PRESENT AND PAST NUTRIENT DYNAMICS OF A SMALL POND IN SOUTHWEST FLORIDA BY JAMES MARK COLEMAN A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1979 .;-?< TABLE OF CONTENTS LIST OF TABLES iv LIST OF FIGURES vi ABSTRACT - viii INTRODUCTION 1 BACKGROUND • • • 3 The Present Environment • 3 The Historical Environment 11 Recent Trends 1^ BULK PRECIPITATION 20 Introduction 20 Methods 20 Results 23 Discussion 27 GROUND WATER 31 Introduction • • 31 Methods ..... 32 Results and Discussion 40 SEDIMENTS 54 Introduction 54 Methods 55 Results and Discussion • 61 MACROPHYTES 73 Methods 73 Results and Discussion 73 WATER 80 Methods 80 Results and Discussion 80 n NUTRIENT DYNAMICS OF THE POND SYSTEM. . 90 Introduction 90 Methods 90 Sediment Nutrient Dynamics 91 Sediment/Groundwater Interaction 96 Available Phosphorus and Groundwater Concentrations 103 THE POND SYSTEM: PRESENT AND PAST 107 Present Nutrient Budget 107 Historical Nutrient Budget 110 CONCLUSIONS 119 APPENDICES A CHEMICAL COMPOSITION OF BULK PRECIPITATION 124 B CHEMICAL COMPOSITION OF THE POND SEDIMENTS 131 LITERATURE CITED 150 BIOGRAPHICAL SKETCH 158 m LIST OF TABLES Table Page 1 Departure of post-1950 mean temperatures from pre- 1950 means and some influencing factors at six stations in peninsular Florida 15 2 Comparison of total phosphorus in bulk precipitation collectors at Port Charlotte, Florida 25 3 Comparison of total phosphorus in bulk precipitation collectors in the study pond (North Port, Florida) 25 4 Comparison of total phosphorus in bulk precipitation collectors in the sandy flatlands near the study pond (North Port, Florida) 25 5 Comparison of total nitrogen in bulk precipitation collectors in Port Charlotte, Florida 26 6 Comparison of total nitrogen in bulk precipitation collectors in the study pond (North Port, Florida) 26 7. Comparison of total nitrogen in bulk precipitation collectors in the study flatlands near the study pond (North Port, Florida) 26 8 Comparison of total phosphorus between North Port, Florida, sites 28 9 Comparison of total nitrogen between North Port, Florida, sites 28 10 Comparison of total phosphorus between Port Charlotte and North Port, Florida 29 11 Comparison of total nitrogen between Port Charlotte and North Port, Florida 29 12 Concentration of phosphorus and nitrogen in groundwater input wells in 1978 . , 4' 13 Concentration of phosphorus and nitrogen in groundwater output wells for 1978 ^2 iv . Table 14 15 16 17 18 19 20 21 22 23 24 25 26 27 £m§. Groundwater movement through the study pond 47 Percent standard deviation 61 Percent standard deviation 63 Summary of data for center sediment cores 64 Summary of data for the first concentric ring of sediment cores 65 Summary of data for the second concentric ring of sediment cores 66 Summary of data for the third concentric ring of sediment cores 67 Summary of data for the fourth concentric ring of sediment cores 68 Plant above-ground biomass data (June-July, 1976). ... 75 Concentration of phosphorus, nitrogen and carbon in the plant species of the pond during June and September, 1976. 76 Total amount of phosphorus, nitrogen and carbon in the plant compartment of the pond during June, 1976 77 Surface hydrology of the pond (1978) 81 Nutrient data for the pond (1978). ...... 82 Regression analysis of nitrogen and phosphorus on organic matter 92 -flf-; LIST OF FIGURES Figure ^^9^ 1 Location of the study pond 4 2 Generalized cross-sectional view of the study pond environs. 7 3 Annual 10-year mean temperature and precipitation changes at Tampa, Florida 18 4 The study site environs 33 5 Calculated groundwater equipotential contours on July 2, 1976 34 6 Groundwater equipotential contours and flow directions during 1975 at Pond 11 35 7 Location of groundwater wells at the study pond 37 8 Cross-section of the pond showing input (east) and output (west) wells . 39 9 Groundwater equipotential contours and flow directions for 1978 sampling dates 43 10 Direction of groundwater flow during 1976 and 1978 ... 46 11 Head loss during 1976 and 1978 50 12 Area of the planar section passing through the pond center during high and low water-level periods (mean of 1977 and 1978) 51 13 Study pond water heights during 1977 and 1978 53 14 Sediment sampling scheme 56 15 Two cross-sectional views of the study pond basin. ... 58 16 Total organic matter in the sediments of the pond. ... 69 17 Total nitrogen in the sediments of the pond 70 VI Figure P^9^ 18 Total phosphorus in the sediments of the pond 71 19 Nutrient concentration and water volume changes during 1978 85 20 Atmospheric inputs and nutrients in the water column 87 21 Available phosphorus distribution with depth 95 22 Three-dimensional view of a quarter section of the pond sediments showing volume changes with distance from the center 98 23 Areal view of the sediments showing bands of total phosphorus parallel to mean groundwater flow . . . 99 24 Distribution of total phosphorus in the sediments encountered by the groundwater front as it passes through the sediments 101 25 A, Distribution of total phosphorus in the sediments; B. Predicted groundwater phos- phorus concentration down-gradient from the pond 102 26 Present-day nitrogen and phosphorus inputs, outputs and storages in grams per year 109 27 Sedimentation rate curve. . Ill 28 Morphogenesis of the study pond basin 112 29 Amount of phosphorus that has fallen on the pond surface since the pond began functioning 114 30 Amount of phosphorus lost to ground water since the pond began to function 115 31 Nitrogen and phosphorus inputs, outputs and storages in kilograms for the life of the pond 117 vn Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy PRESENT AND PAST NUTRIENT DYNAMICS OF A SMALL POND IN SOUTHWEST FLORIDA . - By - James Mark Coleman June, 1979 Chairman: Edward S. Deevey, Jr. Major Department: Botany Nutrient dynamics of a small pond in southwest Florida were modeled in space and time. The primary storage compartment of the system is the sediments, and the primary sources and sinks for nutri- ents are the atmosphere and ground water. Of the 93 g yr of phos- phorus entering the pond, primarily as bulk precipitation, approxi- mately 69 percent is stored within the system and the remainder leaves through the ground water. About 2400 g of nitrogen enter the pond annually, and of this, 12 percent and 5 percent exit the system via the atmosphere and ground water, respectively. The pond's age, determined by radiocarbon dating, is approximately 5000 years, and during this time the sediments have accumulated 124 kg of phosphorus and 3,140 kg of nitrogen. The atmosphere and ground water have made a net contribution (input minus output) of about 124 kg of phosphorus and 3600 kg of nitrogen during the past 5000 years, based on present-day rates and estimated changes in the sizes of the viii receiving surfaces. The remainder, in the case of nitrogen, is assumed to be atmospheric loss. The importance of the groundwater sink for phosphorus is demon- strated, and its potential role as a nutrient input source for surface- water discharge boundaries is discussed. Comparison of the annual atmospheric phosphorus input rate to the results of other researchers seems to indicate that the present- day rate may be spatially constant for undisturbed regions. The 5000- year budget for the study pond indicates that the preindustrial -2 -1 atmospheric phosphorus input rate was about 27 mg m yr , about 20 percent less than today's rate. This figure may be close to the preindustrial global rate. Key words: Nutrient cycling; nutrient budgets; groundwater chemistry; bulk precipitation; sediment chemistry. IX INTRODUCTION One of the striking features of the pine flatwoods of southwest Florida is the number of rounded depressions or ponds which dot the landscape. For example, in Sarasota County, excluding the coastal strand, these ponds number an average of 15-20 per square mile. They range in size from a fraction of a hectare to many hectares. The ponds are shallow (one-half to a few meters deep, generally) and con- tain water much of the year. During the dry season (spring) only the deeper ponds retain water, but in the wet season (late summer) water may rise above the rims of the ponds and extend many meters into the pine flatwoods proper. Because of their relatively small size and closed basins, these ponds are promising subjects for nutrient budget- ing considerations. Urbanization in this part of southwest Florida has been extremely rapid with population growth rates approaching 6 percent per year in 1974 and 1975. It has been suggested that as the pine flatwoods are developed, the numerous ponds could be maintained in a somewhat natural condition and that urban runoff could be channeled into them and held until natural processes reduce nutrient concentration in the water column. In addition, the ponds would be connected by swales, and a natural buffer zone would be retained around them to provide a functional and aesthetically pleasing system. :-ita Because of the interest in this concept, it is useful to gain a better understanding of the system dynamics of these ponds. Of primary importance are the natural nutrient dynamics of the pond system including the relative sizes of the constituent components. In any future modeling of treatment capabilities, these baseline pa- rameters are of critical importance. Secondly, assuming the ponds are natural nutrient accumulators, it is important to know if the pond sys- tem is tight, that is, do those nutrients which accumulate remain bound within the system "forever" or does the system release them? Thirdly, how has "flow through" changed over the life of the system and what are the implications of these changes with respect to system development? This study is designed to answer these questions and is organized in the following manner. The present-day setting, environmental history and recent environmental trends are presented as background information. The next chapter discusses the primary input to the pond system, i.e., bulk precipitation. Ground water, which is the means by which a con- servative nutrient, such as phosphorus, would leave the system, is dis- cussed at this point. The following three chapters address the sizes and some interrelationships of the pond system storage compartments. The next chapter deals with the interaction between the major storage compartment, sediments, and groundwater output. In the next to last chapter the present-day nutrient budget, which is derived from ele- ments of the previous chapters, is illustrated and discussed. Also in this chapter the derivation of the "lifetime" budget of the pond is presented and the "lifetime balance sheet" is discussed. The final chapter addresses some basic considerations about nutrient cycling, past and present, and ecosystem development of the pond system. BACKGROUND The Present Environment Description, Location and Regional Physiography The study pond is located in southern Sarasota County, Florida, between the Peace and Myakka Rivers. It is 2.9 km north of the Charlotte County line and 400 m east of Myakkahatchee Creek (Big Slough) (Figure 1). ItsMercator Projection coordinates are 27° 03' 33" north latitude and 82° 13' 31" west longitude. The region is in the coastal lowlands part of the Floridian section of the Coastal Plain province (Fenneman, 1933). According to White (1970), this physio- graphic region is the Gulf Coastal Lowlands of the Mid-Peninsular Zone. The province is extremely flat with a very gentle slope in a generally southwestern direction. In the immediate vicinity of the study pond, the slope is to the south-southwest at an approximate rate of one meter per thousand. The province is bordered on the north and east by the DeSoto Plain; on the south by the Immokalee Rise and Southwestern Slope; and on the west by the Gulf Coastal Lagoons, Gulf Barrier Chain, and the Gulf of Mexico. The Gulf Coastal Lowlands reach their maximum areal extent in this part of the state where, in the Caloosahatchee Valley, they follow the valley all the way to Lake Okeechobee. From the Caloosahatchee Valley, the Lowlands gradually narrow northward until near Bradenton, Florida, they are only about 15 km wide (White, 1970). 3 •, [• •-ra; 4 GULF OF MEXICO 50 km Figure 1. Location of the study pond. Climate The climate of the region is typified by warm, somewhat humid summers of long duration and short, mild winters with occasional in- vasions of cool northern air (Bradley, 1972). This climatic type was classified by Trewartha (1961) as humid mesothermal , humid subtropical subgroup and by Thornthwaite and Mather (1955) as moist, subhumid with a moisture surplus of 0 - 20 percent. The dominant factors controlling the climate are latitude and proximity to the Atlantic Ocean and Gulf of Mexico (Bradley, 1972). Solar radiation for the region, according to Landsberg (1961), amounts to nearly 160 Kcal cm'^yr"^ at the surface and about half is stored as net radiation (Budyko et al . , 1962). The mean annual temperature at Fort Myers, Florida, for the period 1937-1976 was 23.3°C; the mean January temperature for that period was IS.rc and mean July temperature, 27.9°C. Relative humidity year-round is usually 80-90 percent at night and decreases to 50-60 percent in the early afternoon. The mean summer wind speed is 11.6 km hr , and mean dry season wind speed is 13.9 km hr'^ Trom October through December, the direction of the prevailing wind is from the northeast; and for the remainder of the year from the east (NOAA, 1976). The mean annual precipitation at Fort Myers from 1937-1976 was 135.5 cm, 65 percent of which fell during the summer months (June through September). An average of 95 thunderstorm-days occurred each year with 78 percent of these in the summer months (NOAA, 1976). The thunderstorm frequency during the summer months in peninsular Florida reaches a maximum for the United States and possibly for the entire earth (Trewartha, 1961). This phenomenon, according to Byers 1 and Rodebush (1948), results from strong low-level convergence caused by afternoon sea breezes moving into the peninsula from both east and west. This double sea breeze convergence stimulates the vertical growth of convective clouds. The convergence prevails up to an al- titude of about 1,200 m with a maximum reached in the late afternoon when the two-sided sea breeze is usually strongest (Trewartha, 1961). Tropical storms have, at times, contributed a significant amount of precipitation to the region. Court (1974) estimates that tropical storms from 1931-1960 accounted for 10-15 percent of the June to October rainfall in peninsular Florida. The chance of a storm of hurricane intensity striking the Fort Myers area in any given year has been estimated by Bradley (1972) to be 1 in 11. Geology and Geomorphology The sandy flatlands, as Parker and Cooke (1944) have called the region, are poorly drained and dotted with shallow ponds (Figure 2). These ponds are often nearly circular in shape, with diameters to a few hundred meters and are generally about one meter or so in depth. They occur in deep sands as well as in places where the sand mantle is thin. They may be related to solution of the underlying consolidated strata or to inequalities in the floor of a previously regressing sea (Parker and Cooke, 1944). The surficial sands rest uncomformably upon the Caloosaha tehee Marl which in turn uncomformably overlies the Tamiami Formation. The surficial sands are generally medium to find grained, sometimes mottled, and with occasional fossil iferous members (Dubar, 1962; Brooks, 1966). The Caloosahatchee, a sandy, shell marl, indurated at the top ■4 o i- •r- > C 0) ■o c o CL >> •o 13 4-> to 0, j -c ' ^ 1 4- * o 5 QJ •f— > < o CD • i» C\i d 8 and containing abundant fossils, is generally less than one meter in thickness. Along the Myakkahatchee Creek, about 1 km NNE of the study pond, it is 60 cm thick (personal observation). The Tamiami is a fossil iferous, medium to coarse calcareous sand (Dubar, 1962; Brooks, 1966). The thickness of the Tamiami is undetermined here; however, it is most likely relatively thin since the underlying Hawthorne is known to outcrop a few kilometers to the north (personal observation; Vernon and Puri, 1964). In recent years there has been considerable discussion about the ages and relationships of these strata. The following is a summary of Brooks' (1968) interpretation of the Plio-Pleistocene stratigraphy of the region. The Caloosahatchee Formation has two members. The Fort Denaud Member is late Pliocene age and corresponds to the Okeefenokee eustatic sea-level stand of +120-140 feet (36-43 m). The Bee Branch Member is Aftonian in age and corresponds to the Wicomico Sea which was at +90 to 100 feet (27-30 m). The surficial sands are divided into two formations. The Fort Thompson Formation (three members) is of Yarmouthian age and is related to the Penholoway (+70 feet, 21 m) and Talbot Terraces (+42 feet, 13 m). The Sangamonian age Pamlico Sea (+25 feet, 8 m) is represented by the Coffee Mill Hammock Formation. Apparently, the study pond has been above sea level since the Sangamonian interglacial period. Soils • The dominant soil type in the sandy flatlands of the region is the Immokalee fine sand. This type is classified as a Ground-Water Podzol which is typified by a thin organic surface layer above a light grey. ' 'i-i ■■"^ ■i: leached layer that rests abruptly upon a black to dark greyish-brown B horizon (USDA, SCS, 1959). In the most recent soil classification system, this soil would be a sandy, siliceous, hyperthermic, arenic haplaquod (USDA, SCS, 1977). The soil (sediment) of the study pond is classified as Delray fine sand in the center and Pompano fine sand in a concentric band between the center and the Immokalee fine sand of the sandy flatlands surrounding the pond. The Delray soil is a Humic Gley which is a poorly drained, hydromorphic group of soils with dark colored organic mineral horizons of moderate thickness underlain by mineral gley horizons. The Pompano soil belongs to the Low-Humic Gley group of soils. The group is characterized by poor drainage and a thin surface horizon moderately high in organic matter which overlies undifferen- tiated, mottled grey and brown, gley-like mineral horizons (USDA, SCS, 1959). In current soil taxonomy terminology, the Delray would be a loamy, mixed hyperthermic gross arenic argiaquoll, and the Pompano, an arenic or gross arenic ochraqualf (USDA, SCS, 1977). In 1898, Dokuchaev first recognized the importance of several environmental factors in the formation of soils. Jenny (1941), elabo- rating on Dokuchaev' s work, proposed the relationship that any soil property was a function of climate, organisms, relief, parent material, and time. The three soils of the study area dramatically illustrate this relationship. High rainfall and low relief dominate the soil forming processes for these soils. In combination, the two factors produce a groundwater table that is near the surface year-round. The three soils, however, represent a micro-environmental sequence of .A < i'-,' M 10 relief which results in very different soil types. The surface of the Immokalee is about one meter above that of the Delray. The height of groundwater ranges from one to two meters below the surface of the Immokalee in the dry season to just above the surface during the rainy season. The same groundwater stand in the Delray is just above the surface to one-half meter below the surface in the dry season, and in the wet season a meter or more of surface water occupies the Delray depression. This phenomenon results in the leaching of the surface layers of the Immokalee soil as the dominant process and the accumula- tion of the leachates in the vicinity of the mean low water level. The acidity of the rainfall, as well as the acidity of the litter and leachate from the dominant plants, hastens the removal of organic matter and minerals from the surface layers of the Immokalee. In the Delray, however, the occurrence of standing surface water for much of the year minimizes oxidation and results in the accumulation of organic matter in the surface layers. However, in the dry years, especially with low winter rainfall, the water table drops below the surface and spodosolic processes may dominate in the Delray also. In the Pompano, neither process dominates and hence an intermediate soil type is formed. None of the soils exhibit much pedogenic development. This is the result of the interaction of time and parent material. It is not known how long it takes for a well-defined soil profile to develop, and, perhaps, under the prevailing climatic and relief regimes of the study site, one could never develop. Other factors aside, the time required is directly related to the resistance to weathering of the parent material. The parent material of the study area soils is almost pure quartz sand (Dubar, 1962) which is a highly resistant substrate. These I :!Zl^^m 11 materials have only been exposed to the agents of weathering since the regression of the Pamlico Sea (probably Sangamonian Age). , . The Historical Environment The pond system is four-dimensional, and the fourth dimension, r, time, may be the most critical for understanding the nature of the sys- tem. The agents of time are environmental conditions, which may be static or changing in the time frame of the pond's existence. Static conditions have a chronic effect upon the system, tending to drive it in one direction, and given sufficient time the end result will be the , filling in or drying up of the pond with complete oxidation of sedi- ments. Changing environmental conditions can have the same effect if the change is unidirectional, thereby intensifying the effects of , static conditions. However, if the change is reversible, the effect will be preservation of the system as long as the period of any one direction does not exceed the system's capacity for resilience. The pond system came into being about 5000 years ago (4565 ±120, University of Miami Radiocarbon Dating Laboratory"-#UM1494). Since that time, it has been subject to the influences of sea level and climate as they affect groundwater height. Sea-level changes are the subject of much controversy today. Several authors (Shepard, 1963; Scholl and Stuiver, 1967; Milliman and Emery, 1968; Scholl et al., 1969) believe that sea level has risen continuously for at least the last 5000 years. The effect of a continuously rising sea level, and hence ground water, would be an increasing sedimentation rate. How- ; ever, using the Scholl et al . (1969) curve, the increasing rate would be 12 ■'iR decelerating for the past 5000 years and approaching stasis at the present. A second group of investigators (Fairbridge, 1961; Morner, 1969; Fairbridge, 1974) have indicated that sea level reached its present stand at about 6000 BP and has been fluctuating since then. The effect of fluctuating sea level, and hence groundwater height, I upon the pond would be to establish the sedimentary process as dominant during relatively high stands, but during low stands, an oxidizing environment would prevail and the pond would act more like a periodi- •: ' , cally flooded soil. The interaction of these two regimes would result , , 1 in a pond system with a very slow net sedimentation rate. Several -l shallow Florida lakes and ponds are known to have very slow sediment 4 accumulation rates, for example. Mud Lake's recent history, 0.39 mm -*''; yr~ (Watts, 1971), Spanish Pond, 0.17 mm yr~ (Deevey and Brenner, unpublished), and Site No. GDF--125, 0.2 mm yr~^ (Clausen et al . , 1979). :^ Climatic fluctuations, instead of sea-level changes, may explain vj the peculiar sedimentary histories of these ponds. During periods of , high precipitation and low evaporation, the sedimentary system would dominate in the pond and, the reverse being true, the oxidation process would dominate. It can be inferred from Denton and Karlen (1973) and LaMarche (1974), among others, that there have been alternating warm and cool periods during the late Holocene. The link between cooler temperatures and decreased precipitation is fairly well documented in late-glacial times (Damuth and Fairbridge, 1970; Bonatti and Gartner, 1973; Parmenter and Folger, 1974; Williams et al., 1974; Deuser et al., 1976; Gates, 1976), and Simpson and Hebert (1973) and Moran .ii (1975) believe that in peninsular Florida this link may be due to the -4^ ■ '■ hi-,' . 13 inhibitory effect of decreased sea-surface temperatures on hurricane formation. From recent work in the Caribbean and equatorial Atlantic, several researchers have, in fact, reported differences in paleo- temperatures ranging from 2 to 6°C, between glacial and nonglacial stages (Emiliani, 1966; Shackleton, 1967; Dansgaard and Tauber, 1969; Lynts and Judd, 1971). A decrease in hurricane activity would not only result in decreased precipitation but also a decrease in cloud cover during the high evaporation season of summer and early autumn. Seasonal variation in precipitation and evaporation, apart from long-term climatic or sea-level changes, may be the dominant causal 1 •t, y agent in the sedimentation pattern of the pond. A wet and dry cycle 't' with the "^ery short period of one year would have the same effect on .''1 ■ i total accumulation as long-term cycles. It seems likely that some combination of seasonal and long-term climatic and sea-level changes have caused variations in groundwater heights which have resulted in an alternating accumulation-decomposition system in the pond. Following Scholl et al . , (1969), sea-level rise -J would be a unidirectional environmental change in the experience of the pond. Long-term climate, on the other hand, is bidirectional and con- tains the nested bidirectional set, seasonal variation. The influence of these patterns on the past nutrient dynamics of the pond has probably been considerable. It is evident that in the decomposition mode nitrogen and phosphorus would become available for exchange between components of the system. Perhaps less obvious is the fact that with changing groundwater heights, the sizes of the inter- faces between components would also change and, hence, so would rates of exchange. 14 Recent Trends i: '^ < <£ M We have seen that environmental conditions have been different in the past, and it is interesting to speculate on what may be in the future for this region. The pattern of glacial and interglacial cycles is well documented (Prell, 1974; Shackleton and Opdyke, 1973; Imbrie et al . , 1973; Kukla, 1970; Hays et al . , 1969) as is the pattern of cold and warm periods between major events, especially in recent times (LaMarche, 1974; Dansgaard et al . , 1971; Lamb, 1969; 1966). According to Mitchell (1963; 1972),Reitan (1971), and Bryson (1974), we are headed toward another cool period. Whether it is just a cool fluctuation or a more pronounced cold period is unknown, as are the effects of man-made interferences. The annual mean temperature change at Tampa, Florida, was compared j to the average change for the Northern Hemisphere (Reitan, 1971; J Mitchell, 1972) with relatively good agreement. The Tampa record extends sporadically into the 1820's, but no records exist from the ."^ late 1850' s to the mid-1880' s. From the available record, it can be •' seen that temperatures rose rather rapidly in the 1840' s; there was a decline around the turn of the century and then another relatively rapid rise; a level ing-off occurred in the 20' s and 30's and then a slight rise in the 1940's; and finally a post-1950 decline. Bryson (1974) has described the 1940's as a period of unprecedented warmth in the past millenium and both the Tampa and Northern Hemisphere curves seem to substantiate this claim for recent times. . V With this in mind, the post-1950 temperature regimes for six peninsular Florida stations were compared to the 1940's thermal maxi- mum (Table 1). The annual mean temperature for peninsular Florida -:^i". 15 to 3 r^ M- C •>" c iO E o lO o» 1 1 01 s- Q. E o s- M- W O s- 3 ■P (0 s- OJ n. B • XJ •I— c: i- to o 0) ^— EU. o s- in la cr> t^m r— 3 1 (/) •M c V) • r- O c Q. S- 00 => C 4-> o s- •r- ro +-> Q. ra O fO ro -I- >, 3 S -!-> X fO e I fO 3 -o C Cn-r- 1 — cC c -a u. >, O rtJ X _j a: o CIJ (0 •r— >, fc 5 +-> X (0 H 1 rs Dl •r— r— CO c ■o Ll_ >^ o rtj _l X _l q: o 1 (13 •»— >, 3 ■u X « oo 00 UD o CT> cn n 1 (0 Z2 -a C\J C>J <* kO 5 o _l _i I o t/5 CO ^I> UD CO ^O V£) <0 V£3 ^^ ^^ CT» CT> CT^ cr> cr> cr> r^ r^ CTl CT> cn 00 I— I — CT> LO cn cn 1 — 1 — 1 — fo CO 00 cn cn cn CT» CO cn E <: CM f— o r— r— o s- rs c 1 • • • • • • (TJ OO •!" (U o o o CD o o Q. c 1 + 1 + + C U- CsJ CO «3 r^ r— CO i- -r- C 1 * ■ • • ■ • (0 3 -r- • r — o o o o o Q. o 1 1 1 1 + 1 CU M-IX QJ Q O Q OJr- 5- to O 3 30 o CO 00 00 CO r— 4J C LO o CM CM CO o S- C C • • • • • • (0 <: -f- o o o o o o Q. 1 + 1 1 + + 0) M-IX Q O ■o (/> ^ S- M- O cn cn cn r~ U3 cn (O O J CO n CO CO 00 CO - q; o o CO in o I o I a. o ■o c fO S- o S- >> o > IX k cn CT> c cn •a: o LlJ O ai ID O 00 a bj&A,»^'. V 16 decreased by 0.12°C, but the winter temperature declined by 0.53°C and the summer by only 0.01°C. One possible scenario for this pattern of temperature decline is the interaction between long-wave radiation flux and the CO2 content of the atmosphere. Rasool and Schneider (1971) have shown that tempera- ■ ture increases as the logarithm of atmospheric COp content, and Machta (1971) and Machta and Telegadas (1974) have shown a rapid rate of in- crease in COp content in the last 40 years. Dansgaard et al . (1971) believe that, as indicated by the Camp Century ice core cycles, we should be in a cooling period, but Broecker (1975) says that the in- 1 crease of COp in the atmosphere has interf erred with the natural cycle t| ■ i and modified the decline in temperature. This interference may be '^ more significant in the summer when the long-wave radiation flux is ;^ 13 percent greater than in winter in peninsular Florida (Table 1). ^ As a result, summer temperatures have changed little, but winter -'i temperatures have declined at about the rate predicted by the Camp Century core. The net result is an annual change very close to that predicted by Broecker' s (1975) combined effect of CO^ and the Camp Century cycles. ' ;■ Hydrologic evidence from peninsular Florida indicates that a dry period is approaching. Moran (1975) and Coleman (in preparation) have demonstrated that peninsular Florida has experienced unusually arid conditions in recent times and have attributed these to the decline in hurricane activity (Hope, 1975) in recent years due to a drop in low latitude sea-surface temperatures and persistently stronger upper-level westerlies over the Caribbean Sea (Simpson and Hebert, 1973). Supportive evidence of this hypothesis can be found in the . ■■■■^T.j.i.V; • 17 1 decline in river flow volumes in peninsular Florida. Coleman (in preparation) established that a sharp decrease in river flow in the Peace and Kissimmee Rivers had begun in the early 1950's. In addi- tion, ten rivers, representing a combined drainage area of over 20,000 km^ and a range in period of record from 27 to 46 years, were compared using post- and pre-1960 averages. The result was a 16-38 percent decrease in flow after 1960 (USGS, 1978). The implication is .j that peninsular Florida is experiencing drought conditions when i compared to recent records. .,1 at Tampa, Florida (Figure 3). A rapid warming occurred in the 1840's followed 40 years later by a substantial increase in precipitation. Temperature declined in the 1890's and precipitation 10 years later. This same pattern reappears later with temperature increasing rapidly from 1900-1920 and decreasing in the 1950's. Precipitation increase lags temperature again by 40 years and the decrease by only 10. Ap- parently, the response time for temperature-linked precipitation increase is about 4 times the response time for decreases. With regard to the sea-surface temperature/hurricane activity hypothesis, it appears that the warming of the sea surface is a slower process than cooling. It is interesting to note that there has been little change in summer air temperatures in peninsular Florida in the last 40 years, but there has been a one-half degree centigrade drop in winter temperatures (Table 1). Since there has been little change in summer temperatures, it would seem that the evaporative and convective forces which control the growth of thunderstorms may not have changed. A link between temperature and precipitation changes is evident -J i ,1 "^ 18 O (^0) 39NVH0 N0!lVlldl33dd o 1 1 — \. ,.-.^-'-''""""" \ V. \ •\ •v. '"\ i v \ • ^^^""""-^ \ — ...,,^^ j ^"'*'*'v^^ ,,*■» • ^*'**«^.,_^ • "^ * •^ ^***^^ ""^ * ^"""'^1^ z^*'" ^!^^ y' ^^^,,_--'— -"^^^^ ■^j^ll-— —""'^ ^^^-■^ - 0-. 1 ' o o CM < LlJ >- CO tp CO a (Oo) 39NVH0 3dniVd3d*/J31 o M «> on c u c o •r- +-> -t-> O) 3 C to • QJ 00 re cr> s- I— re OJ •> ^$ c o i instituted, sample preservation can be a problem. Some researchers ; have attempted to circumvent this problem by employing refrigerated : samplers (Gambell and Fisher, 1966; Pearson and Fisher, 1971; Mattraw and Sherwood, 1976). Refrigerated samplers are generally based on a modification of one described by Gambell and Fisher (1966) and consist of a glass funnel connected to a reservoir by tubing. The reservoir is contained in a commercial refrigeration unit or ice chest, and the j temperature is artificially maintained at about 4°C. These collectors 1 are expensive to install and maintain, and the samples, according to ' EPA (1974), should still not be held for more than 24 hours. In i ■■i addition, the funnel is not the best receptacle for dry fallout. Dry \ particles falling on a dry surface are subject to removal by wind ,] action. In my study, due to economic constraints and the uncertainty of ;; refrigerated preservation, I decided to use open polyethylene buckets with several centimeters (actual amount depended on the season) of acidic water in them. The pH (3.9) of this water was the same as the mean pH, i.e., x of -log [H^], of the study pond. This pH was ob- tained by adding 0.01 N HCl to distilled, deionized water. The rationale behind this method is that, although the ponds and buckets differ considerably in physical, chemical and biological properties, by mimicking the acidity the receptacles could approach the functional regime of the pond. With respect to phosphorus, this method was con- sidered to be adequate. Since phosphorus does not have a gaseous j phase and since the particulate and soluble phases of total phosphorus ,i •■'i-^^ii 22 are used to detemine the final number, the interchange between these two components was considered for this study to be unimportant. As for total nitrogen, the results should be viewed more critically. In the absence of clear knowledge of the interplay between gaseous and soluble phases of nitrogen, I cannot be sure that nitrogen exchange was not occurring at the air-water interface, and hence the nitrogen results should be interpreted as indicative of nitrogen inputs. With regard to biological contamination due to bird feces, it was predetermined to discard those samples that were apparently contaminated. Samples with insects in them were analyzed to be compared with those without insects to see if there was a consistent and significant dif- ference. Chlorophyll content was measured in several samples as a check for algal contamination. Six bulk precipitation collectors were installed in duplicate on wooden platforms about 1.5 m above the ground surface at three sites in the study area. Two side-by-side collectors were installed in the study pond, two in the sandy flatlands about 20 m from the western edge of the pond and two in downtown Port Charlotte about 18 km south- east of the study pond. Samples were collected biweekly from the beginning of June to the end of October, 1978. Samples were transported, on ice, to the labora- tory where they were filtered immediately. The filter papers were oven dried and stored in jars to await sediment analysis. The filtrate was analyzed for nutrients by the following methods: for TP: Persulfate digestion Automated Colorimetric Ascorbic Acid Reduction Method (EPA, 1974) 23 for TKN: Sulfuric add digestion Automated Selenium Method (EPA, 1974) for NO3+ NO2: Automated Cadmium Reduction Method (EPA, 1974) Filter papers and filter paper blanks were digested on a block digester in Fisher high temperature bath oil. The oil is used to allow uniform heating of the digestion tubes. The filters were digested by the sulfuric acid-hydrogen peroxide method (modified from EPA, 1974; see discussion in chapter on sediments). The digested sample was then analyzed by the same methods as the solution phase. -2 -1 Concentration raw data were converted to mg m yr by the following formula: C (mg r^) X V (1) X 10,000 cm^ m"^ x 365 days yr"^ N (mg m" yr"') = ■ 5- A (cm"^) X D (days) where: N = amount of nutrient C = concentration of nutrient -^ V = field volume for solution phase; digestion tube volume for particulate phase A = a rece rea of the plane defined by the top of the eceptacle (374.11 ±1.72 cm^) D = number of days sample was exposed to the atmosphere Results The nutrient data were averaged over the sampling period with the result that one number was obtained for each phase (solution, particu- late and total) in each of the six collectors (raw data appear in Appendix, Tables A-1 - A-6). Several samples, however, were less than ■■'■Tx m" V-5 ^^^^^^ 24 n 4 i s detection limits, and these presented somewhat of a problem. The first impulse is to exclude them from the mean. However, this has the effect of establishing an unreal istically high mean since all the ex- cluded values are at the low end of the range. A better estimate of the true mean can be achieved by including them. But what is the ^ best way to deal with values that are less than detection limits? -'j^ - . "^i The best estimate of the true values for these samples can be obtained by narrowing the range as much as possible and then taking the mid- point. The range was narrowed, in the case of phosphorus, using the orthophosphate phosphorus value as the low end of the range when this value was above detection limits. As for nitrogen, the low end was established by the total value of ammonia and nitrate+nitrite when these were above detection limits. In some cases, the measured con- ' ■■;"';'* ^ stituents of total phosphorus and total nitrogen were also less than detection and zero was used as the low end of the range. The first priority of data analysis was to determine if statistical differences existed between duplicate collectors. The differences be- tween the mean of duplicate collectors were compared using a t-test. At an a of 0.05 there is no difference between duplicate collectors at any of the three sites for either phosphorus or nitrogen (Tables 2-7). Based on this conclusion, duplicate collectors were lumped at each site, increasing the N (number of samples), and thereby allowing for more sensitive intersite comparisons. The next question to consider is: Do the ponds receive different amounts of phosphorus and nitrogen than the sandy flatlands? To answer this question, the new means, achieved by averaging the results from intrasite collectors, were compared using the t-test of the 25 ? 1 Table 2. Comparison of total phosphorus (mg m" yr"') in bulk precipi- tation collectors at Port Charlotte, Florida. Phase North Collector South Collector X ±s X ±s Solution Particulate TOTAL 75.9 ±48.6 8 46.8 ±20.8 8 122.7 ±42.6 8 52.3 ±29.5 8 1.174 0.272 33.6 ±19.9 8 1.297 0.220 85.9 ±33.7 8" 1.916 0.080 1 2 1 Table 3. Comparison of total phosphorus (mg m" yr" ) in bulk precipi- tation collectors in the study pond (North Port, Florida). Phase North Collector South Collector t a X ±s n X ±s n Solution Particulate TOTAL 11.9 ± 6.0 20.6 ±11.7 32.5 ±14.5 9 9 9 9.8 ± 7.8 16.2 ± 6.8 26.0 ±10.3 7 7 7 0.610 0.882 1.002 0.558 0.394 0.344 2 -1 Table 4. Comparison of total phosphorus (mg m yr ) in bulk precipi- tation collectors in the sandy flatlands near the study pond (North Port, Florida). Phase East Coll ector West Collector t n X ±s n X +s n Solution Particula TOTAL ite 21.3 ±19.0 17.9 ±14.5 39.2 ±26.0 11 11 11 17.1 ±11.2 14.2 ± 9.1 31.6 ±16.9 11 11 11 0.632 0.717 0.813 0.539 0.483 0.427 26 2 -1 Table 5. Comparison of total nitrogen (mg m yr ) in bulk precipita- tion collectors in Port Charlotte, Florida. Phase North Collector South Collector X ±s X ±s Solution Particulate TOTAL 1,231 ±269 8 238 ±164 8 1 ,470 ±328 8 1,470 ±967 8 200 ±166 8 1,670 ±989 8 0.673 0.513 0.461 0.664 0.543 0.606 -2 -1 Table 6. Comparison of total nitrogen (mg m yr ) in bulk precipita- tion collectors in the study pond (North Port, Florida). Phase North Collector South Collector t X ±s n X ±s n Solution Particulate TOTAL 776 ±300 77 ± 48 853 ±317 9 9 9 571 ±282 95 ± 71 666 ±298 7 7 7 1.391 0.606 1.201 0.189 0.561 0.260 2 -1 Table 7. Comparison of total nitrogen (mg m yr ) in bulk precipita- tion collectors in the sandy flatlands near the study pond (North Port, Florida). Phase East Collector West Collector t a X ±s n X ±s n Solution Particulate TOTAL 752 ±528 81 ± 92 833 ±546 11 11 11 788 ±559 76 ± 54 864 ±580 11 11 11 0.155 0.155 0.129 0.880 0.880 0.899 •'•"1 27 difference between two means. Once again, with an a of 0.05, no dif- ferences were observed in either phosphorus or nitrogen, and hence all four collectors at the two sites were combined to establish a new mean for a relatively undisturbed natural area in North Port, Florida -2 -1 (Tables 8 and 9). These means were 104.3 ±41 .7 mg m yr and 33.0 ±18.5 mg m"^ yr~^ of total phosphorus at Port Charlotte and North -2 -1 Port, respectively. Total nitrogen was 1,569 ±717 mg m yr at Port Charlotte and 816 ±461 mg m~^ yr~^ at North Port (Tables 10 and 11). These means were then compared to see if there is a difference between atmospheric nutrient input to a small but rapidly growing urban area. Port Charlotte, and a relatively undisturbed area. North Port. The results are illuminating indeed. The differences between both phosphorus and nitrogen are very highly significant and approximately three times as much phosphorus and twice as much nitrogen are falling on Port Charlotte as on North Port, near the study pond (Tables 10 and 11). The nitrogen to phosphorus ratio is also different between Port Charlotte and North Port. The N:P ratios in the soluble, particu- late, and total components of bulk precipitation are: 21.1, 5.4 and 15.0 for Port Charlotte and 46.8, 4.7 and 24.7 for North Port (Tables 10 and 11). Discussion According to Brezonik and Messer (1977), studies on nutrient inputs in the subtropics are extremely scarce. However, there is one study in peninsular Florida which can be compared to these results. At Gainesville, Florida, 290 km north of this study, Brezonik et al . -2 -1 (1969) reported rainfall input values of 44 mg m yr of phosphorus 28 -2 -1 Table 8. Comparison of total phosphorus (mg m yr ) between North Port, Florida, sites. Phase Pond Collectors Flatlands Collectors X ±s X ±s Solution Particulate TOTAL 11.0 ± 6.7 16 18.7 ± 9.8 16 29.7 ±12.8 16 19.2 ±15.4 22 1.991 0.056 16.2 ±11.8 22 0.691 0.495 35.4 ±21.8 22 0.933 0.364 -2 -1 Table 9. Comparison of total nitrogen (mg m yr ) between North Port, Florida, sites. Phase Pond Collectors Flatlands Collectors t X ±s n X ±s n Cl Solution Particulate TOTAL 686 ±302 85 ± 58 771 ±313 16 16 16 770 ±531 79 ± 74 849 ±550 22 22 22 0.568 0.269 0.509 0.582 0.797 0.624 -^ 29 -2 -1 Table 10. Comparison of total phosphorus (mg m yr ) between Port Charlotte and North Port, Florida. Phase Port Charlotte North Port t X ±s n X ±s n a Solution Particula TOTAL te 64.1 ±40.7 16 40.2 ±20.8 16 104.3 ±41.7 16 15.7 ±13.0 17.2 ±11.0 33.0 ±18.5 38 38 38 6.641 5.314 8.765 <0.001 <0.001 <0.001 -2 -1 Table 11. Comparison of total nitrogen (mg m yr ) between Port Charlotte and North Port, Florida. Phase Port Charlotte North Port t X ±s n X ±s n a Solution Particula TOTAL te 1,351 ±696 219 ±161 1,569 ±717 16 16 16 735 ±446 81 ± 67 816 ±461 38 38 38 3.897 4.483 4.617 <0.001 <0.001 <0.001 30 -2 -1 and 580 mg m yr of nitrogen. It is not known whether these values include dry fallout. Pearson and Fisher (1971) studied atmospheric nutrient inputs in New England, New York and Pennsylvania and found an 2 -2 annual input of 16 mg m of phosphorus and 297 mg m of nitrogen. The nutrient input of phosphorus at North Port is greater than that of the New England study, but peninsular Florida is thought to be a high phosphorus area. The nitrogen input at North Port is greater than either of the above studies, but the variance around my mean is more than half of the mean, and the variance in the two comparative studies is unknown. In addition, my study only encom- passes about half of a year, although it includes elements of both wet and dry seasons. 4 The Port Charlotte nutrient inputs are high when compared to the .| North Port results and the northern studies. The Port Charlotte values, however, are low by comparison to those obtained in a recent study of bulk precipitation (East Central Florida Regional Planning Council Report, unpublished). In an improved pasture, based on one sample, a rate of 200mg-pm" yr'' was calculated and at Tampa, Florida, -2-1 based on two samples, 300 mg-p m yr . V, '■i ■ c % .■■a -^ GROUND WATER Introduction In light of the almost total absence of relief and high soil permeabilities of this region, it was suspected that the surface of the water table is the major sink for nutrients, particularly phosphorus, which does not have a gaseous phase in its cycle. Data on the nutrient composition of the water-table aquifer of the region are not abundant, and data on Sarasota County are unknown to the author. However, the U. S. Geological Survey (1978) has monitored wells, tapping various aquifers in surrounding counties and found that phosphorus and nitrogen are highly variable, ranging from a few hundredths of a milligram per liter to several milligrams per liter. Sutcliffe (1973) has analyzed the chemical composition of several wells in Charlotte County and found nitrates in the water-table aquifer in the Cape Haze area to average 0.8 mg 1~ (two observations) but has no data on phosphorus in this aquifer. In the shallow artesian aquifer (sampling interval = 20-26 m), he reports values of 0.14 and 5.8 mg ^ of phosphate and nitrate, respectively, based on a single observation. The need for more exten- sive nutrient composition studies on this important sink seems fairly obvious. 31 ii-s"' •: -tt^jti _o! 4 o^i^LLffsSS •1 32 Methods In 1976, four shallow groundwater wells (1.2 m below ground sur- face) were installed around pond 11 (about 850 m northeast of the study pond. Figure 4) at the major compass points. Water height was measured in these at varying intervals from July to November, 1976, and once in June, 1977. With these data, the direction and strength of the head can be calculated. For example, on July 2, 1976, the groundwater height in the south well was 7 cm above the water height in the east, 23 cm above the north and 30 cm above the west. In order to determine the groundwater equipotential contours for this date, it is necessary to find the point on the north-south transect at which groundwater height would be 7 cm below the water height in the south well (Figure 5). The same is done on the west-south transect, then a line is drawn through the two points and the east well, giving a 7 cm equipotential contour relative to the south (highest groundwater stand) well (Fig- ure 5). Subsequent contours are represented by lines equidistant from the original contour at all points. Groundwater flow direction is perpendicular to the contours at any point. Figure 6 shows the groundwater contours and flow direction for all 1976 sampling dates (variation in flow direction is dis- cussed later). The direction of flow was generally east to west in 1976. Based on this analysis in April, 1978, ten wells were in- stalled at the study pond in the following configuration: four replicate wells were placed two meters apart on a line perpendicular to the east-west transect on the eastern edge of the pond; four wells were placed on a line perpendicular to the same transect with the same spacing on the western edge of the pond; and one well each on the western end of the northeast-southwest transect 33 GULF OF MEXICO Figure 4. The study site environs. % ■■'.!c J* 34 4,64 KEY Calculated GW contour — Equidistant supplementary contours y^ ^ Points of equal potential with E-well relative to S-well ® Pond center ^ I GW well with height (m msl ) > Direction of GW flow / / 14.57 4.80 / / / / / Figure 5. Calculated groundwater (GW) equipotential contours on July 2, 1976. 35 c o "r— 4-> O Ol $- 3 o to i- zs o +-> c o o 4-> r— C .— OJ +-> "U o c: Q. o •t- Q. CT 4J CU (O S- <£> -!-> en 3 -a o> c c 3 •!- O i. S- 3 CD -O S-- 3 /' i ,,^^, 36 and the soiitheast-northwest transect (Figure 7). These last two served a double purpose: to provide more than two points so that the groundwater surface could be quantified in the manner described above; and to insure that the groundwater flow results obtained from the pond 11 wells, upon which the placement of the study pond wells is based, were not anomalous. All ten wells were placed at a depth of about 1.5 m (Figure 8). This depth was approximately 0.5 m below the bottom of the center of the pond insuring that the wells would be receiving water that had passed through the pond sediments. All wells were screened for 0.5 m of their length, i.e., the region below the bottom of the center of the pond. The east group of wells, therefore, would monitor inputs of water and nutrients to the pond sediments and the west group the outputs from the sediments. The wells were sampled monthly from April through November, 1978, by the following method. Water heights were measured by dropping a weighted tape in the wells and recording the difference between the top of the well and the surface of the water in it. The wells were then pumped dry and allowed to refill before taking a water sample to avoid sampling the possibly contaminated water standing in the pipe. Water samples were placed on ice and returned to the laboratory for nutrient analyses. Nutrients were analyzed by the same methods described in the bulk precipitation chapter. Groundwater contours and flow direction were calculated by the method described for pond 11 wells. 37 Pine-Palmetto Direction of GW Flov/ i Pine-Pa]mettG 0 J I 20 m Figure 7. Location of groundwater (GW) wells at the study pond. X = groundwater v/ell. 4^; 3 ■fJ 3 Q. O •o I/) Q. cn 3 o j:: 00 s- C7> 39 UJ E o o; > O) f— ,_ S- +-) QJ (O ;S XJ S- c QJ 3 ■M O m i- 5 C7^ IX IX 4 ■^ 40 Results and Discussion Analysis of the nutrient data from the groundwater wells indicates a substantial difference in the total phosphorus concentration but not in the total nitrogen concentration between the east and west well groups (Tables 12 and 13). Before the wells were grouped, they were tested for differences within the group, and when none was found for either parameter, the four east wells were combined and likewise the v/est. Mean total phosphorus concentration in the east wells was C.16 mg r and in the west, 0.338 mg 1 . This difference was tested for statistical significance and was found to be so at an a of 0.0019. Mean total nitrogen concentration was 2.09 mg 1" in the east and 2.04 mg 1" in the west. These were rather obviously not significantly different from one another. Figure 9 shows groundwater contours and direction of flow at the study pond for the 1978 sampling dates. (The August-October contours are missing because surface water was standing at the wells during this period.) The direction of flow is generally westward toward Myakkahatchee Creek discharge boundary; however, there is considerable variation in the direction of the flow. This was also seen at pond 11 in 1976. This variation is believed to be the result of manipulation of surface-water levels in Snover and Cocoplum Waterways (Figure 4). Both of these canals have numerous control structures, and if, for example, water is held in Snover and released from Cocoplum, the groundwater gradient would swing around toward the south. Conversely, if surface water is held in Cocoplum and released from Snover, the direction of maximum head loss would tend to be more northerly. The ancestral flow patterns are, therefore, apparently interrupted v'..^J 41 CO 3 Q. 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O) >5-a ^ S. 0) >^ -o +J i— (O .— m c nl (O -r- o 5 E -r- (0 -tJ 1 — +j m r— CI '^ OJ O 4J S o (O -o +J 0) .« .» (/) c OJ OI •r— r— n~ ^ J3 to a. a. %. E -H E E 0) O (d (O T— OlX (/> (/I ^- +-> O O 3 z z o 1 -Hns 1 •n 43 s- • o s- *+- 0) +J 1/5 c c QJ o u '^- +j -a o c o. (O E 5 fO x> c 3 CO O rv. i. en o 1— ^,1^^ 44 periodically, but these manipulations have only occurred since the waterways were constructed several years ago. Also, they have ap- parently not significantly affected the basic east to west flow of phosphorus, as is evidenced by the concentration differential between the east and west wells and is not evident between the east and south- west or northwest wells. The results from Figure 9 were plotted (Figure 10), and the monthly areas under the curve calculated and used to obtain the monthly means (Table 14). Also plotted on Figure 10 is the curve for July to November, 1976, which was developed from data on pond 11. The mean annual direction of flow in 1978 was 282°, between west and west-northwest. The mean dry season (April -June) direction was 220° or southwest and the mean for wet and intermediate seasons (July-March) was 302°, between west-northwest and northwest. The generally westerly direction of groundwater flow supports the phosphorus concentration differential and indicates a net movement of phosphorus by groundwater through the pond, elevating concentrations down- gradient from the pond. In order to quantify this effect in terms of amount of phosphorus 3 -1 moved, it is necessary to know the discharge (m year ) of water mov- ing through the pond. Discharge (Q) can be calculated by Darcy's Law: where: Q = PIA P = permeability of the water-table aquifer (m3day~lm~2) I = head loss (m m~ ) CO en c ro at en c ■r- S- ■o 3 o ■♦-» % 3 o s- o ■M U 0) s. 0) o> 46 to 00 • o o o O o in ro C4 CM O (o) MOnJ yBlVMQNnOdO dO NOI133dia 47 O) CDJZ i~ -•-> res c -— -c ooo o s: E to — ■ -1- i- Q 0) IX c o -o -P to 0} 4-> o S- c (U E > o $- -t-J tn ■o c o t- C3 ^ o C0CO_ o •F— o o OJ ro C/5 --^ QJ CM S- S- E cC (O c IX (o (U JQ -C X! CD O E Q_ S- U O) — - IX +-> (/I c/> - — • Or— _i I IX E -a fO E c: o +->^ — IX O o CD ^- -t-> Q LT) l£3 00 CO 5- 00 CM o ID en I-- o CM •vj- 00 CO "=]- 00 in * to to ^1 — r^cocMCMOO'^ «d-ooi — Locr>i — LD o CM Ln to o 00 CO ^ tn r— I — I— I— corOi — r— Oi — CM r^ 1 — Ln 1 — en CO Ln CO CM CM CM oo CO , — r~- en r— r^ CO r— CM CM CM 1 — to en 00 O r— CM CM CO CO CO ro c -Q i~ i- >, c , — en Q. +J > 0 tn (1) m Q. frt 3 n :3 CU CU CO to ^ +1 0 CM •r— 00 4-> CM > rtJ C _l -0 — !< <: => s- 1— 2: 0 0 z: Ll_ IX 1— <: (O 4 l.fl-iL-^ ' S^i^^Sf^M 48 A = area (m ) of the planar section passing through the center of the pond and sediments perpendicu- lar to the line of flow. The first term of the equation (P) was obtained from the Soil Interpre- tation Record for the Immokalee Soil Series (National Cooperative Soil Survey, 1977) and field inspection and personal communication with Warren Henderson, the regional soil scientist. Permeability was de- 3-12 termined to be 3.66 m day m . The head loss at the study pond for each sampling date was ob- tained by calculating the difference in water height between ground- water contours along a line perpendicular to the groundwater contours (Figures 5 and 9). The values for each date are then plotted and the area under the curve gives monthly means (Figure 11). The average head loss at pond 11 was obtained in the same manner and plotted on Figure 11. Apparently during the wet season, high-water months, there is a decrease in gradient steepness that was not recorded in 1978 since water level was above the surface at all four sets of wells. This gradient change was incorporated into the 1978 data (Table 14) by using the area under the dashed line (Figure 11), an approximation of 1976, for these months. The mean annual head loss is 1.84 mm m . The third term of the equation (A) is somewhat more difficult to obtain. Area (A) is defined as that planar section which passes through the center of the pond perpendicular to the line of flow and limited on the bottom by the bottom of the sediments, and on the top by the surface of the sediments (Figure 12). The bottom of the sediments was located at several points along a transect perpendicular to mean flow direction. Water height varies throughout the year. Two years, 1977 •S^-!..^ V. -^ •;,' ',■'■ -■-li'iU -1 ■a 00 a> o •p o 0) s. o u 00 r^ en >— -o c en (0 c-a •^— 5_ U3 3 t^ -o ^— t/> V) c: o o *" -a ■o Q) fO Sj-^ii^t,' .!»>■« «^ 50 (i.m ujuu) SSOI aV3H m 51 00 ■D c to I — en c ■D 10 4-> -C CD fO -a c o Q. >^ ■a 4-> s- o> o o o o o o o ^ o ID CM CM CD (^0) HldBQ 1 i :i-J 52 and 1978, of water height data are plotted in Figure 12; 1977 was a relatively dry year and 1978 relatively wet. The areas under the curves were calculated per month, and the months averaged to give a representative year (Table 14). The mean water heights were then drawn on figures like Figure 13 and the enclosed area calculated (Table 14). The mean daily discharges for each month were computed using the formula Q = PIA (Table 14). These were then multiplied by the days in the month which gives mean monthly discharges which when summed give 3 total annual discharge. The total discharge per year was 54.53 m (Table 14). An approximation of the net amount of phosphorus leaving the pond per year can be obtained by multiplying the concentration difference between east and west wells by the volume of water passing through the pond. This difference is 0.178 mg 1"^ The amount of phosphorus lost is 9.7 g. i:t„ 53 Figure 13. Area of the planar section (hatched) passing through the pond center during high and low water-level periods (mean of 1977 and 1978). Note: dashed line equals water height. .J ii: ,ii,^ ?-''"*^?ai ^'1 SEDIMENTS Introduction In an earlier, preliminary study it was determined that the great majority of nutrients was contained in the sediments of these pond systems (unpublished). This is, of course, expected since the sedi- ments are the oldest and most functionally conservative component of the pond. Most analyses of sediment deposition have been based on a single core from the deepest point of a basin (for example, Davis, 1959; Kerfoot, 1974; Likens and Davis, 1975). This approach was con- sidered to be inadequate for this study. Several researchers have shown that sediment deposition is not uniform throughout a basin but rather that more sediment is deposited in the deeper portions than in the shallower (Wilson and Opdyke, 1941; Deevey, 1955; Lehman, 1975). This observation is compounded by varying decomposition rates which are expected to be greater in the shallower parts of a basin than in the deeper. Particularly, this should be true, given their inter- mittent nature, of the shallow ponds of southwest Florida. A second criticism of the single core approach is that it does not address the problem of areal distribution in sediments. The homo- geneity or lack thereof can be determined only by a multiple core approach. 54 -'(i ■ yJL^.^d . 55 Methods Figure 14 is a representation of the sediment sampling scheme that was determined to define most adequately the sediment compartment, given the economic constraints imposed upon the study. The basic plan is three replicate center cores and four concentric rings, with four cores each, at 20 cm intervals of elevation. The center cores are within 1.5 m of the deepest point in the pond. The placement of cores on the concentric rings alternates between cardinal and minor points of the compass. Three additional center cores were obtained for radiocarbon dating, but only one was needed since it contained suffi- cient carbon for reliable dating. The center and inner three rings of cores were collected in the spring of 1978 and the outermost on August 30, 1978. The cores were collected using a rig which consisted of a tripod with an adjustable chain fastened at the top. A piston, composed of two rubber stoppers and an eyebolt with washers and adjustable nuts, was connected to the end of the chain. The coring tubes were of U. S. Plastics Corp., 1/16" (0.16 cm) thick, clear Lexan polycarbonate tubing. When the appropriate place for a core was located, the piston was inserted into a clean tube and the nuts tightened until a good seal was obtained. The chain was then adjusted until the piston rested on the top of the sediment. The tube was then pounded gently into the sedi- ment down to and slightly beyond the point at which significant re- sistance was encountered. This occurs in nearly pure sand or clay, which was interpreted to be the bottom of the pond sediments. The remainder of the tube was then filled with water to equalize pressure. 56 Pine-Palmetto Pine-Palmetto t I I 1 0 20m Figure 14. Sediment sampling scheme. NOTE: (•) = sediment core; ( ) = 20 cm-interval surface elevation contours; and ( ) = the edge of the pine- palmetto association. 5^' pulled up by hand, and capped at the end. The tube was sawed off at the piston and this end also capped. The advantage of clear plastic tubes, although some strength must be sacrificed, is that the core can be immediately inspected to insure that the maximum amount of informa- tion with regard to stratigraphy, etc., has been preserved. The cores were returned to the laboratory for extrusion and sec- tioning. The cores were extruded by pushing a rubber stopper through the tube with a wooden rod. All cores were inspected and the top 3 cm removed as it was determined that this was a well-defined root-mat zone. The three center cores were sectioned at 5 cm intervals below the top three. The three radiocarbon cores were also measured. The six center cores all displayed rather well-defined sediment/underlying material boundaries. The boundaries were defined by a rather abrupt lightening in color and increase in sand and particularly clay. The range in occurrence of this boundary was from 78-87 cm with a mean at 82 cm. The outer cores exhibited less well-defined boundaries. The color gradient was more gradual, and there was little increase in clay. This was expected, however, since the clayey underlying material is essen- tially flat and the bottom of the sediments curve up away from the center (Figure 15). The approximation of the bottom of these outer sediments was made on the basis of color change, and the cores below the top 3 cm were sectioned into the same number of intervals (16) or multiple thereof as the center cores. This was done in order to equate all cores in depositional time as more sediment accumulates in the deeper parts of the basin (Lehman, 1975; etc.). The outer two concentric-ring cores contained so little pond sediment (in all but i«J--- ■. ■ ■ ■ , /■ .t- '-'rt^aiitJ 58 Figure 15. Two cross-sectional views of the study pond basin. -A;:* ■'■:'\.ii^S 59 one case 6 cm or less below the top 3 cm) that it was impractical to follow this scheme. After sectioning, all segments were measured to determine volume, placed in labelled jars and oven-dried at 105°C for 20 hours. Some samples were dried for longer periods with no additional change in weight (Black et al . , 1965, Methods of Soil Analysis, specifies an overnight drying time is sufficient for soil analyses). The dried sediment samples were weighed and their bulk densities (dry weight in gm/ volume in cm ) recorded. The organic matter content of the samples was determined by loss on ignition. This technique was deemed acceptable since previous ground and surface water analyses showed negligible amounts of inorganic carbon. The difference in sample weights before and after one hour in a muffle furnace at 550°C was determined to be the weight of organic matter in a sample. Several samples were tested with longer ignition times, but no additional weight loss was obtained and so one hour was found to be adequate. Several digestion techniques for phosphorus were tried using a block digester. It had been predetermined that a precision error of 10 percent of the mean and a recovery of 90 percent would be acceptable and allow for a meaningful interpretation of the results. Three methods were tried on the block digester: perchloric acid (after Black et al . , 1965), perchloric acid - nitric acid (modified from Jackson, 1958) and sulfuric acid - hydrogen peroxide - selenium dioxide (modifed from EPA, 1974); but all three yielded poor repro- ducibility or recovery. .>3 ■-;-!. ..-■•U: 60 It was thought that the problem might lie in nonuniform heating capacity of the block digester. To overcome this problem, Fisher high-temperature bath oil was added to the block digester prior to in- serting the digestion tubes. With this new technique, the simplest and safest digestion method, sulfuric acid - hydrogen peroxide, was attempted with favorable results. During the three months that the nutrient analyses were run, 24 samples of National Bureau of Standards (MBS) Standard Reference Material (SRM) green cement were analyzed. This standard was chosen because its phosphorus content was at the upper end of the range of phosphorus in the pond sediments. The re- sults of the NBS cement analyses were as follows: recovery 99.6 percent; standard deviation, 7 percent of the mean. As a double-check on the method, a sample of Lake Michigan sediment, which closely ap- proximated the texture of the pond sediments, was analyzed in dupli- cate, and 0.0080 and 0.0082 percent phosphorus were found. The Canadian Center for Inland Waters had analyzed the same sample and reported 0.0089 percent phosphorus. One advantage of the method is that it can be used simultaneously for nitrogen determinations. The quality of the nitrogen data was periodically checked by analyzing samples of orchard leaves (NBS, SRM). Eight samples were analyzed during the three-month period with a mean recovery of 116 percent and a mean standard deviation of 3 percent of the mean. The concentration of nitrogen in the orchard leaves was at the high end of the range of nitrogen in the pond samples. After digestion, the samples were analyzed using the Single Reagent Method (EPA, 1974) on a Technicon autoanalyzer. In this method the reaction of orthophosphate with anmonium molydate followed 61 by reduction with ascorbic acid produces a blue color which can be colorimetrically measured. For nitrogen, the reaction of armionia, sodium hydroxide, alkaline phenol and sodium hypochlorite develops a blue color designated as indophenol (EPA, 1974). Results and Discussion The basin appears to be hypersinusoidal in shape and basically symmetrical along the east-west transect (Figure 15). On the north- south transect the basin floor slopes more gradually toward the north than the south, and consequently there is more accumulated sediment on the north side of the center. The raw data, converted to mg cc" by multiplying by the bulk densities, aretabulated in Appendix Tables B-1 - B-19. As to the reliability of the data, several samples were run in triplicate for organic matter, nitrogen and phosphorus. Table 15 shows the standard deviations about the means of these samples expressed as percent of the means. It had been predetermined that the percent standard devia- tion should be less than or equal to ten in order for the analyses to be of maximum use. This criterion was met; however, the median is probably a more useful measure of the precision of the chemical analyses since the mean tends to overweight outliers. Table 15. Percent standard deviation Parameter jripl'ica^L ^""^^ ^'"^ ^ ^^°^ '^'^^^"^" ^^^ Organic matter 27 0.8 - 23.3 4.9 3.9 Nitrogen 34 1.5 - 21.3 7.4 5.1 ;^ Phosphorus 37 0.4 - 18.5 6.2 5.6 : ,- w 62 In addition, two samples were run in triplicate for nitrogen and phosphorus on several different days to test for day-to-day sources of error. One sample was run on five different days, and the standard deviation as percent of the mean was 6.6 for phosphorus and 13.7 for nitrogen. The other sample, run on six days, was 7.1 percent for phosphorus and 8.7 percent for nitrogen. It appears from these analyses that the between-day error is greater than the within day error, and the nitrogen is more sensitive to between-day error than phosphorus. As previously mentioned, the sediment/underlying-substrate boundary- was well defined at the pond center, but away from the center the boundary is somewhat indistinct. I decided to use organic matter con- tent to determine this boundary away from the center. The mean or- ganic matter content immediately below the boundary in the center was 43 mg cc"^ (Appendix Tables B-1 - B-3). Therefore, it was decided that if organic matter content drops below this concentration for two successive segments, the boundary had been passed. The two successive segments rule was chosen to preclude the possibility that sand lenses in the sediment would be considered as the boundary. In light of this definition of the bottom of the sediments, the reliability of the data from the sediments only was analyzed with somewhat better reproducibility for nitrogen and phosphorus than was found in all samples (Table 16). The data in Appendix Tables B-1 - B-1 9 were averaged and totaled for each parameter. The means for the center cores and within concen- tric rings were compared for each parameter using a "t" test of the two most different means within a group. No significant (a = 0.05) 63 Table 16. Percent standard deviation Parameter TripficatL "^^"9^ (°^^ ^ ^"^"^ ^^''''" ^°^^ Organic matter 24 0.8 - 23.3 5.3 4.2 Nitrogen 28 1.5-13.1 5.3 4.1 Phosphorus 31 0.4 - 13.4 5.1 4.4 differences were found for any parameter between the center cores or within concentric rings. It was determined to combine the center cores and the cores within each ring, resulting in an average center core and an average core for each ring (Tables 17-21). The mean totals for organic matter, nitrogen and phosphorus in the center and each ring (Tables 17-21) were plotted against distance from the center (Figures 16-18). Carbon was not plotted since its value was derived from organic matter and nitrogen. To calculate the total amount of each substance in the sediments, the formula for computing the vol- ume of a solid of revolution was borrowed from solid geometry and modified as follows: V = 2Tr A r 1 000 where: V = Total amount (kg) A = Area under the curve (g cm" ) r = Distance from the axis of symmetry to the center of gravity (cm) The axis of symmetry in this case is a line passing through the center of the sediments (Figures 16-18). The center of gravity for any plane ^:!. ;■ 64 to (D c/oi XIX "O in +1 s- Ln c II (U o c IX o c c o cu E ro i. 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The basically terrestrial Eupatonlum doubled its concentration, and the woody HypMlaum exhibited only a small increase (Table 23). This pattern suggests that submerged plant parts have the ability to absorb phosphorus and that the more of the plant that is submerged, the greater the absorptive capacity, i.e., increasing the \ 75 ■7^ Table 22. Plant above-ground biomass data (June-July, 1976) Plant spp. Area Occupied (m2) Biomass (g tn-2) Total Weight (kg) Mupha/L 221 15 ± 6 3.3 Elzocha/uA 548 a a Parvicum (live) 1085 179 ± 70 194.2 Panlcum (dead) 1085 732 ± 263 794.2 HypMlcum 7222 0. 75 ± 1.9 5.4 EupatoKAjuum 7222 44 ± 27 317.8 Andiopogon (live) 7222 46 ± 44 332.2 Andfiopogon (dead) 7222 27 ± 46 195.0 TOTAL 9076 1842.1 Biomass for EZe.ochjcULLi> was not obtained. ■-^ 76 Table 23. Concentration (%) of phosphorus, nitrogen and carbon in the plant species of the pond during June and September, 1976. Phosphorus Nitrogen Carbon Plant spp. j^^ ^gp jj^^ 5gp j^^ 3gp NuphoA leaves 0.242 0.796 3.04 4.06 petioles 0.223 0.576 1.08 1.37 ElzochaAAJ> 0.220 0.854 1.75 1.75 Payvicim leaves (live) 0.122 0.368 2.82 2.88 stems 0.109 0.250 0.67 0.33 leaves (dead) 0.064 a 0.84 a Hijp(ZMA.cum leaves 0.110 0.141 1.63 1.45 stems 0.033 0.051 1.64 0.59 roots 0.054 a 1.83 a Eapato^im leaves 0.143 0.287 3.06 2.97 stems 0.085 0.192 1.22 1.55 roots 0.087 a 1.10 a Andtopogon shoots (live) 0.082 a 1.12 a roots 0.032 a 1.07 a shoots (dead) 0.014 a 0.30 a ^Data not collected. 44.0 48.2 37.2 42.5 46.6 45.7 46.6 48.5 43.7 46.9 46.0 a 56.2 63.5 50.3 50.6 50.2 a 52.2 54.0 46.8 47.1 47.2 a 48.9 a 46.9 a 46.9 a 77 Table 24. Total amount (kg) of phosphorus, nitrogen and carbon in the plant compartment of the pond during June, 1976.^ Plant spp. Phosphorus Nitrogen Carbon NuphoA 0.008 0.07 1.3 Elzochcuvli, b b b Panlcjum live 0.224 3.39 87.7 dead 0.508 6.67 365.3 Hyp2AA.cuin 0.004 0.09 2.9 EapatoAxxm 0.362 6.80 157.3 AndAopogon live 0.272 3.72 162.4 dead 0.027 0.59 91.5 Total live 0.870 14.07 411.6 Total dead 0.535 7.26 456.8 TOTAL 1.405 22.83 868.4 ^Based on mean concentration in above-ground parts. No biomass data for Eluod/mhAj^. 78 surface to volume ratio with respect to phosphorus appears to be directly related to concentration of phosphorus in the plant. There is substantial evidence to support this contention. For example, Twilley (1976) and Twilley et al . (1977) found that MuphoA tutzam does, in fact, absorb phosphorus through its leaves, and other researchers (McRoy and Barsdate, 1970; Bristow and Whitcombe, 1971; DeMarte and Hartman, 1974) have reported this phenomenon for other submerged and emergent macrophytes. Another interesting phenomenon is the apparent phosphorus con- servation mechanism implied by the difference in concentration in liv- ing and dead plant parts (Table 23). Panlcum apparently translocates 48 percent of the phosphorus from dead leaves to other living parts of the plant whereas And/iopogon translocates 83 percent. This may be controlled by an evolutionary mechanism which is related to the species' ability to occupy aquatic habitats. The basically terrestrial hid/iopoQon retains considerably more of its phosphorus than the emergent Panicxm since the former must meet its phosphorus needs through root absorption only. Seasonal differences in nitrogen concentrations are slight with the exception of HypeAlcum stems which lose about two-thirds of their nitrogen between June and September. Nitrogen is mobile in plants (Gauch, 1972), and this change may reflect transport of nitrogen from the stem to actively growing plant parts as the season progresses. This hypothesis is supported by the fact that both Panlcum and And/iopogon tend to conserve about two-thirds of the nitrogen in dead plant parts (Table 23). Carbon concentrations are interesting in the fact that nearly all parts of all species increased in carbon content as the season progressed 79 (Table 23). This may be the result of an increasing amount of lignin production later in the growing season. The starch and cellulose molecules are 44 percent carbon, and most common sugars and organic acids are about 40 percent carbon. However, the three primary aro- matic alcohols in all angiosperm lignins, coniferyl alcohol, sinapyl alcohol and p-courmaryl alcohol (Salisbury and Ross, 1969), contain 67 percent, 63 percent and 72 percent carbon, respectively (Freudenberg, 1965). The increased production of these "carbon heavy" compounds could account for the increase in carbon content observed in September (Table 23). /• WATER Methods Nitrogen and phosphorus in the pond water were collected and ana- lyzed according to the methods described in the bulk precipitation chapter. Total organic carbon in a sample was converted to carbon dioxide by catalytic combustion in an Oceanography International total carbon analyzer. The carbon dioxide formed is measured directly by an infrared detector. The measured carbon dioxide is directly pro- portional to the concentration of carbonaceous material in the sample (EPA, 1974). Results and Discussion Table 25 contains water height, surface area and volume data. Water height was measured directly. Surface area was determined by plotting the respective water heights on a predrawn figure of the basin shape and then calculating from the diameter. Volumes were cal- culated by addition of frustra for several water heights and then plotting a water height-volume curve from which the remaining volumes were obtained. Table 26 contains the nutrient data for the pond water during 1978. Unlike static surface water features where changes in concentra- tions of nutrients usually reflect planktonic population "blooms" and "crashes," the study pond's biological dynamics are confounded by 80 81* Table 25. Surface hydrology of the pond (1978). Date Water Height (m) Area (ni2) Volume (m3) 10 Jan .47 1,512 220 24 Jan .50 1,653 275 9 Feb .59 2,073 475 23 Feb .70 2,734 822 6 Mar .74 3,043 950 21 Mar .80 3,685 1253 3 Apr .68 2,574 775 14 Apr .55 1.934 365 26 Apr .43 1,345 170 10 May .27 452 45 24 May .34 915 85 7 Jun .21 244 18 21 Jun .21 244 18 6 Jul .61 2,124 525 19 Jul .85 4,286 1525 4 Aug 1.20 9,076 4366 16 Aug 1.21 9,076 4484 30 Aug 1.10 9,076 3522 12 Sep .93 5,558 2025 28 Sep 1.05 7,815 2800 10 Oct .99 6,865 2490 27 Oct .89 4,855 1775 9 Nov 1.00 6,977 2520 21 Nov .91 5,153 1875 6 Dec .85 4,286 1525 20 Dec .76 3,217 1080 Br Table 26. Nutrient data for the pond (1978) • Date Amount Concentration (mg rb TP (g) TN (kg) TOC (kg) TP TN TOC 10 Jan 46.42 .47 5.61 .211 2.12 25.5 24 Jan 105.05 .42 7.38 .382 1.52 26.9 9 Feb 53.68 1.34 10.76 .113 2.83 22.7 23 Feb <279.48 1.45 19.11 <.340 1.76 23.3 21 Mar 145.35 1.68 27.82 .116 1.34 22.2 3 Apr <60.45 1.67 34.49 <.078 2.16 44.5 14 Apr <40.15 .71 13.87 <.110 1.94 38.0 26 Apr 87.38 .67 7.46 .514 3.92 43.9 10 May 6.44 .17 2.37 .143 3.68 52.6 24 May 15.98 .22 3.77 .188 2.55 44.4 7 Jun 2.27 .08 1.28 .126 4.60 71.2 21 Jun 2.81 .09 1.24 .156 5.10 68.7 6 Jul 19.43 .99 17.59 .037 1.89 33.5 19 Jul 74.73 2.44 65.27 .049 1.60 42.8 4 Aug 183.37 5.02 152.37 .042 1.15 34.9 16 Aug 98.65 5.29 129.14 .022 1.18 28.8 30 Aug 186.67 6.52 138.77 .053 1.85 39.4 12 Sep 125.55 2.90 84.65 .062 1.43 41.8 28 Sep 89.60 4.54 88.48 .032 1.62 31.6 10 Oct 59.76 3.66 92.13 .024 1.47 37.0 27 Oct <81.65 3.11 N.A. <.046 1.75 N.A. 9 Nov 40.32 3.40 83.16 .016 1.35 33.0 21 Nov 155.63 3.00 94.69 .083 1.60 50.5 6 Dec 111.33 1.77 63.75 .073 1.16 41.8 20 Dec 19.44 1.74 41.26 .018 1.61 38.2 TP = Total Phosphorus TN = Total Nitrogen T0C= Total Organic Carbon N.A.=contaminated 83 changes in water volume. To understand this relationship, assume that there is a constant amount of some substance in the water. When water volume increases, the concentration of the substance would decrease, and conversely a decrease in volume of water would show an increase in concentration. Therefore, changes in concentration do not necessarily reflect changes in productivity rates. These rate changes can be ascertained by comparing the magnitude of volume and concentration changes (Figure 19). For example, total organic carbon triples from March to June, but water volume decreases by two orders of magnitude and so an apparent bloom is, in fact, a crash. When concentrations are converted to amounts, changes in productiv- ity become readily apparent (Figure 20). There are three population blooms: one large summer increase and two smaller ones in early spring and late fall. The pattern yery closely follows changes in water vol- ume which appears to be a dominant population controlling mechanism. As volume increases so does productivity, to fill the new habitat; but as volume declines, the population crashes as many more individuals are removed from the water column than are added. The net effect of this pattern is to keep concentrations relatively constant. The ratio of maximum to minimum water volume is approximately 250 to 1 ; f or amount total organic carbon, it is about half of this; and for nitro- gen and phosphorus, about 82 to 1 . By contrast, concentration maxima of carbon and nitrogen are only 3 to 4 times their respective minima and phosphorus 32 times. Another interesting effect of fluctuating water height and its consequent changes in surface area is the change in the area available for receiving atmospheric inputs. Figure 20 shows the total amounts ••"=3! 00 en en SI- Z3 ■o M 0) cn c= u ■M •o c Id i- ■M C 0) u c o u c 0) •T" /■ o» 3 cn 85 ^^ OOOi? 00C2 0 (i-lBiii) NO11VH1N33NO0 mi. c r— o o s- +J rO 0} I/) ■p c •r— s- 3 ■o -!-> Q. C 4-> < U •r— i.. OJ -C a. I/) o E /" o CM e o O O AS A • • 9 9 S' 3 A Center B First concentric ring 9 Second concentric ring Figure 21. Available phosphorus (P) distribution with depth (Z). ■t 96 Vihen the "new" rains came, they were relatively low in phosphorus con- tent, and apparently there was little leachable phosphorus left at the top of the sediments, and hence the 15 cm well was substantially lower in phosphorus content than the previous reading in the 45 cm well. The deeper well also showed a reduction in phosphorus from the earlier sample, but this is thought to be an artifact of the mixing of upper and lower water since water can enter the well pipe from the sides as well as the bottom. If, indeed, the total phosphorus bulge is the result of vertically translocated available phosphorus, then the phosphorus at the bulge should have been measured as available but was not (compare Figure 21 with Appendix B tables). One explanation for this discrepancy is that the phosphorus that has been moved is complexed with iron when it reaches the vicinity of the mean low water level. In soils subject to alternating oxidizing and reducing conditions, iron tends to accumulate (Hesse, 1971). Under these conditions a silica-iron-phosphate complex would be formed which would render the phosphorus inactive with respect to available phosphorus analysis. Sediment/ Groundwater Interaction In the previous section we have seen that some of the phosphorus in the sediments is unbound and can potentially be removed from the sediments in the ground water. In the chapter on ground water, it was shown that phosphorus concentrations are higher on the down-gradient side of the pond. Apparently ground water does remove at least some of the unbound phosphorus from the sediments; however, to predict the expected areal concentration distribution of phosphorus on the output 97 side of the pond, it is necessary to understand the geometry of the pond sediments. The sediments are hypersinusoidal in shape, and a front of water passing laterally through such a body would encounter considerably more volume at the center than at the periphery of the body. The volume of sediments decreases in all directions from the center and with reference to the front of water decreases in two dimensions, both parallel and perpendicular to the axis of flow. Figure 22 illus- trates this point. If we imagine columns of water of arbitrary width on the water front, we can see that the column which passes directly through the center will encounter more sediment volume than those passing at some distance from the center. The effect of this phenomenon on the areal distribution of phos- phorus removal, and therefore on the expected concentration distribution of phosphorus in the ground water, can be quantified by double integra- tion of phosphorus over distance. The first integration variables are total phosphorus, a function of depth, and distance parallel to the axis of flow. Total phosphorus values (mg under 1 cm ) are obtained for the center and four concentric rings from Tables 17-21, and these values are plotted against distance for each one-centimeter wide band in Figure 23. For example, the band that passes through the center of the pond contains nine phosphorus data points, two for each concentric ring and one for the center. The total phosphorus under each band was calculated and these totals are indicated in Figure 23, At this point we have the total phosphorus encountered by seven one-centimeter wide columns of water passing through the pond sediments at discrete intervals. However, in order to determine the "phosphorus '■M 98' ■■^m o > c o ■M c «a f— +j (0 Wl E •p- o -o 'r— C/^ j= c ■*■> m T" B 3£ •r— TD (/> (U 0} o> 0) c S- fO x: ^ 1— o • CO CM Q) i- 3 a> tl.« c o 0 • 01 +-> c I/) QJ +J E c ••- (U -o E +J c 4- o n s- <4- c o s- •r- -»-> 13 frs jQ 3 • r- -a s- c +-> 3 to o • r- i- Q C7> CM (U S- 13 at (6) SndOHdSOHd lN3'/Jia3S 102 >vw (j_I&^) SndOHdSOHd dBlVMONflOdO CO CD -^ CVJ d 00 o S- s- 01 C •r- a> c o a. « -o -o i- E CO O) O S- 4-> S- CD (O 'I- I 2 C T3 3 c t/1 O 3 -M -a o c $- CD c a> E o •r- -r- II ■O -M O) fO --^ CO S- X •M -CO)'" +-> U C C O C O •■- •r- O 4-> n3 to w i. 3 3 +-> S- S- C O O Ol J= -C o a. CL c 10 to o • O O O -M Q. Q.+J •!- 3 O I— i- CL Q. re +j .,- ra o ns +-> +-> Six (o •o -a 4- C II o 3 , -M o c C £- , CU O C7> I E 3 J3 1 -o LU to •r- O I— s- +-> to r- O II ■o s- o a. cC CO CM ■o O C (B) sndOHdSOHd lN3lMia3S O) > 103 in direction of about 10° toward the north would account for the discrepancy. It should be pointed out here that the mean groundwater flow direction measured today may not be the same as the mean flow direc- tion for the last several years. This is an important consideration since, owing to the slowness of groundwater flow, the phosphorus recorded in the wells today left the center of the pond several years ago. Groundwater flow velocity will be discussed in detail in the next section. If the peaks of the two curves in Figure 25 are aligned and com- pared in the region where they overlap by linear regression, the follow- ing results are obtained: r^ = 0.84, a = 0.03. This groundwater model is admittedly statistically weak, but the weakness is believed to be the result of high variation in groundwater phosphorus and the low number of sample wells. From a logical standpoint, based on the phosphorus distribution in the sediments through which the groundwater must pass, this model is by far more acceptable than to assume a uniform concentration differential across the pond. The mean concentration difference between input and output wells estimated by the new model is obtained by computing the area defined by curve B and the dashed line (input concentration. Figure 25). This concentration difference is 0.426 mg l" , and the total amount of phosphorus loss per year is 23.2 g. Available Phosphorus and Groundwater Concentrations The phosphorus which moves in the ground water should be that which is in the available state in the sediments. If we assume that 104 all of the available phosphorus dissolves in the ground water and moves laterally, we can calculate the expected concentration in the output wells by the following formula: where: C = concentration in the interstitial water (mg 1 ) P = available phosphorus in the sediment (yg cc ) e = porosity (% expressed as a decimal). Porosity is determined in the following manner (Black et al . , 1965): [(OM)K^ + (1-0M)K2] - BD e = (OM)K^ + (1-0M)K2 where: 6 = porosity (% expressed as a decimal) OM = organic matter (% expressed as a decimal) K, = particle density of cellulose (1.61 g cc ) Kp = particle density of quartz sand (2.65 g cc" ) BD = measured bulk density (g cc" ) /■ The concentration in the interstitial water was calculated for each segment in the center and first ring for which available phosphorus had been measured. These were then plotted against depth to arrive at a mean concentration in the interstitial water of the sediments at the pond center. The mean concentration was 1.84 mg l" which is approxi- mately 1 mg 1"'^ higher than the maximum predicted concentration at the output end of the system. This result leads to one of three possible conclusions. All of the available phosphorus measured in the sediments may not become i,»j ■::,-, 105 soluble and therefore would not move out of the pond system in ground 2+ 3+ v/ater. This may be dependent on, for instance, the Fe /Fe balance which in turn is dependent on the redox potential of the sediment interstitial water matrix. Another possible explanation of the dis- crepancy involves the mechanism by which water level drops in the dry season. If the level drops by In ^liu. evaporation, the effect would be to concentrate the interstitial available phosphorus resulting in relatively high concentrations in the groundwater wells. However, if water level drops due to negative artesian pressure caused by evapora- tion of distance recharge areas, there would not be a concentrating of interstitial available phosphorus resulting in lower concentration in the groundwater wells. The third possible explanation lies in the fact that phosphorus sampled in the output wells reflects sediment nutrient dynamics and hence available phosphorus some time in the past, which may have been different than today. This is based on the fact that the velocity of groundwater flow is extremely slow. Velocity (V) can be calculated by a modification of Darcy's Law (see, for example, Domenico, 1972): e A where: Q = discharge (m^^yr" ) e = porosity {%) A = Area (m ) of the planar section. Discharge (54.53 m"^yr"^ ) divided by porosity (0.36, calculated from the material underlying the sediments) times annual mean area of the 9 -1 planar section (40.1 m'^) equals about 3.78 m yr which means that the KH-. -'..'a!).:- . _ -^ -^^-.N..*",,. 106 concentrations sampled in the west wells consist of, at least in part, phosphorus molecules which left the planar section passing through the pond center about 13 years earlier. r THE POND SYSTEM: PRESENT AND PAST Present Nutrient Budget :om- The inputs, outputs and storages of nitrogen and phosphorus cc puted in the previous chapters can be combined into a nutrient budget for the pond in its present state (Figure 26). For those components which are indirectly functions of water height, i.e., atmospheric input and groundwater input and output, the mean for 1977 and 1978 was used to calculate their multipliers. The rationale here is that 1978 was a relatively wet year and 1977 relatively dry. This pattern of alternating wet and dry years is the norm for this part of Florida (NOAA, 1976; USGS, 1978), and it was felt that by using the data from the two years, a better estimate of the present prevailing conditions could be obtained. The mean area of the pond water surface in 1977 and 1978 was 2,812 m^ (based on the mean area of surface water, calculated from mean water heights in Figure 13), and the yearly atmospheric input of nitrogen and phosphorus was 2,295 g and 93 g, respectively. Based on the discharge calculated in the groundwater chapter, a net gain of 23 g of phosphorus and a net loss of 3 g of nitrogen is observed across the pond (Figure 26). In the case of nitrogen, a condition of stasis ap- parently exists. Since the sediments were sampled in April through June, June, and April through June values were calculated for the plant and water components, respectively. Only those plants within the mean 107 cx o c 10 +» 3 o. M &. o x: Q. V> o x; Q. ■a • E v_^ c c •r" > W) «o ■o • «» %~ +J «o c (U (U >> I/) O) i. s- - -^ ■T-*:^ Tta 109 in CO CO LU 11 Ol ^ l< > :c a. i/i CJ ^ s: LD CO 1— en en CM r— C •r- ou -o r— ' (O s~ s- CD (U ■fj s- «n 0) ■3 -t-> rO 0) 5 o X) rO c M- :3 5- o 3 i~ «/1 tn I X I I i I no area of pond water surface (see above) are included in the budget, that is, the Panlcum, ElzochcuU^ and Nuphan.. Plants and water were minimal storage compartments. Their combined nitrogen and phosphorus were less than 1 percent of the total in storage (Figure 26). At the present rates of exchange, the system appears to be storing 69 percent of the phosphorus input. There is no net loss of nitrogen in ground water, but nitrogen can leave the system through the at- mosphere. This rate was not measured but can be calculated after some additional groundwork is laid (see later). Historical Nutrient Budget Four radiocarbon dates were obtained from the study pond (Figure 27). Net accumulation of organic matter began about 5,250 earth years ago (based on C^'* date correction after Fairbridge, 1974). At this time water height was lower and hence water surface area smaller (Figure 28). The inputs from the atmosphere would have consequently been smaller and groundwater output no different than input since there had been no net accumulation of nutrients in the sediments. As sea-level rose (Shopard, 1963; Scholl et al . , 1969; Morner, 1969; among others) groundwater level also rose tipping the accumulation- decomposition balance in favor of accumulation, and the sediment com- partment began to grow. Figure 28 shows the morphogenesis of sediments in the pond basin. Points away from the pond center were obtained by assuming the same percent change throughout the basin (Lehman, 1975). The amount of phosphorus input is obtained by multiplying the area of the paleo-pond water surface by the measured input rate (33 mg m"^ yr'^), assumed to be constant through time. The paleo-pond water m SIDEREAL YEARS (BP) 0 !0 5000 4000 3000 2000 1000 0 / 20 / 30 / 'e ^40 / 50 1 / 60 70 J ■ 80 y 5000 4000 3000 2000 C'"^ YEARS (BP) 1000 0 Figure 27. Sedimentation rate curve. 112 «t to • fO O) Q- t •r— «% LU OJ h- CD O 03 ■z. s- OJ > • rO c •r- 00 - (0 1 ^ 1 — r-^ -a CTi c ^— o Q. 0) sz >,-l-> XI 3 o ■fJ ■>-> CO i- 0) (0 jC r— +J •1— C= «♦- o 10 lO O) CJ>XJ o cu x: F Q. 3 S- (/> o CO s: (O . 00 C>J la i. o +» i/i c at (A ■P 3 O. 4^ 3 O ■M O. . C X) ••- c o - — Q. C_ — ' C) CO +J 3 S- M- O O x: Q. O) — - o z *♦- C E 0) ro O) i. O O) S- O -M r— •r* -r- Oi 3 'iJ 117 !*«. «* «* LU II a: z: ll 1 :c a. •r- OJ TD r-~ rtJ s- %- CT1 cu +-> i- rrt rtJ ■■ ■. 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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Donald A. Graetz Associate Professor of Soil Science This dissertation was submitted to the Graduate Faculty of the College of Agriculture and to the Graduate Council, and was ^"^Pjf pjf P^^^?^' fulfillment of the requirements for the degree of Doctor of Philosophy. June, 1979 OucA ^ ' ^-^ College of Agricju^ture Dean, Graduate School UNIVERSITY OF FLORIDA 3 1262 08553 8923