Environmental geochemistry and quality assessment of surface and subsurface water of Mahi River basin, western India

The hydrogeochemical study of surface and subsurface water of Mahi River basin was undertaken to assess the major ion chemistry, solute acquisition processes and water quality in relation to domestic and irrigation uses. The analytical results show the mildly acidic to alkaline nature of water and dominance of Na⁺ and Ca²⁺ in cationic and HCO₃ ⁻ and Cl⁻ in anionic composition. In general, alkaline-earth elements (Ca²⁺ + Mg²⁺) exceed alkalis (Na⁺ + K⁺) and weak acids (HCO₃ ⁻) dominate over strong acids (SO₄ ²⁺ + Cl⁻) in majority of the surface and groundwater samples. Ca²⁺–Mg²⁺–HCO₃ ⁻ is the dominant hydrochemical facies both in surface and groundwater of the area. The weathering of rock-forming minerals mainly controlled the solute acquisition process with secondary contribution from marine and anthropogenic sources. The higher concentration of sodium and dissolved silica, high equivalent ratios of (Na⁺ + K⁺/TZ⁺), (Na⁺ + K⁺/Cl⁻) and low ratio of (Ca²⁺ + Mg²⁺)/(Na⁺ + K⁺) suggest that the chemical composition of the water is largely controlled by silicate weathering with limited contribution from carbonate weathering and marine and anthropogenic sources. Kaolinite is the possible mineral that is in equilibrium with the water, implying that the chemistry of river water favors kaolinite formation. Assessment of water samples for drinking purposes suggests that the majority of the water samples are suitable for drinking. At some sites concentrations of TDS, TH, F⁻, NO₃ ⁻ and Fe are exceeding the desirable limit of drinking. However, these parameters are well within the maximum permissible limit except for some cases. To assess the suitability for irrigation, parameters like SAR, RSC and %Na were calculated. In general, both surface and groundwater is of good to suitable category for irrigation uses except at some sites where high values of salinity, %Na and RSC restrict its uses.