Effects of ice cover on diversity and community assembly of benthic algae in a stream system of northern China

Ice cover is common phenomena in aquatic systems of cold regions; however community succession and community assembly of aquatic organism in relation to ice cover have received less attention. Since ice cover usually dominant a majority period of freshwater ecosystem, especially in high latitude or high altitude regions, it is crucial to evaluate the impacts of ice cover on aquatic systems. In this study, effects of ice cover on environments and benthic algal communities were studied with a six-month field investigation in a stream system of northern China to verify ecological succession between the ice-free period and the ice-covered period. Results showed that ice cover significantly altered environmental conditions, manifest as decreased dissolved oxygen and water temperature, as well as increased total phosphorous (TP). We also observed obvious changes in benthic algal community structure, characterized by a rise in Chlorophyta and Euglenophyta, alongside declines in species richness and multiple facets of functional diversity. In addition, functional homogenization in algal community was found because ice cover reduced β -functional diversity. At last, we observed that community assembly of benthic algae was governed by deterministic processes both before and after ice cover, although strength of these processes was significantly weaker during ice cover. This work demonstrates that ice cover can act as a strong environmental filter, reducing biodiversity and altering community assembly, which may provide crucial insights for forecasting ecological responses in seasonally frozen streams.