Quantify phosphorus transport distinction of different reaches to estuary under long-term anthropogenic perturbation

Typical diffuse pollutants such as phosphorus (P) have long been a hot topic in the surface-water research field. As the fifth-largest river in the world, the Yellow River Basin (YRB) suffers from significant soil erosion and relatively high intensity of agricultural activities, which bring large amounts of P loads. However, owing to the large drainage area, few studies have investigated the transport and attenuation dynamic processes or provided a precise calculation of the total phosphorus (TP) load for the entire YRB. In this study, the SPAtially Referenced Regressions on Watershed Attributes (SPARROW) model was used to simulate and investigate the spatial variation and transport mechanism of P in the YRB. The YRB was divided into 60 sub-basins, and the data of drainage area, spatial attribute, streamflow, and monitored flux were integrated into the model correspondingly. Calculated R² values confirm that 84% of the spatial variability in annual TP loads can represent regional processes. The estimated YRB TP load was 41,760 tons per year, contributed by farmland (64%), construction land (27%), grassland (5%), and forest (4%). In addition, the P transport dynamic process, contribution, and sensitivity of different P flux sources in different reaches were represented and identified. Our study highlights the significance of farmland as the most significant factor exacerbating TP pollution. As the study conducted the first attempt to develop a SPARROW model, integrated management strategies that consider the spatially varying P sources and associated TP transport were proposed. Additionally, to improve the ecological health of basin, it is critical to further increase P utilization efficiency and enhance cross-regional cooperation throughout the basin.