Source and seasonal variation in the major ion chemistry of two eastern Himalayan high altitude lakes, India

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A chemical survey of two high-altitudes lakes, i.e., Tsokyo Tso and Sella, was conducted during pre-monsoon (May) and post-monsoon (November) 2011. Lake water is found to be pure with very low EC values even lesser than rainwater. This shows where lake water receives most of its contribution. A comprehensive and systematic study on the seasonal pattern of major ions (Cl � ,P O4 3� , HCO3 � ,N O3 � , SO4 2� ,N a + ,K + ,C a 2+ ,M g 2+ , and SiO2) was carried out to understand the geochemical processes controlling water qual- ity. There was marked seasonal variation observed for almost all ions. Factor analysis identifies geochemical controls, snow melting, and evaporative enrichment as main controlling fac- tor. The partial pressure of CO2 (pCO2) value has increased in the post-monsoon probably due to higher atmospheric CO2 duringwinter.Overall,factoranalysisidentifiedprocesseslike geochemical control, snowmelt water input, and evaporative enrichment in the pre-monsoon, atmospheric input and dilu- tion of ions due to rainfall, microbial activities, and accumu- lation of weathered material lake system in the post-monsoon as governing processes switching among themselves in differ- entseasons.HYSPILTbacktrajectorymodelwasusedtotrace the source of long-range transport of pollutant. Results show for boththelakes that air arrivingtothevicinityofthe lakehas an origin from the southeast direction during pre-monsoon and the mid-Gangetic plain during post-monsoon season, re- spectively. The results show that both the studied lakes have significant impacts of long-range transport of air pollutants rather than local interferences. Long-term monitoring of the fluctuation in key parameters can further verify the findings of this study.