Impact of small hydropower plants on microbial community structure and functions in benthic biofilms.

The development of small hydropower plants (SHPs) has significantly altered river connectivity and biodiversity, with its ecological impacts increasingly gaining attention. Previous ecological impact studies have biologically focused on aquatic organisms such as fish, macroinvertebrates and algae, while research on benthic biofilms, a dominant microbial life form, remains limited. Thus, we established sampling sites at 15 SHPs in the Oujiang River Basin, located upstream of the dam (S1), within the reservoir area (S2), in the dewatered section with ecological flow (S3), and downstream where natural flow is restored (S4). By comparing the microbial community composition, beta diversity, co-occurrence network structure, and functional predictions of benthic biofilms across different river sections, we assessed the response of benthic biofilm microbial communities to habitat changes induced by SHPs under ecological flows. The results revealed that the microbial community structure and beta diversity of benthic biofilms in S2 is significantly different from other sampling sites, with a higher proportion of Bacteroidetes. Co-occurrence network analysis indicated that the network complexity of S2 and S4 was lower than those of S1 and S3. Functional predictions showed that S2 had weaker organic matter degradation capabilities and lower functional abundance in nitrogen cycling. In contrast, S3 with ecological flows exhibited functional similarities to S1 and S4, which experienced natural flow conditions. Overall, this study demonstrates the significant impact of SHPs on benthic biofilm microbial communities in S2 and underscores the importance of ensuring sufficient ecological flow release and enhancing the management of downstream human activities.