Characterization of phosphorus behavior and microbial response in the river-lake confluence area of Nanfei River and Chaohu Lake

The complex hydrodynamic conditions at the river-lake confluence play a critical role in the transport and transformation of pollutants, particularly phosphorus (P). This study focuses on the river-lake confluence area of the Nanfei River and Chaohu Lake, examining the variations in P forms in both the overlying water and sediments, with respect to flow direction and water depth. It also analyzes variations in P fluxes at the watersediment interface. Pearson's correlation and principal component analyses (PCA) were applied to assess the relationships between P and various physicochemical indicators. The results show that total phosphorus (TP) in the overlying water maintains a relatively stable and uniform distribution pattern, whereas inorganic phosphorus (IP) in the sediments was the primary driver of TP variation in the surface sediments of Chaohu Lake. Correlation and PCA analyses indicated that domestic sewage and industrial wastewater are the main phosphorus sources in the river-lake confluence area. Microbial community analysis revealed that Proteobacteria and Chloroflexi dominate in the degradation of organic pollutants. Based on these findings, it was concluded that P pollution at the river-lake confluence area of the Nanfei River is more severe. Considering the total phosphorus load per unit area along the flow path, targeted dredging within a 2.0 km radius from the inlet is recommended. This study improves understanding of phosphorus distribution and microbial communities in the Nanfei River-Chaohu Lake confluence area, offers strategies for targeted dredging, and provides valuable insights for the protection of Chaohu Lake's aquatic ecosystem.