Abstract: Origin and infiltration patterns of soil water were investigated using environmental isotopes under different land use types in arid area. Soil water samples were collected from four soil profiles representing different land use types in Sangong River Basin, Xinjiang, China. Vertical variations of stable isotopes of soil water were analyzed based on the values of stable isotopes, i.e. δD and δ¹⁸O. The results show that the soil water in uncultivated regions suffers stronger evaporation than that in cultivated areas. The influencing depth of evaporation in uncultivated and cultivated regions are 1.2-1.6 m and 0.8-1.2 m, respectively. The results also show that soil water experiences mixture during infiltration and the isotopes in soil water presents a cyclic variation, i.e., one infiltration event involved the procedures that the newly infiltrated water and existing soil water mix with each other, causing the values of δD and δ¹⁸O deplete to the minimum, which indicates the end of infiltration of recharge water, then the soil water moved downward and further mixes with the old soil water, influenced by evaporation, the isotopes are finally enriched to the values of existing soil water. δD of soil water in uncultivated and cultivated regions vary from -112.93‰ to -102.58‰ and from -111.07‰ to -94.44‰, respectively, which is more depleted than that of groundwater and surface water. This indicates that the soil water mainly originates from precipitation. Under strong evaporation, irrigation water hardly moves downward to recharge groundwater. The infiltration patterns of soil water have changed under the water-saving irrigation method in the oasis. This study lays a solid foundation for estimating vertical recharge in oasis and for assessing accurately water resource in Sangong River Basin.

Key words: unsaturated zone, sangong river basin, hydrogen and oxygen isotopes, δD isotopes peak