Spatial characteristics and correlation analysis of Nitrogen pollution from land and sea in Guangdong province

Total nitrogen (TN) from land-based sources is the main source of dissolved inorganic nitrogen (DIN) pollution in coastal waters of Guangdong province. Clarification of the structure, discharge pressure and main influencing factors of nitrogen emissions from the land area is needed to manage marine nitrogen pollution. We utilized observation data of water quality and statistical data of pollution sources to analyze the Spatial characteristics, source structure, emission intensity and regional differences of nitrogen pollution in Guangdong Province. Pearson correlation analysis was used to reveal the main influencing factors of nitrogen emissions. The results show that: (1) The concentrations of TN are ranged from 1.10 mg/L to 9.19 mg/L in the rivers during 2020－2022. The high concentration sites of TN were mainly distributed in the river network area of the Pearl River Delta, the rivers in eastern Guangdong, and the lower reaches of the Dongjiang Rive. The total nitrogen concentration in low water period was higher than that in wet season. (2) Domestic sewage is the main source of TN pollution in Guangdong Province, which accounting for 59.79%, followed by agricultural pollution accounting for 36.10%. The distribution of marine pollution and the intensity of land-based nitrogen pollution emission are spatially consistent. There is a largest number of pollution emissions in the the the Pearl River Delta, the shoreline sections belonging to it carry the greatest emission pressure. Correspondingly, the Pearl River estuary is the primary zone in which the water quality inferior to Class Ⅳ. Population size is the main factor affecting TN discharge in this area.