Seasonal responses of microbial communities to water quality variations and interaction of eutrophication risk in Gehu Lake.

Gehu Lake, as a key upstream reservoir of Taihu Lake, China, plays a crucial role in improving the water quality, and eutrophication control of the Taihu Lake Basin. Although the microbial communities are significantly important in maintaining the ecological health of lake, the microbial response to water quality, especially for eutrophication has been rarely reported in Gehu Lake. In this study, the water quality parameters and the corresponding effects on the structure and function of microbial communities were determined seasonally. It was found that the poorest water quality in summer (Water Quality Index = 116.52) with severe eutrophication (Trophic Level Index >70), was primarily driven by agricultural non-point sources (33.4%) and seasonal pollution (23.8%). The chemical oxygen demand (COD) was the most important indicator of water quality that affected the concentration of Chlorophyll-a (Chla) according to Pearson correlation analysis (p < 0.001), random forest modeling (p < 0.01), and structural equation modeling (path coefficient = 0.926). Redundancy analysis revealed that total nitrogen, total phosphorus, Chla, and COD significantly influenced the microbial community (p < 0.05). Microbial co-occurrence networks demonstrated significantly seasonal variations, and winter exhibited a more complex structure under lower temperature and limited nutrients compared to the other seasons. In addition, the Chla-sensitive microbial species that involved in nitrogen and phosphorus metabolism were identified as the biological indicators of eutrophication in response to the changes of seasonal water quality. These findings have taken insights into the interactions between water quality and microbial communities, and might provide the basis for improvement of the ecological and environmental management of Gehu Lake, as well as the control of eutrophication in Taihu Lake.