Department of Land, Air and Water Resources, University of California, Davis, CA, 95616, USA.
Department of Pesticide Regulation, California Environmental Protection Agency, Sacramento, CA, USA.
Water Res. 2024 Dec 1;267:122442. doi: 10.1016/j.watres.2024.122442. Epub 2024 Sep 14.
Groundwater aquifers worldwide experience unsustainable depletion, compounded by population growth, economic development, and climate forcing. Managed aquifer recharge provides one tool to alleviate flood risk and replenish groundwater. However, concerns grow that intentional flooding of farmland for groundwater recharge, a practice known as Ag-MAR, may increase the leaching of pesticides and other chemicals into groundwater. This study employs a physically based unsaturated flow model to determine the fate and transport of residues of four pesticide in three vadose zone profiles characterized by differing fractions of sand (41 %, 61 %, and 84 %) in California's Central Valley. Here, we show that the complex heterogeneity of alternating coarse and fine-grain hydrogeologic units controls the transit times of pesticides and their adsorption and degradation rates. Unsaturated zones that contain a higher fraction of sand are more prone to support preferential flow, higher recharge rates (+8 %), and faster (42 %) water flow and pesticide transport, more flooding-induced pesticide leaching (about 22 %), as well as more salt leaching correlating with increased risks of groundwater contamination. Interestingly, considering preferential flow predicted higher degradation and retention rates despite shorter travel times, attributed to the trapping of pesticides in immobile zones where they degrade more effectively. The findings underscore the importance of considering soil texture and structure in Ag-MAR practices to minimize environmental risks while enhancing groundwater recharge. The study also highlights that selecting less mobile pesticides can reduce leaching risks in sandy areas.
全球地下含水层正经历不可持续的消耗，这是由于人口增长、经济发展和气候因素共同作用的结果。含水层人工补给为缓解洪水风险和补充地下水提供了一种手段。然而，人们越来越担心，为了给地下水补给而故意将农田淹没，这种做法被称为 Ag-MAR，可能会增加农药和其他化学物质向地下水淋滤的风险。本研究采用基于物理的非饱和流模型，确定了加利福尼亚中央谷三个不同砂分（41%、61%和 84%）包气带剖面中四种农药残留的归宿和运移。结果表明，粗砂和细砂相间的复杂非均质性水文地质单元控制了农药的传输时间以及它们的吸附和降解速率。砂分含量较高的包气带更容易发生优先流，具有更高的补给率（+8%）和更快的（42%）水流和农药运移速度，更多的洪水诱导的农药淋滤（约 22%），以及更多的盐分淋滤，这与地下水污染风险的增加相关。有趣的是，尽管优先流的传输时间较短，但考虑到农药被固定在非活动区，因此预测优先流会导致更高的降解和保留率，因为农药在这些区域中降解更为有效。研究结果强调了在 Ag-MAR 实践中考虑土壤质地和结构的重要性，以最小化环境风险，同时增强地下水补给。研究还表明，选择更不易移动的农药可以降低砂质地区的淋滤风险。
