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(021) Bio-availability of sediment trace metals and effects on benthic communities in Dutch flood plain lakes. van Griethuysen, Corine1, Peeters, Edwin1, van Baren, Joyce1, Koelmans, Albert1, 1 ABSTRACT- Historically, Dutch rivers have been polluted with trace metals, leading to the accumulation of a diffuse layer of poor quality sediments in their flood plains. To enable site-specific risk assessment, magnitude and ranges of contamination levels, geochemical behavior and the possible effects on the benthic community were investigated at various flood plains. Effects are assessed by a) measurement of bio-accumulation in target organism Oligochaeta and b) analysis of the community structure of benthic invertebrates. These organisms are chosen because they take up contaminants from sediment and pore waters, are in close contact with the polluted sediment and are the link between the benthic and pelagic food chain. In some earlier studies into the structuring the benthic community in various aquatic systems, the contribution of trace metals was significant. We selected 10 flood plain lakes along the major tributaries of the Rhine river, with similar morfology and a maximal range in inundation frequency along each tributary as a predictor of the contamination level. Within each lake, four locations were sampled for surface water, sediment and benthic macrofauna. Geographical and water quality variables were recorded in the field. Sediment samples were analyzed for bulk chemistry and trace metal chemistry, SEM-AVS and CaCl2 extractable metals. Macrofaunal species were determined at the species level. Results show that ranges in sediment metal concentration were large and were related to texture and organic matter content of the sediment as well as to inundation frequency and lake history. SEM-AVS differences were predominantly above 0 and CaCl2-extractable amounts are very low, indicating a low bio-availability. Accumulated trace metals did not vary much between the lakes, regardless of the high variability of sediment concentrations, possibly because of internal regulation. Clear differences were found regarding species composition in the various tributaries. In conclusion, geochemistry and species composition varied between tributaries whereas effects on ecosystem components due to trace metals appeared to be small. Key words: sediment trace metals, bio-availability, benthic community, ecological effects |
