Major ion chemistry of the Teesta River in Sikkim Himalaya, India: Chemical weathering and assessment of water quality

Study Region: Teesta River of Eastern Himalayas, India. Study Focus: This article addresses the mechanisms of weathering in the Teesta River, for the first time based on the original data of major ions. Water samples were collected along the Teesta River in Sikkim Himalaya, India. The evaluation of the major ion and trace elements against the standard guideline values and the average chemical composition of world rivers were discussed. New Hydrological Insights: The predominance of Ca, Mg and HCO₃ in all waters reflects the influence of carbonate weathering on the Teesta River. However, an increase in the Na/Ca ratio was linked to the increase of Si downstream, indicating that silicate weathering was predominant in the lowlands of Teesta drainage. The rate of silicate weathering is dependent on an overall balance of key factors including gradient, contact time, temperature and vegetation. The higher concentration of cations was balanced by the SO₄ originating from the action of H₂SO₄ and H₂CO₃ on carbonates and silicates. Rock weathering (carbonate-silicate weathering) is the key mechanism that controls the major ion chemistry of the Teesta River followed by evaporite dissolution.