Spatiotemporal Variation of Total Nitrogen and Total Phosphorus in Yilong Lake and Its Inlets

Nutrient input from agricultural activities contributes significantly to the eutrophication of Yilong Lake in the plateau ecosystem of Yunnan Province, China. This study investigated nutrient spatiotemporal distribution patterns in this water system through nitrogen (N) and phosphorus (P) concentration monitoring during the dry and wet seasons in 2023. Water and soil samples were collected systematically from five major inflow rivers and corresponding lake areas of the Yilong Lake basin. The results show the status of N enrichment (total N: 2.22 mg·L^-1) coupled with P limitation (total P: 0.036 mg·L^-1); the primary contributors to lake nutrient loading are the Chengbei and Longgang rivers. Riverine TN/TP ratios and watershed soil nutrient contents were significantly correlated (P < 0.05) across different hydrological periods. Variable precipitation led to spatial heterogeneity in nutrient content, including higher wet-season TN levels in the Chenghe, Dashui, and Longgang rivers compared to the dry season, as well as elevated nutrient concentrations at the northern and southern extremes of the lake compared with central regions. These findings provide critical spatiotemporal benchmarks for targeted pollution control strategies and establish a scientific basis for the integrated management of shallow eutrophic lakes in plateau ecosystems.