[Temporal and Spatial Distribution Characteristics and Difference Analysis of Nitrogen and Phosphorus in Daihai Lake]

Based on the historical monitoring survey data from 2018 to 2019, the temporal and spatial distribution characteristics and main influencing factors of nitrogen and phosphorus in the overlying water in Daihai Lake were analyzed, and the differences of the temporal and spatial distribution were discussed. The results showed that the content of total nitrogen and total phosphorus in the overlying water was at a high level, especially the total nitrogen content was obviously higher than that in other lakes in China. The content of total nitrogen ranged from 3.29 mg·L^-1 to 4.99 mg·L^-1, with a mean value of (3.93±0.33) mg·L^-1; the content of total phosphorus ranged from 0.063 mg·L^-1 to 0.163 mg·L^-1, with a mean value of (0.111±0.023) mg·L^-1. In spring and summer, the content of total nitrogen and total phosphorus in the overlying deep water from the middle of the lake was significantly higher than that in the surrounding area. In autumn, the contents decreased from east to west, and in winter, the contents in the shallow water of the southern area were higher than that in the northern area. Nitrogen and phosphorus in the overlying water were mainly in the dissolved state, and the proportions of total dissolved nitrogen and phosphorus were 86.62% and 77.84%, respectively. The dissolved nitrogen was dominated by nitrate, whereas dissolved phosphorus was dominated by organic phosphorus. The concentration of lake water and the release of endogenous nutrient salts are the main reasons for the high total nitrogen and phosphorus. To prevent further deterioration of water quality, it is suggested to carry out endogenous treatment and ecological restoration in combination with engineering measures.