Using stable isotopes to determine dew formation from atmospheric water vapor in soils in semiarid regions

Moisture sources for dew formation in soils can be classified into soil water and atmospheric water vapor. Discriminating respective contribution of the two moisture sources is important for knowledge of water balance valuation. Stable 2H and 18O of atmospheric water vapor are temporal variation; thus, they may be different to that in soil water, which makes it feasible to discriminate moisture sources between soil water and atmospheric water vapor. In this paper, we took soil samples in the semiarid northern Chinese Loess Plateau and extracted the soil water using the high-temperature vacuum distillation method. Stable isotope profiles and δD-δ18O slopes of the soil water showed that the dew condensed from atmospheric water vapor occurred mainly in the upper 20 cm of the soil layer. The atmospheric water vapor hardly influenced the soil water at 30-cm depth and the deeper soil layer. The significantly low deuterium excess of the soil water at the depth of 10 and 20 cm indicated that the dew in the soil underwent intensive evaporation after the dew formation.