Effects of thermal effluents from the Bergum Power Station on the zooplankton in the Bergumermeer

The influence of thermal discharge from a 640 MW steam electric power station on the Bergumermeer (shallow, eutrophic lake) was investigated. The temperature of the thermal effluent did not exceed 30 °C. The lake was sampled extensively from 1975 to 1978. Zooplankton densities at different depths in the heated and non-heated parts of the lake were compared. A vital staining technique was used to assess entrainment mortality of cladocerans. The entrainment mortalities for the most abundant cladocerans were only 2 to 3% but for Leptodora kindtii 19% and about 25% for Diaphanosoma brachyurum, Ceriodaphnia pulchella and the cyclopoid nauplii. The ecological consequences for the lake ecosystem are discussed.