A comprehensive 3-dimensional hydrodynamic and eutrophication model, the environmental fluid dynamics code model (EFDC) with three functional phytoplankton groups, was applied to simulate the algal dynamics in a mesotrophic P-limited subtropical plateau lake, Lake Erhai, Southwestern China. Field investigations revealed the seasonal patterns in external total phosphorus (TP) input and TP concentration, as well as the composition of the phytoplankton community. The model was calibrated to reproduce qualitative features and the succession of phytoplankton communities, and the net primary production was calculated. The modeled daily net primary production (NPP) ranged between −16.89 and 15.12 mg C/m²/d and exhibited significant seasonal variation. The competition for phosphorus and temperature was identified as the primary governing factor of NPP by analyzing the parameter sensitivity and limitation factors of the lake. The simulation of four nutrient loading reduction scenarios suggested high phytoplankton biomass and NPP sensitivity to the external TP reduction. A significant positive correlation was found among NPP, total phytoplankton biomass and TP concentration. Overall, this work offers an alternative approach to estimating lake NPP, which has the potential to improve sustainable lake management.

Spatial-temporal distribution patterns, contamination assessment and source apportionment of Cd, As, Pb, Cu, Zn, and Cr in sediments of Erhai Lake, a large plateau lake in southwest China, were investigated. The results indicated that elevated concentrations of Cr, As, Cu, and Zn were primarily distributed in the eastern and central regions of Erhai Lake, whereas Cd and Pb were mainly concentrated in the west-central region. Cd exhibited the most severe pollution, with 15.4% of samples reaching extremely high single factor pollution index levels, followed by As, for which 65.8% of samples showed high contamination. Cu and Cr presented moderate pollution levels. In contrast, the geoaccumulation index indicated that 70.0% of Zn and 84.6% of Pb samples were unpolluted. Tourism, agricultural activities, and industrial activities contributed 29.90%, 15.32%, and 54.78% respectively by positive matrix factorization model. Specifically, Cu, Zn, As, and Cr originated predominantly from industrial activities, Cd showed strong associations with agricultural practices, and Pb was mainly ascribed to traffic-related pollution. Industrial sources contributed the most to ecological risk (62.50%). The temporal trend derived from the sediment cores revealed a surge in pollution levels during the early 21st century, which may be related to rapid economic growth and non-ferrous metal production. Overall, the results provide a valuable baseline for environmental monitoring and management in Erhai Lake.