Nitrogen and phosphorus in sediments in China: A national-scale assessment and review

A national-scale investigation of total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), and pH in sediments was performed. The sediment samples investigated in this study were collected from 10 major basins in China (Songhua River Basin (SRB), Liao River Basin (LRB), Hai River Basin (HRB), Yellow River Basin (YRB), Huai River Basin (HuRB), Yangtze River Basin (YtRB), Southeastern River Basin (SeRB), Pearl River Basin (PRB), Southwestern River Basin (SwRB), and Northwestern River Basin (NwRB)). And then, a pollution assessment was performed by comparing the data with established sediment quality guidelines (SQGs) and organic nitrogen index values. Results demonstrated that the mean TN content in the sediments of the 10 basins was 1.070g/kg, while the mean TP content was 0.733g/kg. The TN contents displayed significantly positive correlations with the TP contents in the sediments of SRB, LRB, YtRB, SeRB, PRB, and NwRB. Moreover, the concentrations of TN in the sediments of nine basins (SRB, LRB, HRB, YRB, HuRB, YtRB, SeRB, PRB, and NwRB) and TP concentrations of four basins (LRB, YtRB, SeRB, and PRB) were possibly related to the TOC contents, and the distributions of TN concentrations in eight basins (SRB, LRB, HRB, YRB, YtRB, SeRB, PRB, and NwRB) as well as the TP concentrations in LRB might be affected by the pH of sediments. By comparing the data in our study with those obtained in other periods (1990-2013), we found that the TN contamination situation in HuRB and the TP contamination situation in PRB have potentially worsened over time, which deserves more attention. According to the results of SQGs and organic nitrogen index assessment, among the 10 basins, SeRB was the worst watershed polluted by N and HRB was the worst watershed polluted by P.