Seasonal variations in groundwater discharge and associated nutrient fluxes in Changhu Lake

Objective To assess contribution and seasonal variation in groundwater discharge (LGD) to lake water and nutrient budgets, Methods this study investigated Changhu Lake in the middle reaches of the Yangtze River. Field sampling was conducted during both the wet and dry seasons using multiple tracing techniques, including electrical conductivity (EC), stable isotope (2H and 18O), hydrochemical element (Ca2+ and Mg2+), and 222Rn isotope data. The 222Rn mass balance model was employed to quantify the LGD and associated nutrient fluxes in different seasons. Results Results show that LGD rates during the wet and dry seasons were 64.52 mm/d and 14.95 mm/d, respectively, with significant differences between these seasons. Furthermore, during the wet and dry seasons, groundwater carried TN inputs of approximately 25.68×106 g/d and 5.58×106 g/d, respectively. The TP inputs were approximately 8.14×106 g/d and 0.17×106 g/d in the wet and dry seasons, respectively. The differences in the LGD rates between the wet and dry seasons lead to differences in groundwater carrying TN and TP inputs, and inputs of TP during the wet season is also influenced by agricultural activities during that period. Sronger precipitation and evaporation during the wet season drive greater LGD intensity and their carrying TN and TP fluxes. Conclusion The research can provide scientific reference for water resource management and aquatic ecosystem preservation efforts in the Changhu area.