Hydrochemistry, controlling mechanisms and water quality index in hot springs of the Kullu-Manali region, India

Abstract

The present study highlights the unique chemical characteristics of hot springs and their comparison with cold springs, surface water, and groundwater in the same area. The hot springs' temperature ranges from 27 to 96 °C, which induce variable degree of hydrochemical alteration of hot springs' water. The concentrations of Na+ and K+ are highly correlated with Cl−, HCO3−, and SO42− in hot springs, while Ca2+ and Mg2+ behave erratically. The Na/Cl ionic ratios give clues of a restricted geological environment of thermal waters, mixing in cold springs and groundwater, and a meteoric origin of the surface water. The SiO2 behave conservatively, with little change in different water types except surface water. The concentrations of SiO2, highest in the hot springs and lowest in the surface water, help draw depth profiling of different water types. Mixing of ascending hot springs with overlying waters of different origins creates ambiguity in chemical interpretations. Due to mixing with different water types, Chalcedony thermometry better represents hot springs than Na–K–Mg geothermometry. As a result, hot springs alter from Na–Cl and Na–Cl–SO4 type facies with high SiO2 and gradually evolved in Ca–Mg–Na–HCO3–Cl type water. Similarly, most cold springs show mix-type and Ca–HCO3 water types. The chemical characteristics of cold springs are similar to groundwater and equally sensitive to seasonal variation due to mixing with meteoric recharge. The surface water is characterized by Ca–Cl2 type water. All water types acquire unique chemical signatures due to the combined effect of geological formations, depth, temperature, degree of meteoric recharge, and, to some extent, anthropogenic pollution. The Water Quality Index (WQI) assessment revealed that three samples from the Kullu and Kalath regions fall in poor WQI, requiring immediate protection from anthropogenic pollution.