Factors controlling nitrate fluxes in groundwater in agricultural areas
Factors controlling nitrate fluxes in groundwater in agricultural areas
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DOI：
10.1029/2011wr011008
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发表时间：
2012-06
影响因子：
5.4
通讯作者：
L. Liao;C. T. Green;B. Bekins;J. Böhlke
中科院分区：
文献类型：
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作者：
L. Liao;C. T. Green;B. Bekins;J. Böhlke
农用化学品对地下水水质的影响取决于生物、地球化学和水文因素的相互作用。为了确定影响农业硝酸盐在地下水中分布的关键过程，在美国14个地点应用了一个简约的运移模型。通过调整补给率、非饱和区行程时间、淋洗到地下水中的N和Cl-−输入的比例、O2还原速率、O2反硝化阈值和反硝化速率等参数，模拟了NO2、来自反硝化的N2、O2和Cl2的垂直分布，并与地下水年龄的环境示踪进行了匹配。模型结果揭示了生物、地球化学和物理因素之间的重要交互作用。地表和地下水位之间的氯通量减少可能是由于收获作物中的氯−输出(平均占地表氯−输入的22%)。对O2还原和反硝化的零级速率进行了关联。深层的反硝化速率通常超过上覆的氧气还原速率，可能是因为反应电子供体的浅层地质来源已经耗尽。预测表明，在反硝化速率为+lt；0.25 mg-N的L−−1年−1处，NO_3−锋继续向下迁移。NO_3−的稳态深度与施用量、淋失率、补给量以及NO_3和O2反应速率有相似程度的依赖关系。各含水层的稳态总质量主要取决于施氮量。除了管理地表施肥量外，有效的水利用可能会减少地下水中N的深度和质量，因为较低的补给量与较低的淋滤量有关。减少氮素淋失的管理行动可以针对补给率高、反硝化率低的含水层。
The impact of agricultural chemicals on groundwater quality depends on the interactions of biogeochemical and hydrologic factors. To identify key processes affecting distribution of agricultural nitrate in groundwater, a parsimonious transport model was applied at 14 sites across the U.S. Simulated vertical profiles of NO3−, N2 from denitrification, O2, Cl−, and environmental tracers of groundwater age were matched to observations by adjusting the parameters for recharge rate, unsaturated zone travel time, fractions of N and Cl− inputs leached to groundwater, O2 reduction rate, O2 threshold for denitrification, and denitrification rate. Model results revealed important interactions among biogeochemical and physical factors. Chloride fluxes decreased between the land surface and water table possibly because of Cl− exports in harvested crops (averaging 22% of land‐surface Cl− inputs). Modeled zero‐order rates of O2 reduction and denitrification were correlated. Denitrification rates at depth commonly exceeded overlying O2 reduction rates, likely because shallow geologic sources of reactive electron donors had been depleted. Projections indicated continued downward migration of NO3− fronts at sites with denitrification rates <0.25 mg‐N L−1 yr−1. The steady state depth of NO3− depended to a similar degree on application rate, leaching fraction, recharge, and NO3− and O2 reaction rates. Steady state total mass in each aquifer depended primarily on the N application rate. In addition to managing application rates at land surface, efficient water use may reduce the depth and mass of N in groundwater because lower recharge was associated with lower N fraction leached. Management actions to reduce N leaching could be targeted over aquifers with high‐recharge and low‐denitrification rates.