The geochemical study of fluvio-lacustrine aquifers in the Kathmandu Basin (Nepal) and the implications for the mobilization of arsenic |
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Authors: | Jaya K. Gurung Hiroaki Ishiga Mohan S. Khadka Nav R. Shrestha |
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Affiliation: | (1) Department of Geoscience, Shimane University, Matsue 690-8504, Japan;(2) Nepal Bureau of Standards and Metrology, Government of Nepal, Kathmandu, Nepal;(3) Department of Irrigation, Government of Nepal, Kathmandu, Nepal |
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Abstract: | The geochemical analyses of fluvial-lacustrine aquifer sediments of the Kathmandu Valley have been made as a step in assessing the environment for the mobilization of arsenic in groundwater. Elements measured by X-ray fluorescence (XRF) include 4 major oxides (Fe2O3, TiO2, CaO, P2O5) and 14 trace elements (As, Pb, Zn, Cu, Ni, Cr, V, Sr, Y, Nb, Zr, Th, Sc and TS). Elution tests of 15 selected core samples were also carried out to determine the potential leaching of arsenic from the sediments. The XRF results show that average bulk concentrations of the major oxides and trace elements are similar to modern unconsolidated sediments and average upper continental crust. However, the abundance of elements varies with grain size, with higher concentrations in finer-size grades. Variations in elemental abundances within the basin are strongly controlled by sediment facies. The elution tests show that greater amounts of arsenic are generally eluted from the fine sediments, although the rates are variable. The results overall suggest that As concentrations in the bulk sediments are not a controlling factor for elevated As in the Kathmandu Basin groundwater, and the roles of other factors such as redox conditions and organic matter contents are likely to be more significant. |
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Keywords: | Kathmandu Basin Arsenic Groundwater Sediment geochemistry Reducing condition |
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