[Dry and Wet Deposition of Atmospheric Nitrogen in Small Catchments]

Atmospheric nitrogen deposition is one of the important pathways for the transmission of terrestrial pollutants and nutrients to aquatic ecosystems. A considerable amount of nitrogen substances is delivered into the surface water environment via atmospheric deposition in the catchments, which are greatly affected by human activities, and have serious negative effects on the nutrient level and aquatic habitat environment. The Shixia Catchment north of the Miyun Reservoir was selected as study area. Samples of particulate dry and wet deposition were collected and tested. Subsequently, the variation of the atmospheric nitrogen deposition flux and factors impacting it were determined; ultimately, the contribution of atmospheric nitrogen deposition to the nitrogen budget of the catchment was estimated. The major results are as follows:① The total nitrogen deposition flux of particulate dry and wet deposition is characterized by a significant temporary variation. Regarding the total nitrogen, the ammonia nitrogen and wet deposition flux are the highest in summer and dissolved organic nitrogen is the highest in spring. However, the flux of nitrate nitrogen shows no notable seasonal fluctuation. The general trend of the particulate dry deposition flux is supreme in winter, followed by that in autumn and spring. In detail, the total nitrogen and ammonia nitrogen deposition are the largest in winter, while the seasonal variance of nitrate nitrogen appears to be less apparent. The dry deposition flux of dissolved organic nitrogen is the greatest in autumn. ② The total flux of nitrogen deposition is 43.14 kg·hm^-2 in the Shixia Catchment; the wet and dry deposition flux account for 39.85% and 60.15%, respectively. ③ Rainfall and wind speed conditions are important factors impacting the atmospheric nitrogen deposition. The rainfall and rainfall intensity are negatively correlated with the wet nitrogen deposition concentration. With respect to the particulate dry deposition, the average wind speed during the monitoring period is important to ammonia nitrogen. ④ The contribution of atmospheric nitrogen deposition to the total nitrogen input in this catchment is approximately 15.09%, second only to livestock and poultry farming and rural life. The results of this study provide information that is useful for the nitrogen management in the catchment.