[Land-based Nitrogen Pollution Source Structure and Spatial Distribution in Guangdong-Hong Kong-Macao Greater Bay...

Total nitrogen pollution from land-based sources carried by rivers is the main source of inorganic nitrogen entering the sea. Inorganic nitrogen pollution in the coastal waters of Guangdong-Hong Kong-Macao Greater Bay Area(GBA) is a serious problem. The water quality of an adjacent large area of the sea is classified as poor-category Ⅳ. Therefore, clarification of the scale, structure, and discharge pressure of nitrogen emissions from the land area of the GBA is needed to manage marine nitrogen pollution. Based on multi-source data, including land use, socio-economic statistics, and pollution source census information, the scale, source structure, and regional differences of total nitrogen discharge in GBA and surrounding cities were evaluated using administrative and watershed units. The results show that:①The total nitrogen emissions from the study area are approximately 332500 t. Residential waste is the main source of pollution, accounting for 55.4%, followed by cultivation, with 28.18%, while the contribution from animal husbandry and industrial production is relatively limited. ②The regional differences of total nitrogen emissions are obvious, and the total emissions from GBA(231400 t) are significantly higher than those from neighboring cities(101100 t). ③The distribution of marine pollution and intensity of land-based nitrogen pollution emissions are spatially consistent, which indicates that there is a large number of pollution emissions in the East River Basin, Northwest River Delta Basin, and Tan River Basin; the shoreline sections belonging to the basins carry the greatest emission pressure, lead to serious pollution in the Lingding Sea, Jin Bay, and Huangmao Sea.