Lacustrine groundwater discharge as an important hidden source of nutrients to a large eutrophic lake: Implications...

Lake eutrophication driven by excessive nutrient inputs has become a global issue, but the potential impact of lacustrine groundwater discharge (LGD) as a nutrient source on lake eutrophication remains largely unknown. This study assessed the contribution of LGD-derived nutrient loads and revealed their potential impact on lake eutrophication in Taihu Lake, a typical large shallow and eutrophic lake in China, based on the segmented radon mass balance model and nutrient data. The total LGD flux was estimated to be 6.59 × 10⁹ m³ a^-1, representing 57.8 % of the annual flux from inflowing rivers. LGD was a significant hidden nutrient source, contributing total nitrogen (TN) and total phosphorus (TP) loads to the entire lake comparable to those of the inflowing rivers. Dissolved inorganic forms dominated these LGD-derived nutrient loads. Spatially, the majority of TN (59.9 %) and TP (62.4 %) loads derived from LGD originated from sub-area III (southwest), which differed from the dominant area of riverine inputs, sub-area II (northwest). In addition, the significant enrichment of nitrogen observed in LGD suggests its potential to mitigate nitrogen limitation in the lake. The increasing nitrogen limitation in Taihu Lake and the prevalence of nitrogen limitation in eutrophic lakes worldwide indicate that nitrogen is a key nutrient in managing LGD-derived nutrient loads. This study highlights the importance of integrating LGD-derived nutrient loads into nutrient reduction strategies to reverse eutrophication in large eutrophic lakes, especially those with nitrogen limitation.