Hydro-geochemical conditions under projected climate change scenarios of Marshyangdi River, Nepal

Assessment of hydro-geochemical parameters in snow and glacier fed Himalayan rivers is crucial to understand the changes in water quality due to natural and anthropogenic stressors in the context of global climate change. Hence, the hydro-geochemical conditions of river water were assessed in a snow-fed Himalayan Watershed, Marshyangdi, located in western Nepal for the current and predicted future scenarios based on multiple regional climate models under the medium and pessimistic representative concentration pathways (RCP 4.5 and RCP 8.5) scenarios. This study was conducted in two seasons: pre- and post-monsoon in 2019. Of the total 21 sites, the river flow at each sampling site was estimated by Soil and Water Assessment Tool (SWAT) hydrological model, and subsequently the water quality for the future scenarios is predicted. A descriptive analysis of water quality along with Piper and Gibbs plots were applied to evaluate the hydro-geochemical status of the river water for the current and future scenarios. The results reveal alkaline river water based on pH. In the both seasons, Piper plots depict ionic dominance of Ca2+ > Mg2+ > Na+ + K+ for cations and HCO3− > Cl− > SO42− for anions indicating the carbonate dominated lithology in the Marshyangdi Watershed for the current scenario. The predictions for future scenarios illustrate that the dominance of cations in the pre- and post-monsoon seasons that follow the order of Ca2+ > Na+ + K+ > Mg2+ and Na+ + K+ > Mg2+ > Ca2+, respectively, while the anion composition corresponds to current scenarios for both seasons under both RCPs scenarios. Furthermore, under both RCPs, Gibbs diagrams show that rock weathering is prevalent in the present and future scenarios for the both seasons.