Soil water sources in permafrost active layer of Three-River Headwater Region, China

Abstract

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.