| Summary: | Sampling and testing were conducted on the groundwater level depth, soil water content, and vegetation coverage in the delta oasis of the WeiGan-KuChe River Basin, and a method for analyzing soil water balances for groundwater-dependent vegetation (GDV) was developed using the soil water balance model with the Richards equation. Three typical observation points (sites A, B, and C) were selected to understand the relationship between plant transpiration, soil water content changes, and groundwater level depth via HYDRUS-1D model simulations. The model calibration results showed that the simulated water contents at each site and in each soil layer fit well with the measured data and the comparison results of each sites are R2A = 0.81, R2B = 0.89, R2C = 0.78, in respectively. The soil water balance model of the three different sites demonstrated that vegetation transpiration was related to the groundwater level depth, vegetation cover, and plant age (P. euphratica). According to field observations within the WeiGan-KuChe River delta oasis, the groundwater level depth influenced the soil moisture and soil salinity, which are the most important environmental factors determining the distribution and changes in GDV. When the groundwater level depth was below 1 m or above 6 m, the plant species occurrence frequency decreased by 10%, and the degree of land desertification was severe. These simulations and field investigation results showed that the groundwater level threshold for salinity control was approximately 1 m, the ecological warning threshold varied by approximately 5 m, and the preferred groundwater level for GDV growth varied between 2 and 4 m. The findings of this study have important implications for groundwater resource management and ecological preservation in arid and semiarid areas.
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