Abstract

Water in permafrost soil is an important factor affecting the ecology of cold environments, climate change, hydrological cycle, engineering, and construction. To explore the variations in soil water in the active layer due to permafrost degradation, the soil water sources in the Three-River Headwater Region were quantified based on the stable isotope data (δ2H and δ18O) of 1140 samples. The results showed that the evaporation equation was δ2H = 7.46 δ18O - 0.37 for entire soil water. The stable isotope data exhibited a spatial pattern, which varied over the soil profile under the influence of altitude, soil moisture, soil temperature, vegetation, precipitation infiltration, soil water movement, ground ice, and evaporation. Based on the stable isotope tracer model, precipitation and ground ice accounted for approximately 88 % and 12 % of soil water, respectively. High precipitation contributed to the soil water in the 3900–4100 m, 4300–4500 m, and 4700–4900 m zones, whereas ground ice contributed to the soil water in the 4500–4700 m and 4900–5100 m zones. Precipitation contributed approximately 84 % and 80 % to the soil water in grasslands and meadows, respectively, whereas ground ice contributed approximately 16 % and 20 %, respectively. Precipitation; evapotranspiration; physical and chemical properties of soil; and the distribution of ground ice, vegetation, and permafrost degradation were the major factors affecting the soil water sources in the active layer. Therefore, establishing an observation network and developing technologies for ecosystem restoration and conservation is critical to effectively mitigate ecological problems caused by future permafrost degradation in the study region.

Highlights

  • Soil water is the critical element of the water cycle and is closely associated with precipitation, surface water, groundwater, and plant water (Sprenger et al, 2016)

  • The evaporation line (EL) decreased in the following order: 40–60 cm, 60–80 cm, and 80–100 cm soil layers, which may be explained by three reasons as follows

  • Stable isotopes of soil water were affected by altitude (Fig. 11), no evident effect was observed for the 0–20 cm soil layer, likely due to intense solar radiation and evaporation from the surface soil

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Summary

Introduction

Soil water is the critical element of the water cycle and is closely associated with precipitation, surface water, groundwater, and plant water (Sprenger et al, 2016). Soil water holds most of the information pertaining to surface hydrological processes. It influences the infiltration and runoff ratios of rainfall and evaporation and controls the distribution of water and energy (Jean et al, 1998). Seasonal variations in soil water can directly or indirectly affect plant physiological metabolic processes, change the distribution of elemental contents in plants, and alter plant resource acquisition strategies and biomass distribution patterns, thereby affecting the community structure and species diversity of the ecosystem (Liu et al, 2021)

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