Effects of Land Use Characteristics, Physiochemical Variables, and River Connectivity on Fish Assemblages in a Lowland Basin

Human disturbances can have severe environmental impacts on freshwater ecosystems. The main aim of this study is to detect the influences of physiochemical variables, land-cover characteristics, and river connectivity on fish assemblages in the Lake Chaohu Basin, China. A cluster analysis of river connectivity variables identified four groups of sites characterized by significantly different connectivity gradients at a local scale. These four groups of sites showed increasing connectivity from the upper reaches to the lower reaches. At the same time, among the four groups, the values of environmental variables generally increased from the upper reaches with less human activities towards the lower reaches with more human activities. For instance, some main physiochemical variables (e.g., river width, water depth, nitrate, phosphate) significantly increased among the four groups. In contrast, fish taxa richness and diversity indices were not significantly different among the four connectivity groups. However, fish assemblages showed significant variations among the connectivity groups (p = 0.026). In addition, the study determined that upper riparian land uses (e.g., woodland and grassland), flow velocity, and elevation were environmental variables regulating the variance of fish communities. As for the connectivity variables, only river order and the number of branches along a path to the left of the main stem affected the variance of fish communities. Therefore, new practices aimed at maintaining and even increasing riparian canopy coverage and the flow velocity of rivers should be integrated into local conservation planning for freshwater ecosystems, especially in the upper reaches of the basin.