Factors affecting the trophic state of Iowa lakes

Transcription

1 Retrospective Theses nd Disserttions 1992 Fctors ffecting the trophic stte of Iow lkes Lorin Kent Htch Iow Stte University Follow this nd dditionl works t: Prt of the Terrestril nd Aqutic Ecology Commons, nd the Wter Resource Mngement Commons Recommended Cittion Htch, Lorin Kent, "Fctors ffecting the trophic stte of Iow lkes" (1992). Retrospective Theses nd Disserttions This Thesis is brought to you for free nd open ccess by Iow Stte University Digitl Repository. It hs been ccepted for inclusion in Retrospective Theses nd Disserttions by n uthorized dministrtor of Iow Stte University Digitl Repository. For more informtion, plese contct digirep@istte.edu.

2 Fctors ffecting the trophic stte of Iow lkes by Lorin Kent Htch A Thesis Submitted to the Grdute Fculty in Prtil Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Deprtment: Animl Ecology Mjor: Animl Ecology (Limnology) Signtures hve been redcted for privcy iversity Ames, Iow 1992

3 n TABLE OF CONTENTS Pge ABSTRACf INTRODUCTION Iow Lke Studies World Lke Studies Resons For A New Study Objectives MEIHODS 1979 Survey Methods 1990 Survey Methods IV PART 1. WATER QUAUTY SUMMARY FOR IOWA LAKES IN 1979 AND Generl Trends in Wter Qulity Reltionships Between Wter Qulity Prmeters Evlution of Lke Rnking System PART II. ASSESSING THE USE OF LAKE MORPHOMETRY AND WATERSHED CHARACTERISTICS AS PREDICITVE TOOLS Lke Origin nd Geogrphic Loction Men Depth Mximum Effective Fetch Wtershed Are to Lke Are Rtio Phosphorus Loding Models Model Development Modelcu1tions Dt Anlysis Implictions

4 111 DISCUSSION 77 Lke nd Dt Vribility 77 Trophic Stte versus Wter Qulity 78 Implictions for Lke Mngement 79 Implictions for New Lke Plnning 80 LITERATURE CITED 82 ACKNOWLEDGEMENTS 88 APPENDIX A. LAKE SURVEY MEANS AND INDIVIDUAL LAKE DATA 89 A Lke Survey Summer Mens 89 A Lke Survey Summer Mens 92 A Individul Lke Dt 98 APPENDIX B. PHOSPHORUS LOADING PARAMEfERS 131

5 IV ABSTRACT Ninetly-five Iow lkes were surveyed for wter qulity indictors of eutrophiction during the summer of 1990, including mny smpled in the 1979 Iow Clen Lkes Clssifiction study. Secchi disk depth, totl nd inorgnic suspended solids, chlorophyll ii, totl phosphorus, nd totl nitrogen were mesured during the 1990 survey. Iow lkes were found to be highly eutrophic, but highly vrible with respect to trditionl indictors of eutrophiction. Wter trnsprency ws best predicted by totl suspended solids concentrtion, while other wter qulity reltionships were not s precise. High levels of precipittion during the yer led to high levels of totl nd inorgnic suspended solids, which my hve obscured wter qulity prmeter reltionships. Lke morphometry nd wtershed chrcteristics were evluted s predictive tools with respect to wter qulity. Lkes on the Des Moines glcil lobe hd higher levels of nitrogen nd phosphorus. Lke men depth held the most promise with respect to wter qulity prediction, while mximum effective fetch nd wtershed re to lke re rtios did not predict wter qulity with stisfctory results. Phosphorus loding models were lso exmined for Iow lkes, but wter qulity correltions were lower thn hs been reported in the literture lthough they fell within expected errors. The smpling scheme, estimtion of certin prmeters, nd the similrity of Iow's lkes my hve lso contributed to much of the dt vribility. Trophic stte nd wter qulity were found not to be closely relted in mny Iow lkes where poor wter trnsprency is due more to suspended inorgnic prticles rther thn lgl biomss. Considertions for lke mngement nd plnning for improved wter qulity include men depths greter thn 4 meters, low wtershed re to lke re rtios, nd low mximum effective fetches.

6 I INTRODUcnON The trophic stte of lke my be defmed s the rte t which orgnic mtter is supplied by (utochthonous inputs) or to (llochthonous inputs) the lke per unit time (Wetzel 1983). Brod ctegories of lke trophy hve been estblished, the two most generlly recognized being eutrophic nd oligotrophic. A eutrophic lke tends to hve high level of productivity while n oligotrophic lke tends to hve low level of productivity. Chnges in the degree of nutrient input to lke, whether by humn or nturl cuses, my result in chnge of the lke's productivity. An increse in lke productivity, otherwise known s eutrophiction, cn led to mssive lgl blooms, which reduce the level of wter qulity desirble for drinking wter, swimming, nd the esthetic vlue of the lke. Whether eutrophiction is or is not problem in Iow lkes is of concern for lke mngers throughout the stte. There hve been severl studies on Iow lkes, the mjority of which took plce in the 1970s nd erly 1980s (Bchmnn & Jones 1974; Jones & Bchmnn 1974; Jones & Bchmnn 1975; Bchmnn & Jones 1976; Jones & Bchmnn 1976; Jones & Bchmnn 1978; Jones & Bchmnn 1978b; Jones & Bchmnn 1978c; Cnfield et l. 1982). A lrge effort ws undertken in 1979 when n Iow lke survey ws conducted for the Clen Lkes progrm of the U.S. EPA, which ws summrized in report issued by Bchmnn et l. (1980). The results of these studies hve shown tht Iow's lkes hve n extremely high level of eutrophiction, mong the highest in the world ccording to Pulsen (1982). An EPA study (Omemik 1977) showed tht Iow strems contined some of the highest levels of phosphorus nd nitrogen in the United Sttes, which my become nutrient source for lge in Iow's lkes. Although these studies hve shown tht ll of Iow's lkes fll into the ctegory of eutrophic, there is still gret del of vribility from the best wter qulity lkes to the worst wter qulity lkes. Vluble insight into the problem of eutrophiction in Iow's lkes cn be gined by exmining the results of the previous studies on Iow lkes. Iow Lke Studies A study of six lkes in northwestern Iow took plce from 1971 to 1973, which signified the first mjor effort to evlute Iow lkes in recent times. Jones nd Bchmnn (1974) conducted generllimnologicl survey by exmining such things s morphometry, wtershed chrcteristics, wter trnsprency, wter chemistry, nd lgl crops. They concluded tht lke West Okoboji experienced n increse in eutrophiction from the 1920s to

7 2 the 1970s s evidenced by drop in hypolimnetic oxygen concentrtion. The six lkes were rnked bsed on plnt-nutrient concentrtions, summer lgl crops, nd wter trnsprency. Wtershed re to lke volume rtios were deemed the cuse for the differences seen between the lkes (due to nnul nutrient dilution). Bchmnn nd Jones (1974) furthered the understnding of these lkes by ttributing summer lgl crops to rtios in nnul totl phosphorus input to lke volume. Secchi disk depth, chlorophyll g, nd totl phosphorus reltionships were estblished. These reltionships indicted tht phosphorus inputs would hve to be reduced to extremely low levels before significnt increses in wter trnsprency would be chieved. Strem nutrient inputs were exmined by Jones nd Bchmnn (1975) in four of the six northwestern Iow lkes in n ttempt to correlte phosphorus budget informtion with lgl biomss. Significnt reltionships were ttined between potentil nitrogen nd summer chlorophyll nd for potentil phosphorus nd summer chlorophyll In 1975, sixteen lkes throughout Iow were exmined for wter qulity chrcteristics (Bchmnn nd Jones 1975), which reveled tht high verge chlorophyll concentrtions were ccompnied by poor Secchi disk depth vlues. The results of this study, long with n ssocited study which included n dditionl 127 lkes from round the world (Jones nd Bchmnn 1976), showed high correltion between lgl levels nd summer totl phosphorus concentrtions (r 2 = 0.95) nd mesured chlorophyll nd predicted totl phosphorus (r 2 = 0.89). After determining tht Iow's lkes were limited by phosphorus (high concentrtions of plnktonic lge were to be expected due to the lrge concentrtion of phosphorus in Iow's lnd runoff), they begn to pply phosphorus loding models to Iow lkes. A sedimenttion coefficient for the Vollenweider loding model (Vollenweider 1969) ws determined which led to good phosphorus concentrtion estimtion. It ws lso found tht rtificil lkes in Iow hd higher sedimenttion rtes thn nturl lkes, which could led to overestimtion of the predicted phosphorus vlues. These greter sedimenttion rtes were determined to solve this discrepncy (Jones nd Bchmnn 1978). Severl centrl Iow reservoirs were surveyed, nd the rtes were repplied to the phosphorus loding model with better success. A lrge survey of Secchi disk trnsprency indicted tht limits in wter trnsprency were due more to lgl density thn to suspended inorgnic mtter, lthough some rtificil lkes hd poorer Secchi disk depths in the spring due to high suspended solids ssocited with

8 3 runoff (Jones & Bchmnn 1978b). These lkes clered up, however, fter the suspended mtter settled lter in the yer. Glcil geology nd lke origin were determined to hve n effect on the wter qulity in Iow's lkes (Jones nd Bchmnn 1978c). Lkes on the Des Moines Lobe of the most recent Wisconsinin glcition hd greter totl ion concentrtions thn lkes off of the lobe, nd similr distribution ws found with respect to totl nitrogen concentrtions. Artificil lkes were found to hve better wter qulity thn nturl lkes due to differences in the dynmics of the phosphorus cycles. The Iow Clen Lkes Study of 1979 represented mssive effort to clssify Iow's lkes ccording to lke wter qulity for the U.S. EPA Clen Lkes Progrm (Bchmnn et I. 1980). A totl of 107 lkes cross Iow were smpled during the summer for wter qulity, wtershed chrcteristics, nd lke use. All lkes were determined to be eutrophic (Wetzel 1983), with wtershed soil runoff contributing the greter prt of the nutrients. Lkes were rnked ccording to their wter qulity nd their potentil to be restored. A study of phosphorus sedimenttion rtes on four nturl nd four rtificil lkes in Iow generlly represents the end of intensive lke studies in Iow up to the present time (Cnfield et I. 1982). It ws determined tht the phosphorus sedimenttion rtes did not significntly differ between the nturl lke group nd the rtificil lke group, but there were significnt differences mong individul lkes. Phosphorus sedimenttion rtes were strongly correlted with inorgnic sediment concentrtions nd inorgnic mtter sedimenttion rtes. World Lke Studies Attempts to predict the trophic stte of lkes hve been going on for decdes, with much of the erly work being ccomplished by Germn limnologists. Thienemnn (1927) ws one of the first investigtors to suggest tht bsin shpe ffected lke productivity, most notbly lke men depth. Numnn (1929) expnded these ides to come up with the clssifictions of eutrophic nd oligotrophic, bsed lrgely upon lke types nd plnkton popultions. Edphic (chemicl) nd morphometric fctors determining oligotrophy were lter distinguished by Lundbeck (1934). These concepts were pplied to North Americn lkes when Rwson (1939,.1942) combined Lundbeck's ides with climtic fctors s vribles tht ffect lke productivity. Rwson went on to demonstrte high correltion between men depth nd nnul fish hrvest for the Lurentin Gret Lkes long with severl lrge lkes in centrl nd western Cnd

9 4 (Rwson 1952). Technologicl improvements in the estimtion of primry production llowed for further refmement of these concepts. In Jpn, Skmoto (1966) estblished significnt correltion between chlorophyll concentrtion nd men depth, nd lso demonstrted tht shllower lkes hd higher productivity thn deeper lkes. Totl dissolved solids concentrtion, long with men depth, were shown to hold promise s good estimtors of productivity by Northcote & Lrkin (1956), lthough the reltionships were prtilly obscurred by other fctors t work in the Cndin British Columbi lkes surveyed. Ryder (1965) divided totl dissolved solids concentrtion by men depth to form new vrible, the "morphoedphic" index, which ws significntly correlted with fish production. Ogelsby (1977) went on to show tht fish production could be better estimted by combining the use of the morphoedphic index long with chlorophyll concentrtion nd primry productivity estimtions. A significnt chievement in the determintion of fctors controlling trophic stte cme with the development of nutrient-loding models by Vollenweider (1969). The degree of eutrophiction lke might expect to ttin (summer phosphorus concentrtion nd subsequent lgl development) could be estimted by knowing lke's men depth, rel phosphorus loding, phosphorus sedimenttion rte, nd hydrulic flushing rte. The estblishment of phosphorus s the most likely limiting nutrient ws mjor chievement, bsiclly putting to rest the ide of crbon s the most limiting nutrient (Americn Society ofumnology nd Ocenogrphy 1972). This led to greter success in the field of lke mngement, with Lke Wshington s notble exmple (Edmondson 1972). Humn-induced eutrophiction ws reversed when treted sewge effluents were diverted from flowing into this lke in the northwest United Sttes, s ws shown by lowered levels of phosphte d chlorophyll long with higher Secchi disk depths nd hypolimnetic oxygen concentrtions. Reserch on Lke Thoe (Goldmn 1975), n ultr-oligotrophic lke long the Cliforni-Nevd border, demonstrted tht lthough the mjor sources of sewge hd been diverted, subtle humn ffects such s soil nd vegettion disturbnce could still contribute to the lke's ongoing eutrophiction. Summer chlorophyll concentrtion ws predicted by totl phosphorus t spring overturn for lkes in southern Ontrio with gret success by Dillon & Rigler (l974), further dvncing the groundwork lid by Vollenweider. Jones & Bchmnn (1976) chieved similr results using Iow lkes long with lke dt from the literture. Nicholls & Dillon (1978)

10 5 refmed these ides further by using summer verge lgl cell volume rther thn chlorophyll i! content to better predict phytoplnkton biomss in Ontrio lkes. The quntittive clssifiction oflkes ccording to trophic stte hs been ttempted with numericl trophic stte indices, most notbly tht of Crlson (1977). His trophic stte index is bsed on scle of 0 to 100, with ech ten unit increse representing doubling in lgl biomss. Secchi disk trnsprency, chlorophyll concentrtion, or totl phosphorus concentrtion could be used for the clcultion of the index number. The ecoregion concept hs recently been pplied in n ttempt to improve the clssifiction of lkes. The bsic ide of the ecoregion concept is tht lke will reflect the lnd use ptterns nd soil chrcteristics of its wtershed. Ongoing efforts in the field of lke mngement hve tken this ide into considertion in n ttempt to ttin wter qulity gols (Heiskry & Wilson 1989). Resons For A New Study A new study of Iow lkes seemed wrrnted for severl resons. One reson is tht there ws essentilly no repliction of the lke smpling survey tht took plce in Thus rndom error might be plying lrge role in ffecting results, nd there is good possibility tht the lkes exhibit yer-to-yer vrition ssocited with differing mounts of precipittion. Additionlly, there my be chnges in the lkes in the 11 yers since the lst study. Such chnges might include sediment buildup in the reservoirs nd chnges in lke wter depth in ll lkes. Another reson is tht studying dt set by itself bises the person conducting the sttisticl nlyses towrds drwing only upon previously-developed ides. This person should visit the lkes in order to come up with new hypotheses to explin lke differences. Loctionl differences ssocited with ech lke my provide the key to the problem. Although the determintion of the sources of these lke differences is n impetus for scientific inquiry itself, there re immedite prcticl pplictions for such knowledge. The Iow Deprtment of Nturl Resources hs been crrying out lke restortion progrms in which n intensive study of lke's properties tkes plce before ny mjor remedies re ttempted. The plnning of new lkes is being undertken, lso. The 1990 lke survey my provide useful insights for restoring lkes or plnning new lkes more effectively.

11 6 Objectives My specific objectives were to: (1) describe the trophic stte oflow lkes, (2) determine cusl fctors where possible, nd to (3) pply the results to ides for lke restortion projects nd how to evlute new lke sites.

12 7 MEIHODS 1979 Survey Methods During the 1979 survey (Bchmnn et l. 1980) totl of 107 lkes were monitored, ech lke being visited three times from lte June through erly October. Three sites on ech lke were chosen for smpling, one of which ws the deepest prt of the lke. Wter smples were collected by using VnDorn or Kemmerer bottle. Three to six wter smples were collected t pproximtely 2 m intervls through the wter column in unstrtified lkes, while three smples were tken in the mixing lyer nd one smple in the hypolimnion in strtified lkes. Smples were stored on ice until lbortory nlysis. For the purpose of brevity, only the tests comprble to the 1990 survey will be discussed, lthough there were more prmeters included in the 1979 survey. Secchi disk redings were tken during ech lke smpling. Chlorophyll concentrtions were determined by extrcting the pigment with 90% cetone nd using the trichromtic spectrophotometric method (Americn Public Helth Assocition 1976). Suspended solids, inorgnic suspended solids, nd totl phosphorus concentrtions were determined by methods comprble to the 1990 survey methods. Anlysis for the vrious nitrogen species took plce only once during the 1979 survey, thus no summer mens were vilble for nitrogen nd it ws not included in the present nlysis of dt. Lke contour mps were used to determine lke surfce re, volume nd men depth. It should be noted here tht I found tht some of the scles in the legends on the smll mps in the published document of the 1979 study (Bchmnn et l. 1980) were incorrect, though this did not ffect their morphometric mesurements since they were mde from the lrge scle originls. I ttined the originl full-sized mps, mde pproprite mesurements, nd corrected the reduced-mp scles before I mde ny mesurements. Lke wtershed res were determined by using USGS topogrphic mps Survey Methods I monitored totl of 95 lkes from mid-my through mid-august. They re locted throughout ll ofiow except the northest section of the stte (Figure 1). Missouri River oxbow lkes nd few other lkes from the 1979 survey were excluded becuse they re in isolted prts of the stte nd would hve been difficult to include in the survey due to time constrints.

13 8 All lkes were smpled on monthly bsis, with five to seven lkes being visited ech dy. Thus ech lke ws smpled three times, t pproximtely monthly intervls. Smpling runs of four to five dys were undertken due to the wide distribution of lkes throughout the stte. Wter smples were tken t three loctions, pproximtely 100 m prt, t ech lke. One of the sites ws t the gretest depth of the lke, where Secchi disk reding nd temperture profile were tken. A tube smpler mde of 305 x 2.5 cm piece of PVC tubing ws used to collect wter smple of the mixed lyer of the lke. This served s composite smple tht ws representtive of ll depths tht were mixed. More thn one smple my hve been needed t ech loction due to the shllowness of some lkes. For exmple, smple t depth of 1 meter would not yield enough wter through the tube smpler to conduct ll of the tests. The smple ws poured into bucket nd mixed well. Totl phosphorus nd totl nitrogen smples were plced into 50 ml nd 25 ml (respectively) prwshed screw-top glss tubes for lter nlysis. Since totl phosphorus nd totl nitrogen were nlyzed, there ws no need to worry bout inter-conversion between the vrious phosphorus nd nitrogen forms within the seled continers. Anerobic denitrifiction to nitrogen gs ws deemed unimportnt, thus there ws no need for concern bout gseous losses of either compound. One liter ws plced on ice nd sved for chlorophyll!!, totl suspended solids, nd inorgnic suspended solids nlysis. Thus there were 3 smples ech of totl phosphorus, totl nitrogen, chlorophyll totl suspended solids, nd inorgnic suspended solids per lke visit. At the end of ech smpling dy, n oxidnt (sodium persulfte) ws dded to the totl nitrogen smples. The smple vils were then plced into pressure cooker for 30 minutes t 15 pounds of pressure in order to convert ll forms of nitrogen to nitrte for lter nlysis. A wter smple from ech loction ws filtered through 0.7 J.lm glss-fiber filter (just until the filter begn to clog) for chlorophyll nlysis, using low-pressure vcuum filtrtion pprtus. Ech filter ws plced on lbeled piece of bsorbent pper. The pper ws folded, secured with pper clip, plced in jr of desiccnt, nd stored on ice until lbortory nlysis. A wter smple from ech loction ws lso filtered (just until the filter begn to clog) through 1.5 J.lm glss-fiber filter tht were pre-weighed (fter combustion in 500 C muffle oven) for totl suspended nd inorgnic solids nlysis. These filters were plced into individully-lbelled foil envelopes nd plced into desiccnt-lined plstic box for lter nlysis.

14 9 At the end of ech smpling run, fml nlyses were conducted in the Limnology Reserch Lbortory t Iow Stte University. Ech chlorophyll filter ws extrcted in 5 ml of9o% ethnol ccording to the procedures of Srtory nd Grobbelr (1984). The tube holding the filter nd the ethnol ws heted to 78 C for 5 minutes nd then extrcted in the drk t room temperture for 24 hours to complete the extrction. Following extrction, the smples were trnsferred to 1-cm cuvette for spectrophotometric nlyses. Opticl densities were red t 665 nd 750 nm (see Appendix A.2 for n explntion of correction fctor tht ws used). The opticl density t 750 nm (the turbidity correction) ws subtrcted from tht t 665 nm. The difference ws multiplied by 1l.7 to fmd the concentrtion of chlorophyll 9 in the extrcting solution. This ws multiplied times the volume of extrctnt used (5 ml) nd divided by the number of liters of lke wter filtered. Multipliction times 1000 converted this mesurement to milligrms per cubic meter of chlorophyll g. Totl suspended solids filters were dried in 104 C oven for 1 hour, weighed, then dried gin until constnt weight ws ttined (Americn Public Helth Assocition 1989). Division of the weight difference by the volume oflke wter filtered nd multipliction by 1000 converted this mesurement to milligrms per liter of totl suspended solids. Inognic suspended solids concentrtions were detennined by igniting the totl suspended solids filters in 500 C muffle oven for 15 minutes (Americn Public Helth Assocition 1989). The filters were then removed from the oven nd llowed to cool. The filters were then trnsferred to desicctor for finl cooling before weighing. The difference between the pre-filtrtion filter weight nd the finl weight is divided by the volume of lke wter filtered nd multiplied by 1000 to rrive t the vlue for inorgnic suspended solids in milligrms per liter. Totl phosphorus smples were oxidized with mmonium persulfte in n utoclve to convert ll the phosphorus to orthophosphte following the procedure of Menzel nd Corwin (1965). This phosphorus ws mesured with the modified single solution method of Murphy nd Riley (1962). The method ws clibrted with series of phosphorus stndrds run on the sme dy s the nlyses. Totl nitrogen smples (converted to nitrte) were nlyzed using the technique of second derivtive spectroscopy (Crumpton et l. 1992; Siml et l. 1985) on Perkin Elmer Lmbd 3B UVMS scnning spectrophotometer connected to microcomputer. A copyrighted computer progrm developed by Softwys Incorported (Moreno Vlley, CA)

15 10 ws used to clculte the second derivtives. The method ws clibrted with series of nitrte stndrds run on the sme dy s the nlyses. Precipittion nd runoff vlues were obtined for specific lke regions for ech wter yer (U.S. Environmentl Dt Service 1978, U.S. Environmentl Dt Service 1979, U.S. Environmentl Dt Service 1989, U.S. Environmentl Dt Service 1990, U.S. Geologicl Survey 1979, U.S. Geologicl Survey 1990). Iow's counties re divided into nine climtologicl regions for record-keeping purposes, nd I lumped the lkes tht I smpled into these regions in order to estimte precipittion for ech lke. Annul totls were tken during the specific wter yer (1979 or 1990) for convenience, which runs from October of the previous yer to September of the stted yer. An nnul runoff vlue ws tken from strem from ech of the nine districts. (Wter Resources Dt for Iow 1979, Wter Resources Dt for Iow 1990). A given strem ws chosen becuse it hd reltively smll dringe re, which I feel dequtely represents the size of the dringe res of the Iow lkes surveyed. Both precipittion nd runoff vlues for the nine regions re given in Tble 1. One cn see tht ll regions showed higher precipittion in 1979 thn 1990 except in the northwest region.

16 N I 1 I,. I. r- h-, 1 em =27.5 km I I J Figure 1. Ninety-five lkes smpled in the 1990 lke survey. The shded re represents the Des Moines lobe of the most recent Wiseonsinin glcition. The mp is dpted from Prior (1976)..-..-

17 12 Tble 1. Precipittion nd runoff vlues for the nine Iow climtologicl regions Region Precipittion (cm) Runoff (cm) Precipittion (cm) Runoff (cm) Northwest (Spencer) Avergeb Northcentrl (Klemme) Averge Northest (Elm) Averge Westcentrl (Pisgh) Averge Centrl (Ames) Averge Estcentrl (Ldor) Averge Southwest (Stnton) Averge Southcentrl (Chriton) Averge Southest (Oklnd Mills) Averge strem sttions where runoff vlues were tken re indicted in prentheses. byerly precipittion verge ( ) for the nine Iow climtologicl regions.

18 13 PART I. WATER QUALITY FOR IOWA LAKES IN 1979 AND 1990 The 19791ke survey included 107 Iow lkes smpled between July nd October of tht yer, while the 1990 survey included 95 lkes smpled between My nd August, so both surveys included the months of July nd August when lgl chlorophylls tend to be t their pek in Iow lkes. Complete dt tbles re locted in Appendix A. There were 94 lkes in common for 1979 nd 1990, nd the mens for severl mesured vribles re used in the comprisons tht follow. The descriptive sttistics for both lke surveys re presented in Tble 2. Inorgnic suspended solids nd totl nitrogen summer mens were not vilble for the 1979 lke survey. Student t-tests showed tht mens for Secchi disk depth, totl suspeneded solids, chlorophyll, nd totl phosphorus were significntly different between the two yers (p < 0.001). Generl Trends in Wter Qulity Wter trnsprency is good generl wter qulity prmeter tht provides quick but effective ssessment of lke's trophic condition. Averge Secchi disk depth ppers to hve remined the sme, with n increse of only 0.08 m from 1979 to 1990 (Figure 2). The distribution for both yers ppers to be bout the sme with round hlf dozen lkes in 1990 hving higher Secchi disk depths. Totl suspended solids re most likely to ffect wter trnsprency, vi the scttering nd/or the bsorption of light. Totl suspended solids vlues incresed two-fold on the verge between 1979 nd 1990, from to mgll (Figure 3). The distributions pper similr, but there re severl lkes in 1990 which hve reltively high concentrtions of totl suspended solids. Suspended solids re comprised of two frctions, orgnic nd inorgnic. Algl biomss comprises prt of the orgnic mtter in Iow lkes nd cn be estimted by chlorophyll!l mesurement. Chlorophyll!l concentrtions styed bout the sme, decresing only 2.37 mg/m3 from 1979 to Figure 4 revels reltively even distribution of chlorophyll!l concentrtions throughout the entire rnge for 1979 vlues, while there is lrger rnge nd more scttered distribution for the 1990 vlues. The other frction of totl suspended solids is inorgnic suspended solids, which ws nlyzed becuse there ws n bundnce of suspended mtter being wshed into lkes

19 Tble 2. Sttisticl description of wter qulity vribles mesured in 94 Iow lkes in the summers of 1979 nd 1990 Secchi Totl Inorgnic Totl Nitrogen Disk Suspended Totl Totl Suspended to Totl Depth Chlorophyll Solids Phosphorus Nitrogen Solids Phosphorus (m) (mg/m3) (mgll) (mg/m3) (mg/i) (mg/l) Rtio 1212 n Men lo2.20 SEM Minimum Mximum Rnge Medin Vrince Stnd. Dev lo Q n Men SEM Minimum Mximum Rnge Medin Vrince Stnd. Dev llo.81 3.lO comprble dt not vilble for 1979.

20 , CJ C :::: :::1' _ _...._..._----_._..._._..._ _ O Secchi Disk Depth (m) CJ C :::: :::1' o Secchi Disk Depth (m) Figure 2. Secchi disk depth (m) frequency histogrms for 94 Iow lkes smpled in both 1979 nd 1990

21 mmmi:i!l iiiiiii j ""---..._..._--_._._..-..._._..._-_..._._._-._.._. 10 o. o Totl Suspended Solids (mg/l) C"j c ::I C" 10 o o Totl Suspended Solids (mg/l) 160 Figure 3. Totl suspended solids (mgll) frequency histogrms for 94 Iow lkes smpled both in 1979 nd 1990

22 ',- _._----_.-." 12 >. V c ::I ::J' o o Chlorophyll!l (mgfcu. m) 20, o o Chlorophyll!l (mgfcu. m) Figure 4. Chlorophyll (mglm3) frequency histogrms for 94 Iow lkes smpled both in 1979 nd 1990

23 18 due to excessive rinfll in A men vlue of mgll ws obtined for inorgnic suspended solids, which is slightly over hlf the vlue of mgll for totl suspended solids. The distribution of vlues ppers to be similr to tht for totl suspended solids (Figure 5). A mjor nutrient ffecting the mount of chlorophyll i! is phosphorus. Totl phosphorus vlues incresed roughly 50% from 1979 to 1990 (Figure 6). In 1990, there re lrger number of lkes with more thn 175 mglm3 of totl phosphorus thn in Additionlly, there were no lkes in 1990 hving concentrtions less thn 25 mg/m3. The totl nitrogen to totl phosphorus rtio hs been used to determine whether lke is limited by nitrogen or phosphorus. Skmoto (1966) demonstrted tht between rtios of 10 TN:TP 17, chlorophyll becme incresingly dependent on phosphorus. Smith (1982) furthered this work by showing tht phosphorus limittion occurs t rtios greter thn 20. A men vlue of for Iow lkes in 1990 (Tble 2) implies tht the mjority of Iow's lkes re phosphorus-limited. Most of Iow's lkes fll bove rtio of 10 (Figure 7), implying the presence or onset of phosphorus limittion. Another limiting nutrient in certin qutic systems is nitrogen. Totl nitrogen ws mesured once in the summer of 1979 lke survey. It ws included in the 1990 survey (3 smpling periods) to see wht role it hd in nutrient dynmics nd how it vried with the other wter qulity prmeters. A men vlue of 3.3 mgll dequtely describes the mjority of the lkes (Figure 5), however there re number of lkes with much higher vlues. Reltionships Between Wter Qulity Prmeters The most noticeble spect of wter qulity, especilly with respect to the public, is wter trnsprency (Crlson 1980). I used the mesurement of Secchi disk depth to estimte wter trnsjmency. Secchi disk depth is highly correlted with totl suspended solids (Figure 8). Secchi disk depth decreses s totl suspended solids concentrtion increses, which is intuitive becuse when there re more prticles in the wter, wter trnsprency is reduced. There is still some sctter in the grph, which Crlson (1977) nd Megrd et l. (1980) might rgue is to be expected due to prticulte mtter other thn lge. Forsberg nd Ryding (1980) gree tht scttered picture is wht one should nticipte in this sitution. This leds to the question of wht influences totl suspended solids concentrtion. This question cn be deduced by dividing totl suspended solids into n orgnic nd n inorgnic

24 u :: = r.. 10 o o Inorgnic Suspended Solids (mgli) u :: =' Q" o o Totl Nitrogen (mgli) Figure 5. Inorgnic suspended solids (mgll) nd totl nitrogen (mgll) frequency histogrms for 95 Iow lkes smpled in 1990

25 IEr:] o o Totl Phosphorus (mg/cu. m) ,.. (oj C ::I o o Totl Phosphorus (mg/cu. m) Figure 6. Totl phosphorus (mglm3) frequency histogrms for 94 Iow lkes smpled both in 1979 nd 1990

26 C C' == s o o Totl Nitrogen: Totl Phosphorus Figure 7. Totl nitrogen to totl phosphorus rtio frequency histogrm for 95 Iow lkes smpled in

27 22 E -.t: 10 B -Q. CD C.:.: B II) C.t: U U CD en log Y = log X r-squred = Totl Suspended Solids (mg/l) 10 log Y = log X r-squred = E -.t: -Q. CD Q :.:.: II) C 1 :c u CD en B r:/%lb B B Totl Suspended Solids (mg/l) 1000 Figure 8. Secchi disk depth vs. totl suspended solids for 94 Iow lkes smpled both in 1979 nd 1990

28 23 frction. Since prt of the orgnic mtter in lkes is composed of lgl biomss, chlorophyll ws chosen s n estimtor of the orgnic frction. The reltionship between chlorophyll nd totl suspended solids is positive in generl, with tighter reltionship in 1979 thn in 1990 (Figure 9). Lmbou et l. (1982) rgue tht tht light ttenution due to prticles other thn lge cn cuse erroneous predictions of chlorophyll. A possible reson for the poor ssocition in 1990 is the fct tht there ws gret del of inorgnic suspended mtter present in 1990 due to hevy rinfll. This ide led me to see if inorgnic suspended solids, rther thn lgl biomss, ws reducing wter trnsprency. Secchi disk depth decreses s inorgnic suspended solids concentrtion increses (Figure 10), indicting tht the ltter prmeter is noticebly ffecting wter trnsprency. An investigtion by Hoyer nd Jones (1983) on Midwest.reservoirs reveled tht the presence of inorgnic suspended mtter ffected the prediction of wter qulity prmeters. They lso regressed chlorophyll nd inorgnic suspended solids concentrtions to predict Secchi disk depth. I pplied my 1990 dt to their multiple regression technique, which cn be seen in Figure 11. I chieved the sme r-squred vlue whether I used their eqution on my dt or I generted my own multiple regression. However, the regression using only totl suspended solids explined more of the vrince thn this multiple regression. Perhps lgl biomss would hve yielded better regression since it is wht chlorophyll is ttempting to estimte. Jones nd Bchmnn (1978b) noted tht reduced Secchi disk depths in Iow in 1975 were due more to lgl densites thn to inorgnic suspended solids. In contrst, the lower grph in Figure 10 revels tht there is strong ssocition between totl nd inorgnic suspended solids. This is to be expected becuse inorgnic suspended mtter is by definition prt of totl suspended mtter. One cn lso note tht over hlf of the totl suspended mtter ws comprised of inorgnic mtter (Tble 2). Heiskry nd Wilson (1989) noted tht the totl suspended solids concentrtion in lkes in southern Minnesot ws comprised of 40 to 50 percent inorgnic suspended solids. Thus one cn see tht the chlorophyll - totl suspended solids reltionship is wekened by the predominnce of inorgnic suspended mtter. This leds one to sk wht influences chlorophyll il concentrtion. It ws mentioned previously tht reserch on Iow lkes hs shown phosphous to be the most limiting nutrient with respect to production (Bchmnn nd Jones 1976). The reltionship between these two prmeters hs been of gret interest to investigtors. Pioneering work took plce in the middle

29 log Y = log X r-squred = E u -CJ El El cl El >..c Co 0 0 ::c 0 10 El El El Totl Suspended Solids Cmg/L) 1000 log Y = log X r-squred=o.ll E CJ E -cl 100 El El >..c Co 0 0 ::c 0 10 El El El e El Totl Suspended Solids (mg/l) 1000 Figure 9. Chlorophyll vs. totl suspended solids for 94 Iow lkes smpled both in 1979 nd 1990

30 25 E -.c -CL CI) C. en i5 :c u CI) en 10 log Y = log X r-squred = Inorgnic Suspended Solids (mg/l) log Y = log X r-squred = en :'2 C) E "0 100 en CI) c: CI) CL en :::I en :s 10 o Inorgnic Suspended Solids (mg/l) Figure 10. Secchi disk depth nd totl suspended solids vs. inorgnic suspended solids for 95 Iow lkes smpled in 1990

31 26 2 r-squred = 0.68 o Predicted Secchi Disk Depth (m) Figure 11. Predicted Secchi disk depth vs. Secchi disk depth for 95 Iow lkes smpled in 1990; Predicted Secchi disk depth = log chlorophyll log inorgnic suspended solids; from Hoyer nd Jones (1983)

32 's, most notbly by Dillon nd Rigler (1974) nd Jones nd Bchmnn (1976). These reserch tems discovered high correltion between these two wter qulity indices when lkes from brod geogrphicl regions were nlyzed. Schindler (1978) dded to this line of investigtion by noting tht there my be ltitudinl effects on this reltionship. Vribility between lkes in close proximity of one nother my weken the bility of globl models to predict wter qulity (Preps nd Trew 1983, Pridmore et l. 1985), while in-lke vribility my lso reduce the effectiveness of these models (Smith nd Shpiro 1981). There hve been other investigtions which hve filed to chieve the high correltions ttined by these reserch tems. Skmoto (1966) noted tht lrge phytoplnkton blooms could result in self-shding, where lge t lower depths receive less light due to light ttenution. This condition could result iii lower mximum stnding crops of phytoplnkton thn one would expect to see for given mount of phosphorus (Hickmn 1980). Vribility in externl phosphorus loding contributed to n inconsistent reltionship in Netherlnd lkes, s is noted by vn Liere et l. (1990). Severl resons contributing to the vribility seen in this reltionship were noted by Nicholls nd Dillon (1978). These investigtors pointed out tht there is gret del of Vribility ssocited with different studies due to different smpling nd nlyzing techniques. They lso noted tht cellulr chlorophyll content vries up to ten percent, nd tht nutrient vilbility nd usbility my be quite vrible within given lke. Solr rdition nd phytoplnkton popultion dynmics my lso contribute to the vribility seen (Nicholls nd Dillon 1978). Temporl vritions were lso noted by Allen (1980), who dded tht different smpling schedules my yield different results due to the phytoplnkton blooms nd crshes. Cnfield nd Bchmnn (1981) found tht phosphorus-chlorophyll reltionships differed between nturl nd rtificil lkes presumbly due to differing suspended solids concentrtions. The gret del of importnce plced upon this reltionship wrrnts ttention, which between cn be seen in Figure 12, where poor reltionship ws seen in both yers. I m not sure bout wht fctors contributed to the poor reltionship in 1979, but perhps s mentioned previously, the reltionship in 1990 is due to high concentrtions of inorgnic suspended solids. Lee nd Jones (1984) rgue tht globl eutrophiction models were developed in prt for lkes with low inorgnic turbidity. Jones nd Novk (1981) noted tht inorgnic suspended mtter ws pprently wekening phosphorus-chlorophyll reltionships. Hoyer nd Jones (1983) lso discovered tht the presence of inorgnic suspended mtter could lter the reltionship between phosphorus nd chlorophyll. They found tht when the phosphorus

33 E ;:; g) E -cl 100 >..s:. Q :c 0 10 EI I!J EI I!J I!J Totl Phosphorus (mg/cu. m) E ::i g) E -cl >-.s:. Q s: I!J 10 I!J EI I!J I!J 1 ;---rr-----r---rrt Totl Phosphorus (mg/cu. m) Figure 12. Chlorophyll vs. totl phosphorus for 94 Iow lkes smpled both in 1979 nd 1990 (lines drwn represent the Jones nd Bchmnn (1976) eqution nd 95% confidence intervls)

34 29 concentrtion ws held constnt, chlorophyll concentrtion decresed s inorgnic suspended solids concentrtion incresed. To test this ide, I used the phosphorus-chlorophyll eqution developed by Jones nd Bchmnn (1976) to predict chlorophyll concentrtion. The difference between mesured nd predicted chlorophyll concentrtion provided n estimte of devition due to the presence of inorgnic suspended mtter. The results of this line of investigtion cn be seen in Figure 13. One cn see tht the devitions increse s inorgnic suspended solids concentrtions increse. But one cn lso see tht there re lrge devitions t low concentrtions of inorgnic suspended solids. In ddition, the model seems to lwys overestimte chlorophyll concentrtion, phenomenon lso noticed by Bierhuizen nd Preps (1985). In order to see if there ws direct ffect of inorgnic suspended mtter on chlorophyll concentrtion, I plotted these two prmeters (Figure 14). One cn see tht there is slight positive reltionship between totl phosphorus nd inorgnic suspended mtter, but there is still gret del of vrition present Obviously there re other fctors t work, one possibly being zooplnkton grzing depleting the mount of lge one would expect to see. A fish kill my hve resulted in n bundnce of zooplnkton. Pce (1984) noticed tht the presence of lrge zooplnkton reduced the mount of chlorophyll one would expect to see for given mount of totl phosphorus. Another possibility is tht lge ws not the dominnt plnt form in some lkes, resulting in most of the chlorophyll being tied up in mcrophytes, whose chlorophyll content ws not mesured. Finlly, some lkes my not hve been phosphorus-limited, but were nitrogen- or light-limited. There hs been extensive work with Secchi disk depth - chlorophyll - totl phosphorus reltionships (Bchmnn nd Jones 1974, Crlson 1977, Cnfield nd Bchmnn 1981). The bsic premise behind these studies is tht phosphorus concentrtion ffects the mount of lge (chlorophyll ) tht cn develop, which in tum cn reduce Secchi disk depth. While the.chlorophyll - totl phosphorus reltionship ws discussed erlier, n inspection of the Secchi disk depth - chlorophyll reltionship seems to be pproprite. One cn regrd Figure 15 nd notice generl inverse reltionship. The ssocition is poorer in 1990, probbly due to high precipittion nd subsequent high concentrtions of inorgnic suspended mtter discussed previously. Non-lgl prticulte mtter in the wter column hs been cited s reson for the clouding of this reltionship (Lorenzen 1980, Megrd et l. 1980, Edmondson 1980, Crlson 1980).

35 E E - 'tl CI) E u E :i.g :0 200 CI) C).. E. g - cl.. III C'G >. CI) Q E 'tl \I) -400 :s 600 E :e E E E Inorgnic Suspended Solids (mg/l) 200 Figure 13. Chlorophyll vrition vs. inorgnic suspended solids (mesured chlorophyll vlues re from the 1990 survey predicted vlues re from Jones nd Bchmnn (1976) log Chlorophyll = -l.09 + l.46 log Totl Phosphorus)

36 log Y = log X 1990 r-squred = E :i u -g) E -cl >..c Q ::c I!! I!! 1!!"bri\;P I!! I!! I!! II:J I!! I!! I!! I!! I!!I!! I!! I!! l:b' I!! I!! I!! I!! 111 I!! I!! I!! Inorgnic Suspended Solids (mg/l) / ;:, o.c 100 o.c Q. i o I Inorgnic Suspended Solids (mg/l) Figure 14. Chlorophyll nd totl phosphorus vs. inorgnic suspended solids for 95 Iow lkes smpled in 1990

37 32 10 E -.c: -Q. II) C en C :c u Chlorophyll (mg/cu. m) c: -Q. II) c en C :c u II) UI iii iii iii 18m m If! iii :J m I:EJ m! m iii ili Chlorophyll (mg/cu. m) Figure 15. Secchi disk depth vs. chlorophyll il for 94 lkes smpled both in 1979 nd 1990; lines shown represent the eqution from Jones nd Bchmnn (1978) where log Secchi Disk Depth = log (Chlorophyll il )

38 33 The Secchi disk depth - totl phosphorus reltionship completes this line of investigtion. There is poor reltionship for both yers, with Secchi disk depth decresing with incresing totl phosphorus concentrtion (Figure 16). There ppers to be n increse in Secchi disk depth t high phosphorus concentrtions. Upon reviewing the field observtions tht I recorded, I found tht these lkes hd visibly lrge mounts of Aphnizomenon or flked lge. It hs been rgued tht one cn still 'see through' this type of lge nd get resonbly good Secchi disk depths even though there is high chlorophyll i! concentrtion (Edmondson 1980). This seems to be piu sble explntion for the upturn in Secchi disk depth vlues. Since Secchi disk depth is highly correlted with totl suspended mtter, it seemed prudent to see if there ws reltionship between totl suspended mtter nd totl phosphorus. A generlly positive reltionship cn be seen in Figure 17. This might be explined by the ide tht there ws good del of the prticulte frction of phosphorus in the wter column, which is ssocited with suspended mtter. Bergmnn nd Peters (1980) noted tht n estimte of. totl suspended mtter regressed upon totl phosphorus yielded higher correltion thn did chlorophyll i! nd totl phosphorus. Totl nitrogen ws exmined in the 1990 survey becuse previous studies hve shown tht nitrogen cn be limiting nutrient in some qutic systems (Forsberg 1977, Forsberg nd Ryding 1980, White 1983). To see if nitrogen plys n importnt role in Iow's lkes, I exmined how totl nitrogen concentrtion chnged with the other wter qulity prmeters mentioned previously. Secchi disk depth generlly decreses with incresing concentrtions of totl nitrogen (Figure 18). Totl suspended solids generlly increse with totl nitrogen. There ppers to be no reltionship between chlorophyll i! nd totl nitrogen (Figure 19). Brydges (1971) noticed no reltionship between chlorophyll i! nd inorgnic nitrogen in Lke Erie. The concentrtion of totl phosphorus generlly increses with totl nitrogen. Pridmore (1985) discovered significnt correltions between totl nitrogen nd both chlorophyll i! nd totl phosphorus in New Zelnd lkes. There ppers to be slight incresing trend between inorgnic suspended solids nd totl nitrogen (Figure 20). Evlution of Lke Rnking System In 1979, Bchmnn nd his reserch ssocites developed priority rnking system for Iow's lkes for the purpose of restortion, which ws in complince with US EPA guidelines (Bchmnn et l. 1980). This rnking system ws comprised of three criteri: severity of wter qulity problems, probbility of lke restortion success, nd expected public benefits. The

39 34 E - 10 log Y = log X r-squred = 0.41 D D.. EI D D II:!' D!D:I IE e ee I!mI:E IlEJ IE ElelD e e e r Totl Phosphorus (mg/cu. m) log Y = log X r-squred = 0.46 E -.c -Q. Q) C It).- i5.c u Q) en Totl Phosphorus (mg/cu. m) Figure 16. Secch disk depth vs. totl phosphorus for 94 Iow lkes smpled both in 1979 nd 1990

40 ::::! CI E -III :5! '0 100 (/) "C CD "C c: CD Q. III (/) co 10 '0 t- log Y = log X r-squred = Totl Phosphorus (mg/cu. m) - ::::! CI E III :5! '0 100 en "C CD "C c: CD Q. III en co 10 '0 t- log Y = log X 1990 r-squred = _T_r Totl Phosphorus (mg/cu. m) Figure 17. Totl suspended solids vs. totl phosphorus for 94 Iow lkes smpled both in 1979 nd 1990

41 E.r: -Q. Q) C.!! C :c u Q) (J) 10 log Y = log X 1990 r-squred = 0.23 I!I I!I I!I r::j I!I I!I I!lIE I!I I!I I!I Totl Nitrogen (mg/l) - =::! 0) E... : '0 100 (J) 'tj Q) 'tj c:: Q) Q. ::l (J) S 10 o t- log Y = log X 1990 r-squred = 0.21 r::j r::j I!I Totl Nitrogen (mg/l) Figure 18. Secchi disk depth nd totl suspended solids vs. totl nitrogen for 95 Iow lkes smpled in 1990

42 log Y = log X r-squred = E CJ -01 E -1\'11 -;..s= Q U = B I!I I!I m I!I I!I I!I I!I I!I I!I.1 10 Totl Nitrogen (mg/l) log Y = log X r-squred = 0.42 I!I en ::l... o.s= 100 o.s= Q. S o t Totl Nitrogen (mg/l) 100 Figure 19. Chlorophyll!l nd totl phosphorus vs. totl nitrogen for 95 Iow lkes smpled in 1990

43 38 - :::! CI E -ctj 1000 :2 100 '0 tj) "tl Q) "tl C Q) 10 :::l tj) (,) 'c cu CI... o.= log Y = log X r-squred = Totl Nitrogen (mgll) Figure 20. Inorgnic suspended solids vs. totl nitrogen for 94 Iow lkes smpled in 1990

44 39 first criteri step ws to rnk lkes ccording to Secchi disk depth, totl phosphorus concentrtion, chlorophyll concentrtion, totl suspended solids concentrtion, nd fish winterkill frequency. The lke with the worst wter qulity problems ws rnked first nd the lke with the best wter qulity ws rnked lst for ech ctegory. Then these five rnks were combined to generte n overll wter qulity rnking list. The rnking ccording to probbility of lke restortion success ws ccomplished by giving lkes with multiple problems first priority with respect to restortion effectiveness rnking. Lkes with fewer potentil lke restortion problems followed in rnking. The rnking ccording to expected public benefits ws ccomplished by combining rnkings derived from public use surveys with rnkings of potentil use by residents within SO miles of the lke to rrive t the finl rnking. All three of these rnkings were combined to crete finl lke rnking, which ws used to evlute whether or not prticulr lke would be worth restoring. I used the wter qulity dt from the 1979 nd 1990 lke surveys to exmine how vrible the rnking system is nd how vrible Iow lkes re in generl. If the rnking system is stble nd Iow lkes re not highly vrible, one would expect to see little chnge for lke rnkings between 1979 nd If the rnking system is not stble nd Iow lkes re highly vrible, one would expect to see good del of chnge in the lke rnkings between 1979 nd I did not hve ny dt on fish winterkill in 1990, so I dropped tht prmeter from the 1979 list nd reclculted the rnking list. Thus I rnked the lkes by Secchi disk depth, totl phosphorus concentrtion, chlorophyll concentrtion, nd totl suspended solids concentrtion. The lke with the worst wter qulity problems ws rnked lst nd the lke with the best wter qulity ws rnked first for ech ctegory. For given lke, I verged these four ctegoricl rnkings to rrive t n overll ter qulity rnking. I computed this overll rnking for ll lkes, rriving t the finl wter qulity rnking list. The finl rnking list I derived for both dt sets contins only 94 lkes since there were only 94 lkes in common between the two dt sets with respect to wter qulity informtion. The rnkings cn be seen in Tble 4. To compre the rnkings between the two sets, I plotted ech lke's 1979 rnking ginst its 1990 rnking (Figure 21). As one cn see, the rnking of the lkes chnged gret del between the two surveys. About one-third of the lkes improved, one-third got worse, nd one-third remined reltively unchnged. It ppers s though the wter qulity prmeters, nd Iow lkes in generl, re highly vrible reltive to ech other. This might be reson why it

45 40 Tble 4. Lke wter qulity rnkings for Iow's lkes in 1979 nd Lke Rnk Rnk Lke Rnk Rnk Ahqubi Mnteno Anit Mripos Arbor Medow Arrowhed 10 8 Mimi BIger Minnewsht BeOOs Moorehed Big Creek Mormon Tril 8 9 Big Spirit 38 5 Nelson Blckhwk Nine Egles Bobwhite North Twin Briggs Woods Oldhm Center Orient Centrl Otter Creek Cler Ottumw Lgn Cold Springs Phoj Corneli Pierce Creek Crwford Creek Plesnt Creek Crystl Pollmiller Drling Pririe Rose Dimond RedRw 32 3 Dog Creek Rock Creek Don Willims Rodgers Prk Est (Clrke) Silver (Del.) Est Okoboji Silver (Dick.) Ester Silver(Plo A.) Eldred-Shwood Silver (Worth) Five Islnd Slip Bluff 3 36 Geode Smith GeorgeWyth Spring 7 7 Green Cstle Storm Green Vlley Swn Hnnen Thyer Hickory Grove Three Fires Hickory Hills Trumbull Icri 3S 43 Tuttle Indin Union Grove Inghm Upper Gr Iow Upper Pine Kent Prk Viking Keomh Wpello Lcey-Keosqu 9 2S West Okoboji 5 2 Little Sioux Prk 56 4 Willimson Pd Little Spirit Willow 4 22 Little Wll 1 31 Wilson (Lee) 6 6 Lost Islnd Wilson (Tyl.) Lower Gr Windmill McBride J7 49 Ylm Rou Gis 2 1

46 IZI IZI IZI IZI IZI IZI IZI IZI 80 IZI IZI IZI IZI IZI (2) IZI... IZI (2) 60 IZI IZI IZI c IZI cu IZI IZI r:p IZI 40 IZI IZI IZI IZI IZI IZI IZI e s s IZI IZI IZI 20 IZI IZI... IZI.. e IZI 0 IZI S e e rnk1990 Figure 21. Comprison of the wter qulity rnkings for 94 Iow lkes smpled both in 1979 nd 1990 IZI

47 42 ws difficult to rrive t solid wter qulity prmeter reltionships. I believe tht the vrition seen in Figure 21 is indictive of Iow's lkes, s ws shown in the previous section tht compred wter qulity prmeters. Spcie nd Loeb (1990) rgue tht chnges in nutrient levels smller thn 35% my be msked by the nturl vribility of the lkes. Another wy of looking t this problem is to mke yer-to-yer comprisons for ll lkes in common for the 1979 nd 1990 lke surveys with respect to wter qulity. Such comprison cn be seen in Figure 22, where yer-to-yer plots of Secchi disk depth nd totl suspended solids re depicted. It ppers s though lkes incresed significntly only with respect to Secchi disk depth, but there were lso mny lkes which got worse in Totl suspended solids concentrtion seemed to increse from 1979 to 1990, with seven lkes incresing significntly. Chlorophyll concentrtion lso showed gret del of vribility between the two yers (Figure 23). Totl phosphorus concentrtion seemed to increse between the two yers in generl, with two notble exceptions. Rnking Iow's lkes ccording to wter qulity hs shown tht Iow lkes re highly vrible. It ws noted erlier tht previous studies hve shown tht Iow lkes vry gret del within the clssifiction of eutrophic. The rnking system provides n excellent exmple of this ide, offering snpshot in time of the vribility of Iow lkes.

48 43 :[.s::. -Q. Q) C CII C.s::. u Q) tn " BI:]. 1 I:I!:EJ' Y = X r-squred = 0.18 I:] I:] I:] I:].. Eb m I:].... ::' :[;LGI.'... -e 1:]1:] O r o Secchi Disk Depth (m) Y = X r-squred = 0.13 o Totl Suspended Solids (mg/l) 200 Figure 22. A yer-to-yer comprison of 94 Iow lkes smpled both in 1979 nd 1990 with respect to Secchi disk depth nd totl suspended solids concentrtion

49 44 ;:, CI en ;:,... o.r:. c. en o.r:. 400 Q. CII (5... 0),... Y = X r-squred == I!I I!I I!I I!I O r r----- o Totl Phosphorus (mg/cu. m) Figure 23. A yer-to-yer comprison of 94 Iow lkes smpled both in 1979 nd 1990 with respect to chlorophyll nd totl phosphorus concentrtion

50 45 PART II. ASSESSING me USE OF LAKE MORPHOMEfRY AND WATERSHED CHARACTERISTICS AS PREDICTIVE TOOLS USING me 1979 AND 1990 IOWA LAKE DATA SETS The development nd construction of new lkes is n ongoing process in Iow It would be very helpful for lke plnners to be ble to predict the wter qulity of lke by using lke nd wtershed chrcteristics tht re redily vilble. In this section I use vribles such s lke origin, geogrphicl loction, men depth. mximum effective length nd fetch, nd the wtershed re to lke re rtio in n ttempt to predict lke wter qulity in Iow's lkes. Lke Origin nd Geogrphic Loction An rtificil lke will be defmed s lke tht ws constructed by humns for the purpose of recretion nd/or for drinking wter supply. A nturl lke will be defined s lke tht ws the result of nturl processes such s glcil ctivity or the formtion of n oxbow lke. The most recent glcil ctivity in Iow ws the Wisconsin glcition, which receded pproximtely 12,000 yers go (Prior 1976). The Des Moines lobe of this glcition covered ppoximtely one-third of north-centrl Iow. The term 'lobe' is used to refer to this re (Figure 1). Totl ion nd totl nitrogen concentrtions on the lobe were found to be higher thn lkes off the lobe in Iow, most likely due to the fct tht the lkes off of the lobe hve been subject to more leching over time thn lkes on the lobe (Jones nd Bchmnn (1978c). My nlyses centered on n ttempt to determine if the origin (rtificil or nturl) nd the loction (on-lobe or off-lobe) of Iow's lkes were relted to their wter qulity. I divided Iow's lkes into four ctegories for nlysis. There were 61 rtificil lkes off of the lobe, 24 nturl lkes on the lobe, 9 rtificil lkes on the lobe, nd 1 nturl lke off of the lobe. Since there ws only one nturl lke off of the lobe (Ottumw Lgoon, n oxbow lke), I decided to drop this lke from further nlyses so the results would not be skewed due to n insufficient number of smples. Thus ll nturl lkes included were formed from glcil ctivity. I first nlyzed the ffect of lke origin nd loction on morphometric prmeters. Initil inspection of dt reveled tht ntur11kes on the lobe (s group) re bigger thn the rtificil lkes (s group), whether on or off of the lobe (Tble 5). This is evidenced by lrger mximum effective lengths nd fetches (defined in the section Mximum Effective Fetch) long with lrger wtershed nd lke res. Artificil lkes on the lobe hve roughly the sme mximum effective lengths nd fetches s rtificil lkes off of the lobe, but hve somewht lrger wtersheds nd wtershed

51 46 Tble 5. The influence of lke origin nd loction on selected morphometric prmeters of 95 Iow lkes ARTOFF ARTON NATON ARTOFF ARTOFF ARTON Men Men Men ANOVA vs. vs. vs. SEM SEM SEM p-vlue ARTON NAroN NATON Men Depth (m) Mximum Depth * (m) Mximum Effective * * * Length (m) Mximum Effective * * * Fetch (m) Wtershed Are * * (h) Lke Are (h) * * * Wtershed Are to * * * * Lke Are rtio n= ART or NAT = rtificil or nturl lke, OFF or ON = off or on the Des Moines lobe. *designtes significnce t the 0.05 level.

52 47 re to lke re rtios (Tble 5). It should be noted here tht lke's mximum effective length is defined s stright line connecting the two most distnt points on the shoreline without crossing over lnd (Hknson 1981). I used morphometric mps from Bchmnn et l. (1980) to determine this prmeter. I then clculted mximum effective fetches (defined by Hknson 1981), using the method described by Wlker (1987). I clculted this prmeter by using the points on the shoreline s given by my mximum effective length determintions. As rule I chose the lrger vlue of mximum effective fetch to use for further nlyses. More in-depth nlysis ws undertken using nlysis of vrince tests, which ws conducted using SAS sttisticl softwre. Univrite tests determined tht ll vribles were normlly distributed, which is necessry in order for the nlysis of vrince tests to be vlid. The results cn be seen in Tble 5. Mximum depth for on-lobe rtificil lkes is significntly higher thn for the nturl lkes. This is probbly due to the fct tht rtificil lkes re constructed in reltively deep rvines while nturl lkes were formed by retreting glciers which generlly flttened ll terrin tht they pssed over. Mximum effective lengths nd fetches re significntly higher for the nturl lkes thn for either the on- or off-lobe rtificil lkes. Agin, glcil ctivity tended to crete reltively lrge lkes during retrets by scouring the terrin nd by leving lrge blocks of ice to melt nd fill the depressions. The nturl lkes hve significntly lrger wtershed res thn off-lobe rtificil lkes. The reltively flt terrin left by glcil ctivity on the lobe creted dringe systems lrger thn those seen off of the lobe. Both types of rtificil lkes hve significntly smller lke smfce res thn the nturl lkes. As with the lengths nd fetches, glcil ctivity hs creted these reltively lrger lkes. All types of lkes hve significntly different wtershed re to lke re rtios. The lrgest rtios re seen for the rtificil on-lobe lkes. This is most likely due to the lrge dringe systems creted by glcil ctivity nd the reltively smller lke re in comprison to the nturl lkes, which hve the smllest rtios (Tble 5). Artificil off-lobe lkes, while comprble to the on-lobe lkes with respect to smfce re, re locted in reltively hillier terrin. Thus the dringe re is reduced, nd the smller rtios re seen. I focussed on the 'effect of lke origin nd loction on wter qulity prmeters. Secchi disk depths for rtificil lkes on the lobe re significntly higher thn those in the nturl lkes in 1979 (Tble 6). Jones nd Bchmnn (1978c) found tht rtificil lkes tended to hve greter Secchi trnsprencies thn nturl lkes. This might be explined by the fct tht totl

53 48 Tble 6. The influence of lke origin nd loction on wter qulity prmeters for 94 Iow lkes smpled both in 1979 nd 1990 ARTOFF ARTON NATON ARTOFF ARTOFF ARTON Men Men Men ANOVA vs. vs. vs. SEM SEM SEM p-vlue ARTON NATON NATON 1979 Secchi Disk * Depth (m) Totl Suspended * * * Solids (mgfl) Chlorophyll (mg/cu. m) Totl Phosphorus (mg/cu. m) Secchi Disk Depth (m) Totl Suspended Solids (mg!l) Chlorophyll * * (mg/cu. m) Totl Phosphorus (mg/cu. m) Inorgnic Susp Solids (mg!l) Totl Nitrogen O.(XX)1 * * * (mgll) n= ART or NAT = rtificil or nturl lke, OFF or ON = off or on the Des Moines lobe. *designtes significnce t the 0.05 level.

54 49 suspended solids concentrtions were significntly different between the nturl lkes nd both types of rtificil lkes. Since it ws noted erlier tht there ws high correltion between totl suspended solids nd Secchi disk depth, one would expect to see significnt differences between the Secchi disk depths, lso. This ws not the cse in 1990, when there were no significnt differences between the three lke types. This might be explined by the fct tht the totl suspended solids concentrtions for the three lke types did not differ significntly in Agin, since it ws noted erlier tht there ws high correltion between totl suspended solids nd Secchi disk depth, one would not expect to see ny significnt differences between the three lke types with respect to Secchi disk depth in Upon inspection of the mens, chlorophyll concentrtions were pprently higher for the nturl lkes in 1979, but sttisticl nlysis did not revel ny significnt differences. In 1990, however, there ws significnt difference between the nturl nd rtificil lkes. This phenomenon ws lso noted by Jones nd Bchmnn (1978c). They ttributed this to the fct tht the nturl lkes hd higher totl phosphorus concentrtions in their study, but this ws not the cse in 1990 (Tble 6). Totl phosphorus vlues were not significntly different in 1979, either. There were no significnt differences between the three lke types with respect to inorgnic suspended solids concentrtions in An extremely low level of significnce implies tht the effect of this prmeter is unifonn in the lkes cross Iow. Artificil lkes on the lobe hve significntly higher totl nitrogen concentrtions in 1990 thn either of the other lke types. While the on-lobe rtificil lkes hve wtersheds comprble in size to the nturl lkes, they hve significntly lrger wtershed re to lke re rtios, indicting tht they will hve more nitrogen loding per unit re thn the nturl lkes (Tble 5). Extensive use of nitrogenous fertilizers on the highly-tillble soils found on the lobe my lso contribute to the mount of nitrogen reching lkes. Thus one would expect to see higher totl nitrogen concentrtions for on-lobe rtificil lkes. Following these results the lkes were divided into the lke types nd were ssigned new vrible, LAKEfYPE, depending on their origin or loction. The lkes were lso given vlue, clled STRA T, depending on whether they were thermlly strtified or not. Therml strtifiction ws inchidcd becuse I discovered tht 63 to the 70 rtificil lkes were thermlly strtified in In ddition, 19 of the 24 nturl lkes were not thermlly strtified in 1990.

55 50 These two vribles were then tested to determine if they would improve the power of the physicl vribles to predict the wter qulity vribles. SAS sttisticl softwre ws used, with the results presented in Tble 7. Secchi disk depth nd chlorophyll concentrtion cn be better predicted by physicl vribles if therml strtifiction is tken into considertion. Artificil lkes re the type of lkes tht tend to strtify, so they deserve to be exmined closer. First of ll, totl suspended solids concentrtions incresed considerbly from 1979 to 1990 (Tble 6). Second, there is high correltion between totl nd inorgnic suspended solids (Figure 9). If one ssumes tht the inorgnic suspended solids concentrtion ws lowered reltively s much s totl suspended solids in 1979 in comprison to 1990, then the Secchi disk depth - chlorophyll reltionship would not be interfered with s much s it ws in 1990 where there ws no model improvement. Hoyer nd Jones (1983) noticed this phenomenon in Missouri reservoirs. They found tht inorgnic suspended mtter ws cusing clssicl phosphorus - chlorophyll - trnsprency reltionships to be wekened due to light ttenution. Lke type ws shown to improve model prediction for totl suspended solids nd totl phosphorus concentrtions (Tble 7). Nturl lkes hve the highest totl suspended solids, totl phosphorus, nd chlorophyll concentrtions, lthough the 1990 vlues for totl phosphorus tend to not follow this trend (Tble 6). Figures 9 nd 15 show tht there were better reltionships for 1979 over 1990 for the chlorophyll - totl suspended solids nd the Secchi disk depth - chlorophyll reltionships, respectively. As ws sserted previously, lower totl suspended solids concentrtions in 1979 imply lower inorgnic suspended solids concentrtions, thus the trditionl phosphorus - chlorophyll - trnsprency reltionships would not be s dversely ffected by inorgnic suspended mtter (Hoyer nd Jones 1983). Totl nitrogen ws found to be the only prmeter in 1990 to be significntly ffected by lke origin nd loction. As previously discussed, lkes with high vlues tended to be rtificil in origin nd locted on the Des Moines glcil lobe. Men Depth The men depth of lke my be defined s the volume divided by the surfce re, which gives good estimte of the lke's physicl dimensions nd bsin shpe. Skmoto (1966) rgues tht men depth hs been shown to be n importnt morphologicl mesurement ffecting trophic stte. Rwson (1952) demonstrted tht there is high correltion between men depth nd nnul fish hrvest for the Lurentin Gret Lkes long with severl lrge

56 51 Tble 7. The influence oflke type nd therml strtifiction upon wter qulity prediction in 941kes smpled both in 1979 nd 1990 Wter Qulity Lke PR>F PR>F Model Vrible Grouping Type ISS TypeITI SS Improvement 1979 Secchi Disk LAKETYPE NO Depth (m) STRAT YES Totl Suspended LAKETYPE YES Solids (mgll) STRAT NO Chlorophyll LAKETYPE NO (mg/cu. m) STRAT YES. Totl Phosphorus LAKEfYPE YES (mg/cu. m). STRAT NO.l22Q SecchiDisk LAKEfYPE NO Depth (m) STRAT NO Totl Suspended LAKEfYPE NO Solids (mgll) STRAT NO Chlorophyll LAKETYPE NO (mg/cu. m) STRAT NO Totl Phosphorus LAKETYPE NO (mg/cu. m) STRAT NO Inorgnic Susp. LAKETYPE NO Solids (mgll) STRAT NO Totl Nitrogen LAKEfYPE YES (mgll) STRAT NO

57 52 lkes in centrl nd western Cnd. Ryder (1965) continued long these lines by showing how men depth cn be incorported into morphoedphic index to predict potentil fish production. In this study there is bsiclly no reltionship between Secchi disk depth nd men depth (Figure 24). However, there re no lkes with men depth greter thn 4 m tht hve the lowest Secchi disk depths (less thn pproximtely 0.75 m). There is no solid reltionship between totl suspended solids concentrtion nd men depth (Figure 25). Even so, there re no lkes bove 4 m hving high totl suspended solids concentrtions. These concentrtions re 15 mgil nd 50 mgil for 1979 nd 1990, respectively. However, there re lkes with low men depths with low concentrtions of suspended solids, lso. Obviously there re other processes tking plce tht re yet unccounted for. There is no reltionship between chlorophyll concentrtion nd men depth (Figure 26). Agin, s ws seen with suspended solids, lkes with men depths greter thn 4 m do not hve excessive wter qulity problems. These lkes hve concentrtions less thn 60 mglm 3 for both yers. However, there re lkes with low men depths possessing good wter qulity, which cn not be redily explined. Skmoto (1966) demonstrted tht there is n inverse curviliner reltionship between chlorophyll content nd men depth. Pridmore et l. e 1985) rgue tht lkes with different men depths increse the vrince in chlorophyll -phosphorus reltionships. Smith (1985) used men depth nd totl phosphorus to predict blue-green lgl biomss in North Americ nd in Sweden (Smith et l. 1987). There is no definite reltionship between totl phosphorus nd men depth, more so in 1990 thn in 1979 (Figure 27). One might be ble to sy tht there re no lkes with men depths greter thn 4 m with poor wter qulity, but there re lso lkes with men depths less thn 4 m hving good wter qulity with respect to totl phosphorus concentrtions. There is no reltionship between inorgnic suspended solids nd men depth (Figure 28). Lkes with men depths greter thn 4 m do not hve high concentrtions of inorgnic mtter, but there re lkes with low men depths nd low concentrtions of inorgnic mtter. There is no reltionship between totl nitrogen nd men depth, nd the 4 m cutoff vlue pprently does not pply here. Jensen et l. (1990) incorported men depth into their equtions predicting in-lke totl nitrogen concentrtions.

58 53 5 :[.c -Q. Q) C ox III C.c (,) (,) Q) (/) 4..., 'b "'l!jl!jl!j : ", :' ' II!! : '..,'::: : rp II!! O '----r---'------, o Men Depth (m) 5 4 :[.c Q. Q) c 3 ox III C.c (,) (,) 2 Q) II!! (/) EJ e?:fi " _8 EJ o+--":"=ej'' o Men Depth (m) Figure 24. Secchi disk depth vs. men depth for 94 Iow lkes smpled both in 1979 nd 1990

59 54 :::J -0).. f/j :E '0 en -,:, CP -,:, c CP Q. f/j :::l en iii -0 I r:p '& 1: :1 Men Depth (m) :::J -0) E -f/j :E '0 en -,:, CP -,:, c CP Q. f/j ::I en iii -0 I o Men Depth (m) Figure 25. Totl suspended solids vs. men depth for 94 Iow lkes smpled both in 1979 nd 1990

60 E 200 CI E -C'CII.c >. 100 Q c Men Depth (m) E 200 CI.. C1II > c 0 d'l Men Depth (m) Figure 26. Chlorophyll!\ vs. men depth for 94 Iow lkes smpled both in 1979 nd 1990

61 56 E 800 :i 600 C) E - en... ::s,g III 400 o.r:: o t- 200 O-r--r--T o Men Depth (m) 800 E ::s 600 C) E -In... ::s o.r::. 400 o.r::... iii -o t- 200 I!I I!I I!I I!I o Men Depth (m) Figure 27. Totl phosphorus vs. men depth for 94 Iow lkes smpled both in 1979 nd 1990

62 57 :2 - '" o 3 -ell E en "C CD "C c:: CD :::l en.!:! c:: cu CI... o.e o J-eoi%. o Men Depth (m) CI E - c:: CD CI 0... Z '& I!I I!I I!I I!I I!I I!I 0 :: :. ::,Il:l.. HI. '.. s:j iii iii... iii Men Depth (m) Figure 28. Inorgnic suspended solids nd totl nitrogen vs. men depth for 95 Iow lkes smpled in 1990

63 58 Mximum Effective Fetch I hypothesized tht lkes with longer fetches will be more subject to wind-generted wves, thus incresing the potentil for nutrients being stirred up from the lke bottom or from nutrients lower in the wter column. These nutrients could become ssimilted by lge nd cuse lgl blooms, which re ssocited with poor wter qulity. Additionlly, bottom sediments could be stirred up nd cuse poor wter trnsprencies. The mximum effective fetch used for this study ws tken from the point where the mximum effective length intersects the shoreline. The fetch ws mesured from both shoreline intersections nd the lrgest vlue ws used for nlysis becuse it represented the gretest potentil fetch ffect on the lke. Mximum effective length my be defined s the stright line connecting the two most distnt points on the shoreline over which wind nd wves my ct without interruptions from lnd or islnds (Hknson 1981). Melck (1984) rgues tht lkes with long lengths re more. subject to wind-induced mixing thn round lkes of similr lengths. Hnn (1990) used this prmeter to predict thermocline depth. The mximum effective fetch ws chosen to be used in this study becuse it tkes into ccount wind ffects from severl directions nd reflects the irregulr shpe of the shoreline. Fetches were clculted using the method generted for the U.S. Army Corps of Engineers (Wlker 1987). There is no pprent reltionship between Secchi disk depth nd mximum effective fetch (Figure 29). However, in generl the lkes with fetches greter thn pproximtely 2000 m do not hve high trnsprency vlues. There re still lkes with poor wter qulity which hve fetches less thn 2000 m, which leds one to believe tht other fctors re ffecting Secchi disk depth. There is no reltionship between totl suspended solids concentrtion (Figure 30), chlorophyll il concentrtion (Figure 31), totl phosphorus concentrtion (Figure 32), or inorgnic suspended solids or totl nitrogen concentrtions (Figure 33) nd mximum effective fetch. Poor wter qulity, i.e. high nutrient concentrtion, should be seen in lkes with lrge fetches, but the opposite is seen in this study. The evidence presented fils to support my ssertion tht lkes with lrge mximum effective fetches will hve poor wter qulity due to wind-induced resuspension of nutrients. Other processes re probbly tking plce tht hve not been ccounted for, which hve yet to be determined t this time.

64 59 5 :.c -Co CII o.:.i: It) C.c u CII fa I:l III III r::j r::j O '------r o Mximum Effective Fetch (m) 5 - E -.c -Co CII 0.:.i: If) C :2 u CII fa 4 EI EI 3 EI 2 cp " :: EI... "" e. " " :",. QW 0 ": " r::j I!I:l Mximum Effective Fetch (m) Figure 29. Secchi disk depth vs. mximum effective fetch for 94 Iow lkes smpled both in 1979 nd 1990

65 60 ::J' -C'I.. til :2 '0 U) 'tl CD 'tl C CD Q. til :::J U) c :1 1:1 1:1 1:1 1: :1 1:1 1:1 1:1 1:1 1:1 1: Mximum Effective Fetch (m) ::J' -C'I E -til :2 '0 U) 'tl CD 'tl C CD Q. til :::J U) c 'b 1:1 1:1 1:1 I!I 1:1 1:1 1:1 1:1 1:1 1:1 e 1:1 1:1 EI e... 1:1 1:1. e iii 1:1....I!I IB 1:1. 1:1 1:1.. EI EI Mximum Effective Fetch (m) Figure 30. Totl suspended solids vs. mximum effective fetch for 94 Iow lkes smpled both in 1979 nd 1990

66 E C) E 200 -C'II1 >. 100.c EI Co c 0 0 EI EI EI EI EIEI Mximum Effective Fetch (m) EI EI EI

67 :s 600 OJ E - en :s...,g 400 o.&: 0- S o die! tfl I!l O------r---r---r----- o Mximum Effective Fetch em) 800 E :s 600 OJ E -III :s... o.&: 400 o.&: 0- S o t- 200 o Mximum Effective Fetch (m) Figure 32. Totl phosphorus vs. mximum effective fetch for 94 Iow lkes smpled both in 1979 nd 1990

68 63 E -It) '0 en." CD." c: CD ::l en. c: co C)... o c: o o Mximum Effective Fetch (m) 20 C) E - c: CD C) Z ftj r---r-----r--- o Mximum Effective Fetch (m) Figure 33. Inorgnic suspended solids nd totl nitrogen vs. mximum effective fetch for 94 Iow lkes smpled in 1990

69 64 Wtershed Are to Lke Are Rtio The wtershed re to lke re rtio provides n estimte of wht levels of nutrients one cn expect to see in lke on n rel bsis. This rtio my be defined s the rtio of lke's dringe bsin to the lke's surfce re. I hypothesized tht lkes with lrger rtios would hve more lke nutrients per unit lke volume thn lkes with smller rtios. Thus lkes with higher rtios would be subject to poorer wter qulity mnifested through the lgl blooms tht ccompny the higher nutrient levels. Previous work in this re hs shown tht differences in the trophic sttes of lkes in northwestern Iow were ttributed to different wtershed dynmics (Jones nd Bchmnn 1974). Fishing qulity in Iow lkes ws predicted using models tht incorported the wtershed re to lke re rtio (Hill 1986). Fukushim nd Murok (1988) demonstrted how wtershed chrcteristics could be used to predict wter qulity in Jpnese lkes. Rsmussen et l. (1989) used wtershed chrcteristics to predict wter color in northern temperte lkes. In this study there is no pprent reltionship between Secchi disk depth nd wtershed re to lke re rtios (Figure 34). However, lkes with rtios greter thn 50 tend to only hve poor wter qulity with respect to wter trnsprency. There re lkes with rtios less thn 50 tht lso hve poor wter, so there re some other processes tking plce tht re ffecting this reltionship. There is no pprent reltionship between totl suspended solids concentrtions (Figure 35), chlorophyll concentrtion (Figure 36), totl phosphorus concentrtion (Figure 37), or inorgnic suspended solids or totl nitrogen concentrtions (Figure 38) nd wtershed re to lke re rtios. One would expect to see poor wter qulity, i.e. high nutrient concentrtions, in lkes with lrge fetches, but the opposite is seen ip. this study. The evidence presented fils to support the ide tht lkes with lrge wtershed re to lke re rtios will hve poor wter qulity due to more lke nutrients per unit lke volume. As ws seen with the mximum effective fetch, other processes re probbly tking plce tht hve not been ccounted for, which hve yet to be discovered.

70 65 5 E -.r:. -Q, CD C.:.= (I) C.r:. u CD en 4 : :. e... e ee o; _ ,_ o Wtershed Are: Lke Are 5 E -.r:. -Q, CD C.:.= (I) C.r:. u CD en 4 3 lei 2 ee I!J e.. ejl e e... ee e e e 1:1 I!I... e. :. e e. :. e 1:11:1 r9l SSe Wtershed Are: Lke Are Figure 34. Secchi disk depth vs. wtershed re to lke re rtio for 94 Iow lkes smpled both in 1979 nd 1990

71 :J' -CI E -; 150 '0 UJ 'tl CD 'tl 5i 100 Co CI) UJ S o o o=-=p---, Wtershed Are: Lke Are - =:::! CI E o o Wtershed Are: Lke Are Figure 35. Totl suspended solids vs wtershed re to lke re rtio for 94 Iow lkes smped both in 1979 nd 1990

72 Wtershed Are: Lke Are E :::i C) E -cl >. c ::c I!I I!I o o Wtershed Are: Lke Are Figure 36. Chlorophyll vs. wtershed re to lke re rtio for 94 Iow lkes smpled both in 1979 nd 1990

73 :s 600 C) E -en :s...,g I!I g. 400 o.c Q. o I- 200 f!j I!I. I!I......:. Ib I!I 1It1iISit!I... r O , o Wtershed Are: Lke Are 800 E :s 600 I!I C) E -en... :s o.c g. 400 o.c Q. o I- 200 o , , , o Wtershed Are : Lke Are Figure 37. Totl phosphorus vs. wtershed re to lke re rtio for 94 Iow lkes smpled both in 1979 nd 1990

74 69 :J' ""- en E II) "0 en II) c:: II) Q. II) ::l en.2 c:: c en... 0.E s 100 I:J e t:j t:j t:j I:J e 0 m e e I:J I:J t:j I:J e Wtershed Are: Lke Are :J' ""- en E - c:: II) en Z :s 0 I I:J e 1:1 IS 1:1 t:j e I:J 1:Ir:fJ :...!!Ie.. ee e 1:1 1:1 e.'. 'Kg e 1:1 1:1 t:j 1: Wtershed Are: Lke Are t:j I:J Figure 38. Inorgnic suspended solids nd totl nitrogen vs. wtershed re to lke re rtio for 94 Iow lkes smpled in 1990

75 70 Phosphorus Loding Models Model Devevopment Phosphorus loding models my be considered refinement of the previously mentioned morphometric prmeters such s men depth nd wtershed re to lke re rtios becuse they incorporte these ides in order to predict lke phosphorus concentrtions. Since phosphorus vilbility my determine the extent of lgl growth, totl phosphorus concentrtion is n importnt indictor of lke trophic stte (Vollenweider 1968, Dillon nd Rigler 1975). The importnce of phosphorus s limiting nutrient in Iow lkes hs been demonstrted by Jones nd Bchmnn (1976). Vollenweider (1969) developed model to predict totl phosphorus concentrtion in lke bsed upon fctors which re reltively esy to mesure: where TP=L/z«(J+p) TP = totl phosphorus concentrtion in the lke wter (mg 1m3) L = nnul phosphorus loding to the lke wter (mg I m2 1 yr) z = lke men depth (m) (J = phosphorus sedimenttion coefficient (yr -1 ) p = hydrulic flushing rte (yr -1 ). Cnfield nd Bchmnn (1981) tested the predicting bilities of severl phosphorus loding models, ech of which vried slightly from the previous eqution due to different estimtions of phosphorus sedimenttion. They concluded tht the best estimtes for the sedimenttion coefficient (J were: (J =O.162( LIz )0.458 for nturl lkes, nd (J = 0.114( LIz )0.589 for rtificil lkes which cn be incorported into Vollenweider's eqution to yield: TP= L0.542 I [ O.l62(zO.542) + zpl ] for nturl lkes, nd TP = LO.411 I [0.114(zO.411) + zpl ] for rtificil lkes. Model Clcultions I modeled the expected totl phosphorus concentrtion for the smpled Iow lkes. The morphometric vribles were obtined from the 1979lke survey (Bchmnn et l. 1980), while precipittion nd runoff vlues were obtined for specific lke regions for ech wter yer (U.S. Environmentl Dt Service 1978, U.S. Environmentl Dt Service 1979, U.S.

76 71 Environmentl Dt Service 1989, U.S. Environmentl Dt Service 1990, U.S. Geologicl Survey 1979, U.S. Geologicl Survey 1990). Iow's counties re divided into nine climtologicl regions for record-keeping purposes, so I lumped the lkes tht I smpled into these regions in order to estimte precipittion for ech lke. Annul totls were tken during the specific wter yer (1979 or 1990) for convenience, which runs from October of the previous yer to September of the stted yer. An nnul runoff vlue ws tken from strem from ech of the nine districts which cn be seen in Tble 1 (U.S. Geologicl Survey 1979, U.S. Geologicl Survey 1990). A given strem ws chosen becuse it hd reltively smll dringe re, which I feel dequtely represents the size of the dringe res of the Iow lkes surveyed The pproprite prmeters, long with predicted totl phosphorus vlues, re listed in Appendix B. Vribles necessry to predict totl phosphorus vlues were clculted s follows: Lke Volume = Men Depth * Lke Are * Annul Wter Input = [Wtershed Are * Runoff + Lke Are * (Precipittion - Evportion)) * 100 Externl Phosphorus Loding = 369 * Wtershed Are * Runoff I Lke Are * 100 It should be noted tht for externl phosphorus loding, 369 mg/m3 ws determined to be the verge concentrtion of totl phosphorus in severl Iow strems (Jones, Borofk, nd Bchmnn 1976; Jones nd Bchmnn 1978; Jones 1981; Bumnn nd Lutz 1987). Dt Anlysis To test the bility of these models to predict mesured totl phosphorus vlues, dt from both the 1979 nd the 1990 lke surveys were nlyzed. A pictoril nlysis of the models' predictive bilities is shown in Figure 39. The two grphs depict lke-by-lke comprison of how ctul mesured totl phosphorus vlues compre to the predicted vlues. Exmintion of these grphs revels tht the dt generlly fits within the 95 % confidence intervls, which rnge from % of the clculted totl phosphorus vlues (Cnfield nd Bchmnn 1981). Yet it is pprent tht there is not strong correltion for either yer. Cnfield nd Bchmnn (1981) found tht ctul nd predicted totl phosphorus concentrtions were high! y correlted (r 2 = 0.69). Dillon nd Rigler (1974b) rrived t higher correltion with Ontrio lkes (r2 = 0.81). Jones nd Bchmnn (1976) found n even better correltion (r 2 = 0.84), which does not gree with the results given bove.

77 log Y = log X r-squred = 0.10 en ::;,... o.s::. 100 o.s::. Q. Cii -o I- 10; r_ Predicted Totl Phosphorus (mg/cu. m) 1000 E ::;, 0) E - en ::;,... o.s::. 100 o.s::. Q. j o I- log Y = log X r-squred = '---TTr Predicted Totl Phosphorus (mg/cu. m) Figure 39. Totl phosphorus vs. predicted totl phosphorus for 94 Iow lkes smpled both in 1979 nd Additionl lines represent 95 % confidence intervls (Cnfield nd Bchmnn 1981)

78 73 The discrepncy seen my be due, in prt, to the fct tht Iow's lkes spn reltively nrrow rnge of trophic sttes. The studies mentioned bove were comprised of lkes rnging from highly oligotrophic to highly eutrophic. Due to the wide rnge of trophy in their studies, there ws not s much vrince in their reltionships s is seen in Iow lkes, which cn be ttributed to the reltively nrrow rnge of trophy seen in Iow lkes. Preps nd Rigler (1981) believe tht this eqution my not work very well in shllow nd enriched lkes, due to different sedimenttion dynmics nd turnover times. This is pplicble to Iow lkes becuse shllow nd enriched lkes re quite prevlent. Precipittion in 1990 ws much higher thn verge, so the vlues for nnul wter input nd externl phosphorus loding my be lower thn they should be. Thus there is n underestimtion of phosphorus concentrtion, s cn be seen by exmining the second grph in Figure 39. Another reltionship worth exmining is tht between chlorophyll concentrtions nd predicted totl phosphorus. Chpr nd Trpchk (1976) were ble to predict chlorophyll concentrtions from phosphorus loding nd rel wter loding dt. Jones nd Bchmnn (1976) found strong correltion between these two prmeters (r 2 = 0.79), but this ws not the cse in 1979 or 1990 (Figure 40). There ppers to be no reltionship for either yer. Allen (1980) rgues tht this reltionship my be wekened becuse lrge reductions in phosphorus re needed in order to cuse only smll reductions in lgl biomss. Smith (1979) modified this predictive eqution to predict photosynthetic rtes, which he felt might more ccurtely describe in-lke processes. Internl phosphorus loding, light limittion, or other nutrients my be limiting lgl growth nd subsequent chlorophyll concentrtions. Since Secchi disk depth is simple nd effective predictor of wter qulity, comprison of Secchi disk depth nd predicted totl phosphorus seems ppioprite. There ppers to be wek negtive trend in the 1979 dt (Figure 41), which is stronger for the 1990 vlues. This seems logicl becuse higher phosphorus concentrtions imply higher lgl biomss (nd chlorophyll concentrtions), which in tum cn reduce Secchi disc trnsprency. Implictions In summry, I do not believe tht the equtions to predict totl phosphorus concentrtions re very helpful in evluting Iow lke wter qulity. There seem to be other fctors influencing the mount of phosphorus nd chlorophyll in Iow's lkes thn externl phosphorus loding. As ws mentioned previously, high vrince due to nrrow rnge of

79 E ::; u -CI E -cl >. J::. Q J::. 0.:g 100 B r9 "" " "b ): d'e 10 IQ EI ' rr-----r Predicted Totl Phosphorus (mg/cu. m) E ::;..g CI E -cl >. J::. Q :E 0 EI B El 100 rfl"b EI " /RI EI ": :1 EI EI - - EI 10 EI EI EI dlj rrr-----r Predicted Totl Phosphorus (mg/cu. m) Figure 40. Chlorophyll i vs. predicted totl phosphorus for 94 Iow lkes smpled both in 1979 nd 1990

80 75 10 E -J:: -Co Q) o en C J:: U U Q) U) rr------_r Predicted Totl Phosphorus (mglcu. m) 10 - E -J:: -Co Q) 0 en C J:: u Q) U) I:J C C rf} C I:J C C CI:J I:J Cc I::II:J C "b d'b I:J... '& C C C e IPb e e Iril IE:J e III e C el:jl:jl:jl:j C m C I:J I:J I:J C I:J r:: I:J r--_e_e--r_,_,_ Predicted Totl Phosphorus (mg/cu. m) Figure 41. Secchi disk depth vs. predicted totl phosphorus for 94 Iow lkes smpled both in 1979 nd 1990

81 76 trophy my be plying n importnt role. Iow lkes re reltively shllow with lrge mount of littorl re, which contributes to the reson why mny of them re highly eutrophic. Another reson for the high vribility seen is the fct tht mny of the prmeters hve been estimted. Externl phosphorus loding ws estimted using n verge strem phosphorus concentrtion tken from severl studies. Differing sedimenttion rtes nd turnover times between the lkes my lso be contributing to the highly vrible results seen here (Preps nd Rigler 1981). Precipittion vlues my lso be ffecting the bility of the Vollenweider equtions to predict totl phosphorus. The vlues for precipittion were from October of the previous yer to September of the survey yer, nd thus probbly re not s precise s one would like for ccurte predictions. Yer-to-yer fluctutions in precipittion my cuse the verge phosphorus concentrtion in the wter to vry from yer to yer, lso. The mounts of precipittion in both 1979 nd 1990 my be fr from the nonn, especilly with the high rinfll in Finlly, evportion vlues re difficult to estimte nd my be very specific to ech lke. Evportion vlues were tken from U.S. Wether Bureu Technicl Pper (Kohler et l. 1959), which re given for regions of the country nd re not lke-specific. Light limittion my lso be ffecting lgl biomss (nd chlorophyll concentrtions), which my be highly vrible from lke to lke. Inorgnic suspended solids concentrtion hs been shown erlier to be n importnt fctor in mny Iow lkes with respect to light limittion. Potentil chlorophyll production my be much less thn would be expected given the mount of phosphorus present becuse the lge popultions re hindered by the lck of dequte light. In lkes with low concentrtions of inorgnic suspended solids, high lgl concentrtions my cuse light ttenution few meters below the lke surfce, reducing the mount of lge tht the lke cn produce. The degree to which light limittion ws tking plce could not be detennined in the generl lke surveys in 1979 nd This leds to the notion tht phosphorus my not be the only nutrient/fctor influencing lke wter qulity to gret extent Alge in Iow lkes receive high concentrtions of nitrogen nd phosphorus from frm runoff, perhps more thn cn be effectively ssimilted. Other fctors seem to be t work, which hve not been redily ssessed t this time.

82 77 DISCUSSION The studies of Iow's lkes in the pst twenty yers hve shown tht Iow lkes re eutrophic but vry to gret degree within the clssifiction of eutrophic. The present study hs reconfirmed these findings. Averge Secchi disk depths of just over meter long with chlorophyll men vlues round 50 mglm 3 tken from the 1979 nd 1990 surveys show tht Iow lkes re very productive. Iow lkes hve very high levels of phosphorus nd nitrogen, which implies tht there is no shortge of these nutrients for lge nd mcrophytes. Omernik (1977) demonstrted tht Iow strems hve some of the highest nutrient levels in the country. Intensive row-crop griculture in Iow uses tremendous mounts of fertilizers, which contin high concentrtions of nitrogen nd phosphorus. Highly-efficient frm dringe systems remove excess wter from the fields, shuttling it into nerby strems nd eventully lkes in certin instnces. Thus nutrient -lden runoff in wtershed cn rech lke in reltively short period of time, which in turn cn become vilble to lge nd crete mssive blooms. This reduces wter trnsprency nd cretes the conditions seen in mny Iow lkes. The nutrient loding tht lke receives depends gret del on the dynmics of its wtershed. Recent dvnces in lke mngement hve plced hevy emphsis on how wtershed influences lke, most notbly the ecoregion concept Heiskry nd Wilson (1989) divided Minnesot's lkes into severl regions depending on wht type of geogrphy nd humn ctivities were tking plce within the wtersheds. Good wter qulity ws seen in the northern regions where there is greter tree coverge, corser soils, nd reltively little humn ctivity. Poorer wter qulity ws seen in the southern regions where tree coverge is sprse, frming is intensive, nd wste products re more prevlent In my study, I begn to divide Iow's lkes into different ctegories, bsed on lke origin nd loction. There re definite differences between lkes tht lie on nd lkes tht lie off of the Des Moines lobe of the most recent Wisconsin glcition. Lkes tht lie on the lobe hve lrger wtersheds nd higher nitrogen concentrtions. All ofiow's nturl (glcil) lkes lie. on the lobe, which is further evidence tht dividing Iow's lkes into ctegories bsed on lke origin nd loction is the strt of the development of lke ecoregions in Iow. Lke nd Dt Vribility One of the most noticeble outcomes of this study is the gret mount of vrition seen in Iow lkes. Iow lkes pper to be quite similr, with their nturl vribility creting

83 78 difficulty in developing wter qulity reltionships. Grphicl nd sttisticl nlysis hs shown Iow lkes to be clustered, leving no esy mesurement to predict Iow lke wter qulity. The exmintion of the lke rnking system highlights this ide. The comprison of the lke rnkings for the two yers displyed lrge mount of sctter, chrcterizing how Iow lkes re highly vrible from yer to yer. Wter qulity prmeter comprisons (e.g totl phosphorus versus 1990 totl phosphorus concentrtion) lso showed how Iow lkes cn shift with respect to wter qulity. Another source of dt vribility tht should be ddressed is the smpling scheme. Smpling lke three times in summer t monthly intervls my not be dequte due to the periodic events occurring in nd round the lke. For exmple, if I smpled lke few dys fter rinstonn, runoff nd bottom resuspension could result in very turbid lke. High suspended solids concentrtions would result. However, if I hppened to visit the lke few dys before rinstorm, the lke might be reltively cler, with low suspended solids concentrtions. Periodic lgl blooms nd crshes could lso weken the choice of my smpling scheme. IfI visited lke during the pek of n lgl bloom, high chlorophylls would result If I smpled prior to bloom or severl dys fter crsh, low chlorophylls would result It is no surprise tht there is dt vribility when one considers how periodic events cn remrkbly ffect lke wter qulity. Additionl yers of lke smpling my reduce dt vribility by reveling the extent to which given lke my vry. The two mjor surveys exmined in this study my be only presenting smll picture of the rnge to which Iow lkes nturlly vry. There is lso vribility inherent in the phosphorus loding models becuse some of the prmeters hd to be estimted Precipittion long with phosphorus loding nd sedimenttion coefficients re exmples of this, which without doubt re introducing vribility to the modelling results. Trophic Stte versus Wter Qulity In this study I hve ttempted to use wter qulity prmeters to ssess nd predict the trophic stte of Iow lkes. In the lrger deeper lkes, trophic stte nd wter qulity re closely relted. Orgnic mtter in these lkes generlly tkes the fonn of plnktonic lge, which re the primry fctor influencing wter trnsprency. These lkes re more representtive of the

84 79 North Americn temperte lkes tht were used to develop wter qulity reltionships in the pst. However, mny Iow lkes re reltively shllow (men depth < 4 m) nd turbid. Trophic stte nd wter qulity re not closely relted in these lkes where poor wter trnsprency is due more to suspended inorgnic mtter rther thn lgl biomss. The concept of eutrophiction does not redily pply itself to these lkes becuse primry producers re not the mjor cuse of poor wter qulity. Inorgnic suspended mtter is one of the most importnt fctors influencing Iow lke wter qulity. It is difficult to determine whether this prmeter originted from the wtershed or from sediment resuspension for given lke becuse inflows. were not monitored. Implictions For Lke Mngement Lke restortion projects re currently tking plce in Iow in conjunction with the Iow Deprtment of Nturl Resources nd the U.S. Environmentl Protection Agency. The results of my study hve led to some insights s to how these restortions might be improved. Lke mngers re generlly striving for good wter trnsprency s fr s wter qulity is concerned. The source of wter trnsprency problems must be determined before remedy cn be prescribed. If wter qulity monitoring yields high lgl chlorophylls, then steps to control lgl popultions would be the best choice of ction. Nutrient btement mesures or the use of lgicides would be considered. If inorgnic turbidity is the mjor problem, close monitoring of inflows nd the lke proper would determine whether internl resuspension or wtershed runoff is the source of the turbidity. Resuspension might necessitte lke dredging to remove the esily suspended bottom sediment Sedimenttion structures nd/or wtershed conservtion prctices my reduce turbidities if the source of the problem is wtershed runoff. The ffect ofbenthivorous fish (e.g. crp) on Iow lke turbidities hs lso not been redily ssessed. Improved wter qulity following the removl of rough fish in lkes hs been noticed, but hs not been documented in scientific study for Iow lkes. I believe tht such system will yield the best results for ll prties involved. This is similr to the pproch tken by Bchmnn et l. (1980), nd hs been used in the 1980's for lkes being restored in Iow with resonble results.

85 80 Implictions For New Lke Plnning Growing needs for public recretion nd/or n dequte drinking wter supply cretes need for the development of new reservoirs. I believe tht the results of my study cn provide helpful informtion for the cretion of new lkes with good wter qulity. In my study I looked t severl lke morphometry nd wtershed chrcteristics to evlute their use s predictive tools. With the development of new lkes, whether or not lke is on the Des Moines glcil lobe is very importnt. Lkes on the lobe re subject to very high levels of phosphorus nd nitrogen during wet yers (e.g. 1990), which cn pose problems. High nutrient levels cn produce mssive lgl blooms, creting poor wter qulity for recretionl use. Additionlly, totl nitrogen vlues exceeded 10 mg/l in severl instnces. This is the level tht the U.S. EPA hs set s the onset of wter qulity problems with respect to drinking wter. Although their guidelines specify nitrte, the mjority of the totl nitrogen in Iow is the nitrte ion due to nitrifiction of mmoni-bsed fertilizers. New lkes on the lobe should be monitored very crefully for phosphorus nd nitrogen for these resons. The prmeter which holds the most promise s predictive tool is men depth. It ppers s though lkes with men depths greter thn 4 m do not hve the potentil for gret wter qulity problems. These deeper lkes will most likely strtify nd develop region of decomposition in lower lyers which cn remove phosphorus from the photogenic zone. Lke plnners cn esily clculte potentil lke's men depth by determining how high the dm is built. I recommend t lest 4 m men depth for better potentil wter qulity. Bchmnn (1990) hs lso endorsed this ide in the evlution of potentil Iow lke. Although mximum effective fetch nlysis filed to yield ny solid results, I still believe tht the ides behind this nlysis hve merit. I feel tht the construction of islnds in the lke proper cn cut down on wve ction nd potentilly reduce fetch effects. Additionlly, islnds cn provide fish hbitt, esthetic beuty, nd potentil future site for dredge spoil. On the sme note, I feel tht wtershed re to lke re rtios hold promise s predictive tools. Although my nlysis did not yield positive results, Jones nd Bchmnn (1974) demonstrted tht different wtershed re to lke re rtios were the reson for the differing degrees of wter qulity seen mongst severl lkes in northwest Iow. The fct tht most of Iow's lkes re shllow with extensive littorl res probbly obscured ny wtershed effects. I feel tht lower wtershed re to lke re rtio mkes the most sense s to the reduction of externl nutrient loding. Perhps future reserch will be ble to probe further into

86 81 wtershed ffects nd discover importnt principles to id in the understnding of lke wter qulity nd trophic stte.

87 82 UTERATURE CITED Allen, R.I The indequcy of existing chlorophyll /phosphorus concentrtion correltions for ssessing remedil mesures for hypertrophic lkes. Environmentl Pollution (Series B) 1: Americn Public Helth Assocition Stndrd methods for the exmintion of wter nd wstewter. 14th edition. Americn Public Helth Assocition, New York, NY. Americn Public Helth Assocition Stndrd methods for the exmintion of wter nd wstewter. 15th edition. Americn Public Helth Assocition, New York, NY. Americn Society of Limnology nd Ocenogrphy Nutrients nd eutrophiction: The limiting nutrient controversy (ed. by G. E. Likens), pp Spec. Symposi 1, Am. Soc. Limnol. Ocenogr. Spec. Symp., 1. Bchmnn, R W Projected limnologic1 Conditions in the "Finger Lkes" Proposed for Five Sites (3, 3b, 6, 8, 13) t Brushy Creek. report submitted to the Iow. Depent of Nturl Resources, October, pp. Bchmnn, RW. nd J.R Jones Phosphorus inputs nd lgl blooms in lkes. Iow Stte Journl of Reserch 49(2, prt 1): Bchmnn, RW. nd J.R. Jones Nutrient Inputs nd Algl Blooms in Iow Lkes. Completion Report (Project A-049-IA) for the Iow Stte Wter Resources Reserch Institute 31 pp. Bchmnn, RW., M.R Johnson, M.V. Moore nd T.A. Noonn Clen lkes clssifiction study of Iow's lkes for restortion. Finl report submitted to the Iow Conservtion Commission nd the Iow Deprtment of Environmentl Qulity. 715 pp. Bumnn, RE., nd D.S. Lutz Wter qulity studies -- Red Rock nd Sylorville Reservoirs, Des Moines River, Iow, Iow. Engineering Reserch Institute, Annul Report. ISU-ERI-Ames-87185, Iow Stte University, Ames, Iow. Bergmnn, M. nd R.H. Peters A simple reflectnce method for the mesurement of prticulte pigment in lke wter nd its ppliction to phosphorus-chlorophyll-seston reltionships. Cn. J. Fish. Aqut Sci. 37: Bierhuizen, J.F.H. nd E.E. Preps Reltionship between nutrients, dominnt ions, nd phytoplnkton stnding crop in pririe sline lkes. Cn. J. Fish. Aqut Sci. 42: Brydges, T.G Chlorophyll -totl phosphorus reltionships in Lke Erie. Proc. 14th Conf. Gret Lkes Res. (Internt Assoc. Gret Lkes Res.) Cnfield, D.E., Jr. nd RW. Bchmnn Prediction of totl phosphorus concentrtions, chlorophyll, nd Secchi depths in nturl nd rtificil lkes. Cn. 1. Fish. Aqut Sci. 38:

88 83 Cnfield, D.E., Jr., J.R. Jones nd R.W. Bchmnn Sedimentry losses of phosphorus in some nturl nd rtificil Iow lkes. Hydrobiologi 87: Crlson, R.E A trophic stte index for lkes. Limnol. Ocenogr. 22(2): Crlson, R.E More complictions in the chlorophyll-secchi disk reltionship. Limnol. Ocenogr.25(2): Chpr, S.C. nd SJ. Trpchk A chlorophyll model nd its reltionship to phosphorus loding plots for lkes. Wter Resources Reserch 12(6): Crumpton, W., T. Isenhrt nd P. Mitchell Nitrte nd orgnic nitrogen nlyses using second derivtive spectroscopy. (in press, Limnol. Ocenogr.). Dillon, P J. nd F.H. Rigler The phosphorus-chlorophyll reltionship in lkes. Limnol. Ocenogr. 19(5): Dillon, PJ. nd F.H. Rigler. 1974b. A test of simple nutrient budget model predicting the phosphorus concentrtion in lke wter. J. Fish. Res. Bord Cn. 31: Dillon, P J. nd F.H. Rigler A simple method for predicting the cpcity of lke for development bsed on lke trophic sttus. J. Fish. Res. Bord Cn. 32: Edmondson, W.T Nutrients nd phytoplnkton in Lke Wshington. in Nutrients nd eutrophiction: The limiting nutrient controversy (ed. by G. E. Likens), pp Spec. Symposi 1, Am. Soc. Limnol. Ocenogr. Spec. Symp., 1. Edmondson, W.T Secchi disk nd chlorophyll. Limnol. Ocenogr. 25(2): Forsberg, C Nitrogen s growth fctor in fresh wter. Prog. Wt. Tech. 8(4/5): Forsberg, C. nd S.-O. Ryding Eutrophiction prmeters nd trophic stte indices in 30 Swedish wste-receiving lkes. Arch. Hydrobiol. 89: Fukushim, T. nd K. Murok Simple model to predict wter qulity in 90 Jpnese lkes. Verh. Internt. Verein. Limnol. 23: Goldmn C. R., nd E. de Amezg Sptil nd temporl chnges in the primry productivity of Lke Thoe, Cliforni-Nevd between 1959 nd Verb. Internt. Verein. Limnol. 19: Hknson, L A Mnul of Lke Morphometry. Springer-Verlg, Berlin Heidelberg. 78 pp. Hnn, M Evlution of models predicting mixing depth. Cn. J. Fish. Aqut. Sci. 47:

89 84 Heiskry, S.A. nd C.B. Wilson The regionl nture of lke wter qulity cross Minnesot: An nlysis for improving resource mngement. J. Minn. Acd. Sci. 55(1): Hickmn, M Phosphorus, chlorophyll nd eutrophic lkes. Arch. Hydrobiol. 88: Hill, K.R Ossifiction of Iow lkes nd their fish stnding stock. in Lke nd Reservoir Mngement, Volume II. North Americn Lke Mngement Society, Merrifield, VA. pp Hoyer, M.V. nd J.R. Jones Fctors ffecting the reltion between phosphorus nd chlorophyll in midwestern reservoirs. Cn. J. Fish. Aqut. Sci. 40: Jensen, J.P., P. Kristensen nd E. Jeppesen Reltionships between nitrogen loding nd in-lke nitrogen concentrtions in shllow Dnish lkes. Verh. Internt. Verein. Umnol. 24: Jones, B.L Nonpoint source phosphorus lodings to Iow rivers nd lkes. M.S. Thesis. Iow Stte University, Ames, Iow. Jones, J.R. nd R.W. Bchmnn Umnologicl fetures of some northwestern Iow lkes. Proc. Iow Acd. Sci. 81: Jones, J.R. nd R.W. Bchmnn Algl response to nutrient inputs in some Iow lkes. Verh. Internt. Verein. Umnol. 19: Jones, J.R. nd R.W. Bchmnn Prediction of phosphorus nd chlorophyll levels in lkes. Journl WPCF 48(9): Jones, J.R. nd R.W. Bchmnn Phosphorus removl by sedimenttion in some Iow reservoirs. Verh. Internt. Verein. Umnol. 20: Jones, J.R nd R.W. Bchmnn. 1978b. A survey of wter trnsprency in Iow lkes. Proc. Iow Acd. Sci. 85(1): 6-9. Jones, J.R. nd RW. Bchmnn. 1978c. Trophic sttus of Iow lkes in reltion to origin nd glcil geology. Hydrobiologi 57(3): Jones, J.R, B.P. Borofk, nd R.W. Bchmnn Fctors ffecting nutrient lods in some Iow strems. Wter Res. 10: Jones, J.R. ndj.t. Novk Umnologicl chrcteristics of Lke of the Ozrks, Missouri. Verh. Internt. Verein. Umnol. 21: Kohler, M.A., T J. Nordenson nd D.P. Bker Evportion mps for the United Sttes. U.S. Wether Bureu Technicl Pper No pp. Lmbou, V.W., S.C. Hem, W.O. Tylor nd LR. Willims Chlorophyll, phosphorus, Secchi disk, nd trophic stte. Wt. Res. Bull. 18(5):

90 85 Lee, G.P' nd R.A. Jones Summry of US OECD Eutrophiction Study. Results nd their ppliction to wter qulity mngement. Verh. Internt. Verein. Limnol. 22: Lorenzen, M.W Use of chlorophyll-secchi disk reltionships. Limnol. Ocenogr. 25(2): Lundbeck, J Uber den "primr oligotrophen" Seetypus und den Wollingster See ls Dessen Mitteleuropischen Vertreter. Arch. Hydro., 27: Megrd, R.O., J.C. Settles, H.A. Boyer nd W.S. Combs Jr Light, Secchi disks, nd trophic sttes. Limnol. Ocenogr. 25(2): Melck, J.M Amzon floodplin lkes: Shpe, fetch, nd strtifiction. Verh. Internt. Verein. Limnol. 22: Menzel, D.W., nd N. Corwin The mesurement of totl phosphorus in sewter bsed on the libertion of orgniclly bound frctions by persulfte oxidtion. Limnol. Ocenogr. 10: Murphy, J., nd J.P. Riley A modified single solution method for the determintion of phosphte in nturl wters. Anl. Chim. Act 27: Numnn, E Einige neue Gesichtspunkte zur Systemtik der Gewssertypen, mit besonderer Berucksichtigung der Seetypen. Arch. Hydrob., 20: Nicholls, K.H. nd Pl. Dillon An evlution of phosphorus -chlorophyllphytoplnkton reltionships for lkes. Int. Revue ges. Hydrobiol. 63(2): Northcote, T.G. nd P.A. Lrkin Indices of productivity in British Columbi lkes. J. Fish. Res. Bd Cnd 13(4): Ogelsby, R.T Reltionships of fish yield to lke phytoplnkton stnding crop, production, nd morphoedphic fctors. J. Fish. Res. Bord Cn. 34: Omernik, JM Nonpoint source-strem level reltionships: A ntionwide study. EPA Ecologicl Reserch Series EPA-600/ U.S. Fnvironmentl Protection Agency, Corvllis Environmentl Reserch Lbortory, Corvllis, Oregon. 151 pp. Pce, M.L Zooplnkton community structure, but not biomss, influences the phosphorus-chlorophyll reltionship. Cn. J. Fish. Aqut. Sci. 41: Pulsen, S.G Primry productivity in selected Iow lkes. Unpublished Msters Thesis, Iow Stte University, Ames, Iow. Preps, E.E. nd P.H. Rigler A test of simple model to predict short-term chnges in the phosphorus concentrtion in lke wter. Verh. Internt. Verein. Limnol. 21:

91 86 Preps, E.E. nd D.O. Trew Evlution of the phosphorus-chlorophyll reltionship for lkes off the Precmbrin Shield in western Cnd. Cn. J. Fish. Aqut. Sci. 40: Pridmore, R.D., W.N. Vnt nd J.C. Rutherford Chlorophyll-nutrient reltionships in North Islnd lkes (New Zelnd). Hydrobiologi 121: Prior, J.C A regionl guide to Iow lndforms. in Iow Geologicl Survey Eductionl Series #3, pp (pub. by the Stte ofiow, Des Moines). Rsmussen, J. B., L. Godbout nd M. Schllenberg The humic content of lke wter nd its reltionship to wtershed nd lke morphometry. Limnol. Ocenogr. 34(7): Rwson, D. S Some physicl nd chemicl fctors in the metbolism oflkes. Problems of Lke Biology. Am. Assoc. Advnc. Sci., Pub. No. 10, pp Rwson, D. S A comprison of some lrge lpine lkes in western Cnd. Ecology 23: Rwson, D. S Men depth nd the fish production of lrge lkes. Ecology 33(4): Ryder, R.A A method for estimting the potentil fish production of north-temperte lkes. Trns. Amer. Fish. Soc. 94: Skmoto, M Primry production by phytoplnkton community in some Jpnese lkes nd its dependence on lke depth. Arch. Hydrobiol. 62(1): Srtory, D. P., nd J. V. Grobbelr Extrction of chlorophyll!l from freshwter phytoplnkton for spectrophotometric nlysis. Hydrobiologi 114: Schindler, D. W Fctors regulting phytoplnkton production nd stnding crop in the world's fresh wters. Limnol. Ocenogr. 23(3): Siml, J., M. A. Lge, nd I. Inglesis Second derivtive ultrviolet spectroscopy nd sulfmic cid method for determintion of nitrtes in wter. J. Assoc. Off. Anl. Chern. 68: Smith, V.H Nutrient dependence of primry productivity in lkes. Limnol. Ocenogr. 24(6): Smith, V.H The nitrogen nd phosphorus dependence of lgl biomss in lkes: An empiricl nd theoreticl nlysis. Limnol. Ocenogr. 27(6): Smith, V.H Predictive models for the biomss of blue-green lge in lkes. Wt. Res. Bull. 21(3): Smith, V.H. nd J. Shpiro Chlorophyll-phosphorus reltions in individul lkes. Their importnce to lke restortion strtegies. Environ. Sci. Technol. 15(4):

92 87 Smith, V.H., E. Willen nd B. Krlsson Predicting the summer pek biomss of four species of blue-green lge (Cynophyt/Cynobcteri) in Swedish lkes. Wt. Res. Bull. 23(3): Spcie,A. nd S. L. Loeb Long-term trends in trophic stte of Indin Lkes (USA) following phosphorus reduction. Verh. Internt. Verein. Limnol. 24: Theinemnn, A Der Bu des Seebeckens in seiner Bedeutung fur den Abluf des Lebens im See. Verh. Zool. Bot. Ges., 77: U.S. Environmentl Dt Service Climtologicl Dt Annul Summry: Iow 89(13): U.S. Environmentl Dt Service Climtologicl Dt Annul Summry: Iow. 90(13): U.S. Environmentl Dt Service Climtologicl Dt Annul Summry: Iow 100(13): U.S. Environmentl Dt Service Climtologicl Dt Annul Summry: Iow. 101(13): U.S. Geologicl Survey Runoff nd precipittion dt for in Wter Resources Dt for Iow - Wter Yer U.S.G.S. Wter Dt Report 1A pp. U.S. Geologicl Survey Runoff nd precipittion dt for in Wter Resources Dt for Iow - Wter Yer U.S.G.S. Wter Dt Report 1A pp. vn Liere, L, O.F.R. vn Tongeren, L Breebrt nd W. Kts Trend in chlorophyll nd totl phosphorus in Loosdrecht lkes, The Netherlnds. Verh. Internt. Verein. Limnol. 24: Vollenweider, R. A Scientific fundmentls of the eutrophiction of lkes nd flowing wter, with prticulr reference to phosphorus nd nitrogen s fctors in eutrophiction. OECD Tech. Rep. DAS/CSU68, 27,159 pp. Vollenweider, R. A Possibilities nd limits of elementry models concerning the budget of substnces in lkes (Ger). Arch. Hydrobiol. 66: Wlker, W. W., Jr Empiricl methods for predicting eutrophiction. in Impoundments Report 4, Phse ill, Applictions Mnul. Tech. Rep. E pp. Wetzel, R. G LimnoloKY. W. B. Sunders, Phildelphi 2nd edition. 858 pp. White, E Lke eutrophiction in New Zelnd - comprison with other countries of the Orgnistion for Economic Co-opertion nd Development. New Zel. J. Mr. Freshw. Res. 17:

93 88 ACKNOWLEOOEMENTS This project ws supported in prt by the Iow Agriculture nd Home Economics Experiment Sttion (Project 2823). I wish to thnk Dr. Roger W. Bchmnn for his guidnce, ptience, nd confidence tht 1 could hndle such lrge project. My pprecition is lso extended to the members of my committee, Dr. Willim G. Crumpton nd Dr. Robert C. Summerfelt, who helped me through the referrl of journl rticles nd extended converstions. I m lso indebted to Tom Loughn of the ISU Sttisticl Lbortory for his tedious help with sttisticl nlyses. I would lso like to thnk severl people for field nd lbortory ssistnce; Lrry nd DrleneHtch, Timothy Hoymn, Pul Prueitt, Evelyn Giser, Michel Birminghm, Chrles Brun, John Degn, nd Todd Royer. Thnks should lso be extended to Dr. Robert Cruden, Acting Director of the Iow Lkeside Lbortory, for llowing me to use the lbortory during my excursions to tht prt of the stte, nd to the Wehrspnn fmily for providing excellent fcilities for my use t the Iow Lkeside Lbortory. Extended discussions with Dr. Kenneth Lng lso provided vluble insight I would lso like to thnk Dr. Richrd V. Bovbjerg for tht converstion in the summer of 1988 which turned my studies towrds qutic ecology, move tht I hve never regretted. I would like to extend thnks to the mny prk rngers nd prk users who helped me with informtion bout recent lke history. Thnks lso to the numerous lke mngers who sent me ll the current informtion bout the lkes tht I surveyed, nd to Don Bonneu, Mrion Connover, nd Lrry Mitzner of the Iow DNR for their dvice nd encourgement. I would especilly like to thnk my fmily nd my close friends for their support during this project This work is dedicted in memory of my fther.

94 89 APPENDIX A. LAKE SURVEY MEANS AND INDIVIDUAL LAKE DATA Appendix A.l 1979 Lke Survey Summer Mens The dt in the following tbles represent the lkes included in the 1979 Clen Lkes Survey tht were used for comprison with the 1990 dt. Although tested for in 1990, summer mens for inorgnic suspended solids nd totl nitrogen concentrtions were not vilble for the 1979 survey. Abbrevited county nmes re given fter the Silver nd Wilson lkes in order to differentite them. Specific lke informtion is given in Appendix A.3.

95 Secchi Totl Totl Lke Disk Depth Suspended Chlorophyll Phosphorus Nme (m) Solids (mgll) (mglcu. m) (mglcu. m) Ahqubi Anit Arbor 0.5 2l.4 6l ArrowhedSAC Bdger l Beeds l Big Creek Big Spirit l Blckhwk Bobwhite Briggs Woods Center Centrl Oer Cold Springs 0.9 1l Corneli l.4 Crwford Crk l Crystl l.9 Drling Dimond Dog Creek Don Willims Est (Osceol) Est Okoboji Ester Eldred-Sher Five Islnd Geode l GeorgeWyth Green Cstle l Green Vlley Hnnen Hickory Grove Hickory Hills leri Indin Inghm l l Iow Kent Prk Keomh l Lcey-Keos LittleSiouxPk 2.6 l Little Spirit Little Wll Lost Islnd Lower Gr McBride

96 Secchi Totl Totl Lke DiskDeptb Suspended Chlorophyll Phosphorus Nme (m) Solids (mgll) (mglcu. m) (mglcu. m) Mnteno l Mripos Medow Mimi Minnewsht Moorehed Monnn Tril Nelson Nine Egles North Twin Oldhm Orient l.8 Otter Creek Ottumw Lgn Phoj Pierce Creek Plesnt Creek Pollmiller Pririe Rose Red Hw Rock Creek Rodgers Prk Silver (Del.) Silver (Dick.) Silver (Plo A.) Silver (Worth) Slip Bluff Smith Spring Storm Swn Thyer Three Fires Trumbull Tuttle Union Grove Upper Gr Upper Pine Viking Wpello West Okoboji WillimsonPd Willow Wilson (Lee) Wilson (Tylor) Windmill YenRouGis

97 92 Appendix A Lke Survey Mens The following tbles hve been condensed for the convenience of the user. Prmeters for ech lke hve been orgnized so tht ech will pper in the order in which they were presented in the text. The following orgniztionl scheme cn be used to locte prticulr dt for ech individul lke. Row I Row 2 ColumnA: ColumnB: ColumnC: ColumnD: ColumnE: ColumnF: ColumnG: ColumnH: Column I: ColumnA: Column B: ColumnC: ColumnE: ColumnG: ColumnH: Column I: Secchi Disk Depth (m) Totl Suspended Solids (mgll) Chlorophyll (mglcu. m) Totl Phosphorus (mglcu. m) Inorgnic Suspended Solids (mgll) Totl Nitrogen (mgll) Lke Origin (Artificil or Nturl) Therml Strtifiction (Prtil = t lest once during the summer) Loction with respect to the Des Moines g1cillobe (On or Oft) Men Depth (m) Mximum Depth (m) Mximum Effective Length (m) Mximum Effective Fetch (m) Wtershed Are (b) Lke Are (h) Wtershed Are to Lke Are Rtio Informtion bout the individul smpling dtes cn be found in Appendix A.3.

98 93 2 Y = X r-squred = 0.94 t:l E c n co co -s 1 >- in c II) C Ci u Q. 0 Ell Opticl Density t 650 nm Figure 42. Chlorophyll correction cwve for 1990 lke swvey dt During the first six weeks of the 1990 swvey, chlorophyll opticl densities were mistkenly red t 650 nm insted of the required opticl density of 665 nm. For the rest of the swvey, opticl densities were red t both 650 nm nd 665 nm nd regression ws mde to see if one could dequtely predict the 665 nm vlue from the 650 nm mesurement Although chlorophyll fluoresces t 665 nm nd there is no biologicl reson for the two wvelengths to be correlted, the 650 nm wvelength ws pprently close enough to the 665 nm pek to chieve good correltion (Figure 42). Chlorophyll vlues for the first six weeks were clculted using the eqution given bove, while vlues for the rest of the survey were clculted directly using the mesured 665 nm opticl densities.

99 94 Lke Nm A B C D E F G H I Ahqubi Artificil Yes Off Anit Artificil Yes Off Arbor Artificil Yes Off Arrowhed Artificil Prtil On Bdger Artificil Yes On Beeds Artificil Yes On Big Creek Artificil Yes On Big Spirit" Nturl No On Blckhwk Nturl No On Bobwhite Artificil No Off Briggs Woods Artificil Yes On Center Nturl No On Centrl Artificil Yes Off Ger Nturl No On Cold Springs Artificil Yes Off Corneli Nturl No On Crwford Ck Artificil Yes Off Crystl Nturl No On Drling Artificil Yes Off Dimond Artificil Yes Off Dog Creek Artificil Yes Off Don Willims Artificil Yes On Est (Osceol) Artificil Yes Off Est Okoboji Nturl Pcntil On

100 95 Lke Nm A B C 0 E F G H I Fster Artificil Yes Off Eldred-Sher Artificil Yes On Five Islnd Nturl No On Geode Artificil Yes Off George Wyth Artificil Prtil Off Green Cstle Artificil Yes Off Green Vlley Artificil Prtil Off Hnnen Artificil Yes Off Hickory Grv Artificil Yes On Hickory Hills Artificil Yes Off Icrl Artificil Yes Off Indin Artificil Yes Off Inghm Nturl Prtil On Iow Artificil Yes Off Kent Prk Artificil Yes Off Keomh Artificil Yes Off Lcey-Keos Artificil Yes Off Little Sx. Pk Artificil No Off Little Spirit Nturl No On Little Wll Nturl No On Lost Islnd Nturl No On Lower Gr Nturl No On McBride Artificil Yes Off Mnteno Artificil No Off

101 96 Lke Nme A B C D E F G H I Mripos Artificil Yes Off Medow Artificil No Off Mimi Artificil Yes Off MillCreek Artificil Yes Off Minnewsht Nturl Prtil On Moorehed Artificil Yes Off Mormon Tril Artificil Yes Off Nelson Artificil Yes Off Nine Egles Artificil Yes Off North Twin Nturl Prtil On Oldhm Artificil Yes Off Orient Artificil No Off Otter Creek Artificil Yes Off Ottum. Lgn Nturl No Off Phoj Artificil Yes Off Pierce Creek Artificil Yes Off Plesnt Crk Artificil Yes Off Pollmiller Artificil Yes Off Pririe Rose Artificil Yes Off Red Hw Artificil Yes Off Rock Creek Artificil Yes Off Rodgers Prk Artificil Prtil Off Silver (Del.) Artificil Prtil Off Silver (Dick.) Nturl No On

102 97 Lke Nme A B C D E F Q H I Silver(PloA) Nturl No On Silver(Worth) Nturl No On Slip Bluff Artificil Yes Off Smith Artificil Prtil On Spring Nturl No On Storm Nturl Prtil On Swn Artificil No Off Thyer Artificil Yes Off Three Fires Artificil Prtil Off Trumbull Nturl No On Tuttle Nturl No On Union Grove Artificil Yes Off Upper Gr Nturl No On Upper Pine Artificil Prtil Off Viking Artificil Yes Off Wpello Artificil Yes Off West Okoboji Nturl Yes On WillimsonPd Artificil Yes Off WIllow Artificil Yes Off Wilson (Lee) Artificil Yes Off Wilson(Ty1.) Artificil Yes Off Windmill Artificil No Off YenRouGis Artificil Yes Off

103 98 Appendix A Individul Lke Dt The following tbles contin ll the dt obtined for ech lke during the 1990 survey. Secchi disk depths were tken only once per smpling period, while the other wter qulity prmeters were tken in triplicte (three different sites on the lke, one being the deepest spot). Lke Nme (County) Smple Dte SECC = Secchi Disk Depth (m) TP = Totl Phosphorus (mg/cu. m) = Totl Suspended Solids (mg/l) INORGSS = Inorgnic Suspended Solids (mg/l) = Chlorophyll (mg/cu. m) TN = Totl Nitrogen (mgll) = Temperture proftle (degrees C) beginning with surfce mesurement nd continuing every meter until the bottom ws reched = Field notes tken while smpling

104 99 Lke Ahqybi {Wrlen} My 29 SECC 1.4 TP INORGSS TN sunny, breezy, vlley lke, good tree coverge June 27 SECC 0.05 TP INORGSS TN mostly sunny, hot July 25 SECC 0.1 TP INORGSS TN overcst, light breeze Lke Anit (Css} June 6 SECC 4.0 TP INORGSS TN overcst, showers, gentle slopes, exposed July 9 SECC 0.9 TP INORGSS TN cloudy, breezy, smll bright green lge August 7 SECC 0.8 TP INORGSS TN prtly sunny light breeze Arbor l.k (Poweshiek). My 31 SECC 1.4 TP INORGSS TN mostly sunny. breezy. lots of ducks nd geese. protected from wind. possibly spring July 3 SECC 0.9 TP INORGSS TN cler, breezy July 31 SECC 0.7 TP INORGSS TN prtly cloudy. clm, pe soup

105 100 Arrowhed Ulke (S!;) June 14 SECC 3.5 TP INORGSS ILl 13.0 TN cler nd windy, good tree cover, sheltered from wind, sndy res, n old grvel pit July 14 SECC 2.0 TP INORGSS TN cler, breezy but lke clm, ded qutic plnts round shore August 13 SECC 2.0 TP INORGSS TN cler, breezy D!IDier Ulke QYebster) June 18 SECC 0.2 TP INORGSS TN cler nd breezy, steep slopes, good tree coverge, fudgecolored wter July 13 SECC 0.7 TP INORGSS TN cler, breezy August 11 SECC 1.9 TP INORGSS TN prtly sunny, light breeze, dying lgl mts long shore, l&ptidor on filter Heeds Lke ffrnokjiol My 28 SECC 0.9 TP INORGSS TN sunny, light breeze, gentle slope with trees U round June 29 SECC 0.7 TP INORGSS TN mostly sunny, clm July 27 SECC 0.1 TP INORGSS TN overcst, showers, breezy, high wter, scttered duckweed, lots of flood debris, muddy, rpid inflow

106 101 BiJ: Creek Lke (Polk) June 2 SECC July 7 August 5 SECC SECC 1.9 TP INORGSS TN mostly cloudy. windy. exposed 1.0 TP INORGSS TN mostly sunny. clm 1.3 TP INORGSS TN cler, breezy BiJ: Spirit Lke (Dickinson) My 26 SECC June 30 SECC July 28 SECC 5.0 TP INORGSS TN prtly cloudy. light breeze. very exposed 3.0 TP INORGSS TN cler. breezy, lrge unicellulr lgl bloom (Gleotrichi) 1.9 TP INORGSS TN l.l mostly cloudy. breezy l.l Blckhwk Lke (Sc) June 14 SECC July 14 SECC August 13 SECC 0.9 TP INORGSS TN sunny nd windy, flt terrin, whole plce reeks of ded fish 0.6 TP INORGSS TN cler, light breeze. smll-type Apbnjzomenon 0.2 TP INORGSS TN cler, light breeze, dtk nd umddy

107 102 Bobwhite lke <Wyne) June 8 SECC July 7 August 5 SECC SECC 0.05 TP INORGSS 'IN overcst, muggy, lots of trees, bttle with locl frmers for soil conservtion prctices, drined 2 yers go to get rid of crp, but sediment wsn't removed, thus very muddy wter 0.05 TP INORGSS 'IN mostly sunny, windy, muddy TP INORGSS TN prtly sunny, windy, muddy Briiis Woods lke (HmiltQ!l) June 2 SECC July 3 SECC July 30 SECC 1.5 TP INORGSS TN rin nd wind, good tree coverge 0.9 TP INORGSS 'IN cler, windy, lgl mts long shore 1.0 TP INORGSS TN prtly cloudy, windy ent lke (.DkkiD) My 26 SECC June 30 SECC July 28 SECC 0.9 TP INORGSS TN mostly sunny,light breeze, grdul slope, exposed to wind 0.7 TP INORGSS 'IN cler, breezy 0.8 TP INORGSS 'IN mostly cloudy, breezy

108 103 Centrl Lke (Jones) My 21 SECC 1.1 TP INORGSS N overcst, light breeze, gentle slopes, sprse tree coverge, lots of peninsul/islnds June 21 SECC 1.6 TP INORGSS N overcst, breezy, lgl bloom in progress (Aphnizomenon) July 20 SECC 0.9 TP INORGSS N rin, smll bright green lge CI Lk (Cerro Gordo) My 28 SECC 0.4 TP INORGSS N mostly sunny, clm, exposed, filters clogged June 29 SECC 0.3 TP INORGSS N mostly sunny, light breeze July 27 SECC 0.4 TP INORGSS N overcst, breezy, smll dull-green lgl bloom, some smll-type Apbniromenon CQld Sprinl:::Z Lke (CB s) June 6 SECC 1.3 TP INORGSS N overcst, sprinkles, firly well sheltered by trees July 9 SECC 0.9 TP INORGSS N mostly sunny, breezy August 7 SECC 0.6 TP INORGSS N prtly sunny,light breeze

109 104 Lke Corneli (Writl My 28 SECC June 29 SECC July 27 SECC Crwford Creek Yke d) June 14 SECC July 14 August 13 SECC SECC. Crystl LUre <Hncock) June 18 SECC July 13 SECC August 11 SECC 1.0 TP INORGSS N mostly sunny, cool breeze, exposed, hs been dredged 0.9 TP INORGSS N mostly sunny, breezy 0.4 TP INORGSS N overcst. breezy 1.5 TP INORGSS N sunny nd breezy, hilly but very exposed, no trees, lgl bloom on the rise 0.9 TP INORGSS N cler, breezy, smil Aphniwmenon 1.7 TP INORGSS N prtly sunny, breezy, tiny Aphnizomenon 2.0 TP INORGSS N sunny nd windy, cler to bottom, rolling terrin, exposed 0.6 TP INORGSS N cler, breezy, ertore present, lgl bloom (pe soup), stinks 0.5 TP INORGSS N mostly sunny, breezy, light cly colored wter, "fluffy" lgl bloom

110 105 Lke Orlio: <Wshinon) My 19 SECC June 24 July 22 SECC SECC 0.6 TP INORGSS TN prtly cloudy, windy nd choppy (SW wind), good tree coverge ll round, gently sloping medows 0.5 TP S INORGSS TN IS.4 IS.3 IS.2 cler nd wrm, muddy wter 0.05 TP INORGSS TN cler, breezy, muddy, wter level looks up hlf foot S Dimond Lke (Poweshiekl My 20 SECC June 25 July 23 SECC SECC 1m Creek Lke (O'Brien) June 13 SECC July 17 SECC August 15 SECC 2.1 TP INORGSS TN overcst, light breeze, lots of peninsuls/inlets, gently sloping, lots of Apb!!nj wmenon 0.4 TP S.4 INORGSS TN mostly cloudy, light breeze 1.0 TP INORGSS TN mostly sunny, light breeze S TP INORGSS TN cler, clm, steep bills but modest tree coverge, Aphnizomenon 0.8 TP INORGSS TN prtly cloudy, windy, smll-type.anblm., lgl mts long shore 0.8 TP INORGSS I.S TN prtly sunny, light breeze, lgl mts long shore

111 106 Don Willims Lke <Boone) June 2 SECC July 2 SECC July 30 SECC 0.4 TP INORGSS ILl 6.1 TN rin nd wind, generlly flt terrin TP INORGSS TN cler, windy 0.1 TP INORGSS TN mostly cloudy, windy, muddy Est Lke (t Osceol. Clrke County) June 8 SECC 0.7 TP INORGSS TN mostly sunny, breezy, decent tree coverge, possible fish kill, filmentous greens long shore July 8 SECC 0.7 TP INORGSS TN mostly cloudy, breezy, monster bss August 6 SECC 0.8 TP INORGSS TN cler, breezy, smll-type Aphnjzomenon bloom, sprse noxious blue-greens long shore Lke Est Olmboji {Dickinson) My 27 SECC 3.0 TP INORGSS TN mostly cloudy, breezy, exposed July 1 SECC 1.5 TP INORGSS TN showers, Apbnjzomenon bloom July 29 SECC 1.7 TP INORGSS TN prtly cloudy, breezy, lrge Apbnizomeuon bloom

112 107 Ester Lke (polk) June 2 SECC July 7 SECC August 5 SECC 0.6 TP INORGSS N prtjy cloudy, very windy, generlly exposed 0.8 TP INORGSS N cler, windy 0.7 TP INORGSS N mostly sunny, windy Ekked-Sherwood Lke CHncock) My 28 SECC. June 29 July 27 SECC SECC Five Islnd I.ke (Plo AIW> June 15 SECC July 16 August 14 SECC SECC 1.0 TP INORGSS N mostly sunny, light breeze, snke-like lke, gently sloping hills, generlly exposed 0.8 TP INORGSS N mostly sunny, breezy, Aphnizomenon bloom 0.5 TP INORGSS N ov,breezy,muddy,levelup,l\phnizod1enon TP INORGSS 1N mostly cloudy, breezy, flt terrin, good tree coverge, long nd thin lke, DNR killed fish 6 yers go 0.1 TP INORGSS N cler, windy TP INORGSS 1N cler nd windy,lrge pumping (dredging?) opertion ILl

113 108 Udce Geode <Hemy) My 19 SECC June 24 SECC July 22 SECC Geofie Wyth Lke (Blck Hwk) My 21 SECC June 21 July 20 SECC SECC Green Cstle Lke fmmbll) My 31 SECC July 3 SECC July 31 SECC 2.8 TP INORGSS TN steep bnks, covered with trees, lots of rocks 0.4 TP INORGSS TN mostly sunny, breezy, gryish wter 1.0 TP INORGSS TN prtly sunny, breezy, smll lgl bloom, some Aphnizomenon present, noxious blue-green stins long shore 1.4 TP INORGSS TN l.l overcst with sun, cool breeze, lke looks ltered, lots of rye plnted long shoreline, dredged?, modest coverge, low slope 1.0 TP INORGSS TN overcst, breezy, lrge lke expnsion 2-3 yers go 1.3 TP INORGSS TN mostly cloudy, light breeze 4.5 TP INORGSS TN prtly sunny, windy, exposed TP INORGSS TN cler, windy, lke cquired by govt. in 1977, no swimming/boting llowed, excellent wlleye fishing, cly-like soils long shore 1.9 TP INORGSS TN prtly cloudy, light breeze

114 109 Green Vlley Lke <Union) June 6 SECC July 9 SECC August 7 SECC 1.0 TP INORGSS TN sunny, clm. gentle slope, modest tree coverge 0.8 TP INORGSS TN prtly cloudy, windy, smll filmentous (smll Aphnjzomenon?) bloom, noxious blue-greens long shore 1.3 TP INORGSS TN mostly sunny,light breeze, bright green unicellulr, smll-type Aphnjzomenon, I...t>tidor on filter Hnnen lke (Benton) My 22 SECC June 22 SECC July 21 SECC 1.9 TP INORGSS TN cler, clm, gentle slopes, sprse trees 1.0 TP INORGSS TN overcst, clering 2.3 TP INORGSS TN ov,lightbreeze Hickmy Grove Lke (Stor.y) My 31 SECC July 3 SECC July 31 SECC 1.0 TP INORGSS TN cler, windy, exposed, ertol' (or fish cge?) present 0.7 TP INORGSS TN mostly sunny, breezy TP INORGSS TN cler, breezy. duckweed round perimeter

115 110 Hickory Hills Lke (Trn) My 22 SECC Jlme 21 July 20 SECC SECC Lke Icn (Adms) Jooe6 SECC July 9 SECC August 7 SECC Indin Ylke (Vn Buren) My 19 SECC Jooe 24 July 22 SECC SECC 2.9 TP INORGSS TN sunny, plesnt, clm lke, gently sloping hills, modest tree coverge, drined 5 yers go 0.6 TP INORGSS TN overcst, clm. genuine ertor present, smll Aphnizomenon nd unicellulr bloom 1.1 TP INORGSS TN cloudy, bright green lge TP INORGSS TN cler, breezy, gentle slopes, exposed, red DphniA. drined recently 1.2 TP INORGSS TN mostly cloudy, windy, lrge Apbpjzomenon bloom 0.8 TP INORGSS TN mostly sunny, clm. bright green unicellulr bloom. some red zooplnkton TP INORGSS TN sunny, not much wind, silty nd turbid, rnger sid ONR killed lke recently, thick trees, medium-sloped sides TP INORGSS TN cler, wrm prtly sunny, breezy TP INORGSS TN

116 III Inh!!ID Lke (Emmet) June 15 SECC 0.2 TP INORGSS TN prtly sunny, light breeze, flt terrin, good tree coverge July 16 SECC 0.3 TP INORGSS TN cler, clm August 14 SECC 0.3 TP INORGSS TN cler, breezy Lke Iow (Iow) My 20 SECC 2.4 TP INORGSS TN overcst, cool, gentle hills, S nd SE fces exposed June 25 SECC 0.6 TP INORGSS TN mostly sunny, clm July 23 SECC 0.9 TP INORGSS TN cler,clm Kt Prk Lke (Johnson) My 21 SECC 0.7 TP INORGSS TN overcst, cool, light breeze, gently sloping vlley lke, sprse tree cover June 21 SECC 0.3 TP INORGSS TN overcst, light breeze, smells like ded fish July 21 SECC 1.0 TP INORGSS TN overcst, sprinkles

117 112 Lke Keom:lb (Mhsk) My 20 SECC 1.0 TP INORGSS TN overcst, little wind, hevy trees June 25 SECC 1.1 TP INORGSS TN mostly sunny, wrm, Aphnjzomenon bloom July 23 SECC 1.0 TP INORGSS TN mostly sunny, light breeze Lke Lce-Keosqy Nn Buren) My 19 SECC 2.0 TP INORGSS TN windy but clm lke, nestled in steep bnks in hevy trees, ertor (or fish cge?) present June 24 SECC 0.3 TP INORGSS TN mostly sunny, cool July 22 SECC 0.4 TP INORGSS TN prtly sunny, light breeze, slightly muddy Little SiOllX Prk Idk (woodb) June 14 SECC 2.6 TP H.8 INORGSS TN prtly cloudy, light breeze, exposed round shore but surrounded by woods, sndy bottom, greenish wter, like grvel pit July 14 SECC 3.1 TP INORGSS TN cler, light breeze August 13 SECC 3.5 TP INORGSS TN prtly sunny, light breeze, cler to bottom, very cler wter

118 113 Little Sl2irit Lke (Dickinson} My 26 SECC June 30 SECC July 28 SECC 0.4 TP INORGSS TN clm, prtly cloudy, no slope into lke, exposed 0.3 TP INORGSS TN cler, breezy, resident sys tht bcteri is problem in locl lkes (ccording to DNR), fish kills mostly cloudy, breezy TP INORGSS TN Little Wll Lke (Hmilton) June 18 SECC July 13 SECC August 11 SECC Lost Islnd Lke (plo Alto} June 15 SECC July 16 August 14 SECC SECC TP INORGSS TN sunny, light breeze, exposed 1.5 TP INORGSS TN cler, breezy, cler to bottom, smll bright green lgl bloom 1.5 TP INORGSS TN prtly sunny, clm, cler to bottom, very cler wter, lots of clms TP INORGSS TN mostly sunny, breezy, flt terrin, exposed, sewge system instlled recentl y TP INORGSS TN cler, breezy, pe soup -lots of lge, lgl blobs, sndy bottom, lots of fom nd noxious blue-greens long shore 1.2 TP INORGSS TN mostly sunny, very windy, hevy fom long shore, Gleotrichi

119 114 Lower Gr Lke (Dickinson) My 27 SECC July I SECC July 29 SECC Lke McBride (Johnson) My 21 SECC June 21 July 21 SECC SECC Mnteno Lke (Shelby) JuneS SECC July 10 August 8 SECC SECC 0.5 TP INORGSS TN missing 0.4 TP INORGSS TN overcst, Aphnjwmeoon bloom. muddy 0.6 TP B.2 INORGSS TN prtly cloudy, windy, Apbniwmeuon bloom 1.0 TP INORGSS TN overcst, cool, steep bnks with dense trees, dm fce exposed 0.2 TP INORGSS B TN IB overcst, clm, muddy wter 1.0 TP INORGSS TN overcst, clm' TP INORGSS TN B sunny, breezy, steep hills but exposed, dense submergent vegettion ner shore TP INORGSS TN 1.3 probe broken overcst, windy, sprse overcst, Aphllnjzomeuon present, diverse qutic vegettion long shore O TP INORGSS 'IN mostly cloudy, light breeze, lgl mts long shore, cly-like bottom

120 115 Mripos Lke (Js.per) My 31 SECC July 3 SECC July 31 SECC 0.3 TP INORGSS TN cler, wndy, exposed, fir tree coverge, muddy like river 0.7 TP INORGSS TN cler, breezy 0.8 TP INORGSS TN mostly sunny, light breeze, smll bright-green lge Medow Lke (Adir) June 6 SECC July 9 August 7 SECC SECC Lke Mimi (Monroe) My 29 June 27 July 25 SECC SECC SECC 1.9 TP INORGSS TN overcst, cool, gentle slopes, exposed, drwn down hlfwy (11 feet) recently nd refilled. leri ws drwn down. new lke north of Dexter (Bever Lke), piles ofbrush everywhere 1.1 TP INORGSS TN mostly cloudy, breezy, smll bright green lgl bloom P INORGSS TN prtly sunny, light breeze, unicellulr lgl bloom P INORGSS TN cler, light breeze, exposed. mny swmped trees in hedwters 0.2 TP INORGSS TN mostly sunny, hot P INORGSS TN bzy,windy

121 116 Mill Creek Lke (O'Brien) June 13 SECC 2.2 TP INORGSS TN cler, breezyjow slope,modest tree coverge,buttments.np-rp July 17 SECC 0.9 TP INORGSS TN prtly cloudy, very windy but deep re protected from wind August 15 SECC 0.9 TP INORGSS TN mostly cloudy, light breeze, bright green unicellulr bloom Lke Minnewsht (Dickinson) My 27 SECC 2.0 TP INORGSS TN missing July 1 SECC 1.2 TP INORGSS TN overcst, Aphnjzomenon bloom July 29 SECC 1.6 TP INORGSS TN prtly cloudy. windy, Aphnjzomenon bloom Moorehed Lke d) June 14 SECC 0.8 TP INORGSS TN sunny, breezy, good tree coverge, hilly, mssive ApbnjmenQll bloom July 14 SECC 0.7 TP INORGSS TN cler, light breeze, smll lgl bloom August 13 SECC 1.1 TP INORGSS TN mostly cloudy, clm, bright green unicellulr bloom

122 117 Mormon Iril Lke (Adir) June 6 SECC 2.0 TP INORGSS TN overcst, clm, gentle slope, exposed, lgl bloom, lots of wterfowl droppings July 9 SECC 1.0 TP INORGSS TN cler, breezy August 7 SECC 1.7 TP INORGSS TN mostly sunny, light breeze Nelson Lke (Crwford) JuneS SECC 2.6 TP INORGSS TN sunny, breezy, nestled in vlley, good tree coverge, clen July 10 SECC 1.9 TP INORGSS TN probe broken wind nd rin, MyriQPbyllum ptches emerging everywhere August 8 SECC 1.4 TP INORGSS TN II.8 mostly cloudy, breezy, lke clered up, lgl mts long shore Nine Ed I.!!G (Dectur) June 7 SECC 1.9 TP INORGSS TN clm, overcst, well-sheltered with trees, reddish-brown hue to wter, fish cge/ertors present July 7 SECC 1.1 TP INORGSS TN cler, windy but clm on lke August 5 SECC 0.9 TP INORGSS TN prtly sunny, breezy

123 118 North Twin Lke {ClhOYD) June 14 SECC 0.7 TP INORGSS TN cler, wind from north, flt terrin, good tree coverge but exposed, smll unicellulr lge July 14 SECC 0.4 TP INORGSS TN cler, breezy, smll unicellulr rmy-green lge August 13 SECC 0.5 TP INORGSS TN cler, light breeze, bright green unicellulr bloom OWblml Lke (MQIlon) JuneS SECC 0.8 TP INORGSS TN sunny nd breezy, very exposed, in frmlnd, lots of stumps long shore re (in wter) July 10 SECC 0.7 TP S INORGSS TN probe broken overcst, breezy August S SECC 0.9 TP S 6S.6 IS.3 14.S 15.6 INORGSS TN S prtly sunny, breezy Lke Orient {Adir) lune6 SECC 0.6 TP INORGSS S.1 4S TN clering skies, windy, very exposed, mssive ApbnjzomeJlOD bloom, like pe soup, lots of tightly-pcked Lngmuir spirls July 9 SECC 0.3 TP INORGSS S TN S 25.0 cler, breezy August 7 SECC 1.0 TP IS.2 IS INORGSS S 20.S TN mostly sunny, light breeze, lots of zoopl. s compred to before

124 119 Otter Creek Lke (Trnl My 22 SECC June 22 July 20 SECC SECC Ottumw Lmon Lke (Wpello) My 20 SECC June 25 July 23 SECC SECC Lke Phqj (Lyon) June 13 SECC July 17 August 15 SECC SECC. 2.0 TP INORGSS TN cler, clm, gently sloping hills, sprse tree coverge, smll floting lgl mts (2 sq. in.) scttered bout 0.4 TP INORGSS TN probe broken overcst, thretening, breezy, lgl bloom 0.4 TP INORGSS TN overcst, showers, pe soup, mssive bright green lgl bloom 0.4 TP INORGSS TN overcst, clm wter, very yellowlbrown wter, steep short bnks, tll trees, blck nd slimy sediment, lots of ctfish cught 0.4 TP INORGSS TN mostly cloudy, breezy 0.3 TP INORGSS TN mostly sunny, clm, wter level up 2.1 TP INORGSS TN cler nd windy, wrm, very exposed, flt, frmlnd, filmentous greens long shore, Aplumjromenon in pelgic re 1.9 TP INORGSS TN prtly cloudy, very windy, fom on windwrd shore, otherwise. firly clen 0.5 TP INORGSS TN cler, light breeze, smll Al2bim., bright green unicellulr

125 120 Pierce Creek Pond (e) June 7 SECC July 8 August 6 SECC SECC Plesnt Creek Lke (l.inn) My 22 SECC June 22 July 21 SECC SECC TP INORGSS 1N thunderstorms pproching, generlly exposed, fish kill recently (due to temperture fluctutions?) 0.1 TP INORGSS N cler, breezy, nruddy TP INORGSS N mostly sunny, breezy, muddy 3.0 TP INORGSS N cler, clm nd sunny, sprse tree coverge, gentle slopes, lot of? probe broken mostly cloudy, windy TP INORGSS 1N TP INORGSS N overcst, clm, smll bright green lge (not very dense) Poll miller I Me (Lee) My 19 SECC June 24 SECC. July 22 SECC 2.2 ip INORGSS N missing 1.0 TP INORGSS N prtly sunny, wrm 0.9 TP INORGSS N prtly cloudy, breezy

126 121 Pririe Rose Lk!;l (Shelb) JuneS SECC 1.4 TP INORGSS N sunny, breezy, gentle slope, exposed, Aphnizomenon? July 10 SECC 0.5 TP INORGSS N overcst, showers, smll bright green lgl bloom August 8 SECC 0.8 TP INORGSS N mostly sunny, light breeze, unicellulr lgl bloom, red zoopl. Red Hw Lke (Lucs) June 8 SECC 3.5 TP ll INORGSS N overcst, breezy, showers, good tree coverge, somewht exposed jumbo Dphni July 7 SECC 3.2 TP INORGSS N cler, windy August 5 SECC 4.3 TP INORGSS N mostly sunny, breezy, silttion dms t hed, very cler wter, lots of Cldocer Rock Creek Lke (Js.per) My 31 SECC 0.5 TP INORGSS N prtly cloudy, windy, exposed, gentle slopes July 3 SECC 0.4 TP INORGSS N cler, breezy July 31 SECC 0.5 TP INORGSS N prtly cloudy, clm, dense smll bright green lgl bloom, smlltype Aphspizommon bloom

127 122 Rod Prk Lke (Benton) My 22 SECC June 22 July 21 SECC SECC Silver Lke (Delwre) My 21 SECC. June 21 July 20 SECC SECC 0.3 TP INORGSS TN mostly sunny, clm, wter looks muddy like river, shllow slope, ends exposed, trees elsewhere 0.05 TP INORGSS TN probe broken hilstorm., very nruddy 0.6 TP INORGSS TN overcst, light breeze, some duckweed present 0.5 TP INORGSS TN cool breeze, overcst, successionl vegettion levels, dense CertQPhyllum emergents, looks like river wter, crp, lke level down, springs plugged up with cly by locl officils, spillwy problems, good lke 2-3 yers go 1.5 TP INORGSS TN overcst, breezy, lrge duckweed mts, dense Certo.phyllum, bullrushes long shore TP INORGSS TN prtly smmy, breezy, dense I.&mIm over windwrd hlf of lke Silver Lke (Dickinson) My 26 SECC June 30 SECC July 28 SECC 0.6 TP INORGSS TN prtly cloudy, light breeze, lke is firly exposed 0.4 TP INORGSS TN mostly sunny, breezy 0.3 TP INORGSS TN cler, light breeze, sprse AphnilOmenon

128 123 Silver Lke (Plo Alto) June 15 SECC 0.2 TP INORGSS N sunny nd windy, flt terrin, exposed Ju1y 16 SECC 0.2 TP INORGSS N cler, breezy August 14 SECC 0.2 TP INORGSS N cler, very windy Silver Lk (Worth) My 28 SECC 0.4 TP INORGSS N cler, clm, yello-brown wter, lots of mrshy res, sediments (drk brownlblck) kick up when rowing, very flt terrin, filters clogged June 29 SECC 0.5 TP S INORGSS N mostly sunny July 27 SECC 0.8 TP 8S S INORGSS 6.S IS.5 1N prtly sunny, breezy, very cler to bottom Still Bluff Lke (Dectur) JuneS SECC 0.4 TP INORGSS N S overcst, fog, good tree coverge, like river wter, lots of Cnd geese, few flooded trees July 7 SECC 0.7 TP INORGSS S N S mostly sunny, windy August 5 SECC 0.9 TP INORGSS S N prtly sunny, breezy, cly-like colored wter

129 124 Smith Lke (Kossuth) June 15 SECC 0.2 TP INORGSS TN prtly cloudy, breezy, flt terrin, pririe prk lke, fluorescent green wter, grss crp introduced, weeds bsent July 13 SECC 0.3 TP INORGSS TN cler, breezy August 11 SECC 1.1 TP INORGSS TN mostly sunny, breezy, some noxious blue-greens long shore, tiny Aphnizomenon Sprinl:: Lke (Greene) June 2 SECC 2.0 TP INORGSS TN windy, rin, cler to bottom, flt terrin, good tree coverge July 2 SECC 1.7 TP INORGSS TN cler, windy, cler, to bottom July 30 SECC 1.4 TP INORGSS TN mostly cloudy, breezy Storm Lke (Buen Vi:2t) June 13 SECC 0.4 TP INORGSS TN clm, sunny, sucer lke July 14 SECC 0.7 TP INORGSS TN cler, clm August 13 SECC 0.3 TP INORGSS TN prtly sunny, breezy

130 125 Sw!Yl Lke (Crroll) JuneS SECC 1.4 TP INORGSS TN IS IS.7 IS.1 sunny, good tree coverge but generlly exposed, Avbnizomenon bloom July 10 SECC 0.3 TP INORGSS TN probe broken overcst. breezy. drizzle. smll bright green lgl bloom August 8 SECC 0.4 TP S INORGSS TN prtly cloudy. light breeze, bright green unicellulr bloom. smells like there's livestock opertion just beyond the dm Thl:er Lke (Union) JuneS SECC 1.3 TP INORGSS TN mostly sunny, breezy, tll trees, mrshy bckwters, reder sunfish July 8 SECC 1.0 TP INORGSS TN cler, breezy, deeper wter smells like hydrogen sulfide gs August 6 SECC 1.0 TP INORGSS S8.5 TN cler, breezy, short filmentous greens Lke Qf Three cires (I)':lor) June 7 SECC 0.4 TP S INORGSS TN prtly sunny, breezy, good tree coverge, Aphpizomeuon nd smll unicellulr lge July 8 SECC 0.6 TP INORGSS TN cler, windy, unicellulr lgl bloom August 6 SECC 0.4 TP INORGSS TN cler, light breeze, bright green unicellulr lgl bloom

131 126 Tnlmbull Lke (Cly) June 15 SECC July 16 SECC August 14 SECC Tuttle Lke (Emmet) My 28 SECC June 29 SECC July 27 SECC INORGSS TN prtly cloudy, breezy, sucer lke, very shllow, exposed 0.2 TP INORGSS TN cler, windy, lge-<:overed qutic plnts scttered on surfce, lots of fom long shore 0.1 TP INORGSS TN mostly sunny, very windy, hevy fom long shore TP INORGSS "IN sunny, cler, light breeze, exposed flot terrin, filters clogged 0.4 TP INORGSS TN mostly sunny, clm, bd winterkill, summerkill few yers go, wter just overflowed for the first time in 2 yers INORGSS "IN mostly sunny, windy UWQD. Grove Lke ITm) My 31 SECC July 3 SECC July 31 SECC 0.7 TP INORGSS TN cloudy, breezy, good tree coverge, dredge present 0.9 TP INORGSS TN cler, windy, dredge working t north end 0.9 TP INORGSS TN prtly cloudy, clm

132 127 Upper Gr Lke (Dickinson) My 27 SECC July 1 SECC July 29 SECC TP 3.2 INORGSS TN mostly cloudy, breezy, choked with vegettion, gently sloping 0.6 TP INORGSS 'IN overcst, Aphnjzomenon bloom 1.2 TP INORGSS TN prtly cloudy, windy, Aphnizomenon bloom Upper Pine Lke <Hrdin) My 30 SECC. June 26 SECC July 24 SECC 1.2 TP INORGSS 'IN cler, clm steep slopes, good tree coverge 0.3 TP INORGSS 'IN cler, wrm 1.5 TP INORGSS 'IN prtly cloudy, light breeze Vikjn Lke (Montomery) June 7 July 8 August 6 SECC SECC SECC 3.2 TP INORGSS 'IN S overcst, cool, gint lge/plnt mts, red Dphni, good tree coverge but exposed 0.7 TP 10S INORGSS S TN cler, breezy, duckweed Eckmn spirls, unicellulr lgl bloom 0.7 TP INORGSS TN IS S 14.1 mostly sunny, breezy, unicellulr, smll Aphpjzomeuon

133 128 Lke Wpello (Dvis) My 20 SECC June 25 SECC July 23 SECC Lke West Okoboji (Dickinson) My 27 SECC July 1 July 29 SECC SECC 0.9 TP INORGSS TN overcst, modertely sloping hills, forested, yellowlbrown wter 0.9 TP INORGSS TN mostly sunny, breezy 1.1 TP INORGSS Ll TN mostly sunny, clm 5.0 TP INORGSS TN U ILl ILl ILl ILl 11.1 ILl ILl llll1.11ll ll11.1 mostly cloudy, breezy 5.0 TP INORGSS TN overcst, breezy 4.5 TP INORGSS TN prtly cloudy, windy, some Aphnizomeooo present

134 129 Willimson Pond (!.ycs) June 8 SECC 0.1 TP INORGSS TN clering off. breezy, good tree coverge, duckweed long shore, nruddy wter July 7 SECC 0.05 TP INORGSS TN cler. breezy, muddy August 5 SECC 0.05 TP INORGSS TN mostly sunny, light breeze. muddy Willow Lke (Hrrison) JuneS SECC 2.8 TP INORGSS TN sunny, breezy, exposed, stumps nd trees in wter everywhere, good crppie lke, PotmQeton everywhere on shoreline July 10 SECC 1.4 TP INORGSS TN overcst, clm August 8 SECC 1.5 TP INORGSS TN mostly sunny, breezy Wilson Lke (Lee) My 19 SECC 2.6 TP INORGSS TN missing June 24 SECC 2.0 TP INORGSS TN mostly sunny, light breeze July 22 SECC 1.1 TP INORGSS TN mostly sunny, breezy

135 130 Wilson Lke {T}:lor) June 7 SECC 1.2 TP INORGSS TN mostly overcst, light breeze, shllow slope, exposed, lge like Three Fires, lots of filmentous greens long shore July 8 SECC 0.5 TP INORGSS TN cler, breezy, unicellulr lgl bloom, redlbrown lge long shore August 6 SECC 0.8 TP INORGSS TN cler, breezy Windmill Lke (I}:lor) June 7 SECC 0.7 TP INORGSS TN clm, overcst, gentle slopes, exposed, poor tree coverge, mssive Aphnizomenon bloom July 8 SECC 0.7 TP INORGSS TN cler, breezy, unicellulr lgl bloom August 6 SECC 0.7 TP INORGSS TN cler, light breeze, bright green unicellulr lgl bloom Yen Rou Qis Lke (Keokuk) My 20 SECC 4.5 TP INORGSS TN old qurry, hills on west side, opl-colored wter June 25 SECC 3.1 TP INORGSS TN IS.8 IS.2 prtly sunny, breezy July 23 SECC 4.0 TP S INORGSS TN S IS.0 cler, light breeze

136 131 APPENDIX B. PHOSPHORUS LOADING PARAMETERS The following tbles contin the dt used for predicting totl phosphorus in the section on phosphorus loding models. The first pge listed for given lke contins dt on the lke's morphometric vribles, which re used in the clcultions for both yers. The pge following contins clculted model vribles nd predicted totl phosphorus vlues for The third pge contins clculted model vribles nd predicted totl phosphorus vlues for 1990.

137 Lke Runoff (cm) Precip. (cm) Evportion Are Men Depth Wtershed Are Lke Volume Nme (]979/1990) ( ) (cm) (h) (m) (h) Origin (cu, m) Ahqubi 22.33/ Artificil Anit 22.53/ / Artificil Arbor 32.89/ / Artificil Arrowhed 14.94/ / Artificil Bdger 32.89/ / Artificil Beeds / Artificil Big Creek 32.89/ Artificil Big Spirit 23.70/ / Nturl Blckhwk / Nturl Bobwhite 22.33/ Artificil Briggs Wds / Artificil Center 23.70/ / Nturl Centrl 42.04/ Artificil Cler / Nturl Cold Springs / Artificil Corneli / Nturl Crwford Ck / Artificil Crystl / Nturl Drling 21.84/ / Artificil Dimond 32.89/ / Artificil Dog Creek 23.70/ / Artificil Don Willims 32.89/ / Artificil Est (Osceol) / Artificil Est Okoboji 23.70/ / Nturl Ester 32.89/ Artificil Eldred-Sher / Artificil Five Islnd 23.70/ / Nturl Geode / Artificil George Wyth 33.99/ Artificil Green Cstle 32.89/ Artificil Green Vlley 22.33/ / Artificil Hnnen 42.04/ Artificil W N

138 1979 Dt Annul Annul P Hydrulic P Sedimenttion Predicted Lke Wter Input Loding Flushing Rte Coefficient Totl P Nme (cu. m) (me / sq. m) (1 / yr) (1 / yr) (me / cu. m) Ahqubi Anit Arbor Arrowhed Bdger Beeds Big Creek Big Spirit Blckhwk Bobwhite Briggs Wds Center Centrl Cler Cold Springs Corneli Crwford Ck Crystl Drling Dimond Dog Creek Don Willims Est (Osceol) Est Okoboji Ester Eldred-Sher Five Islnd Geode George Wyth Green Cstle Green Vlley Hnnen w w

139 1990 Dt Annul Annul P Hydrulic P Sedimenttion Predicted Lke Wter Input Loding Flushing Rte Coefficient Totl P Nme (cu. m) (mg / sq. m) (1/ yr) <1/ yr) (mg / cu. m) Ahqubi Anit Arbor Arrowhed Bdger Beeds Big Creek Big Spirit Blckhwk Bobwhite Briggs W ds Center Centrl Cler Cold Springs Corneli Crwford Ck Crystl Drling Dimond Dog Creek Don Willims Est (Osceol) Est Okoboji Ester Eldred-Sher Five Islnd Geode George Wyth Green Cstle Green Vlley Hnnen w

140 Lke Runoff (cm) Precip. (em) Evportion Are Men Depth Wtershed Are Lke Volume Nme (1979/1990> (1979/1990> (cm) (h) (m) (h) Origin (cu. m) Hickory Gr / Artificil Hickory HIs / Artificil leri / Artificil Indin 21.84/ / Artificil Inghm 23.70/ / Nturl Iow 42.04/ Artificil Kent Prk 42.04/ Artificil Keomh / Artificil Lcey-Keos / Artificil Little Sx. Pk / / Artificil Little Spirit 23.70/ / Nturl Little Wll 32.89/ / Nturl Lost Islnd 23.70/ / Nturl Lower Gr 23.70/ / Nturl McBride 42.04/ Artificil Mnteno 14.94/ / Artificil Mripos 32.89/ / Artificil Medow 22.53/ / Artificil Mimi / Artificil Mill Creek 23.70/ /66: Artificil Minnewsht 23.70/ / Nturl Moorehed / Artificil Monnon Trl / Artificil Nelson / Artificil Nine Egles 22.33/ Artificil North Twin / Nturl Oldhm / Artificil Orient 22.53/ / Artificil Otter Creek 32.89/ / Artificil Ottum. Lgn / Nturl Phoj 23.70/ / Artificil PierceCreek 22.53/ / Artificil VJ Ul

141 1979 Dt Lke Nme Hickory Gr. Hickory His. Icri Indin Inghm Iow Kent Prk Keomh Lcey-Keos. Little Sx. Pk. Little Spirit Little Wll Lost Islnd Lower Gr McBride Mnteno Mripos Medow Mimi Mill Creek Minnewsht Moorehed Mormon Trl. Nelson Nine Egles North Twin Oldhm Orient Otter Creek Ottum. Lgn. Phoj Pierce Creek Annul Annul P Hydrulic P Sedimenttion Predicted Wter Input Loding Flushing Rte Coefficient Totl P (cu. m) (m!! / s. m)_ul yr) (] / yr) (mg / cu. m) v..> 0\

142 199() nt Annul Annul P Hydrulic P Sedimenttion Predicted Lke Wter Input Loding Flushing Rte Coefficient Totl P Nme (Cll, m) (mg / sq, m) (1 / yr) (1 / yr) (mg / ell. m) Hickory Gr Hickory HIs , ,9 Icri , Indin , ,1 Inghm Iow ,2 Kent Prk Keomh Lcey-Keos, , , LittleSxPk , Little Spirit Little Wll Lost Islnd , Lower Gr , McBride , ,2 Mnteno , ,0 Mripos ,5058 8, Medow Mimi ,7 MiJI Creek , Minnewsht \ ,3 Moorehed ,6 Mormon Trl Nelson , Nine Egles , , North Twin ,3162 0, Oldhm , Orient , ,7 Otter Creek Ottum, Lgn ,7 Phoj ,9171 6, Pierce Creek W -.J

143 Lke Runoff (cm) Precip. (cm) Evportion Are Men Depth Wtershed Are Lke Volume Nme (1979/1990) (1979/1990) (cm) (h) (m) (h) Origin (cu. m) Plesnt Ck / Artificil Pollmiller 21.84/ / Artificil Pririe Rose / Artificil Red Hw 22.33/ / Artificil Rock Creek 32.89/ Artificil Rodgers Pk / Artificil Silver-Del / Artificil Silver-Dick / / Nturl Silver-PloA 23.70/ / Nturl Silver-Worth / Nturl Slip Bluff 22.33/ / Artificil Smith / Artificil Spring / Nturl Stonn 23.70/ / Nturl Swn / Artificil Thyer 22.33/ Artificil Three Fires 22.53/ / Artificil Trumbull 23.70/ / Nturl Tuttle 23.70/ / Nturl Union Grove 32.89/ / Artificil Upper Gr 23.70/ / Nturl Upper Pine 32.89/ / Artificil Viking / Artificil Wpello / Artificil West Okoboji 23.70/ / Nturl Wi1limsonPd 22.33/ Artificil Willow / Artificil Wilson-Lee 21.84/ / Artificil Wilson-Tyl / Artificil Windmill 22.53/ / Artiticil Yen Rou Gis 21.84/ / Artificil V-i 00