Changes in zooplankton abundance and community structure in the cooling channel system of the Konin and Pątnów power plants

The aim of the research was to analyze changes in crustacean and rotifer plankton communities in the cooling system channels of the Konin and Pątnów power plants (central Poland). Only small amounts of zooplankton (Rotifera and Crustacea biomass) were detected in the channels investigated in this study. The total zooplankton population in the intake channels ranged from 100 to 200 indiv. dm^-3, and biomass did not normally exceed 1 mg dm^-3. The zooplankton population did not exhibit distinct changes immediately past the stream condensers zone (thermal shock) or immediately past the turbines of the pumping station in one of the channels (mechanical and pressure stress). Decreases in biomass of as much as 96% were noted several kilometers beyond the heated water discharge sites. Greater zooplankton mortality rates were recorded in the summer when the temperature of the discharged water exceeded 30°C, and there was a rise in water temperature (5-6°C). The loss of plankton in the Konin Power Plant (KPP) cooling system channels was greater than that in the Pątnów Power Plant (PPP) cooling system channels. The large decrease in zooplankton biomass in the channel beyond the pumping station suggests that the mechanical and pressure stress in the turbines that the Rotifera and Crustacea were subjected to was the principal reason for the high mortality rate.