期刊
APPLIED GEOCHEMISTRY
卷 29, 期 -, 页码 102-116出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.apgeochem.2012.11.001
关键词
-
资金
- French National Research Agency (ANR) through the VMC programme (project MOHINI) [ANR-07-VULN-08]
Overexploitation of crystalline aquifers in a semi-arid climate leads to a degradation of water quality, with the main processes responsible for the observed salt loads probably being irrigation return flow (IRF) and a high evaporation rate. The present study has focused on modelling the F- accumulation caused by IRF below rice paddy fields in the small endorheic Maheshwaram watershed (Andhra Pradesh, Southern India). The transient simulation was performed with a 1D reactive transport PHREEQC column and took into account IRF evaporation, kinetically controlled mineral dissolution/precipitation, ion adsorption on Fe hydroxides, and mixing with fresh groundwater. The results revealed the role of cationic exchange capacity (CEC) in Ca/Na exchange and calcite precipitation, both favouring a decrease of the Ca2+ activity that prevents fluorite precipitation. Iron hydroxide precipitation offers a not inconsiderable adsorption capacity for F- immobilization. The principal sources of F- are fluorapatite dissolution and, to a lesser extent, allanite and biotite dissolution. Anthropogenic sources of F-, such as fertilizers, are probably very limited. After simulating an entire dry-season irrigation cycle (120 days), the results are in good agreement with the observed overall increase of Cl- in the Maheshwaram groundwater. The model enables one to decipher the processes responsible for water-resource degradation through progressive salinization. It shows that F- enrichment of the groundwater is likely to continue in the future if groundwater overexploitation is not controlled. (c) 2012 Elsevier Ltd. All rights reserved.
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