Excessive nitrogen (N) inputs to coastal waters can lead to severe eutrophication and different chemical forms of N exhibit varying levels of effectiveness in fueling primary production. Efforts to mitigate N fluxes from coastal watersheds are often guided by models that predict changes in N loads as a function of changes in land use, management practices, and climate. However, relatively little is known on the impacts of such changes on the relative fractions of different N forms. We leveraged a long-term dataset of N loads from over 100 river stations to investigate how the fraction, that is, the ratio of to total N (/TN), changes as a function of spatio-temporal changes in TN loads in the Chesapeake Bay watershed. We built a hierarchical model that separates the response of to changes in TN load occurring at different scales: Across river stations, where differences in TN loads are largely driven by spatial differences in anthropogenic inputs, and within stations, where inter-annual variability in hydrology is a key driver of changes in TN loads. Results suggest that while increases in TN loads resulting from changes in anthropogenic inputs lead to an increase in the fraction, a decrease in the fraction may occur when increases in TN loads are driven by increased streamflow. These results are especially relevant in watersheds that may experience changes in N loads due to both management decisions and climate-driven changes in hydrology.

中文翻译：

---

使用多级建模方法量化氮形态对切萨皮克湾流域水文的响应

向沿海水域输入过多的氮 (N) 会导致严重的富营养化，不同化学形式的氮在促进初级生产方面表现出不同程度的有效性。减轻沿海流域氮通量的努力通常以模型为指导，这些模型预测氮负荷的变化是土地利用、管理实践和气候变化的函数。然而，关于这种变化对不同 N 形式的相对分数的影响，人们知之甚少。我们利用来自 100 多个河流站的 N 负荷的长期数据集来研究分数，即与总 N ( /TN) 的比率，如何随着切萨皮克 TN 负荷的时空变化而变化湾分水岭。我们建立了一个分层模型，将响应分开不同尺度下发生的 TN 负荷变化：跨河流站点，TN 负荷的差异主要由人为输入的空间差异驱动，而在站点内，水文的年际变化是 TN 负荷变化的关键驱动因素。结果表明，虽然人为输入变化引起的 TN 负荷增加会导致分数增加，但当 TN 负荷增加是由增加的水流驱动时，分数可能会下降。由于管理决策和气候驱动的水文变化，这些结果与可能经历氮负荷变化的流域尤其相关。