Phytoplankton community assessments of seven southeast U.S. cooling reservoirs

Abstract

The phytoplankton community structure, productivity and biomass of seven southeastern United States cooling reservoirs were investigated between 1979 and 1986, with emphasis on data from 1984 to 1986. These reservoirs represented a variety of trophic states and geographic provinces, and included three piedmont systems, two coastal plain systems and one each in the mountains and sandhills. The study reservoirs differed from northern temperate lakes in seasonal phytoplankton taxonomic patterns, the dominance of flagellated chrysophytes and cryptomonads, lack of spring diatom blooms and generally low abundance of blue-green algae, particularly in the larger systems. The small reservoirs were more susceptible to algal blooms, caused by nutrient trapping and elevated temperatures from thermal loading. Direct thermal discharge effects upon the phytoplankton communities were either localized or non-significant, depending upon site-specific circumstances. Indirect effects of thermal loading caused ecosystem-wide alterations both from top-down (fish) and bottom-up (phytoplankton) effects. In one acidic reservoir, power-plant operational changes reduced concentrations of water-column metals, with major concurrent alterations in phytoplankton taxonomic structure.