Source of soil water in cold regions based on stable isotope tracers

Abstract

Soil water plays a key role in vegetation growth and ecological stability in cold regions. The soil water sources in the Qilian Mountains of the northeastern Tibetan Plateau have been quantified based on stable isotope data (δ2H and δ18O) of 1913 samples. The results indicated that δ18O of soil water ranged from ˗14.13–11.21‰, with an average of ˗6.78‰, and on a spatial scale, it increased gradually from the southeast to the northwest, where it became more positive. The stable isotopes of soil water are affected by evaporation, leading to a lower slope and interception of the evaporation line: δ2H = 3.23 δ18O–32.51 (R2 = 0.71, p < 0.01). The relationship between soil water and other water bodies showed that the soil water was mainly replenished by precipitation and ground ice meltwater. End-member mixing analysis (EMMA) showed that precipitation and ground ice accounted for approximately 91 % and 9 % of soil water, respectively, during heavy ablation. In the 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm soil layers, the contributions of ground ice meltwater to soil water were 0 %, 3 %, 7 %, 13 %, and 18 %, respectively. Notably, the contribution of ground ice meltwater to soil water gradually increased with elevation, whereas that of precipitation decreased. This study has obtained relevant data for the cold region, where it is typically difficult to conduct observations and sampling. More importantly, it analyzes the source and influencing factors of soil water in cold regions using the stable isotope method, which is of great significance for the study of the water cycle in cold regions.