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(020) Assessing effects on benthic invertebrates in the delta of the rivers Rhine and Meuse. Den Besten, Pieter1, Heugens, Evelyn1,2, Hendriks, Jan1, 1 2 ABSTRACT- Different approaches have been followed to determine the ecological risks of sediment contamination. The sediment Triad method was used in studies in the delta of the rivers Rhine and Meuse to demonstrate the relation between effects on benthic macroinvertebrates, bioassays and sediment pollution. In addition, multivariate statistical methods were applied to estimate the influence of ecological and toxicological factors on macrofauna species composition. In situ field bioassays with midge larvae Chironomus riparius were used to compare the effects of multiple stressors in the field with the responses of test species in laboratory bioassays. For instance, the influence of surface water quality was demonstrated in translocation experiments, in which clean sediment was placed in polluted locations, and polluted sediment was translocated to reference sites. Experiments with laboratory and field bioassays with C. riparius revealed negative correlations between sediment toxicity and temperature. From a literature review it was estimated that the differences between toxicity measured in the laboratory and toxicity at relevant field conditions range from a factor of 1.7 to 130 for temperature, from 1.2 to 10 for nutritional state (difference factors depending on the effect parameter used). In order to determine the role of chemical stressors more specifically, biomarkers and toxicity identification evaluation techniques are proposed. The "burden of evidence" derived from these studies has triggered a number of sediment remediation projects in the Rhine-Meuse delta. Ecological data collected during pilot sediment remediation projects suggest improvement of the meio- and macrofauna community after the dredging polluted sediment. Key words: sediment contaminanion, triad approach, multi-stress, in situ bioassays |
