PHYTOPLANKTON COMMUNITY ASSESSMENTS OF 7 SOUTHEAST US COOLING RESERVOIRS

The phytoplankton community structure, productivity and biomass of sev en southeastern United States cooling reservoirs were investigated bet ween 1979 and 1986, with emphasis on data from 1984 to 1986. These res ervoirs represented a variety of trophic states and geographic provinc es, and included three piedmont systems, two coastal plain systems and one each in the mountains and sandhills. The study reservoirs differe d from northern temperate lakes in seasonal phytoplankton taxonomic pa tterns, the dominance of flagellated chrysophytes and cryptomonads, la ck of spring diatom blooms and generally low abundance of blue-green a lgae, particularly in the larger systems. The small reservoirs were mo re susceptible to algal blooms, caused by nutrient trapping and elevat ed temperatures from thermal loading. Direct thermal discharge effects upon the phytoplankton communities were either localized or non-signi ficant, depending upon site-specific circumstances. Indirect effects o f 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-colum n metals, with major concurrent alterations in phytoplankton taxonomic structure.