Xueyu Cave watershed is located in Fengdu County in the outskirts of Chongqing, where rainfall events were monitored continuously from July 2015 to December 2017. We explored the variation of mass concentration of atmospheric dissolved inorganic nitrogen (NH4+-N and NO3--N), and quantitatively calculated its wet deposition fluxes, then the sources of NH4+-N and NO3--N were tracked using the Xueyu cave air mass backward trajectory model. The results showed that:①During the monitoring period, the average annual dissolved inorganic nitrogen (DIN) deposition in the watershed was 14.25 kg·(hm2·a)-1, of which NH4+-N and NO3--N were 7.72 kg·(hm2·a)-1 and 6.53 kg·(hm2·a)-1, accounting for 54% and 46% of DIN wet precipitation, respectively, and indicating that NH4+-N is the dominant species, followed by NO3--N; ②DIN wet deposition flux and concentration showed marked seasonal changes. The DIN wet deposition flux in spring and summer was 50% higher than that in autumn and winter, while the DIN concentration of wet deposition in autumn and winter was 30% higher than those in spring and summer. ③NH4+-N/NO3--N was between 0.29 and 2.27, and NH4+-N/NO3--N > 1 during the rainy season (April to October) and NH4+-N/NO3--N < 1 during the dry season (November to March), indicating that the main sources of DIN wet deposition results from agricultural activities in the rainy season, and urban contributions in the dry season. ④In the study area, the southeastern winds are dominant in the rainy season but southwestern winds are dominant in the dry season. These determine the sources of DIN wet deposition (agricultural or urban).
Keywords: NH4+-N; NO3--N; Xueyu Cave watershed; nitrogen wet deposition; source analysis.