The temporal-spatial distribution characteristics, sources and influencing factors of nitrogen and phosphorus in the coastal area of Jiangsu province

In recent years, the rapid economic development and frequent human activities along the coast of Jiangsu province have input excessive nitrogen (N) and phosphorus (P) into the sea, resulting in a continuous deterioration of water quality and a serious threat to the health of the ecosystem. Based on the water quality data of Jiangsu coastal waters from 2020 to 2022, the spatial and temporal distribution characteristics, the level of pollution, sources and influencing factors of nitrogen and phosphorus nutrients were analyzed. The results showed that the average concentrations of inorganic nitrogen (DIN) and inorganic phosphorus (DIP) were 0.234 mg/L and 0.012 mg/L in 2020-2022, respectively, with the highest concentration of DIN and DIP pollutants in 2020 (0.342 mg/L and 0.015 mg/L, respectively). In terms of spatial and temporal distribution, the concentrations of nitrogen and phosphorus nutrients gradually decreased from nearshore to offshore, and the concentrations of nitrogen and phosphorus nutrients in summer was higher than that in spring and fall. From 2020 to 2022, the coastal waters of Jiangsu Province were in a mild eutrophication state, but the N and P pollution in estuarine and bay areas was more serious. Among the coastal cities in Jiangsu coastal zone, the estuaries entering the sea in Yancheng city have the most inputs of the total annual DIN and DIP (19,600 tons and 600 tons, respectively). The sources of DIN and DIP were mixed sources of agriculture and aquaculture (60.54% and 75.36%), and mixed sources of manufacturing and domestic sewage (29.29% and 22.11%). DIN and DIP were mainly affected by agriculture, aquaculture and industry (72.69%). Among them, DIN was positively correlated with agriculture and livestock indicators, and DIP was positively correlated with agriculture and industry indicators. These findings suggest that source control of N and P pollution should be strengthened, organic agriculture and ecological farming systems should be built, and sewage treatment systems should be strengthened.