Linking land subsidence to deep arsenic release in the Mekong Delta aquifer system

将地面沉降与湄公河三角洲含水层系统深层砷释放联系起来

• 批准号: 1313518
• 负责人: Steven Gorelick
• 金额: $ 25.64万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-15 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1313518&HistoricalAwards=false
• 关键词: Linking; land; subsidence; deep; arsenic

An estimated 100 million people living in floodplains in Asia are exposed to arsenic in groundwater that is derived from Himalayan sediments. Arsenic is a toxin linked to cancer and a variety of other serious ailments through direct ingestion of contaminated groundwater. Growing exploitation of these contaminated aquifers increases the number of people facing these health risks, and exposes still greater populations to the hazard of consuming agricultural products irrigated with arsenic-contaminated groundwater. Despite widespread awareness of the arsenic hazard, understanding of the relationship between groundwater exploitation and arsenic contamination remains limited, particularly in deep aquifers, which are increasingly providing a larger portion of total pumped groundwater.In this work, we focus on the Mekong Delta, where we have obtained a comprehensive, unique, unanalyzed dataset consisting of 42,000 dissolved arsenic measurements from southern Vietnam showing widespread contamination (1000 sq km) in deep aquifers (200m) that are used extensively for water supply. One hypothesis is that deep pumping has induced shallow dissolved arsenic or arsenic-mobilizing solutes to move deeper. However, preliminary analysis does not support this mechanism in the Mekong Delta given the observed widespread deep arsenic contamination in the presence of thick clay deposits that serve as relative vertical flow barriers. We hypothesize a previously unrecognized deep arsenic source mechanism in which water containing arsenic is expelled from storage in clays that compact when overlying and underlying deep aquifers are exploited. This work combines spatial statistical modeling of groundwater arsenic observations, 3D aquifer flow and compaction simulation, and remote measurement of land subsidence using satellite radar imagery (InSAR). Our goal is to explore the notion that deep groundwater arsenic may be due to the release of pore-waters containing arsenic trapped in clay beds deposited millions of years ago. This research has important implications to science and society. First, our formerly unrecognized contamination mechanism may be fundamental to understanding arsenic occurrence in aquifer systems and the associated health risks of deep groundwater exploitation. Our investigation will have implications for water resources development and human health in the arsenic-affected basins of Southeast Asia where some regions of planned deep aquifer exploitation may unknowingly expose people to deep-source arsenic. This work has consequences for analogous arsenic-affected aquifer systems in sedimentary basins around the world containing interbedded compressible clays that may harbor arsenic and other contaminants. Second, in terms of methods, the link between subsidence and arsenic release has significant potential as a reconnaissance tool, particularly in underdeveloped regions where the impacts of excessive pumping on land subsidence have not been recognized. The use of satellite radar to detect land deformation can serve as a means to identify areas where clay compaction and consequent arsenic release may be occurring.

据估计，生活在亚洲洪泛平原的1亿人暴露在来自喜马拉雅沉积物的地下水中的砷。砷是一种毒素，通过直接摄入受污染的地下水，与癌症和其他各种严重疾病有关。对这些受污染含水层的日益开采增加了面临这些健康风险的人数，并使更多的人面临消费用受砷污染的地下水灌溉的农产品的危险。尽管人们普遍认识到砷的危害，但对地下水开采和砷污染之间的关系的了解仍然有限，特别是在深层含水层，这些地下水越来越多地提供了总抽水地下水的更大比例。在这项工作中，我们专注于湄公河三角洲，在那里我们获得了一个全面、独特、未经分析的数据集，其中包括来自越南南部的42,000个溶解砷测量数据，显示广泛用于供水的深层含水层(1000平方公里)普遍受到污染(1000平方公里)。一种假设是，深抽导致浅层溶解的砷或动员砷的溶质移动到更深的地方。然而，初步分析并不支持湄公河三角洲的这种机制，因为在作为相对垂直流动障碍的厚厚粘土沉积物的存在下，观察到广泛的深度砷污染。我们假设了一种以前不为人知的深层砷来源机制，在这种机制中，含有砷的水被从粘土中排出，当开采上覆和下面的深层含水层时，粘土致密。这项工作结合了地下水砷观测的空间统计建模、三维含水层流动和压实模拟以及利用卫星雷达图像(InSAR)进行的地面沉降遥感测量。我们的目标是探索这样一种观点，即深层地下水中的砷可能是由于数百万年前沉积在粘土层中的含有砷的孔隙水的释放所致。这项研究具有重要的科学意义和社会意义。首先，我们以前未被认识到的污染机制可能是了解含水层系统中砷的存在以及深层地下水开采相关的健康风险的基础。我们的调查将对东南亚受砷影响的盆地的水资源开发和人类健康产生影响，在这些地区，一些计划进行深层含水层开采的地区可能会在不知不觉中使人们接触到深源砷。这项工作对世界各地沉积盆地中类似的受砷影响的含水层系统产生了影响，这些盆地含有可能含有砷和其他污染物的夹层可压缩粘土。第二，就方法而言，沉陷和砷释放之间的联系作为一种侦察工具具有很大潜力，特别是在尚未认识到过度抽水对地面沉降的影响的欠发达地区。利用卫星雷达探测土地变形可以作为确定可能发生粘土压实和随之而来的砷释放的地区的一种手段。