Mesocosm observations on the ecological response of an aquatic community to sediment contamination

Between 1992 and 1997 the effects of contaminated sediment on an aquatic community were studied in outdoor mesocosms (2m 3 ), one filled with ‘naturally’ polluted sediment from the sedimentation area ‘Ketelmeer’, the other with relatively clean sediment from the shallow lake ‘Oostvaardersplassen’. Negative effects of the contaminated sediment were observed on the population development of the amoeba species Arcella megastoma and Difflugia accuminata , the mysid shrimp Neomysis integer , the microlepidopteran Cataclysta lemnata and the cladoceran community, whereas the biting midge Culex sp. showed a preference for the contaminated system. The reduction of the grazing capacity of the cladoceran community resulted in higher algal densities in the ‘Ketelmeer’ mesocosm despite the fact that nutrient concentrations in the water column of both mesocosms were comparable.