Major Ion Chemistry of the Bheri (Snow-Fed) and the Babai (Rain-Fed) River Systems in Western Nepal: Implication on Water Quality

Inter Basin Water Transfer (IBWT) is a water resource stressor globally with negative environmental impacts. This study describes the major ions and hydrochemistry of the first ever ongoing IBWT from snow-fed Bheri River to rain-fed Babai River in Western Nepal. Water samples from 10 sites, five from each river system, were collected in HDPE bottles for major ions (Ca^(2+), Mg^(2+), Na^+, K^+, HCO_3^-, Cl^-, SO_4^(2-), NO_3^-, CO_3^(2-)) along with the estimation of pH, temperature and conductivity encompassing winter, spring, summer, and autumn in 2018. Ca^(2+)and HCO_3^- were the most dominant cation and anion, respectively, with 〖Ca-Mg-HCO〗_3 water type in both the river systems. Mann Whitney test revealed significant variation (p<0.05) between the two river systems with regard to Ca^(2+), Mg^(2+), HCO_3^- , and SO_4^(2-). Kruskall Wallis test revealed significant variations between seasons in pH, temperature, Na^+, K^+, and Cl^- in Bheri River system, and in pH, TDS, temperature, Na^+, K^+ , Cl^- and SO_4^(2-) in Babai River system. Carbonate weathering was the main mechanism of ionic sources with insignificant contribution from silicate weathering. Relatively higher concentrations of the major ions during the dry seasons probably indicate the dilution effect of monsoon. Higher concentrations of the ions in the Babai River system reflect the latter’s bedrock geology with susceptibility to erosion. With Nepal’s future plans of IBWTs and their environmental implications, this finding could be helpful in mitigating the negative consequences of IBWTs in the impact assessment and management of IBWT projects because of their implications on management of aquatic resources.