Appliance of oxygen and hydrogen isotope in the process of precipitation infiltration in the shallow groundwater areas of North China Plain

In the shallow groundwater areas of North China Plain water cycle mostly occurs as infiltration,evaporation and evapotranspiration in the vertical direction,in which the unsaturated zone plays an important role in precipitation and groundwater. Isotope can be used to trace the process when the precipitation infiltrates and recharges groundwater. In this paper Cangzhou and Hengshui sites are selected as the typical shallow groundwater areas to research the difference of the infiltration process under the different precipitation features,soil textures and vegetation conditions. The results show that at the site with the heterogeneous soil texture the precipitation infiltrates and moves in soil as the piston mode and the mixture effect,and the evapotranspiration effect during the infiltration process is significant in the distribution of soil water. Some evidence is provided for the existence of the preferable flow at 100 m depth. The groundwater is mainly recharged by precipitation1 However,at the homogeneous site the infiltration process is uniform and the soil water moves as piston mode,too. Both deep soil water and groundwater are totally recharged by precipitation. After precipitation the recharged groundwater experiences strong evaporation effect.