丹江口水库淅川库区大气氮湿沉降特征

大气氮沉降是除河流输入外水库水体重要的外源氮输入途径。以丹江口水库淅川库区为研究区，于2018年11月至2019年10月在库区周边设置了6个采样点，采集并分析了库区大气氮湿沉降样品，探讨氮湿沉降的时空分布特征以及对水库水体外源氮输入的贡献。研究结果表明，研究区大气氮湿沉降量为24.21 kg hm^-2 a^-1，其中氨氮占比（47.45％）为最大，有机氮占比（36.34％）次之，硝氮占比（16.21％）最小。硝氮湿沉降量在空间上表现出显著差异性。氨氮、有机氮湿沉降量的季节差异显著，氨氮是以夏季最高，秋季次之，冬季最低，而有机氮是以秋季最高，夏季次之，冬季最低。氨氮、硝氮、有机氮湿沉降量之间存在显著相关性，氨氮、有机氮湿沉降量与降水量之间存在显著相关性。总氮、氨氮湿沉降量分别为1321.98 t/a和627.34 t/a，分别占河流总氮、氨氮入库量的10.82％、34.85％。研究结果可为探索有针对性的库区水体氮污染控制途径提供重要理论基础。

Atmospheric wet deposition characteristics of nitrogen in the Xichuan area of Danjiangkou reservoir

Globally, large increases in anthropogenic emissions of reactive nitrogen because of energy and agricultural development and rapid urban growth have led to the terrestrial and aquatic ecosystem nitrogen deposition. Approximately 55% of the artificially fixed nitrogen is redistributed back to the atmosphere as NO_X and NH₃. Excessive nitrogen deposition has caused negative impacts on ecosystem health and services, such as water body deterioration, biodiversity loss, soil degradation, stratospheric ozone reduction and increased susceptibility to secondary stresses. Danjiangkou reservoir is a gorge-type reservoir and forms a total 1050 km² reservoir area. The reservoir plays a central role in the drinking water source of the South-North Water Transfer Project, which is designed to relieve the water shortage and support sustainable social and economic development in northern China. Hence, both government and public have been increasingly concerned of the water quality of the reservoir. Atmospheric nitrogen deposition is an important pathway for the exogenous nitrogen input to reservoir, except for the loading of rivers into reservoir. However, until now, less attention has been paid on the flues of nitrogen deposition in the large scale reservoir. This study aimed to discuss the spatiotemporal distribution characteristics of nitrogen wet deposition and quantify its contribution to total nitrogen loads for Danjiangkou reservoir. The Xichuan area of Danjiangkou reservoir was selected as the study area, and the wet deposition samples of atmospheric nitrogen were collected and analyzed at the six sites around the reservoir from November 2018 to October 2019. The results showed that the fluxes of nitrogen wet deposition was 24.21 kg hm^-2 a^-1 in the study area, and the fluxes were in the following order:ammonia nitrogen (47.45%) > organic nitrogen (36.34%) > nitrate nitrogen (16.21%). Nitrate wet deposition fluxes showed significant difference in the space. The wet deposition fluxes of ammonia nitrogen and organic nitrogen exhibited significant difference among four seasons. The wet deposition fluxes of ammonia nitrogen were in the following order:summer > autumn > spring > winter, while the order of organic nitrogen fluxes was autumn > summer > spring > winter. There were significant positive correlations among the wet deposition fluxes of ammonia nitrogen, nitrate nitrogen and organic nitrogen, and so were the correlations between the wet deposition fluxes of ammonia nitrogen and organic nitrogen and precipitation. The wet deposition fluxes of total nitrogen and ammonia nitrogen were 1321.98 t/a and 627.34 t/a, respectively, which accounted for 10.82% and 34.85% of the loading of rivers into the reservoir. The results of this study can provide the important theoretical basis of controlling pathway for nitrogen pollution in the reservoir.