Influence of nitrogen wet deposition on nitrogen output in a typical watershed in the Three Gorges Reservoir Area

In order to explore the influence of wet nitrogen (N) deposition on N output in watersheds, this study selected a typical small watershed (Chenjiagou, CJG) in the Three Gorges Reservoir (TGR) area based on one-year observation of rainfall-runoff N forms. Characteristics and sources of N output were clarified by chemical statistics and isotopic abundance, and the contribution of N deposition to the N output was quantified by the output coefficient method. The N flux of wet deposition was estimated at 18.53 kg N ha−1 yr−1, and originated mostly from agricultural activities. Watershed N was significantly accumulated from upper to lower reaches due to frequent human activities. Seasonal changes of riverine N were strongly affected by chemical fertilizer, with the highest concentration in spring and the lowest in winter. Nitrate was mainly derived from chemical fertilizer, accounting for 38.83% of all sources. N concentration in processes of different rainfall events had a hysteresis effect corresponding to the flow rate. Three rainfall events greatly changed DTN (Dissolved total N) outputs: rainstorm caused 91.26 kg DTN output, which was 11 times that of moderate rain (8.46 kg) and 4 times that of heavy rain (20.80 kg). N deposition contributed 19.89% of riverine N output in the watershed. The results can provide theoretical support for the control of N pollution in the TGR area.