EVIDENCE OF DISSOLUTION FROM STABLE CARBON ISOTOPES OF WATER ALONG AN ALTITUDINAL GRADIENT IN THE EASTERN HIMALAYA MOUNTAINS, NEPAL

Glacier-fed rivers from the Himalaya Mountains transport dissolved inorganic carbon, reflecting the connection between glaciers, chemical weathering, and the global carbon cycle. Measuring the stable carbon isotopes (d¹³C) in water samples allows the identification of dissolved inorganic carbon sources. In the years 2018 and 2019, we collected water samples (n= 42) along an altitudinal gradient in the upper Dudh Koshi River Basin, Sagarmatha National Park, during the pre-monsoon season in the Eastern Himalayas. This study includes local drinking water sources (surface, spring, and piped/transported water) commonly used along the trekking routes from 2550m to 4950m elevation. d¹³C_VPDB values range from -0.76 to -20.52 ‰, suggesting the influence of dissolution of atmospheric CO₂ and microbiological activity, and shallow groundwater from aquifers with active carbonate weathering. Surface and pipe/transported water samples DIC values correspond to carbonate dissolution, whereas spring water samples also indicate a microbiological influence. Our findings pertain to a snapshot of pre-monsoon weather conditions and establish a baseline for future hydro-geochemical studies in the region.