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.
