The effects of intermittent power generation on the fish fauna and benthic invertebrates of several Austrian rivers have been investigated quantitatively. In contrast to the more or less local adverse effects of impoundments or stream channelization, artificial flow fluctuations generally disturb a long section of a given river. Within all the river sections investigated, a breakdown of the benthic invertebrate biomass of between 75 and 95% was observed within the first few kilometres of river length. A reduction of between 40 and 60% of biomass compared with undisturbed areas could be detected within the following 20-40 km. The reduction of the fish fauna is within the same order of magnitude and correlates well with the amplitude of the flow fluctuations. Several reasons for the breakdown are summarized and proposals for the minimization of these detrimental effects of artificial short-term fluctuations are given.
The EU Water Framework Directive (WFD) requires river assessment systems based on benthic invertebrates. The AQEM project is developing, at a European scale, such a methodology, based on a comparison of communities of reference streams and degraded streams. The project is focussing on three main impact types: morphological degradation, organic pollution and acidification. This paper presents the outline of the AQEM project with special emphasis on: -an overview of assessment systems with benthic invertebrates presently applied in Europe -an overview of stream typology approaches in Europe -the selection process of the stream types investigated in AQEM -the criteria used to select reference sites -the design of the sampling programme -the microhabitat-based sampling method applied in AQEM -the links and possibilities of integration between AQEM and existing assessment systems.
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