Variation Trend and Driving Forces of Water Quality in Lake Erhai, China

Lake Erhai is an important plateau freshwater lake in China. It serves not only as a crucial drinking water source for the local region but also as the core area of the Cangshan Erhai National Nature Reserve. Consequently, Lake Erhai plays an extremely significant role in the local economy, society, and ecology. However, since the 1970s, the lake has experienced a series of problems, including declining water levels and water pollution. In recent years, the water quality of Lake Erhai has continued to deteriorate, showing a eutrophic trend. To identify the primary driving forces behind these water quality changes, this study employed stepwise regression analysis. Climate conditions, socio-economic development within the basin, and implementation of environmental protection measure (IEPM) were considered as influencing factors for a comprehensive and systematic analysis of Lake Erhai's water quality. The results indicate that air temperature primarily affects total phosphorus (TP) concentration and exhibits a positive correlation. Rainfall predominantly influences TP and total nitrogen (TN) concentrations, also showing positive correlations. Wind speed affects chemical oxygen demand (CODMn), TP, and TN concentrations, exhibiting negative correlations with each. Socio-economic development mainly affects CODMn concentration. Based on these findings, this paper proposes recommendations focusing on formulating more effective non-point source pollution control measures and strengthening water quality monitoring in Lake Erhai during summer. This study systematically analyzed the anthropogenic and natural factors affecting Lake Erhai's water quality, identified the dominant influencing factors, and provides technical support for the subsequent enhancement of Lake Erhai protection measures.