Extreme Hydrological Shifts Trigger Water Quality Variations in Shallow Lake Ecosystems: Insights from Hydroclimatic Behaviors

Shallow lakes are highly sensitive to hydrological changes and human activities; however, the effect of hydrological extremes on water quality dynamics remains unclear. In this study, we investigated hydroclimatic and water quality changes in Datong Lake (a typical shallow lake within the Yangtze River Basin) over the period 2021–2024, with the objective of detecting the dynamic response of lake water quality to its driving factors during extreme hydrological years. Our analysis suggested that precipitation, water level, and temperature of Datong Lake all fluctuated during the study period. Total nitrogen (TN) concentrations increased to 1.25 mg/L, 1.42 mg/L, and 1.05 mg/L in the lake, inlets, and outlet, respectively, driven largely by external nutrient inputs from agricultural and aquacultural activities. Precipitation and water level were significantly higher in the wet year (1051.15 mm and 27.26 m, respectively) than in the dry year (805.05 mm and 27.05 m, respectively). TN and total phosphorus (TP) concentrations at the river inlet were higher in wet years than in dry years, whereas TN and TP in the lake showed the opposite trend. Notably, both TN and TP were positively correlated with temperature, water level, and turbidity, and negatively correlated with dissolved oxygen and electrical conductivity. Among these drivers, turbidity emerged as key influential variable (R2 ranging from 0.18 to 0.41) in modulating lake water quality during extreme hydrological years, followed by temperature (R2 ranging from 0.11 to 0.17) and water level (R2 ranging from 0.12 to 0.13). These findings reveal that extreme hydrological shifts drive changes in lake water quality, underscoring the necessity of integrated management strategies to alleviate climate change impacts on shallow lake ecosystems.