Influences of Low-Head Dams on Fish Assemblages in the Headwater Streams of the Qingyi River, China

Based on the data collected in the headwater streams of the Qingyi River, China, during the period from 2009 to 2012, we examined how low-head dams affect fish assemblages . First, at a reach scale, low-head dams may substantially modify local habitat conditions  in the impounding upstream and plunging downstream areas. But significant variations in fish assemblages were only observed in the impoundments, of which a general pattern showed as more lentic but less lotic fish. Second, at a stream or tributary scale, low-head dams may have similar effects on fish assemblages with that observed at reach scale, because the streams in which numerous dams were built showed wider channel, smaller substrate, less lotic but more lentic fish than those presenting less dam. In addition, multiple dams may lessen the correlations between elevation and fish assemblages, suggesting the destruction in the longitudinal pattern of fish assemblages by dams. Third, when looking at a river-network scale, dams may weaken the spatial autocorrelation of local species richness of fish in a river network, because fish species richness in 1st-–3rd-order streams were mainly determined by local habitat features, but tributary spatial position variables were less important.