Abstract: Honghu Lake, the seventh largest freshwater lake in China, has been undergoing serious eutrophication in recent years. Investigating into the content and distribution characteristics of nitrogen, phosphorus and organic matters in the sediment of Honghu lake is of great significance for acquiring its eutrophication status and ecological risks of nitrogen and phosphorus pollution. In the present research, we deployed eight sampling points and collected 50 cm height columnar sediments in October 2019. By measuring the content of total nitrogen (TN), total phosphorus (TP) and organic matters (OM) of sediment specimens from different depths, we examined the spatial distribution patterns of TN, TP and OM and their correlations. Furthermore, we evaluated the corresponding pollution status by using comprehensive pollution index. Results manifested that the TN content of Honghu sediments ranged from 467.8-8 454.5 mg/kg, averaging 2 167 mg/kg, indicating heavy pollution. Nearly half of surface sediments presented a TN content over 5 000 mg/kg. TP content ranged from 502.7 to 1 252.4 mg/kg, with an average value of 693.8 mg/kg. Except for Yangchai lake which suffered heavy pollution, most of the areas were subjected to medium TP pollution. The content of organic matters ranged from 5.0% to 24.9%, with an average value of 9.6%, also implying heavy pollution. In vertical scale, TN, TP and OM accumulated significantly in the surface layer of the sediments from 0 to 20 cm, and then declined rapidly with the increase of depth.

Key words: water environment, sediment, nitrogen, phosphorus, organic matter, pollution evaluation, distribution characteristics, Honghu Lake