关键词: 地下水埋深, 覆被类型, 土壤水分动态, HYDRUS-1D, 毛乌素沙地

Abstract: To explore the effects of groundwater depth on soil moisture dynamics and distribution of different land cover types in Mu Us Sandy Land, we examine the hydrology dynamics across three typical land cover types (bare land, grassland and Salix psammophila land) under the shallow buried area (2 m) and deep buried area (10 m) of groundwater in the southeastern margin of Mu Us Sandy Land. Through field sampling and HYDRUS-1D numerical simulation, we analyzed the effects of groundwater depth on soil moisture distribution dynamics of different vegetation types, as well as the differences of evapotranspiration intensity, bottom (150 cm) water exchange and water storage capacity among three vegetation types. The results showed that the soil moisture dynamics in the deep buried area of groundwater were significantly driven by precipitation and evaporation, while the shallow buried area maintained a stable state due to the longterm recharge of groundwater through the capillary zone. There were significant synergistic interactions between groundwater depth and cover type on soil moisture dynamics. Under the 458 mm rainfall condition, the evapotranspiration loss in deep buried area was the largest in grassland (427 mm), followed by Salix psammpphila land (395 mm) and bare land (284 mm). In contrast, due to the support and replenishment of groundwater in shallow buried areas, Salix psammpphila land and grasslands consumed groundwater, resulting in higher evapotranspiration losses (590 mm for Salix psammpphila land and 620 mm for grassland) than deep burial area. In addition, cover type significantly affected the redistribution of soil moisture. Soil water content at 40-60 cm depth in the root zone of grassland and Salix psammophila land was the lowest in the study period, which was 0.02 and 0.05 cm³·cm^-3 in the deep buried area and shallow buried area, respectively. In contrast, the bare land showed higher soil water content, the deep buried area and shallow buried area were 0.05 and 0.08 cm³·cm^-3, respectively. The vegetation in the shallow buried area increased evapotranspiration by absorbing water from the envelope zone and the saturated zone, while the vegetation in the deep buried area completely depended on soil water in the unsaturated zone, and the evapotranspiration was limited. Among the cover types, grassland showed the highest evapotranspiration and the lowest leakage, indicating that grassland had significantly higher water use efficiency and evapotranspiration regulation ability in the short term. However, this high evapotranspiration and low leakage characteristics may limit its capacity to recharge groundwater reserves and affect long-term water conservation. Therefore, it is necessary to comprehensively consider the synergistic effect of groundwater depth and cover type in the process of ecological management and vegetation restoration, and optimize vegetation configuration to balance water use efficiency and water conservation.

Key words: groundwater depth, cover type, soil water dynamics, HYDRUS-1D, Mu Us Sandy Land