Hydrogeochemical evolution of a glacier-fed Himalayan mountain system: Upper Ganga Basin

This study presents a comprehensive assessment of dissolved trace metals, heavy metals, and stable isotope (δ¹⁸O) geochemistry in glacier ice, snowmelt, river water, and groundwater of the Upper Ganga Basin (UGB) during the pre-monsoon season. Pearson correlation analysis, principal component analysis (PCA), and hierarchical cluster analysis (HCA) were applied to identify the dominant geochemical controls. Trace-metal distributions show clear upstream–downstream variability driven by lithology, weathering, and water–rock interaction. Elevated Fe, Ti, and Zn in glacier melt and headwaters reflect active erosion and weathering, whereas downstream Sr and Ba enrichment indicates longer residence times, tributary mixing, and mineral dissolution. Strong correlations among Ti, V, Cr, Fe, Sr, and Ba (r = 0.81–0.95, p < 0.01) and the dominance of PC1 (53.3% and 30.7% variance in river water and groundwater, respectively) confirm lithogenic weathering as the primary control on trace-element distribution, while localized enrichments of Zn, Pb, Sr, U, Fe, and Ti reflect lithological heterogeneity and tectonically enhanced weathering. Variations in electrical conductivity (EC) and δ¹⁸O, supported by HCA clustering, distinguish glacier-fed headwaters from downstream waters influenced by hydrochemical evolution, groundwater–river interaction, and tributary mixing. Although basin hydrochemistry is primarily controlled by geogenic processes, elevated heavy metal concentrations in glacier ice and meltwater near the river source indicate anthropogenic inputs transported from the Indo-Gangetic Plain (IGP) and northwestern India, with localized impacts more evident near inhabited and high-traffic areas such as Harsil, Uttarkashi, Kamand, Karanprayag, and Rudraprayag. This study is based on a single pre-monsoon sampling, and future multi-seasonal, long-term investigations are needed to better constrain atmosphere–cryosphere–hydrosphere interactions.