Wet deposition of dissolved inorganic nitrogen (N) is declining nationally, accompanied by a shift in stoichiometry from predominantly oxidized to reduced forms of N. Stoichiometric trends that include the organic fraction of N wet deposition have yet to be assessed in light of anthropogenic pressures and global change, including shifting seasonality. Here we use 17 years of weekly, year-round wet deposition data from a temperate watershed in New Hampshire (USA) to assess long-term and seasonal trends in NO₃⁻, NH₄⁺, and dissolved organic nitrogen (DON), and quantify the dependence of N stoichiometry on precipitation type (rain or snow). Concentration, load, and relative abundance of DON are increasing, a pattern previously unreported in the U.S. Deposition of total dissolved nitrogen at this site is declining, but is increasingly depleted in NH₄⁺, contrary to national trends. The stoichiometry of inorganic N is highly sensitive to precipitation type with snow containing significantly more NO₃⁻ than rain, which was relatively enriched in NH₄⁺. The effects of climate change on seasonality such as warmer winters could result in a greater proportion of precipitation entering the biosphere as rain that is relatively enriched in reduced N, with significant implications for watershed biogeochemical cycles at the regional scale. This study demonstrates variability in contemporary N deposition inputs including trends in stoichiometry and explores the role of organic N and seasonality in regulating inter- and intra- variability in N deposition stoichiometry.

溶解无机氮 (N) 的湿沉降在全国范围内正在下降，伴随着化学计量从主要氧化形式向还原形式 N 的转变。包括 N 湿沉降的有机部分在内的化学计量趋势尚未根据人为压力和全球变化，包括季节性变化。_{在这里，我们使用来自新罕布什尔州（美国）温带流域的 17 年每周、全年湿沉降数据来评估 NO 3} ^-、NH ₄ ⁺的长期和季节性趋势和溶解有机氮 (DON)，并量化 N 化学计量对降水类型（雨或雪）的依赖性。DON 的浓度、负荷和相对丰度正在增加，这是以前在美国未报道的模式 该地点的总溶解氮沉积量正在下降，但在 NH ₄ ⁺中逐渐耗尽，这与国家趋势相反。无机N的化学计量对降水类型高度敏感，雪中NO ₃ ^{-含量明显多于雨水，而雨水中NH} ₄ ⁺相对富集. 气候变化对季节性的影响（例如温暖的冬季）可能导致更大比例的降水进入生物圈，因为雨水相对富含减少的 N，这对区域范围内的流域生物地球化学循环具有重要意义。本研究展示了当代氮沉积输入的可变性，包括化学计量的趋势，并探讨了有机氮和季节性在调节氮沉积化学计量的内部和内部变异中的作用。