期刊
CHEMICAL GEOLOGY
卷 277, 期 1-2, 页码 42-60出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chemgeo.2010.07.009
关键词
Chemical weathering; Primary minerals; Smectites; Modelling; Tropical; Watershed
资金
- French Institute of Research for Development (IRD)
- Embassy of France in India
- Indian Institute of Science
- IRD
- INSU/CNRS (Institut National des Sciences de l'Univers/Centre National de la Recherche Scientifique)
- Indo-French programme IFCPAR (Indo-French Center for the Promotion of Advanced Research [W-3000]
- Karnataka Forest Department
We investigate the chemical weathering processes and fluxes in a small experimental watershed (SEW) through a modelling approach. The study site is the Mule Hole SEW developed on a gneissic basement located in the climatic gradient of the Western Ghats, South India. The model couples a lumped hydrological model simulating the water budget at the watershed scale to the WITCH model estimating the dissolution/precipitation rates of minerals using laboratory kinetic laws. Forcing functions and parameters of the simulation are defined by the field data. The coupled model is calibrated with stream and groundwater compositions through the testing of a large range of smectite solubility and abundance in the soil horizons. We found that, despite the low abundance of smectite in the dominant soil type of the watershed (4 vol.%), their net dissolution provides 75% of the export of dissolved silica, while primary silicate mineral dissolution releases only 15% of this flux. Overall, smectites (modelled as montmorillonites) are not stable under the present day climatic conditions. Furthermore, the dissolution of trace carbonates in the saprolitic horizon provides 50% of the calcium export at the watershed scale. Modelling results show the contrasted behavior of the two main soil types of the watershed: red soils (88% of the surface) are provider of calcium, while black soils (smectite-rich and characterized by a lower drainage) consumes calcium through overall carbonate precipitation. Our model results stress the key role played by minor/accessory minerals and by the thermodynamic properties of smectite minerals, and by the drainage of the weathering profiles on the weathering budget of a tropical watershed. (C) 2010 Elsevier B.V. All rights reserved.
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