Abstract: Nitrogen deposition is a vital pathway for the input of exogenous nitrogen into reservoir waters, which has a direct effect on aquatic ecosystems. By collecting 162 atmospheric nitrogen dry deposition samples from the Xichuan area of the Danjiangkou Reservoir, we analyzed the characteristics of nitrogen dry deposition fluxes, the contribution of typical agricultural periods to nitrogen deposition, and potential ecological impacts. The results showed that the nitrogen dry deposition flux was 22.60 kg N·hm^-2·a^-1 and that organic nitrogen deposition accounted for approximately 50.8% of the total nitrogen deposition fluxes. The dry deposition was dominated by organic nitrogen deposition. The nitrogen dry deposition fluxes were higher in the northeast and southwest regions than that in the north and southwest regions of the reservoir. Fluxes of total nitrogen, organic nitrogen, and urea deposition were higher in spring and autumn than in summer and winter. Seasonal characteristics were related to nitrogen source, agricultural production activities, and meteorological factors. The mean value of monthly nitrogen dry deposition during the typical agricultural period was 1.75 times higher than that during the atypical agricultural period. The contribution of agricultural activities to the total deposition could not be ignored. Atmospheric nitrogen dry deposition flux was 2.26 times that of the critical load of total nitrogen deposition from nutrients in lakes in China and was associated with the potential risk of water eutrophication. Given that agricultural activities significantly affect nitrogen deposition, attention should be paid to the effects of typical agricultural activity periods on aquatic ecosystems.

Key words: Danjiangkou Reservoir, nitrogen deposition, spatial and temporal characteristics, agricultural activity, ecological impact.