Wie problematisch sind Stauraumspülungen aus Sicht der Fischökologie? Ein Überblick mit Fokus auf eine fischökologische Fallstudie an der Unteren Möll

The problem of increasing reservoir sedimentation will continue to require more scientific research in the future, which should ultimately contribute to the development of sustainable and ecologically compatible sediment management concepts. Existing studies mainly focus on the technical aspects of sediment management, but detailed studies on the ecological consequences of reservoir flushing are largely lacking. This paper analyses the available literature on the effects of reservoir flushing on fish and then presents the results of a case study on the Lower Möll River. The effects of reservoir flushing on the populations of brown trout, grayling and rainbow trout were analysed and compared with the development of fish populations in an upstream control section, which was affected by a natural flood but not by flushing. Flushing the reservoir during a 12-year flood resulted in a drastic reduction in fish density of up to 80%. In comparison, the 20-year flood in the control reach resulted in only a marginal decline in fish abundance. The results are discussed in the context of morphological conditions (hydraulic stress, refugial habitats) and species composition, and the need for further research to develop ecologically compatible, more targeted sediment management strategies is emphasised.