The δD and δ18O vertical profiles of soil water were measured prior to and after a rainfall event.Mechanisms of soil water movement were deciphered by comparing the soil water isotope profiles with the isotopic composition of precipitation.The results show that evaporation at the upper depth led to enrichment of the heavy isotopes.Compared to the loess profile,the shallow soil water of sand profile is relatively enriched in D and 18O due to macro-pore and low water-holding capacity.The precipitation is infiltrated into soil in piston mode,accompanied with significant mixing of older soil water.The preferential fluid flow in loess was observed at depths of 0-20 cm,caused by cracks in the depths.The hydrogen and oxygen isotopic compositions in outflow are close to the precipitation,which shows a mixing of the precipitation and old soil water,and indicates that the isotopic composition of outflow water is mainly controlled by that of the precipitation.The δD and δ18O in outflow decreased with time until stable δ values of outflow are close to those of the precipitation.
