Impacts of water storage dams on substrate characteristics and stream invertebrate assemblages

Our objective was to evaluate the effects of dam construction on the substrate and stream invertebrate assemblages below dams. Few studies have directly measured both substrate characteristics and stream invertebrate assemblages in stream reaches above and below dams. We measured a range of habitat characteristics and collected samples of stream invertebrates in the reaches above and below a series of water storage dams in three river systems. The invertebrate assemblages in the reaches downstream of the storage dams were significantly different from those in the upstream reaches. The downstream sites were grouped in the domain in which the values for the second axis of the non-metric multidimensional scaling (NMS) were high. This difference was associated with changes in the characteristics of the substrate below the dams. Stone embeddedness and the frequency of stone movement were higher in the upstream reaches than in the downstream reaches (two-way ANOVAs). Stone embeddedness and stone movement were also negatively correlated with the NMS axis 2. Our results suggest that the condition of the substrate is an important determinant of the invertebrate assemblages up and downstream of dams. Given this, we believe that it is important to measure substrate characteristics when evaluating the effect of storage dams on stream ecosystems.