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

发现于20世纪90年代中期，孟加拉国和印度西孟加拉邦地下水中砷(As)含量的升高已被证明是一个有点神秘的问题。已发现溶解相砷的毒性水平普遍存在于100,000平方公里的恒河-雅鲁藏布江三角洲平原的一半以上，影响到数千万人。然而，在局部尺度(101-103米)，地下水砷的分布是非常不均匀的，在短距离内变化了数量级(5-2000毫克/L)。这些异质性表明，需要一套高度专业化但并不罕见的条件，才能发展出高度专业化的AS。从最近的实地研究中可以明显看出，近地表泛滥平原地质是这种非均质性的最主要控制因素。根据新出现的想法，拟议的研究将侧重于两个主要目标：(1)确定开发高水位地下水所需的准确地质条件；(2)导致这些条件的泛滥平原演变的历史和过程。这项研究的动力来自于对浅层管井数值与近地表(6米)泛滥平原沉积的平均沉积物结构之间的强烈相关性的认识。这种关系在与哥伦比亚大学砷研究小组的联合实地计划(2001年1月)中得到确认，该研究小组由NIEHS/Superfund基础研究计划资助。哥伦比亚-SBRP研究的自然科学部分侧重于孟加拉国202公里研究区域(Araihazar)的地球化学和水文学。这里提出的研究是对哥伦比亚-SBRP项目的补充，将在合作中进行。基本目标是通过整合这两项研究的生物医学、地球化学、水文学和地质学成分，发展对AS问题的多学科理解。单独而言，这项研究将确定复杂水文状况的地质基础及其在当地地下水As水平上升中的作用。

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.