SPATIAL AND TEMPORAL DISTRIBUTION OF BENTHIC MACROINVERTEBRATES AND SEDIMENTS COLLECTED IN THE VICINITY OF THE J.H. CAMPBELL PLANT, EASTERN LAKE MICHIGAN, 1979 By Michael H. Winnell and David J. Jude Spec. Rep. No. 77 of the Great Lakes Research Division The University of Michigan Ann Arbor, Michigan November 1980 ACKNOWLEDGMENTS This study was funded by a grant from Consumers Power Company, Jackson, Michigatn, through their Environmental Services Department. We are indebted to Dr. Ibrahim Zeitoun and John Gulvas for their congenial treatment and help through all phases of this project. Nelson Navarre from the Great Lakes and Marine Waters Center was also very helpful with the administrative aspects of the study. We would like to express our gratitude to Great Lakes Research Division benthos personnel whose invaluable assistance helped produce this report.. Special thanks are due Polly Fairchild who sorted and identified the majority of the animals collected. We are thankful to Thomas Zdeba who identified the pisidia, Dr. David White for confirmation of trichopteran identifications, and Jarl Hiltunen who aided with distinguishing the naidids. In addition, Polly Fairchild, Roger LaDronka, Cathy Zawacki, Tom Zdeba, Dave McPherson, Fredric Leutheuser, Zeny Catalan, and Mary Jo Caterall aided in collection of animals and sediments during field surveys and are thanked for their assistance. We are grateful to the crew of the R/V Mysis (Captain Ed Dunster and Earl Wilson) and to George H^iufelder and Cliff Tetzloff for scheduling, logistics, and patience. Appreciation for sediment analysis is extended to Dr. Ronald Rossmann. Special thanks are given to Dr. William Chang for editing and untiring help with the statistical problems associated with this project, Dr. David White for encouragement and editing, Polly Fairchild for the tedious job of inking all figures, Linda Gardner and Polly Fairchild for their careful typing all the tables, and Steve Schneider for assistance in the production of this report. We thank Frank Tesar for his thorough review and many helpful comments regarding this report. Sherry Stapleton, Judy Farris, and Jan Farris are thanked for handling requisitions, time cards, and travel requests. iii CONTENTS Acknowledgments iii Table of Contents v Introduction • 1 Methods • • • • • 3 Benthos and Sediment Survey Design 3 Benthos and Sediment Sample Collection and Processing 5 Statistical Analysis of 1978-1979 Preoperational Data 7 Statistical Analysis of Preoperational and Operational Data (1978-1981) 9 Results 14 Total Animals 14 Chironomidae 32 Naididae 42 Tubif icidae 52 Turbellaria 55 Enchytraeidae 66 Stylodrilus heringianus 71 Pisidium 71 Sphaerium 78 Gastropoda 78 Pontoporeia hoyi 86 Sediment Distribution 96 Discussion 101 Literature Cited 107 Appendix 1 112 Appendix 2 115 Appendix 3 121 Appendix 4 • • • • 127 INTRODUCTION The J. H. Campbell Plant is comprised of three coal-fired operational units. While Units 1 and 2 have used and will continue to utilize Lake Michigan water drawn through Pigeon Lake for cooling purposes, Unit 3 draws cooling water from an intake structure located in approximately 11 m (1.1 km offshore) of water in Lake Michigan. Heated water from Units 1, 2, and 3 are discharged through the offshore discharge structure. While Unit 3 was not operational during 1979, in September 1980 all three units began discharging heated effluents at approximately 6 m (0.3 km offshore), thereby ending the preoperational period. Data have been collected for preoperational years 1978 and 1979. This is the third in a series of benthos reports that began in 1977 concurrent with reports on larval, juvenile, and adult fish (Jude et al. 1978, 1979, and 1980). The first benthos report (Jude et al. 1978) was a pilot study ascertaining the approximate density and variety of benthic macroinvertebrates near the Campbell Plant during June 1977. In addition, variance and sample replicability were addressed. The second report, based on 1978 data (Winnell and Jude 1979), presented quantitative and qualitative differences between a treatment and two reference areas near the plant for benthic taxa and sediments. The purpose of this report is to present and analyze all preoperational data collected during 1978 and 1979. Analysis will be oriented toward determining monthly, depth, and regional distribution similarities for benthic and sediment parameters between control and treatment regions in 1979 and between the years 1978 and 1979. The overall purpose of this study is to determine whether density and species composition of benthos collected from 1978 and 1979 differ significantly from estimates covering the operational period. Analyses will be conducted after collection of 1981 samples in accordance with the statistical analysis technique (Johnston 1973, 1974) utilized at the D.C. Cook Nuclear Power Plant, southeastern Lake Michigan [see METHODS - STATISTICAL ANALYSIS OF PREOPERATIONAL AND OPERATIONAL DATA, (1978-1981)]. The general distribution of benthos in southeastern and eastern Lake Michigan has been studied by Powers and Robertson (1965), Robertson and Alley (1966), Hiltunen (1967), Alley (1968), Mozley and Garcia (1972), Mozley and Winnell (1975), and Alley and Mozley (1975). However, the most comparable benthic studies were conducted in the immediate vicinity of the Campbell Plant by Truchan (1970) and Beak Inc. (Consumers Power Company 1975) to determine the effect of the shoreline thermal discharge on benthic macroinvertebrate distribution. While Truchan (1970) did find evidence of greater diversity near the discharge canal when compared with reference areas, he found no adverse impact on local benthos populations in the treatment area. In addition, studies completed by Beak Inc. from 1968 to 1974 indicated that, although some differences in benthic numbers were evident between treatment and reference areas , there appeared to be no "appreciable harm to the benthic community" due to shoreline thermal discharge (Consumers Power Company 1975). Based on information from the June 1977 pilot study, Jude et al. (1978) concurred with earlier conclusions made by Beak Inc. In the more extensive 1978 survey (Winnell and Jude 1979) we found that, although depth and time had the greatest impact on benthic macroinvertebrate density, region (i.e., treatment and reference areas) was an important consideration in several instances. Completion of benthos sampling in the second and final preoperational year (1979) ensured a sound data base, verified depth, time, and regional trends from 1978 to 1979, and noted regional differences and similarities within 1979 as they relate to benthos and sediments collected near the Campbell Plant. Significant differences between years or regions have been noted and tentative causes for these differences suggested. However, evaluation of any thermal effects due to plant operation must await collection and analysis of 1981 benthic samples . METHODS BENTHOS AND SEDIMENT SURVEY DESIGN The survey was composed of 10 stations located along two transects per- pendicular to the shoreline (Fig. 1). Along each transect, stations were located at 3-, 6-, 9-, 12- and 15-m depths. The first transect represented the treatment area (inner region) near the present thermal discharge. The second transect represented the reference area (outer region) located 5.0 km north of the discharge canal. During both April and July 1979, the inner transect was located 0.16 km north of the present thermal discharge canal. Due to con- struction activities during October 1979, it was necessary to move the inner transect 0.32 km north of the discharge canal. The 1978 survey design was modified in 1979 by eliminating the intermedi- ate region and including only inner and outer regions. In addition, during 1978, benthic and sediment parameters for each region were estimated from three replicates at each of two stations located equidistant north and south of the discharge canal at each depth. In 1979, the same parameters were estimated by one station sampled six times at each depth within a region. Since estimates of the benthos and sediments from 1978 were made by combining the two sets of three replicates collected at a selected depth and region, replication from 1978 to 1979 remained constant at six within a given region and depth. 0) o CD X o LU < 0) c c OJ oc u • cd !£ ^ o • CO •-) •H T3 OJ ^ rH 4J cd E 13 OJ (1) ^ C 4J c: 4J bC -H (U en CO 0) (U T3 J-4 p. >. 0) M > CO J-4 +J CO o II ^ 4J u c O (1) C rO c M P^ u tH • II r-1 1-4 Q) V^ ^ • OJ o. &0 -u e •H p Cd |i4 O a BENTHOS AND SEDIMENT SAMPLE COLLECTION AND PROCESSING Benthic macroinvertebrate and sediment samples were collected on 19 April, 20 July, and 16 October 1979 in the vicinity of the J.H. Campbell Power Plant, eastern Lake Michigan. Sixty samples were collected for benthos and sediments during each sampling month from the University of Michigan's R/V Mysis. During 1979, 180 samples were collected for each parameter. No samples were lost due to breakage or spillage* Benthos and sediment samples were collected using a triplex (three- chambered) Ponar grab sampler (Mozley and Chapelsky 1973). Each chamber of the Ponar grab samples 0.0165 m^. A conversion factor of 60.6 was used to convert numbers of animals present in each grab to numbers per square meter. One side chamber of the Ponar grab was used to estimate ntimbers of benthic macroinvertebrates occurring in a square meter. Contents from the remaining two chambers of the Ponar were emptied into a tub and mixed, and approximately 30 g of sediment removed for sediment analysis. Six replicates (A-F) were collected to estimate benthic populations and sediments at any particular depth and region during each month sampled. The portion of the Ponar grab used to estimate benthic macroinvertebrates was placed in a "funnel-shaped hopper" (see Mozley 1975 for details) aboard the R/V Mysis. Benthic samples were washed through a 0.2-mm mesh net to concentrate animals and remove excess sediment and debris. The mesh size of the net used to sieve organisms from sediments was reported as 0.35 mm in Jude et al. (1978) and Winnell and Jude (1979). However, the material supplied to us as 0.35-mm mesh and from which our nets were constructed was in fact 0.2 mm. Concentrated samples were stored in externally and internally labelled 1-pint Mason jars and preserved with carbonate-buffered, 4% formaldehyde solution. Samples were returned to the Great Lakes Research Division benthos laboratory for sorting and identification. Sorting and initial identification of organisms were performed using dissecting microscopes (3-30X) • Specimens unidentified at the genus/species level (Chironomidae, Naididae, and Tubificidae) were mounted on slides with Amman's lactophenol clearing medium and identified using compound microscopes (40-lOOOX). Initial generic identification of chironomids was determined using an unpublished trial key to the chironomids (A.L. Hamilton and O.A. Saether, personal communication, Freshwater Institute, Winnipeg, Manitoba, Canada and Zoological Museum and Department of Morphology, Systematics and Animal Ecology, University of Bergen, Bergen, Norway). In cases where species were determined for chironomid genera, "cf." refers to uncertain larval identification at the species level. Most species designations concur with reared specimens from the D.C. Cook Plant, southeastern Lake Michigan, which are maintained in the Great Lakes Research Division benthos laboratory's permanent collection. Larval, pupal, and adult chironomid associations at the D.C. Cook Plant have been reviewed by Mozley (1975). However, since none of the chironomid larvae from the J.H. Campbell Plant have been reared, identifications at the species level have been assigned the uncertainty designator "cf." The designator "gr.," which refers to a "group" of species undeterminable from larvae, was associated with the genera Polypedilum , Chironomus , and Paracladopelma . Morphology and taxonomy of other chironomid genera and species were determined from the following references: Lenz (1954), Roback (1957), Curry (1958), Beck and Beck (1969), Saether (1969, 1971, 1973, 1975, 1976, and 1977), Hirvenoja (1973), Jackson (1977), and Soponis (1977). Naidids and tubificids were identified using an unpublished key to aquatic oligochaetes of the Great Lakes (J.K. Hiltunen, personal communication, Great Lakes Fishery Laboratory, U.S. Fish and Wildlife Service, Ann Arbor, Michigan). Gastropods and pelecypods were identified using a key to molluscs of the Great Lakes being prepared at the Great Lakes Research Division (G. Mackie, D. White, and T. Zdeba, personal communication, University of Mchigan, Ann Arbor, Michigan) . While aboard the R/V Mysis, sediments were stored in sealed plastic bags bearing external labels. Standard mechanical sieving of sediment samples was performed at the Great Lakes Research Division sediment laboratory. Folk, Inman, and moment measure statistics were computed for each sample collected. Data were expressed in terms of phi units following Krumbein (1938). Upchurch (1969), Coakley and Beal (1972), and Seibel et al. (1974) indicated that moment measure statistics were the "preferred method for deriving sediment textural par^imeters ." Two moment measure statistics, mean grain size and standard deviation of the mean grain size, were used in this report. Standard deviation has been used as a measure of sorting, following Seibel et al. (1974). In addition to moment measure statistics, percentage of sediments occurring within any given sediment grain size based on units of phi has been included in this report. Description of sediment grain sizes followed that of Seibel et al. (1974), who adapted theirs from the standard Wentworth scale. STATISTICAL ANALYSIS OF 1978-1979 PREOPERATIONAL DATA The preoperational data set (1978-1979) was analysed for annual and regional differences, either within 1979 (inner vs. outer region comparisons) or differences between years (inner 1978 vs. inner 1979 and outer 1978 vs. outer 1979). To determine the presence of preoperational differences. Student's t tests were performed using the Michigan Interactive Data Analysis System (MIDAS) on the AMDAHL 470V/7 computer at the University of Michigan. MIDAS computes Student's t tests according to the following equation given by Dixon and Massey (1969): ^1-^2 S P ^V^ t = calculated Student's t statistic X, and X^ « mean from populations 1 and 2, respectively N, and N^ = number of observations from populations 1 and 2, respectively 2 S = pooled variance where; a = 0.05 such that, NS = no significance * = 0.01 < P 1 0.05 ** « 0.001 < P 1 0.01 *** = P <. 0.001 - = no test performed due to no variance or mean estimate available for one or both populations tested All analyses were performed on log(x + 1) transformed values. Elliott (1971) considered the log transformation the most effective transformation when dealing with benthic data that are contagiously distributed, i.e., characterized by a variance to mean ratio significantly greater than one (x^ "" test). Transformation of raw numbers to log (x + 1) transformed values is generally used to condense the range of values observed in the raw data in order to more fully meet assumptions of normality and homogeneously distributed variances upon which validity of the derived significance level for the t test is based. Because no transformation of raw data can gxiarantee that the transformed data set or subsets thereof meet the assumptions above, we prefer to consider inferences made in the 0.05 - 0.01 probability range as marginal. 8 Differences between populations based on probability for values of p > 0.01 are considered as significant in this study. It is thought that the differences observed at p >_ 0.01 were considered disparate enough in this system that improvement upon the assumptions by transformations would not alter the conclusion (Chang and Winnell 1980). STATISTICAL ANALYSIS OF PREOPERATIONAL AND OPERATION^!- DATA (1978-1981) In a previous report (Winnell and Jude 1979), we stated that data on benthic macroinvertebrates collected near the J.H. Caimpbell Plant from 1978 to 1981 would be analyzed statistically following Johnston (1974). With completion of the ^preoperational survey (1978-1979) and prior to presentation of operational survey data (1980-1981), examination of Johnston's model for the analysis of thermal discharge effects on benthic populations and its application to the Campbell survey area is appropriate. Although this subsection of the METHODS section will not be utilized in this report, it is presented in order to clarify the direction of the 4-yr benthic study design and the statistical methodology undergirding the study prior to the collection of operational data in 1980 and 1981. Johnston's model has two major objectives. The first objective is to determine thermal effects using an F-ratio comparison derived from a mixed-model, nested analysis of variance (ANOVA). Completion of the analysis for the first objective provides the error mean square estimate used to calculate subsequent parameters used in second objective calculations. The second objective is to determine the sensitivity of the 4-yr survey design regarding the degree of change necessary to detect a thermal effect within treatment area benthic populations when compared with reference area benthic populations . Quantification of the sensitivity is determined by first calculating Sokal and Rohlf's (1969) least detectable true difference (6) from the equation: \nj a[v] 2(1-P)[v] 6 = least detectable true difference o = true error standard deviation V = degrees of freedom of the error mean square n = number of observations at each of the two treatment levels t = Student's t a = significance level P = power (the desired probability that a difference will be found to be significant) and secondly by determining R from Johnston's derivation of Cohen's (1969) equations to: R >^ 10 ^ or R 1 10 R = least detectable true ratio 6 = least detectable true difference Johnston's mixed-model, nested ANOVA has five essential factors: construction time, year, month, depth, and region (treatment and control areas) (Table 1). The model asstunes that the effect of month and depth are additive, thereby eliminating the difficulty of "assigning ecological interpretation" to higher-order interactions. Furthermore, Johnston uses Kirk's (1968) justification that once the investigator has selected the components expected to be major contributors to the total variance based on the investigator's knowledge of the system, all other components become part of the experimental error. Of the model's five main effect factors, all are fixed-effect factors 10 TABLE 1. Major factors considered in the mixed-model, nested MOVA to be applied to benthic populations surveyed from 1978-1981 near the J. H. Camp- bell Plant, eastern Lake Michigan (After Johnston 1974) • Name of Factor Number of Type of factor abbreviation levels factor Construction time (Before, After) C 2 (Before, After) Fixed Year (1978 - 1982) Y 2 (1978 - 1982) Random (nested within C) Region R 2 (Inner, Outer) Fixed Month M 3 (April. July, October) Fixed Depth D 5 (3, 6, 9, 12, 15 m) Fixed Error E 6 (Number of replicates) — Total number of observations -2x2x2x3x5x6=7 20 Total degrees of freedom = 719 except year which is random and nested within construction time. In all, 32 interaction components are possible, but Johnston considered only nine essential for determination of heat effects (Table 2).. The term used to deteinaine thermal effects is the interaction (C x R) of construction time (C) and region (R). The null hypothesis assumes that Qqr = 0, i.e., the beginning of discharging heated water through the offshore discharge diffusers has had "no €iffect on the difference between the mean transfoinned benthic density" in the inner region (area of thermal discharge) and in the outer region (reference area). The F-ratio of the estimated mean squares (MS) for CR (Construction time X Region) and YR (Year x Region) interactions: MS F « CR MS, YR 2 2 e YR can be used to test the null hypothesis that Bq^ = 0. Terms in the F-ratio measure sampling error variance or variability among replicates (o 2) and the annuatl variability of the "difference between inner and outer populations, averaged over- all months and depths "(c^^yr)* Since the null hypothesis assumes c^CR =' ^9 then the F-ratio becomes (a ^ + 90a^^)/(a 2 + 90o^^) distributed as 11 TABLE 2. Important sources of variation, their respec- tive degrees of freedom and expected mean squares derived from the mixed-model ANOVA to be applied to benthic populations surveyed from 1978-1981 near the J. H. Campbell Plant, eastern Lake Michigan. Deriva- tion of expected square coefficients assumes the depth factor (D) has five levels. See Table 1 for key for abbreviated source of variation factors (After Johnston 1974). Source of Degrees of Expected variation freedom mean square C ^ ^E^ "^ ^^° ^C^ "^ ^^° ^x' Y 2 0^ + 180 a^^ R 1 a/ + 360 a/ + 90 o\^ M 2 a/ -h 240 a^ ^ D 4 a J- + 144 aJ- CR 1 a/ + 180 a\^ + 90 o^^ YR 1 qJ- + 90 a^ 206_ 0^ Total 719 E " YR 2 12 an F(l,2). Johnston uses a ^ + 900^-0 in the denominator in the F-ratio, making the quantity (a ^ + 90a^YR) ^^^ appropriate error standard deviation (a ) for use in the power equation. Calculation of the least detectable true change ( 5 ) using the error standard deviation from the 4-yr design assumes a 5% significance level and 95% power, i.e., "is the minimum amotmt by which the true treatment means must differ if there is to be a 95% probability that the means of two samples of size n will be found significantly different at the 5% level." When 6 (least detectable true change) is applied to R (least detectable true ratio), which is derived from Cohen (1969), resulting values of R will estimate the relative increase or decrease of the inner region benthic populations when compared with outer region benthic populations necessary to detect a heat effect using the 4-yr survey design. Benthic populations and respective depths to be considered in the above analyses include: Chironomidae (3-15 m) , Turbellaria (3-15 m) , Naididae (3-15 m), total animals (3-15 m) , Tubificidae (9-15 m) , Pisidium (9-15 m) , Pontoporeia hoyi (9-15 m) , Gastropoda (12-15 m) , Enchytraeidae (12-15 m) , and Stylodrilus heringianus (15 m) . Depths not included in the analyses of benthic groups for either 1978-1979 or 1978-1981 data have been excluded due to low density and frequency of occurrence under the assumption that it is more advisable to test for effects on the main body of a population than on the fringe of the population. Consequently, coefficients for the expected mean square term will differ for those populations where the number of depth factors included in the analysis are less than five. While the coefficients presented earlier were based on five depths, fewer depths tested will not change the F-ratio relationship (MScr/MSyr) but will only alter the magnitude of the coefficients for the expected mean square term. The exception is S_. 13 heringianus which has only one level (15 m) for depth. In this case, there will be no depth factor in the ANOVA. RESULTS TOTAL ANIMALS The number of identified benthic macroinvertebrate taxa collected from samples taken near the Campbell Plant in 1979 (82) was slightly greater than the revised number of taxa collected during 1978 (76). Based on all samples collected from 1977 through 1979 (660), 105 benthic macroinvertebrate taxa have been collected and identified (Table 3). Representation of the 105 benthic taxa among major taxonomic groups was as follows: Chironomidae (37), Naididae (19), Pisidium (16), Tubificidae (13), Gastropoda (5), Sphaerium (3), and miscellaneous others (12). During 1979, 73 benthic forms were collected in each of the inner and outer regions (Table 4). Combining 1978 and 1979 surveys, the inner region was represented by 82 taxa and the outer region by 81 taxa. Comparing the number of taxa collected in the inner and outer region during 1979, the greatest difference was observed at 3m. At 3 m, there were twice as many taxa present in the inner region (22) when compared with the outer region (11), which was mainly the result of regional chironomid and naidid taxa differences. Detail regarding these differences will be presented in the chironomid and naidid sections to follow. Percent occurrence of major taxonomic groups (i.e., Chironomidae, Naididae, Tubificidae, Enchytraeidae, S tylodrilus heringianus , Pisidium , Sphaerium , Gastropoda, Pontoporeia hoyi , and Turbellaria) among months, depths, and regions sampled during 1979 near the Campbell Plant are summarized in Table 5. Chironomids, naidids, and turbellarians were the predominant forms at 3-6 m. A change in the dominant taxon observed at 9 m was primarily due to an 14 TABLE 3. Benthic macro invertebrates, identified from samples collected from 1977 through 1979 at 3 to 25 m near the J, H. Campbell Plant, eastern Lake Michigan. Coelenterata Hydrozoa Hydridae Hydra sp. Platyhelminthes Turbellaria Unknoxm sp. 1 Unknown sp. 2 Annelida Oligochaeta Enchytraeidae spp. Lumbr icul idae Stylodrilus heringianus Naididae Amphichaeta leydigii Arcteonais lomondi Chaetogaster diaphanus Chaetogaster diastrophus Chaetogaster setosus Dero sp. (? digitata ) Nais communis Nais elinguis Nais pardalis Nais simplex Nais variabilis Paranais literal is Parana is simplex Piguetiella michiganensis Pristina foreli Pristina osbomi Stylaria lacustris Uncinais uncinata Vejdovskyella intermedia Tubificidae Aulodrilus limnobius Aulodrilus pigueti Limnodrilus angustipenis Limnodrilus claparedeianus Limnodrilus hoffmeisteri Limnodrilus profundicola Limnodrilus spiralis Limnodrilus udekemianus Peloscolex freyi Peloscolex superiorensis Potamothrix moldaviensis Potamothrix vejdovskyi Rhyacodrilus coccineus Hirudinea Glo ss iphoniidae Helobdella stagnalis Other Hirudinea spp. Arthropoda Acari Hydracarina spp. Crustacea Amphipoda Gammaridae Gammarus sp. Haustoriidae Pontoporeia hoyi Mysidacea My s idae Mysis relict a Insecta Diptera Chironomidae Chironominae Chironomini Chironomus f luviatilis- gr . Chironomus halophilus- gr . Cladopelma sp. Cryptochironomus sp. 1 Cryptochironomus sp. 2 Cryptochironomus sp. 3 Cryptochironomus cf . rolli Endochironomus sp. Parachironomus cf . abort ivus Paracladopelma cf . nereis Paracladopelma cf . undine Paracladopelma cf . winnelli Paratendipes sp. Phaenopsectra sp. Polypedilum cf . fallax- gr. Polypedilum cf . halterale Polypedilum cf . scalaenum Polypedilum sp. 2 Robackia cf . demeijerei Saetheri a cf . tylus Tanytarsini Cladotany tarsus sp. Micropsectra sp. Tanytarsus sp. Orthocladiinae Cricotopus (£. ) sp. Cricotopus (C^. ) /Orthocladius (0^. ) sp . Cricotopus (I^.) sylvestris~ gr. Heterotrissocladius cf . changi Heterotrissocladius cf . oliveri Hydrobaenus sp. Nanocladius sp. Orthocladius ( Euorthocladius ) sp. Orthocladiini sp. 2 Psectrocladius sp. Th i enemann i e 1 1 a sp. 15 TABLE 3 . Continued . Diamesinae Monodiamesa cf . tuberculata Potthastia cf . longimanus Tanypodinae Procladius sp. Trichoptera Molannidae Mo 1 anna sp. Leptoceridae Nectopsyche sp. Mollusca Gastropoda Ctenobranchiata Hydrobiidae Amnicola sp. Bythinia tentaculata Somatogyrus sp. Valvatidae Valvata sincera Pulmonata Lymnaeidae Lymnaea sp. Pelecypoda Heterodonta Sphaeriidae Pisidium adamsi Pisidium casertanum Pisidium compressum Pisidium convent us Pisidium fallax Pisidium ferrugineum Pisidium henslowanum Pisidium idahoense Pisidium lilljeborgi Pisidium milium Pisidium nitidum f . nitidum Pisidium nitidum f . pauperculum Pisidium subtruncatum Pisidium supinum Pisidium variabile Pisidium walkeri Sphaerium nitidum Sphaerium striatinum Sphaerium transversum 16 00 r^ CU ON iH rH rH ^ 1 iH Cd Cd Cd 4J 0) ■u r^ocncnocaino ■M 0\cnCMOiH.oor-icnmsf C3 •H o 00 incnoN<3NCM*d'r>-ON ON r-i n CJN CM m ^ , VO CM tH CO x: u TJ "H iH fH rH a fH 0) 3 4J 0) »n Cd 4J CMrH^CMOOtnsr Cd U iHrOOOONCM-sTvOm 0) "IS Cd u rHlTkONCMCMinOOCM o CM rH s^ CM rH SO o Cn rH fH 00 O ^ • o H H rH H 0) ^ •^ 4J § :3 c o rH rH a •H •H •H H a -H Cd 00 o^ mcjNfOooocoo 0£ ON OOCMvOOOCMCn-^cn 00 0) ON vOC0ONrHCM»ni>»fn O iH M iH I2i CfN fH en (^ CJN iH H in oe; C3N CM rH rH P^ tH u 0) iH 0) fH CO .CMrHCnf^00 a rA -H ^ ON •H CM ON fH ^ C3N CM iH tH VO B U Q» »H tH rH o :3 i •H U S CO TJ o ^ . OOsor^ocnmrH 0) r>. ooor>-rHcninooo-> M M M M Pi o\ ,_4 rH Pi ON rH c>i H m pes ON rH CM rH vO 0) o 0) cd u u i-i 0) ■M 3 3 0) 3 •H T3 CO O 00 O CO O 00 Tj a oj c cd rH Cd ON •H ocoooooiH^a- fH iH C3N rH ONOmr^rHcMinoN iH H sr ON mop^cTvcMcnp^cn fH rH m >% a tiO tH S -H a a a ^ cd jci m cd m c/3 u CO ON fH •H tH "H fH r-l pH •H CO • 4-1 ON (U CQ Cd Cd ■U r^OOOOOCMCJN .u ^OvOOiHCMf^O 4J OCMP^ONCMlOr^CM 5 fH iH CM 5 CM iH rH vO s CM rH VO a 4J r^ ^ o c g -:i oc ON OC ON OC ON •H CO p4T> el s ON iH CMOOOOOOCMCM tH CM £ ON oo«3NvONOocsjsrm iH ^ £ ON iH r^ONvooocMinvoen fH m ^ d a M u (U M V4 o o cd CU 0) u u a g U HQCO CO 0) r>* Cd M 00 ON sfvOOOOOCMCM rH CM M 00 C3N fH«»in00iHCMvOrH CM tn M 00 p*» c^ mrHincotHcMvooo fH «H ^ ^ a ON (U r-^ rH rH S "H H da a 25 O W) O a C3 M O -H M-l • >S bii 0) CD -i 'T3 -H -H U Cd o to U U r-A u % 01 c 9000- 4> O o 2 3000- 12 15 Depth (m) —2 Fig. 2. Mean density (number m ) of total animals collected at 3- 15 m during 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates at each depth were computed by averaging over all months within each year (n = 36) . Standard error denoted by vertical bar. 20 Total Animals - I5000H CVJ o c c O c o 10000- 500O —1978 -1979 April July Month October -2. Fig. 3« Mean density (number m *") of total animals collected during April, July and October 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estiLmates for each month were com- puted by averaging over all depths within each year (n = 60). Standard error denoted by vertical bar. 21 T3 03 Q) C 4J O 1 O -H U 0) 4J 0) rH Cd o- rH > o u 4J O 0) CO CO 0) CO U3 4J a o :3 o O U-l a M o 00 ti M O 0) 1 • •H ^ /-N e a A TS o :3 »— 4 (U a a o 4J O O CO S " • o 0) 4J C V %«• CO u c o a a o •r-) Cd •H CO <}0 ii 4J e -H CO ^ 4C rH M-4 O •K :3 O 2j •K o- s o CO «« a 0) Q) 1— 1 •H ^ O x: 4J Cd O u •H ^J • o CO o ^ C C (U M A M TJ (U o 4-1 a (2 CO 0) CO CO A c: 0) » u • o iH a O M-4 M CO CO rH ii (U (U p^ 4J >> 4C cO iH •K g J-i iH •H O (U •t ■U M-4 ^ f-4 CO ao - r-- a u a\ C o c ^ CO u (U u CO d vo ^ O ^3 00 a TJ M C 9^ hJ -H ii a ^ S C/3 O H T3 Z ^^4 <3> CO > 00 CO Ii /— \ a 4J Q LO a o 3 O 00 CO •3< ^; en •"A -a •a en en en 2: Z •i< 4« en -jc en 2; en 2: en 2: en 21 -K •K 4C •K en en •!< 23 is 4< en en * jz; z -K en iz; en 2: cnencnencncnen-K •K •*: en -a -JC en en en en en en ^ -K ^ Z IS i 2: Z 2: :z; 4C HC en en -K en en -k i ^ en en IS Jz; en 25 4C en en -jc Jz; 2: Hc en en en -K 2: !z; jz: * CO iH 0) CO CO a T> ^ o H CO 0) -H CO a TJ "H •H ^-i T3 "H •H ^ CO 3 2: H 0) CO •H 0) CO u oq c •H u CO I >% O a J5h C 4-» W en CO CO vH TS _, 0) o a M a D O O -H a M n3 o 4J mH ■u CO CO C CO -H o CJ3 Ph Q^ 22 a a- in o r-4 TJ eu I o CO cd Cd 4J 4J o cd CO rH CO 4J 0) Cd • T3 0) O ♦H O TJ -H CO 0) O OJ ()0 0) <>0 Cd a c * CO cd u Cd u T5 th cu Cd I CO C •rl S Cd iH 4J O CO CJ U (U o ^ 13 C 0) -H CO S CO u /-*\ cd a (U 0) O Q II o ^ CO 0) CO >^ rH O 4J Cd cd Cd en fi CD • O 00^-s iH Cd ^ (SO P 4-1 (U (U a > ^ ^ >: ^ 4J cd O -H , hJ (U 0) ^ >H ^ C ^-^ 4J u (U (U ^ 4J 60 4-> CO c a Cd cd » O fH o :3 ■-J o •» X rH cd "H 4J M o ^-^ cd 0) ^ 4.) o o M-4 6 60 r-^ •H O U • +J O CO (U 0) ^ A a Cd o , w' V«^ N.^ CO vo *• >*• N-/ in CO CO 4C CO CO 4C ;z; ^i 4c 25 ^z; 4c CO CO CO 25 23 JZ: in m in m in u-^ in i I I I I I mil I cororococTNCNj r-«cNJo% on CO cu rH (U Cd CD Cd Cd Cd 0) 13 CO 3 cd 6 13 "H cd 'rH 3 (3 cd "H •H ^ ^4 13 cu rH 5 13 OJ d cd Q) •H cd •H •H o 6 M -l 60 a § o C iH 13 v-l 4J 13 C3 O -H a rH CU "H l*-| J>> O •H M 13 o •H Cd J-i ^ 13 •H 43 rH ^ 4J -H 4J >^ 4-i •H M -H ^ CJ >. (U CO CO c o o 43 d Cd :3 c3 4J 43 Cd -H o 43 H CJ H 25 H W CO c:) Pm cu 23 o CO 4J u ^-4 -o c a4T4 C cd 0) o «-' o. o CO 4i 0) M-4 1-4 CO iO 0) !l Cd * <3) CO M 0) o a O 00 o CO 0) ^ o ^ C Q c u CO 25 Ta u ^^ Cd na Q) iH *M-I T) CO M c Cd -tJ 0) (0 c: c: "H CO o cd ' CO 4J Q) ex Q) cd o Q« o 0) (U a O ^ 0) o p CO 4J 4^ a vj - o CO ^ ;3 C 0) O O 00. , M "H cd ^ 00 00 M 4-i • -^ O 4-» tH o ^ Cd u (U jc: > o 3 Cd M-i u > o CO 0) _ .. CO d >*M-4 Cd o iH O 4-J S ^ d CO « -c "^ cd * ^ CO C u o ix] Cd (U o ^ M 4J 00 -M 0) V4 CO c a 6 , o Cd cd » o 0) u 5 }-4 Ui4 ^ c: O 00 4J -H O CO o •d jc 00 >> c: fH -H ^ o iH O •H M-4 Cu >^ ^-^ o 00 *^ ti d cd K •d O d cd cd 0) V4 M-l cd o ^5 M 00 O -H M-l }-i CO 0) 0) X •H U U Cd O > 4J O /-s O TJ • dj O 4-» Vl ^ 4J PU CO II d o * -H ■K Cd iH ^ Pu o o O PU d X 4J A O a a| o o d • o o u 11 o M-i M •ic (U 4J • Cd ^ g O -H • 4-1 O CO (U A d Pu Cd A.I g CJN OS U d d CO > 00 00 ii d PU o 0) d d in CN ON vO 4J d o CO en Z 53 •5< CO IS CO -J? CO CO 2: CO 2 CO CO CO CO 2: CO CO 2: 53 4C 4< CO CO 4< 2 -K CO 2: CO CO * CO CO CO -JC CO 2; •K -JC CO CO 53 2; o u o d u Cd 0) 4J 00.^ pu d g 0) cd ^^ p u § O O O O 00 CM CO CO CO en *-4 »-4 /^ Cvj 00 VO ,-^ ,-H CO CO CO CO CO CO 53 2: 25 2: 53 iz: CO 53 4C 00 * •K CO 4< 53 * CO CO -JC CO CO 53 25 CO CO 2: z CO CO CO CO 2: 13 2: 25 CO CO 25 !3 CO 2: o o o ON ON ON o w^ V-/ Ni-^ 00 vo s-/ >*• m CO -K * 25 -K -K CO CO -K 13 !3 -K CO CO CO 25 13 53 CO 53 m uo m LO m m in m I I I 1 I I mil COCOCOCOONCM ^CNJON I ON 0) Cd ^ cd g Cd (U o tH Cd d fH 'd iH O 0) "H cd J-i U3 TJ 4J .H M "H o X d cd H CJ H 23 Cd TJ 0) Cd •T3 cd a u •H 4-i M-4 >» •H J= d d -H H W CO •H o CO d Cd d cd 'H cd TJ 0) •H o g P 00 pu d o d O -H a vH M TS o M 4J •H 4J OJ CO CO d JS Cd 'H o O Oi p.. I 24 '^ -* •*-* 1 •* A 1 ^3 G. M-i -y ^ "^ QJ r-4 CJ (U iJ r—l O LO CO CO CO •}< CO CO CO CO CO f-^ ^ 2; 12 ;z: ^< 2: 2; ?3 ;z: 25 U CU Q ^-i tH u o o rH CO ^ Cd Cd C /'-N dJ rH ^-1 O -H ii C30 ^aa)cdOO•HTJ u r— • M Ou C -y CO CO g II CM CO CO CO CO CO CO CO CO CO 1—4 :z; 5s ^: 2: 2: a 21 25 25 gcd^S^-U+J-HCUO /*% d SO4jSpuc0 OC ON V-*' g-H^cu+Jdccd r^ CO • I^ , 'd CO 6 cd T-i C3N /-> sc U 2; 25 13 Z 2: 25 25 ^ ►-5 4J 50 14-1 iH 0) rd c5 c: >^ n3 a 4J 4J 4J(UO^c:n3-i d P4 ^g^, OO-d-HCU 0) COP ')-^a "H CO Cd CO 'X^ ON 4C -K T^r^o^coojcuiz »—» CO •K -K -K -JC OJC^ •HcUrHQ-^^'t3 4C 4C 4C -JC ^,-|.^O60puO4 /--S /'-S /-^ /—S /-^ /^N /^S /-s /■-s d d 00 Csl /^ CM 00 00 s-/^ CO CO on CO 1-H f-4 vO «-^ *— • ^w' S-/ Ni-^ f-H a ;3 > . -w CO pw ^-s d 1 ^ S d CO •?< CO CO 2: •?< IS IS -K 4C CO CO CO 25 2: 2: CO 2J 4j:3 (Ucotjojo -^z-v ^: »-) CO M U X: (UwQ'Hi-^'d a)V4a)»g*HOGOoa) p:S •H •H 5J CO -H w|4J COgTJ^r-ld'dCO^' M CO CO CO CO CO CO CO CO CO CO ON 5* ^ :z ';2: :zi :zi :z 25 PS 13 25 -Od^rHOd CO r^ <: 4JdcO_cOOcd(UD-d ON d ^ -^ 9 f-H SXJ^4JMd>»-UII*H ncJCdX^C>0-K Cd d -^ vO 00 vo *• ON ON 0^ ON lO CO ^ CO m in cnM-H_ u -H-jcd s N.-/ V^^ \„^ N,^ >*.• ^<^^ S,^ >^#' N»^ ''^*' ^^0 »d -o * 15 CU § .T-)V-|0(U^r-40 *0 5 6 CO cd o^d «jooT4iHf-4 a* CO ^,lWCdd>-i^^ 00 psi cd cd ^ td >s Xi dCOQ-U M-I^MA cd ^^'d 0'-*0 Q* d g 1 i i 1 1 i m 1 1 1 4Ja)*HO ON cn'T3^T4.£:dcd,i3 -M p V-i f-H f-H ^ ooo^jo 000 4Jd'Ha) o>-»cd M-4 cdcdS^^-fiocdcuii 4J (U ^^ 4J 0) 0) CO 0) , CO g ,^^ -K 4-> fH 0) Cd CD ^0)0)3 04CCd Cd cd cd 0) 'd CO d Cd rH cd CiO TS M g g na nH cd -H d e Cd •H • cdtJC* u U -^-H •H "H M TS 0) I— 1 3 '5 c=* 0) o>d cdoo a- d qj j-i iw d CO "H • 0) d iH -a -H j-j 'O d^ -H a M cd(Ux:*Hd% •H JH T3 •H h4 4J 4J -H d Cd M ^ -a -H ^ rH M U -H u >^ pa i-icoa4a)'OMa)A cd <^ocd(DP4dcdu:: 0) ^ 4J •H M -H ^ > (U CO CO d ^ d Cd d d •M -c Cd -H x: H'-M-ua.g H H H 2: H W CO CJ3 p.. a. 25 O C c T3 03 (U >> II Q) B J=^ B U 1 ^3 o -a Q) a M-< 0) -^ Nl Cd ;-< 4J '-^ •H 0) p O u u 0.0)0 CO 0) CO • • s ^ OJ Q) O /-^ e e: 5-1 ^ w 'd D -H OJ CO [5 ^ • a "H iH O (U ^ (U -^ ^ .. c CO ^o u a II o a •H Cd o x: s TS •«« u CO a P * o •H Cd (U d M-i V4 0) ^ JQ •» cd Cd «d *-* (U a 4J H^ o u S Cd TJ • Cd o c: c o € O ^3 v^ cd •H 0) OJ A •u iJ -u 4J >s CO CO a CO rH a 0) 0) . X • X '+j > fH cd K cd -H cd 4J 4J C o a ()0 M Cd M "^ '^ T! 0) o O CO N •H 1-) 0) -H cd cd ^ ^ 2 o •a ^ >M 3 C 4-) 4J M M 4J 11 OJ CO o Cd cd •H 1+-I (U CO TJ ^ a CO !2 cd CO XJ ^ T3 +J ^3 CO -M ^ M O S CU U M-l Cd a W -H U CO hJ CO (U >% •u pq G W rH X CO ON 0) ON ps: o CO o CO M I CD 25 O M O B m B B 6 CO a o 3 M ^ a o •-5 U o o 3 o o o ^ a. < o 3 U <: 2: o ■JC CO 2; CO 2 CO 2: •3< CO •3C CO 25 •3< •3< CO 2 4< CO CO •3< CO 5S CO 25 CO 25 CO 2: CO •i< CO 25 •J< CO CO CO 2: CO CO 25 CO 2: CO 25 CO 25 CO 2: CO 2: CO 2; CO 25 CO •5C 4< CO CO CO 2: CO CO 4< CO :2: CO 25 CO 2: CO 2 1 CO CO :2: CO 25 1 CO 25 CO 25 CO CO CO CO 2: ;z: z -K ^2: CO -K -K CO Z -JC * -K Z CO CO CO CO CO :2: ^ :2: :2: :z CO CO CO CO ^2: :zi ^ :2: CO 25 CO 25 CO 25 CO CO 2: CO 2 CO -JC 2: -K CO 25 -Jc CO CO •}« 25 25 4C CO 25 •J< -JC •!< •J« 4< -K I ^< -K I •K -K I CO ^1 Cd B •H Cd '■a •H g o c o (U cd O ^ Cd •H a •H •H 3 a >■ W CO CO 3 cd c cd «H cd T3 CJ •H o e M to 0- 3 o c O -H p- •H M T3 o •H }^ •U -H 4J >^ (U CO CO c o 4= cd 'H o rC ej eu fi^ 26 E ro O E < o 15 I o o o o o T o o o o o o CVJ o .CO (^.UJ *0U) A4JSU9G U08M «k O tH • 00 •H 4J CTN M c M iH CU CO CO > CO • u 4J iH •-3 U •H cd CO a 0) o d •H X 4J Q) C 4J Q CO M CO tH CO a • • CO CU o CO 0) •M d Oi (U rH O CO M rQ 4J a 0) CO CO iH U-4 m V4 a> •H O tH o o CO 1 a d > /-N m 0) CO CM fl i^ 1 jj o 0) 5> a CO •H tM a 60 o o u C 0) M o 0) CO U >•• •H a 'd CO S H d -d CO o 0) 0) CU CO •H M • CO CO 4J CO ^-x > iH o tH rH CO u CO M 4J C ^-1 O (U d O •H U 0) •H • ^ M T> >» 0) o 0) a ^ 60 o 4J CO U :3 'd CO -d o 00 . d CO CiO iH CO 0) 'd •H 3 4J M d Pt4 ♦-D C/3 O* CO 27 E CD JO a E < ^ « -O I o o o T" o o o CVJ o o o T" o o o (^-uj 'ou) Xiisuao uo9^ T3 a o o to •H Pt4 28 o 0» 0) 00 E D O -CO < "a o H la I o -00 0> 03 0) a o o o o o o o 00 o o (^.uj *ou) Xiisuao UD0V4 00 Pt4 29 .00 O .00 0» O <7) CM £ < o .00 0/ K CO o = o I o .00 I ^H 0) c •H o "T- o o 04 nr o o o o CD 0> nr o o 00 (^-UJ ou) X4tsu9q uo8^ 00 30 o -03 0) 0) O C7> £ ID .00 01 a "E < o <7> O -00 0) = o I o -CD (7) C7> 13 (1) :3 C o u T" o o o o o o o o 1^ o o o o (2-U4 -OU) X4|SU9a U09W (30 P&4 31 CHIRONOMIDAE Chironomids were represented in 95% and 94% of the samples collected during 1978 and 1979, respectively (Table 11). While chironomids comprised 34% of the 1978 annual benthic mean density, the relative abimdance of chironomids decreased to 15% of the 1979 annual benthic mean density. TABLE 11. Frequency of occurrence of major taxonomic groups among benthic samples (n = 180) collected during 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Taxon % Taxon % Chironomidae 94.4 Gastropoda 37.8 Ollgochaeta 79.4 S. heringianus 13.9 P. hoyi 78.9 Sphaerlum 5.6 Naididae 71.1 Hydracarina 4.4 Tubificidae 64.4 Hydra 2.8 Turbellaria 64.4 Hirudinea 1.7 Pisidium 52.2 M. relicta 0.6 Enchytraeidae 42.8 Samples with Animals 96.7 The chironomid genera/ species list has been revised and updated from 1978 (Table 3). The primary revisions have been to condense Parakiefferiella sp. and Orthacladius (0_O sp. 1 and sp. 2 into Cricotopus/Orthocladius (O^O sp. 1. Previously, there had been some confusion in that early and late ins tars differed morphologically.. Having seen ins tar and depth association patterns over 2 yr has helped coalesce some differences observed previously. In addition, what had been thought to be an early instar orthocladiini (sp. 2) has subsequently been noted to be a last instar individual as yet unidentified (only one specimen has been collected). 32 A total of 37 chironomid taxa have been identified from 1977 to 1979 (Table 3), Generally, the number of chironomid taxa collected was similar between years for a given depth and regional comparison (Table 4). The largest difference occurred at 3 m where the inner region had 17 taxa present and the outer region had only 10 taxa present over both years. Examination of these regional differences did not appear to indicate any significant differences between regions based on kinds of chironomids observed. Twenty-six chironomid taxa were found in the inner region over all depths and months in 1978 and 1979. In the outer region 25 chironomid taxa were observed in 1978 and 24 during 1979. Overall, in the inner region chironomids have been represented by 31 taxa, while 28 chironomid taxa have been identified in the outer region. Based on annual chironomid mean density, Chironomus fluviatilis- gr ., Cryptochironomus sp. 2, Paracladopelma camptolabis- gr . , Polypedilum cf. scalaenum , Robackia cf . demeijerei , and S aetheria cf . tylus were the most numerous chironomids collected in each yeair. Relative importance of these taxa differed between years with S_. cf . tylus (24%), P_. camptolabis- gr . (18%), £. fluviatilis- gr. (12%), and P^. cf . scalaenu m (12%) most abundant in 1978. During 1979, £. cf tylus (25%), R. cf . demeijerei (24%), P^. cf . camptolabis- gr. (10%), and Cryptochironomus sp. 2 (10%) were the most numerous chironomid taxa (Appendix 2). The greatest change observed was a decrease in relative abundance of £. fluviatilis- gr . and an increase for R . cf . demeijerei . Distribution of chironomids with respect to depth and month during 1979 differed from the pattern observed in 1978 (Figs. 5 and 6). While the largest mean chironomid densities were observed at 6-12 m during 1978, all depths had a similar average abundance of chironomids in 1979. In particular, the 1979 9- and 12-m mean density estimates were significantly lower when compared with 33 Chironomidae 4000- X 3000 o c Q I 20 2 1000- •1978 •1979 15 Depth (m) -2^ Fig, 5. Mean density (nmnber m ) of chironomids collected at 3-15 m during 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant • Density estimates at each depth were computed by averaging over all months within each year (n =» 36) . Standard error denoted by vertical bar. 34 Chironomidae 3000-1 2400- ^ 1800 o c in c a> Q c o 200- 3031 •1978 •1979 600- Aprll July Months October -2^ Fig. 6. Mean density (number m ) of chironomids collected during April, July and October 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates for each month were computed by averaging over all depths within each year (n = 60) . Standard error denoted by vertical bar. 35 1978 values (Table &)• The 6-111 average chironomid density was not significantly different between years, although densities were much lower in 1979 than 1978, due to the large variation associated with the 1978 6-m estimate. Overall, the 1979 annual mean chironomid density (1203 m*"^) was significantly less than that observed during 1978 (2198 m""2). Monthly mean density of chironomids was significantly lower in July 1979 when compared with July 1978. The October 1979, 6-m mean chironomid abundance was not different from the October 1978 estimate due to the large variation associated with the latter (Table 6). Comparing inner and outer regional mean densities over all depths and months sampled during 1979, the outer region had a significantly greater number of chironomids than did the inner region. This difference was most evident during July (summed over all depths) and at 3 m (summed over all months) (Table 9). Analysis of July inner/outer regional mean chironomid densities indicated that during 1979, 3- and 6-m chironomid abundances were significantly greater in the outer when compared with inner region values (Table 10). No significant differences were found among remaining depths for July 1978/1979 comparisons. With respect to observed 3-m mean density differences for chironomids, however, the trend observed during July was also evident during April and October. Inner/ outer comparisons for chironomids at 3 m indicated a consistent monthly trend of a decreasing inner region mean density and an increasing outer region mean density from 1978 to 1979. Chironomid abundances at remaining depths tended to increase or decrease in a similar manner from 1978 to 1979 (Fig. 7). Variation in percent occurrence of chironomid species within a given month between inner and outer regions was most extreme during July. The chironomid, Robackia cf . demeijerei , displayed the most consistent inner/outer difference of all chironomid species. The outer region had a consistently greater percent 36 £ CD D "O E o c: o o I — ==H if I 1^ o o o o o o T- o o o (^.lu *ou) Aiisuaa U08N • 00 «» +J 0^ tH a M iH 00 •H cd cd 0) U tH 0) M P4P-1 a <3 r-4 Cd % a • M 4-> ^-D U •H CO CO 00 'd Q) a (J) •H ^ 4J d) 4J ca p ti u TJ cd a • • u Cd 0) •H a 04 '1 /-s m 0) cd CM a M 1 4J 0) 0) s cd 00 ^ 00 .JQ >< •H u 4J :3 ^ (U cd -3 a a CO 4J v-/ •H a •d Cd s M a -d 0) CO ~" CD 0) a. CO •H ^ • CO cd 4J cd /-N >•• a M-i C CO d Cd u •H 0) Q) cd C>0 4J B a ^ 0) fH H rH ClJ M cd U 4-1 C M-4 a 0) ti "~ •H 4J Q) •s •H cn 4J d M 60 r^ M >4 (U o\ 0) d ^ r-4 > o M 'd >» 0) .CD 0) 0) C ^ 00 a •u Cd M __ D TJ Cd -d 'Z 00 (U ^ 0) a. r^ 4J 'd < 0> 'd <3\ CO -d .f^ § iH a •H Cd a> 0) nd "" M ^d 0) U (U tH pQ (U ^ u cd fi g;:! GO d U M •s M M 0) "H 0) 5* • n3 TJ tH r«. a J-i 4J CO cd cd • >> a CO W)r-I cd 0) TJ •H 3 u M r: fe ^ CO Cu cd 37 -CO o -GO 0> 0> .00 £ CD o .CO 0) CD O £ o 0) 0> O o '5» :0 I o — 00 0) (U o o 0> 1^ o o o o o o ro (3.U1 °ou) X4ISU90 uoa^ 38 o .00 0) T^7^ E CD .00 O "O E o c o Jr^- 1 0) 0> 0> 00 0) o 1^ o o CO o o o o o 'I- CVi o o (^.ui 'ou) ^lisuao uo»M PS4 39 -CO 0> o -CO ^ o> o <3) -00 0> CD D o .(O 0> E o c o <3> 0) GO 0> O I o -CO 0> cs •H a o 1^ o o o GO o o o o o o o o o (^_ui 'ou) X^isuao uoa^ PX4 40 .CD 0) 0) LO .00 0) CD a o -CD 0) £ O o 0) CO 0> O II I o .00 0> 00 0) o o nr o o o o o o 1^ o o o I o o o (^.uj 'ou) AijsusQ uoa^ fa 41 occurrence of R. cf . demei jerei than the inner with this difference becoming more extreme with each month sampled. The absolute difference in this chironomid's density between regions was 10% in April, 32% in July, and 42% in October. Another chironomid species, Cryptochironomus sp. 1, that occurs with R. cf . demei jerei and comprised 3-7% of the overall chironomid density during July and October, also was notably absent from the inner region. With the exception of R. cf . demei jerei , there were no obvious differences regarding percent occurrence among regions for chironomid species during April (Appendix 2). In addition to regional differences observed for R. cf . demei jerei and Cryptochironomus sp. 1, the inner region at 3-9 m during July had a disproportionate increase in percent occurrence of chironomid taxa normally found at finer sand depths (9-15 m) when compared with the outer region (39% and 11%, respectively) . Chironomid species showing increases in the inner region at 3-9 m during July were Cyptochironomus sp. 2, Heterotrissocladius cf . changi , Hydrobaenus sp., Micropsectra sp., Monodiamesa cf. tuber culata , Polypedilum cf . scalaenum , Potthastia cf . longimanus , and Procladius sp. These same differences were observed in October but were reduced in intensity. NAIDIDAE Naidids comprised 22% of the 1979 annual benthic density and occurred in 71% of the samples collected during 1979 (Table 11). Of 19 species of naidids collected from 1977 to 1979, 15 species were identified from the inner region and 14 species from the outer region during 1979 (Tables 3 and 4). Compared with 1978, there was a change in naidid species composition in the survey area. Whereas in 1978 Piguetiella michiganensis (49%), Chaetogaster diaphanus (17%), Stylaria lacustris (15%), and Uncinais uncinata (12%) were the most abundant naidid species, samples collected in 1979 were dominated by 42 Vejdovskyella intermedia (52%) and £. michiganensis (23%) (Appendix 3). All other naidid species comprised less than L0% of the annual naidid mean density. It also appeared that at 3 m, in 1978 and 1979 combined, the inner region consistcmtly supported a greater number of naidid species (10) than the outer region (4). While the first three of the four 3-m outer region naidid species ( Amphichaeta leydigii , P« michiganensis , £. diaphanus , and £. diastrophus) were also found in the inner region, Nais e Unguis , Nais pardalis , Nais simplex , Nais variabilis , £. lacustris , U. uncinata , and V^. intermedia were identified only from the inner region at 3 m. However, all of the above naidid species, with the exception of N. simplex , occurred at one or more other depths in both regions. Although all remaining depths had similar niombers of naidid species, there were additional qualitative regional differences which will be discussed after an analysis of quantitative annual and regional depth and monthly differences . Mean annual density of naidids observed during 1979 (1782 m"'^) was somewhat greater but not significantly different from 1978 average density (1134 m'"2) (Table 6). The depth distributional pattern for naidids collected during both years followed the same pattern although there was a significant difference noted at 9 m (Fig. 8). Monthly naidid mean abundances were similar and followed the same trend during both years (Table 6, Fig. 9). Annual wi thin-region comparisons for year, month, or depth indicated that neither the 1979 inner nor outer naidid densities were significantly different from naidid densities in corresponding regions in 1978. Within 1979, although there were no regional naidid density differences for year, month, or at the 6-, 9-, 12-, and 15-m depths, there were significantly more naidids in the inner compared with the outer region at 3 m (Tables 7-9). Further analysis of regional naidid density differences at each depth sam.pled in each month 43 Naididae 2350- CM I E d c c I360H a c o 350- •1978 •1979 12 15 Depth (m) -2 Fig. 8. Mean density (number m ) of naidids collected at 3-15 m during 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates at each depth were computed by averaging over all months within each year (n = 36) . Standard error denoted by vertical bar. 44 Naididae 5000- OJ o c 2 3000- a c o 1000 1978 1979 April July Month October -2. Fig. 9. Mean density (number m ^) of naidids collected during April, July and October 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates for each month were computed by averaging over all depths within each year (n = 60) . Standard error de- noted by vertical bar. 45 indicated the pattern observed at 3 m during July 1978 was maintained in July 1979 (Table 10). Naidid densities at 3 m in July were consistently greater in the inner region compared with the outer region in both years (Fig. 10). However, during July 1978 at 3 m the naidid species, Uncinais uncinata , was the dominant naidid taxon (70%); whereas, during 1979, Vejdovskyella intermedia (39%) and Amphichaeta leydigii (33%) were dominant. Dominance of U^. uncinata at 3-9 m in 1978 was replaced by V^« intermedia in 1979, particularly during July when U^. uncinata was most abundant. Comparing inner and outer regions and combining the 3-9-m depths during July 1979 indicated that V^. intermedia was also an abundant species in the outer region (32%), but not to the extent it was in the inner region (77%). In the inner region, V^. intermedia and A. leydigii comprised 89% of the July naidid mean density at 3-9 m. In the outer region, the same two species comprised only 33%. Other naidid species such as £• ^ CO 0^ rH W CO tH 3 W a •-D >-l T3 a d GO « • cd 0) iH *J M •H C cd M cd cd 0) 4J o> (U CJ 6 cd iH •M B iH • cd -H HI » •H 0) 4J U TJ ^ •H •H 4J CO CO d nd d V4 a 0) cd Q iM (U a a CO ^ U cd • 3 » a a U (U 3 ^-^ cd ^-1 60 cd bo 0) M a 4J a Oi 3 rH ;3 S __ >.0 M •— 'S ^ ?^ 0. T^ a p < a Cd TJ • C7> 2 Cd 0) 0) a 00 4J 00 u r^ M a ON a cd s «-» 0) ^ TJ a T3 a 43 TJ cd • u 4J MHO) • 0) cd ^ T> C rH 60 TJ }-4 (U H •H a cd J3 -H Pt4 Cd 'V U ^ 47 o -CO a H-^^ 0> £ o -CO en D O -CO o -CO 0> ^o U (7> C3 o T" o o o 0^ o o o (0 "T" o o o ro (3.U1 °ou) Xiisuaa uoav^ t30 Pt4 48 h^ o -00 0) £ CD O I o o o 1^ o o o o o o "T- o o o o -CO '^0> (^.Ui'OU) XllSUaO UD8M a o a to 49 0> o -OO 0) o> o 00 E (M .00 0> o -CO CD O "O 5 00 .00 0) o .00 (3> = o I 0> 0) OO 0) {3 o o o T" o o CO o o IT o o (^.ui *ou) X^isuao U08II4 50 o .00 0) I----H o> o 00 £ LO .00 0) o .00 o CD D --_H 00 = o I o .00 ^ri P^H (7> a> 0) a o o o o 1^ o o o 1^ o o o (^.uj 'ou) X4{$uao uoayv 51 much greater numbers of P_- michiganensis present in the outer region compared with the inner region. Exclusive of the above observed differences, all other comparisons were not significantly different and exhibited consistently increasing or decreasing trends across regions. TUBIFICIDAE Tubif icids comprised 9% of the 1979 annual mean benthic density and occurred in 64% of the samples collected (Table 11). Thirteen species of tubif icids have been identified from 1977 to 1979 (Table 3). The most numerous of nine tubif icid species collected in 1979 was Potamothrix moldaviensis , having an annual mean density of 21 m""^. Although tubif icids were more numerous in 1978 (859 m'"^) than during 1979 (735 m""^)^ there was no significant difference between estimated annual densities (Table 6). While the depth distribution of tubif icids was similar between years, there were significantly more tubif icids present at 9 m in 1978 when compared with 1979 and at 15 m in 1979 compared with 1978 (Fig. 11, Table 6). The tubif icid density difference foxind at 9 and 15 m between years was related to yearly regional depth differences. Monthly mean densities for 1978 and 1979 followed similar seasonal abundance trends with no significant differences noted among respective monthly tubif icid abundance comparisons (Fig. 12). Tubif icids exhibited similar abundances in the outer region from 1978 to 1979 and in the inner region from 1978 to 1979 (Tables 7 and 8). In the outer region tubif icids were significantly more numerous at 9 and 15 m in 1979 than in 1978. Overall, the outer region had significantly more tubificids (1485 m"^) than did the inner region (903 m"^) based on a yearly average over the combined depths 9-15 m. The difference between 1979 inner and outer regions was most apparent during July (averaged over 9-15 m) and at 15 m (averaged over all months) 52 Tubificidae •1978 •1979 600- CVJ o c c O 200- 2 800- 400 Depth (m) -2 Fig. 11. Mean density (number m ) of tubificids collected at 3-15 m during 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates at each depth were computed by averaging over all months within each year (n = 36) . Standard error denoted by vertical bar. 53 -7 I50CH CsJ O c 0) c O c o 0} 1000 500- Tubificidae 1978 1979 April July Month October -2, Fig. 12. Mean density (niimber m ") of tubificids collected during April, July and October 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates for each month were computed by aver- aging over all depths within each year (n = 60). Standard error denoted by vertical bar. 54 (Fig« 13). During July, there were significantly more tubificids observed in the outer region for the combined depths 9-15 m when compared with the inner region (Table 9). Averaging over months, the greatest density difference was obseirved at 15 m where outer region tubificids were more numerous than those in the inner region. Specific comparisons between 1979 inner /outer tubificid densities within each month at each depth sampled indicated that only at 15 m during April and October were there significant density differences (Table 10). Inner/outer trends paralleled one another from 1978 to 1979 at 9 and 12 m, but were in opposing directions during April and October 1979 at 15 m (Fig. 13). TURBELLARIA Turbellarians occurred in 64% of the samples collected during 1979 (Table 11), but comprised only 6% of the 1979 annual mean density of macroinvertebrates . Two morphologically different turbellarian species were identified, with species 1 found primarily at 3-9 m and species 2 at 9-15 m during all months (Appendix 1). Compared with 1978, there were significantly more turbellarians collected during 1979, which may reflect increased recognition of nearshore species 1 turbellarians. Turbellarian density diff€irences between 1978 and 1979 were significant at 3, 6, and 15 m (Fig. 14). In addition, during April and July, significant increases in turbellarian mean density were observed (Fig. 15, Table 6); however, with respect to 1979 monthly inner/outer regional mean density comparisons over all depths combined (3-15 m) , no difference in turbellarian abundance was found. When turbellarian abundance was averaged over all months at each depth in 1979, the only significant difference occurred at 3 m where the outer region mean density was greater than the inner region mean density (Table 9). Inner/outer density trends tended to be in the same direction from 1978 to 1979 (Fig. 16). 55 E CD D "o = o I iH cd •;h ^ Pu 'TS a 0) Cd U u o 0) • fH W f-l O • O ►-3 CO 0) 'd ^ •H 4J O •H M M-4 Cd •rl 0) •s a :3 4J a o 00 a\ U tH cd 0) M c o M-l Cd 0) CO cd 4J S 4J a a CO U 0) Cd u u CO o c p CO a • • o cd 0) p4 Q) H CO v^ ^ 0) Cd u 0) 0) o o 0) •H *w a (U u u o ^ M u 0) cd tf CO 4J CJ TJ cd H a -TO o P4 CO • CO cd u u II o :3 O 60 o M "H O cd 60 4J GO •H <3N 0) 60 r>* 0) C3N U r^ o U t3 CO Q) a 0> 4J Cd ■"" 3 ~ O 00 a. r^ < -d a\ 0> s-^ u U 0) 4J § V4 O C3 >* 0) O ^ 60 O M tj cd "d 0) ^ 0) 4J O 'd O CO TS e: "H cd 'd ^ a CO 60 tH cd 0) 'd d 4-1 00 CS ON 0) iH 4J V4 a Pm t-0 CO O4 cd 56 OJ O .Z3 = o ! O o o o 0) o 0) CO 0> o GO 0> - a • < ^3 0> (1) 2 a •H 00 o h- o 0> T" o o o o CO (^-UJ'OU) A4ISU9G u»aM 57 E in CD o "o -Q = o I o o o o o o "T" o o o ^ *^ s 0) 3 0> a — •H 4-t O 00 o fw 0> (^.lu *ou) Aijsuaa uoa^ CO 00 Pt4 58 Turbellaria 1200- 9 00- o c o 60 o c o 300- 1509 12 Depth (m) —2 Fig, 14. Mean density (number m ) of turbellarians collected at 3-15 m during 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates at each depth were computed by averaging over all months within each year (n = 36). Standard error denoted by vertical bar. 59 Turbellaria -1978 -1979 800- CVJ I E d c 0) c Q c o ' ^^-^-^ — 60 o ro o ^_ Z3 c: a. •^§ (U 4J • O JC ^ • CO -H iH Q) CD ^ M a CO Q -H CO ^ CO 0) 0) CO S-" o o CO a o a. CO (U , VO O H " «"= o CO CO 0) u 0) fl ^-'•H •H M 6C M =0 o o o o o o o o o 0) CO 0) CO CO a CO O (1) -d CO S r^ o> r-4 iH CO o a •H CO 60 0) 0) 0) ^ 60^ >. u .iS CO H ^ O -A 0) 00 1^ O -d H 00 CO H 01 a CO 0) O U 4J (^.Ul *0U) X|{8Uaa U09M SJ CO • •-) VO iH •* • 60 M CO •H Q4rH P«4 <3 Pm O 4J CX> fl ON 0) iH CO 0) M M O a«M-i U CO CO o 0) 4J a CO _ s CO "H 0) 4J M CO CO Q) 61 o o -CD <7> E CD -CO 0) o -CO CD = o I .CO O ^0> 53 O o 1^ o o (^.lu ou) Aijsuoo uoa^ <30 P:4 62 E en D "53 ^_ 13 -CO o — CD I o o "T" o o T" o o "T" o o o -.00 0) (2. Ill *0U) A4I8U9G UI39M ^3 0) a 4J a o (Z4 63 .00 O .CO <7> O 0) £ CO -CD a o .CD <3i 1 -CO = o I o -CO \ 0> CO o o o o o 00 (^.ui 'ou) A4)SU8<] uoayv 1^ o o rH 64 H-^ T «r^ 00 0) LO -CO 0) o o -00 0> 0) CO 0» = o I o -00 U O T" o o "T" o o (^.Ul *0U) X4I8U8G U09M to 65 ENCHYTRAEIDAE Occurring much more frequently in samples collected during 1979 (43%) than during 1978 (14%) (Table 11), enchytraeids comprised 2.4% of the annual 1979 benthic density and were significantly more numerous when compared with 1978 populations (Table 6). Although low abxmdance of enchytraeids was noted at 6-9 m, regular occurrence and increased densities were observed primarily at 12-15 m (Fig. 17, Appendix 3). As in 1978, maximum abundance of enchytraeids occurred during October (Fig. 18). During 1979, significantly higher numbers of enchytraeids were observed at both 12 and 15 m and during April when compared with 1978 (Table 6). While a t test could not be computed for July data, it was obvious that July 1979 samples had significantly more enchytraeids than were present during July 1978. No enchytraeid density difference between years was observed in October. Both the inner and outer regions diiring 1979 had significantly greater numbers of enchytraeids present when compared with their respective regions during 1978 (Tables 7 and 8). Comparison of 1979 inner and outer enchytraeid mean density at 12 and 15 m indicated no significant density differences between regions (Table 9). A similar comparison of monthly densities over the combined depth range 12-15 m indicated that only during July were there significant inner/outer differences, with the outer region having significantly more enchytraeids than the inner region. The July enchytraeid density difference was most evident at 12 m with outer region organisms significantly more numerous than in the inner region (Table 10). Increasing or decreasing enchytraeid density trends from 1978 to 1979 tended to be similar or have broadly overlapping standard errors for all comparisons made, with the exception of the 12-m July comparison (Fig. 19). 66 Enchytraeidae 500 (M (0 S 30 a 100- •1978 •1979 9 Depth (m) 15 -2 Fig. 17 « Mean density (nximber m ) of enchytraeids collected at 3-15 m during 1978 and 1979 in eastern Lake MiLchigan near the J» H. Campbell Plant. Density estimates at each depth were computed by averaging over all months within each year (n = 36) . Standard error denoted by vertical bar. 67 Enchytraeidae -1978 -1979 300- cvj o c O o 2 20O 100" April July Month October -2. Fig. 18 • Mean density (number m"^) of enchytraeids collected durxng April, July and October 1978 and 1979 in eastern Lake Michigan near the j: H. Campbell Plant. Density estimates for each month ^|" ^J^^^^^J^r by averaging over all depths within each year (n « 60). Standard err denoted by vertical bar. 68 e CM CD O "D CD a o « 5 3 c c 1 LlI 1 1 "T" o o o o 0) "1- o o 1^ o o (^.lu *ou) Aijsuao U09M • o •» w 00. tH C a\ •H CTJ u rH M r-l cd O*^ (U u -00 < a o O • Q) >. t-D u u CO AJ •H 'O 0) CO •H ^ O d 00 0) 4J •U «» 0) a • • ^ a o cd 0) o Oi _ /--viH 1 -M o (U 0) B CO •H »w a C)0 Q) O M a 0) j-4 a Q Q) cd M 0) -00 ^ C)0 o ^ 0> 6 *H M 4J *" :3 ^ 0) Cd >» a o a CO 4J "a >-' -H a nd Cd "3 a M a Tj 0> CO o Q) 0) Oi CO •H ^ • CO cd 4J Cd /— \ 0) •H hJ vO V4 0) CO }-i u 00 a 11 o :3 -h- 0) M O CiO 0) TJ -• a *w PS CO o cd cd V4 •H O 0) Q) Cd bO U a ^ 0) a M >. H O rH iH cd M Cd M 4J a ^^ O t)Or^ U o u (U ON o U TS >» d rH CJ •H Cd _rw Cd (U 13 0) U TJ Q) ~* U 0) rH ^ 0) ^ M o O a 'H a 4J M U rH CO M O U 0) -H 0) o (U ^ 1^ 4J rH cd 13 rH 4J 00 fl CJN T3 0) rH • >» a CO W) iH cd 0) 13 •H 3 •u u a Pt4 >n CO Q« Cd 69 o 0) D D O c LlI .00 0> o -00 o I o .CO 0) I O 1^ o o o o oo o o (^.ui *ou) A4!SuaG uoa^ PL4 70 STYLODRILUS HERINGIANUS Stylodrilus heringianus was found in 14% of the samples collected and comprised 1.2% of the macrobenthos during 1979 (Table 11). In 1978, ^* heringianus was found at 9 and 12 m in very low densities, with the major occurrence during both years at 15 m (Fig. 20). In 1979, ^. heringianus occurred only at 15 m (Appendix 3). Monthly distribution of S_« heringianus in 1979 was very similar to that observed during 1978, with low densities in April increasing to a maximum in October (Fig. 21). Annual density comparisons for year, month, and depth (15 m) indicated there were no significant density differences even though there were fewer individuals collected during 1979. Most year, depth, and month comparisons for S^. heringianus indicated there were few significant regional density differences (Tables 7-10), except during October when the 1978 inner region had significantly more S^. heringianus than did the 1979 inner region. I^en comparing regions in 1979, it was noted that the inner region had significantly fewer S. heringianus when compared with the outer region, and that this difference was most prononmced during October at 15 m (Table 10, Fig. 22). PISIDIUM Pisidium comprised 6% of the benthic invertebrates collected during 1979 and occurred in 52% of the samples (Table 11). The pisidia were represented by 13 species in 1979, bringing the total number of Pisidium species identified from the survey area to 16 (Table 3). Based on annual mean density, Pisidium casertanum (130 m""^), Pisidium fallax (89 m"'^), and Pisidium nitidum (80 m"2) were the most abundant pisidia during 1979 (Appendix 4). During 1978, Pisidium nitidum (83 wT^), Pisidium casertamun (62 rxT^), and Pisidium fallax (28 m"^) were the three most abundant pisidia based on annual 71 Stylodrilus heringianus 800- 600- E d c 0> a o 400- 200- 3 6 9 12 Depth (m) ^2 Fig, 20. Mean density (ntimber m ) of S^. heringianus collected at 3-15 m during 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates at each depth were computed by averaging over all months within each year (n = 36) . Standard error denoted by vertical bar. 72 Stylodrilus heringianus 300- I E Q c O c o a> 200" 100 Fig. 21. Mean density (number m ) of S. heringianus collected during April, July and October 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates for each month were computed by averaging over all depths within each year (n = 60) . Standard error de- noted by vertical bar. 73 o at o I J T- 8 (^.ui 'ou) A4!Suao uo9M § I 1 a •H 0) 0) ,X3 a 'O a* 4J 5>. . tH • 0) rH rH W O O -H O 4J Cd 0.1 >-3 > CO • Cd K CO TJ Cd d 0) d 0) 0) a ^ o M a cd 4J a« Cd o •H CO o GO Ofl M 0)0)0) 0> Cd u o ^ •H 0) u a V4 o 0) cd Q) O M 4J ^ a 0) Cd C ^^ ^d . m O 0) cn|r-i •H Ki CO 00 cd ^M 4J 0) o O CO M -M 0) M •i /-N a U (0 c^ CO (U ^ (30 1 00 a a -H a -H d o ^ JC M 04 u o CO o o 0) iH 0) -M .00 ^ :s: • M J> a ^ M >> >« D 0) vO O r-i 3 a ^ o tJ -3 >-/ OJ II ^ d Oi »^ d 0) .r- CO d O M 0) 0) rH rH 00^ Cd >^ u es 'ij JQ cd fH o a ^ H O •H cd -d O •H •s (A 0) CO ^ 0) C30 4J ^ u r^ O TS H o\ d CO M iH 0) fH ON o 0) •d g iH "2 4J M :3 . cd CUM-4 -b iH 4J :3 en M CO • »-3 cd 0) CM 0) 4J CM * • d Cd rH 2: 400 200 April July Month October Fig* 24. Mean density (number m" ) of Pisidium collected during April, July and October 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates for each month were computed by aver- aging over all depths within each year (n = 60) . Standard error denoted by vertical bar. 77 averaged over all months (Tables 7 and 8). However, inner /outer regional comparisons made within each month and depth sampled indicated that, although both regional mean densities increased during October at 12 m, the inner region Pisidium density was significantly greater than that observed in the outer region; the opposite trend was noted at 15 m during October (Fig. 25, Table 10). Remaining inner/outer regional comparisons of Pisidium mean densities indicated similar density trends or widely overlapping standard errors. SPHAERIUM Sphaerium occurred in 6% of all samples collected in both 1978 and 1979 (Table 11). In addition, very low annual mean densities of Sphaerium were recorded (4-5 m"^) during both years. A similar depth distribution pattern was observed in 1978 and 1979 (Fig. 26). Sphaerium stria tinum exhibited highest abundance among Sphaerium in both years. Although Sphaerium transversum was not observed in the inner or outer region during 1978, it was collected in equal densities from both regions (1 m*^) during 1979 and was the second-most numerous Sphaerium species (Appendix 4). Sphaerium nitidum annual mean density decreased during 1979 (0.3 m"'^) when compared with 1978 (1.3 m""^). Since all three species occurred infrequently in the survey area, it was difficult to assess the significance of annual changes. Inner/outer regional comparisons were not made for Sphaerium . GASTROPODA Gastropods were found in 38% of the samples taken in 1979 (Table 11) which was similar to the frequency of occurrence noted for 1978 (32%). The benthos was comprised numerically of only 1.2% gastropods, with the majority of gastropods occurring from 12 to 15 m. Of the five species of gastropods 78 e •I = o I 1^ o o fO o o o o 4J I (2-Ui*0U) XilSUdQ UD8^ rH a CO GO •H (U 0) 0) u rH 6 aiH 4J >» TJ CJ O O Cd Ji (U 4J H o 4J • •H o a ;i: CO • cd a o N 2 tH • fi a Cd a O 00 u a CO ^A 0) cd Q) o 00 ^ W) . M o •H /^ M 4J o> 3 43 vO O d O o >» >. >*-• ♦H li H 3 :s3 a -u -3 CO a o tf 0) (U 0) ^-^ •H 0) 0) •H Ai 00 }-4 4J cd M 4J a a CO •H o 'd CO Cd •U (U (U 0) U 'O s ^ U O CI M-« ,ia Cd ^ o ^ •H C3N 'vi o f^ W3r-. (D CO rH .00 (U o> 4J -H -H (7> M tH O TJ 15 M TJ 0) tH H 0) a Td cd 00 o 4J cd S CTi .00 13 J-i C »H 0> O 00 o M Ts a o u 0) M 0) 00 (U ^ cd CO o% g O TJ • TJ Cd m a (U CO CN cd • >% a Cd Cd Cd (u a MtH •H 3 rH J-l "H PC4 »-l p^ Cd ^ 79 o -CO 0> o> o 0> 00 E (M .1 a; .00 o .00 >::. I .00 o -00 0> 0> o "T" o o CSJ O o o o 00 (^.UI'OU) X^I.SUaQ U09M 60 80 o -CD E LO I .1 -CD 0> O -CO 0> 0> 00 O :0 I 0) 00 o 1^ o o 1^ o o o o o (^.Ul *0U) X4|SU9a UI>9M in to •H 81 Sphaerium 1978 1979 20- CM 1 E - 6 c ^-^ >% <*i> c 10- O / /■ ;i h / c • r / / o / / J a> / / 2 A^ / y^ ^ X / X / jX / y / X / X / 9 Depth (m) 12 -2 Fig. 26. Mean density (number m ) of Sphaeritan collected at 3-15 m during 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates at each depth were computed by averaging over all months within each year (n = 36). Standard error denoted by vertical bar. 82 identified during 1979, only Somatogyrus sip. was not identified in 1978 (Table 3). However, the distinction between Somatogyrus sp. and small individuals of Amnicola sp. is difficult, subject to error, and was not made in 1978. Although each individual identified as Somatogyrus sp. definitely had a shell aperature greater than one-half the longitudinal length of shell height, distinction between Somatogyrus sp. and smiall individuals of Amnicola sp. still remains questionable. Valvata sinera was the dominant snail found in 1978 (73%) and 1979 (57%) in both regions. The second-most ntjmerous gastropod in 1978 was Amnicola sp., comprising 23% of the gastropod population over the year. However, from 1978 to 1979 there was a shift from Amnicola sp. (9%) to Lymnaea sp. (27%) as the second-most numerous snail (Appendix 4). Even if Som • o> CNJ • W) •H P^ 88 Ponfoporera hoy/ 8000- CM I E d c >% *to c (D Q c o 6000 1978 •1979 4000- 2000 Depth (m) -2 Fig. 30. Mean density (number m ) of IJ^. hoyi collected at 3-15 m during 1978 and 1979 in eastern Lake Mi.chigan near the J. H. Campbell Plant. Density estimates at each depth were computed by averaging over all months within each year (n = 36) • Standard error denoted by vertical bar. 89 5000' CM I £ c O o 2 1000- Ponfoporera hoy/ -1978 -1979 April July Month October -2. Fig. 31* Mean density (nxjmber m" ) of P^. hoyi collected during April, July and October 1978 and 1979 in eastern Lake Michigan near the J. H. Campbell Plant. Density estimates for each month were computed by aver- aging over all depths within each year (n = 60) • Standard error denoted by vertical bar. 90 than in outer 1978 to 1979 regional comparisons when averaged over months, combined depths 9-15 m, or both (Tables 7 and 8). In fact, only the outer region showed an overall significant increase in P^. hoyi density between years, which was most evident in April and October. While yearly within-region changes were extensive, 1979 regional comparisons of P. hoyi mean density for months, depths, and regions indicated there were no significant regional differences in 1979 (Table 9). However, analysis of each month and depth sampled in 1979 indicated that at 12 and 15 m during July 1979 P^. hoyi mean density was significantly greater in the inner region when compared with the outer region (Table 10). While the outer region generally had a greater abundance of £. hoyi in 1979, only at 15 m in October did the outer region density significantly exceed inner region density (Table 10, Fig. 32). Analysis of P^. hoyi size classes in 1978 indicated a large percentage of P. hoyi in the inner region was one size class larger than in the outer region (Fig. 33). This trend was particularly evident during April at 9-15 m and in July at 9-12 m, but not at these depths in October 1978. Analysis of P^. hoyi size classes in 1979 suggested a pattern similar to but not exactly like that observed during 1978. During April 1979, P^. hoyi individuals in the outer region at 9-15 m were primarily gravid having not released their brood as of 19 April. While this same condition prevailed at 12 and 15 m in the inner as well as the outer region, individuals collected at 9 m in the inner region were either spent females (i.e., having already released their young) or yoimg, recently released P. hoyi (< 3 mm). Subsequent collections made in July further suggested that there was an inner/outer P^. hoyi size-class difference, not only at 9 m but at 12 and 15 m also. However, the percent composition differences for a given size class were not as extreme as those observed during April at 9 m. It was also noted at 91 o .00 cs »-! 0) 00 0> O Hi E (J) .0) 03 I o .00 0> 0) GO 0> = o I o .00 0> 0> \ o o "T" o o 00 o o nr o o (^.Ul *0U) ^4|SU90 U09M 92 o .00 0> GO E CO o .00 0> 0> .00 0) I o .00 0) CO at < T3 a •H o o o o o o o o 0> "T" o o o 1^ o o o (3.UJ 'ou) X4ISU0O uoa^ CM en to Ft* 93 E in 0) 0) o 0> 00 0) ^ <: o .CD 0) I -^^ — I I o .00 0> 0) GO *T3 a) o o o o o o o o 1^ o o o o o o o ( ^.lu *ou) Xijsuaa U08M CO (30 94 Ponfoporeia hoy/ I- i. — mm «__»_ "T — I — I — I — I — I — r •5 50- T — I — I — I — I — r IOO» -■ 1 I ■ e oi 50- ■ JL % H^^*B I '2 • 3 • 4' 5 ' i2m April July I i I i I I I I October \\ ' I ' 2 ' 3 • 4 ' 5 ' rP' Size Class 15m -I — I — J — I — I — I — r — "^^Hf n — I — I — I — I — I — r li- I ' 2 ' 3 ' 4 ' 5^6^^ Size Classes' I *<3mm 2« S'Smm 3" 5-7mm 4">7mm 5* Qravid 6* Spsflt Fig. 33. Percent distribution of P. hoyi size classes in the inner and outer regions at 9-15 m during April, July and October 1979. Samples were collected from eastern Lake Michigan near the J. H. Camp- bell Plant. (* = <2%). 95 9-15 m in 1979 that ]P. hoyi individuals were more advanced in their life cycle in the shallower depths when compared with those from deeper water in the inner region during April, in both regions during July, and only very slightly in both regions during October. A similar pattern was observed during 1978 for both regions in April and July, but not October. Finally, in 1979 as well as in 1978, P^. hoyi size classes were nearly identical between regions during October at 9-15 m. It appeared that growth and development of P^. hoyi occurring in both regions at 9-15 m on 19 April 1979 were reduced relative to 18 April 1978. By 18 April 1978, the majority of P^. hoyi individuals were either spent females or newly released young. However, on 19 April 1979 when compared with 18 April 1978, there were more gravid specimens, fewer spent ones and fewer newly released individuals in samples. SEDIMENT DISTRIBUTION The general sediment distribution pattern near the Campbell Plant during 1979 was similar to that observed during 1978. Sediments collected during both years were described as well to moderately sorted, fine sand. Depth zonation of sediment types (i.e., grain size as measured by weight percent distribution among phi size classes) was evident. The 3-m zone was characterized by medium and fine sands, 6 m by coarse to fine sands, 9 m by fine sand, 12 m by fine to very fine sands, and 15 m by medium to very fine sands. Composition of sedi- ments from the 6- and 9-m depths during 1979 deviated distinctly from those same depths sampled in 1978. In 1979, 6-m sediments tended toward a finer type than observed in 1978. The 1979 9-m depth had only small amounts of very fine sand and large amounts of fine sand and was consequently slightly coarser than was found in 1978 (Table 12). 96 11 a (U A •H a CO 4.) 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