Spatial relationship of groundwater arsenic distribution with regional topography and water-table fluctuations in the shallow aquifers in Bangladesh |
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| Authors: | M Shamsudduha L J Marzen A Uddin M-K Lee J A Saunders |
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| Institution: | (1) Department of Geology and Geography, Auburn University, Auburn, AL 36849, USA;(2) Department of Geography, University College London, Pearson Building, Gower Street, London, WC1E 6BT, UK |
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| Abstract: | The present study has examined the relationship of groundwater arsenic (As) levels in alluvial aquifers with topographic elevation,
slope, and groundwater level on a large basinal-scale using high-resolution (90 m × 90 m) Shuttle Radar Topography Mission
(SRTM) digital elevation model and water-table data in Bangladesh. Results show that high As (>50 μg/l) tubewells are located
in low-lying areas, where mean surface elevation is approximately 10 m. Similarly, high As concentrations are found within
extremely low slopes (<0.7°) in the country. Groundwater elevation (weekly measured by Bangladesh Water Development Board)
was mapped using water-table data from 950 shallow (depth <100 m) piezometers distributed over the entire country. The minimum,
maximum and mean groundwater elevation maps for 2003 were generated using Universal Kriging interpolation method. High As
tubewells are located mainly in the Ganges–Brahmaputra–Meghna delta, Sylhet Trough, and recent floodplains, where groundwater
elevation in shallow aquifers is low with a mean value of 4.5 m above the Public Works Datum (PWD) level. Extremely low groundwater
gradients (0.01–0.001 m/km) within the GBM delta complex hinder groundwater flow and cause slow flushing of aquifers. Low
elevation and gentle slope favor accumulation of finer sediments, As-carrying iron-oxyhydroxide minerals, and abundant organic
matter within floodplains and alluvial deposits. At low horizontal hydraulic gradients and under reducing conditions, As is
released in groundwater by microbial activity, causing widespread contamination in the low-lying deltaic and floodplain areas,
where As is being recycled with time due to complex biogeochemical processes. |
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| Keywords: | Arsenic SRTM digital elevation model Spatial distribution Groundwater gradient Bangladesh |
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