Depth-dependent phosphorus leaching risks in littoral soils of Lake Dianchi under extreme rainfall.

Littoral zones and constructed riparian buffers of eutrophic lakes receive long-term non-point phosphorus (P) inputs and are widely used to buffer agricultural runoff, yet under intensifying rainfall events they may turn into important P sources that threaten the sustainability of lake restoration efforts. This study quantified depth-dependent P release, adsorption and leaching along a 0-60 cm soil profile in the Lake Dianchi littoral zone using batch sorption-desorption experiments and dynamic column tests that simulated short, high-intensity rainfall and groundwater rise. All horizons contained extremely high total P (TP;1.19-2.21 g kg-1) but showed contrasting P mobility. The 0-10 and 30-40 cm layers combined high legacy P and organic matter with low additional sorption capacity and slow adsorption kinetics, leading to rapid breakthrough, high C/C₀ values and the largest P leaching loads. The 50-60 cm layer displayed higher sorption capacity and fast initial uptake under static conditions, but released Fe-bound P under prolonged saturation and reducing conditions, indicating limited long-term buffering. During elution, effluent P concentrations in all layers generally exceeded influent levels, showing that storm infiltration mobilised both incoming and soil-stored P. These results identify the 0-10 and 30-40 cm horizons as critical "leaky layers" that control vertical P transfer from littoral soils to groundwater and the lake, highlighting the need for depth-targeted vegetation and soil-amendment strategies to sustain the long-term effectiveness of littoral zones as nature-based solutions for eutrophication control in plateau lakes.