THE DISTRIBUTTON AND ABUNDANCE 0F BENTHIC MACROINVERTEBRATES NEAR THE WESTERN SHORE OF LAKE ERIE Thesis for the Degree of M. S MICHIGAN STATE UNIVERSITY JACK EDWARD KELLY 1976?? ; - ' ~ -.‘.'._. - -——4‘ o O.~.‘N' ‘ sq ‘40!d‘|.'|“" .THESIS 0x 4! I Elillp 101:}! \llvl" l‘llllTNI'J-I’ci ' \ 0 I.- ‘L Qt.._ J . ), It ABSTRACT THE DISTRIBUTION AND ABUNDANCE OF BENTHIC MACROINVERTEBRATES NEAR THE WESTERN SHORE OF LAKE ERIE By Jack Edward Kelly Benthic macroinvertebrate populations were studied from'May, 1970 to June, 1975 in the vicinity of the Monroe power plant on western Lake Erie. Samples were collected with a Ponar dredge and subsequently washed free of sediments in a 0.5 mm diameter wire screen tub. Onedway analysis of variance and Tukey's multiple range comparison tests were used to assess apparent differences in densities, mean sizes, and age ratios. Although eight major taxonomic groups were collected during the study, two groups (Tubificidae and Chironomidae) comprised 99% of the total organisms. Some ramification of power plant Operation depressed benthic macroinvertebrate abundances in the plant's discharge canal and an adjacent, shallow tributary, but appeared to have no effect at the lake stations. Benthic macroinvertebrate densities and diversities, otherwise, seemed to be related to sediment size and other related environmental factors. THE DISTRIBUTION AND ABUNDANCE OF BENTHIC MACROINVERTEBRATES NEAR THE WESTERN SHORE OF LAKE ERIE BY Jack Edward Kelly A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Fisheries and Wildlife 1976 ACKNOWLEDGEMENTS I would like to express my appreciation to Dr. R. A. Cole for his help throughout this study and aid in preparation of the manuscript. Appreciation is also expressed to my graduate committee members, Drs. Charles Cress, Howard Johnson and Richard Merritt, for their advice and review of the manuscript. I would like to thank my fellow graduate students for their assist- ance with the rigorous field sampling. Iwould also like to thank Gary Ruezinsky, A. Lee Miller and Barb Hamming for their assistance in field sampling and laboratory work. Special thanks is extended to Marge Spruitt for her tubificid slide examinations during 1970 and spring, 1971. Thanks are also extended to George Jackson for his chironomid verification. This study was supported by a grant from the Detroit Edison.Com- pany to the Institute of Water Research at Michigan State University. Partial tuition funding was made possible through a grant from.the U. S. Environmental Protection Agency. To my wife, Peg, for her constant encouragement and help through- out this endeavor, I am deeply indebted. Appreciation is also extended to my relatives and friends for their interest and concern. ii LIST OF TABLES . LIST OF FIGURES INTRODUCTION . . . MATERIALS AND METHODS TABLE OF CONTENTS Description of the Study Area . . Power Plant Description . Field and Laboratory Procedures Data Analyses RESULTS . . . Environmental Characteristics of the Benthic Biotope Oxygen . Temperature . Carbon and Nitrogen Sediment Distributions . Benthic Macroinvertebrates Total Density and Biomass . Species Diversity and Equitability . Tubificidae . Chironomidae DISCUSSION . Changes in the Benthic Fauna of Lake Erie Environmental Effects Power Plant Operation Raisin River . Sediments LITERATURE CITED . APPENDIX.A . APPENDIX B . iii iv DJ [0me l4 l4 14 16 16 20 20 26 29 34 42 42 45 45 46 46 50 53 65 A1. A2. A3. A4. B1. B2. B3. B4. LIST OF TABLES Meteorological data for the study area from 1970 to 1974 O O O O O O C O O O O O O O O O O 0 Average density (no./m2) of benthic macroinvertebrates collected in the study area from 1970 to 1974 . . . . The coefficient of variation and relative variability of the sediments and macroinvertebrate abundance, and the average depth and slope in the study area, 1970 to 1975 . . . . . . . . . . . . . . . . . . . . . . . Density (no./m2) of benthic macroinvertebrates in 1930, 1961 and 1970 in the Raisin River area . . . . . . . Collection dates during the study period . . . Percent carbon in the sediments of the study area . . Percent nitrogen in the sediments of the study area 1975 sediment particle size . . . . . . . . . . . . Percent silt and clay in the sediments of the study area I O O C O O I O O O O O O O O O 0 O O O O O Explanation of abbreviations used in Appendix B . Tukey's multiple range comparison test for benthic macroinvertebrates . . . . . . . . . . . . . . . . . . Tukey's multiple range comparison test for Tubificidae . Tukey's multiple range comparison test for Chironomidae. iv Page 21 25 44 53 58 59 6O 64 65 66 69 73 LIST OF FIGURES Figure 1. Map of the study area . . . . . . . . . . . 2. Recent lake levels compared to the long-term mean 3. 10. ll. lake level over the past century (data from the United States Corps of Engineers and the United States Lake Survey) . . . . . . . . . . . . . . . . . . . . Map of the sampling stations during spring, 1975 . . . . Mean seasonal dissolved oxygen concentrations measured just above the water-sediment interface (values shown are means from four dates per season) ... . . . . . Mean seasonal temperatures measured just above the water-sediment interface (values shown are means from four dates per season) . . . . . . . . . . . . . . . . . Relation of the organic carbon and nitrogen concen- tration in the sediment to the amount of silt and clay in the sediment of the lake stations (spring, 1975) O O O O I 0 O O O O O O O O O O O O O O O O O O Generalized map of the sediments in the study area during spring, 1975 (map constructed from Table A4) . . Mean yearly biomass (mg/m2) in the study area, 1970 to 1974. Biomass is broken down seasonally by a) individual stations and b) combined stations . . . . Density (no./m3) of benthic macroinvertebrates in the study area. Tukey's test for significantly different stations marked with an asterisk are shown in Table B2. Vertical bars are mean densities for each year of the study, 1970 to 1974 or 1975 . . . . . . . . . . . Species diversity and equitability for benthic macro- invertebrates in the study area. Tukey's test for significantly different stations marked with an asterisk are shown in Table B2 . . . . . . . . . . . . . . . Relation of species diversity and number of species to mean sediment size during spring, 1975. Vertical bars represent one standard error either side of the mean . V Page 15 17 18 19 22 24 27 28 Figure 12. l3. 14. 15. 16. l7. l8. 19. 20. 21. Al. Density (no./m2) of Tubificidae and Limnodrilus hoff- meisteri in the study area. Tukey's test for signifi- cantly different stations marked with an asterisk are shown in Table B3 .r. . . . . . . . Density (no./m2) of Limnodrilus maumeensis and Limno- drilus cervix variant in the study area. Tukey's test for significantly different stations marked with an asterisk are shown in Table B3 . . . . . Relation of the mean number of tubificids to the carbon concentration and sediment size during spring, 1975. Vertical bars represent one standard error either side of the mean . . . . . . . . . . . . . . The mean size and ratio of immatures to adults for Tubificidae in the study area. Tukey's test for sig- nificantly different stations marked with an asterisk are shown in Table B3 Density (no./m2) of Chironomidae and Chironomus sp. in the study area. Tukey's test for significantly different stations marked with an asterisk are shown in Table B4 Density (no./m2) of Procladius sp. and Coelotanypus sp. in the study area. Tukey's test for significantly different stations marked with an asterisk are shown in Table B4 Relation of the mean number of chironomids to the car- bon concentration and sediment size during spring, 1975. Vertical bars represent one standard error either side of the mean Relation of the mean number of individual species of Chironomidae to the sediment size during spring, 1975 Mean yearly density (no./m2) of individual species of Chironomidae at each station from 1970-1974; a) Chir- onomus sp., b) Procladius sp., c) Coelotanypus sp. and d) Cryptochironomus sp. Mean size of chironomids in the study area. Tukey's test for significantly different stations marked with an asterisk are shown in Table B4 . Relation of the length and dry weight for Tubificidae. Dry weight represents a total of 50 worms per sample . Relation of wet weight and dry weight of a) Tubific- idae and b) Chironomidae . . . . . . vi Page 30 31 32 33 35 36 37 38 39 41 54 55 Figure Page A3. Characteristic features for the most abundant species collected in the study area . . . . . . . . . . . . . . . 56 vii INTRODUCTION There has been an increasing concern about the changes that have occurred during past decades in Lake Erie. Dramatic changes in the benthic fauna probably more than any other event served to focus atten- tion on the degree of damage already caused to the western basin. Britt (1955) associated a 90% reduction in the mayfly population, over a few weeks time, with the depletion of oxygen from the bottom waters. Since then, Carr and Hiltunen (1965) have reported on the changes in the benthic community which occurred in western Lake Erie since Wright's (1955) sur- vey in 1928-30. The diversity of the macroinvertebrate benthic community has decreased to one dominated by a few species of Tubificidae, Chirom- idae, Gastropoda and Sphaeridae. The benthic macroinvertebrates are subject to many natural and artificial environmental factors. The effect of these factors are not independent of one another but may form complex interactions. Natural events that could have an effect on benthic abundances include water level changes, meteorological changes, changes in food availability (bacteria populations, phytoplankton papulations, other benthic animals and the sediment detritus base), changes in predatory fish populations, changes in the physical and chemical environment (mainly temperature and oxygen), and changes in the sediment size composition. Artificial factors which may have an effect include municipal and industrial wastes, dredg- ing and power plant operation (dike building, heated effluent and reduced oxygen beneath the plume). 2 The Monroe power plant, owned and operated by the Detroit Edison Company, has been the focal point of a comprehensive ecological sampling program.through which data for this paper were gathered. The objectives of this research are: l) to examine the distribution and abundance of the benthic macroinvertebrates that occur in the study area, 2) to analyze population changes over the duration of the study, and 3) to discuss the relative impacts of artificial and natural changes in the environment upon any observed changes in the benthic populations. MATERIALS AND METHODS Description of the Study Area The study area is located in the western basin of Lake Erie near the mouth of the Raisin River at Monroe, Michigan (Figure 1). The west- ern basin is a shallow, turbid body of water. Beeton (1961) attributes the high turbidities to wind-generated resuspension of bottom sediments, river discharge and, to a lesser extent, plankton densities. The pre- vailing southwesterly winds along with the interaction of the Detroit (95% of the drainage water entering Lake Erie) and Maumee (3%) Rivers generally cause the water along the western shore to circulate in a clockwise eddy (Hartley, gngL., 1966). Temperatures in the lake are generally quite uniform from tap to bottom because of the continuous mix- ing in the shallow basin. Secchi disc tranSparencies in the study area averaged between 1 and 2‘m. Water levels in the study area have been higher than the long term mean.during the study period from 1970 to 1975 (Figure 2). Water levels increased to a peak in late spring, 1973 and then began to retreat. At least a portion of this increase was related to an extremely wet fall in 1972, but precipitation patterns in the upper Great Lakes watershed probably influenced Lake Erie levels even more. Except for fluctuations in the total precipitation, meteorological parameters remained relatively constant for the duration of the study (Table 1). There are an average of twenty-three days per year with a sustained wind velocity of 51 km/hr. or more. The western shores of Lake Erie are subject to flooding when 3 Benthos Collection Stations: all-9 A ‘6 I Monroe 3,8,, E * Bay 4’. . , b‘o ’ ., Q75 *2 A> “V AKE / ERIE .5 er , Q . Plum x9 Creek K " A <7", *3\ Discharge 8 ‘ . I‘ll “\__ anal ' 4H .1 H I. 16;, La Plaisance Bawr 2? \ Figure 1. Map of the study area. .A>o>tam axmm moumum payee: ogu new mtoacflmcw mo mchu mououm conga: osu scum mumov >taucou umma ago to>o _o>o_ oxa. cams Etouumco_ ocu cu cutaneoo m_o>o_ oxm_ acooom .N otsmau mm ohm. ARE mum. «#2 Km. Ohm. m. .2 S. q. 2 m 3 .2 .2 1 Z .4 2 1 Z w a 2 2 a z m a. 2 .2 q. 2 w a 2 2 a 10 came. 6.37.9.6... . I \I/ \I/ \II x. I: \I I I I x I s I z s z s I a _ I I \ I s I s I I I \ I I \ I \ 1 Il\ /I..\ /I\\ II... II‘\ III\\ 4 (w 2'24: 19) wnioa ”NM NM anoqv smiaw .oOatoa onm_n_:m_ ago tam Utouot co woman atm m_metoz .mammto>m >_tmo> oto motamwu m .E_muuoo new sutozuom .umozuuu .cuDOmuw_ .ummuumo ..a.H "Luca: onto Eat» moatmao mo mcou CHM .chwum>tomoo mo tapas: any >n nooH>Ho moooam ocm mcowuoatwo use: $0 Eam tauuo> org me paw: Hana—amam .0gco .Ono_0h .o6to850u mo ucoEutmaon .m .3 on» Back mumou _ 3m: m~.m_ mm.oom .m.m m4 Nocwz acou_ama¢ com: com: .Jmm_ cu onm_ sot» mono >osum ozu tam oumo .muwmo_otoauoz ._ ®_omh 7 the lake level is high and prolonged periods of east to northeast winds prevail. The lake bottom of the study area is fairly uniform with relatively gentle slopes and a maximum depth of 6 m. Bottom slopes are steepest near Stoney Point (Station 1), a shoal off the mouth of the discharge canal (Stations 4 and 5) and along the dredged access channel to the Raisin River (Station 3). Stations 2 and 6 are located over the deepest water where the bottom slopes very gradually. Plum Creek (Station 7) is a relatively shallow, flat bottomed tributary to the discharge canal (Station 8) which contributes less than 1% to the volume flow through the discharge canal. The Raisin River (Station 9) and discharge canal (Station 8) are dredged to a depth of 7 m. The Detroit Edison Company dredged the discharge canal in 1969 prior to the study period. The U. S. Corps of Engineers have dredged the Raisin River each year of the study from mid-September to mid-October. At the beginning of the study period, the Raisin River was highly polluted, particularly with oxygen demanding municipal and industrial wastes. Certain aspects of the water quality in the river improved after May, 1972 when a new activated sludge waste treatment plant for Monroe, Michigan began Operating. The plant has operated continuously since 1972 except for two very brief interruptions from power failures. Power Plant Description The power plant is operated by the Detroit Edison Company at a full production level of 3150 megawatts, and requires cooling water at the rate of nearly 100 m3/sec. The first of four 788 megawatt units began operating in June, 1971 and the fourth unit was completed in May, 1974. Cooling water from the Raisin River (annual average flow of 17 malsec.) 8 and Lake Erie enters the plant through a 100 m long intake canal which is located one-half kilometer upstream from.the mouth of the river. At full production, virtually all the river water flows into the plant. Inside the plant, the water passes through a condenser where water temperatures are elevated about 10 C above ambient. The heated water then flows down a concrete conduit and enters the discharge canal about twenty minutes later. Less than 10% of the heat is lost as water passes through the 150 m wide and 2000 m.long discharge canal into the lake. The thermal plume from the discharge canal may extend 4 kilometers into the lake and moves with the wind over a wide arc in the discharge zone where surface water temperatures can be measured above ambient temperatures. Field and Laboratory Procedures Samples were collected from May, 1970 through June, 1975. Dupli- cate bottom samples were taken at each of the nine stations in the study area. Three collection dates per season were included in the analyses with the exception of spring, 1972, when.samples were collected on only two dates (Table A1). Midwinter sampling was not conducted because of hazardous weather conditions. Water temperature and dissolved oxygen were usually recorded.within a day of the benthic samples and sediment samples were usually collected once a season from 1970 through 1974. Sampling procedures were slightly modified during spring, 1975 to assess the representativeness of data collected from Stations 1 to 6 as compared to the whole study area. These changes included triplicate sampling at Stations 3, 6, 8 and 9 and eight random samples taken from both the discharge zone and the adjacent water body segment (Figure 3). The discharge zone was defined by that area covered by a recognizable plume at one time or another. Perhaps one-fourth of the discharge zone 1975 RANDOM SAMPLING STATIONS ¢ ¢ {)3 <>¢ o ¢¢0 0<>.<>¢o Ce” Monroe. ¢ ¢ , 0 ¢ ¢.¢n " r¢<><><>0<><>=° WV oo¢¢¢¢003° Plum 9 . .*§>al¢ O . ¢ {>46 Creek) Ham ¢ ¢ h’h‘g o o o .5. Dichhare a o‘e o <> <> on Cam »\»'\\¢<><>w ~.¢‘\¢¢‘\¢\¢¢¢w oxoohoo‘qocrom .¢¢\¢‘e‘e‘e‘e¢¢0m <><>¢¢\<>¢‘e<><><>m o¢¢¢¢¢0¢¢¢¢¢m c¢¢¢¢¢¢~¢¢¢¢m _<><>¢-¢o<>o¢¢<>¢m .¢¢¢¢¢¢¢¢¢¢¢w , §Ba,bc .¢o¢o¢éo¢¢¢m ¢ . ¢ . . ¢ 0 ¢ ¢ (we: Sampled Stations 0 ¢ ¢ ¢ 9 ¢ 9 ¢ 4’ 0"” Nan-Sampled Stations <5 4} ¢ ¢ ¢ ¢ ¢ ¢ ¢n99 Discharge-zone Stations ‘1 ¢¢¢¢¢¢2os .Kmn Figure 3. Map of the sampling stations during Spring, 1975- 10 will be covered by the plume at any one time. Three different dates were examined for bottom fauna while five collection dates of bottom samples were brought back to the laboratory for detailed sediment analysis. The Ponar dredge (520 cm2 sampling area) was used throughout the study and performed well in most of the substrates present in the study area (Hudson, 1970). Some difficulty was encountered in taking samples on compacted bottoms of clay or sand. Samples were placed in plastic bags aboard ship and taken ashore. If a sediment sample was needed, approximately 10% of the total sample was extracted and placed in a glass bottle. The bottom material was then transferred from the plastic bags to 0.5 mm diameter wire screen tubs (Tyler sieve number 32) and washed' free of sediments. The screened material, including the animals, was preserved in a 10% formalin solution and brought back to the laboratory. Organisme from all samples were subsequently hand sorted, identified and counted. Oligochaetes were measured to the nearest 5 mm, wet weighed, cleared in.Amman's lactophenol and later mounted in CMC (Turtox) mounting medium. Wet weights were not recorded in 1970 and 1971; therefore, a length-dry weight relationship was derived for these two years (Figure A1). A.con- version equation for arriving at dry weight from.the wet weight was developed to enable a biomass estimate for each sample (Figure A2a). Oligochaete identification under lOOX or greater magnification was carried to the specific level. All of the Oligochaetes examined belonged to the family Tubificidae. Nomenclature of the tubificids followed the work of Brinkhurst (1965) and Hiltunen (1967, 1973) with the exception of keeping Limnodrilus spiralis (Eisen) as a variant form of Limnodrilus hoffmeisteri Claparéde. 11 The larvae of the dipteran family Chironomidae (midges) were measured to the nearest 2mm, wet weighed and identified at the generic level. The head capsule or entire body of smaller specimens was permanently mounted and identified using Mason's (1968) and Usinger's (1971) keys. A wet weight-dry weight conversion equation was also developed for the midges (Figure A2b). Characteristic features of the four genera of Chironomidae and the six most abundant species of Tubificidae can be seen in Figure A3. A portion of the tubificids and chironomids sampled were broken or had distinguishing parts missing. These specimens were listed as "un- identifiables," but contributed to the total sample biomass and density. In samples where densities were extremely high, all organisms were counted, measured and weighed, but only representative portions of the samples were examined microscopically. The proportionate amount of each genus or Spe- cies was then related back to the total population count. Organisms which were infrequently encountered throughout the study area were identified only to the family level. These relatively rare organisms were not included in any statistical analysis, since they never comprised more than 1% of the density collected on any one date. The bottom sediments were transported back to the laboratory and examined for particulate size composition and carbon and nitrogen concene trations. The size composition of each sample was determined by a combi- nation of wet and dry sorting. Clay and silt were removed from the balance of the sediments on the basis of settling time after an aliquot is stirred vigorously in water (Cummins, 1962). Coarse materials that settled in less than 15 seconds were dried and sieved, using Tyler sieve numbers 5, 16, 28, and 60. The supernatant containing the clay and silt from the first separation was reagitated and again allowed to settle for 15 minutes. Those particles that settled during that period were defined 12 as silt. The remaining aqueous solution was siphoned off and allowed to settle for 24 hours. These settled materials were defined as clay. The mean sediment size of each sample was calculated by multiplying the mean size of the Tyler sieve by the corresponding percent that segment made up of the total. The division of the sediments into categories was based on their mean size using Wentworth's classification of the sediments (Welch, 1948). Chemical analyses of organic carbon and nitrogen were conducted on a Perkin-Elmer Elemental Analyzer (Model 240). Temperature and oxygen measurements were usually conducted biweekly during the ice-free season using a Y.S.I. oxygen meter which was calibrated against a mercury ther- mometer and Winkler determinations made at the surface. Data Analyses As a result of the observed differences between means, Bartlett's test (Snedecor and Cochran, 1967) was used to assess whether or not all the variance estimates being compared were estimates of the same total population variance. Results showed that significant differences occurred in a portion of the data.- To reduce the heterogeneity of variance, log transformations, log10(x + 1), were performed on all the density and bio- mass calculations (Elliot, 1971). A onedway analysis of variance was applied after transformation to test for differences at stations and seasons across the years of the study. Parameters examined included densities, biomass estimates, species diversity, species equitability (evenness), mean macroinvertebrate sizes and the age ratio of tubificids. Tukey's multiple range comparison tests were used to sort mean values at o<= 0.05 when differences were determined to be significant (o(= 0.05) in the analysis of variance. The coefficient 13 of variation (C = s/i, where s = the standard deviation and'i = the sample mean) was used to determine the relative amount of variation among the sediments and benthic papulation over the years of the study (Snedecor and Cochran, 1967). The benthic species diversity was measured on densities using Shannon's formula (Pielou, 1966): d a=A-§51(Ni/N) [log10(Ni/N)] where Ni = the number observed for each species, N = total number of all species grouped together and S = the number of different Species. The equitability index (the ratio of observed diversity to maximum diversity for the same number of species) was calculated from the formula: e - diversity/loglos, where S = the number of different species (Pielou, 1966). RESULTS Environmental Characteristics of the Benthic Biotope Queer; Oxygen concentrations in the study area outside the discharge canal remain close to saturation at all depths during the colder months of the year, but as water temperatures increase during the warmer months, bottom oxygen concentrations may drop to-half of the concentration found at the surface and less than 50% of the saturation concentration. All of the six lake stations and Plum Creek.had seasonally similar oxygen concentra- tions (Figure 4). The Raisin River carried a high organic load from municipal and industrial wastes during the first two years of the study. Oxygen concentrations in the river decreased almost to anoxic levels in early fall, 1970. Installation of a new waste treatment plant during late spring, 1972 apparently has increased oxygen levels in the river. The commencement of power plant operation in 1971 created immediate changes in oxygen concentration in the discharge canal. During early operation, a greater proportion of cooling water came from oxygen depleted river waters. As more lake water was drawn in later years and as the river water itself improved because of better sewage treatment, the mean seasonal oxygen concentration in the discharge canal approached saturation. Temperature Temperatures in the lake generally are quite uniform from top to bottom because of continuous mixing in the shallow basin. Some temporary l4 15 .AcOmoom can mount Lao» sot» memos otm czocm mo:_o>v oommtoucfl ucoEHoom tempo: 0;» o>0nm umsfi potamooe mcoaumcucoocoo com>xo oo>_0mmfio .ocOmmom coo: 444m. muff-4m . 025mm ZZZ/bl ZZZ/Al [ZZZ/.1 7831.0 VCZIO 9.78.610 I G 106.1. . I (- rH||%JrIIIA=w.s. T 0 Temp 1 A T 3 a n9. lrl—JI —l_l.r|—ldll —l’|(_\r_/T O 106 X 1 A romp 9 3 N. i 3 we a J51. .8 I 5 your V I. n I u 10¢ av .. I. $66 .I I 0 our m 0 .33— «missm 022mm ZZZ/.11 9787910 .: ocsmfim I O V I 6T6 go a ION? ) NSDAXO 03A1OSSI tour [at a: (Nonivxnivs % é gr G <5 33 m Q' 00 _. l6 stratification occurs when water temperatures rise above 20 C but this usually lasts less than a day. Seasonal bottom temperatures in the Raisin River and the lake varied by 1 or 2 C from each other (Figure 5). The bottom temperatures in the discharge canal and P1um.Creek have increased over the duration of the study as a result of power plant oper- ation. Most of the impact of the heated effluent was confined to the discharge canal and P1um.Creek. Bottom temperatures in the discharge zone of the lake were undifferentiable from adjacent lake waters. Carbon and Nitrogen The carbon and nitrogen content of the sediments is related to the size of the sediments (Figure 6); finer sediments have higher concentra- tions of carbon and nitrogen. The analysis of carbon and nitrogen con- centrations in the sediments reflects the combined variation in concen- tration per sediment size class and the distribution of sediments in the study area (Tables A2 and A3). The relatively high carbon and nitrogen values found at the inshore stations (7, 8 and 9) are caused partly by relatively large amounts of allocthonous plant remains and other organics in the sediments. Sediment Distributions The nearshore bottom of the study area was composed primarily of coarse, medium and fine sand (Figure 7). The relative amount of silt in the sediments increased at the deeper, offshore stations. The size of the sediments at the nine fixed sampling stations varied considerably in composition (Table A5). Stations 4 and 5 are located on the sandy shoal off the mouth of the discharge canal. Sediments at Stations 1 and 2 intergrade between silt, clay, sand and some pebbles. Station 3 is .53. uuuuu communes“ ucoefinomutoumz any o>oom umam nocammoe monouocoaeou .chmmom coo: «mZZDm [lb/.11 78310 022mm [ZZZ/.1 9787?...0 .Acommom can mount Lao» eat» some one czosm mo:_m>v rt rk 1V— I—N Twm. 1 l l l l a>'-'v h. N N I'— 3 I! n J.‘V 8 El d VV 3 Lu. cu.— Tmm F E“ T 5‘ i i E i— T. F. rt ivpll 1N Tom 0 fl N .34.”. uuuuu «wIZDm 023mm [[1 unsanm .m otsmam -1 IN SN it u 1v. W In a Imus. in V 13.1 in“ fimmua r F i— #— r‘i‘ rc— fin IV_) 1_N.n nmN1\ F i i iv— rpw [mm .v l8 100- ¢ ¢ e e e 9 e 9 9CF‘ ¢ Q :h. EHJ‘ e 9 0 ¢ — 70- U 4» 60- ¢ ¢ £ ¢ 5C?- 2 t 9 e- 40" i!) 30- Q 9 4 r :0760 \° 20— 44° ° ' o ¢¢ ¢ 10‘ I 9 e , §E%:" 439?¢ Q 77 l 1 l l I ‘ I 113 '2‘) ' 343 4J3 - Percent Carbon 1001 99 ¢ ¢ 9 4° ¢ QCP' ¢ ¢ >~ so— . . 2 7O 9 U . o a 60- 9 6 50 i :: . ° 2;; 4!) _ 3 ¢¢ 2.903 O . o\ 20 3" 4“° 9 1 '9‘ e ¢§ ‘9 1— I 1 r l [ JO .20 .30 Percent Nitrogen Figure 6. Relation of the organic carbon and nitrogen concentration in the sediment to the amount of silt and clay in the , sediment of the lake stations (Spring, I975). l9 SILT AND CLAY .MED AND FINE SAND .comse SAND Ensues ”‘0 { . “ l 737.. he; 3 e...“ ./ ‘ 3"} Figure 7. Generalized map of the sediments in the study area during Spring, 1975 (map constructed from Table A4). 20 predominantly sand, but is highly variable because of nearby Raisin River dredge deposits. Station 6 is located in deeper water where the gradually sloping bottom is covered with fine silt. Sediments in the Raisin River, discharge canal and the protected marshy shallows at Station 7 were composed of silt, clay and recognizable plant debris. Benthic Macroinvertebrates Total Density and Biomass Eight major taxonomic groups were present in the samples taken during the study period. Of all the organisms found, members of the Tubificidae and Chironomidae were the most common (Table 2). Tubificids were collected at all stations and contributed 83.2% of the total organisms. Chironomids were also collected at all stations but were less numerous (16.7% of the total organisms). In addition to the species of adult tubificids listed in Table 2, unidentifiable immature tubificids comprised about one-half the total tubificids collected during each year of the study. Random sampling conducted in 1975 at stations identified in Figure 3 produced no species which had not been collected in sampling conducted from 1970 through 1974. Chironomid larvae made up approximately 10 to 20% of the total benthic density at each station. In terms of biomass, this percentage remained somewhat the same except for Stations 5, 6 and 7 (Figure 8a). The occur- rence of considerable numbers of relatively large Chironomus spp. at these stations accounted for this shift in percentage. The yearly average spring biomass was higher than either the summer or fall biomass (Figure 8b). Total benthic biomass reached a low in summer and flhen increased again.in fall. A large portion of the summer decline can be attributed Table 2. Average density (no./m2) of benthic macroinvertebrates collected 21 in the study area from 1970 to 1974. Taxon 1970 1971 1972 1973 1974 MEAN Limnodrilus hoffmeisteri 300.1 57.7 137.4 57.8 98.6 130.3 Chironomus spp. 142.8 51.3 58.7 120.5 44.3 83.5 .L-.EE£!$§ (variant) 91.6 45.8 71.0 44.6 44.1 59.4 L: maumeensis 159.3 29.1 36.7 25.6 32.3 56.6 Procladius Spp. 80.6 25.5 36.3 16.1 7.7 33.2 L: Eéillé 57.9 17.2 2.7 8.3 8.1 18.8 .L- claparedianus 66.6 5.4 5.0 0.2 14.2 18.3 .L. udekemianus 20.9 12.4 40.7 8.4 8.3 18.1 Coelotanypus Spp. 19.3 20.9 14.7 6.3 11.4 14.5 Branchiura sowerbyi 26.8 3.61 5.5 6.1 4.2 9.2 L, profundicola 3.0 1.1 15.5 8.9 3.2 6.3 Potamothrix moldaviensis 17.4 5.1 3.7 1.8 1.0 5.8 Cryptochironomus Spp. 3.1 2.6 3.6 1.5 2.5 2.7 AulodriIusgpluriseta 2.9 0.5' 0.4 0.0 0.0 0.8 Potamothrix vejdovskyi 1.1 0.2 0.0 0.0 0.3 0.3 Aulodrilus americanus 0.2 0.4 0.4 0.0 0.0 0.2 Aulodrilus pigueti 0.7 0.0 0.0 0.0 0.0 > 0.1 Glossiphoniidae 0.01 0.04 0.04 0.02 .-0.02 0.03 Sphaeriidae 0.01 0.01 0.05 0.02 0.04 0.02 Gammaridae 0.00 0.01 0.02 0.01 0.01 0.01 Elmidae 0.00 0.00 0.00 0.00 0.04 0.01 Asellidae 0.00 0.00 0.01 0.01 0.00 0.01 Unionidae 0.01 0.01 0.01 0.00 '0.01 0.01 TOTAL 994.3 279.0 432.4 304.4 280.1 458.0 22 g? :5 Z 53 < 22 (O m- In CHIRONOMIDS I TUBIFICIDS TOTAL DIN 11105 CH1 IONOMlDS . ruomcros E MEAN ANNUAL BIOMASS (x 10’) SPRING SUMMER FALL Figure 8. Mean yearly biomass (mg/m2) in the study area, 1970 to 1974. Biomass is broken down seasonally by a) individual stations and b) combined stations. 23 to the absence of mddge larvae in the samples. The emergence of many adult chironomids reached a peak in late spring and early summer and continued, to a lesser degree, into early fall. Benthic macroinvertebrate densities were highest at most stations during the first year of the study (Figure 9). However, abundances at the six lake stations varied erratically from year to year with no consistent trend after 1970. The number of river animals generally appeared to increase during the study period, especially during the sum- 'mer and fall seasons. Densities in.Plum.Creek (Station 7) and the dis- charge canal (Station 8) steadily decreased during the study. Some facet of power plant operation apparently reduced densities, particularly from 1972 to 1975. Temporal variabilities of the sediments were calculated (Tables A2, A3 and A5) and compared to benthic macroinvertebrate populations from corresponding dates (Table 3). The depth and slape for each station.were also recorded. Spatial and temporal variability among the sediments appeared to be related mostly to sediment size composition, depth, bottom slope and exposure to wave action. Variability (as measured by the coef- ficient of variation) between replicates (spatial) and years (temporal) was calculated at several representative stations (2, 3, 4, 6 and 8). Those stations with a relatively high proportion of silt and clay in the sediments (Stations 2, 6 and 8) eXhibited much less temporal variability. These stations were also the deepest, had the least slope and were least affected by wave action. Replicated analysis of their sediments indicated that spatial variability was from one-half to one-eighth the temporal variability. Temporal variability was much greater among the stations composed of larger sediments (Stations 3 and 4). Both of these stations 3.11 2.0 4.0 3.0 2.0 DENSITY 4.0 LOG... 2.0 Figure 9. 24 SPRING o 7 7 ’9 ‘ SILNIAAEII e I I- e I a e a e FALL a a e ' 7‘ 7 1 2 3 5 6 7 8 9 4 STATION Density (no./m2) of benthic macroinvertebrates in the study area. Tukey's test for significantly different stations marked with an asterisk are shown in Table 82. Vertical bars are mean densities for each year of the study (1970 to 1974 or 1975). 25 _ m m a N m oao_m : m P m N o guano m a F m N m moumcnouta>c_otomz m m a _ N a >m_u ac. A__m : m m p N m comocu_z a m _ m N a coatmu o_am_tm> umoz o_nm_tm> ammo; o_nm_tm>. mzo_ep_5_m<_¢<> oo.o oo.o oo.o no.0 n_.o wo.o -.o mo.o m~.o AN-o_ xv uao_m o.n o.“ m._ m.m m.; m.m m.a m.m o.: Aev guano mm.o mm.o Fm.o -.o m~.o Nm.o am.o N~.o mN.o moumtamuto>c_otumz a~.o m~.o mm.o .m.o m~._ m_._ mm._ 00.0 .m.o >m_u new u__m m~.o m~.o ma.o mm.o mm.o am.F um.o mq.o ma.o comotu_z -.o -.o m~.o mm.o no.0 Na._ om.o oa.o mm.o coatmu m m A o m a m N _ m_nm_tm> mzo.hozum ozu c_ ago—m ocm suave ommto>m ago new .oocmncznm oumtnouto>c_otome new mucoemoom on» ma >u___nm_tm> o>_um_ot new co_um_cm> mo uco_ummmooo are .m o_nmh 26 are relatively shallow and exposed to greater wave action than other stations. Spatial variability between replicates was similar to temporal variability. In general, those lake stations with the least variable sediments, greatest depths and lowest slopes also had the highest, least variable benthic abundance. Species Diversity and Equitability Macroinvertebrate species diversity at all stations except the dis- charge canal varied erratically and revealed no recognizable trends (Fig- ure 10). Diversities at Station 9 and, to a lesser extent, Station 4 were lower than those found at the other stations. A significant impact of the plant discharge on macroinvertebrate diversity was suggested by the decline in diversity at Stations 7 and 8 over the study period during all seasons. This re3ponse was caused mainly by a redistribution of abundances among Species without a change in the number of species as borne out by the equitability indices. Diversities in P1um.Creek (Station 7) decreased significantly-over the study period during-the spring and summer seasons and the number of species that occurred in Plum Creek also decreased over the duration of the study. Sampling conducted in 1975 showed that diversity and the number of different species found at each station is related to the mean size of the sediments (Figure 11). As the mean size of the sediment decreases the diversity and the number of Species increases. This may partially explain the relatively low diver- sity seen at Station 4 during the previous years of study, since its sedi- ments were among the most coarse in the study area. The diversity indices at all stations were relatively low when compared to other benthic studies. The dominance of one species, Limnodrilus hoffmeisteri, at most of the stations sampled was the cause for the low values recorded. 27 .Nm o_omk ca czorm otm xmatoumm cm so“: noxtme mcoaumum ucotommap >_ucmoawacmam Lam umou mr>ox3h .motm >o3um or» ca muumtnouto>caotome oazucon Low >uH_HnmuN3ao ocm >uamto>an moaooam 7-nv_ b.4‘.h.mw N o m c ,.Au _h.4‘gum o n v 0 N p a b ca 44¢; AK J. 1'1 113 \I.L.I EICDEB muffin» C C daft...“ O O 2.5:; 62.5.... .o_ otamaa ALISHEAIG .cmoe ago mo . moan Lozuao Lotto ocmvcoum oco ucomotaoc mama .moauto> .mnm_ .mcatam meatao oNam ucoEanom :moe ou moauoam mo Logan: ocm >uamto>ao mofiooam mo coHum_om .__ otamam 28 OF SPECIES NUMBER 3525 \AEEV mum z mmu¢w> .5.” O.« 0.. _.0 5.0 _ ._ wirie . _ _ _ _. _ r p p _ _ 1:. .1 rec . / . a .. \ -«d a / /. I a; a 10.0 A a 1 4.0 U L.- S m .. he I. .— I. m; M .3 A 5.. rbgu .. 3.3.5 - . m Isl . 1.55332 no 1.. taxman m1 5.0 29 Tubificidae Tubificid abundances were responsible for most of the observed changes in the total benthic abundance (Figure 12). Abundances at Station 3 (dredge deposits) and Station 4 (shifting, sandy bottom) were highly variable. Power plant operation had a definite impact on the tubificids. The decline of tubificids in the discharge canal (Station 8) was caused mainly by the response of Limnodrilus maumeensis Brinkhurst and Cook (Figure 13). Limnodrilus hoffmeisteri, by far the most abundant species in the study area, appeared to be least affected by power plant production. Except for a drop off in summer, densities remained rela- tively constant throughout the study. An increasing trend in Limnodrilus hoffmeisteri abundance at Station 9 is the main reason for the Raisin River's increased benthic abundance. Random sampling conducted in 1975 showed that tubificid abundance is partly influenced by the size and organic carbon content of the sedi- ments. Aquatic Oligochaetes, like their terrestrial counterparts, are believed to indiscriminately ingest all sedimentary particles below a certain size and digest some fraction of these particles. The abundance of tubificids appears to increase as the percent carbon (food content) increases and the mean sediment particle size decreases toward a silty composition (Figure 14). This may explain some of the observed changes occurring at the various lake stations during the study period. Although tubificid sizes frequently changed significantly from year to year, the changes were generally without trend over the study period (Figure 15). The mean size appeared to significantly increase in the river during the last two years of the study. Part of the observed size fluctuations may be caused by a change in the ratio of juvenile to adult 30 .mm o_nmh ca czozm otm xmatoumm cm so“: noxtme mcoHumum ucotommao >_ucmoamacmam tom umou m.>ox:k .ooco >oaum ocu ca “LoumHoEmwoL m:_HtoocENu new omvaofimansh mo A~E\.ocv >uamcoo .~_ acumen ZO_._.<._.m ZO_._.<._.m o m v n N w m h o . m v C O m e 1 .35. . O . 2232.52. 4 9 . s .35. 0 cm! 32.3.— . s o m nu ma N GO muzzam . 28:25.0... 4 . U 322:... 002923....— . .A 02.53 10.32.52. :— 0039333. cu o‘5)01 AlISNElG 31 .mm o_nmh ca czosm ocm xmatoumm cm cu“: noxtme mcoaumum acotoemao >_ucmo«macmam to» umou m.>ox:k .mocm >oaum 0;» ca ucmfltm> xH>Lou m:_atooc2«4 new mamcooESmE m:_atn0ceau mo ANE\.ocV >uamcoo .m. acumen m w h ZOO—”(hum n N p m m h oZO—W-(h-vm a N p 1.. =2 a. --_-_ E: :. _____ _____ _____l .1--- __._— -_-_. _---_ _.__. ----_ __--_ -____ _.__= Q. 1 2 o 2 .3(5 (as as; J 9 = .mnm_ .mcacam maggot oufim ucoENoom new coaumtucoocoo contmo org ou moaoawanau mo Logan: some or» mo soaps—om .a. Seaman u4m<<EEv mN-fl Z “flu? 2032.“? mud... 33%.; . 5.... 0.. . .d . _Q.O __ r.. _ _ r _ _ _. A c _ . _ r . o L - w 3 . V N 1 n W N .13 “a I . a). 1 V W .4 Tom 1. a. 11* ammiaz .rlrfi:ll..ll. < 2091 0 flow 33 .mm m_nmh cw exacm who xmagoumm cm nu“: vmxgme mcoflumum ucmgowmav >_ucmu«mucm«m Lam umou m.>ox:k .mogm >vaum ocu ca omuauamgnsh Low mu_:vm cu magnumEEa uo oaumg vcm ouqm came och ZO_._-<._.w ZO_._.<._.m c h o n v ..o v a N w a o h a o =_ucmo«m«cm«m cam umou m.>ox:h .uoum >vabm ocu ca .am m350c0cacu new omvHEococano mo A~E\.ocv >uamcoo .0. mean“; 00 ON =_ucmoamwcmam tam umou m.>oxah .mocm >vaum ocu ca .am msaxcmuo_oou now .am moans—oocm mo ANE\.ocv >uamcoo .n_ otsmau 20...: 20.55 a m c n a p a a h a n v 0 O O 1 4415 do Catacegzfl 0 44(5 in 2.2.1.0.: « = 1 1 1w 1 _ 9 o o u =_____ _.___ _ ._ m 3 a 2 a N a S Buss—am .au lath-.5300“ u o Comiiam in 082330.: c 0 IA “‘ ‘ ““ “‘ I‘ ‘ ‘ __—— —-—— - - -I-| ‘ 1 - ll 0.“ 3.. O 2 —C& u in Can‘t-50.00“ O z _ 8 t a in lass-£06.: o‘901 AllSNBCI , .cooE ocu mo ova» cognac Lotto numncmum oco ucomotaoc meme _moauto> .mmm_ .mcatam madcap ouam ucoefivom new cofiumcucoocoo contmo ago on mnaeocotaso mo Logan: cmos ocu mo coaum_ox .m_ otzmwm 37 % CARBON/SAMPLE ’MEAN Sa<<E§ ”N...“ 252‘ oz«ncw mo census come on» $0 coHum_om u._._<<E§ an..." 235 ozuu at can .am mao>cmuo_oou Au ..am moans—ootd An ..am m380c0cwcu Am “Jam—nonm_ 50cm cowumum coma um onquOc0cacu mo moauoam .mana>wnca mo A~E\.o:v >uamcon >_Lmo> cmoz .ON otamam £3.52.” mzoZEm a n v n a — a a s o n v n u — a p m we ...._ run In gum AMI r m u r. 22:5 mzczfim a m c. m N — a a .m m m e. n N — an I? W Ir ..I._ IQ A [N L. m, < «an...» Fm (mm) Al Isnao (.mx) ALISNJO 40 Cryptochironomus spp., was most common in fine and medium sand and was found almost entirely on the sandy bottom at Station 4. Coelotanypus spp., also relatively low in abundance, occurred most commonly in the highly silty sediments of Station 6. Chironomus spp., by far the most abundant chironomid, was mostly present in bottoms ranging from fine sand to silt. Its densities were highest at Stations 3 and 5 (both silt-sand) and Station 6 (mostly silt). Procladius spp. did not have such distinct patterns of abundance, but did have relatively high densities at the sandy-silt Stations 1 and 2. Significant changes in the chironomid mean size rarely occurred in the lake throughout the study period (Figure 21). In contrast, the mean size of midges decreased during all seasons at P1um.Creek and the discharge canal. Mean sizes in the river fluctuated without trend. The comparatively high values seen at Station 6 and somewhat at Station 5 are the result of high populations of the relatively large Chironomus SPP- #1 SPRING E : I I “Ill . . g“ lull-” '" .. SUMMER m .. N I: 5 '2 FALL MEAN O 7 8 : | I!” I II I 5 IL. .I. :IQL “I 3 4 5 6 STATION Figure 21. Mean size of chironomids in the study area. Tukey's test for significantly different stations marked with an asterisk are shown in Table 83. DISCUSSION Changes in the Benthic Fauna of Lake Erie A comparison of studies undertaken by Wright (1955) in 1930 and Carr and Hiltunen (1965) in 1961 showed that significant long-term changes have taken place in the pOpulations of bottom dwelling organisms in western Lake Erie. Five stations located in the Raisin River area made up a portion of these two studies. Their reports indicated a sixfold increase in the number of Oligochaetes, a twofold increase in the number of midge larvae, a twelvefold increase in the number of finger- nail clams and a tenfold increase in the number of gastropods. Burrowing mayfly nymphs (Hexagenia sp.) were not abundant in 1930, but were present in moderate numbers at three of the five stations. Only four specimens were collected in 1961. The only wideSpread genera of midges in the west- ernmost part of Lake Erie were Procladius, Coelotanypus and Cryptochiron- 2935, Chironomus Spp. (the most abundant midge species during our study) was neither widely distributed nor abundant. Oligochaete Species of the genus Limnodrilus were extremely abundant in the mouth of the Raisin River. Additional studies by Beeton (1961), WOod (1963) and IJC (1969) generally confirm the changes and distribution of organisms observed in the western basin by Carr and Hiltunen (1965). Changes in the abundance and distribution of the benthic fauna within the study area from 1960 to 1975 were not as dramatic as those shown for the period from 1930 to 1960. Although benthic densities were not quite as high as those reported by Carr and Hiltunen (1965) in 1961, comparable 42 43 stations from the present study had relatively equal species composition (Table 4). By 1970 virtually 99% of all benthic macroinvertebrates were composed of four species of Chironomidae and eight species of Tubificidae. The Sphaeriidae, Gastropoda, Hirudinea and Amphipoda were rarely encoun- tered from 1970 to 1975 although moderate abundances were reported for 1960. Therefore, it appears that subtle changes in composition have con! tinued since 1960 to the present. Brinkhurst (1967) suggests that the proportion of Oligochaetes to other forms of life and the relative contribution of Limnodrilus hoff- meisteri may be a very useful guide to the degree of organic pollution. The four species of Chironomidae found in the study area were also clas- sified by Brinkhurst g£_gl, (1968) as tolerant of eutrophic conditions. The input of the Raisin and Maumee Rivers' organic wastes could have been partially responsible for the Species composition found over the duration of the study. However, the impact of these two rivers on the changes observed in the benthic abundances at the various stations appears to be negligible. No obvious gradients in.macroinvertebrate densities related to these two point sources materialized in the study. Benthic abundances were particularly high during the preoperational year (1970) of the study. The drOp in densities during subsequent years, other than in the discharge canal and Plum Creek, does not appear to originate from power plant operation. Remote reference Stations 1, 2 and 6, relatively unaffected by thermal discharge, also showed decreases in.benthic abundances from the high values recorded in 1970. Densities increased again in 1972, but values were still only 50% of those recorded in 197O.T It appears that 1970 was an exceptionally good year for the benthic organisms. Unfortunately, this kind of annual variation is one .mumb 02 u?» .moumv ocac co>o ommco>m.>_umo> m 0cm nonma— mos—nPG o _.o :._ o _.o m._ hzmumma u>Hb<4m¢ o m :m o m. .4 z o o m.o m.__ m.m m.o_ m.mw n.mm ~.mw hzmummm m>Hh<4m¢ o _ m_ mNN Nm: w:~ om_~ Nana mmm_ 24m: 0 o as m_m mum , «S Nmmm ::_J as N am II: o o o um_ o_m mm. mum. .__mm_ comm m an o_~ o s 0 ma 5 8 $2 . 38 o m a S: o o o: m_m :mm o:m mmm_ mm_: o m m. m_# 05m; _mm_ 0mm. cum. .mm_ 0mm. omm_ .owc omm_ cum. .mm. 0mm— macommxo: omnaeoc0cacu muomcuomw_o consaz coeumum vcm.cmo> .mocm co>a¢ .camamx men an abmm_ ucn .mm_ .omm_ ca moamtnomto>caotume uacucon co A~2\.ocv suamcmo .: o_nme 45 of the arguments against having only one year as a preOperational refer- ence for studying the impact of power plant operation. Environmental Effects Power Plant Operation The onset of power plant operation in.the summer of 1971 had a definite impact on the benthic organisms in the discharge canal and Plum Creek. The decrease in the number of tubificids at these two stations appears to be a negative response to increased temperatures. Oxygen iconcentrations were low in 1971, but as more lake water was drawn into the plant in later years, and as the river water itself seemed to improve because of better sewage treatment, oxygen concentrations approached saturation in the discharge canal.- Concurrent studies on the same area have shown a significant increase during the study period in the number of bottom feeding fish occurring in the discharge canal (unpublished data). Studies conducted on other power plants have also shown flhat certain species of fish tended to concentrate in the effluent-outfall area (Mount, 1969; Gammon, 1970; Neill and Magnuson, 1974). Predation, as determined by close examination of stomach contents for undigestible parts (e.g..setae), Showed negligible impact on tubificid numbers in the discharge canal and Plum Creek (Kenaga and Cole, 1975). Predation plays a much larger role in.the dynamics of the chironomids. Chironomidae (particularly Procladius spp. and Chironomus spp.) form a large percent of the food organisms occurring in the stomachs of fish captured during the study (Kenaga and Cole, 1975). The increased numbers of benthic feeding fish in the discharge canal and P1um.Creek may have caused a portion of the decrease in chironomid abundance at these two 46 stations. Size-selective predation by the fish may also have caused the reduction in the mean size of the chironomids. Increased velocities caused by the addition of pumping units over the study period may have contributed to the decrease in densities appar- ent in the discharge canal. Velocities average between 0.10 to 0.15 m/sec. at full production. However, benthic abundances also decreased in the shallow, protected waters of Plum Creek where current velocity changes appeared to be negligible. It would appear that some factor or combination of factors other than increased velocity is mainly responsible for the decrease in benthic densities in the discharge canal. Raisin River The benthic abundances in the Raisin River are much lower compared to the other stations. In general, the tubificids are known for their ability to survive in organically polluted streams and lakes. As long as some oxygen is available from time to time, and the poisonous products of anaerobic breakdown of organic matter and metabolic wastes do not accumu- late, then the rich food supply usually permits rapid growth of many tubificid species (Brinkhurst, 1971). The low abundances in the river 'may be caused by a complex interaction.between periods of low oxygen and toxic contaminents. The diversion of the river water through the power plant and the subsequent heating may have caused an intensified effect on the benthic macroinvertebrates in the discharge canal and Plum Creek. Sediments The abundance of tubificid species at the lake stations appears to be related mainly to the sediments or factors associated with sediment types such as slope, depth and exposure to wave action. Other environmental 47 factors such as oxygen and temperature remained relatively constant throughout the lake stations. The densities of tubificids and chironmmids are both related to depth. The abundance of tubificids increases in the deeper, offshore areas of a lake (Mozley and Alley, 1973; Brinkhurst and Jamieson, 1971; Kinney, 1972). The number of chironomids is inversely related to depth, with the greatest number occurring at the Shallowest depth (Thut, 1968). Although the Lake Erie water levels have risen during the past five years, the shallow, relatively uniform depth in the study area is not likely to vary enough for depth to directly influence the distribution of the tubificids and chironomids. However, minor variations in depth are probably related to the impact of wave action on sediment size composition. The variability of the sediments had an impact on benthic abundances at the lake stations. The depth and Slope of the bottom are related to the amount of silt at a particular station. Those lake stations with a high percentage of silt in the sediments were less variable over the duration of the study and also exhibited much less Spatial variability. Benthic abundances at these stations were relatively high when.compared to shallower, sandy sediments. The percent of organic carbon and nitrogen in the sediments (food availability) appears to have an impact on benthic abundances. Wachs (1967) showed that Oligochaetes would move into sediments with the highest nutritional potential in terms of organic carbon and nitrogen regardless of the texture of the sediment. In the present study, the carbon and nitrogen content of the lake sediments proved to be closely related to the sediment size. Mezley and Alley (1973), in their paper on southern Lake Michigan, also stated Oligochaetes were associated more with silty than coarse sediments. However, unpredictable abundances of tubificids 48 at "less preferable" locations frequently occurred throughout the study period. A.more detailed analysis of the type of food material available for the detritus feeding tubificids may be needed. Brinkhurst and Chua (1969) found that the free organic matter and the available bacteria may prove to be more directly related to tubificid abundance than either the physical or chemical factors. As a group, the chironomids appear to be related to sediment size, but when examined individually, the food habits and life histories of the species tend to dictate the type of sediment on.which they are found. Procladius spp. is primarily predacious feeding upon cladocerans, copepods, ostracods, tubificids and other chironomid larvae (Thut, 1968). Procladius Spp. is found at the surface of sediments composed of very fine sands. Chironomus spp. functions as a filter feeder, constucting a salivary net across the lumen of their mud-tubes and undulating their bodies to create a current through the tubes. Coelotanypus spp. was found mainly in the silty sediments at Station 6. Cryptochironomus spp. appeared to prefer sediments composed of medium sized sand particles. In summary, power plant operation decreased benthic abundances in the discharge canal and Plum Creek (either through a negative response to the heated effluent, increased predation or the impact of diverted Raisin River water), but appeared to have negligible impact on the six lake stations. Changes in the abundance of benthic macroinvertebrates at the lake stations appear to be related mainly to the sediments (size, variability and food content). Other environmental factors remained relatively constant throughout the study period. The discharge canal empties onto a brbad sandy shoal which may be one of the best places along the western shore such a thermal release could be made on the basis 49 of macroinvertebrate abundance. This sandy area is characterized by highly variable sediments, Shallow depths and increased wave action and is among the least suitable for benthic macroinvertebrates. LITERATURE CITED LITERATURE CITED Beeton, A. M. 1961. Environmental changes in Lake Erie. Trans. Amer. Fish. Soc. 90:153-159. Brinkhurst, R. 0. 1965. Studies on the North American aquatic oligo- chaets. II. Tubificidae. Proc. Acad. Natur. Sci. Philadelphia 117: 117-172. Brinkhurst, R. O. 1967. The distribution of aquatic oligocheates in Saginaw Bay, Lake Huron. Limnol. Oceanogr. 12:137-143. Brinkhurst, R. O. and K. E. Chen. 1969. A.preliminary investigation of some potential nutritional resources by three sympatric tubificid Oligochaetes. J. Fish. Res. Ed. Can., 26(10):2659-2667. Brinkhurst, R. 0., A. L. Hamilton and H. B. Harrington. 1968. Compo- nents of the bottom fauna of the St. Lawrence Great Lakes. Publ. Great Lakes Inst. Univ. Toronto 33:1-49. Brinkhurst, R. O. and B. G. M. Jamieson. 1971. Aquatic Oligochaete '2: the World. Oliver and Boyd, Edinburgh, Great Britain. 860 pp. Britt, N. W. 1955. Stratification in Western Lake Erie in summer of 1953, effects on the Hexagenia (Ephemeroptera) population. Ecol. 36:239-244. Carr, J. F. and J. K. Hiltunen. 1965. Changes in.the bottom fauna of western Lake Erie from.l930-l961. Limnol. and Oceanogr. 10: 551- 569. Cummins, K. W. 1962. An evaluation of some techniques for the collec- tion and analysis of benthic samples with special emphasis on lotic waters. Amer. Mid. Nat. 67:477-503. Elliot, J. M; 1971. Some Methods for the Statistical Analysis gf Samples 2f Benthic Invertebrates. The Ferry House, London, England. 148 pp. Gammon, J. R. 1970. Aquatic life survey of the Wabash River, with special reference to the effects of thermal effluents on popula- tions of macroinvertebrates and fish, 1967-1969. DePauw Univ., 65 pp. (mimeo.). Hartley, R. P., C. E. Herdenforf and M. Keller. 1966. Synoptic water' sampling survey in the western basin of Lake Erie. Proc. Ninth Conf. Great Lakes Res., Inter. Assoc. Great Lakes Res., Ann Arbor, Michigan. Pub. No. 15:301-322. 50 51 Hiltunen, J. K. 1967. Some Oligochaetes from Lake Michigan. Trans. Amer. Microscop. Soc. 86:433-454. Hiltunen, J. K. 1973. Keys to the tubificid and Naidid Oligochaete of the Great Lakes region. Great Lakes Fishery Lab., Ann Arbor, Michigan. Hudson, P. L. 1970. Quantitative sampling with three benthic dredges. Trans. Amer. Fish. Soc. 99:603-607. International Joint Commission (report to). 1969. Pollution of Lake Erie, Lake Ontario and International section of the St. Lawrence River. Volume 2 - Lake Erie. International Lake Erie Water Pollution Board and the International Lake Ontario-St. Lawrence Water Pollution Board. Kenaga, D. E. and R. A. Cole. 1975. Food selection and feeding relation- ships of of yellow perch Perca flavescens (Mitchell), white bass Morone chrysops (Rafinesque), freshwater drum.Aplodinotus grunniens (Rafinesque) and goldfish Carassius auratus (Linneaus) in western Lake Erie. Technical Report No. 32.5, Institute of water Research, Michigan State University, East Lansing. 50 pp. Kinney, W. L. 1972. The macrobenthos of Lake Ontario. Proc. 15th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res. p. 53-79. Mason, W. T. 1968. An introduction to the identification of chironomid larvae. Federal Water Pollution Control Administration, U. S. Department of the Interior, Cincinnati, Ohio. 89 pp. Mbunt, D. I. 1969. Developing thermal requirements for freshwater fishes.j_[_n Biological Aspects of Thermal Pollution, P. A. Krenkel and F. L. Parker, eds. Vanderbilt Univ. Press, Nashville. p. 140- 147. iMozley, S. C. and W. P. Alley. 1973. Distribution of benthic inverte- brates in the south end of Lake Michigan. Proc. 16th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res. p. 87-96. Neill, W. H. and J. J. Magnuson. 1974. Distributional ecology and behavioral thermoregulation of fishes in relation to heated efflu- ent from a power plant at Lake Monona, Wisconsin. Trans. Amer. Fish. Soc. 103:663-710. Pielou, E. C. 1966. Ag,Introduction.tg'Mathematical Ecology. Wiley, New York. 286 pp. Snedecor, G. W. and W. G. Cochran. 1967. Statistical Methods. Iowa State University Press, Ames, Iowa. 593 pp. ' Thut, R. N. 1968. A study of the profundal bottom fauna of Lake wash- ington. Ecol. Monog. 39:79-100. Usinger, R. L. 1971. Aquatic Insects gf_California with Keys £2_North American genera and California species. University of California Press, Berkeley. 508 pp. 52 Wachs, B. 1967. Die Oligochaeten-Fauna der Fliessgewasser unter besounderer Berucksichtigung der Beziehungen Zwischen der Tubificiden-Besiedlung und dem Substrat. Ingrinkhurst and Jamieson, 1971. Welch, P. S. 1948. Limnological Methods. McCraw-Hill Book Company, Inc., New York. 381 pp. Wood, K. G. 1963. The bottom fauna of western Lake Erie, 1951-52. Great Lakes Res. Div., Inst. Sci. and Tech., Univ. Mich., Publ. NO. 10, p. 258-2650 Wright, S. 1955. Limnological survey of western Lake Erie. U. 8. Fish and Wildlife Serv., Spec. Sci. Rept., Fisheries 139. 341 pp. APPENDIX A 53 06/24/75 Table Al. Collection dates during the study period. SPRING SUMMER AUTUMN 04/30/70 07/20/70 09/14/70 05/27/70 08/03/70 IO/l0/70 06/22/70 09/01/70 ll/07/70 05/01/71 07/08/7l 09/07/7l 05/17/71 08/03/7l 09/22/7l 06/15/71 08/26/7l 10/16/71 05/15/72 07/06/72 09/06/72 * * * * 08/01/72 09/28/72 06/17/72 08/l6/72 10/26/72 05/07/73 06/26/73 08/10/73 05/24/73 07/22/73 08/28/73 06/22/73 08/01/73 09/28/73 05/23/74 07/0l/74 09/05/74 06/05/74 07/18/74 09/18/74 06/20/74 08/0l/74 10/08/74 03/18/75 05/06/75 54 ’6: g . h- : Z 6 0 HI . 2 a . r :0937 1 T f _1_ 20 30 40 50 LENGTH(mm) Figure Al. Relation of the length and dry weight of Tubificidae. Dry weight represents a total of 50 worms per sample. 55 30 I\ o "} 30 +- 5 o 0.095. I— 20 0a” a v a: o 3 E ‘0 r=.996 a . O 0 50 ICC 150 200 WET WEIGHT (mg) 45 . E3 ’5 g . 30 o ,s‘ g 30 ’03. E *‘ 5:". ' . E >415 r = .987 g :3 o O C O 80 160 240 320 WET WEIGHT (mg) Figure A2. Relation of wet weight and dry weight of a) Tubifi- cidae and b) Chironomidae. 56 - IOOX Head capsule of Chironomus Sp. Head capsule of Procladius Sp. Station 6, 8/26/71 Station I, 8/26/7l sax IOOXT . Head capsule of Coelotanypus sp. Head capsule of Cryptochironomus Sp. Station 6, 8/26/7l Station 4, 7/8/7l I 3.1 '- i , 15:: ': \ ‘ 3.". -. ' '. ""7"..." ".231 no . ‘f.'.'°'.." m, 1*; 2'. , , Mj‘» 1,50 - .35. 9,1"1,/,'/{.:':- ’ Penis tube of Limnodrilus hoff- Penis tube of Limnodrilus maumeensis. meisteri. Station 6, 9723/72 Station I, 8/l/72 Figure A3. Characteristic features for the most abundant species collected in the study area. 57 1‘.$7I; g.::f?;.:. - : '5 {::}//:1 "2. h. " :0: .' 9 .‘ s ‘ f 0 I °.,.' ‘: I t ‘ ’u I‘.. o.-‘ O . o. D. ' :. / ‘ .1 . .5_ ~_.' “_ . ‘ ’., . - o ', I." ‘ ‘:.;;‘- n“. :.:.o:: ’.\ .. :‘ I. a 'va ,5. .\ .‘ . I-' .. ‘... . ._° . ,l . ‘. ‘ I" ’- }(. " .°-. .-‘ ‘..'¢.. '. “I ‘0',- QUSLZUZS'243°1‘; ‘.“;£. ' HEX JOQK 1' ‘ ' ° '} ,1 = , . I f Penis tube of Limnodrilus cervix Penis tube of Limnodrilus cervix variant. Station 5, 7/6/72 variant (side View). Station I, 6/20/74 a z ”" n .o_aEmm oco Eocm mum momma. mo:_m>m m~.m om.: mm.m No.~ .m._ mn.o w~.o mm._ mm.~ 24m: ozn .o_aEmm oco so.» new moon“. mo:_m>m .0.0 00.0 00.0 00.0 0..0 00.0 00.0 0..0 0..0 zamz 0z<00 00.0 00.0 3.0 3.0 2.00: 00.0 00.0 0..0 00.0 000\:0\00 .0.0 00.0 00.0 00.0 020000 00.0 00.0 00.0 0..0 000\0.\00 00.0 00.0 00.0 0..0 ...0 00.0 .0.0 0..0 00.0 240: 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0..0 00.0 0:0\..\.. 00.0 0..0 00.0 00.0 0..0 00.0 00.0 00.0 00.0 000\0~\00 00.0 0..0 0..0 00.0 as 00.0 .0.0 0..0 00.0 0:0\.0\00 00.0 00.0 00.0 0..0 00.0 .0.0 00.0 ...0 00.0 z<0z 00.0 .0.0 00.0 00.0 00.0 00.0 ...0 00.0 0..0 000\.0\00 00.0 00.0 00.0 00.0 00.0 .0.0 .0.0 0..0 00.0 000\00\00 00.0 00.0 00.0 .0.0 0..0 00.0 00.0 0..0 00.0 0~0\0.\00 00.0 00.0 00.0 00.0 0..0 ...0 0..0 00.0 0..0 z<0z 00.0 00.0 00.0 00.0 00.0 0..0 ...0 00.0 0..0 0.0\0.\0. 00.0 00.0 00.0 00.0 00.0 00.0 00.0 0..0 00.0 .0.0\00\00 00.0 00.0 00.0 00.0 00.0 ...0 .0.0 00.0 0..0 0.0\0.\00 00.0 00.0 00.0 0..0 .0.0 .0.0 .0.0 0..0 00.0 z<0z 00.0 00.0 0:. 00.0 .0.0 .0.0 .0.0 00.0 .0.0 000\0~\00 00.0 00.0 00.0 00.0 .0.0 .0.0 .0.0 0..0 00.0 000\00\00 .0.0 00.0 00.0 0..0 .0.0 .0.0 00.0 00.0 ...0 000\00\00 0 0 0 0 0 a 0 0 . 0000 02000<00 .motm .630 of mo mucosanom or: c.“ comotuac ucmotom .mm_u u—mm pcmm mcpm_hwmmmzfiw_wmmu¢mumm omumou mo_:cmco mo_nnoa oumo co_umum .0N.m 0.0.0.00 0005.000 000. .0< 0.000 61 0000000.. ..000 0.0 0.. 0.00 0.00 0.0 0.0 0.0 0\0 00 ..0 0.0 0.00 0.. 0.0 0.0 0.0 0\0 00 000..000 ..0 0.0 0.00 0.00 0.0 0.0 0.0 -\0 00 0.. 0.0 0.00 0.00 0.0 0.. 0.0 0.\0 00 ..0 0.0 0.00 0.00 0.0 0.0 0.. 0~\0 00 ..o ... 0.00 0.00 0.: 0.. 0.0 0\m 00 ..0 0.0 0.00 0.00 0.0 0.. 0.0 :~\0 00 0000000.. ..000 0.0 ..0 0.00 0.0 0.0 ..0 ..0 ~N\0 00 0.0 0.. ..00 0.. 0.0 ..0 0.0 0~\0 00 0.0 0.0. 0.00 0... 0.0 0.. 0.0 0\0 00 0.0 0.00 0.00 0.0. 0.. 0.0 0.0 0~\0 00 0000000.. ..000 0.0 0.. 0.00 0.00 0.0 0.. 0.0 0.\0 00 0.0 0.0 0.00 0.0 0.0 0.0 0.0 0~\0 00 0000000.. ..000 0.0 0.0 0.00 0.00 0.0 0.0. 0.0 0.\0 00 0.0 0.0: 0.00 0.00 0.: 0.0 0.0 -\a 00 0000000.. ..000 ..0 ..0 0.00 0.00 0... 0.0 0.0 0\0 00 0.0 0.0. 0.00 0.0. 0.. 0.0 0.0 0N\0 00 0000000.. ..000 ..0 0... 0.00 0.0. 0.. 0.0 0.0 -\0 00 0:0..000 0.. :.m~ 0.00 0.: 0.0 0.0 0.0 0.\0 :0 000..000 0.0 0.0 0.00 0.0 ... 0.0 0.0 -\0 00 mucmEEOu >m—u uZm tcmw Germ-Fflmmmxfim_wumumwumm OmLmOU mm—acmuo mO—nnum mama cO_umum ...0_0couv :< 0.000 62 0.0 0.00 0.0 0.0 0.0 0.0 0.0 0.\0 00. 0.0 0.00 0.0. 0.0 ..0 0.0 0.0 0~\0 00. ..0 0.0 0.00 ... ..0 ..0 0.0 0N\0 N0. ..0 ..0 0.00 0.0. 0.0 0.0 0.0 0.\0 00. 0.0 0.0. 0.00 0..0 0.0 0.0 0.0 0~\0 00. 0.0 0.0. 0.00 0.0. 0.. ..0 0.0 0~\0 00. 0.. 0... 0.00 0.0. 0.0 0.0 0.0. 0.\0 .N. 0000000.. ..000 0.0 ..00 0.0. 0.0 0.0 0.. 0.0 0\0 0.. ..0 0.0 ..0 0.. 0.0 ..0~ 0.00 -\0 0.. 0.0 ..0 ..0; 0.00 0.0 0.0 0... 00\0 ... 0000000.. ..000 ..0 0.00 ..0: 0... 0.0 ..N 0.0 0.\0 ... 0.. 0.00 0.00 0.0. ,0.0 0.0 0.. 0~\0 00. ..0 ... 0.00 0.0 0.0 0.0 ..0 0N\0 00. ..0 0.0 0.00 0..0 ..0 0.0 0.0. -\0 00. 0.0 0.0 0.00 0.00 0.0 0.0 0..0 0.\0 00. ..0 0.0. 0.00 0... 0.0 0.0 ~.. -\0 00. 0.. 0.00 0..0 0.0. 0.. 0.0 0.0 0~\0 00. 0000000.. ..000 0.. 0.0 0.00 0.00 ..0 0.0 0.. ~0\0 00. 0000000.. ..000 ..0 0.. ..00 0.00 0.00 ... 0.0 0\0 00 0.0 0.0 0.0. 0.00 ...0 0.0 0.0 0N\0 00 mucoEEOQ >m_u u__m pcmw o:.. 0:00 53.00: pcmw omcmoQ mu_:cm.o 00.nnom oumo co_umum zo_h_momzou hzmummm ...0.0000. 00 0.000 63 00.0 000000000 0 0 0 z < 0 0 z 0.\0 00. 00.0 000000000 0 0 0 z 0 0 0 z 0N\0 00 00.0000 00.00 m 4 0 z < m o z w.\m a: 00.0000 00.00 0 0 0 z < 0 0 2 0x0 00 00.0000 00.00 0 0 0 z < 0 0 z 0~\0 0. 00.0000 00.00 0 0 0 z < 0 0 z 0~\0 0. 00.0000 0m.0m m 4 0 z < m o z m~\m o 0.0 0.00 0.0 ..0 0.0 0.0 0.0 0~\0 00. 0.0 0.0 0.00 0.0. 0.0 0..0 0.0. 0\0 00. 0.. 0.00 0.00 0.0 0.. 0.. 0.0 0~\0 00. 0.0 0.00 0.00 0.0 0.0 ..0 0.0 0\0 00. 0.. 0.00 0.00 0.. ..0 ..0 0.0 0~\0 00. 000..000 0.0 0.00 0.00 0.0. 0.0 0.0 0.0 -\0 00. ..o 0.. 0.00 0..: 0.0 0.0 ~.o 0\m 00. 0000000.. ..000 0.0 0.0. 0.00 0.0 0.0 0.0 0.0 -\0 00. 00:0EEOU >0_u u__m ocmm 0:. 0:00 53.00: :00 00.00u 00.:cmcu 00_0000 ouma comumum z _h_momzou hzuum m ...0.0000. 00.0.00. .00000..00. 00.50 50.. 0:005 0.0 0000.. 00:.m>o .00000..00. oz. 50.. 0:005 0.0 0000.. 00:.0>0 .0.0500 0:o so.» 0.0 0000.. 00:.m>0 64 ~.mm 5.55 :..w w.mw m.m_ —.: m.m— «.0: 0.5m zpzu0 0;. mo 00:05.000 0:0 :. >m.o 0:0 u..0 0:00.00 .m< 0.00» APPENDIX B 65 Table Bl. Explanation of abbreviations used in Appendix B. Abbreviation Meaning TOTAL . . . . . Total macroinvertebrate density SHANN Shannon's Species diversity index EQUIT Equitability index TUBIF Tubificidae density LHOFF Limnodrilus hoffmeisteri density LMAUM Limnodrilus maumeensis density LCERV Limnodrilus EEEXEE variant density OSIZE Tubificidae mean size RATIO Ratio of immature to adult Tubificidae CHIRO Chironomidae density CHRSP Chironomus sp. density PROCL~ Procladius sp. density COELO Coelotanypus Sp. density CSIZE Chironomidae mean size a,b,c Years having the same small letter are 22$ signif- icantly different from each other ’ 66 Table 82. Tukey's multiple range comparison test for benthic macro- invertebrates. Variable Station Season l97O l97l I972 I973 l97h I975 TOTAL 3 Spring a a a a a b b b TOTAL 8 Spring a a a b b b b b TOTAL 9 Spring a a a a a b b b b b TOTAL l Summer a a a a b b TOTAL 2 Summer a a a a b b TOTAL 3 Summer a a a a b b TOTAL 6 Summer a a a a b b TOTAL 8 Summer 3 a a b b ‘ c c TOTAL 9 Summer a a a b b TOTAL 2 Fall a a a b b b TOTAL A Fall a a a a b b 67 Table 82 (cont'd.). Variable Station Season l970 l97l l972 l973 l97h l975 TOTAL 7 Fall a a b b b b TOTAL 8 Fall a a a a b b SHANN 3 Spring a a a a a b b b SHANN 8 Spring a a a b b b c c c d d d SHANN 2 Summer a a a a b b b b SHANN 8 Summer a a a b b b SHANN 4 Fall a a a b b b SHANN 8 Fall a a b b b EQUIT 3 Spring a a a a a b b EQUIT 8 Spring a a a a a b b b EQUIT 2 Summer a a a a Table 82 (cont'd.). 68 Variable Station Season l97O l97l 1972 1973 1974 I975 EQUIT 7 Summer a a a a b b b b EQUIT A Fall a a a a b b EQUIT 8 Fall a a b b b 69 Table 83. Tukey's multiple range comparison test for Tubificidae. Variable Station Season I970 l97l I972 l973 I974 l975 TUBIF 3 Spring a a a a b b b b c c c c TUBIF h Spring a a a a b b TUBIF 8 Spring a a a b b b b b TUBIF 1 Summer a a‘ a a b b b b TUBIF 2 Summer a a a b b b b TUBIF 3 Summer a a a a b b b b TUBIF 5 Summer a a a a b b b b TUBIF 6 Summer a a a a b b b b TUBIF 8 Summer a a a b b b c c TUBIF 9 Summer a a a b b TUBIF 4 Fall a a a a b b b b Table 83 (cont'd.). 70 Variable Station Season I970 l97l I972 I973 l97h I975 TUBIF 7 Fall a a b b b c c c TUBIF 8 Fall a a a a b b b b LHOFF 3 Spring a a a a b b b LHOFF 4 Spring a a a a b b b LHOFF 3 Summer a a a a b b LHOFF 8 Summer a a b b b c c LHOFF 9 Summer a a a b b LHOFF 7 Fall a a b b b b LHOFF 9 Fall a a a b b b LMAUM 3 Spring a a b b b b c c c LMAUM 8 Spring a b c c d d d Table B3 (cont'd.). 71 Variable Station Season I970 I97l I972 I973 I97h I975 LMAUM 3 Summer a a a b b b b LMAUM 6 Summer a a a b b b b LMAUM 8 Summer a b b b c c c LMAUM 8 Fall a a b b b b LCERV 3 Spring a a a a b b b LCERV A Spring a a a a b b b b LCERV 7 Spring a a a b b LCERV 7 Summer a a b b b b LCERV 7 Fall a a a a b b b OSIZE I Spring a a a b b b c OSIZE 2 Spring a a a b b b Table 83 (cont'd.). 72 Variable Station Season I970 I97I I972 I973 I979 I975 OSIZE A; Spring a a a b b c c OSIZE 6 Spring a a a a b b b b b OSIZE I Summer a a a a b b b OSIZE 2 Summer a a a a b b b b OSIZE 8 Summer a a a b b OSIZE 9 Summer a a a b b c c OSIZE 9 Fall a a a b b b l RATIO 8 Summer a a a a b b RATIO 9 Summer a a a b b c c RATIO 9 Fall a a a a 73 Table BA. Tukey's multiple range comparison test for Chironomidae. Variable Station Season I970 I97I I972 I973 I97h I975 CHIRO I Spring a a a a b b b b b CHIRO 2 Spring a a a a b b b b CHIRO 7 Spring a a b b b CHIRO 8 Spring a b b b b b CHIRO I Summer a a ’a a b b CHIRO 7 Summer a a -b b b b CHIRO 8 Summer a b b b b CHIRO I Fall a a a a b b CHIRO 2 Fall a a a a b b b b CHIRO 6 Fall a a a a b b CHIRO 7 Fall a b b b b 74 Table Bk (cont'd.). W Variable Station Season I970 l97l I972 I973 I979 I975 CHIRO 8 Fall a b b b c c CHRSP I Spring a a a a b b b b CHRSP 7 Spring a a b b b b CHRSP 8 Spring a b b b b b CHRSP I Summer a a a a b b b CHRSP 7 Summer 3 a a b b b CHRSP 8 Summer a b b b b CHRSP I Fall a a a a . b b CHRSP 6 Fall a a a a b b CHRSP 7 Fall a b b b b CHRSP 8 Fall a Table Bh (cont'd.). 7S Variable Station Season I970 I97I I972 I973 l97h I975 PROCL 2 Spring a a a a b b b b PROCL 6 Spring a a a b b b b b PROCL 7 Spring a a b b b b PROCL 8 Spring a b b b b b PROCL 9 Spring a a a b b b b b PROCL 2 Summer a a b b b b PROCL 3 Summer a a a a b b PROCL 6 Summer a a a b b b PROCL 7 Summer a a a a b b b b PROCL 8 Summer a b b b b PROCL I Fall a a b b b b 76 Table BA (cont'd.). w Variable Station Season 1970 I97I I972 I973 I974 I975 PROCL 6 Fall a a a b b b PROCL 8 Fall a a b b b b COELO 5 Spring a a a a b b b b COELO 6 Spring 8 a a b b b b c c c COELO 2 Summer 3 a a a b b b b COELO 5 Fall a a a a b b b b CSIZE 6 Spring a a a a a b b b b b CSIZE 7 Spring a a b b b CSIZE I Summer a a a a b b b CSIZE 7 Summer a b b b b CSIZE 8 Summer a b b b b CSIZE 7 Fall a 77 Table Bh (cont'd.). Variable Station Season I970 I97I I972 I973 I97“ I975 CSIZE 8 Fall a a b b b b "IIIIIIIIIII'IIIIIIIII