598 CAMPBELL 



the aquatic ecosystem after the completed power plant began 

 operation. 



The lake, which lies in the Piedmont section of North Carolina, 

 has a surface area of 1500 ha, a retention time of ~1000 days, and a 

 mean depth of 15 m (maximum depth is ~40 m). Belews Lake has 

 been the subject of an environmental study for 7 years. Year 1 

 (August 1970 to April 1971) was a preimpoundment study. Dam 

 closure marked the beginning of year 2 (May 1971 to June 1972). 

 Lake filling continued to completion in the spring of year 3 (July 

 1972 to June 1973), and in this year the phytoplankton studies 

 began. Year 4 (July 1973 to June 1974) was the first 12-month 

 period in which the lake existed at full-pool level. The first unit of 

 the Belews Creek Steam Station, with a capacity of 1145 MW, 

 commenced operation at the beginning of year 5 (July 1974 to June 

 1975). The second unit went on-line in the middle of year 6 (July 

 1975 to June 1976); this doubled the generating capacity and 

 pumping rate. Results of studies in the lake over this period have 

 been the subject of several reports (Weiss et al., 1974; 1975; 1978a; 

 Weiss, Anderson, and Lenat, 1972). 



Comparatively few studies have been made of the effects of 

 thermal discharge on algae in lakes (Patrick, 1974). The possible 

 effects of such conditions on phytoplankton are various. If the 

 temperature tolerances of algae are exceeded because of excess 

 thermal input, species composition will change, and, if the increase is 

 great enough, shifts in the flora from diatoms to mainly green algae 

 or blue-green algal flora may occur (Patrick, 1969). A heat-enhanced 

 shift to a grazing-resistant blue-green community may eliminate 

 many consumer species, and, once the blue-greens become suffi- 

 ciently dominant, the noxious character of their abundance has an 

 adverse effect on water quality (Foerster, Trainor, and Buck, 1974; 

 Patrick, 1974). The heat shock to phytoplankton passing through 

 power-plant condensers can inhibit productivity (Gurtz and Weiss, 

 1974). Heat addition can result in lower phytoplankton numbers and 

 diversity (Warinner and Brehmer, 1966; Kullberg, 1968) and in- 

 creased dominance by tolerant species at the expense of less hardy 

 taxa (Knight, 1973). Under certain conditions the heat shock may 

 cause synchrony in reproduction by creating incipient cell divisions 

 (Foerster, Trainor, and Buck, 1974). Heat shock for extremely short 

 periods of time may have only temporary adverse effects on many 

 species of algae, however, and moderate temperature increases from 

 the low end of the tolerance range towai'd optimum temperature can 

 increase algal biomass and diversity (Patrick, 1969; 1974). Examples 

 of such increased phytoplankton productivity have been found in 



