Abstract:
In the upper Ganga basin particularly in Himalayan terrain, precipitation and/or snow/glacial melt
contribute towards the flow of the Ganga river in the form of surface and sub-surface water. In the
present study, river–subsurface water chemistry is compared to infer river–subsurface water
interactions in higher Himalayan region. Forty-one water samples from the Ganga river and its
small tributaries between Gomukh and Dabrani section as well as subsurface water were collected
during the months of March, May, September, October and November 2016 with in-situ
measurements of pH, Electric Conductivity, temperature and bicarbonates. The samples were
analysed for major ions and isotopes of oxygen and hydrogen. The results revealed that major ion
chemistry of sub-surface water and river water is influenced by seasonal mineral dissolution and
rock weathering reactions in the sub-surface water. A dominance of Calcium (36–43% in surface
and 61–71% in sub-surface water), bicarbonate (13–66% in surface water and 45–85% in subsurface
water) and sulphate (31–86% in surface water; 15–47% in sub surface) is observed. High
carbonate dominance is observed in surface water during the pre-monsoon (May 2016) suggesting
more carbonate dissolution while high sulphates are found in March and September. The isotopes
characterization of the surface and sub-surface water indicated highly evaporated sub-surface
water in pre-monsoon season while in post monsoon season the slope and intercept values of
δ18O and δD plot was more close to that of surface water suggesting its influence. The study helps
understand to river–subsurface water interactions in the Himalayan terrain of the Ganga basin. The
understanding of river–subsurface water interactions can help in management of the Ganga river
water and in addressing downstream environmental issues associated with the river.
