Influences of local habitat, tributary position, and dam characteristics on fish assemblages within impoundments of low-head dams in the tributaries of the Qingyi River, China.

Low-head dam impoundments modify local habitat and alter fish assemblages; however, to our knowledge, the pattern of how fish assemblages in the impoundments relate to local habitat, tributary position, and dam characteristics is still unclear. We used data collected in 62 impoundments created by low-head dams in headwater streams of the Qingyi River, China, to examine relationships between fish assemblages and local habitat, tributary position, and dam characteristics. We also assessed the relative importance of the three groups of factors in determining fish species richness and composition. Linear regression models showed that fish species richness was related to substrate heterogeneity, confluence link, and dam number upstream. Redundancy analysis showed that fish species compositions were influenced by substrate heterogeneity, confluence link, dam height, dam numbers upstream and downstream. Overall, dam characteristics were more important in affecting fish species richness but less important in determining fish species composition than local habitat (i.e., substrate heterogeneity) and tributary position. Our results suggest that low-head dam may affect fish species richness in impoundments by modifying local habitat and constraining fish movement, and the relative abundances of those fish species may depend more on species habitat presences and stream size than on impoundment size and number.