Spatiotemporal variations in water quality parameters and assessment of the current status and challenges of eutrophication in Lake Dian

Understanding the spatiotemporal distribution and evolutionary patterns of lake water quality parameters is essential for formulating precise ecological management strategies. This study aimed to investigate the high-resolution spatial and temporal variations in water quality parameters across different regions of Lake Dian (including Caohai and Waihai) and its major inflowing rivers, as well as to objectively assess its pollution status and future trends. Comprehensive experiments and field measurements were conducted at 150 high-resolution sampling points. The analyzed parameters included total nitrogen (TN), total phosphorus (TP), chlorophyll-a (Chl-a), water temperature (WT), and other physicochemical indicators. Spatial interpolation, correlation analysis, and time-series modeling were employed to explore the distribution patterns and interaction mechanisms of these parameters. Results revealed significant spatial heterogeneity in nitrogen and phosphorus concentrations across Lake Dian. Nutrient gradients followed the order: Caohai > Waihai, bottom water > surface water, and nearshore estuarine areas > central lake regions, with an overall pollution pattern decreasing from north to south. Phytoplankton blooms exhibited distinct seasonal and spatial clustering, predominantly occurring from May to October, with hotspots concentrated in Caohai, northern Waihai, and shallow bays. Chl-a concentrations showed significant positive correlations with WT, dissolved oxygen (DO), and TN, indicating that algal growth is driven by multiple factors, with phosphorus playing a more prominent role during the rainy season. Comparative analysis of national monitoring data (from March 1979 to June 2023) and laboratory results identified three distinct phases in the evolution of water quality: “deterioration, improvement, and fluctuation”. TN and TP concentrations reached their peaked between 1989 and 2009, with average values of 3.58 ± 0.98 mg/L and 0.35 ± 0.06 mg/L, respectively. Although water quality has shown improvement since 2010, the water environment remains unstable, particularly during the rainy season when nutrient concentrations exceed threshold levels (TN: 0.3 mg/L, TP: 0.02 mg/L). After years of sustained management and restoration efforts, water quality in Lake Dian has gradually improved, and eutrophication has been partially alleviated. However, high nitrogen and phosphorus concentrations continue to present complex and persistent challenges for eutrophication and pollution control, necessitating ongoing attention. External nutrient inputs remain a critical concern, while internal nutrient release from sediment also requires rigorous monitoring and management.