How palaeosols influence groundwater flow and arsenic pollution: a model from the Bengal Basin and its worldwide implication
نویسندگان
چکیده
In the Bengal Basin, the land surface exposed during the last lowstand of sea-level around 20 ka, and now buried by Holocene sediment, is capped by an impermeable clay palaeosol that we term the Last Glacial Maximum Palaeosol (LGMP). The palaeosol strongly affects groundwater flow and controls the location of arsenic pollution in the shallow aquifers of our study site in southern West Bengal and, by implication, in shallow aquifers across the Bengal Basin and As-polluted deltaic aquifers worldwide. The presence of the LGMP defines palaeo-interfluvial areas; it is absent from palaeo-channel areas. A palaeosol model of pollution proposed here predicts that groundwater in palaeo-channels is polluted by arsenic, whilst that beneath palaeo-interfluvial areas is not: palaeo-interfluvial aquifers are unpolluted because they are protected by the LGMP from downward migration of arsenic, and from downward migration of organic matter that drives As-pollution via reductive-dissolution of As-bearing iron oxyhydroxides. Horizontal groundwater flow carries arsenic from palaeo-channels towards palaeointerfluvial aquifers, in which sorption of arsenic minimizes the risk of pollution.
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Palaeosol control on groundwater flow and pollutant distribution: the example of arsenic.
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