Previous studies have evaluated how changes in atmospheric nitrogen (N) inputs and climate affect stream N concentrations and fluxes, but none have synthesized data from sites around the globe. We identified variables controlling stream inorganic N concentrations and fluxes, and how they have changed, by synthesizing 20 time series ranging from 5 to 51 years of data collected from forest and grassland dominated watersheds across Europe, North America, and East Asia and across four climate types (tropical, temperate, Mediterranean, and boreal) using the International Long-Term Ecological Research Network. We hypothesized that sites with greater atmospheric N deposition have greater stream N export rates, but that climate has taken a stronger role as atmospheric deposition declines in many regions of the globe. We found declining trends in bulk ammonium and nitrate deposition, especially in the longest time-series, with ammonium contributing relatively more to atmospheric N deposition over time. Among sites, there were statistically significant positive relationships between (1) annual rates of precipitation and stream ammonium and nitrate fluxes and (2) annual rates of atmospheric N inputs and stream nitrate concentrations and fluxes. There were no significant relationships between air temperature and stream N export. Our long-term data shows that although N deposition is declining over time, atmospheric N inputs and precipitation remain important predictors for inorganic N exported from forested and grassland watersheds. Overall, we also demonstrate that long-term monitoring provides understanding of ecosystems and biogeochemical cycling that would not be possible with short-term studies alone.

以前的研究评估了大气氮 (N) 输入和气候的变化如何影响流 N 浓度和通量，但没有一个综合数据来自全球各地。我们通过综合从欧洲、北美和东亚以森林和草原为主的流域以及四种气候条件下收集的 5 至 51 年的 20 个时间序列数据，确定了控制河流无机 N 浓度和通量的变量，以及它们如何变化使用国际长期生态研究网络的类型（热带、温带、地中海和北方）。我们假设大气 N 沉降较大的地点具有较高的流 N 输出率，但随着全球许多地区大气沉降的减少，气候发挥了更大的作用。我们发现散装铵和硝酸盐沉积呈下降趋势，特别是在最长的时间序列中，随着时间的推移，铵对大气 N 沉积的贡献相对较大。在站点中，（1）降水年率与河流铵和硝酸盐通量和（2）大气氮输入的年率与河流硝酸盐浓度和通量之间存在统计学上显着的正相关关系。气温与流N出口之间没有显着关系。我们的长期数据表明，尽管 N 沉降随着时间的推移而下降，但大气 N 输入和降水仍然是森林和草地流域无机 N 输出的重要预测因子。全面的，