Atmospheric Inorganic Nitrogen Deposition and Its Influence on the Coastal Water Nutrients in Xiamen

Atmospheric nitrogen deposition in coastal areas has a significant impact on water nutrients, with increasing emission of atmospheric nitrogen-containing pollutants. Clarifying the characteristics, source, and nutrient impact of atmospheric inorganic N deposition is therefore critical for targeted eutrophication control in coastal areas. Dry and wet atmospheric nitrogen deposition samples were collected and integrated into the atmospheric deposition model to analyze the influence of the deposition flux and source on coastal water nutrients. The results showed that inorganic nitrogen in the atmosphere over Xiamen’s coast was mainly composed of NH4+-N and NO3−-N. A high concentration of nitrogen was found in the cold season. Source apportionment analysis revealed that NH4+-N mainly originated from agricultural sources, while NO3−-N was primarily derived from traffic sources (24%) and secondary sources (25%). The wet deposition flux of NH4+-N and NO3−-N was significantly larger than the dry deposition flux. The NO3−-N wet deposition flux was elevated during winter and summer, whereas the dry deposition flux peaked in spring and winter. A high NH4+-N wet deposition flux was also found in spring and summer. Spatially, the inorganic nitrogen deposition flux was higher in offshore areas than in the inner bay, which was attributed to the higher wind speed in the offshore region. The atmospheric inorganic nitrogen input accounted for only 0.9% to 1.8% of the inorganic nitrogen input from the Jiulong River to Xiamen Bay; however, the NO3− concentration in Xiamen Bay showed a significant positive correlation with the dry deposition flux of atmospheric nitrogen (p < 0.05). Atmospheric nitrogen deposition directly affects coastal water nutrients without estuarine filtration. This study clarifies the different sources of atmospheric inorganic nitrogen deposition and their contribution to coastal water nutrients, providing an important basis for eutrophication in coastal areas, as well as pollutant control and emission reduction efforts.