Phytoplankton Distribution in Three Thermally Distinct Reactor Cooling Reservoirs

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Abstract
Phytoplankton community structure was studied in relation to physico-chemical characteristics of 3 South Carolina [USA] reservoirs in close proximity and of similar age and bottom type. Thermal alteration, resulting from the input of cooling water from a nuclear reactor, was substantially different in each reservoir. This provided an opportunity to compare water temperature effects separated from season. Water temperature (when examined independently in statistical models) appeared to be less important than other environmental variables in determining phytoplankton community structure. Pond C, a reservoir receiving intensely heated effluent (> 20.degree. C .DELTA.T[temperature change]), displayed low species diversity (Shannon-Weaver H'' < 2.0), except in winter. Unexpectedly, > 50% of the total phytoplankton density in this reservoir was consistently comprised of green algae (principally Chlamydomonas sp.) despite water temperatures that averaged 47.3.degree. C in summer. Par Pond, having a maximum .DELTA.T of 5.degree. C, displayed no temperature-induced alteration of phytoplankton community structure.