Hillslope flow paths in snowmelt and rainfall seasons in permafrost-underlain areas, Northeastern Tibetan Plateau: Investigation based on hydrochemical tracers and end-member mixing analysis

Abstract

Study area

The Binggou and adjacent Yakou catchments in the northeastern Tibetan Plateau.

Study focus

Hillslope flow paths were studied using hydrochemical data of various water types in the spring snowmelt and summer rainfall periods based on hydrochemical tracers and end-member mixing analysis.

New hydrological insights for the study region

End-member mixing analysis confirmed the dominance of surface and near-surface runoff during the spring snowmelt. Specifically, the spring Binggou stream water had 61 % surface runoff, 22 % shallow groundwater, and 17 % near-surface runoff. The spring Yakou stream water had 64 % snowmelt, 25.5 % near-surface runoff, and 10.5 % riparian saturated soil water at a depth of 20 cm. The application of end-member mixing analysis failed in the summer rainfall period, and shallow subsurface flow contributed the most to the streamflow (∼ 100 %). The average acid-neutralizing capacity of the spring Yakou stream water was 611 μeq/L, increasing to 841 μeq/L in the summer, and for the Binggou stream water, the values were 747 μeq/L and 1084 μeq/L, respectively, indicating that the thawed soil layers had a significant buffering effect on stream water chemistry. This study revealed seasonal shifts in flow paths and stream sources, with a transition from surface to subsurface flow influenced by meteorological conditions and the active layer thickness. Future climate change may enhance subsurface flow recharge, leading to less diluted streamflow and stronger water-soil interactions.