Non-point source pollution is widely considered a serious threat to drinking water. Eutrophication in Chinese watershed is mainly due to nitrogen and phosphorus output from agricultural source. Taihu Lake is a typical eutrophic lake in China, a basin representative for the study of the temporal-spatial characteristics of pollution loading of nitrogen and phosphorus to provide scientific basis for reasonable estimation and targeted control measures of nitrogen and phosphorus loss. Based on data from nitrogen and phosphorus loss in agricultural land, livestock breeding, domestic discharge and aquaculture, this study calculated the levels of nitrogen and phosphorus comprehensive loss risk for each pollution source. Using the superposition of ArcGIS raster data, we also described the spatial distribution of nitrogen and phosphorus comprehensive loss risk by the formula of comprehensive loss risk. The results showed that critical risk areas of nitrogen and phosphorus loss mainly originated from livestock breeding and agricultural land during flood period in Tiaoxi watershed. Agricultural land and livestock breeding sources formed major parts of nitrogen loss, accounting for 30.85% and 36.18%, respectively, while phosphorus loss mainly originated from livestock breeding (56.28%). During non-flood period, integrated management of livestock breeding and domestic discharge requires much attention to control nitrogen and phosphorus loss in the critical risk area. Finally, it is of great practical significance to propose spatial-temporal targeted measurements to control nitrogen and phosphorus pollution in watershed for various periods and different areas.

This study explored the spatial distribution of phosphorus fractions in river sediments and analyzed the relationship between different phosphorus fractions and their environmental influence on the sediments within different watersheds in Eastern China. River sediments from two inflow watersheds (Hongze and Tiaoxi) to Hongze and Taihu Lake in Eastern China were analyzed by the sequential extraction procedure. Five fractions of sedimentary phosphorus, including freely sorbed phosphorus (NH₄Cl-P), redox-sensitive phosphorus (BD-P), bound phosphorus metal oxide (NaOH-P), bound phosphorus calcium (HCl-P), and residual phosphorus (Res-P) were all analyzed. The orders of rankings for the P fractions of the rivers Anhe and Suihe were HCl-P > NaOH-P > BD-P > NH₄Cl-P and HCl-P > BD-P > NaOH-P > NH₄Cl-P, respectively. For the rank order of the Hongze watershed, HCl-P was higher while the NH₄Cl-P contents were significantly lower. The rank order for the Dongtiaoxi River was NaOH-P > HCl-P > BD-P > NH₄Cl-P, and that of Xitiaoxi River was NaOH-P > BD-P > HCl-P > NH₄Cl-P. Compared with the phosphorus forms of the Tiaoxi watershed, NaOH-P contents were significantly higher compared to HCl-P, which was significantly higher in the Hongze watershed. In comparison, NH₄Cl-P contents were significantly lower in both. Variations may be attributed to differential discharge of the P form in the watershed due to land-use changes and urban river ambient conditions.

River sediment from two inflow watersheds (Hongze and Tiaoxi) to Hongze and Taihu Lake in Eastern China was analyzed by the sequential extraction procedure. This study aimed to explore a spatial distribution of phosphorus fractions in river sediments and analysed the relationship between different phosphorus fractions and their environmental influence on the sediments within different watersheds in Eastern China. Five fractions of sedimentary phosphorus, including freely sorbed phosphorus, were all analyzed (NH₄Cl-P), redox-sensitive phosphorus (BD-P), bound phosphorus metal oxide (NaOH-P), bound phosphorus calcium (HCl-P) and residual phosphorus (Res-P). The order of rank of the P fractions for the river Anhe was HCl-P>NaOH-P>BD-P>NH₄Cl-P; whereas that of the Suihe river was HCl-P>BD-P>NaOH-P>NH₄Cl-P. For the rank order of the Hongze watershed, HCl-P was higher while the NH₄Cl-P contents were significantly lower. The rank order for the Dongtiaoxi river was NaOH-P > HCl-P> BD-P> NH₄Cl-P and that of Xitiaoxi river was NaOH-P> BD-P> HCl-P> NH₄Cl-P. Compared with phosphorus forms of Tiaoxi watershed, NaOH-P contents were significantly higher in the converse of HCl-P contents were significantly higher in Hongze watershed while both in NH₄Cl-P contents were significantly lower. Variations may be attributed to differential discharge of P watershed form due to land-use changes and urban river ambient conditions.