Spatial Distribution and Environmental Significance of Phosphorus Fractions in River Sediments and Its Influencing Factor from Hongze and Tiaoxi Watersheds, Eastern China.

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.

Spatial variations in and environmental significance of nitrogen forms in river sediments from two different watersheds in eastern China.

Nitrogen is considered an essential nutrient element limiting water productivity, and its distribution in sediments directly affects its release potential. This study aimed to analyse the spatial characteristics, distribution, and influence of nitrogen forms in two different river catchments situated in eastern China. Using sequential extraction methods, the study divided sediment nitrogen into four forms, namely, an ion-exchangeable form (IEF-N), weak acid-extractable form (WAEF-N), strong alkali-extractable form (SAEF-N), and strong oxidant-extractable form (SOEF-N). The results for the two catchments showed significant differences in the physicochemical properties as well as variations in space. The mean proportion of total transferable nitrogen (TTN) in the Anhe, Suihe, Dongtiaoxi, and Xitiaoxi rivers accounted for 50.64%, 32.87%, 34.63%, and 40.45%, respectively. The results also revealed a higher total TTN in the Hongze watershed than in the Tiaoxi watershed. The order of mean TTN in sediments from the Hongze watershed was SOEF-N > SAEF-N > IEF-N > WAEF-N, whereas that for the Tiaoxi watershed was SOEF-N > SAEF-N > WAEF-N > IEF-N. The distribution of nitrogen forms in the sediments was significantly impacted by the sediment composition and environmental factors, as shown by correlation and redundancy analysis (RDA).

[Spatial Distributions of Transferable Nitrogen Forms and Influencing Factors in Sediments from Inflow Rivers in Different Lake Basins].

It is necessary to investigate the distribution of nitrogen forms in river sediments to recognize the water environment quality. In this study, ion exchangeable form nitrogen(IEF-N), weak acid extractable form nitrogen (WAEF-N), strong alkali extractable form nitrogen (SAEF-N) and strong oxidation extractable form nitrogen (SOEF-N) in sediments were obtained by means of sequential extraction procedures.We analyzed the spatial variations of nitrogen forms in sediments from Taihu watershed (Dongtiaoxi River and Xitiaoxi River) and Hongzehu watershed (Anhe River and Suihe River), and expounded the influence factors of nitrogen form distribution. The results showed that the physicochemical properties of sediments from different watersheds varied in space. The concentrations of total nitrogen and nitrogen fractions also showed obvious changes in river sediments. As a whole, the concentrations of total nitrogen and transferable nitrogen in Taihu rivers were higher than those in Hongzehu rivers, but the former showed smaller spatial changes. Sediments from Taihu rivers showed the different concentration order of total nitrogen and transferable nitrogen comparing with those from Hongzehu rivers. The former followed the order of SOEF-N > SAEF-N > IEF-N > WAEF-N, and the latter followed the order of SOEF-N > SAEF-N > WAEF-N > IEF-N.The spatial varitions of transferable nitrogen fractions in Hongzehu rivers were prominent, which was associated with nitrogen sources. The spatial distributions of transferable nitrogen in sediments were obviously affected by their physicochemical properties, especially for organic matter and grain size.