Fine-scale environmental gradients formed by local pollutants largely impact zooplankton communities in running water ecosystems

Many freshwater ecosystems suffer from multiple environmental stressors derived from anthropogenic activities. It is therefore necessary to investigate how environmental changes influence composition and functioning of biological communities such as zooplankton. At fine geographical scales, a well-known view on meta-community dynamics suggests that high dispersal can strongly homogenize community structure along water flows, largely erasing signals left by species sorting. However, a recent study by Xiong et al. (2017; Mol Ecol 26:4351−4360) challenges this view, showing that species sorting derived from an environmental gradient overrode the process of dispersal to determine the zooplankton community structure in running river ecosystems at fine geographical scales (the fine-scale species sorting hypothesis). Here we chose zooplankton communities from Fuyang River in north China to test the newly proposed hypothesis and identified the environmental factors contributing to meta-community dynamics in running water ecosystems. Multiple analyses based on high-throughput sequencing showed significantly varied zooplankton community composition and geographical distribution determined by an environmental gradient. Our study clearly shows that local chemical pollution, such as metal pollutants Cu and Mg, largely contributes to the observed patterns. Our study successfully identified local pollutants that influenced meta-community dynamics. Thus, we support the fine-scale species sorting hypothesis, indicating that a strong environmental gradient at fine geographical scales can strengthen the process of species sorting. As many rivers suffer from anthropogenic environ mental stressors, an urgent need exists to integrate both environmental and community infor mation when investigating how environmental changes influence community composition and functioning.