High resolution profile of inorganic aqueous geochemistry and key redox zones in an arsenic bearing aquifer in Cambodia

Richards, Laura A. and Magnone, Daniel and Sovann, Chansopheaktra and Kong, Chivuth and Uhlemann, Sebastian and Kuras, Oliver and van Dongen, Bart E. and Ballentine, Christopher J. and Polya, David A. (2017) High resolution profile of inorganic aqueous geochemistry and key redox zones in an arsenic bearing aquifer in Cambodia. Science of The Total Environment, 590-59 . pp. 540-553. ISSN 0048-9697

Full content URL: http://dx.doi.org/10.1016/j.scitotenv.2017.02.217

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Abstract

Arsenic contamination of groundwaters in South and Southeast Asia is a major threat to public health. In order to better understand the geochemical controls on the mobility of arsenic in a heavily arsenic-affected aquifer in northern Kandal Province, Cambodia, key changes in inorganic aqueous geochemistry have been monitored at high vertical and lateral resolution along dominant groundwater flow paths along two distinct transects. The two transects are characterized by differing geochemical, hydrological and lithological conditions. Arsenic concentrations in groundwater are highly heterogenous, and are broadly positively associated with iron and negatively associated with sulfate and dissolved oxygen. The observed correlations are generally consistent with arsenic mobilization by reductive-dissolution of iron (hydr)oxides. Key redox zones, as identified using groupings of the PHREEQC model equilibrium electron activity of major redox couples (notably ammonium/nitrite; ammonium/nitrate; nitrite/nitrate; dissolved oxygen/water) have been identified and vary with depth, site and season. Mineral saturation is also characterized. Seasonal changes in groundwater chemistry were observed in areas which were (i) sandy and of high permeability; (ii) in close proximity to rivers; and/or (iii) in close proximity to ponds. Such changes are attributed to monsoonal-driven surface-groundwater interactions and are consistent with the separate provenance of recharge sources as identified using stable isotope mixing models.

Additional Information:Open Access funded by Natural Environment Research Council Under a Creative Commons license CC-BY-4.0
Keywords:Arsenic, Redox zones, Groundwater quality, Groundwater monitoring, PHREEQC, Redox modelling
Subjects:F Physical Sciences > F140 Environmental Chemistry
F Physical Sciences > F850 Environmental Sciences
F Physical Sciences > F852 Hydrology
Divisions:College of Science > School of Geography
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ID Code:28118
Deposited On:04 Aug 2017 10:19

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