oer dh al ee peeetel load ena fo-c0- cael Spurs uel evcheae al cecaeeemesl i Sete times ease een OR ZAIE ccs
BOOS ay ifs ticle ltssecseers OOM Ls creeal i vaste hess iin to) Leer ere pee |e oot ee VO \lsooooe
HSI) OLOX ooboc O©-OA|osc00 OOo o000 Siiloo0e0e 1730 |Keaer Oni P> eamoct
TiSy ee aalerete nates 0.040.047] 0.380.007] 5.11] 0.048] 5.62/0.440] 0.27 | 0.250
1898 |0.45 |0.017| o 27/0 O16] 0.33/0.124] 4.40]...... II. 30/0.023) 3.96 | 0.006
1899 0.18 |o.005 0.810.001 0.280.026 RECA |Sroeaes RO | (to caesee (eec ic les acre eee
Monthly av.|o.213/0.011 0.23'0.021\ 0.27'0.052 4.59! 0.048 6.08l0.232 [EZZ OMS

July August |September} October | November | December

car Woe aos ce omen) sacle

m eI ce g m ro] ms r= = = me

= 2 = ° ao i) = ie) <i Qo = °

= ° = e} — eo) = fe) = fe) ram 9

St oy || = a || =! jy | = a = a = a

Nn Nn nN | 2 a n
Toy WS ATI MN Sone OLG\o5000 ooo 000 @sOii|loocc0a ®@sii@oo000 OO looooco
HIS {90%}. nono MOM ooo HoSAls coon O@sB7loocave SOAs c000 IGEN IG dexter
S10¥8) | oA Ne co oc I.12]0.018] 0.38/0.005] 1.11] 0.005] 0.02/0.005] 0.76 | 0.002
i&leyy Wee) |loooee 3.65/0.652| 8.83/5.130] 5.95]...... I.00|1.671| 0.56 | 0.599
18 0.58 |0.036] 0.91|0.002| 0.69/0.002] 0.24) 0.001 | 0.25/0.001| 0.99 | 0.001
RASS) |lo.6oSalldeto ce cllome col lowier.0l f-o-c'6 bl cron ol lee oes |ole Sas || 0-.08n| lo /ereecie || gree cron loner
Monthly av.!4.23 0.036! 3.88l0.224! 2.561.712 1.70 0,003! 0.8810. 559 0.71 | 0.201

*Amountsin this table are cubic centimeters of plankton per cubic meter of
water after subtracting from the total catch the estimated amount of silt.
meters. This is 4.7 times as much as the average of all the
Spoon River collections—11.5 times, if we omit the two
exceptional collections of September 11 and 30, 1897, and 44
times, if we exclude the low-water period of the autumn of
1897 from both averages. This latter ratio, 1 to 44, represents
the relative plankton content of the two streams except during
periods of prolonged and extreme low water. Even in such
low-water periods the waters of the tributary are less pro-
ductive than those of the main stream. For example, the aver-
ages of the monthly averages of production for July—October,
inclusive, in the two streams are respectively 2.89 and 5.78 cm.*

526

of plankton per m.2 In November and December, however, the
mean production in the tributary, for the only time in our rec-
ords, exceeds by 67 and 7 per cent. the production in the chan-
nel. On the average, however, production in the tributary,
even in most favorable conditions, is less than in the main
stream, and the contributions of the tributary continue to be
generally a diluent of the channel plankton.

If the means of the monthly averages are compared, the
ratio, when all collections are included, between production in
Spoon and I[llnois rivers rises from | to 4.7 to 1 to 10.6. This
ratio, which eliminates somewhat of the error resulting from
differences in the number of collections in the two streams,
probably represents more nearly the actual ratio of production
in the two streams derivable from our data.

In the table which follows, the catches in the two streams
upon coincident—approximately so in five instances—dates
only are averaged. This reduces the number of catches in the
Illinois River from 285 to 33, modifies some of the monthly
averages, and changes the ratios of production in the Illinois
and Spoon rivers, based on means of the monthly averages,
from | to 10.6 to 1 to 9.9, but does not otherwise materially
alter the relationship of production in tributary and channel
waters as determined on the basis of all collections.

If the silt is not eliminated by estimation the average
amount of the silk-net catch in the two streams is respectively
1.41 and 3.98 cubic centimeters per cubic meter. The change
in the ratio is due to the greater proportion of silt carried
by Spoon River.

In the table of plankton comparisons following page 342,
the averages of the amount of plankton per cubic meter of
water in the two streams 1s given by months for the years of
our operations. Decimals to three places are not here indica-
tive of great accuracy of measurement, They result from ef-
forts to represent the small proportion which the plankton
forms of the silt-laden catches from Spoon River. Considera-
ble differences in these small quantities in this table and else-

527

where in Spoon River tables have little significance save as
they express relative quantities in catches of chronological
sequence. Thus, in this table differences in successive months

have more significance than those in the same month of differ-
ent years.

COMPARISON OF MONTHLY MEANS OF PLANKTON PRODUCTION IN ILLINOIS AND
SPOON RIVERS, BASED ON COINCIDENT CATCHES.*

January | February | March | April | May June

al Pel 6 Vee eee eae ee eae

~ a a4 a 4 a ~ a 4 a a a

pas fo) ca) fo) exe fo) me fo) —S fo) ee fo}

= o) — fe) = 2} = ie) = fe) = je)

= je | = a on fay |) =! a. aa S || = a,
Nn Nn n n Ba eS
MSC OM | PRP | creer lsteecccvel licker sye ltt ehcp cearall ee cist cevectel| sistas all ass ancislleroe-ellisaerae Ilo die eicese
NSO Jie willie ca|s sis - 0.040]0.047| 0.380/0.007]5.110]0.048] 5.620]0.440|0.270] 0.250
1898 |0.470.0.017|0.100|0.016] 0.430/0.124].....]..... 10. 310/0.023|5.280] 0.096
IG) |O AAO) COS OUUCHO.COi) Oo HAOOOHA|o.cconllooeocllooccccllscccellbcocdllocooce
Monthly av.|o.345,0.011|0.083|0.021] 0 450|0.052)5 . 100.048 7.965|0.232/2.775| 0.173
July | August |September | October | November} December

seamen Re ee me UN a Med ae (ee

ms eS) oa g ce =| Be | m4 g m4 gE

= fe} = g =F fe} = 2} = 2 = 2

= fe) = lo) = ° = fo) = e} = fo)

= iy |S a. = a, | = a = fy | a
n | | a A | |B Bi, Coun
MSO Oleme | yete se| eet 0.68 |o.004) 0.380/0.005|1. 105)0.005] 0.020:0.005|0.765| 0.002
eoy/ Wee orl leeraee 2.02 |0.056/11.920!5.130].....|..... 0.665'1.671j;0.030| 0.599
1898 jo. 140|0.036/1 .620'0.002| 0.610/0.002/0. 170'0.001 ©, We OO eHss 0.001
SIG) ' ls oS:'al laa vane oherereroll Me.m eel lene oxeeal (eset bac [eleoktrces| esate Sousa Meee [eri lat sea
Monthly av.'o. 140|0.036 1.440'0.021 4.303 1.712|0.638'0.003 0.275 0.55910.685 0.201

*Amounts in this table are cubic centimeters of plankton per cubic meter of
water after subtracting from the total catch the estimated amount of silt.

A detailed comparison of the production of the two streams
by months has been made elsewhere (see pp. 340-350). For
the purposes of the present discussion it will suffice to call
attention to a few salient features found in the somewhat
irregular data of the table.

In but few averages does the plankton in Spoon River
equal in amount that of the Illinois. Not only is this true
of the monthly averages with but three exceptions, but

528

also of almost all of the single catches when comparison is
made of those taken in the two streams on the same day, or
on the nearest dates when they were not coincident. The ex-
ceptions are four, one in February, 1897, when flood conditions
prevailed in both streams and the amount of plankton in each
was small, and three in the autumn of the same year during
the period of prolonged low water. During this period the dis-
charge from Spoon River was very slight, the current scarcely
perceptible, and the temperatures somewhat higher than usual
at this season of the year, so that the tortuous channel of the
stream through the bottom-lands became practically an im-
pounding lagoon. A comparison of Tables III. and IV. and
Plates XI. and XVII. shows a general correspondence during
this period between the two streams in that the autumn maxi-
mum and winter decline are present in both, the maximum
being somewhat greater in the Illinois and the decline some-
what less pronounced in Spoon River. It was during the period
of this winter decline that Spoon River attained a somewhat
greater productiveness than the main stream. The autumn
rains of that year were long delayed and were largely absorbed
by the parched earth, so that the run-off was but slight, and
Spoon River was not subject to the repeated and often almost
continuous flushing which characterizes many autumnal seasons.
By reason of these unusual conditions Spoon River exhibited
at this time more of the environmental features of an im-
pounding backwater than those of a tributary stream, and in
these conditions lies the occasion of the unusual plankton pro-
duction manifested by the tributary at this season. As before
stated, the average for this low-water period was greater in the
main stream than in the tributary, though, as the data in the
tables referred to show, there was a period of about two months
in which the tributary directly increased the relative amount
of plankton in the main stream.

In other years than 1897, and especially in other parts
of the year, the contrast between the amounts of plankton in
the two streams is much more marked. In general it is most

529

pronounced during the spring and early summer at the time
of the plankton maximum. Save in 1897 the contrast between
the two streams is also well marked during the autumn maxi-
mum. ‘The phenomenon of these maxima is thus a function of
the main stream rather than of the tributary.

The great irregularities in the Spoon River plankton as
contrasted with the main stream are due to the more profound
effect of floods upon its life. In the main stream, floods less
frequently and less thoroughly replace its waters owing to its
greater volume and, especially, to its reserve of densely popu-
lated impounded backwaters. The small tributary, on the other
hand, is scoured very completely by every considerable rain,
and has no reserve waters to maintain its equilibrium. The
oscillations in the quantity of life in its waters are thus more
frequent and more extreme than in the main river.

The quantitative effect of the plankton of a tributary upon
that of the main stream may be expressed in the following
simple formula :

in which D and d represent the discharge from the catchment-
basins of the main stream and tributary, P and p, the plankton
per cubic meter of their respective waters, and P’ that of the
main stream below the junction with the tributary, I[n the
case of Ilhnois and Spoon rivers the average discharge is ap-
proximately in the ratio of the areas of the catchment-basins.
Both lie in the same storm belt, and the slightly increased rain-
fall in Spoon River basin, which is the more southerly, is more
than counterbalanced by the accession of water from the Illi-
nois and Michigan Canal due to the pumpage from Chicago
River at Bridgeport. Accepting these areas as a basis for the
ratio of discharge, we find that the average amount of plank-
ton in the IlJinois is reduced from 2.19 cubic centimeters per
cubic meter to 2.00 if the low-water period of 1897 is retained—
a decline of 9 per cent. If the low-water period is rejected
from both averages the amount falls to 1.96 cubic centimeters—

530

a decline of 11 per cent. These figures are based on averages.
Naturally in tributary floods the increased volume and les-
sened plankton will cause a much greater dilution, though of
brief duration. In moderate and low-water stages the decline
will be less than the above average and of longer duration.
The relative discharge of the two streams also enters to fur-
ther complicate the problem. But whatever form the ratio of
production of the two streams may assume in a precise determi-
nation, it is safe to say that the general conclusion drawn
from the present data will be confirmed.

QUALITATIVE COMPARISON OF PLANKTON OF SPOON AND ILLINOIS RIVERS.

The details of this subject, in so far as they pertain to the
constituent species of the plankton of the two streams, will re-
ceive attention in the discussion of species in the second part
of this paper. For the present only the general phases and
most striking contrasts will be discussed.

With a view to presenting in concrete form the contrast in
the relative population of the two streams I have prepared
Table XIV., which gives statistical data compiled from the
enumeration records. The table exhibits the number of indi-
viduals per cubic meter of water of the main groups of plank-
tonts in the thirty-five collections in Spoon River, and in simi-
lar collections made on the same date in the Illinois River. In
a few cases only, the Illinois River collections were made sev-
eral days prior or subsequent to the Spoon River collection.
The groups listed are the alge, diatoms, Rhizopoda, Masti-
gophora, Infusoria, Rotatoria, Entomostraca, msect larve, and
miscellaneous. The total numbers of individuals and of species
are also given. These data are taken entirely from catches
with the silk net, and are subject to the errors arising from
leakage through the silk. The silt interferes in this case only
in so far as it obscures the planktonts to a greater extent in
Svoon River collections, and thus necessitates a greater dilution
in counting and, in consequence, a greater factor in computa-
tion. The margin of error is accordingly somewhat greater in

dd1

data from the silt-laden planktons of Spoon River. The leak-
age affects primarily the smaller flagellates, ciliates, and dia-
toms. For reasons previously given, the leakage introduces
proportionately a greater source of error in the Spoon River
data, and, in so far as it is operative, tends to increase the con-
trast between the two streams. From data now at hand it is
not possible to estimate the extent of this error, but it should
be borne in mind in considering the data in the table concern-
ing these groups especially. In spite, however, of these sources
of error, some points of contrast are so striking that certain
conclusions seem justified.

There is a marked contrast in the total population. The
ratio of the average number of planktonts in a cubic meter
of Spoon River water to that in a like quantity from the main
stream is 750,429 to 28,283,295, or 1 to 38—a ratio much greater
than that found in the volumetric comparisons. It is due to
the relative preponderance of small planktonts, especially the
limnetic diatoms, in the collections from the main stream, as
will be seen on comparison of the ratios of the other groups
listed in the table. If the low-water period of 1897 be excluded
from both averages the contrast between the two streams will
be very much heightened. The data from these grand averages
of all the coincident collections in the two streams are thus
strongly confirmatory of the contrast in productiveness dis-
closed by the volumetric comparisons, and of the fact that
the access of water from Spoon River causes a diminution in
the number of organisms per cubic meter of water in the
main stream.

The comparison of the representations of the various
groups in the collections tabulated, throws some hght on the
qualitative differences in the plankton of the two streams.

The algae, other than diatoms, as in the case of all groups
except the insect larve, are present in smaller numbers in
Spoon River, the total ratio being 1 to 1.4—abnormally low be-
cause of a single unusual collection in the autumn of 1897.
The ratio in 1898 and the latter part of 1896, 1 to 10, is proba-

532

bly a fairer statement. The number of species noted is 20 and
49 respectively. The main stream has a greater variety of the
smaller Chlorophycee and of the blue-green alge, while in both
individuals and species the desmids are well represented in the
tributary. Littoral species predominate in the latter, though
limnetic forms also occur. It is significant that the alge, pri-
mary links in the chain of food relations, have already attained
a considerable development in the tributary waters.

The diatoms present the most striking contrast in the table,
the ratio being 1 to 78. This great disproportion is caused by
the larger numbers of certain lmnetic diatoms, notably Melo-
sira, Asterionella, Fragilaria, and Synedra, in the plankton of
the main stream. These are present in the tributary, but only
in smaller numbers, while species of littoral habitat present in
both streams are relatively more abundant in Spoon River.
The contrast between Quiver Creek and Spoon River in the pro-
portions of their diatom flora is significant. In the creek the
shores and bottom are more immediate and effective features
of the environment than they are in the larger tributary, hence
we find there that the diatoms are largely littoral forms, and
they and the Rhizopoda which feed upon them constitute
almost the total plankton. In Spoon River the same species
occur, though data are lacking for quantitative comparisons
with Quiver Creek. These littoral species are, however, over-
shadowed by the development of other and more typical plank-
ton organisms, so that they constitute here a smaller relative
proportion of the planktonts than they do in Quiver Creek.
The littoral species find a place for development along the shores
and bottom of the tributary streams, and by reason of the pro-
tection there afforded, or of their sessile habit, they have time
for increase. The limnetic forms, on the other hand, are more
at the mercy of the current, and though at low water they ap-
pear in numbers in Spoon River, they rarely find sufficient time
at other seasons for their characteristic increase until they reach
the main stream. The greater fertility of the water in the
river is doubtless also a factor in causing the marked difference
in the diatom flora of the two streams.

533

The Rhizopoda are twelve times as abundant in the Illinois
as in Spoon River. During the winter and spring flood of 1897
the tributary waters contained more Phizopoda than the main
stream, but throughout the remaining period of our collections
the tributary waters would serve, almost as a rule, as diluents of
the rhizopodan fauna of the Illinois. This group of planktonts
did not show an increase in the low-water period of 1897 simi-
lar to that of many other groups—a phenomenon to be ex-
plained by the fact that the diatoms, their main food supply,
made no unusual growth during that period.

The species of Rhizopoda are about half as many in Spoon
River as in the Illinois (17 to 80—see table on page 518), and
all of the species from Spoon River are present in much the
same relative proportions in the Illinois. There do not appear
to be any which find their centers of distribution in the tribu-
tary. Its contributions of rhizopods thus neither diversify nor
relatively increase the plankton in the main stream. j

The data concerning Mastigophora are to a large extent
vitiated by the error of leakage. The tabulations of the silk-
net catches indicate their great predominance in the main
stream, 1 to 24 as an average, though other seasons than the
low water of 1897 exhibit a much greater contrast, that for the
whole year 1898, for example, being | to 3851. In the period of
low water of 1897 the tributary stream showed a greater devel-
opment of these organisms than the main stream, especially of
the green forms. ;

The presence of these organisms in Spoon River in consid-
erable numbers during the heated term of every year is indi-
cated by the remarkable water-bloom which appears on clear
still days about the middle of the afternoon. ‘This is similar
to that of the Illinois, but seems to be better developed, taking
the form of a decided green scum on the surface. How far
this indicates a quantitative predominance of the organisms of
the water-bloom can only be determined when our filter
catches shall have been examined. So far as the silk catches
go they do not show the quantitative predominance of the

dd4

water-bloom organisms in the tributary which the surface ap-
pearances would indicate. The greater turbidity, and the more
sheltered situation and consequently quieter surface of Spoon
River may tend to bring its quantitatively smaller water-bloom
to the surface in a greater proportion than is possible in the
more disturbed channel waters. These organisms form an early
linkin many chains of food relations in the plankton, and it is
significant that they reach a considerable development in the
plankton of tributary streams.

The species of Mastiyophora are less than half as numerous
in Spoon River as they are in the Illinois (28 to 62), and none
was found peculiar to the tributary, or having there its center
of distribution. Thus, excepting in periods of prolonged low
water, the Mastigophora fauna of the plankton of the tributary
neither increases nor diversifies that of the main stream.

The Infusoria in Spoon River are greatly exceeded by those
of the main stream, the ratio being 1 to 20. The only marked
exception to this relation occurs during the early part of the
low-water period of 1897, when the ciliates, principally Codo-
nella, attained a greater development in Spoon River. This
excess was soon masked by the usual autumnal increase of
Carchesium and Epistylis, and of the free ciliates preying upon
these sessile forms, in the main stream. This autumnal in-
crease is not shared to any great extent by the tributary, proba-
bly by reason of its lesser contamination by sewage. The in-
fusorian fauna was by no means fully determined in the two
streams, but so far as identifications were made, they indicate
much less diversity in the infusorial fauna of Spoon River and
no species peculiar to, or predominant in, the tributary. Thus,
excepting the period of low water in early fall, the contribu-
tions of Infusoria from the tributary do not enrich the plank-
ton of the main stream, and at no time do they tend to diver-
sify it.

The Rotatoria, according to the grand average in Table, XIV.,
are almost equally abundant in the two streams (1 to 1.9).
This equality at once disappears if the low-water period of 1897

539

be excluded from the averages. The ratio in 1898 is 1 to 36,
and as this isa year of normal hydrograph it may represent
more nearly the true proportion in the production of rotifers
in the two streams. The data in the remainder of 1897, in
1896, and in 1899, so far as they go, sustain this higher ratio.
This ratio is somewhat greater than that of the alge, rhizopods,
and infusorians, which form earlier links in the chain of food
relations. The rotifers, on the other hand, depend upon these
groups for food, and become later links in the chain, and conse-
quently do not, for lack of time, attain the development in
tributary waters that they doin the main stream. The diatoms
and Mastigophora also form considerable elements in the food
of the rotifers, and since these groups are proportionally less
frequent in Spoon River than in the main stream, the deficiency
in this food element may be one cause of the lessér develop-
ment of rotifers in the tributary. Most rotifers, however, do
not exhibit such limitations in diet, and the effect of this de-
ficiency in food must be largely quantitative.

The number of species of rotifers found in Spoon River is
much less than that in the main stream (44 to 107—<see p. 519),
and none peculiar to the tributary was noted. The Bdelloida,
which are principally shore-loving and bottom forms, constitute
a relatively greater proportion of the species and individuals in
the tributary, though their absolute numbers per cubic meter
of water are rarely in excess.

In the low-water period of 1897 the limnetic species com-
mon in the main stream and in the residual backwaters reached
an unusual development in Spoon River, even in excess of that
in the main stream. The conditions then prevalent, the higher
temperatures of a late autumn, stagnating water with little or
no current, and the absence of the usual autumnal flushings,
combined to favor the unusual phenomenon. During this sea-
son the contributions of Spoon River to the rotiferan fauna of
the main stream would increase the amount of rotiferan plank-
ton therein, though not diversifying it—as will be seen on com-
parison of the relative number of species in the two streams at
that season.

536

Excepting, then, in seasons of prolonged low water in the
autumn, the contributions of Spoon River to the rotiferan
plankton of the main stream stream result in its dilution, and
aside from a greater proportion of the littoral fauna they add
little to its diversification.

The Entomostraca are numerically a very small factor in
the hfe of Spoon River and form a very small volume of its
plankton product, the ratio of the entomostracan population
in the two streams being on an average | to 28. This ratio is
well maintained if the years are considered individually, being
1 to 32 in that portion of 1896 represented in our collections, |
to 35 in 1898, and 1 to 23 in 1897. The ratio in this latter year
thus shows some effect of the prolonged low water, but not to
the degree which is shown in the case of the rotifers. The
Entomostraca illustrate most clearly the effect of the time ele-
ment in the development of the plankton. Their growth is less
rapid than that of any other type of planktonts, and in conse-
quence they cannot attain in tributary waters the numbers that
they do in the older waters of the main stream and its back-
waters. The number of species is also much smaller in Spoon
River than it is in the Illinois (18 to 49), and none peculiar to
the tributary was noted. Most of the adult Copepoda belonged
to a single species, Cyclops serrulatus, and it is probable that
most of the immature stages should be referred to the same
species. This seems to be a creek species, and to have its center
of distribution here rather than in the main stream, where 1t
never attains the numbers that most of the other Copepoda do.

The contributions of Hntomostraca made by the tributary
are thus very small at all times, and have only a diluent effect
upon the entomostracan plankton of the main stream, adding
some diversification in the case of a single species of Cyclops.
Spoon River carries no marked contributions of littoral Entomos-
traca to the main river.

Of all the groups of planktonts the insect larvee (principal-
ly Chironomus, with a few Dixa and Tanypus larve) alone are

present in larger numbers per cubic meter in Spoon River than

5370

in the main stream. They are essentially littoral forms es-
pecially common about driftwood, which abounds in Spoon
River—a fact which doubtless accounts for their frequent oc-
currence in the plankton of that stream.

The total number of species of planktonts noted in the col-
lections from the two streams in my enumerations of the
plankton, and listed in Table XIV., is not to be taken as repre-
senting the total number present. But a small part of each
catch was examined, and rare species in both streams usually
escaped detection. Their relation to each other, however, af-
fords an index of the relative number of species present in dif-
ferent collections in the same or different streams provided the
method of examination is similar. The silt makes uniformity
of dilution impossible in niany cases, and thus introduces some
error into the data. The average number of species noted in
a Spoon River collection was 24 to 69 in the Illinois, a differ-
ence less marked than that disclosed by the volumetric or the
statistical comparison, but still significant of the relative
paucity of the plankton of Spoon River and the more limited
range of its constituent organisms.

The total number of species recorded from Spoon River is
170, while the Illinois yielded 429. The greater number of col-
lections examined from the latter stream may explain a part
of this difference. Without exception, all the identified species
found in Spoon River have occurred also in the Illinois above
the mouth of Spoon River. The only species in the tributary
which seem to reach as great a development there as they do in
the Illinois, or a still greater one, are the species of Surirella,
especially S. splendida, several forms of Closteriwm, Cyclops
serrulatus, and the dipterous larve above mentioned.

A comparison of the total population of the two streams
throughout the thirty months covered by our collections, as
shown in the final columns of Table XIV., throws some further
light-on the relations between the plankton of the two-streams.
Traces of the same seasonal routine appear in both; the spring
maximum appears in both at about the same time, while the

538

midsummer decline and the autumn maximum are evident, but
not in all cases well defined. The environmental factors com-
mon to both, especially that of temperature, thus tend to pro-
duce similar effects. Throughout all these changes, save in the
low-water period of 1897, the marked contrast in the total
population continues unbroken, a constant witness to the effect
of the great points of difference in the two habitats, namely,
the age of their respective waters and their relative richness in
the immediately available elements for the support of life. It
is only when these points of contrast in the environment van-
ish, by reason of the slight current, as in the low water period
of 1987, and by reason of the increase of the products of or-
ganic decay at such times in the water of Spoon River, that the
plankton of the two streams approaches equality in production
and exhibits a comparable assemblage of constitutent organ-
isms.

The contrast between the autumn planktons of 1896 and
1898 and that of 1897 is not only due to the low water of this
year, but also to frequent flushings which were caused by the
many minor rises during the autumn of the two years first
named. (See Plates X., XI.) These autumnal rises are due to
general rains, which, as a rule, affect both Spoon River and the
main stream at about the same time. The difference in their
effect upon the plankton of the two streams is very evident in
the data of Table XIV. The autumnal plankton of the I[lh-
nois shows a somewhat similar population in all three seasons.
Spoon River, on the other hand, shows a great falling off in
numbers—from several million to a few score thousand—in
both autumns, in which these rises are frequent. The effect of
these minor floods is thus deleterious to the plankton of the
tributary in accordance with the general principle that they
decrease the time for breeding the plankton in its waters. They
also prevent the development of plankton maxima in the
tributary by repeated removals of whatever accumulations are
produced. Owing to the differences in their volumes and in
the slope of their channels, these flushings are more complete

539

and more rapid in the tributary than in the main stream, and
their relative effect upon the plankton is greater in the former
than in the latter.

How far the conclusions here drawn regarding the rela-
tions of tributary waters to the main stream will hold true for
other localities can be determined only by examination. The
local conditions in this instance are in some respects peculiar.
The large amount of sewage in the main stream and the rela-
tively small size of the tributary have here enhanced the con-
trast between their plankton content. The distinction between
tributary and main stream in this instance is only an illustra-
tion of a wider generalization, broached in the discussion of the
relation of the current to the plankton. In all types and con-
ditions of the environment, time for breeding is a fundamental
factor, and in the relation of tributary and main stream a con-
trast in the length of time afforded for this development is evi-
dent. Wherever this contrast occurs we may reasonably ex-
pect, other things being equal, that the o/dev stream water will
support the more abundant plankton, and that it will also ex-
hibit the greater diversification in its constituent organisms.

The facts derived from the examination of the tributary
waters of Quiver Creek and Spoon River indicate clearly that
streams of this kind add but little to the total plankton of the
main stream, and diversify it only by increasing the proportion
of littoral species already present. Owing to the slight devel-
opment of plankton in their waters, the immediate effect of
their access isa dilution of the plankton per cubic meter of
channel water. The initial steps in the sequence of plankton
development in these tributary waters have been taken in the
erowth of the smaller alge and diatoms, but the degree attained
is still below that in the channel.

Channel plankton is therefore xot in any considerable de-
eree derived from or maintained by the contributions of plank-
ton from tributary streams of the kind here examined, and
these are typical of most of the tributaries of the Illincis not
modified by industrial agencies. It is not merely the mingled

540

plankton of confluent streams, for in quantity and components
it is much greater and more diversified than that of the tribu-
taries. The tributaries add to the total resources of the chan-
nel, and increase the total population slightly, while diluting
some of the food elements and the plankton perm.’ These re-
sources are utilized in the channel and backwaters, and the di-
lution of the plankton is thus made good. Tributary waters,
then do not directly contribute to the channel plankton, and
only, indirectly aid in its maintenance. They are in the main
diluents of channel resources and of its plankton.

RELATION OF BACKWATERS TO CHANNEL PLANKTON.

The discussion of the relation of the backwaters to the po-
tamoplankton is one fraught with difficulty both on account of
the lack of full data and also because of the complexity of
those at hand. The quantitative studies which have been
made of Quiver, Dogfish, Thompson’s, Flag, and Phelps lakes,
each representing a particular type of the bottom-land waters,
enable me to compare the amount of plankton present in these
various regions with that of the main stream. So, also, the
cursory examinations made on many of the collections afford a
basis for some general statements as to the nature of the con-
tributed plankton, though the data on which these statements
rest cannot be given here, and their final verification will
come, if at all, when the qualitative analyses of the plankton
of these several regions shall have been completed. The ab-
sence of any accurate data as to the volume of water discharged
into the river from the regions in question adds another ele-
ment of uncertainty, while the problem is further complicated
by the fact that many bottom-land waters receive tributary
streams, of minor importance, as a rule, for the river as a whole,
and yet of a size sufficient to affect profoundly the waters
which they impound.

The slight development of the flood-plain, the low gradient,
and the retardation of the run-off due to the floods of the Mis-
sissippi River, all combine to accentuate the importance of the

541

impounding action of the backwaters of the Illinois River as
compared with that of other streams. It thus seems probable
that its plankton exhibits to an unusual degree the effect of
such impounded backwaters upon the potamoplankton as a
type.

The amount of water impounded, as compared with that in
the channel, can be estimated roughly from data given by
Cooley (97). The area of the bottom-lands is 704.8 square miles,
of which 76.6 are water and 60.6 marsh. The area of the river
itself presumably included in the above area, from the mouth
to Utica, is 32.4 square miles, having an average width of 755
feet and a length of 227 miles in the limits given. The aver-
age width of the bottom-lands is 3.1 miles exclusive of the
river. At low-water stages the marshes have little water in
them, and the average depths of the bayous and lakes are slight
—probably less than one half that of the river, which at this
stage has, according to the averages of Cooley’s estimates, an
average depth of 7.5 feet. From these data it follows that
the total volume of impounded waters at low-water stages is
somewhat less than that in the river channel itself, and much
of this iscut off from the river at that stage. Rises in the
level of the river up to ten feet above low water—which is
about the average bank height—increase the impounded vol-
ume. In lower levels this increase is slight, but 1t becomes rela-
tively greater as the level rises. When a height of ten feet is
reached, connection has been established with the greater part
of the permanent waters and marshes of the bottom-land, and
the impounded volume must be at least double or triple that of
the channel. At this level, overflow begins, though the higher
bottoms are not covered until a depth of sixteen feet is reached.
At a stage of overflow each additional foot of rise in the im-
pounded area is equivalent approximately to the volume in the
channel. Thus, at a:maximum flood of eighteen feet there is
about ten or eleven times as much water in the impounding
area as is found in the channel. These estimates accord in a
general way with the observed facts of current and run-off. A

542

bank-full river has a current sufficient to discharge its content
in five days, and, allowing for increase of current and discharge
in these conditions, the maximum flood would require about
fifty days for its run-off. Accessions of water during the run-
off would naturally tend to prolong the process to some extent.
An examination of the hydrograph (PI. VII.) will show that
the decline from the flood maximum to the ten-foot level (ces-
sation of overflow) is accomplished in the neighborhood of fifty
days in some ¢€ases, as, for example, in 1898.

A small part of the flood is thus impounded for the full
period of the run-off, while in case of the greater part of the
impounded volume sufficient time elapses before discharge into
the channel for the breeding of an abundant plankton, so that
the backwaters become very important factors in determining
both the quantity and the nature of the plankton in the main
channel. Contributions from tributary streams form the other
large factor, but the ratio existing between the contributions
from the two sources is not easily ascertained. The only data
available are the areas of the catchment-basins of the tribu-
taries, the statistics of rainfall, and the estimated volume of
the impounded water. A rough comparison of these data
would indicate that during the decline of the flood to the stage
of initial overflow (bank height), the impounded waters con-
tribute somewhat more than the tributary streams to the main
channel. ‘Their contributions decrease as the river falls, and
the more rapidly below the level of bank height, while those
from tributary streams come to form an increasing proportion,
and at low-water stages almost the only natural source, of
channel waters.

With a view to setting forth the contrast in the productiv-
ity of the plankton in all the areas concerned in this problem
I have drawn up the table following page 342, which gives data
compiled from Tables III. to IX. showing the average number
of cubic centimeters of plankton per m.’ of water for each month
in which collections were made, from June, 1894, through March,
1899. The silt has been eliminated by estimation, and all cor-

543

rections, such as coefficient, have been made, so that the data are
as comparable as the circumstances will permit. The data in
the table are derived from 642 catches, and covera sufficient
range of seasons and years to yield averages significant of any
larger relations existing between the several bodies of water
examined, and also to illustrate the influence of certain com-
mon, as well as some contrasting, factors in this fluctuating en-
vironment.

The backwaters in the list of stations examined by us are
typical of practically the whole range of the bottom-land wa-
ters of the Illinois, including, as they do, a reservoir and a
spring-fed lake, both tributary at practically all seasons, a
marsh, and a lake tributary for only a part of the season and
free from vegetation. Results derived from an examination
of these will therefore afford some conception of the relation-
ship between the plankton of the backwaters of the stream as
a whole and that of the channel.

In the discussion of production in these backwaters (pp.
350-454) J have noted the periods when hydrographic condi-
tions permitted a run-off of the backwaters impounded in the
several localities to the main channel, and instances in which
their plankton contents served to increase or dilute that of the
channel. It will suffice in the present connection to note that
production is less in the backwaters than in the channel in
only 48, or 26 per cent., of the 185 monthly averages—the total
number of all of the monthly averages of all stations but the
Illinois and Spoon rivers. In Quiver Lake we find 80 months
out of 53, or 57 per cent., deficient in production as compared
with the channel; in Dogfish Lake, 6 out of 25, or 24 per cent.;
in Flag Lake, 2 out of 24, or 8 per cent.; in Thompson’s Lake, 8
out of 52, or 15 per cent.; and in Phelps Lake, 2 out of 31, or 6
per cent.

Lakes most free from access of tributary water and from
vegetation are most constant in their excess of production over
channel waters. hus we find that of these 48 instances of
deficient production in the backwaters 30 occur in Quiver

344

Lake, where tributary creek and spring waters form a larger
proportion of the content of the lake, and 19 of the 30 are in
the low-water period, July-November, when the proportion of
tributary waters is greatest and the impounding function at its
lowest level, and vegetation at its height. Of the remaining
18 instances of deficiency, 6 are in Dogfish Lake, which is to
some extent under the influence of the hydrographic condi-
tions of Quiver Lake, and is likewise dominated by vegetation.
Three of the 6 cases of deficiency appear in July-August, in
the height of the dominance of vegetation and at times of
slight run-off. Two instances at the same season and under
similar conditions of vegetation and discharge appear in the
monthly averages of Flag Lake. In the monthly averages of
Thompson’s Lake there are 8 instances of deficiency, but in half
of these the deficiency is less than 80 per cent. There are but
2 cases of deficiency in Phelps Lake, both at times when Spoon
River tributary water was passing through the lake. Further-
more, 33 of the total 48 instances of deficiency in production
in backwaters, as compared with channel, occur in July—De-
cember, during the low-water period of least run-off of im-
pounded backwaters, and of the remaining 15 instances during
the January—June period some probably result from insufficient
data, and others are found when the stagnation (Moina) pulse
of June, 1895, occurred in the river.

We must, therefore, conclude that the greater part of the
backwaters predominantly bring to the channel in their run-off
a richer plankton than that with which their contributions are
mingled. The extent of this predominance and its changes
with the seasons and from year to year will be seen in the
table of monthly means following page 342. It is summarized
in the following table, which gives the mean plankton content
in channel waters for each month and the average of the
monthly means of the five backwaters, Quiver, Dogfish, Flag,
Thompson’s and Phelps lakes, together with the ratios between
channel and backwater production in each month.

An inspection of this table shows that during the colder

Jan. Feb. March April | May June July

Channel plankton..| .21 ee al oe B27], 4.59 6.08 7.22% 4.23
Backwater plankton] 1.63 2.06 2.46 11.43 18.91 6.19 | 3.927
IRE) Go nceeeineee I to8| I too Itog | 1to2.5 | I to3 | I to .of |1 to.9|l
Mean
Aug. cas Oct. Nov. Dec. Nene
Channel plankton.. 3.88 | 2.86 1ojon bin 88 mo] 2.71
Backwater plankton 13.90 12.92 14.78 15.10 | 6.81 9.18
Rei I to 3.6 a NOR | T@Bl? || MOI? | TOO. |nios.0

*Omitting 1895, 1.42. Omitting 1895, 2.96. [Omitting 1895, 1 to 4.4.
|| Omitting 1895, 1 to 1.3.

months, from November to March, the backwaters have from
8to 17 times the plankton content of the channel, and in
the warmer season, from April to October, from 0.8 to 5 times
as much. Omitting the aberrant record of June, 1895, from
channel data, it becomes apparent that there is least difference
between channel] and backwaters in April-May and July, pre-
dominantly the months of greatest run-off of impounded back-
waters.

Channel plankton of the Illinois River, therefore, has its
source in a large degree in impounded backwaters, and is main-
tained to a considerable extent by their run-off.

INDIGENOUS PLANKTON OF THE CHANNEL.

It does not seem probable that the channel plankton is
only the mingled plankton of the tributaries and backwaters.
Growth and reproduction, modified, however, by the cyclic
phenomenon, continue in the channel after plankton-laden
backwaters unite with it. This increase is facilitated by the
fact that channel waters are generally richer (see Tables
XXIII.) in nitrogenous matters and the other products of
decay than the backwaters. During high water, when the cur-
rent is more rapid, the time for further breeding is considera-
bly reduced, even to five days, from Utica to the mouth of the

546

Ihnois. Under these circumstances the plankton indigenous
to the channel itself is of small volume as compared with that
contributed from backwaters. At low water, however, it may
take 23 days, or more, for the water to traverse this distance.
This frequently results in such a development of channel
plankton that it not only rises above that in many of the
backwaters, but also takes on a characteristic facies which
at once stamps it as largely indigenous in the channel itself in
its origin. Instances of this phenomenon appear with pro-
longed low water, as in June-July, 1895, when channel plankton
exceeded that in ail the backwaters and was characterized by
the great abundance of Moina. In like manner in November-
December of every low-water year there has been an unusual
development of Ci/iata, principally Carchesiwm lachmanni and
predatory forms feeding upon it. This, at least as shown by
the catches of the silk net, does not often exceed the plankton
content elsewhere, but its dominant organisms form relatively
a small proportion of the backwater plankton at such times.
The channel plankton is, then, largely indigenous. The autumn
of 1897 saw a similar indigenous devevelopment of Chlamy-
domonas in the river which was not equaled in the backwaters.

The plankton of the Illinois River is the result of the
mingling of small contributions by tributary streams, largely
of littoral organisms and the quickly growing alge and flagel-
lates, and of the rich and varied plankton of tributary back-
waters, present to an unusual degree in the Illinois because of
its shghtly developed flood-plain, and from which it is never
entirely cut off even at lowest water. Data are lacking as to
the effect of the contributions of the Illinois and Michigan
Canal upon the plankton of the river. To these elements is
added such further development of the contributed or indigenous
organisms as time permits or the special conditions of nutri-
tion and sewage contamination facilitate. Though continually
discharging, the stream maintains the continuous supply of
plankton, largely by virtue of the reservoir backwaters—the
great seed-beds from which the plankton-poor but well-fertilized

d47

contributions of tributary streams are continuously sown with
organisms whose further development produces in the Illinois
River a plankton as yet unsurpassed in abundance.

TOTAL ANNUAL PRODUCTION.

In the absence of any precise figures of the total annual
discharge of the Illinois River at its mouth or at Havana, it is
futile to attempt to compute with any considerable degree of
accuracy the total plankton production of this stream or of any
of its tributaries or backwaters examined by us. The estimates
which follow, contain, therefore, a large element of conjec-
ture.

On page 132, computations from available data indicate
a run-off at Havana of approximately 0.688 second-foot per
square mile of the drainage basin of 15,250 square mules.
The mean of all the monthly averages (see table p. 429) of
plankton production in channel waters is 2.71 cm.* per m.' of
water. On this basis the total discharge in the average year
becomes 25,408.38 cubic meters of plankton permanently re-
moved each year by the discharge of the stream at Havana.
From the stream as a whole, given the same plankton content
and run-off per square mile as at Havana, the total production
becomes 67,598.8 cubic meters of plankton. These figures rep-
resent in a measure the wnutilized and permanently lost organic
matter available for the support of the larger, more permanent
animals resident in the river and its connecting waters. They
are the net production over and above that plankton utilized by
the organisms which retain their residence in the river or its
backwaters above Havana or the mouth, and those whose death
and decay have removed them from the plankton by sedimen-
tation or solution. The total production is therefore greater
in some unknown and apparently undeterminable ratio.

It is evident that production varies greatly from year to
with the varying plankton content and discharge of the stream.
In the accompanying table I have computed the total annual
production of the Illinois River on the basis of a run-off of .688

548

cubic second-foot per square mile of the watershed of 27,914
square miles, and a plankton production equaling that of the
average for the several years of the monthly means as deter-
mined by our collections at Havana.

TOTAL PLANKTON PRODUCTION.

Mean river |Estimated run-|Mean plankton| Total plankton
Year stage, in feet, off—in content per cu-| discharged —
above low water| cubic meters bic meter | in cubic meters
1894 4.63 18,085 ,780,000 2.53 45,757
1895 3.61 14,101,560,000 5.91 83,340
1896 6.98 27,265 ,620,000 1.05 28,629
1897 6.90 26,953,120,000 3.28 94,605
1898 8.02 31,328,120,000 2.03 63,596
INSURE 3608 6006 66 6.40* 25,000,000,000* 2.71 67,750*

*A pproximate average, omitting 1894.

It should be borne in mind that the records for 1894 and
1895 are very incomplete, and do not as accurately represent
the production as do those of later years. The change in dis-
charge from year to year has also been computed as directly pro-
portional to the average river stage. This is necessarily only a
rough approximation, for discharge generally increases and
decreases in greater ratios than river stages, so that the differ-
ences between the several years are probably greater than the
figures indicate.

While the amounts given in the table are based on some
conjectural factors, it may still be that more significance at-
taches to the direction of the differences in total production in
the several years. The total production varies, it seems, con-
siderably from year to year, the greatest departures from the
mean being + 40 per cent. in 1897, a year of high production
and river levels above the average, and — 58 per cent. in 1896,
when recurrent floods checked production, at least at Havana,
in the upper river, though it is not improbable that if the back-
waters and the lower river were taken into account this seem-
ing deficiency would be largely removed. These divergences
from the mean total production are considerably less than
those from the mean plankton content, 2.71 cm.* per m.*, which

549

in 1895 and 1896 reach limits of + 118 per cent. and — 61 per
cent. respectively. This greater uniformity in total production
is brought about in part by the compensating effects of lessened
plankton content in years of high water, and increased con-
tent in years of low water.

The mean total discharge is 67,750 cubic meters, or 149,-
050,000 pounds if we compute its weight as equal to that of the
same volume of water. This represents the mean annual loss
of living organic matter from the watershed of the Illinois.
The total production, including the plankton impounded in the
backwaters and that utilized there and in the channel as food
by other organisms, as well as that perishing within the water-
shed and contributing by its wastes and decay to the growth of
the coarser aquatic vegetation,—this total must indeed be much
greater than the amount indicated by these imperfect computa-
tions. If we add to this the undetermined but probably not in-
considerable volume which leaks through the meshes of the silk
net and is therefore not at all represented in our computations,
we reach a total annual production of still greater magnitude.

TOTAL PRODUCTION AS AFFECTED BY LEAKAGE THROUGH
THE SILK NET.

In an earlier paper (’97b) I have called attention to the
extent of leakage through the silk as determined by the enu-
meration of catches made by silk, filter-paper, and the Berkefeld
filter. An attempt was also made later, in connection with
the enumeration of the organisms of the filter-paper catches,
to determine the volumetric catch of plankton by this method.
It was my endeavor to estimate the proportions of silt and
plankton in these catches, as had previously been done in the
case of those of the silk net. There is, however, in these filter-
paper catches a silt of very different character. To that which
we find in the catches of the silk net there is added a large
amount of fine loam, clay, and sand which passes directly
through the silk, and a very considerable quantity of minute
flocculent particles, presumably bacterial zodglea. This floc-

590

culent matter occupies a large part of the field as the catch is
seen in the Rafter cell. It is a difficult matter to estimate
with any certainty the proportion which such silt forms of the
filter-paper catches. Nor is it possible to use the same standard
of estimation upon the catches of both the silk and filter-paper,
owing largely to the considerable volume of the flocculent debris
in the distributed plankton and the uncertainty as to its compres-
sibility in the centrifuge. My estimates of the silt, which will
be found in the table beginning on page 552, in the light of the
tabulated results of the enumeration seem to be too large,
probably as the result of the influence of the standard used on
the silk catches. It is, therefore, my opinion that the quanti-
ties of plankton given in this table are in the main below
rather than above the actual amounts present. The facts upon
which this opinion is based will appear in the discussion of the
results of the enumeration. It should be said that the relative
values of the estimated quantities of plankton in this table are
probably above the actual ones. They are of more importance
in indicating the direction of the seasonal movement in pro-
duction than they are in expressing the exact amounts of
plankton present.

Because of this great increase in the proportion and quan-
tity of the silt found in these filter-paper catches, even in our
clearest waters, the filter-paper method does not satisfactorily
solve the volumetric problem. It is not a satisfactory method,
and, indeed, it seems probable that the same difficulty will be
metin all methods which remove all suspended solids in all
but the clearest lake or ocean waters. This same difficulty has
balked the efforts of Lohman (’03) to determine satisfactorily
the volumetric loss by leakage through the silk in the applica-
tion of the Hensen method to a marine plankton, which leaks
through the silk. In passing, it may be noted that this plank-
tologist of the Hensen school at Kiel, working with the subven-
tion of the University of Kiel and the German Commission for
the Investigation of the Sea, after testing upon the plankton of
the Baltic and Mediterranean seas the correctness of my eriti-

5d]

cisms (’97b) upon the Hensen method, concludes thatthe loss is
volumetrically of some importance, and numerically as large
as that indicated by my determinations of the leakage in our
field of operations, indeed, slightly larger in some instances.

The table beginning on page 552 gives the volume of water
filtered, the total catch, the computed catch per m.’, the esti-
mated per cent. of silt, and the computed volumes of silt and
plankton (filter-paper catch) per m.’ The volumes of plankton
per m.°* taken at the same time and place by the pump and silk
net are also given, and the averages at the end of the collec-
tions for each year refer only to the coincident catches of this
table. The omission of several silk-net catches in the data of
1896 and 1897 in this table makes its averages differ slightly
from those of Table III.

The filter-paper catches, as in the case of the silk-net
catches, represent the plankton from a vertical column of water
from bottom to surface. Prior to the autumn of 1897 this wa-
ter was collected by hose and pump, either in equal quantities
ata series of levels from bottom to surface or during a continu-
ous transit of the hose through this region, due precautions be-
ing taken to secure proportionate amounts from all levels. Af-
ter this date a water-trap, consisting of a brass tube six feet in
length and four inches in diameter, with a gate at the bottom,
was used for securing the water for filtration. The water was
taken to the laboratory, and after thorough agitation of the col-
lection a sample of the required volume was withdrawn for
filtration. The paper used was a hard-pressed filter-paper from
Schleicher and Schill, No. 575, and filtration was hastened by
washing the filtering surface frequently by a spray from a rub-
ber hand-bulb. The penetration of the small organisms among
the fibers of the filter-paper, and perhaps even through it, causes
some loss of material, so that the volume of the catch is some-
what reduced thereby. The estimates of silt in the table were
not revised with reference to the silk-net records or after tab-
ulation.

Recognizing the fact that these volumetric data are to an

Dd2

FILTER-PAPER CATCHES, ILLINOIS RIVER.
All volumes in cubic centimeters.

n = A ao 4.
6 + Q Cr D oO 2s g ae
eo | 2 | 22) 5 | ee |eee| ee | See
ne ws te oy pa le ee Sah O 14
Qe A Ss s Zs, | eee © &, 3 ae

< is = lst gs

1896
22,366 e 3, VIII 2500 gI 364 99.50 | 362.18 82 | ©.20
PBS) Gl || ss, WIDU 1000 08 80 99.00 | 79.20 .80 | 2.60
22,430 d | 15, VIII 1000 16 160 99.00 |} 158.40 L360 || T.i©
22,436 d | 21, VIII 1000 "22 220 98.00 | 215.60 4.40 0.28
22,455 d | 26, VIII 1000 al 130 99.00 | 128.70 1.30 | 0.43
22,464 d | 29, VIII 1000 .08 80 98.50 | 78.80 1,20 || ©. 50
2251 CONG |ntOwmnlaXt 1000 II 110 98.00 | 107.20 22) || Ooi}
PPih73s Cl || 30) IDK 1000 O7 70 99.00 | 69.30 of || On233
Dpiesit Cl isl, IK 1000 08 80 99.00 | 79.20 .80 | 0.18
Denar? Cl |) WF 2X 1000 o4 40 96.00 | 38.40 1.60 | 0.02
22,509 d 3, XII 1000 03 30 90.00 | 27.00 ACO || OG
pepsi) Gl I) Ao, 2IUL 1000 .05 50 Fs OO) | ATO) 12.50 | 0.94
IAWieralg Ce ane oh ean cae. ae 2.66 0.64
1897

PPE Gl. ||, By. it 1000 03 30 90.00 | 27.00 3.00 | 0.03
22,527 d | 26, Il 1000 04 40 g0.00 | 36.00 4.00 | 0.05
Dp jseres la), SUL 500 .03 60 g0.cO | 54.00 6.00 | 0.38
Dey Satoy Gl || Bi, NW, 1000 07 70 80.00 56.00 WA,OO || 5» ii
PES Gl | a5, WW 1000 08 80 88), 00) || 7040) S17 OO | 02
22,561 d | 28, VI 500 o iit 220 99.00 | 217.80 22 | O27
22,564 d | 14, VII 1000 .08 80 75.00 | 60.00 | 20.00] 8.16
22,5 OAMeNn| LON miValel 1000 13 130 80.00 | 104.00 26.00 6.40
PPS Gl || Dit, WAUE 1000 oi 130 96.00 | 124.80 5.29 | ©.68
22,580 d | 30, VII 1000 00 60 96.00 | 57.60 2.40) 1.05
22,588 d | 10, VIII 1000 .05 50 96.00 | 48.00 BOO || 2OP
22,592 d | 17, VIII 1000 Keyl 40 96.00 38.40 1.60 1.98
22,595 d | 24, VIII 1000 .06 60 97.50 | 58.50 L550 | 2.77
22,601 d | 31, VIII 1000 .20 200 75.00 | 150.00 | 50.00} 9.45
22,603 d Ay WX 1000 34 340 65.00 | 221.00 | II9.00 | 8.47
eros; Gl || ih, DS 1000 Os 50 82.00 | 41.00 9.00 | 19.80
22,010 d | 21, IX 1000 19 190 90.00 | 171.00 | 19.00 | 3.00
Pon Gl || Ao, 1D 1000 14 140 80.00 | 112.00 |} 28.00] 4.04.
22,618 d 5 x 1000 18 180 75.00 | 135.00 | 45.00 | 12.92
22,619 d | 12, xe 1000 05 50 95.00 | 47.50 DiI | Bat
22,622 d | 19, X. | 1000 09 go 93.00 | 83.70 6.30 | 1.86
22,624 d ; 26, xX 1000 | 04 40 99.00 | 39.60 AG | ©.20)
PD Gl || 2B Xi 1000 | 03 30 99-50 | 29.85 SISHOnCo
Paes Cl || G, dil 1000 O4 4o 99.50 | 39.80 BO ©.82
POY Gl || iis, XII 1000 05 50 | 99.50] 49.75 25 1.86
POO Gl || 23), Xl 1000 03 30 99.20 | 29.76 Pal || ii Ol
PPAR © || BO, HI 1000 07 70 99.90 | 69.93 Of || Wo2z
22,043 C Texel 1000 02 20 | 99.90] 19.98 (2 | O70
22OMANCa ie xelile 1000 .02 ZOmLOOROO 19.98 1 || ©2310
22,647 d | 28, XII. 1000 .06 60 ' 99.90! 59.94 .06 | 0.03
DNA Geld or Me eR eS ECan Re mater ea Ie oe: IAGO || 3.52

FILTER-PAPER CATCHES, ILLINOIS RIVER— Continued.

553

wn : a a © | ke,
Bs ee g 85 | Se. | eo Fe | Se
G2 2 28 5 SE | See | 2 jam |e &
aE w Be) =e Ele 2 Eo oy val Oo 4
b 2 7 Ee | 8 | Sk eee | Se se) oe

< Y B Ss i) a. = ee

1898

22,649 d | 11, I. 1000 05 50 99.70 49.85 15 0.07
E205 MG) 21, I. | 1000 06 60 99.90 | 59.94 .06 | 0.81
22,654 d | 25, 1. 1000 16 160 99.50 | 159.20 .80 | 0.47
22,656 d R, ne Ioco 03 30 98.00 29.40 C0 || O67
22,658 d 8, ne 1000 08 80 99.00 79.20 .80 | 0.28
22,660 d | i5, Il. 1000 12 120 99.50 | I19.40 .60 0.04
aPNOORNG|-22, | ll |) 1000 4I 410 99.99 | 409.96 .04 | 0.10
22605 Gl || iy WN |) nero) O4 4o 99.90 | 39.96 .04 | 0.02
P2AHOORGm| oy) LUE | 1000 O4 40 99.90 | 39.96 .04 | 0.06
2aioyii Cl Was, Ile |) atetero) 05 50 99.50 | 49.75 .25 | 0.38
Pro medei22) Til: 1000 0S 50 99.20 | 49.50 55Q || O77
BDA Gl || Zo, IIL 1000 O4 40 99.80 | 39.92 G3 || ©.43
PPOSONGm 558 VE | 1600 04 40 99.80 | 39.92 23 || O53
P2.082ds i251. | 1000 03 30 99.20 | 29.76 -24 | 0.13
PROSs Gs | To, IVE 1000 o4 4o 93.00 | 37.20 2.80 RNP
22,603) d) 26, — LV: 1000 06 60 45.00 | 27.00 | 33.00 | 15.84
22,696 d Br We 1060 07 70 35.00 24.50 45.50 | 35.68
22,697 d | Io, We 5000 08 16 30.00 4.80 11.20 | 10.31
BRO Gl || 17f, We 1000 08 80 60.00 | 48.00] 32.00] 5.22
Z2AOS Gl ||, Wo || skelelo) 12 120 95.00 | II4.00 6.00 | 3.45
Peinede 31, Vi. | 1000 08 80 92.00 | 73.60 6.40 | 1.84
DD.7its Gl Cyt SNAG 1000 o4 40 90.00 | 36.00 4.00} 5.28
Dai) Gl |) ile Wille 1000 03 30 94.00 | 28.20 180 || O69
Zac Gl | Bit, Wile 1000 07 70 S560} FO.59 || UO.5O || Batts
Paeaude 285 Vil, 1000 08 80 85.00 | 68.00 12.00 | 0.69
ams Gl || is WANE || ieteyo) 07 70 96.00 | 67.20 2.80 | 0.14
2D.) Gl | i, WIE 1000 £05 50 96.00 | 48.00 2200) ||) 1OnO4
273 Gl | aie Wl [OOO .05 50 g2.00 46.00 4.00 0.88
BBG) aXe WALI 1000 .06 6c 30.00 18.00 42.00 0.67
22,749 d 2, WAM 1000 o4 40 94.00 37.60 2.40 1.62
22708, Gl || @y WAU 1000 08 80 80.00 | 64.00 16.00 | 0.97
2s Gl || 1, WAU 1000 05 50 92.00 | 46.00 4.00 | 0.61
Ze Fhois) Gl || Bar WANK 1000 06 60 94.00 56.40 3.60 0.51
22,770 d | 30, VIII. 1000 o4 40 @3,00) 3720 2.80 | 0.82
22.73, @ || @, IDX, | see) 06 60 97.00 | 58.20 1.80 | 0.90
2 Ge| 13) | XC) |) 1000 07 70 98.50 | 68.95 1.05 | 0.61
DRI Gl || Boy, IW 1000 06 60 99.00 | 59.40 RCOm MORO
2B Gl | oe) IDS 1000 06 60 g2.00 | 55.20 4.80 | 0.31
POT Ol |) i, dS il) lero) O4 40 95.00 | 38.00 2.00 | 0.17
22,788 d | 11, X. | 1000 07 70 99.50 | 69.65 045 || O22
BDO Gly |) ine} xe 1000 03 30 99.00 | 29.70 130 || O.42
P27 OSnGu | 2550 XG) |) 1000 08 80 99.70 | 79.76 .24 | 0.16
27S Gl | it) DN 1000 II 110 99.90 | 109.89 ol |) OWA
22,709 e i, Xl 1000 08 80 g9.80 | 79.84 si |} OO”
BASOZ Gin eL 54 Sol) LOO 12 120 99-95 | 119.94 .06 | 0.10
DDO, Gl || 2, 2 1000 20 200 99.99 | 199.98 62 | O.22
BBO) Gl || Ao, « ICI, 1000 04 40 95.00 | 38.00 2.00 | 0.75
22 Soond |||) (6,. XcTe 1000 03 30 93.00 | 27.90 DMO) | i 40
DP) © || us, SIV 1000 O4 4o 85.00 | 33.00 7.00 | 0O.OI
22,014 d | 15,. XII 1000 03 30 65.00 | I9.50| 10.50] 0.58
22,016 d | 20, XII 1000 04 40 85.00 | 34.00 6.00! 1.98
22,819 d | 27, XII 1000 02 20 75.00 15.00 5.00 1.06
INGER A hla. a GU enn I Ce pee ae 5.64 | 2.13

5d4

FILTER-PAPER CATCHES, ILLINOIS RIVER—Covztinued.

g fey so} cs Bh ‘3 Sp ie AS ‘Oo »
op 2 Fe Oe cee) Sep ak | ae

® & og = = 4 & Ow, Sy, S, O
oS A eh w So | se 9 = am
og a ro) oO ao fe = fe Oa

1899

22,821 d De 1000 o4 40 82.00 | 32.80 7.20 | 0.22
22,826 d | Io, I 1000 025 25 8€.00 21.40 3.60} 0.15
22,828 d | 17, ie 1000 .05 50 95-50} 47-75 25 | 0.50
22,831 d | 24, Ie 1000 £045 45 99.00 | 44.55 45 0.03
22.833 d | 31, I 1000 .O4 40 99.00 | 39.60 40 | 0.01
PPE || Gy, WE 1000 05 50 98.00 | 49.00 1.00} O.II
22,841 d | 14, Il. 1000 .05 So 90.00 | 45.00 5.00 1.15
22,845 d | 21, Il. 1000 .05 50 60.00 | 30.00 | 20.00 1.92
22,847 d | 28, II. 500 41 820 99.99 | 819.92 .08 | 0.07
22,850 d | 7, III. 500 .20 400 99.90 | 399.60 .40 | 0.54
22,853 d | 14, Ill. | t000 .16 160 99.90 | 159.84 sO || ORS
22,850 d |21, III. | 1000 B28) 230 99.80 | 229.58 .42 | 0.21
22,858 d | 28, III. | t000 04 4o 99.80 | 39.92 .08 | 0.01
AVEnA BORN 5 cicesrardambiselainte edie etn oer 3.16 | 0.41

undetermined extent invalidated by the errors above noted, I
wish to call attention to the fact that they may still serve to
indicate in some degree the extent of the leakage and its sea-
sonal distribution—conclusions which are in some measure
corroborated by the results of enumeration. The ratios of the
volumetric determinations of the plankton by the silk and fil-
ter-paper methods in August-December, 1896, in 1897, in 1898,
and in January-March, 1899, as shown by the averages, are
respectively 1 to 4.1, 1 to 3.6, 1 to 2.6, and 1 to 7.7, or, averaging
all collections, 1 to 3.3. If these figures approach the actual loss
by leakage it becomes a matter of some volumetric importance.

An examination of the table reveals the fact that in a third
of the cases the estimated plankton in the filter catch is exceed-
ed by that of the silk net. It will be seen that most of these
cases occur in instances of small plankton, where the tendency,
above noted, to overestimate the silt is most effective in caus-
ing this apparent deficiency. In all cases the total filter catch
greatly exceeds the total silk catch per m.’ (cf. Table II]. and
the one under discussion).

In general the preponderance of the filter catches is greatest
in the warm season of May—September, the growing period of

559

vegetation, in which green flagellates and small alge and dia-
toms are most abundant numerically, and, therefore, quanti-
tatively. Moreover, in 46 of the 105 instances the movement
in production, as shown in the rise and fall of the plankton
taken by the filter-paper and silk net, is in the same direction,
though amplitudes reached are rarely proportionate. The co-
incidence is most marked when the catches of the silk net re-
veal changes in production of considerable magnitude, as, for
example, during the rise and fall of the vernal pulse in 1897
and in 1898, and during the winter changes of 1898-99. There
are suggestions in these records of vernal pulses of considerable
magnitude, of a large midsummer production, and of a great
development in the low water of 1897, when an enormous
growth of Chlamydomonas turned the river to a livid green, and
contributed to the maximum filter-paper record of 119 cm.’ per
m.*, 14-fold the coincident catch (8.47) of the silk net. There
is also, even in these erratic data of the filter-paper catches,
some evidence of the pulse-like character of the production of
these minute organisms which form the greater part of the
catch. This appears often to be coincident with the cycle
movement in the volumetric data of the silk net, and may best
be seen in the records of the winter of 1898-99. The enumer-
ation confirms beyond all question the existence of these recur-
rent pulses, dimly suggested in these volumetric records. The
spring and summer plankton which leaks through the silk is
largely made up of small alge, flagellates, and diatoms, with
some ciliates, principally Codonella, andrhizopods. The winter
plankton thus lost is largely composed of broken colonies of
Synura, together with many predatory and elusive Infusoria,
largely representatives of the Holotricha, which multiply abun-
dantly with the autumnal increase in bacteria.

It can be apparent to no one more than to the writer that
such data as these are unsatisfactory in determining the pre-
cise volumetric extent of the leakage through the silk. That
this leakage is, however, beyond all question considerable must
become evident to any one who actually works over collections

556

made by some finer filter than that of the silk net. The work
in this ine which I have done since the publication of my tests
of the leakage through the silk net (Kofoid, ’97b) has only
confirmed my opinion as additional data, volumetric and enu-
merative, have accumulated. The corroboration of the cor-
rectness of my criticisms on this point by the recent work of
Lohmann (08) on marine plankton adds to the testimony
against the Hensen plankton-method as a complete quantitative
test of the productivity of water. The criticisms which Brandt
(799), Reighard (98), and Ward (799) have passed upon my con-
clusions in this respect have not stood the test of actual inves-
tigation, in so far as the work of Lohmann (’03) and Volk (OL
and ’03) and my own investigations, as given in the preceding
pages, are concerned. To my mind, owing to s7/t contamination,
no purely volumetric test is sufficient to solve adequately the
problem of productivity of water. It may be possible by pure
cultures and measurements of many individuals to establish
unit values for the various planktonts, so that volumetric de-
terminations can be made from enumerative data, and to sup-
plement these by chemical analyses, so that chemical values in
proteids, silea, ete., can be in like manner approximated with
sufficient accuracy for scientific purposes. This may seem chi-
merical at a distance, and it raises at once the question as to
the utility of so great an undertaking. Something of the sort
is, however, necessary if quantitative plankton investigations
are to cease being merely desultory and disconnected and be-
come joined in a substantial structure which comparative sci-
ence alone can rear. The development of a scientific aquicul-
ture demands some standard of this kind as a basis for its per-
manent success.

COMPARISON WITH OTHER BODIES OF WATER.

Comparisons of the quantitative production in the Illinois
River with that in other localities are obviously of value only
when based on similar or approximately similar data. Asa
result of our operations upon the Illnois and its backwaters we

Bay

are able to compute the mean annual production on the basis
of 235 observations extending over a period of five years. At
present writing no series of observations of like, or even approx-
imately like, extent has been published concerning any other
body of water. Comparisons upon this basis are therefore not
possible.

The scientific or economic value of comparisons upon other
bases than the mean annual production or the full seasonal
course of production cannot be great, unless it be for coinci-
dent seasons. Furthermore, data of production without com-
parable environmental data lose much of their significance.

The volumetric determination of the plankton of streams
elsewhere has not been carried on to any considerable extent.
Steuer (701), in his paper upon the entomostracan fauna of the
backwaters of the Danube at Vienna, gives a brief list of organ-
isms observed in the plankton of the Danube itself, but no vol-
umetric determinations. His conclusion regarding the potamo-
plankton—a term whose very validity he contests—is: “Das
elnzige wichtige Ergebniss der ‘ Potamoplanktonforschung’
scheint mir bis jetzt die Feststellung der grossen Armuth un-
serer fliessenden Gewasser an Mikroérganismen zu sein.” It
isin a similar vein that Whipple (99) notes the paucity of
plankton organisms in rivers, resulting presumably from sani-
tary examinations of streams of New England. The results of
our investigation upon the Illinois River place limitations on
these conclusions. It is a question of time and nutrition and
the absence of deleterious industrial wastes. Given ordinary
stream water free from poisonous industrial wastes and suffi-
cient time for breeding, atypical plankton may be expected, it
seems, 1n every river, especially the larger ones, and in the
lower reaches of those of the smaller type.

Steuer’s volumetric work on the two backwaters of the
Danube, covering, it seems, nineteen collections in a period of
fifteen months, from June, 1898, to August, 1899, indicates a
planktograph somewhat similar to our backwater plankto-
graphs in that he finds a vernal pulse in May and a midsum-

558

mer rise in August. No trace, however, of the phenomenon of
recurrent volumetric pulses-so prominent in our fuller records
—appears in his infrequent data. His statement, “Den ganzen
Winter hindurch ist hier constant das Planktonvolumen unmess-
bar gering” (italics are his) has no counterpart in winter pro-
duction in our backwaters.

The plankton of the Elbe and its backwaters has been in-
vestigated by Schorler (’00), but no volumetric determinations
were made of its channel plankton because of the difficulties
occasioned by the current and by detritus in suspension. The
quantity of plankton per m.’ in three of the backwaters was de-
termined in twelve instances in April-October. There are in
the data suggestions of a May-June maximum and of one in
August, and the quantities are generally higher than the aver-
ages in our backwaters, though the greatest amount, 146 cm.°
per m.’, falls below the highest of our records. The channel
plankton of the Elbe was found generally to contain fewer
species and individuals than its contiguous backwaters.

The plankton of the Oder has been examined by Zimmer
and Schréder (799), but no volumetric determinations were
made. Regarding the quantitative conditions, Zimmer makes
the general statement that these are influenced by tempera-
ture. The quantity in December—February is very small, rises
in March, and again, to a greater degree, in May, but attains
the maximum for the year in August, declining rapidly after
the middle of September, and reaching the winter minimum in
December.

A comparison of the seasonal course of production of
plankton in the various lakes that have been explored in re-
cent years, with those of our several stations, does not promise
any profitable results, since most of the quantitative work is
limited in seasons, or has been made at such long intervals as
—in the light of our results—to raise some question as to the
representative value of such collections for comparison. In
addition to this, the very great divergence in the annual plank-
tographs of such localities as have been examined, including

559

our own, raises a doubt as to the value of any conclusions de-
rivable from such data. Steuer (01) has suggested that the
geographical position of the bodies of water in a large measure
determines the character of the planktograph. I should pre-
fer rather to put the emphasis upon temperature, which is not
everywhere merely a matter of latitude, and also to insist upon
the dominance of purely local conditions over those more gener-
ally operative, such, for example, as temperature, in determin-
ing the amplitude of the movements of the planktograph and
the general position of seasonal maxima. Illustrations in sup-
port of this view can be found in our own records—for example,
in Phelps and Quiver lakes. These are bodies of water within
three miles of each other, and with quite similar temperatures,
yet their planktographs are in some years quite as different as
any of those whose difference Steuer seeks to explain by lati-
tudinal positions. Furthermore, the “Sommerschlaf” which
he predicates as probable in tropical waters is least of all evi-
dent in Phelps Lake, the warmest of all our localities, where
temperatures during midsummer approximate those of the
tropics. More chronological series of collections at brief in-
tervals, not exceeding a fortnight, from many localities are
needed before general conclusions of permanent value concern-
ing the seasonal course of plankton production will be possible.

The maximum production has been used by some writers as
a basis of comparison of plankton production in different
bodies of water. It doubtless has a slight value in suggesting
the relative productivity of waters, though it would seem that
an annual average of weekly or fortnightly collections would
be very much more accurate. Difficulty attends these com-
parisons when deep and shallow waters are brought into con-
trast. If the volume of plankton under one square meter is
made the basis the shallow waters are at a disadvantage, while
if the amount per m.’ is made the basis the more barren deeper
strata reduce the average plankton content of deep waters to
a relatively small figure. Since, however, all strata, at least of
most bodies of fresh water, are productive of plankton, it

560

seems best to express the production of a body of water in vol-
ume per cubic meter. I have therefore used this basis through-
out my paper,and employ it in the following table of compara-
tive production in some of the representative bodies of water
thus far reported.

RELATIVE PLANKTON PRODUCTION BASED UPON MAXIMUM RECORD.

Depth | Plankton—in cm.*
Locality Investigator Date —in
: meters | Per sq. ;Per cu. me-
meter ter.
MOONS IRIS, soococcas Kofoid Wo Teal) B83 413.89) 71.36
SHOCOM IRIWEP scocsccods a iti, IDX, no) A, 12 60.11 14.59
OWwiver LAKE oosocoa000 ff Bh V, 1898] 4.2 353.98} 84.28
Doertisin LAKE 5 500 c4b000 SF 7, IW) UBOS| Bo Si 102.16] 40.70
IMeie? ILAIRG ooo bcno coe g Pa V, 1896] 1.64 667.55] 407.04
Thompson's Lake..... % Ii, V, 1895) 1-5 184.32 122.88 |
JPD@lOS ILAKO.bc5co¢c06 2 23, VIII, 1898 2 89.79! 448.096
; (12, VIII, 1896) 1.5 | 1439.5%| 684.*
Turkey Walkers acme Juday, (97) 12, VIII, 1806 6.09 $96. c 135.5%
Lake St. Clair..........|/Reighard, (94) 1%, IDX, KOR 37 74.52 17.05
Lake Michigan......... Ward, (95) 11, VIII, 1894] 107-8 | 176.29 1.64
Danube, backwaters...|Steuer, (oI) ? V, 1898 3h 26 12.
Elbe, backwaters...... Schorler, (99) 20, V, 1898] 3-4 | 438-584) 146.
Garda S€Ssscosccsoaacc Garbini, (’95) -—-— 50 62 1.24
orate SC@scceoaccuan. Zacharias, (’96)| 10, VIII, 1895] 4o 862 21.55
Plemer SECs go000000000 Apstein, ('96) GI, iloa} it 1242 73.07
Dobersdorfer See...... Apstein, (’96) A, X, 1891} 19.5 4242| 218.05
INiavierm Seen necaaceicr Huitfeldt-Kaas,
(98) ? 7 520| 74.29
Sognsvandet See....... Huitfeldt-Kaas,
(98) 30(?), VI, 2? Ishallow 240 —
Waterneverstorfer See.)Lemmermann,
(98) 1898 2 70 35.
Lac Leman. .|Jang, (99) 1, Wil, H@ofs, 129 Iol.9 0.85
Vierwaldstiitter See... .|Burckhardt, |
(‘oob) ? ? 150. ==
Neuenburger See...... Fuhrmann, (’00); 27, V, 1899 do Oil 3} 2.24
ISIS SOC 550000 9000 0|/Avamloxerde, (110) 14, XI, 1898 5 6.2 1.24
Shatlayanvere SES coco cococclelieroy, (eo) ©, WIM, 1898 | 23 2340 IOI .79

*Reduced to settling method of measurement by multiplying by 5. See Juday (’97).
+All records for our ‘stations reduced to settling method of measurement by multi-
plying by 2. See page 256.

A comparison of this maximum production in these various
localities, upon the basis either of plankton per square or cubic
meter, ranks our localities (barring Spoon River) among the
more fertile regions. If the content per cubic meter be the ba-

561

sis, production in Phelps and Flag lakes exceeds that reported
in any other body of water save only from the shoaler part of
Turkey Lake (Juday, 97). This greater production in Turkey
Lake disappears 1f centiifuge measurements are employed in both
planktons, the ratios being 203.52 and 224.48 cm.* for Flag and
Phelps lakes to 136.8 and 27.1 cm.* for Turkey Lake. The ten-
dency on the part of this maximum production in all of the lo-
ealities to fall in either the April-May period or in that of
August-September is apparent, though in some cases, as, for
example, those of Lakes Michigan and St.Clair, and Turkey
Lake, the limitation of collections to a few weeks in midsum-
mer precludes the possibility of a vernal pulse appearing in
their records.

562

Hconomic CONSIDERATIONS.

The [linois River and its backwaters, under present con-
ditions, contribute annually to the wealth of the state over 10,-
000,000 pounds of marketable fish and 15,000 dozen turtles, with
a wholesale market value of about $375,000. This amount will
be very considerably increased if to this sum be added the in-
crease due to retailers’ profits, to the unmarketed catch of
local fishermen and visiting sportsmen, and to the annual har-
vest of migrant water-fowl which are shot in great numbers for
local use as well as for shipment to distant markets.

Fish from the Illinois River find their way into the local
markets and are shipped by the car-load from the principal fish-
ing centers, such as Peoria, Havana, and Beardstown, to Chi-
cago, St. Louis, and New York City. The remarkable increase
in the catch of the introduced German carp from practically
nothing in 1894 to 5,890,200 pounds in 1901 is one of the fac-
tors which assures the economi¢ value of the fishing industry in
this stream. These fish find a ready sale among the foreign
population of our great cities, and hold the market without fear
of rivalry by any of our cheaper native food fishes.

In addition to these economic phases of the fishing industry
of the Illinois River there are other considerations which arise
from its value to the state at large as a field for sport and rec-
reation. This cannot be estimated in dollars and cents. The
backwaters and marshes teem with migrant water-fowl in
autumn and spring, and the spring-fed lakes are the home of
large-mouthed black bass (Micropterus pallidus), while the crop-
pies, the striped bass, the white perch, and the various sunfish,
to say nothing of the catfish and bullpouts, provide no mean
sport for the less fastidious angler.

Are these present resources of the stream economically
utilized under existing conditions? How may they be best con-
served? What developments are possible which will tend to in-
crease the production of this stream and multiply the numbers
of those who resort to it for recreation and sport? Does the
investigation reported in this paper have any bearing upon

563

these problems? These are questions which continually occur
to one familiar with this locality, observant of the operations
of fishermen, and cognizant of some of the seasonal flux of
life and matter inthis water world of which fish are but a
part.

The plankton is an integral part of the chain of food rela-
tions which extends from the water, with the gases, salts, and
products of decay dissolved therein, on the one hand, to the
fish and other vertebrates of commercial importance upon the
other hand. The water, the carbon dioxid dissolved therein,
the nitrogenous matters, and various salts in solution are util-
ized either by the grosser aquatic vegetation or by the micro-
scopic phytoplankton. In the former case the growing plants
are rarely utilized directly as food by any aquatic animals. A
possible exception to this statement is found in the case of the
turtles. Fishermen are accustomed to feed these animals,
when penned up for the market, upon “moss” or Ceratophyllum,
though it may be that the insect larvee and mollusks found in
the vegetation constitute the more important elements of
the food. It is only when this growth of vegetation decays
that it releases into the water the elements which conduce to
its fertility.

The phytoplankton, on the other hand, multiplies very rap-
idly and is immediately available for the support of the micro*
scopic animals of the zoéplankton, and this, and to some ex-
tent also the phytoplankton itself, is the immediate food of
most young fish upon hatching and the customary food of some
adult fishes,—such as Polyodon (Forbes, 88, and Kofoid, ’99) and
many minnows,—of the bivalve mollusks, and of many other or-
ganisms of sessile habit. The plankton is thus the prime source
of food of fishes and of many other organisms utilized by fish
as food. The chain of food relations, for example, between
the food elements of the water and the black bass is in the
main a short one, with the plankton as the principal link. Pro-
fessor Forbes (780) has shown that 86 per cent. of the food of
the game fish consists of other fishes, principally Dorosoma with

564

perch and minnows. In its youngest stages the black bass was
found to be a plankton (Hntomostraca) feeder, and later chang-
ing to a fish diet. It is interesting to note that its principal
fish food, young Dovosoma, is itself in its younger stages a
plankton feeder, secondarily adopting a limophagous habit.
The bottom shme thus eaten by the growing and adult Dorvo-
soma is a food largely because it contains so many organisms
normal or adventitious to the plankton. Thus at all seasons the
plankton forms an important link in the chain of food relations
leading to the black bass.

The buffalo-fishes and the German carp are likewise to a
large degree dependent for food upon the plankton in early
stages of growth, and, like Dorosoma, subsequently adopt the
limophagous feeding habit. The organisms of the plankton
thus at all times enter largely into the sources of their food
supply. The contents of the digestive tracts of these impor-
tant food fishes examined by me at Meredosia during the
spring months of 1899 were found uniformly to contain com-
minuted vegetable debris, which constitutes the greater part of
the unstable ooze or slime which abounds in the backwaters of
the river, and, associated with this, many H/ntomostraca, rotifers,
rhizopods, and unicellular or colonial alge, belonging to species
common in the plankton at that season of the year. The mori-
bund, the spore-forming, the egg-laden organisms of the plank-
ton sink to the deeper strata, and together with the normal
denizens of the bottom slme, which are everywhere adventi-
tious in our plankton, form the food of these fishes of greatest
commercial importance.

A very striking instance of the adaptation of the breeding
seasons of fishes to food conditions is found in their nice ad-
justment, for the most part, to the seasonal course of plankton
production in our waters. Most of our minnows, the dogfish
and gar, the Catostomide, the carp, Dorosoma, and the Htheosto-
mide spawn in central [llinois during April and the first of May,
while the bass, the sunfishes, and many of the Si/uride follow
in May. This brings the maximum number of young fish, re-

569

cently hatched and generally plankton feeders, just at the sea-
son of the vernal plankton pulse, which is often the maximum
production of the year. It may well be that the abrupt dimi-
nution of plankton following the May and June pulses is accel-
erated to a large degree by the plankton-feeding habits of the
fry of these fishes.

The plankton thus enters directly into the food of most
young fishes and of some important adult fishes, and indirectly
it is the primal source of food of most fishes. A knowledge of
its local and seasonal distribution and of the environmental
conditions which favor or impede its development is fundamen-
tal to any scientific utilization of the present resources of this
stream or any future development of resources now unproductive.

The data at hand afford an opportunity of comparing the
plankton production and the annual output of marketed fish.
The reports of the Illinois River Fisherman’s Association for
1894-1898 give the following statistics based upon estimates
and partial records of leading men engaged in the fisheries.
-They are not exact records, but the error involved is no greater
than that in the plankton data.

PLANKTON AND FISHERIES.

Total ber ° 3 __.3 |Llotal plankt
Vicar af stale st Average plankton content in cm." per m.° dieanangesl tin
fish marketed In channel In backwaters| Total cubic meters
1894 8,276,227 2.53 4.40 6.93 45,757
1895 8,588,000 5.91 10.76 16.67 83,340
1896 7,252,311 1.05 7.18 8.23 28,62
1897 9,703,298 3-51 5.85 9.30 94,605
1808 10,647,466 2.03 12.42 14.45 63,596
Aver’ge 8,933,560 2.71 8.42 II.13 67,750

Hydrographic conditions control to some extent the rela-

tive possibilities and efficiency of fishing methods, and this
adds to the difficulties of comparison.

While the relative and absolute amounts of plankton do
not determine the number of marketable fish taken in any
year, they do indicate in a measure the available primal food
supply, and this is a factor in determining the growth, and

566

therefore the weight, of the marketed catch. Some correspond-
ence in plankton and the products of the fisheries might there-
fore be expected, though on account of the complexity of the
problem and the hmitations of our data it is difficult to demon-
strate it in every case.

In 1894, when our data indicate a plankton production be-
low the average in channel, in backwaters, in their sum, and in
the estimated discharge, we find the total production of mar-
ketable fish also below the average (for 1894-1898). In 1895
our collections indicate an increase, approximating 50 per cent.
in plankton production as exhibited by each of the methods
tabulated, and there is also an increase in the product of the
fisheries, though it amounts to only about 4 per cent. The
direction of the change in production is the same in all cases. In
1896 plankton production falls in channel, in backwaters, in
their sum, and in total discharge, the decline in all but the back-
waters being greater than the increase from 1894 to 1895, and
we find, accordingly, that the decline in the product of the tish-
eries is also greater than its antecedent rise to the level attain-
ed in 1895. In 1897 plankton production again rises in the
channel, in the sum of channel and backwaters, and in total
discharge, but not in the backwaters. This apparent decline in
backwater production may be due to the elimination from our
data, for a part of the year, of Phelps, Flag, and Dogfish lakes,
thus giving undue weight to the depressing effect of the Quiver
Lake data. The fact that in Thompson’s Lake plankton pro-
duction rises from 6.67 in 1896. to 10.41 in 1897 is an indication
that plankton production in the open backwaters in 1897 rose
above the level of that of 1896. In correspondence with the
increased plankton production in channel, and total discharge,
we find the product of the fisheries rising from 7,252,811 pounds
in 1896 to 9,703,298 in 1897—a change not exceeded in any
other year of the records. In 1898 the product of the fisheries
continues to increase, reaching 10,647,466 pounds, but plankton
production rises only in the backwaters and in the sum of chan-
nel and backwaters, falling in channel and total discharge.

567

There is thus, in general, a correspondence between plank-
ton production and the product of the fisheries in that the d-
rection of movement 1m both is usually the same. They rise or
fall together. If we compare the changes of the product of the
fisheries with those of the sum of plankton production in chan-
nel and backwaters, as given in the table on page 565, we see
that the direction of the change is the same in both from year to
year in every instance in 1894-1898. If similar comparisons
are made of the product of the fisheries and plankton produc-
tion in channel or backwaters alone, or in total discharge, we
find that in three cases out of four the direction of the change
is the same in both. It is also generally true that years in
which plankton production is below the average are also ones
in which the product of the fisheries falls below the mean.

Plankton production at Havana, provided a similar plank-
ton content is maintained until the run-off reaches the mouth
of the river, would result in an average discharge of 67,750
cubic meters of plankton, equivalent in weight to somewhat
more than 149,050,000 pounds, or 15 times the annual produc-
tion of fish. To this wastage of organic matter, which in great
part is permanently lost to the drainage basin of the Ilhnois,
should be added the unutilized nitrogen and other food elements
in suspension and solution which escape with the run-off, es-
pecially of flood waters (see Table X.).

How shall this waste be prevented and the plankton be
turned into marketable fish? The problem is a complex one,
but the results of this investigation should contribute towards
its solution. The first step will be to impound the richly fer-
tilized flood waters and thus to afford time for the utilization
of their food elements by the developing plankton, which by
various chains of food relations is joined to marketable fish.
An illustration of the productive possibilities of impounded
Spoon River floods is seen in Phelps Lake, our richest plankton
station, and also the home of great numbers of young fish.
Thompson’s Lake, another impounding backwater, not only
breeds an abundant plankton but contributes no insignificant

568

portion of the 1,000,000 to 1,500,000 pounds of fish marketed
annually at Havana.

The development in recent years of extensive systems of
levees in the bottoms of the Illinois River for the purpose of
protecting farm lands from untimely floods increases the impor-
tance of, and necessity for, the reservoir backwaters. In con-
nection with these systems it might be feasible from an engi-
neering point of view, and perhaps even profitable from the
commercial standpoint, to convert some of the adjacent low-
lying: marshes, swamps, bayous, and lakes into reservoirs in
which invading and richly fertilized storm waters might be
impounded and retained as river levels fall. The increased vol-
ume of water thus provided should—-in the light of our results
—yield an abundant plankton, and support a large fish popula-
tion. Under present conditions of abundance of most of our
valuable food fishes in the Illinois, stocking such reservoirs
is relatively a simple matter. If properly protected from es-
cape at high water, such an area once stocked with the now
rapidly disappearing Polyodon, whose roe is much sought for
the manufacture of caviar, might become a very profitable in-
vestment.

As a basis for further development of the fishing industry
it seems desirable that pubhe and private waters should be
more accurately defined, and that fishing privileges for market
purposes in the former should be matters of license or franchise
to responsible parties, so that legislation concerning methods
and seasons of fishing could be more easily controlled. With
the ever increasing industrial development in the drainage ba-
sin of the Illinois River, especially in Chicago and the minor
cities along its banks, there is great danger that industrial
_ wastes will so accumulate in the river waters that not only the
plankton but also the fish and other animal inhabitants will be
driven out or exterminated. Legal supervision over the dis-
charge of such industrial wastes may soon become imperative
for the Illinois River as it has for some European streams.
With the legal status thus clearly defined, and with wise legis-

569

lation which should efficiently prevent pollution of the stream
by deleterious industrial wastes, protect the most desirable
food and game fishes from depletion, and, at the same time, per-
mit the full utilization of the annual crop of matured and mar-
ketable fish, there is no apparent reason why the Illinois River
and its backwaters should not become an increasing source of
wealth to the state, and the great waste which now occurs be
utilized to a considerable extent in future development.

CoNCLUSIONS.

The following are the more important conclusions arrived
at from this examination of the plankton and its environment
in the Illinois River and its backwaters, based upon the study
of 645 collections made in 7 localities in 1894-1899.

1. There is little correlation between the seasonal flux in
chemical conditions (as shown in data of sanitary analyses)
and the seasonal course of plankton production (as shown in
the catches of the silk net). The nitrogenous matters are in-
fluenced by the plankton pulses, especially when diatoms are
multiplying rapidly, but the changes are not uniform or pro-
portional.

2. The plankton in the Illinois River is distributed with
a uniformity approximately equal to that found in German
lakes and in Lake St. Clair. The average departure from the
mean in short distances (3 miles) probably falls within + 10
per cent. Chronological catches in periods of 2 to 15 days in
14 series yield an average departure of + 14.1 per cent. In the
river, in 205 miles of the course the average departure in flood
conditions was + 51 per cent., or + 43 per cent. if the river is
divided into four sections, or + 29.7 per cent. if computations
are based on total catch of the net.

3. The average departure from the mean plankton con-
tent in two tests in a cross-section of the river is + 27.2 or
+ 23.2, or, omitting marginal collections, = 21.9 or + 12.1 per
cent.

4. The plankton method can be applied to a stream as
legitimately as to a lake.

570

5. The mean of the monthly averages of 235 collections
in the Illinois River is 2.71 cm.’ of plankton per m.* of water.

6. The plankton of the river channel is subject to great
seasonal and annual variations. The monthly averages of all
collections indicate a period of minimum production of plank-
ton in January-February, of rising production in March, of
maximum production for the year in April—June, usually cul-
minating ina vernal maximum about the end of April and
often declining rapidly to a low level in June. The average
monthly production declines gradually during the remainder
of the year to the winter minimum in December.

7. Individual years vary greatly from these averages as a
result of hydrographic, climatic, and other environing con-
ditions in varying combinations.

8. The waters of Spoon River contain but a very small
amount of plankton (.465) except at very lowest stages, when
the flow is ata minimum. Its production at other times (.044)
is less than one fiftieth of that in channel waters which it joins.
Chemical conditions in this tributary are apparently such as to
support a large plankton. The recent origin of the water is
the cause of the low production. Its diluent effect on the plank-
ton content of the channel is about 10 per cent.

9. Quiver Lake produces less (1.75) than channel waters.
At high stages its production is relatively larger, and most re-
sembles that in channel waters, while at low levels, when sub-
merged vegetation is dominant and access of tributary waters
of recent origin relatively great, its production is both rela-
tively and actually low. It is predominantly a diluent of
channel plankton.

10. Dogfish Lake produces (3.16) more than channel
waters, freedom from access of tributary waters permitting a
higher production than in the contiguous waters of Quiver
Lake.

11. Flag Lake also produces more (9.28) than channel
waters, the freedom from access of tributary waters, the im-
pounding function, and decaying vegetation favoring high pro-

571

duction. The plantographs of this lake are marked by extreme
changes in brief time, and by depression in production with
the emergence of vegetation.

12. Thompson’s Lake also produces more (8.26) than
channel waters, and maintains its higher level of production
more generally. Its impounding function and the freedom
from access of tributary waters contribute to this result.

18. Phelps Lake produces the most abundant plankton
(22.55) of all our localities, freedom from vegetation and from
access of tributary waters, and the highly developed impound-
ing function contributing to this result. The maximum pro-
duction in our records, 224.5 em. per m.*, was found in this lake
on Aug. 23, 1898. This lake is marked by relatively and abso-
lutely high production in summer and autumn.

14. The course of plankton production in channel and
backwaters throughout the year exhibits a series of recurrent
pulses, culminating in maxima and separated by minima,
which give the planktograph the appearance of a series of
“frequency of error” curves of varying amplitudes. These
pulses generally have a duration of 3 to 5 weeks, and tend to
coincide in their location in all localities coincidently exam-
ined by us. This similarity in the direction of movement in
production amounts quantitatively to 65 per cent. of the possi-
ble comparisons in our records. This cyclic movement in pro-
duction is plainly influenced, accelerated or retarded, or its
amplitude extended or depressed, by environmental factors, but
is not itself traceable to any one or any combination of them.
A brief interval of examination—not more than one week—is
essential to a demonstration of the existence of these pulses.

15. Area and depth, within limits of our environment,
show little relation to plankton production.

16. Age of the water is an important factor in determining
production in streams. Young waters from springs and creeks
have but little plankton, and even such tributaries as Spoon
River (drainage basin 1,870 square miles) contain but little
plankton, principally of more rapidly developing organisms.

572

This barren water, impounded for 10-80 days in backwater res-
ervoirs such as Phelps Lake, develops an abundant plankton.
The rate of run-off and replacement of impounded waters de-
termines to some extent the amplitude of production. This is
greatest where run-off is least and rate of renewal slowest.

17. Fluctuations in hydrographic conditions constitute
the most immediately effective factor in the environment of the
potamoplankton. Rising levels usually witness a sharp decline
in plankton content (per m.’) as barren storm waters mingle
with or replace plankton-rich waters of channel and reservoir
backwaters. Falling levels are periods of recovery and increase
in plankton. Stability in hydrographic conditions conduces to
rise in production at all seasons of the year, and instability is
always destructive. Winter floods tend to lower plankton
production; spring floods increase it.

18. Temperature affects production profoundly. Below
45° the plankton content in the river is only about 9 per cent.
of that present above this temperature, and in backwaters but
29 to 40 per cent. Minimum production is at times of mini-
mum temperature. The vernal pulse in production attends the
vernal rise in temperature and culminates at about 60°-70°.
With the establishment of the midsummer temperatures (about
80°) production falls from 44 to 87 per cent. in channel and
backwaters. It 77ses, however, 68 per cent. in Phelps Lake, so
that other causes than temperature may be operative in pro-
ducing the midsummer decline. The autumnal decline in tem-
peratures is accompanied by decline in production in the channel
and in Quiver Lake, but by an increase in other backwaters,
which exhibit a tendency toward an autumnal pulse. The de-
cline to winter minimum occurs in December.

An early spring accelerates, and a late spring retards, the
vernal pulse, and a late autumn prolongs the autumnal pro-
duction. Summer heat pulses often attend plankton increases.
Minimum temperatures are not prohibitive of large plankton
production. The December production in Phelps Lake in 1898
(43.14 em.’) exceeds the vernal maximum elsewhere in all local-

573

ities but one, but falls much below the summer production in
Phelps Lake. The ice-sheet is not inimical to a considerable
plankton production unless stagnation conditions occur.

19. Light affects plankton production. The half year with
more illumination and fewer cloudy days produces from 1.6 to
7 times as much plankton as that with less illumination and
more cloudy days. Seasons of unusual cloudiness are accom-
panied by depression in production.

20. Lakes rich insubmerged vegetation produce less plank-
ton than those relatively free from it, in an annual ratio of 1 to
6and a monthly ratio varying from 1.5 to 20 to that of 1 to 20.
The higher ratios generally prevail in periods of dominance of
vegetation. Quiver Lake produces more plankton when free
from vegetation than when it abounds in it. The emergent
and rooted vegetation of Flag Lake conduces by its autumnal
and vernal decay to large plankton production, but tends to de-
press production in summer.

21. The normal regimen of the course of plankton pro-
duction in the Illinois River and its backwaters does not form
a definite seasonal planktograph, but consists rather of a series
of recurrent plankton pulses, whose varying amplitudes are
largely determined by the fluctuating environmental factors of
the unstable fluviatile environment. Hence planktographs of
the same locality in different years and of the different sta-
tions in the same year show resemblances only in such funda-
mental features as the winter minimum and the vernal pulse.
The relative productive rank of the several localities is gener-
ally maintained, and more completely in the more Stable en-
vironments.

22. The plankton of the Illinois River is largely autono-
mous. Seepage and creek waters are diluents of its plankton
and add little to its diversity. Even Spoon River is generally
a diluent, reducing the plankton content 10 per cent. and add-
ing but few diversifying species to its population. The reser-
voir backwaters, on the other hand, generally contain a more
abundant plankton than the channel, the amount, on the bases

574

of monthly averages, being from 1.3 to 17 times as great. At all
levels, waters from impounding areas in the bottom-lands are
drawn into the channel, mingled with the plankton-poor contri-
butions of tributaries, and further enriched by the growth of in-
digenous channel plankton. The reservoir backwaters are thus
of great importance both as a source of the channel plankton
of the Illinois River and in its maintenance.

24. The total annual production of plankton in the Ilh-
nois River, on the basis of normal discharge and a plankton
content at the mouth of the river equal to that of our average
record at Havana, is 67,750 cubic meters.

25. Filter-paper catches indicate the presence, on an ay-
erage, of a plankton 3.3 times the volume of that taken by the
silk net. Leakage through the silk is therefore a matter of
some volumetric importance.

26. The annual production of plankton and of the fisher-
ies of the Illinois River show some correlation in their changes
from year to year.

University of California,
August 23, 1903.

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‘

TABLE XIV.
RELATIVE NUMBER OF PLANKTONTS IN ILLINOIS RIVER AND SPOON RIVER.

ALG DIATOMS RHIZOPODA MASTIGOPHORA INFUSORIA
Date a 2 g a @
iS) 5 S g S) gs iC) q iS) |
1S 5 = 5 eS 8 & 8 & 5
= a = a = 5 = 2 a By
= NM 4 Nn lal oD) H Nr il mM
8, 896, oe 11,280} 28,800) 5,960) 1,508, 000 3, 360 23, 800 3, 540
025. 20 2 29, 376] 18, 080 768 110, 000 960 11, 200 192
350, re 3, 360), 16,850) 2, 880 ORS SD |e 40, 106 240
682, 200 6,240] 14,280) 8, 160 755000| Seen 27, 672 2, 400
816, 400 10, 080)) 380,400) = 2, 640) 1, ae 200) 480 65, 200, 1,200
pei asee eahones IG, BNO) ccesscccedl| | By etst0)|} --- AR) | eee 1, 920
064, 500 480) 25,200) 4%, 360 “88, 800 480 44, 000 7, 200
963, 916 7, 200 873 500 179, 606; 240 10, 083 480
G59 60) eee 120) 480 64, 880 120 1, 440 240
745, 583 9, 688]| 16,825) 3,336) 414, 166) 680 27, 988) 1, 935
231, 900 240 300, 720 42, 420 160 3400 ee
339, 480}_.__.. ese 10, 700) 37,440 46, 600) 3, 840 18, 800 2, 880
231, 900 240, 000 2, 240) 105, 600 172,100 9, 600 18, 240} 19,200
328, 414, 320] 102,000} 11,520) 379, 20027, 987, 400] .............. 515,920] 42, 000
9, 827, 200) 3, 048, 000)) 25, 760) 40, 900}| 9, 029, 360) 43, 200 29, 600| 98, 400
1, 937, 600 85, 200] 232, 600) 13, 200 148, 006 3, 700}/12, 186, 000 1,300
2, 318, 160 54, 000 8,400) 1, 200 439, 600 18, 000 27, GOO!) cecescsecce
26 VIIL ee 760 24, 000 847, 320 4,800} 19,200). ......... 408, 160; 53, 000 180, 000 5, 000
11 IX | 406, 400) 816, 000 28 2) 440 662, 400] 118, 000) 28, 800) 1, 624, 800} 5, 030, 400 12, 000} 249, 600
2 XI 28, 980) 145, 000 148, 880. 744, 000 8,900) 2,400 1, 100 33, 600 26,500} 55, 200
30 AL 940 | eee ee 90, 725 24, 000 11,100) 116, 400 244, 420 4,900
28 XII 1,200) 3,600 65, 400 36, 000 reldenes 15, 400 54, 000 45, 600 _ 19,200 200
Averagt| 66,725} 85,534) 34, 644, 610/416, 920|| 37,505] 50,788] 3,577,171] 447,158] 1,109,007) 41, 473
1898 x
25 I BtHflicebend wees 174, 901 16, 800) 66.338) 19,200 22, 059) 2, 400 190,017} 39,000
22 It LOO 211, 653 4,800] 141,524) 21, 600 227,448)... x 69.498} 14, 400
29 IIT 5, 400) 132, 140 27, 320 1,400) 1, 760 324, 800) () 42,020/ 18, 880
10 V || 68,800 , 224, 400} 1, 78, 400) 49, 800) 14, 880/84, 967, 600) 55, 680 129, 600) 11,520
a uaV alan sli 200 803, 600 31,200) 23,600) 21,600] 597, 000 7, 400] 1,516,000) 63, 600
5 WII | 50,040 3, 772, 000 7,200) 19,360) 10,800] 536, 800 51, 600 20, 440} 108, 000
5 VILLI | 308, 040 360, 240. 50, 400) 16,80) 14, 400 252,400) 112, 800 129, 600 3, 600
12 IX || 57, 060) 217, 000 8, 400} 28, 00) 22.800 19, 500 2, 400 56, 640 6, 000
4 x 25, 000) 837, 200 37, 440 1 2 580} 4, 840 265, 600 16, 800 35, 900 1, 440
2 XI || 18.500) 5,500 981, 000 15, 000} 32,060) 2,500 5, 500 3, 600 69, 060} 16, 800
Giexelele 520 eae 201, 250 9,120 1, 000 480|| 1. 708, 000 4, 320] 7, 620 8, 480
Average] 50,373) 4,916) 32, 087, 762 180, 553|| 35,678} 12, 260) 8, 084, 246 23, 422 206, 036} 26, 065_
1899 Mi |
3 I 20 10, 300 8, 840 220) 960 143, 020 3, 360 108, 940 1, 920
i TSN | eee 425 66, 750]. .-... eee 1,125) _ 1,200 117, 000) 7, 200) , il; 200
7 Li 140 | ee 59, 120 800 3, 200) 38, 400 8995200 Reeee ee 30, 820} .-
Average Bl celsate nse 45, 390 1,547 1,515) 13,520 386, 407 3,520) 48, 586 Th 040
Grand Av....| 43,539) 80,513] 23, 031, 820 293, 788}] 289, 637} 23,281] 8,921,328) 161,149] 468, 051 22) 999
Ratio .... 1.4 1 78 1 12 1 24 1 20 i

615

TABLE XIV.—Concluded.
RELATIVE NUMBER OF PLANKTONTS IN ILLINOIS RIVER AND SPOON RIVER.

Date

10

—
wRwrnr
i
A

>

verage

Average
Grand Ay...

Ratio _...

INSECT

TOTAL SPECIES

ROTATORIA | ENTOMOSTRACA LARVA) MISCELLANEOUS TOTAL PLANKTONTS
2D a D a QD i)
iS | Ss = i) q Ss S iS) q is) |
a S & Sep Sih si Ss |) ee] S A ©
S a | eee ont) eal eos Ws oll on a D
— seals pe ease
361,680| 2,720] 68,160/ 600] 160] 240) 4,120] 680] 114] 71] 10,973,920) 34, 460
185, 720 768| 31,480/ 360] S80] 1,488) 1,520] 216] 100] 22] 1,388,120] 34, 704
45,5023, 600) 63, 070] 3, 360]... 240) 2607 | 240) 85] 19 600,005) 14,520
48, 642 960} 16,400] 560)... 280] 2,400 | 1,480] 85 | 20 977, 434 20, 080
131,600 3,560} + 9,120| 480] 320] 80) £640] 240) 68| 22] 2,173) 20, 920
Pe cae ASO ow neesd | DN eed| PA Ll a Ba eG
172,800, 2,880, 4,920) 40/80 | 80] 5,360 | 2,880] 63 | 20] 5,408,460| 17, 880
86, 700 840) 9340) oe, 80] 1,665 |... 56 | 12] 1,252,575 9, 820
100, 340 240| 26,140] 130} 40] 30) 520] 120) 42] 9 362, 720| 1,360
T41, 634)_—«1, 561) 28,539) 899) 85 | 309] 2,854] 655) 77 | 24] 2,892,085) 20, 492
10, 460 500, 3,520] GO|... 40] 1,040]... 44] 10 293,080] 1,720
26,200] 2,880] 2,100) 480). |... 6,400 | 5,280] 45 | 16 450,280| 52, 800
47,180] 20,000) 21,320] 9,600} 440 |_-_... 2) 080 19,200) 81} 11) 1,498,200] 423; 200
1,276,000] 34,800] 67,000] 4,200} 320] 600] 4,000 [28,800] 67) 20] 358)278; 080] 591. 600
2,287,160 217,400] 84,720] G00) 2, 100] 10,240 | 2,500) 90] 36] 91,362, 440] 3:460, 600
351,900 27, 900 71 | 33) 14,968,406] 136,700
658,120 15, 300] 102 | 33) 3,667,220 93, 400
2, 059, 860) 1, 330, 200 80 | 32] 3,782) 800] 1, 418, 000
1, 744, 250) 2, 362, 400) 62| 49] 4;832, 640/11, 467, 600
8,900) 1; 072, 800 65 | 29 239, 660) 2, 061, 000
109, 840} 1, 965, 600 i 46 | 19 520, 165] 2, 113, 900
9,040) 1, 135,200] 5, 720/10, 80g s|| 23] 38 160, 760| 1, 258, 800
715,701) 682, 082) 91,918) 3,987) 85 | 703) 11,757 | 4,898) 67 | 25 || 40, 004, 478| 1, 923, 27
|
126,603) 2,600| 4, 788 5,000] 74] 18 592, 831] 85, 600
48, 649 800) 3,285 200/ 35) 9 708,501] 41, 800
115,880 17,920] 22. 180) 3 720] 100) 31 645,840] 70, 400
2, 663, 400] 24, 480) 235, 400] 2, 800 960] 78 | 40 || 402, 352; 600) 1, 895, 360
903,000] 22, 900| 438, 800/14, 700] 400 | 2, 100] 23, 600 |. 67 | 31] 34,323,200] "165, 900
153,000) 8,400) 4, 920 200] 96| 23] 4,562,360] 209, 100
1,294,240) 61, 200| 22, 160 || 8i| 41) 2,386,920] 261, 200
197,960 2,400) 24.720 1,500! 89| 201 1,603,300] 48; 700
105,020) 2 S80] 33,880.......| 40] 160) 2,700 |........ 79 | 24]| 15287;720| 65,000
156,300 9,600 8, 600 200) 75 | 24]| 1,275,380] 53, 300
64,280| 7,280} 9, 740 LD || econ. 40| 17} 2,043,090] 24. 800
529,848) 14,587 73, 498) 2,089] 167 | S87] 6.202) 798] 74| 25 41,071,067) 260,560
41,300| 6,720] 2,840) 40)._.......|____... 25640) |e 47 | 18 309,280) 16,840
112; 310)... |] 13, 976 600] S61 |. _ al G 318,022) 10, 800
108, 860 B00) 18,500) | 2,140 |12,000) 47 | 6] 1,121,980] 52; 000
87,490, 2,507] 11,72) 2 Pat Se ec eee 41 | 10 583, 094) 26, 547
465, 067| 238, $28| 63,983] 2,255] 104 | 616] 6,805 | 2,430] 69 | 24 |, 28,283,295] 750, 420
1.9 i ih a |) ep ot | eachcls al [eee val 38 1
lI

616

SOLIDS IN SUSPENSION AT STATION KE,

Accession number

TABLE XV.
BERKEFELD FILTER.
: Cu. em. | Cu.em Sut River
Denise strained silt per cl. m. | gage
1897 5, 000 1.40 280 2.6
1897 10, 000 11558) 153 2.8
1897 5, 000 1.50 300 2.8
1897 5, 060 2.75 550 3.2
1897 5, 000 6.56 1,312 3
1897 5, 000 1.28 256° 3.4
1897 5, 000 5.2 1, 052 3.2
1897 5, 000 308) 186 Ch)
1898 5, 000 4.25 850 Bhi
1898 5, 000 7. 60 1,520 5.8
1898 5, 000 5. 01 1, 002 6.8
1898 5, 000 4.00 800 7.4
1898 5, 000 catal 542 eal
1898 5, 000 7.86 1,572 9
1898 5, 000 8.01 1, 602 10.7
1898 5, 000 3. 60 720 11.4
1898 5, 000 2.51 502 abl
1898 5, 000 3.71 742 12,1
1898 5, 000 2.34 468 14.1
1898 5, 100 4.90 961 16.5
1898 5, 000 3.91 782 17.6
1898 5. 000 4,40 880 14.8
1898 5, 000 1.81 362 13.1
1898 5, 000 2.04 408 12
1898 5, 000 2.07 414 elt
1898 5, 000 2.29) 458 10.3
1898 5, 000 3.97 794 10.1
1898 5, 000 3.01 602 13.6
1898 5, 000 eed 422 13.6
1898 5, 000 1.98 396 12.5
1898 5, 000 1.43 286 11.9
1898 5, 000 Zi 254 10.8
1898 5, 000 2.80 560 10
1898 5, 000 1.90 380 8.7
, 1898 5, 000 1.94 388 7
, 1898 5, 000 2.04 408 4.7
, 1898 5, 000 156) 312 2.9
1898 5, 000 1.58 316 Pai
1898 5, 000 2.58 516 3.2
1898 5, 000 1.69 338 Bhi
1898 5, 000 3.08 616 4.2
, 1898 5, 000 2.42 484 3.9
1898 5, 000 2.90 580 4.7
1898 5, 000 2.04 508 4.2
1898 5, 000 2.40 480 4.2
1898 5 000% [us 2 ceen ates | eae 4.9
1898 5, 000 2.30 460 4
1898 5, 000 1.70 340 3.9
1898 5, 000 1.26 252, 3.8
; 1898 5, 000 4.00 800 4.3
, 1898 5, 000 3.20 640 6.3
1898 5, 000 2.77 554 6.7
1898 5, 000 4.41 882 Toa!
, 1898 5, 000 5. 82 1, 164 8.5
1898 5, 000 1.48 296 8.3
1898 5, 000 74 148 Tae
1898 5, 000 3.74 748 6.7
1898 5, 000 iil 234 6.6
[, 1898 5, 000 1.04 208 d.9
[T, 1898 5, 000 1.26 252 (a 1
, 1899 5, 000 4,20 840 6.8
[, 1899 5, 000 3.75 750 7.9
1899 5, 000 6.30 1, 260 8.2
1899 5, 000 4,06 812 8.9
1899 5, 000 3.06 612 8
1899 5, 000 3.42 684 8
IT, 1899 5, 000 1.15 230 7.3
Ti, 1899 5, 000 1.42 284 6.6
1899 5, 000 1.80 360 by)
il, 1899 5, 000 27.08 5, 416 10.2
TII, 1899 5, 000 20.30 4, 060 12.9
ITI, 1899 5, 000 17.40 3, 480 13.1
III, 1899 5, 000 16. 82 3, B64 BL
i 9. BE 1, 870 ils}, 6)

HOQN22

617

TABLE XV.—Continued.
SOLIDS IN SUSPENSION AT STATION M, BERKEFELD FILTER.

P Cu.cem. | Cu.cm, Silt River
Accession number Date strained] silt | percu.m.| gage
30; XT, 1897 5, 000 HEBY/ 314 3.2
28, XII, 1897 5, 000 1.20 240 3.2
25, I, 1898 5,000 | 13.11 2, 622 6.8
Re, II, 1898 5, 000 5. 64 1, 128 010.7
29, III, 1898 2,500 25) 10, 044 16.5
10, V, 1898 5, 000 5.10 1, 020 10.3
7, VI; 1898 5, 000 3.38 676 12.5
5, VII, 1898 5, 000 1.63 326 8.7
5, VIII, 1898 5, 000 3.58 716 2.98
12, LX, 1898 5, 000 6. 62 1,324 4.4
4, X, 1898 5, 000 2.20 440 4
2, _ XI, 1898 5, 000 2. 92 584 6.5
6, XII, 1898 1, 900 61 21 7.2
Bh > 1899 5, 000 2. 56 p12 6.8
16 II, 1899 5, 000 94 188 ao:
7, IIT, 1899 5, 000 40. 35 8, 070 12.9
PVE Ao COMO rl SOS ees nee. ee ey ee Se ee eee 1, 745. 55)
TABLE XV.—Continued.
SOLIDS IN SUSPENSION AT STATION C, BERKEFELD FILTER.
Nae x Cu.em. | Cu.cm. Silt | River
Accession numbe1 Date strained silt per cu.m. | gage
1897 10, 000 .98 98 2.8
, 1897 5, 000 1.47 294 3.2
1897 5, 000 1.50 300 3.4
1897 5, 006 EDS 116 3.2
1898 5, 000 SE Bil 662 eh if
1898 5, 000 Pal 542 6.8
1898 5, 000 2.24 448 fol
1898 5, 000 2.80 560 10.7
1898 5, 000 2.04 408 aa
1898 5, 000 1.66 332 14.1
1898 5, 000 9.38 1, 876 17.6
1898 5, 000 2.68 536 6} al
1898 5, 000 1. 63 326 ileal
1898 5, 000 1.10 220 10.1
, 1898 5, 000 1.58 316 1356
1898 5, 000 1.02 204 12.5
1898 5, 000 . 84 168 10.8
1898 5, 000 - 40 80 8.7
1898 5, 000 1.10 220 4.7
1898 5, 000 1.03 206 Pati
1898 5, 000 1.65 330 By. fy
1898 5, 000 2.01 402 3.9
1898 5, 000 1.85 370 4.2
1898 5, 000 1.62 324 4.9
1898 5, 000 1.06 212 3.9
1898 5, 000 . 89 178 4.3
1898 5, 000 1.14 228 6.7
1898 5, 000 Wg 350 8.5
1898 5, 000 - 93 186 tae
1898 5, 000 .78 156 5.9
1899 5, 000 1.66 332 6.8
1899 5, 000 5.48 1, 096 8.2
1899 5, 000 3.06 612 8
1899 5, 000 2.10 430 8
1899 5, 000 1.12 224 6.6
1899 5, 000 19.78 3, 956 10:2
1899 5, 000 12.99 25,098 ie}, 1
1899 5, 0Q0 8. 82 1, 764 18},5)
PAS rr rer Ty OOo ee ere rece a oe ae ee ae ee sn Ee eo ese 378. 46)

618

TABLE XV.—Continued.
SOLIDS IN SUSPENSION AT STATION G, BERKEFELD FILTER.

: Cu.cm. | Cu.em.| Silt | River
Accession number Wate strained] silt | percum.| gage

DROS Masao n tats Hee a ee ees a 15; XO, 897, 5, 000 7. 85 1,570 2.8
22636. 5 30, <1, 1897 5, 000 5. 36 1, 072 3.2,
22640. 14, XII, 1897 5, 000 7.50 1,500 3.4
22645. 28, XII, 1897 5, 000 1.41 282 phe
22653... 20, , 1898 5, 000 2.10 420 6.8
22657... 8, II, 1898 5, 000 2.26 452 Coil
22661. 22; II, 1898 5, 000 1.92 384 10.7
22667. III, 1898 5, 000 3.23 646 11

22672. 22; III, 1898 5, 000 4.01 802 14.1
22678... IV, 1898 5, 000 4.68 936 17.6
22683... 1959 Vi) 1898 5, 000 3.18 636 13.1
22694 __. h , 1898 5, 000 1. 66 332 11.1
22699 11, , 1898 5, 000 1.37 274 10.1
22003... 24 V, 1898 5, 000 3.10 620 13.6
22713... VI, 1898 5, 000 - 96 192 12.5
22719)... 21, VI, 1898 5, 060 1.25 250 10.8
22724. , WII, 1898 5, 000 1.48 296 8.7
22782. 19, VII, 1898 5, 000 2.42 484 4.7
22750. aot 1, VIII, 1898 5, 000 3. 80 760 2.6
22764. 16, VIII, 1898 5, 000 4.14 828 3.7
22769_ 30, VIII, 1898 5, 000 3.80 760 3.9
22776... 18, IX, 1898 5, 000 4.23 846 ° 4.2
22781. Pile X, 1898 5, 000 2.06 412 4.9
22787 iil, X, 1898 5, 000 6. 86 1,372 3.9
22792 26, X, 1898 5, 000 4.12 824 4.3
22798... » AI, 1898 5, 000 2.85 570 6.7
22803. 22; XT, 1898 5, 000 1.45 290 8.5
22808... 6, XII, 1898 5, 000 1.08 216 (er
22815... 20, XII, 1898 5, 000 1.55 310 5.9
22820.. 35 T, 1899 5, 000 2.66 532 6.8
22827... iY, I, 1899 5, 000 3. 88 776 8.2
22832. 31, I, 1899 5, 000 3.52 704 8

22840... 14, I), 1899 5, 000 3.18 636 6.6
22846 28, II, 1899 * 5, 000 8. 91 1,782 10.2
22852-.-- : 14, IIT, 1899 5, 000 13. 86 2, 712 13.1
R285 ieee Oe ae) SBR Tena Pave tices balers 5 UO 28, IIL, 1899 5, 000 11. 65 2, 330 13.5

AV ORAG ONO BOG seis ees ae RE pen coca gs see te isan Nise ema cng te ee co RENE 556. 48

TABLE XV.—Concluded.
SOLIDS IN SUSPENSION AT STATION KF, BERKEFELD FILTER.

s Cu. em. | Cu. em. Silt | River
Accession number Date strained] silt | percu.m.| gage
22666 3, ITT, 1898 5, 000 4.20 840 il)
22670. a 15, III, 1898 5, 000 9. 08 1, 816 iat
29, ILE, 1898 5, 000 15. 25 3, 050 16.5
12, TV, 1898 5, 000 4.76 952 14.8
26, IV, 1898 5, 000 4.95 990 LZ,
ales V, 1898 5, 000 2.26 452 10.1
Bul, V, 1898 5, 000 6.12 1,224 13.6
14, VI, 1898 5, 000 5. 63 1,126 11.9
28, VI, 1898 5, 000 2. 09 418 10
12, VII, 1898 5, 000 3. 84 768 7
26, VII, 1898 5, 000 7.16 1, 432 2.9
9, VIII, 1898 5, 000 10. 00 2, 000 3.2
23, VIII, 1898 5, 000 2.47 2, 494 4,2
6, IX, 1898 5, 000 24.12 4, 824 4.7
20, TX, 1898 4,500 16. 01 3, 558 4.2
4, X, 1898 5, 000 12.43 2, 486 4
18, X, 1898 5, 000 11.18 2, 236 3.8
2, XI, 1898 5, 000 7.24 1, 448 6.5
15, XI, 1898 5, 000 6.51 1, 302 Coll
29, XI, 1898 5, 000 2.91 582 8.3
13, XII, 1898 5, 000 . 70 140 6.7
27, XID, 1898 5, 000 2.23 446 6.1
10, T, 1899 5, 000 3.90 780 7.9
24, I, 1899 5, 000 2.34 468 8.9
Me II, 1899 5, 000 4.44 888 583
21, IT, 1899 5, 000 1. 64 328 5.5
7, III, 1899 5, 000 9. 48 1, 896 12.9
21, III, 1899 5, 000 18. 57 3, 714 13.7

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EX PILWAINUATHOUN QUE IPILUANICTES

ACRE alte
Map of the Illinois River Basin, modified from a map in Cooley’s “ Lakes

and Gulf Waterway,” facing p. 58. Boundary of catchment-basin of whole system
shaded, those of individual tributaries marked by dotted lines.

PLATE II.

Map of field of operations of the Illinois Biological Station at Havana, IIl.,
1894-1899. Locations of plankton stations in Illinois River (E), Spoon River (M),
Quiver Lake (C), Dogfish Lake (L), Flag Lake (IX), Thompson’s Lake (G), and Phelps
Lake (F).

PLATE III.

Illinois River bottoms at high water in spring flood in March, 1808, looking
westward. River gage about fifteen feet above low-water mark. Taken from base of
the eastern bluff, just below field headquarters (see Plate II.) on Quiver Chute. En-
tire bottoms submerged, Quiver Chute and Illinois River united, Seeb’s Lake show-
ing dimly through the forest on west side, beyond this the broad expanse of Flag
Lake, with low forest intervening between it and Thompson’s Lake. Western bluff
visible.

PLATE IV.

Illinois River at low water during summer of 1894. Taken from same point as
Plate Ill. River gage about 2 ft. above low water, showing minimum levels since
erection of dam at LaGrange. Mud spit between Quiver Chute and Illinois River
exposed. Summer foliage and atmospheric conditions obscuring bottom-land waters

to westward.
PLATE V.

West bank of Illinois River a short distance below plankton station, looking
northeastward. Taken during low water in midsummer of 1894. Sloping shore of
black alluvium covered by low vegetation. Narrow marginal belt of vegetation visi-
ble. River about 400 feet in width.

PLATE VI.

Sun-spots, rainfall], and riverlevels. Upper section of figure taken from Lockyer
(‘o1). Middle section gives fluctuations in average rainfall in Illinois above and be-
low the mean, as given in records of U.S. Weather Bureau. Lower section gives
fluctuations in mean annual river levels, compiled from records at Copperas Creek
dam, 1878-1899. Average of all annual means shown at the left.

* Plates IV., XV., XVII., and XXI. are from the Biennial Report of the Director of this
Laboratory for 1893 and 1894; plates II., V., VIII., XVIII., XIX., and XX., from that for 1895 and
1896 ; and plates III. and XVI., from that for 1897 and 1898.

626

PLATE VII.

Hydrographs of Illinois River, 1879-1899, from records of State Canal Com-
missioners published in reports U. S. Army Engineers, taken at lower gage on Cop-
peras Creek dam, and from records of U.S. Army Engineers, taken at lower gage on
LaGrange dam, 1883-1899. Mean hydrograph at the right based on means of monthly
averages.

PuaTeE VIII.

Seasonal distribution of plankton in Illinois River, Station E, in 1894. Volume
of plankton in cm.’ per m.* of water shown by heavy black ordinants, the diagonal-
lined apices of which indicate the estimated proportion which silt forms of the total
catch. Thermograph in dotted lines, from records of surface temperatures made at
the times of plankton collection. Hydrograph in continuous line, plotted from rec-
ords at Copperas Creek. Heavy black areas at top of plate indicate the relative
number of cloudy days per month at Havana, the vertical space equaling seven days.

PLATE IX.

The same for 1895. Hydrograph from Jan. 1 to Aug. 8 is that at Copperas
Creek, and thereafter in the main from Havana records. Relative thickness of ice-
sheet indicated by black area at bottom of plate, 1 mm. equaling 6 cm. of ice.

IPILAIND, 2X.
The same for 1896. Hydrograph entirely from Havana records.
PLATE XI.
The same for 1897.
PLATE XII.
The same for 1808.
PLATE XIII.
The same for 1899.
PLATE XIV.

Spoon River near its mouth, looking toward southwest from first bend in the
stream. Plankton station (M) located near trestle. Taken at moderately low water.

PLATE XV.

Quiver Lake in midsummer, 1894, at low-water levels, looking northward from
Station C (see Pl. II.) toward the mouth of Dogfish Lake. Littoral vegetation in
foreground. Driftwood indicating high-water margin. Lake rich in vegetation.
Plankton station located in narrow strip of open water in middle of lake.

PLATE XVI.

Quiver Lake, from same location, in low water of 1897. Only a small amount
of marginal vegetation visible. Dogfish Lake also largely free from vegetation.

PLATE XVII,

Western shore of upper end of Quiver Lake, looking northward, showing rich-

627

ness of vegetation. Emergent Ve/umbo lutea Pers., with leaves, flowers, and seed
pods. Submerged Ceratophyllum demersum L. Taken in low water of summer of
1894.
PLATE XVIII.
Dogfish Lake, looking northeastward, in low-water summer conditions. Lake
full of Ceratophyllum, Elodea, and Potamogeton. Plankton station (L) near center

of lake.
PLATE XIX.

Flag Lake in autumn of 1895 at plankton station (K), looking north-northeast-

ward. Scattered dwarfed clumps of Scz7fus and an abundance of Vymphea consti-
tute the principal vegetation in this open area.

PLATE XX.

Thompson’s Lake from shore station (G), looking southwestward, in low-water
conditions of midsummer. Lotus bed in distance, and broad belt of submerged veg-
etation, principally Ceratophyl/um, along shore. Plankton station (G) in open water
to the right (northward).

PLATE XXI.

Phelps Lake, looking southwestward from plankton station (F), in midsummer

in 1894, just as the lake was drying up.

PLATE XXII.

Seasonal distribution of plankton in Spoon River (Station M) in 1896. Scale of
plottings of plankton o.1 cm.’ per vertical unit, instead of 1 cm.*, as in case of all
other stations. Dotted portion of ordinant indicates estimated proportion of silt
in total catch. Thermograph plotted from surface temperatures of water at times
of collection of plankton, and hydrograph from gage-readings in the adjacent II]linois
River at Havana. Ice indicated by black areas below diagram, 1 mm. equaling 6
cm. of ice.

PLATE XXIII.

The same for 1897. The excess of plotted plankton-silt ordinants over limits

of diagram is indicated by figures at top.

PLATE XXIV.
The same for 1898-1890.
PLATE XXV.

Seasonal! distribution of plankton in Quiver Lake (Station C) in 1894. Scale of
plotting of plankton-silt is 0.4 cm.’ per vertical unit. Hydrograph is that of the IlIli-
nois River at Copperas Creek. Thermograph is that of surface temperatures at

times of plankton collections.
PLATE XXVI.

The same for 1895. Hydrograph from Jan. 1 to Aug. 8 is that of the Illinois
River at Copperas Creek, and thereafter, from river gage-readings at Havana.

PLatTE XXVII.

The same for 1896. Hydrograph from gage-readings in the Illinois River at
Havana.

628

PLaTE XXVIII.
The same for 1897.

PLATE XXIX.
The same for 1898-1899.
PLATE XXX
Seasonal distribution of plankton in Dogfish Lake in 1895. Hydrograph from

Jan. 1 to Aug. 8 is that of the Illinois River at Copperas Creek, and thereafter, at
Havana.

PLaTe XXXI.
The same for 1896. Hydrograph is that of the Illinois River at Havana.
PLate XXXII. ;
The same for 1897.
PLATE XXXIII.
The same for Flag Lake (Station K) for 1895-1896.

PLate XXXIV.
The same for 1897-1808.
PLATE XXXV.
Seasonal distribution of plankton in Thompson’s Lake (Station G) in 1894.
Hydrograph is that of the Illinois River at Copperas Creek.
PLATE XXXVI.
The same for 1895. Hydrograph from Jan. 1 to Aug. 8 is that of the Illinois
River at Copperas Creek, and thereafter, at Havana.
PLATE XXXVII.
The same for 1896. Hydrograph is that of the Illinois River at Havana.
PLATE XXXVIII.
‘The same for 1897.
PLATE XXXIX.
‘The same for 1898-1899.

PLave XL.
‘The same for Phelps Lake in 1896.

PuatTe XLI.
‘The same for 1897.
PLATE XLII.
The same for 1898-1899.

629

PLATE XLIII.

Seasonal distribution of chemical data and plankton in Illinois River in 1895-
1896. Chlorine, oxygen consumed, free ammonia, albuminoid ammonia, total or-
ganic nitrogen, nitrites, and nitrates, in parts per million, plotted according to scales
specified at the left, and plankton in cm.* per m.’, according to scale at the left, in
the form of a continuous planktograph. The hydrograph, with scale at the right,
is plotted in the usual form as a continuous curve. The planktograph, and the chlo-
rine and nitrite plots are also in continuous lines, but, owing to distribution of data
are more angular. Nitrite scale should read o.1 to 0.3.

PLATE XLIV.
The same for 1897.

PLATE XLV.
The same for 1898-1899.

PLATE XLVI.

The same for Spoon River (Station M), for 1896-1897. Nitrite scale should
read 0.1 instead of Io.
PLATE XLVII.
The same for 1898-1899. Plankton scale at the left should read 0.1 to 0.4 in-
stead of 1 to 4.
PuaTe XLVIII.

aie same for Quiver Lake (Station C) for 1895 and 1897.

PLATE XLIX.

The same for 1898-1899.
PLATE L.

The same for Thompson’s Lake for 1897, 1898, and 1899. Nitrite scale should
read 0.1 instead of I.

ERRATA AND ADDENDA

Page 99, line 6 from bottom, for (’87). read (85); line 5 from bottom, after Rolfe,

read, (’94).
Page 100, line 3, page 132, line 10, page 264, line 11 from bottom, page 457, lines

7 and 15 from bottom, page 458, line 14, and page 541, line 8, for Ward (’95) read Ward
((96).°

Page 159, Feb. 18, for 6.8 read 8.8; June 30, for 3.5 read 5.5.

Page 160, Oct. 9, for 7.79 read 7.9.

Page 161, Nov. 24, for 6.6 read 8.6.

Page 169, line 14, for Zable J. read Tables [/1.—IX,

Page 170, line 15 from bottom, for V///, read V/Z.

Page 202, line 9, for (’96) read (’97).

Page 253, line 15 from bottom, for (’g7) read (’97a).

Page 263, line 12, for zS99 read 78906.

Page 282, line 11 from the bottom, for—43 per cent. read + 43 per cent.

Page 288, line 2 from bottom, transpose 37.8 and 28.8.

Page 290, line 2, for 2 fo 5 read 7 Zo 75.

Page 295, line 18, omit the first eight words; line 20, for 2.72, 7.08, and 4.0z, read
respectively, ?, 22, 0.72, and 3.94.

Page 311, line 14, and last line page 313, for ode read mode.

Page 310, line 14 from bottom, for Z//. read XZ/V.; line 4 from bottom, for ¢he
read az.

Page 323, line 9 from bottom, read zz 7897 after catches.

Page 332, lines 16 and 17, for exceeded read preceded.

Page 343, line 14, for cm. read cm.’.

Page 350, line 17, for gualztatively read guantitatively.

Page 357, line 6 from bottom, after 76.76 read on the 24th.

Page 358, line 18, after avd read decreases the.

Page 367, after heading Dogyish Lake read Station L.

Page 371, line 4, before decaying read Zo.

Page 372, line 16, after maxzmum read in Quiver Lake.

Page 381, after heading Flag Lake read Station K.

Page 385, line 14, for wbeZ/a read uvella.

Page 403, line 17, for flood read floods; line 18, before /uzly read of.

Page 405, line 1, after ve/ative read annuaZ; \ine 8, for 7597 read 7896.

Page 414, line 12 from bottom, for 7zvex read avea, and for drains to read
reaches.

Page 416, line 12 from bottom, for zsread was.

Page 422, line 7 from bottom, for 5 read 3-5.

Page 424, line 12, for (.¢5) read (45 cm.); line 13, for (.05) read (5 cm.); line 16
from bottom, for flood read floods.

Page 420, line 4 from bottom, for 22,35 read 22.55.

Page 439, line 2 from bottom, for Z/e read ¢hezr.

Page 440, line 8, for wean read means and for the read thezr.

Page 463, line 4, for Zo read zm; liné 5, for peculiar zz read peculiar Zo,

Page 484, in table, transpose Vegetation-foor and Vegetation-rich.

Page 501, line 1, for show read shown.

Page 505, last line of table, column 4, for .y read 4.

Page 510, line 9, add, azd Volk (’03).

Page 546, line 15 from bottom, after zs read zz the mazn. ;
line 1 below heading, page 551, line 1, and page 556, line 3, for (’970

Page 549,
read ('97@).

Page 556, line 7, before ’0? read ’oz and.

Page 560, table, second column, line 4 from bottom, for ('00d) read (’o0),; line 6

from bottom, for /wzg read Yung; line 16 from bottom, for (95) read (’93),; line 17
from bottom, for (99) read (’00); line 19 from bottom, for (’95) read (’96).
Page 584, at head of second column, for 7597 read 7595; under remarks, line 4,

for above read along.

Pages 597 and 508, below table, read *Bottom visible.

Page 598, eighth column, line 7 from bottom, for 0.76 read 0.28.

Pages 599-603, 606-610, 612, and 613, below table, read *Plankton not collected on
same date as sample for water analysis.

Pages 599-613, columns 2-4, meaning of symbols, abbreviations, etc., as follows:
v.d. = very decided.

-+ = rising river level.

— = falling river level. v. m. = very much.

-k = stationary river level. Decimal in color column=volume
c. = considerable. of standard ammonium chloride
d. = distinct ; decided. solution required to develop the
fe ilteneds same tint when diluted to fifty cu-
N, = Intille. bic centimeters with ammonia-

Techs free water and treated with the

n. f. = not filtered. usual amount of nessler reagent

s. = slight.

iff

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THE
ILLINOIS RIVER
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LAKE
MICHIGAN

Sanitary Canal.
Nand Mich. Canal

Boul |
ceay |

—_— 29 eee

LOW WATER.
Drawn ny LYDIA M. HART.

FIELD OF BIOLOGICAL STATION OPERATIONS.

AFTER U. S. GOVERNMENT SURVEYS, REVISED BY MEMBERS OF THE STATION STAFF.

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LOWER GAGE AT COPPERAS ORBEK DAM. Plate Vil

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v mM a ar 7
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emperature F.°

TX Pid ‘OBR J vonag mm YOR Ue) 39 HOVING1AYS IC] youosoa}

:

08%S
<_<

5) River Gage Ft.

| Plantcton Cm

Ay
pie

O}|0E] 0
| !
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0
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i g
A
yi
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TX Pld

Val o\ sie Pci) ale

Uog4ye)_{

JO WOIINgT.YSIC] ToUoseac

1BS9. Plate XL.

S

Ol 9866
«m7

Wi lS
“ma

082s mn
<—_

1

ion of

Seosonal Distvi

Av.

T
N
| Ses =
T
i
i
|
| a
| |
ry oO
é River Gage-Ft. = 5 :
Te | Temperature 3 R br 3 z 5
ey Ce eee
‘| Plankton Cm3 a 2 2 =

Plate XLII

1895.

Distrivution of Chemical Data and Plankton, ot Storion £, 1896.

River Gage Ft. ES S > s 5 iS S Ma S|
[ ‘
0 \\ Ir
3 | aR
: IL fhm ~~
Eales) Z A
; . =
T
H { N 2
Spa V b aT
15 a
. \ q t,
rl i iN
eel +
i ‘
S Lacy
= Na —>+- + = ~
5 \ ~~ S
7 UY 1
Pom alice
= “Tobe
. J
7 iN in t
|
< | N ~.
r ‘|
1 | t se
a I |Z Ez
Z | \] Y
SK | l L =
i *t
Z A Z
‘ i i = rf Te AR
\ \
B
- +
=p
= =
=] > ea
iS iB |
ee aS — fe |
ia tit
* /\7Tt~ a °
: iT f
+ it
E La ~4 hel
5 1]
h 7
i | i 5
| |
u ~ Se |PoR iggess Sy ee
= cmniessarsoocaniey = — fers = oe ee nm.
= ‘uabozIy “BIUOW YY §
=| “s97244IN Saqs2IN aUuPbsIQ | ploulwngy | “eluowupyaasy uabkxo SuNojy9 ‘UOqyUayy

Plate XILIV.

Seosonal Distribution of Chemical Dataand Plankton, at Stotion £ , 18

iver Gage Ft. S be ay A S
_ = N Se
-) Lal ) Lo .
i, it \
- = ‘
‘Rina 1 ?
pa ty 4H
Ss oF - ait
i
7 :
aa ] :
: i | f
a i =
- i
‘ ‘ ¢ i
1 lime | T
Ld 4 \ xs Ib)
! | A
3 7
y im al
i fe i
ks = a Se
: | iD |
f I }
i = #
Ba '* \ Gi
2 SS |
3 Th
its
ta ee
BE th [hal WP
‘ 7 7 ‘meal
é 1 .
yal \ WEIS
i \ , §
rm ‘amy
; AS Bi
ta
i i =
. 7
. 7 ;
f
ra i
s ( AG
. 7 = i
= a =
eS =e
Sh ma > [Yee [wory foots [woot [evar [Lma~
(=| mm |) a) Se |] | seceeeenes —
= ‘uabo.y) “PIUOW LY =
S| saqeiqy | -SaqiZiny BEAD plowing )\ eluouumyeats| UabXsxQ “UILO/YD | “UOqYUe/Y

ale : 3 4 1} J
=u = Ny)
mal | ie J [ z| 3
Ss
4 Wor blo >
Fa
+| =
SIE CECE Ra |
[ cl J a| 8
(fa r- i eT]
| HU L |
7: A t a = re oy £&
Z ACI vei Oni SIS IAN as
; 7 y] oar: @
ES L |S & NE EIU ei et Neem L ; a)
s hl ] 1 2l
9 Al Fae RoI ?
H is ee ee = ri z | 3!
A LJ N [a AL i M4 iS 1 SS
ee ee ia mh ais y W7 \ b | 5
“ i) | i Ye ae / ie x 2 3
ae 7 S z y AS : i \ 1°) S-
h D Net Jatt y ZL x : a [>=
Wht WWE a ry sear jese | ie Jt hap rth yi yt HLL = ¥ jg =
6 i 5 a ee rae NY a ULI 1 eS i$. 2.
5 5 Ur Ny? jas
; mice con cine i -+ aves:
Hl \
+ l=9
StS sae tlealeatell lee S f ass
td ams — =— = >4- 3 2 8 =
N TE 5 1 ls 5
7 1 1 21
a =
LAL | =
ie a MU L ! +
ea eo \ ai a
I H alee
RS a ee aia callolis 3 Te
i Ate } 7 Cl er el Po 1r fi es FS Ge (Ps a er) F | =
8 a 1 ? aie aan &
cs 4 rr 1 = P oy
& L 4 a Be Restle | en | Led | ft =| : be ai oe
RY 7
& WSS LN

NIX d G GSI ‘O68 0 =) uot ja *UOJ{UE]_Y Pe BIE] [eaiiuay 739 ug) 14517) Touosvec;

BIUOW Y
Ploulung /y | euowuly aad

1 Tia fF !
ral ied 2
EEE ; eaeeeaigeelgeea teen! iaaarl
| z mle ia b gw
: SF SR EEE
Lt = IL — | a |B 9
1 i mil td
j i alla 9!
PREECE gaag veaesrstct eae SAN i!
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x Ae cA ‘os eSNG EE 2!
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H 7 a f L fal eine aaa 7 Slims aA tC |
= ; E 7
ie SS S eal 1k ! in “AIT WE aL PANNE } ISIE Neat Pali + |
[= a a | : Y ; SSI Tel NZL se I
— rai i calculates inal = HII &: |
NE | CI OT Ie
g |_| AL XA UE \ a a ia | Spas es | a | A HD
z A : Lar AS IN Dei A we LL Te a “| Nei fatal By
al = Ww t Ni eal ee el LoL bal VI bjt] a
a \ Et = | N, | | ]
1 CONCISE
ore [ i
fe tL at a ia ae ay 1 “ye DES ima TH ia 73H
| Dae Ne CRE
5 fei} be ela oi Ee Si IATL IE es ff 4)_| |a\ aba 4 i At Lo At
fe ; s | ? I
| NIX Ap | d Vi BSI “|| Upto FO “UO LYUEL_) Pub ETE] /eaIWay) yo uoTNgIAIS 1] 1" osoa

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oes
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DEON,
UN
Hilineii

auneyy 9D

Seosonal Distribution of Chemical Data and Plankton.
at Stotion C 1895.

Scales.

E LI I
i
‘ |
: : —=
yz H
+
i i
i || j in
i é
iG j
4
aS bey SS | SS ICO CI SESS COC CR IC) KE GI TRIS Cy |) Sri GO Ss
meee eeeeenen: — _: —_—_—-— —_————] Ss ------~--- teens nee een WS
wabolty, PMOL §
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Vy Ne

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= EN one
a. i

a
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¢
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a Se : sop \ Se eae
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cr s “| = Fa ea pe
J SSeS JE TEE ial 4 Pe =; Sf Ss
SACU
Hi :
SSS [A =. | = :
i —
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y | Se Saray aS
} 4 x a
i +t | _ Ic
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sont
i N

iver Gage Ft.

XIX? id 6 ESI

‘OBBI OD wows mS uo yueLy puerezjequeybo wor

149537] youoseaS

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W4dS 1 Vd

189.9, Plt. L.

hemicalDataand Plankton . wt Stotion CG. 1898.

ion

Seasonal Distri

1897,

River Gage Ft. 8 E q
; 4, |
Z |
by. =
E a A \
H \ B :
y fh
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ae
; [X] 1
; {
| |
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fl oe
Donon ul ake at |
Ne |
: | \ | | |
H t LY |
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j h PVT >
it at |
l \r@ |
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xj . ¢ + 7 _—-
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st ?
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Te.
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5 + =
t q & i
x. rl ~ i |
q > i
H ia \ Noe
: B r -
7
Een
Z) H
{ i
ian
RZ
= 7 =
‘
|
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| |
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Rr “waboiyy | “euouuy | SS Siar 5
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PARTS Per M

hy es

a NIN NVA AR RA ARIAA AR A mm a heyy
"A AAA a a AARAR Annan

ay) arses Sac ae

AAA RAAAAARA =

ee =

aman JES KEN ON > A :
= asacanaase i aprrrnn YY ngs

NN AN algn\gnigmg a a AAT’
ARAAAAAM oc peo Re BORECECPECEOR yr
+ WWAAAAAA aamaRanae en TnARARanace ale
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AAA AAAAAAAY,
saaaaanaaaaanan Snnnaanannnnaiaaal
mam WAAR RAAARARARAR RRR AR ARR ARAANAE
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GAR ARARSAR

“AAAAARR A ARAA AAA Aas
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Wanawanrann= RAAARAAAAAA

y =—V¥_W Ww a

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ARAARAR AAA RAR RAAAAAE
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SRARAPAERRRADOER rap soavoenaaea
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NARA ARARAAA A RA

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RARARRRARAAARA RARBARAAL, _, nanan

ana 2aaaneaneaaame
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saa aa RA Rm ARARAA An ne RARAR AAR:

va

| cm | ln gi

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AAR AAEE NN NAA ARRAN IAA ae
—~ co } ~,
= aan nanmmmaan nee xe TT
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~~~ AARARARAAA Ar ae
a \AAAARAARAARARARARER AN NN NN
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=

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