The effect of heating and water exchange on the zooplankton composition in heated Konin lakes

Abstract

Analyses were made of the zooplankton sampled in 1989-1990 from three lakes of the Konin region. The lakes have been modified to a different degree by the cooling system of two power stations. The main factor modifying the composition and abundance of the plankton fauna was the magnitude of retention of the water bodies. In conditions of an increased flow the biomass in the lakes was reduced to about 1/10 as compared to the control station. The numbers of Cladocera decisively decreased; this reduced the efficiency of energy flow from the producers to the level of nonpredatory plankton. At the same time an increase was observed in the degree of utilization of the production of the first order consumers by the predatory zooplankton. The above changes were decisive for changing the direction of energy flow: phytoplankton, heterotrophic bacteria, small sedimentators (Rotatoria), and predatory forms of Cyclopidae.