EFFECTS OF POWER-PLANT OPERATION ON ZOOPLANKTON 639 



The second group was composed of six taxa that declined over 

 the 3-year period: Keratella crassa, Collotheca spp., Asplanchna spp., 

 Ceriodaphnia spp., Mesocyclops edax and calanoid copepodids 

 {Diaptomus spp.). None of these dechnes could be directly attributed 

 to power-plant operation. 



The third group was composed of four taxa that showed an 

 increase in density over the 3-year period: Hexarthra spp., Ptygura 

 spp., Ploesoma truncatum and Synchaeta spp. Both Ptygura spp. and 

 Hexarthra spp. are warm stenotherms and may have responded 

 favorably to the increase in the duration of maximum summer 

 temperatures brought about by the power plant. The increase in the 

 other two species was associated with natural causes. 



Significant changes in density were not observed at higher 

 taxonomic levels (Rotifera, Cladocera, Copepoda). This indicated 

 that the power plant did not have a detrimental impact on the total 

 standing crop of the zooplankton community of the lake. Changes 

 among the majority of species within the major groups were most 

 often associated with natural causes. 



Circulation of surface water by the power plant appeared to 

 reduce station density differences and bring about a more similar 

 seasonal density distribution for most taxa. This was probably the 

 most notable influence of the power-plant operation on the 

 zooplankton community of the lake. 



ACKNOWLEDGMENTS 



This investigation was funded by the Duke Power Company, 

 Charlotte, N. C, through a research grant to Charles M. Weiss, 

 Project Director, Department of Environmental Sciences and Engi- 

 neering, School of Public Health, University of North Carolina at 

 Chapel Hill, Chapel Hill, N. C. We are indebted to Sheila L. Pfaender, 

 Sarah R. Gnilka, and Arthur L. Buikema for performing the zoo- 

 plankton taxonomy over the course of this study. Our colleague 

 Peter H. Campbell provided the data on phytoplankton densities and 

 biovolumes. Thomas G. Donnelly wrote the programs for the 

 statistical tests. 



REFERENCES 



Ahlstrom, E. H., 1934, A Quantitative Study of Rotatoria in Terwilliger's Pond, 



Put-in-Bay, Ohio, 5u//. Ohio Biol. Survey, 30(6): 3-38. 

 Applegate, R. L., and J. W. Mullan, 1969, Ecology of Daphnia in Bull Shales 



Reservoir, U. S. Bureau of Sport Fish, and Wildlife, Research Report 74. 



