37-3 Regional hydrogeochemical assessment of Trans-Himalayan groundwaters: insights from stable and radiogenic isotopic studies

Session: Innovations in Research of Groundwater-Surface Water Interactions over Multiple Spatio-Temporal Scales

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Abstract:

Observed groundwater chemistry of a region is a result of several inter-related factors operating at various scales: recharge water chemistry, water – aquifer matrix (rock) reactions, mixing with other sources of water, and anthropogenic disturbances. Although sources of solutes and their release mechanisms to groundwater are well established in the middle and lower trans-boundary Indus River basin aquifers, such delineations are relatively scarce in its mountainous stretches. Thus, the objective of the work presented here is to delineate the sources of solutes in the high-altitude Trans-Himalayan aquifers of the Indus River basin of Ladakh, India through the use of stable (¹⁸O and ²H) and radio (⁸⁷Sr/⁸⁶Sr) isotopic systematics. Groundwater and aquifer matrixes were sampled from the valleys of the Indus mainstem and its major tributaries.

Analysis revealed fluvial, fluvio-glacial, aeolian, lacustrine sediments and bedrocks ranging in composition from ultrabasic to acidic and from carbonate to siliciclastic, make up the groundwater aquifers. Hosted waters are near-neutral, post-oxic and are of Ca-HCO₃ and Ca-Mg-HCO₃, Ca-Na-HCO₃ type. Isotopically they are depleted relative to the global and local meteoric water lines, and are more similar to local river and meltwaters. Endmember mixing analysis revealed varying contribution of different end-members to groundwater recharge within the different valleys.  Major-ion chemistry revealed that the waters are affected by a combination of carbonate and silicate weathering. Cation-exchange occurs minorly and is limited to the Indus (mainstream) valley. Geochemical mass-balancing and thermodynamic calculations predicted the weathering of serpentine, olivine, chlorite, pyroxene, biotite, and feldspars to kaolinite, vermiculite and illite. Utilisation of the ⁸⁷Sr/⁸⁶Sr as a tracer pointed towards the dominance of silicate weathering with the existence of multiple silicate sources. Solutes in the Indus valley aquifer systems are derived from the rocks of the suture zone, where as in the Dras and Shyok valley aquifers they come from the Himalayan and Karakoram rocks.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6596

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