Two centuries of nitrogen dynamics: Legacy sources and sinks in the Mississippi and Susquehanna River Basins
Two centuries of nitrogen dynamics: Legacy sources and sinks in the Mississippi and Susquehanna River Basins
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DOI：
10.1002/2016gb005498
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发表时间：
2017-01
影响因子：
5.2
通讯作者：
K. Meter;N. Basu;P. Cappellen
中科院分区：
文献类型：
--
作者：
K. Meter;N. Basu;P. Cappellen
上个世纪，由于农业集约化和大气沉积水平的提高，全球活性氮(N)流量显著增加。尽管实施了广泛的养护措施，但地表水中的氮浓度往往保持稳定或继续增加。尽管这种缺乏反应的原因是地下水库中遗留的N库存在时间滞后，但目前尚不清楚这种库的规模有多大，以及它们如何在浅层土壤水库和深层地下水水库之间分配。在这里，我们合成了数据，建立了214年(1800-2014)N输入到美国大陆陆地表面的轨迹。我们同时开发了一个简明的、基于过程的模型-长期营养轨迹探索(ELEMENT)，该模型将这一输入轨迹与基于旅行时间的方法配对，以模拟沿地下路径的传输和保持。使用该模型，我们重建了美国两个主要流域--密西西比河流域(MRB)和苏斯奎哈纳河流域(SRB)--出口的历史硝酸盐产量。我们的结果表明，在商业氮肥广泛使用之前，这两个流域的氮负荷都显著高于基线水平，这主要是由于森林和草原转变为行作物农业。模型结果还使我们能够量化土壤和地下水池中遗留氮的大小，并突出显示土壤遗产在MRB中的优势以及地下水遗产在SRB中的优势。目前MRB和SRB中约55%和18%的年N负荷被发现超过10年。
Global flows of reactive nitrogen (N) have increased significantly over the last century in response to agricultural intensification and elevated levels of atmospheric deposition. Despite widespread implementation conservation measures, N concentrations in surface waters are often remaining steady or continuing to increase. Although such lack of response has been attributed to time lags associated with legacy N stores in subsurface reservoirs, it is unclear what the magnitudes of such stores are and how they are partitioned between shallow soil and deeper groundwater reservoirs. Here we have synthesized data to develop a 214 year (1800–2014) trajectory of N inputs to the land surface of the continental U.S. We have concurrently developed a parsimonious, process‐based model, Exploration of Long‐tErM Nutrient Trajectories (ELEMeNT) that pairs this input trajectory with a travel time‐based approach to simulate transport and retention along subsurface pathways. Using the model, we have reconstructed historic nitrate yields at the outlets of two major U.S. watersheds, the Mississippi River Basin (MRB) and Susquehanna River Basin (SRB). Our results show significant N loading above baseline levels in both watersheds before the widespread use of commercial N fertilizers, largely due to the conversion of forest and grassland to row crop agriculture. Model results also allow us to quantify the magnitudes of legacy N in soil and groundwater pools and to highlight the dominance of soil legacies in MRB and groundwater legacies in SRB. Approximately 55% and 18% of the current annual N loads in the MRB and SRB were found to be older than 10 years of age.