Regional nutrient emissions and hydrological regime modulate the spatiotemporal patterns of nutrient levels within lake bay

Abstract

Many rivers and lakes worldwide, especially lake bays adjacent to rivers, have experienced eutrophication. However, the effects of nutrient emission reduction and hydrological conditions on the levels and spatiotemporal distribution patterns of nitrogen (N) and phosphorus (P) in lake bays remained insufficiently understood. In this study, a dynamic model was developed to track nutrient transport processes from source areas to rivers and lake bays, and applied it to Zhushan Bay and its upstream region in the Taihu Basin, China. Hydro-chemical analysis results indicated that during the wet season, the total nitrogen (TN) concentration (1.64 mg·L^-1) in the river inflow section was higher than that in the lake bay (1.48 mg·L^-1), while total phosphorus (TP) (0.24 mg·L^-1) was lower than in the lake bay (0.30 mg·L^-1). The model results showed that in 2020, domestic sewage sources (38.24 %) and surface sources from cultivated land (33.14 %) were the primary contributors of fluvial TN, while livestock and poultry breeding sources (59.37 %) were the main sources of fluvial TP. Scenario simulations indicated that a 30 % reduction in nutrient emissions led to a corresponding decrease in TN and TP loads in the lake bays, with more significant reductions observed during the dry season (TN: 3.05 %; TP: 9.51 %). A 12 % reduction in river discharge during the dry season resulted in a corresponding decrease in TN and TP loads in the lake bays, with the reduction in TP (1.81 %) greater than that of TN (1.39 %). This study offered insights into nutrient transport and guidance for managing nutrients in lake basins.