Ghosh, D and Donselaar, ME (2023) Predictive geospatial model for arsenic accumulation in Holocene aquifers based on interactions of oxbow-lake biogeochemistry and alluvial geomorphology. In: Science of the Total Environment, 856 .
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Abstract
The identification of arsenic-contamination hotspots in alluvial aquifers is a global-scale challenge. The collection and inventory of arsenic concentration datasets in the shallow-aquifer domain of affected alluvial basins is a tedious and slow process, given the magnitude of the problem. Recent research demonstrates that oxbow-lake biogeochemistry in alluvial plains, mobilization of geogenic arsenic, and accumulation in geomorphologically well-defined areas are interacting processes that determine arsenic-contamination locations. This awareness provides a tool to identify potential arsenic-hotspots based on geomorphological similarity, and thus contribute to a more robust and targeted arsenic mitigation approach. In the present study, a conceptual predictive geospatial model is proposed for the accumulation of dissolved arsenic as a function of interaction of oxbow-lake biogeochemistry and alluvial geomorphology. A comprehensive sampling campaign in and around two oxbow lakes in the Jamuna River Basin, West Bengal (India) provided water samples of the oxbow-lake water column for analysis of dissolved organic matter (DOM) and microbial communities, and groundwater samples from tube wells in point bars and fluvial levees bordering the oxbow lakes for analysis of the geospatial distribution of arsenic in the aquifer. Results show that abundant natural and anthropogenic (faecal-derived) recalcitrant organic matter like coprostanols and sterols in clay-plug sediment favours microbial (heterotrophs, enteric pathogens) metabolism and arsenic mobilization. Arsenic concentrations in the study area are highest (averaging 505 μg/L) in point-bar aquifers geomorphologically enclosed by partially sediment-filled oxbow lakes, and much lower (averaging 121 μg/L) in wells of levee sands beyond the oxbow-lake confinement. The differences reflect variations in groundwater recharge efficiency as result of the porosity and permeability anisotropy in the alluvial geomorphological elements, where arsenic-rich groundwater is trapped in point-bars enclosed by oxbow-lake clays and, by contrast, levee ridges are not confined on all sides, resulting in a more efficient aquifer flushing and decrease of arsenic concentrations.
| Item Type: | Journal Article |
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| Publication: | Science of the Total Environment |
| Publisher: | Elsevier B.V. |
| Additional Information: | The copyright for this article belongs to the Authors. |
| Keywords: | Anisotropy; Arsenic; Biogeochemistry; Efficiency; Groundwater pollution; Groundwater resources; Hydrogeology; Landforms; Levees; Organic compounds; Porosity; Recharging (underground waters); Sediments, Alluvial plains; Fecal-derived OM; Ground water recharge; Groundwater recharge efficiency; Holocenes; Meandering rivers; Oxbow lakes; Permeability anisotropy; Porosity-permeability anisotropy; Recharge efficiency, Aquifers |
| Department/Centre: | Division of Mechanical Sciences > Centre for Earth Sciences |
| Date Deposited: | 27 Oct 2022 08:56 |
| Last Modified: | 27 Oct 2022 08:56 |
| URI: | https://eprints.iisc.ac.in/id/eprint/77611 |
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