Seasonal fluxes and sources apportionment of dissolved inorganic nitrogen wet deposition at different land-use sites in the Three Gorges reservoir area.

To identify seasonal fluxes and sources of dissolved inorganic nitrogen (DIN) wet deposition, concentrations and δN signatures of nitrate (NO) and ammonium (NH) in wet precipitation were measured at four typical land-use types in the Three Gorges reservoir (TGR) area of southwest China for a one-year period. Higher DIN fluxes were recorded in spring and summer and their total fluxes (averaged 7.58 kg N ha) were similar to the critical loads in aquatic ecosystems. Significant differences of precipitation δN were observed for NH-N between town and wetland sites in spring and between urban and rural sites in summer. For NO-N, significant differences of precipitation δN were observed between town and rural sites in spring and between urban and town sites in autumn, respectively. Quantitative results of NO-N sources showed that both biomass burning and coal combustion had higher fluxes at the urban site especially in winter (0.18 ± 0.09 and 0.19 ± 0.08 kg N ha), which were about three times higher than those at the town site. A similar finding was observed for soil emission and vehicle exhausts in winter. On the whole, DIN wet deposition averaged at 12.13 kg N ha yr with the urban site as the hotspot (17.50 kg N ha yr) and regional NO-N fluxes had a seasonal pattern with minimum values in winter. The contribution to NO-N wet deposition from biomass burning was 26.1 ± 14.1%, which is the second dominant factor lower than coal combustion (26.5 ± 12.6%) in the TGR area during spring and summer. Hence N emission reduction from biomass burning, coal combustion and vehicle exhausts should be strengthened especially in spring and summer to effectively manage DIN pollution for the sustainable development in TGR area.