Patterns of watershed nitrogen (N) retention and loss are shaped by how watershed biogeochemical processes retain, biogeochemically transform, and lose incoming atmospheric deposition of N. Loss patterns represented by concentration, discharge, and their associated stream exports are important indicators of integrated watershed N retention behaviors. We examined continental United States (CONUS) scale N deposition (e.g., wet and dry atmospheric deposition), vegetation trends, and stream trends as potential indicators of watershed N‐saturation and retention conditions, and how watershed N retention and losses vary over space and time. By synthesizing changes and modalities in watershed nitrogen loss patterns based on stream data from 2200 U.S. watersheds over a 50 years record, our work revealed two patterns of watershed N‐retention and loss. One was a hysteresis pattern that reflects the integrated influence of hydrology, atmospheric inputs, land‐use, stream temperature, elevation, and vegetation. The other pattern was a one‐way transition to a new state. We found that regions with increasing atmospheric deposition and increasing vegetation health/biomass patterns have the highest N‐retention capacity, become increasingly N‐saturated over time, and are associated with the strongest declines in stream N exports—a pattern, that is, consistent across all land cover categories. We provide a conceptual model, validated at an unprecedented scale across the CONUS that links instream nitrogen signals to upstream mechanistic landscape processes. Our work can aid in the future interpretation of in‐stream concentrations of DOC and DIN as indicators of watershed N‐retention status and integrators of watershed hydrobiogeochemical processes.

中文翻译：

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美国水文流域过去50年流域氮保留与流失的滞后模式

流域氮（N）保留和流失的方式由流域生物地球化学过程如何保留，生物地球化学转化和损失进入大气的N来决定。以浓度，流量及其相关流出口为代表的流失模式是综合流域N的重要指标保留行为。我们研究了美国大陆（CONUS）尺度的N沉积（例如，潮湿和干燥的大气沉积），植被趋势和河流趋势，作为分水岭N饱和度和保留条件的潜在指标，以及流域N的保留和损失在空间和空间上如何变化。时间。通过基于50年来2200个美国流域的水流数据综合流域氮损失模式的变化和模式，我们的工作揭示了流域氮保留和流失的两种模式。一种是磁滞模式，它反映了水文学，大气输入，土地利用，溪流温度，海拔和植被的综合影响。另一种模式是单向新状态的过渡。我们发现，随着大气沉积增加和植被健康/生物量模式增加的区域，氮保留能力最高，随着时间的推移氮饱和度越来越高，并且与溪流氮出口下降幅度最大有关。所有土地覆盖类别。我们提供了一个概念模型，该模型已在CONUS上得到了空前的验证，该模型将河流中的氮信号与上游的机械景观过程联系起来。我们的工作可以帮助将来将DOC和DIN的浓度解释为流域氮保留状态的指标和流域水生地球化学过程的积分器。