Agriculture is recognized as the major source of groundwater nitrate (NO₃⁻) contamination; yet quantifying its effects is still challenging in large, due to the difficulty to track the transformation and fates of agricultural nitrogen (N) in soils and aquifers. In this study, a HYDRUS-1D model was adopted to explore water content and NO₃⁻ distribution in the unsaturated zone above groundwater table in an agricultural area. The resulting estimates of water flux and NO₃⁻ leaching through the unsaturated zone were used as input data in the application of the groundwater flow model Visual MODFLOW and mass transport model MT3DMS via a concentration recharge boundary. Nitrate leaching occurred mainly between May and September, accounting for 64% of the annual total. Four fertilizer application scenarios were developed, and their effects were compared in predictive simulations of groundwater NO₃⁻ concentrations using MT3DMS and quantitative analysis of NO₃⁻-contaminated areas, the spatial and temporal distribution of groundwater NO₃⁻ concentration using ArcGIS. Predictions in the business as usual (scenario 1) showed that NO₃⁻ continued to accumulate in groundwater in the study area, with the maximum increased from 14 to 18 mg L⁻¹ in 10 years. In the scenario 2 (2% increase in fertilizer application rate), peak groundwater NO₃⁻ was expected to exceed 20 mg L⁻¹ in 2027. However, in both scenarios 3 (2% reduction in fertilizer application) and 4 (4% reduction in fertilization), the maximal NO₃⁻ concentrations were predicted to be lower than 12 mg L⁻¹ in 2027. The integration of HYDRUS-1D, MT3DMS and GIS models offers a powerful tool for evaluating agricultural management impacts on aquifer water quality.

中文翻译：

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使用HYDRUS-1D和MT3DMS模拟施肥对硝酸盐淋失和地下水污染的影响

农业是公认的地下水硝酸盐的主要来源（NO ₃ ^- ）污染; 然而，由于难以追踪土壤和含水层中农业氮（N）的转化和命运，因此量化其影响仍然面临很大挑战。在这项研究中，一个HYDRUS-1D模型获得通过探索水含量和NO ₃ ^-中地下水位之上的非饱和区分布在农业区。将所得的水通量和NO的估计₃ ^-在地下水流模型Visual MODFLOW和传质模型MT3DMS中，通过浓度补给边界将通过非饱和带的淋洗作为输入数据。硝酸盐浸出主要发生在5月至9月之间，占全年总量的64％。四个肥料应用场景被开发，它们的作用在地下水的预测模拟NO进行比较₃ ^-使用MT3DMS和NO的定量分析浓度₃ ^- -contaminated区域，地下水的时空分布NO ₃ ^-使用ArcGIS浓度。在业务预测如常（方案1）表明，NO ₃ ^-继续在研究区域的地下水中积累，在10年中最大值从14 mg L ^-1增加到18 mg L ^-1。在方案2（在施用量2％增加），峰地下水NO ₃ ^-已超过了20毫克的L ^-1在2027年但是，在这两种情况下（在施肥减少2％）3和4（4％在施肥减少），最大NO ₃ ^-浓度预测要低于12毫克的L ^-1 2027年HYDRUS-1D，MT3DMS和GIS模型提供了对含水层水质评价农业管理影响的强大工具的集成。