Major ion chemistry and hydrochemical processes controlling water composition of Teesta River catchment, Sikkim Himalaya, India

The study determines the major ion chemistry of the Teesta River catchment in the Eastern Himalayan region and evaluates hydrochemical processes controlling water composition of the catchment area. Water of the Teesta River basin was in neutral to alkaline condition. HCO₃⁻, Ca^2+, Na⁺, Mg²⁺ and SO₄^2- were identified as the dominant ionic species in the Teesta catchment water composition and Ca-Mg-HCO₃ as the dominant hydrochemical facies. Higher contribution of (Ca²⁺+Mg²⁺) and HCO₃⁻ towards the TZ⁺ and TZ⁻, high ionic ratios of (Ca²⁺+Mg²⁺)/(Na⁺+K⁺), HCO₃⁻/(Cl⁻+SO₄^2-) and low (Na⁺+K⁺)/TZ⁺ ratio suggest carbonate weathering as a major contributor of dissolved ions in the Teesta basin water. Under-saturation with respect to both carbonate and sulphate phase minerals suggests that water can dissolve these minerals during water-rock interaction. Concentration of the analysed water quality parameters were well below the specified drinking and irrigation water limits.