Best management practices mitigate climate-land use amplification of non-point source pollution in the Bailin River Basin.

Agricultural non-point source pollution contributes over 45% of total nitrogen (TN) and 65% of total phosphorus (TP) loads in China's Yangtze River Economic Belt, with its severity amplified by the synergistic interaction between climate change and land use transformation. This study investigates whether Best Management Practices (BMPs) can mitigate this climate-land-use amplification in the Bailin River Basin. Using SWAT and CLUE-S models, we integrated bias-corrected CMIP6 climate projections under four Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5), land-use transition scenarios, and spatially explicit BMP implementation strategies under two land-use pathways (natural development vs. territorial spatial planning). Results show that climate-land-use synergistic effects increase TN and TP loads by 118.23 t and 13.68 t relative to baseline under unmitigated conditions. Strategic BMPs implementation, specifically 20% fertilizer reduction combined with vegetative buffer strips, reduced TN and TP loads by 39.19% and 48.58%, substantially weakening the amplification effect. Under the territorial spatial planning scenario combined with BMPs, TN and TP loads were reduced by 16.5% and 22.0% relative to baseline, indicating that BMPs can reduce pollution loads under moderate climate stress (SSP2-4.5). Our findings demonstrate that BMPs function not merely as pollution mitigators but as partial buffers of climate-land-use amplification. While the quantitative reductions reported here are specific to the Bailin River Basin and the scenario framework examined, the integrated modeling approach and the mechanistic understanding of BMP-climate-land use interactions are transferable to comparable agricultural watersheds facing similar pressures.