Hydrological cycle research by D & 18 O tracing in small watershed in the loess hilly region

The objective of this study was to determine the mechanisms of the hydrologic cycle in the loess area in China. Sixty eight water samples from precipitation, soil water of the 0 – 4 m layer, surface water in the valley, ground water (spring and well) were collected and the Deuterium (D) and Oxygen – 18 (O) of these water samples were analyzed to interpret the relationship among those waters in the watershed in the loess hilly region during 2005 – 2009. The results show that: the D & 18O of precipitation in Yangou was consistent with that of Xi'an, apparently the north migration of water vapor in Xi'an; according to the correlations among the differential waters in D & 18 O, confirmed that precipitation recharge could account for most of the sources of valley flow, with part of the recharge water going to soil water recharge. The D & 18O of groundwater were very close to that of precipitation, likely the soil preferential flow was dominant in groundwater recharge although the infiltration had a certain lag. Under the influence of rainfall and evaporation, the response of the soil moisture profile, and its D & 18O profile were different. The soil moisture had the strong influenced layer in the 0 60 cm range, a weak impacted layer in 60 160 cm, and a stable layer below 160 cm. It was shown that the soil evaporation depth could be up to 160 cm because the D & 18O changed in that depth. The study could increase our understanding of the magnitude and pattern of the hydrologic cycle, which should improve water resources management in the watershed scale.