Distribution Characteristics and Pollution Assessment of Nutrients in Hengshui Lake Sediments

Abstract

Considering Hengshui Lake as the research object, the representative surface sediments at eleven points were collected in March 2019, and the morphological distribution characteristics of carbon, nitrogen, and phosphorus nutrients in the lake sediments were analyzed. The results showed that the total organic carbon (TOC) content in Hengshui Lake sediments was 93.226 mg·g-1, which might lead to a higher risk of potential nitrogen source release. The total nitrogen (TN) content was 1.850 mg·g-1, which was a moderate pollution load; the contents of various nitrogen forms and the proportions in TN were Res-N (0.973 mg·g-1, 52.57%) > WAEF-N (0.531 mg·g-1, 28.69%) > SOEF-N (0.208 mg·g-1, 11.23%) > IEF-N 0.088 (mg·g-1, 4.77%) > SAEF-N (0.051 mg·g-1, 2.75%). These results further indicated that the risk of nitrogen release from sediments in Hengshui Lake was relatively high. The content of total phosphorus (TP) was 1.020 mg·g-1 and that of inorganic phosphorus (IP) was 0.839 mg·g-1, accounting for 82.27% of the TP content, which was a moderate pollution load; the average content of various phosphorus forms and the proportions in IP were Ca-P (0.440 mg·g-1, 52.44%) > Res-P (0.200 mg·g-1, 23.84%) > Fe-P and Al-P (0.169 mg·g-1, 20.14%) > NH4Cl-P (0.030 mg·g-1, 3.58%). In general, the risk of phosphorus release from sediments in Hengshui Lake was relatively low. The analysis of C/N, C/P, and N/P characteristics showed that the organic matter in Hengshui Lake sediments mainly originated from terrestrial grasses and sedge plants, and the phosphorus in the sediments was mainly affected by terrestrial input. Correlation analysis showed that the correlation between carbon, nitrogen, and phosphorus in Hengshui Lake sediment was weak, and the sources of the three nutrients might be different; the correlation between each form of phosphorus was stronger than that of each form of nitrogen, and each form of phosphorus had very good homology. The sources of various forms of nitrogen were diverse and complex. The pollution status of the lake area was evaluated by organic index and organic nitrogen. The results showed that the nutrient pollution in Hengshui Lake sediments was serious, reaching the Grade Ⅳ standard. The potential risk of nitrogen in sediments should be taken seriously and effectively controlled.