Department of Civil and Environmental Engineering, University of California Davis, 1 Shields Avenue, Davis, CA 95616, USA.
Department of Land, Air, and Water Resources, University of California Davis, 1 Shields Avenue, Davis, CA 95616, USA.
J Contam Hydrol. 2019 Oct;226:103521. doi: 10.1016/j.jconhyd.2019.103521. Epub 2019 Jul 8.
Nitrate in drinking water may cause serious health problems for consumers. Agricultural activities are known to be the main source of groundwater nitrate contaminating rural domestic and urban public water supply wells in farming regions. Management practices have been proposed to reduce the amount of nitrate in groundwater, including improved nutrient management practices and "pump and fertilize" with nitrate-affected irrigation wells. Here, we evaluate the feasibility and long-term impacts of agricultural managed aquifer recharge (Ag-MAR) in the source area of public water supply wells. A numerical model of nitrate fate and transport was developed for the Modesto basin, part of California's Central Valley aquifer system. The basin is representative of semi-arid agricultural regions around the world with a diversity of crop types, overlying an unconsolidated sedimentary aquifer system. A local public supply well in an economically disadvantaged community surrounded by farmland was the focus of this study. Model scenarios implemented include business as usual, alternative low-impact crops, and Ag-MAR in the source area of the public supply well. Alternative nutrient management and recharge practices act as remediation tools in the area between farmland and the public supply well. Improved agricultural source area management practices are shown to be an effective tool to maintain or even enhance groundwater quality in the targeted supply well while remediating ambient groundwater. Best results are obtained when lowering nitrate load while also increasing recharge in the source area simultaneously. This scenario reduced nitrate in the supply well's drinking water by 80% relative to the business as usual scenario. It also remediated ambient groundwater used by domestic wells between the source area farmlands and the supply well and showed 60% more reduction of nitrate after 60 years of application. Increasing recharge led to shorter initial response time (five years) and showed the most sustainable impact. Our analysis further suggests that Ag-MAR in a highly discontinuous, wide-spread pattern leads to slow water quality response and may not yield sufficient water quality improvements.
饮用水中的硝酸盐可能会对消费者的健康造成严重问题。农业活动被认为是导致农村家庭和城市公共供水井中地下水硝酸盐污染的主要来源，这些供水井位于农业区。已经提出了一些管理措施来减少地下水中的硝酸盐含量，包括改进养分管理措施和用受硝酸盐影响的灌溉井进行“抽吸和施肥”。在这里，我们评估了农业管理含水层补给（Ag-MAR）在公共供水井源区的可行性和长期影响。为加利福尼亚中央谷含水层系统的一部分莫德斯托盆地开发了硝酸盐归宿和运移的数值模型。该盆地是世界上半干旱农业地区的代表，具有多种作物类型，覆盖着非固结的沉积含水层系统。本研究的重点是一个位于农田环绕的经济贫困社区的当地公共供水井。实施的模型情景包括现状、替代低影响作物和公共供水井源区的 Ag-MAR。替代养分管理和补给实践在农田和公共供水井之间的区域充当补救工具。结果表明，改进农业源区管理实践是一种有效的工具，可以在修复环境地下水的同时维持甚至提高目标供水井的地下水质量。当同时降低硝酸盐负荷并增加源区补给时，可获得最佳效果。与现状情景相比，该情景使供水井饮用水中的硝酸盐减少了 80%。它还修复了源区农田和供水井之间的家庭井使用的环境地下水，并且在应用 60 年后，硝酸盐减少了 60%。增加补给导致初始响应时间（五年）缩短，并显示出最可持续的影响。我们的分析还表明，在高度不连续、广泛分布的模式下进行 Ag-MAR 会导致水质响应缓慢，可能无法产生足够的水质改善。
