Hydrochemical composition and hydrodynamics as proxies to identify the stream water sources and pathways in high-altitude catchments

Abstract

This study investigates the complex relationship between high-altitude stream hydrochemistry and geochemical processes in the Liddar catchment, a representative high-altitude watershed in the Western Himalayas. High-altitude catchments, like the Liddar, are critical as they are major freshwater sources, heavily influenced by snow and glacier melt contributions, making them particularly sensitive to climate change. The high-altitude location intensifies the seasonal contrast in hydrochemical signatures, driven by glacier and snowmelt inputs, which are distinct from low-altitude catchments that rely more on rainfall. We applied geochemical and bayesian stable water isotope modeling to distinguish the hydrochemical signatures during baseflow and intense melting periods. Across the seasons, stable isotope water analyses outline the diverse contributions of snowmelt, precipitation, and groundwater to streamflow. A large portion of streamflow is sourced from meltwater (62.05 ± 6.24%) in summer that reduces in spring by (51.34 ± 7.43%). In Autumn, meltwater contribution drops to 28.30 ± 7.24% and this contribution further drops significantly to 18.87 ± 3.68% during winter. Conversely, during winter and autumn a larger portion of the stream water is sourced from groundwater (60.45 ± 8.54% and 55.78 ± 7.37%) respectively. Groundwater contribution to baseflow decreases from 37.61 ± 5.58% to 28.91 ± 8.51% in spring and summer respectively. Mean residence time (MRT) of stream water, extending to 13 weeks during baseflow and shortening to 7 weeks during melting conditions, points to dynamic storage and flow path characteristics of the catchment. Geochemical modeling highlights the dissolution of minerals such as calcite, dolomite, and gypsum as key drivers of stream water chemistry. Baseflow period shows enrichment of major ions like calcium, magnesium, bicarbonate and trace elements like Ni and Cr exhibiting geochemical signatures suggestive of deeper flow paths and mineral dissolution from host rock formations. However, the intense melting periods demonstrate significant increase in trace elements like, Al, indicative of shallower sources suggesting interactions between melting snowpacks and regolith. Our study demonstrates that in undisturbed high-altitude watersheds the stream, groundwater, and soil chemistry effectively reflect the flow path dynamics. This research offers critical insights for adaptive water resource management strategies in high-altitude regions, which face unique challenges under changing climatic conditions, such as the mobilization of heavy metals and freshwater toxicity.