Long-range transport of atmospheric pollutants threatens the pristine high-elevation environments, highly sensitive to environmental changes such as the global increase of nitrogen (N) emissions. Atmospheric depositions is an important component of N cycle transferring reactive nitrogen species from the atmosphere to terrestrial and aquatic compartments. Despite this, monitoring of atmospheric deposition in Alpine tundra regions is lacking. To reduce this gap, we present the chemical and isotopic composition (N, O in nitrate) of rain and snow deposition collected over a 3-year period (2018–2020) in a LTER site (A. Mosso Scientific Institute) in NW Italian Alps at 2901 m a.s.l. The highest annual volume-weighted mean (VWM) concentrations of oxidized and reduced N species (18 and 22 μeq L, respectively) occurred in summer, while the lowest (5.8 and 3.6 μeq L, respectively) occurred during the snow season. The N wet deposition load (3.9 kg ha y.) greatly exceeded the N critical threshold, revealing that the area is exposed to excessive N input through atmospheric deposition with potentially detrimental consequences for aquatic ecosystems. The contribution of rain to inorganic N varied between 39 and 68 %, highlighting the importance of monitoring the composition of the rain component, in addition to the snowpack, even at high-altitude sites. The nitrate isotopic composition of wet deposition showed seasonal variation with lower δN–NO values (−10.6 ‰ to −2.2 ‰) in the summer months, reflecting the influence of vehicle emissions likely combined with an increase in emissions from agricultural sources, when the air masses originate from the Po Valley. Surface meteorological data coupled to the analysis of stable isotopes and air mass back trajectories showed that local mountain-valley breeze and the elevation of the continuous aerosol layer altitude in the warm season expose the study site to N-air pollutants originating from lowland and more distant anthropized areas (e.g., Po Valley). The reported data suite represents, to date, the first documentation for ecosystems above the tree line in the European scenario.

中文翻译：

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高海拔高山环境中的氮大气沉降：采用化学和同位素方法研究人为地区的影响

大气污染物的远距离迁移威胁着原始的高海拔环境，这些环境对全球氮（N）排放增加等环境变化高度敏感。大气沉积是将活性氮从大气转移到陆地和水生区域的氮循环的重要组成部分。尽管如此，仍缺乏对高山苔原地区大气沉降的监测。为了缩小这一差距，我们展示了意大利西北部 LTER 站点（A. Mosso 科学研究所）在 3 年期间（2018 年至 2020 年）收集的雨雪沉积物的化学和同位素组成（硝酸盐中的 N、O）阿尔卑斯山海拔 2901 m asl 氧化氮和还原氮的年体积加权平均 (VWM) 浓度最高（分别为 18 和 22 μeq L）出现在夏季，而最低（分别为 5.8 和 3.6 μeq L）发生在夏季。雪季。氮湿沉降负荷（3.9千克公顷）大大超过了氮临界阈值，表明该地区通过大气沉降暴露于过量氮输入，对水生生态系统可能产生有害后果。降雨对无机氮的贡献在 39% 至 68% 之间变化，这凸显了除了积雪之外监测降雨成分的重要性，即使在高海拔地区也是如此。湿沉降的硝酸盐同位素组成呈现季节性变化，夏季月份 δN-NO 值较低（-10.6 ‰ 至 -2.2 ‰），反映了车辆排放的影响，可能与农业源排放增加相结合，当空气群众来自波河流域。地面气象数据与稳定同位素和气团回弹轨迹分析相结合表明，当地的山谷风和温暖季节连续气溶胶层高度的升高使研究地点暴露于来自低地和更远地区的氮空气污染物人类居住区（例如波河流域）。所报告的数据套件代表了迄今为止欧洲情景中林线以上生态系统的第一份文档。