Ion chemistry and quality assessment of a post-glacial sacred lake in Sikkim Himalaya: source identification and conservation measures

The present research work aims to investigate the seasonal variations in hydrochemistry and water quality of Khacheopalri Lake, a recognized Ramsar site in Sikkim Himalayas, along with determining the dissolved ion sources and the mechanisms influencing lake water chemistry. The result has shown the acidic nature of lake water with distinct seasonal variation (mean pH 5.61 and 6.02 in the dry and wet seasons). Elevated values for EC, TDS, DO, HCO3 − , Cl − in the lake water during the wet season are due to the precipitation, dissolution, and diffusion of O 2 /CO 2 in the lake system. The hydrochemical facies of lake water is of Ca 2+ –HCO 3 − type, depicts dominance of Ca 2+ and HCO 3 − in ionic composition. Cross plot analyses elucidate that lake water chemistry is majorly governed by bicarbonate weathering, with minor contributions from silicate weathering. Principal component analysis of hydrochemical dataset has confirmed that major cations and anions in lake water have mainly arrived from geogenic sources as a result of weathering and erosion in the lake catchment area. However, run-off water from adjacent croplands, human settlements, and temporal factors also contributed to determining lake water characteristics. Evaluation of water quality index (WQI) has ascertained that the lake water is “good to excellent” in type and pertinent to aquatic life and human uses. The findings from present study can provide essential baseline information which would be crucial for effective management and conservation of this sacred ecological site and can be a good reference for further study on glacial-formed Lesser Himalayan lakes.