人类活动对乌梁素海流域水体氮磷负荷变化的影响OACHSSCD

Wuliangsuhai Lake has experienced worsening eutrophication since the 1990s,primarily driven by substantial inputs of agricultural drainage and municipal wastewater,with nitrogen(N)and phosphorus(P)identified as the major pollutants.This study employed the integrated IMAGE-GNM model coupled with an irrigation drainage module to simulate the spatiotemporal transport and fate of N and P from terrestrial sources to the lake outlet over the period 1990-2022.The objectives were to quantify nutrient sources,elucidate transport mechanisms,and identify dominant anthropogenic drivers affecting nutrient dynamics.Model results indicated that intensive agricultural expansion and accelerated urbanization between 1990 and 2012 significantly increased diffuse nutrient sources(e.g.,synthetic fertilizers,livestock manure)and municipal point-source discharges.These pressures led to a substantial rise in basin-wide nutrient inputs and exports,peaking in 2012 at 1787 t N/a and 84 t P/a at the basin outlet.Spatial source attribution revealed that agricultural groundwater discharge and municipal wastewater collectively contributed approximately 80%of total N inputs to surface waters,while P loading was predominantly driven by sewage discharge,accounting for an average of 69%of total sources.Following 2013,the implementation of policies targeting fertilizer reduction and enhanced use efficiency,alongside major improvements in wastewater treatment infrastructure,led to marked declines in nutrient loads.By 2022,TN and TP exports to the lake had decreased by 63%and 71%,respectively,relative to peak values.Furthermore,the lake's role in nutrient retention increased during the high-load period(up to 56%for N and 53%for P around 2012)due to reduced inflows and slower water velocities,but later declined to 48%(N)and 33%(P)by 2022 as ecological water supplementation enhanced hydrological flushing.These results underscore the critical role of hydrological regulation in improving water quality and highlight the need to prioritize agricultural nutrient management(e.g.,improving nutrient use efficiency,optimizing irrigation practices)and enhancing point-source pollution control for sustainable basin-scale nutrient management in the Hetao Irrigation District.