黄土高原丘陵沟壑区包气带土壤水运移过程

包气带土壤水运移过程是黄土高原生态修复中亟需回答的关键科学问题。环境同位素方法可获取其他方法难以获取的水文过程信息。通过对黄土高原丘陵沟壑区羊圈沟小流域降水、包气带0~150 cm土壤水和绣线菊（Spiraea salicifolia）木质部水等样品的同位素δD和δ18O进行测定。结果表明:羊圈沟小流域降水同位素组成受蒸发作用影响较大，呈现明显分馏效应。包气带土壤水、降水与木质部水同位素组成存在明显月份变化特征。降水是土壤水的主要补给来源，灌丛的水分利用来源主要为降水和土壤水，符合降水-土壤水-植被水的运移特征。灌丛木质部水和20~40 cm土壤水δD和δ18O最为接近，20~40 cm土壤水是灌丛水分利用的主要来源。研究揭示了包气带土壤水运移过程及植物水分利用来源，为土壤水运移过程、模型结构与参数识别等提供科学依据。

Migration process of soil water in the unsaturated zone of the Loess Plateau

The mechanism of soil water migration in the reconstruction and restoration of the Loess Plateau is a key scientific problem that must be solved. Isotopic tracers can provide valuable information associated with complex hydrological problems and are difficult to obtain by other methods. This study investigated soil water migration in the unsaturated zone in the hilly and gully region of the Loess Plateau. Samples were collected from the 0-150 cm unsaturated zone, including precipitation, soil water content, plant xylems, and plant roots, and were analysed. The results showed that the isotopic composition of precipitation in the Yangjuangou River basin was affected by evaporation, as indicated by isotopic fractionation phenomena. The δD and δ¹⁸O isotopic profiles of the soil water exhibited monthly variations. The soil water was recharged by precipitation. The soil water and precipitation were taken up by shrubland. Water migration exhibited a transformation pathway from precipitation to soil water to plant water. Shrubland root systems were distributed in the shallow layer. Root and water uptake increased at a depth of 20-40 cm. The isotopic composition of xylem water was close to that of soil water at a depth of 20-40 cm. These values reflect soil water signatures associated with shrubland uptake at a depth of 20-40 cm. This study investigate the migration process of soil water, identify the source of plant water use, and provide a scientific basis for the migration process of soil water, including model structure and parameter identification.