Disentangling the contributing components of stream water by using environmental tracers

Identifying the various components contributing to river discharge can be challenging. This study relies on stable isotopes and electrical conductivity (EC) of water as tracers to distinguish the different components contributing to total river discharge. Additionally, we have made an effort to comprehend the processes that may influence glacier ice melt as well as the limits of oxygen-based hydrograph separation. Two distinct geographic domains in terms of climates and topographies were examined. The first study site represents the upper Ganga catchment (central Himalaya), while the second site is located in the Chandra sub-basin in western Himalaya. Errors in estimating the proportion of glacier melt in isotope mixing model are likely if end-member isotopic compositions, are not well defined, particularly for rainfall. Hydrograph separation results indicate that snowmelt is the largest contributor to total river flow in both regions. The contribution of snowmelt to the total runoff of the upper Ganga ranged from ~60% to 70%. The estimated contributions of glacier melt varied from 36% to 63% in upper Ganga headwater to 6% to 15% at Devprayag and ~8% at Rishikesh. In the Hamtah River, glacier and snowmelt contributions, quantified using a two-component mixing model, ranged from 10% to 14% during the pre- and post-monsoon seasons of 2013. The significant spatial and temporal variability, coupled with overlapping isotopic signatures, suggests complex glacio-fluvial interactions in these catchments. Local slow-moving air masses with whirling motion closer to the study area irrespective of the direction, and air parcels coming through Bay of Bengal branch are characterized by depleted isotopic rainfall compared to air masses originating from the Arabian Sea.