Spatial Variability of Groundwater Arsenic Concentration as Controlled by Hydrogeology: Conceptual Analysis Using 2-D Reactive Transport Modeling
Spatial Variability of Groundwater Arsenic Concentration as Controlled by Hydrogeology: Conceptual Analysis Using 2-D Reactive Transport Modeling
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DOI：
10.1029/2018wr023685
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发表时间：
2018-12-01
影响因子：
5.4
通讯作者：
Postma, Dieke
中科院分区：
文献类型：
--
作者：
Jakobsen, Rasmus;Kazmierczak, Jolanta;Postma, Dieke
结合地质，水文地质和地球化学控制在东南亚受污染的含水层的砷浓度进行了探讨，从孟加拉国，柬埔寨和越南的数据集的二维（2-D）反应输运建模。对于每个站点，现场数据进行了总结，并用于创建一个概念性的2-D反应传输模型，阐明了影响地下水砷浓度的特征。孟加拉国和越南的模型比较表明，细粒层覆盖年轻的桑迪含水层产生浅的高砷地下水，因为低的垂直地下水流速允许足够的时间从沉积物中释放的动力学As。该模型预测，主要河道下方的地下水垂直流速较低，也会导致地下水停留时间较长，从而导致高砷地下水。年轻的含水层沉积物比老沉积物释放更多的砷，交替的年轻和老沉积物产生复杂的高砷和低砷地下水模式。随着时间的推移，洪泛平原盆地将下沉，河道迁移，造成洪泛平原的沉积和侵蚀，同时创造具有不断演变的水文地质和地下水地球化学的局部环境。我们提出了一个红河洪泛区在过去6000年中沉积和变迁的三阶段模型。结果表明，砷释放和河流迁移的动态之间的时间尺度可比，造成复杂的地下水As的分布，包括地球化学palinopsia长期消失rives.Plain语言摘要超过1亿人在东南亚的影响砷浓度过高的地下水。造成这一问题难以处理的一个问题是，砷的浓度在很短的距离内变化很大，因此难以找到和开采低砷地下水。本文展示了如何这可能是一个复杂的相互作用之间的后果砷从锈涂层的沙子和粘土由于微生物获得能量从溶解锈使用有机物，砷的重新绑定到锈，地下水流，和动态变化的河流三角洲系统，留下化学残留的古代河流在地下水。为了证明这一点，使用二维计算机计算分析了一些经过充分研究的地点，这些计算包括所有提到的过程，包括对这些过程的地球化学数学描述，因为它们随着有机物和铁锈的反应性的降低而随着时间的推移而变化。
Combined geological, hydrogeological, and geochemical controls on the arsenic concentration of contaminated aquifers in SE Asia were explored by two-dimensional (2-D) reactive transport modeling of data sets from Bangladesh, Cambodia, and Vietnam. For each site, the field data are summarized and used to create a conceptual 2-D reactive transport model that elucidates characteristic features influencing the groundwater arsenic concentration. Comparison of models for Bangladesh and Vietnam indicates that fine-grained layers overlying young sandy aquifers generate shallow high arsenic groundwater because low vertical groundwater velocities allow sufficient time for kinetic As release from the sediment. The low vertical groundwater velocity below major river channels, predicted by the model, also creates long groundwater residence times, leading to high arsenic groundwater. Young aquifer sediments release more arsenic than older sediments, and alternating young and older sediments create complex patterns of high and low arsenic groundwater. Over time, floodplain basins will subside, and river channels migrate, causing sedimentation and erosion on the floodplain while creating local environments with evolving hydrogeology and groundwater geochemistry. We have developed a three-step model for the evolution of the Red River floodplain with sedimentation and shifting channels over the last 6000years. The results show comparable timescales between the dynamics of arsenic release and of river migration, causing complex groundwater As distributions, comprising geochemical palinopsia of long vanished rivers.Plain Language Summary More than 100 million people in Southeast Asia are affected by too high arsenic concentrations in their groundwater. One of the issues that makes this difficult to handle is that the concentration of arsenic varies enormously within very short distances, making it difficult to find and exploit groundwater low in arsenic. The paper shows how this can be a consequence of complex interactions between the release of arsenic from rust coatings on the sand and clay due to microbes obtaining energy from dissolving the rust using organic matter, the rebinding of arsenic to the rust, the groundwater flow, and the dynamically changing river delta system, leaving chemical afterimages of ancient rivers in the groundwater. To show this, a number of well-studied sites are analyzed using 2-D computer calculations that include all the mentioned processes including a geochemical mathematical description of the processes as they change over time as the reactivity of the organic matter and the rust decreases.