Silicate or calcite weathering in wet-dry climate in lower Varahanadi basin, Tamilnadu, India – A determinant in global warming

Only about 15% of the water samples are fresh and the remaining is brackish water in the lower Varahanadi Basin, Tamilnadu, India. Four hydrochemical facies of groundwater (Ca²⁺HCO₃⁻ type; Na⁺Cl⁻ type; Mixed Ca²⁺Mg²⁺Cl⁻ type and Mixed Ca²⁺Na⁺HCO₃ type) are identified. Abundance of cations and anions occurs as Na>Ca>Mg>K and HCO₃>Cl>SO₄>CO₃>NO₃. The positive and negative chloro-alkaline indices indicate ion exchange reactions depending on the season, mixing of water and evaporation process. The plots of Na⁺/Cl⁻; Na⁺/Cl⁻ vs EC and Ca²⁺Mg²⁺ Vs SO₄²⁺ HCO₃-suggest predominance of silicate weathering in this wet-dry basin. Cationic ratio indicates higher silicate and lesser calcite weathering. Thus continental silicate weathering which can consume more of carbonic acid could play a role in environmental consequences such as global warming.