MESOCOSM OBSERVATIONS ON THE ECOLOGICAL RESPONSE OF AN AQUATIC COMMUNITY TO SEDIMENT CONTAMINATION

Between 1992 and 1997 the effects of contaminated sediment on an aquat ic community were studied in outdoor mesocosms (2m(3)), one filled wit h 'naturally' polluted sediment from the sedimentation area 'Ketelmeer ', the other with relatively clean sediment from the shallow lake 'Oos tvaardersplassen'. Negative effects of the contaminated sediment were observed on the population development of the amoeba species Arcella m egastoma 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 contam inated system. The reduction of the grazing capacity of the cladoceran community resulted in higher algal densities in the 'Ketelmeer' mesoc osm despite the fact that nutrient concentrations in the water column of both mesocosms were comparable. (C) 1998 IAWQ. Published by Elsevie r Science Ltd.