Ecological water quality assessment of the Butgenbach lake (Belgium) and its impact on the River Warche using rotifers as bioindicators

Abstract

Results are presented on a study of the zooplankton of Butgenbach reservoir and from the Warche and Holzwarche rivers which feed the reservoir (March and October 1996). The zooplankton was dominated by rotifers in spring and by crustaceans (cladocerans and copepods) in summer and autumn. A temperature gradient developed during summer and a drastic depletion of oxygen and increase in ammonia concentrations was observed below 7 m depth. The water quality of the River Warche was compared upstream and downstream of the lake using bioindication by rotifers and by reproduction ecotoxicological tests on Brachionus calyciflorus on the other hand. The bioindicators reveal an overall improvement in water quality of the Warche downstream of the reservoir, whereas the toxicity assays show a decline in water quality downstream of the lake during the stratification period, due to the release of hypolimnetic water from the dam. So, under special conditions, ecotoxicity assays appear to be more sensitive than bioindication using rotifers saprobic valences.