LITTORAL BENTHOS OF BELEWS LAKE 581 



littoral and profundal benthos (C. M. Weiss, T. P. Anderson, Lenat, 

 and P. H. Campbell, manuscript in preparation). 



Benthic macroinvertebrates are well suited to assessment of 

 environmental stress. The benthos are a less mobile and less variable 

 group than plankton or fish and, therefore, serve well to describe the 

 quality of the environment at a particular site (Garton and Harkins, 

 1970). Chemical and physical assessments provide a statement of 

 water quality at the time of sampling, but the benthic community 

 acts as a monitor or integrator of water quality over extended 

 periods. It responds to maximum and minimum conditions of the 

 environment rather than average values and thus functions as a 

 detector of even occasional changes. Studies of the benthos also 

 assess the overall conditions of the environment rather than testing 

 only for specific parameters. 



Since heated discharges tend to "float," we might expect that the 

 greatest potential for thermal stress would occur in littoral areas. 

 Littoral organisms, however, must adapt to a wide temperature range 

 to exist under natural conditions. North Carolina surface waters 

 naturally reach temperatures up to 33° C. This investigation attempts 

 to assess the effects of artificial temperature increments super- 

 imposed over the natural temperature fluctuations. 



STUDY SITE 



Belews Lake is meso-oligotrophic (Weiss and Kuenzler, 1976) and 

 has a surface area of 1500 ha. The maximum depth is 40 m, and the 

 retention time is approximately 1000 days. The geographic and 

 chemical characteristics of the lake act to maximize the effects of 

 thermal stress. The North Carolina Piedmont is located near the 

 transition from a temperate to a subtropical climate. Therefore, 

 temperate species are near their southern limits, encountering 

 temperatures near their tolerance limit (Cairns, 1975). The North 

 Carolina Piedmont generally has very soft water. Alkalinities in 

 Belews Lake, for example, are usually less than 25 mg/liter. 

 According to Cairns, the capacity to adjust to thermal additions is 

 greatest in hard water because of natural buffering processes. 



Belews Lake has been investigated for 7 years. Year 1 

 (1970—1971) was a preimpoundment study, and years 2 and 3 were 

 periods of lake filling. The first power-plant unit started operation in 

 year 5, and the second unit started in year 6. This paper compares 

 data from year 4, the best "control" data, with that from years 5 and 

 6. 



