Modelling the chemical weathering fluxes at the watershed scale in the Tropics (Mule Hole, South India): Relative contribution of the smectite/kaolinite assemblage versus primary minerals

摘要: We investigate the chemical weathering processes and fluxes in a small experimental watershed (SEW) through modelling approach. The study site is Mule Hole SEW developed on gneissic basement located climatic gradient of Western Ghats, South India. model couples lumped hydrological simulating water budget at scale to WITCH estimating dissolution/precipitation rates minerals using laboratory kinetic laws. Forcing functions parameters simulation are defined by field data. coupled calibrated with stream groundwater compositions testing large range smectite solubility abundance soil horizons. found that, despite low dominant type (4 vol.%), their net dissolution provides 75% export dissolved silica, while primary silicate mineral releases only 15% this flux. Overall, smectites (modelled as montmorillonites) not stable under present day conditions. Furthermore, trace carbonates saprolitic horizon 50% calcium scale. Modelling results show contrasted behavior two main types watershed: red soils (88% surface) provider calcium, black (smectite-rich characterized lower drainage) consumes overall carbonate precipitation. Our stress key role played minor/accessory thermodynamic properties minerals, drainage profiles tropical watershed. (C) 2010 Elsevier B.V. All rights reserved.