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(12-01) Responses of benthic invertebrates to combined toxicant and food input in floodplain lake sediments. De Haas, Elske*,1, Reuvers, Bas1, Moermond, Caroline2, Koelmans, Albert2, Kraak, Michiel1, 1 University of Amsterdam, Kruislaan 320, Amsterdam, the Netherlands2 Wageningen University, P.O. Box 8080, Wageningen, the Netherlands ABSTRACT- Benthic communities in flood plain lake ecosystems are often exposed to increased levels of both food and contaminants. Inhibition through toxicants of sensitive species and stimulation through increased amounts of food of opportunistic species have been observed. The aim of this study was therefore to analyze the interactions between food and toxicants and to assess the responses of benthic invertebrates to different levels of food and contamination. To this purpose, seven flood plain lakes located along the river Waal, The Netherlands, with different levels of food and toxicants were selected. The responses of the sensitive mayfly Ephoron virgo and the opportunistic midge Chironomus riparius to these sediments were assessed in 10-day growth bioassays with both species, and a 28-day emergence experiment with C. riparius. A decrease in both survival and growth of E. virgo was observed with increasing contaminant levels. In contrast, C. riparius responded to the food quantity and quality of the sediments, in spite of the toxicants present. Addition of food in midge bioassays prevented reduction of survival, growth and reproduction due to food deficiency, but meanwhile, this food addition may mask toxic effects. We conclude, therefore, that the midge C. riparius is not a suitable test organism for sediment toxicity assessment. Alternatively, it proved to be an appropriate test organism to determine the nutritional value of sediments. The mayfly E. virgo turned out to be a much more appropriate test organism for sediment toxicity bioassays, because it responds to the toxicant levels in the sediments, rather than to the nutritional value. It is concluded that not the toxicant load, but the interaction between food and contaminants determines the persistence of benthic invertebrates and therewith the benthic community composition in complexly polluted ecosystems. Key words: contamination, eutrophication, Chironomus riparius, Ephoron virgo |
