SREL Reprint #1949





Plankton composition, abundance and dynamics in a severely stressed cooling reservoir

Douglas A.Leeper and Barbara E.Taylor
Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA

Abstract. The effects of severe thermal stress imposed by the intermittent operation of a nuclear reactor on plankton abundance and dynamics were investigated in Pond C, a cooling reservoir on the Savannah River Site in South Carolina, USA. Temperatures in Pond C ranged up to 58°C during reactor operation. The thermal effluent eliminated zooplankton from regions where the temperature exceeded 45°C, reduced zooplankton abundance by 1-3 orders of magnitude and typically halved the number of taxa. Reactor operation also reduced phytoplankton biovolume, often by >70%. During intermittent reactor operation, the rotifer Filinia longiseta dominated the zooplankton and two cladocerans of the genus Moina were abundant. These species were not abundant during extended reactor shutdowns. The success of Filinia and Moina was due primarily to their tolerance of high temperatures. Sparse phytoplankton probably limited some zooplankton taxa, although other taxa, such as Filinia may have utilized bacterial resources. Reactor operation may have intensified predation on crustacean zooplankton when fish were concentrated in refuge areas with zooplankton. Processes by which zooplankton repopulated the reservoir after reactor shutdown were inferred from zooplankton distribution patterns, and population growth and birth rates. Repopulation typically occurred within a few days due to rapid growth of populations from refuge areas within the reservoir and colonists brought in through a tributary canal. Mechanisms of zooplankton repopulation in Pond C suggest that refuges or colonization corridors should be maintained when the re-establishment of communities following cessation of stresses is desired.

SREL Reprint #1949

Leeper, D.A. and B.E. Taylor. 1995. Plankton composition, abundance and dynamics in a severely stressed cooling reservoir. Journal of Plankton Research 17:821-843.

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