Donald H. Campbell Christopher M.B. Lehmann M. Alisa Mast Leora Nanus 2018 <p><span>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. δ</span>¹⁵<span>N−NO</span>₃⁻<span><span>&nbsp;</span>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 δ</span>¹⁵<span>N−NO</span>₃⁻<span><span>&nbsp;</span>is significantly lower ranging from −7.6‰ to −1.3‰ while winter δ</span>¹⁵<span>N−NO</span>₃⁻<span><span>&nbsp;</span>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 δ</span>¹⁵<span>N−NO</span>₃⁻<span><span>&nbsp;</span>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 NO</span>₃⁻<span><span>&nbsp;</span>and δ</span>¹⁵<span>N−NO</span>₃⁻<span><span>&nbsp;</span>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 NO</span>₃⁻<span>concentrations and δ</span>¹⁵<span>N−NO</span>₃⁻<span><span>&nbsp;</span>in the Southern Rocky Mountains located near larger anthropogenic N emission sources compared to the Northern Rocky Mountains. NADP Wetfall δ</span>¹⁵<span>N−NH</span>₄⁺<span><span>&nbsp;</span>ranged from −10‰ to 0‰, with no observed spatial pattern. However, the lowest δ</span>¹⁵<span>N−NH</span>₄⁺<span>(−9‰), and the highest NH</span>₄⁺<span><span>&nbsp;</span>concentration (35 μeq/L) were observed at a Utah site dominated by local agricultural activities, whereas the higher δ</span>¹⁵<span>N−NH</span>₄⁺<span>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.</span></p> application/pdf 10.1016/j.atmosenv.2017.12.023 en Elsevier Spatial and temporal variation in sources of atmospheric nitrogen deposition in the Rocky Mountains using nitrogen isotopes article