Assembly of benthic diatom communities in cold region rivers: ecological drivers and mechanism differentiation of dispersal processes

Global warming intensification and anthropogenic activities have shortened the freeze-thaw period of rivers in cold regions. Benthic diatoms, essential components of river ecosystems, serve as both primary producers and reliable water quality indicators. However, existing studies on diatom communities have predominantly examined conventional environments, with limited investigation into their variations across distinct hydrological phases (freezing, thawing, and normal periods). In current study, Asymmetric Eigenvector Map analysis (AEM), Moran's Eigenvector Map analysis (MEM), and the principal coordinate of the neighborhood matrix (PCNM) were performed to explore the diatom community assembly in a seasonal freezing river. The AVD index was the lowest during the normal period, indicating greater stability of community, while the Niche width index reached its minimum during the freezing period. Additionally, environmental filtering played a dominant role in community assembly during three hydrological periods. Among these three dispersal processes, AEM exerted the greatest influence on diatom community assembly. Conversely, dispersal processes played a less substantial role in small-scale rivers. This study provides critical insights into the role of dispersal processes in the community assembly of benthic diatoms in rivers under different hydrological conditions. Additionally, combining dispersal processes with the WQI (Water Quality Index) yields a novel water quality indicator, providing an effective method for water quality assessment. Meanwhile, benthic diatoms retained their indicative significance in freeze-thaw rivers, serving as valuable indicators of environmental change. These findings have important implications for river ecosystem water quality management in cold river basins. • First comprehensive assessment of how dispersal processes type benthic diatom community assembly during river freeze-thaw and normal periods. • Comparison of three spatial processes (AEM, MEM, PCNM) for modeling diatom dispersal in cold-region rivers. • AEM-derived spatial processes are the primary driver of benthic diatom community assembly. • Contrasting assembly mechanisms: In small-scale rivers, environmental filtering dominates the community assembly process, whereas dispersal processes exert a relatively minor influence on this process.