Nature, origin, and geochemical evolution of the Ghodaghodi Lake of Nepal - a Ramsar Site

Ramsar sites across the world are vulnerable to pollution and degradation despite their special status and conservation measures. This study was conducted on the Ghodaghodi Lake of Nepal - a Ramsar Site to assess the seasonal variation of water quality and to detect pollution, if any. Water samples were collected in the pre-monsoon and post-monsoon periods from different parts of the lake. Of the various water quality parameters, temperature, pH, EC, TDS, DO levels were measured in-situ, while concentration of Ca2+, Mg2+, K+, Na+, Cl-, SO42-, NO3-, HCO3-, NH4+, and PO43- ions was analysed in laboratory. Water of the lake is found to be slightly alkaline with mean pH 7.88 and 8.22, in the pre-monsoon and post-monsoon, respectively. In terms of abundance, the major ions follow the order of Ca2+ > Mg2+ > Na+ > K+ for cations and HCO3- > Cl- > NO3- > SO42 > PO43- for anions. Mean concentrations of Ca2+ are 17.87 and 19.58 mg/L, and of HCO3- are 42.14 and 186.2 mg/L, respectively in the two seasons. Statistical tests such as correlation analysis, cluster analysis, and principal component analysis (PCA) and the Piper, Gibbs, and Mixing plots were used further to understand the nature, origin, and geochemical evolution of the lake water. Carbonate-rock weathering is found to be the chief controller of the lake-water chemistry, while anthropogenic activities emerged as the main reason for organic pollution in the lake as is reflected in the low (< 5.0) dissolved oxygen (DO) level. However, comparison with the WHO guidelines and the Water Quality Index (WQI) values (0-25) certify that water of the lake is absolutely safe for drinking and irrigation.