Solute chemistry and arsenic fate in aquifers between the Himalayan foothills and Indian craton (including central Gangetic plain): Influence of geology and geomorphology
Solute chemistry and arsenic fate in aquifers between the Himalayan foothills and Indian craton (including central Gangetic plain): Influence of geology and geomorphology
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DOI：
10.1016/j.gca.2012.05.015
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发表时间：
2012-08
影响因子：
5
通讯作者：
A. Mukherjee;B. Scanlon;A. Fryar;D. Saha;A. Ghosh;Sunil Chowdhuri;R. Mishra
中科院分区：
文献类型：
--
作者：
A. Mukherjee;B. Scanlon;A. Fryar;D. Saha;A. Ghosh;Sunil Chowdhuri;R. Mishra
在中央恒河流域的地下水化学信息可以提供深入了解补给，来源和命运的溶质在砷（As）受影响的地区上游的更深入研究的孟加拉盆地。该区域的地质和地貌单位比孟加拉盆地含水层更容易辨认。此外，该地区是受地下水抽取，这使得解释在孟加拉盆地的分布复杂。研究区域从印度克拉通露头的北方边缘延伸到喜马拉雅山的山麓。该地区的地质单元可大致分为前新生代变质岩和火山岩（PC）、恒河及其支流的较老冲积层（OA）、盆地内恒河及其支流的较年轻或活动冲积层（YA）以及喜马拉雅山麓（皮埃蒙特，PD）的沉积物。稳定同位素分析表明，这些单元的地下水是由大气降水或地表水补给的，这些水一般都经历了一些蒸发。水化学相一般为Ca-HCO 3型。虽然YA地下水中的大部分溶质来自碳酸盐溶解，但许多PD、PC和OA地下水样品受到硅酸盐风化的影响，这表明变质岩和火山岩的沥滤是溶质的主要来源。氧化还原条件在空间上变化很大（从氧化到甲烷，主要是金属还原），在取样的含水层内没有系统的深度变化。YA和PD地下水样品中75%以上的样品中As <0.01mg/L，而OA样品中只有1个样品检出As，PC样品中未检出As。砷可能是通过冲积层中Fe-Mn（oxyhydr）氧化物的还原溶解而动员的，具有竞争性阴离子动员的可能性。因此，相对于孟加拉盆地，除了较低的地下水抽取的影响，在研究区的地下水化学反映了更大的差异，在地质和地貌环境的含水层。
Information on groundwater chemistry in the central Ganges basin can provide insights into recharge, provenance, and fate of solutes in arsenic (As)-affected areas upstream of the more intensively studied Bengal basin. The geological and geomorphological units of the region are much more discernible than the Bengal basin aquifers. Moreover, the region is less affected by groundwater abstraction, which complicates interpretation of As distributions in the Bengal basin. The study area extends from the northern edge of the Indian craton outcrops to the foothills of the Himalayas. Geologic units in the area can be broadly classified as pre-Cenozoic metamorphics and volcanics (PC), older alluvial deposits of the Ganges and its tributaries (OA), younger or active alluvial deposits of the Ganges and its tributaries in the basin (YA), and sediments of the Himalayan foothills (piedmont, PD). Stable-isotopic analyses indicate groundwater in these units has been recharged by meteoric or surface water that has generally undergone some evaporation. The hydrochemical facies is generally a Ca–HCO3type. While most of the solutes in the YA groundwater are derived from carbonate dissolution, many of the PD, PC and OA groundwater samples are influenced by silicate weathering, suggesting that leaching of metamorphics and volcanics acts as a major source of solutes. Redox conditions are highly spatially variable (oxic to methanic, dominated by metal reduction), with no systematic depth variation within sampled aquifers. More than 75% of YA and PD groundwater samples have As⩾0.01mg/L, but As was detected in only one OA sample and no PC samples. Arsenic is probably mobilized by reductive dissolution of Fe–Mn (oxyhydr)oxides in the alluvium, with possibility of competitive anionic mobilization. Hence, relative to the Bengal basin, in addition to lower groundwater abstraction influence, groundwater chemistry in the study area reflects a greater variety of differences in the geological and geomorphological settings of the aquifers.