Headwater Flow Geochemistry of Mount Everest (Upper Dudh Koshi River, Nepal)

Abstract

The aim of this work, conducted in the upper valley of the Khumbu on the southern part of Mount Everest, is to approach in parallel three topics: (i) the dynamics of the water geochemistry, major ions and trace elements; (ii) the stable water isotopes of precipitation and rivers; and (iii) the water uses by the inhabitants. As in most mountain environments, the Khumbu area is threatened by climate change, which impacts the cryosphere and consequently the people and the landscapes. Moreover, changes in water use are also related to new needs stemming from tourism, which strongly affect local livelihood. For the first two topics, new results are presented. They provide details on the global chemical quality of the river water and show how certain elements are seasonally influenced and how other elements allow us to distinguish the water origins within the study zone. Beside the use of stable isotopes to determine mainly the origin of the water flow in the rivers, the isotopic patterns confirm the double climatic influence of the westerly fluxes in the winter season and of the Asian monsoon in the summer season. Regarding water use, the study does not conclude on the potability of the water resource, because microbiologic and organic components have not been investigated; however it confirms that the chemical quality is good. In conclusion, we attempt to predict the future of the geochemistry patterns submitted to the double pressure of climate change and the surge in tourism.

Isoscape of Surface Runoff in High Mountain Catchments: An Alternate Model for Meteoric Water Characterization and Its Implications

“…In DKB, the variation in ILR is largely controlled by the cryospheric input, which also happens to be significantly altered by post-depositional isotopic modification. Non-uniform ILR in a particular season across an elevation transect has been reported from the Himalayas (Chevallier et al, 2020;Voss et al, 2020). Therefore, it would be wise to treat ILR as a changing variable across an el- S5).…”

“…Local environmental factors such as humidity, diurnal temperature, catchment vegetation, cloud type, and so on, actively influence the hydrological processes which result in the isotopic modification in meteoric waters. Failing to account for the local processes and associated environmental variables that affect the isotopic composition of meteoric water leads to differing results for the same basin (Kosi Basin: Chevallier et al., 2020; Florea et al., 2017; Hoffmann et al., 2016; Racoviteanu et al., 2013). The difference may also arise due to the style of sampling adopted, such as non‐selective stream‐order sampling, single reservoir sampling (rivers), and sampling from a limited altitudinal range.…”

“…Earlier studies have shown varying isotopic responses in the meteoric water of the Kosi Basin, partly due to the sampling style employed. For instance, Chevallier et al (2020), Florea et al (2017), Racoviteanu et al (2013), andHoffmann et al (2016) reported distinctly different δ 18 O lapse rates of −2.0‰, −2.8‰, −1.1‰, and −1.3‰ per km, respectively, in the Kosi Basin. Therefore, it is important to adopt a technique for the isotopic characterization of meteoric reservoirs, employing a method for comprehensive sampling of each hydrological components, where stream water sampling is limited to first/second order catchments and post-depositional isotopic modification in various meteoric reserves are accounted for.…”