Testing the Palaeosol Model of Arsenic Pollution in Groundwater

测试地下水砷污染的古土壤模型

• 批准号: NE/G016879/1
• 负责人: John McArthur
• 金额: $ 49.31万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FG016879%2F1
• 关键词: Testing; Palaeosol; Model; Arsenic; Pollution

Groundwater from riverine sedimentary aquifers across the globe provides much of the world's water supply; that drawn from such aquifers in Asian deltas provides a fifth of the SE Asia's population with its drinking water. Since 1995, it has become clear that arsenic-pollution affects groundwater in deltaic aquifers worldwide and that the consequence for human health has been severe. The pollution, and its adverse effects, are most fully documented in West Bengal and Bangladesh. In all polluted deltas, the distribution of arsenic pollution is patchy, but we don't know why. Polluted and unpolluted areas are juxtaposed in a manner that seems random. This proposal seeks to test an hypothesis that explains the randomness of arsenic pollution. The hypothesis will, if confirmed, provide a predictive model of arsenic pollution that will guide aquifer development and remediation in deltaic settings across the world. A predictive capacity would be of benefit to health agencies such as UNICEF (which promoted well development in Bangladesh), governmental and quasi-governmental authorities concerned with water supply (e.g. Department of Public Health Engineering, Bangladesh), and individual consumers affected by arsenic pollution. The hypothesis being tested is best set in the context of sea-level variations over the last 125,000 years. Around 125,000 years ago, sea-level was about the level it is today. As time passed, cooling climate caused the polar ice-caps to grow. The water that went into them came out of the sea. As a consequence, around 20,000 years ago when the ice-caps had grown to their largest size, sea level had fallen by 120 m. The slow decline in sea-level from 125,000 years before present to 20,000 years before present made the sea-shore retreat and exposed to weathering and soil formation large areas of coastal land that had previously been submerged. Although soils formed widely on the exposed landscape, they did not form in the chanells of active rivers. Between 20,000 years and 6,000 years ago the ice-caps partly melted and sea-level returned to its previous level, submerging the old landscape and its surficial soils and allowing them to be buried by renewed sedimentation. The hypothesis to be tested here, termed the 'palaeosol model', is that many of the old soils (termed palaeosols) that are now buried in deltas are impermeable, and so prevent the vertical migration of pollution downwards into the aquifers the palaeosols now cap. As a consequence, the underlying aquifers are protected from downward moving pollution, just as a hat protects the head from rain. Is this hypothesis correct? Can it really explain the patchy distribution of arsenic pollution in deltaic aquifers? The project sets out so find the answes. But there is more. Unfortunately, because the palaeosols did not form in the active river chanells where rivers flowed, pollution can short-circuit the protective palaeosol caps on unpolluted aquifers, and move into them by moving laterally at depth from polluted ancient river channels. How fast can that happen? What is the rate at which As-pollution can move in the subsurface? Knowing the answer to that question is important to establishing just how long the unpolluted aquifers will remain unpolluted. By investigating the rate at which arsenic moves in the subsurface, using both laboratory experiment with sediment and through monitoring groundwater composition in wells over time, we hope to obtain an answer.

来自地球仪的河流沉积含水层的地下水提供了世界上大部分的水供应;从亚洲三角洲的这种含水层抽取的地下水为东南亚五分之一的人口提供了饮用水。自1995年以来，砷污染已明显影响到全世界三角洲含水层的地下水，对人类健康造成严重后果。西孟加拉和孟加拉国的污染及其不利影响记录最为完整。在所有受污染的三角洲中，砷污染的分布是不均匀的，但我们不知道为什么。污染区和未污染区以一种似乎随机的方式并列。这项提案试图验证一个解释砷污染随机性的假设。这一假设如果得到证实，将提供一个砷污染的预测模型，指导世界各地三角洲环境中含水层的开发和修复。预测能力将有益于诸如儿童基金会（它促进了孟加拉国的水井开发）等卫生机构、与供水有关的政府和准政府当局（例如孟加拉国公共卫生工程部）以及受砷污染影响的个人消费者。正在测试的假设最好是在过去125，000年海平面变化的背景下进行的。大约125，000年前，海平面大约是今天的水平。随着时间的推移，变冷的气候导致极地冰盖的增长。进入他们的水来自大海。结果，大约2万年前，当冰盖达到最大尺寸时，海平面下降了120米。从125，000年前到20，000年前，海平面缓慢下降，使海岸后退，暴露于风化和土壤形成之前被淹没的大面积沿海土地。虽然土壤形成广泛暴露的景观，他们没有形成在活跃的河流渠道。在20，000年到6，000年前，冰盖部分融化，海平面恢复到以前的水平，淹没了旧景观及其表层土壤，并使它们被新的沉积物所掩埋。这里要测试的假设，被称为“古土壤模型”，是许多古老的土壤（称为古土壤），现在埋在三角洲是不可渗透的，因此防止污染物垂直向下迁移到含水层的古土壤现在盖。因此，地下蓄水层受到保护，不受向下移动的污染物的影响，就像帽子保护头部免受雨水的侵害一样。这个假设正确吗？它真的能解释三角洲含水层砷污染的不均匀分布吗？该项目开始，所以找到答案。但还有更多。不幸的是，由于古土壤不是在河流流经的活跃河道中形成的，污染物可以使未受污染的含水层上的保护性古土壤帽短路，并通过从受污染的古河道向深处横向移动而进入其中。这能有多快砷污染物在地下移动的速率是多少？知道这个问题的答案对于确定未受污染的含水层将在多长时间内保持不受污染是很重要的。通过调查砷在地下移动的速度，使用沉积物的实验室实验和通过监测威尔斯中的地下水成分，我们希望得到一个答案。

项目成果

Tracing recharge to aquifers beneath an Asian megacity with Cl/Br and stable isotopes: the example of Dhaka, Bangladesh

• DOI: 10.1007/s10040-014-1155-8
• 发表时间: 2014-06
• 期刊: Hydrogeology Journal
• 影响因子: 2.8
• 作者: M. A. Hoque;J. McArthur;P. K. Sikdar;J. D. Ball;T. Molla

Aquifer arsenic source

• DOI: 10.1038/ngeo1277
• 发表时间: 2011-10
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: J. McArthur;P. Ravenscroft;O. Sracek

Sources of low-arsenic groundwater in the Bengal Basin: investigating the influence of the last glacial maximum palaeosol using a 115-km traverse across Bangladesh

孟加拉盆地低砷地下水来源：通过穿越孟加拉国 115 公里来调查末次盛冰期古土壤的影响

• DOI: 10.1007/s10040-014-1139-8
• 发表时间: 2014
• 期刊: Hydrogeology Journal
• 影响因子: 2.8
• 作者: Hoque M