Controls of Floodplain Evolution on the Occurrence of High Arsenic in Shallow Aquifers of the Ganges-Brahmaputra Delta

[229600 . goodbred]在20世纪90年代中期发现，孟加拉国和印度西孟加拉邦地下水中的砷含量升高，这被证明是一个有点神秘的问题。在10万平方公里的恒河-布拉马普特拉河三角洲平原，超过一半的地区都发现了有毒的溶解相砷，影响了数千万人。然而，在局部尺度（101-103米），地下水砷的分布极不均匀，在短距离内的数量级（5-2000毫克/升）不同。这些异质性表明，a的发展需要高度专业化但并不罕见的一系列条件。从最近的实地研究中可以明显看出，近地表洪泛区地质对这种非均质性起着总体控制作用。根据新出现的想法，拟议的研究将集中在两个主要目标上：(1)确定开发高水位地下水所需的精确地质条件；(2)导致这些条件的洪泛区演变的历史和过程。这项研究的动力来自于人们认识到浅管井As值与近地表（6米）洪泛平原沉积物的平均沉积物结构之间存在很强的相关性。这种关系是在2001年1月由NIEHS/超级基金基础研究计划资助的哥伦比亚大学砷研究小组的联合实地项目中认识到的。哥伦比亚- sbrp研究的自然科学部分侧重于孟加拉国202公里研究区（Araihazar）的地球化学和水文学。这里提出的研究旨在补充哥伦比亚- sbrp项目，并将合作进行。基本目标是通过整合两项研究的生物医学、地球化学、水文和地质组成部分，发展对As问题的多学科理解。单独地，这项研究将确定复杂水文制度的地质基础及其在当地地下水砷含量升高中的作用。

0229600GoodbredDiscovered in the mid-1990s, elevated arsenic (As) levels in the groundwater of Bangladesh and West Bengal, India has proven to be a somewhat enigmatic problem. Toxic levels of dissolved-phase As have been found to be widespread across more than half of the 100,000 km2 Ganges-Brahmaputra (G-B) delta plain, affecting 10s of millions of people. Yet, at a local scale (101-103 m) the distribution of groundwater As is extremely heterogeneous, varying orders of magnitude (5-2000 mg/L) over short distances. These heterogeneities suggest that a highly specialized, but not uncommon, set of conditions are needed for elevated As to develop. It is becoming apparent from recent field studies that near-surface floodplain geology is an overarching control on this heterogeneity. Based on emerging ideas, the proposed study will focus on two main objectives: (1) determining the precise geological conditions necessary for the development of elevated groundwater As and (2) the history and processes of floodplain evolution that lead to these conditions. Impetus for the study arose from the recognition of a strong correlation between shallow tubewell As values and the mean sediment texture of near-surface ( 6 m) floodplain deposits. This relationship was recognized during a joint field program (Jan 2001) with the Columbia University arsenic research team funded through NIEHS/Superfund Basic Research Program. The natural-science component of the Columbia-SBRP study is focused on the geochemistry and hydrology of a 202 km study area (Araihazar) in Bangladesh. The study proposed here is designed complement the Columbia-SBRP project and will be conducted in collaboration. The fundamental goal is to develop a multidisciplinary understanding of the As problem by integrating biomedical, geochemical, hydrological, and geological components of the two studies. Individually, this study will identify the geological underpinnings of complex hydrological regimes and their role in the elevated As levels of local groundwater.