Abstract
The chemistry of major ions and elements in Narmada and Tapti river water was studied based on the monitoring of the drainage basins for monsoon and postβmonsoon seasons in 2004. The results show the influence of rock weathering on the concentration of major ions in the surface water. There is a significant contribution from the catchment geologies in the major constituents of water. The total dissolved solids (TDS) concentrations are reflecting the signature of weathering of rocks in the catchment areas. In the Narmada River, $HCO_{3}^{-}$, Ca^2+^ and Mg^2+^ are dominant ions, whereas in the Tapti River the ions dominating major compositions are $HCO_{3}^{-}$, Na^+^ and Mg^2+^. The high concentration of Cl^β^ and $SO_{4}^{2-}$ is a signature of anthropogenic inputs in addition to the contribution of discharge from springs and/or groundwater. The high concentration of $NO_{3}^{-}$ can exclusively be attributed to the anthropogenic activities. The average concentration of dissolved silica being higher than the Indian and world average is reflecting the contribution of silicate weathering. The present study gives the silicate and carbonate weathering rates and the corresponding CO~2~ consumption rates considering the contribution of carbonate rocks present in the selected river basins of the Deccan basaltic province. The mean silicate weathering rates during the investigation period for the Narmada and Tapti Rivers show lower values, but the corresponding mean CO~2~ consumption rates give higher values compared with earlier estimated rates by Dessert et al. (2001. Earth and Planetary Science Letters 188: 459). For the study period, the mean carbonate weathering rates and the associated CO~2~ consumption rates for the Narmada and Tapti Rivers are βΌ12Β·67 t km^β2^ year^β1^ and βΌ7Β·32 t km^β2^ year^β1^ and βΌ0Β·36 Γ 10^6^ mol km^β2^ year^β1^ and βΌ0Β·22 Γ 10^6^ mol km^β2^ year^β1^ respectively. Copyright Β© 2008 John Wiley & Sons, Ltd.