Abstract Variation in source areas and source types of atmospheric nitrogen (N) deposition to high-elevation ecosystems in the Rocky Mountains were evaluated using spatially and temporally distributed N isotope data from atmospheric deposition networks for 1995-2016. This unique dataset links N in wet deposition and snowpack to mobile and stationary emissions sources, and enhances understanding of the impacts of anthropogenic activities and environmental policies that mitigate effects of accelerated N cycling across the Rocky Mountain region. δ15N−NO3− at 50 U.S. Geological Survey Rocky Mountain Snowpack (Snowpack) sites ranged from −3.3‰ to +6.5‰, with a mean value of +1.4‰. At 15 National Atmospheric Deposition Program (NADP)/National Trends Network wet deposition (NADP Wetfall) sites, summer δ15N−NO3− is significantly lower ranging from −7.6‰ to −1.3‰ while winter δ15N−NO3− ranges from −2.6‰ to +5.5‰, with a mean value of +0.7‰ during the cool season. The strong seasonal difference in NADP Wetfall δ15N−NO3− is due in part to variation in the proportion of N originating from source regions at different times of the year due to seasonal changes in weather patterns. Snowpack NO3− and δ15N−NO3− are significantly related to NADP Wetfall (fall and winter) suggesting that bulk snowpack samples provide a reliable estimate at high elevations. Spatial trends show higher NO3− concentrations and δ15N−NO3− in the Southern Rocky Mountains located near larger anthropogenic N emission sources compared to the Northern Rocky Mountains. NADP Wetfall δ15N−NH4+ ranged from −10‰ to 0‰, with no observed spatial pattern. However, the lowest δ15N−NH4+(−9‰), and the highest NH4+ concentration (35 μeq/L) were observed at a Utah site dominated by local agricultural activities, whereas the higher δ15N−NH4+ observed in Colorado and Wyoming are likely due to mixed sources, including fossil fuel combustion and agricultural sources. These findings show spatial and seasonal variation in N isotope data that reflect differences in sources of anthropogenic N deposition to high-elevation ecosystems and have important implications for environmental policy across the Rocky Mountain region.

中文翻译：

---

利用氮同位素分析落基山脉大气氮沉积源的时空变化

摘要 利用1995-2016年大气沉降网络中时空分布的N同位素数据，评估了落基山脉高海拔生态系统大气氮(N)沉降源区和源类型的变化。这个独特的数据集将湿沉积和积雪中的 N 与移动和固定排放源联系起来，并增强了对人为活动和环境政策影响的理解，这些影响减轻了落基山脉地区加速 N 循环的影响。美国地质调查局 50 个落基山积雪 (Snowpack) 站点的 δ15N−NO3− 范围从 -3.3‰ 到 +6.5‰，平均值为 +1.4‰。在 15 个国家大气沉积计划 (NADP)/国家趋势网络湿沉降 (NADP Wetfall) 站点，夏季 δ15N−NO3− 显着降低，范围为 -7。6‰～-1.3‰，冬季δ15N−NO3−范围为-2.6‰～+5.5‰，凉季平均值为+0.7‰。NADP 降水 δ15N−NO3− 的强烈季节性差异部分是由于天气模式的季节性变化导致一年中不同时间源区氮的比例发生变化。积雪 NO3− 和 δ15N−NO3− 与 NADP 降雨量（秋季和冬季）显着相关，表明大量积雪样本在高海拔地区提供了可靠的估计。空间趋势表明，与北落基山脉相比，位于较大人为氮排放源附近的南落基山脉中的 NO3− 浓度和 δ15N−NO3− 更高。NADP 降水 δ15N−NH4+ 范围从 -10‰ 到 0‰，没有观察到空间格局。然而，最低的 δ15N−NH4+(−9‰)，在以当地农业活动为主的犹他州观察到最高 NH4+ 浓度 (35 μeq/L)，而在科罗拉多州和怀俄明州观察到的较高 δ15N-NH4+ 可能是由于混合来源，包括化石燃料燃烧和农业来源。这些发现显示了 N 同位素数据的空间和季节性变化，反映了人为 N 沉积来源与高海拔生态系统的差异，并对整个落基山脉地区的环境政策具有重要意义。