Evaporation, infiltration and storage of soil water in different vegetation zones in the Qilian Mountains: a stable isotope perspective

The processes of water storage have not been fully understood in different vegetation zones of mountainous areas, which is the main obstacle to further understanding hydrological processes and improving water resource assessments. To further understand the process of soil water movement in different vegetation zones (alpine meadow (AM), coniferous forest (CF), mountain grassland (MG) and deciduous forest (DF)) of mountainous areas, this study monitored the temporal and spatial dynamics of hydrogen- and oxygen-stable isotopes in the precipitation and soil water of the Xiying River basin. The results show that the order of soil water evaporation intensities in the four vegetation zones was MG (SWLslop: 3.4) > DF (SWLslop: 4.1) > CF (SWLslop: 4.7) > AM (SWLslop: 6.4). The soil water in the AM and CF evaporated from only the topsoil, and the rainfall input was fully mixed with each layer of soil. The evaporation signals of the MG and DF could penetrate deep into the middle and lower layers of the soil as precipitation quickly flowed into the deep soil through the soil matrix. Each vegetation zone's water storage capacity of the 0–40 cm soil layer followed the order of AM (46.9 mm) > DF (33.0 mm) > CF (32.1 mm) > MG (20.3 mm). In addition, the 0–10 cm soil layer has the smallest soil water storage capacity (AM: 43.0 mm; CF: 28.0 mm; MG: 17.5 mm; DF: 29.1 mm). This work will provide a new reference for understanding soil hydrology in arid headwater areas.