| Soil water was an indispensable part of water circulation and transformation, it was an important hub not only in surface water and precipitation but also in groundwater and vegetation water. Study on soil moisture movement had a very important theoretical and practical significance in the change of groundwater recharge and accomplished reasonable utilization of soil water and groundwater.Stable isotope techniques provided a new research method about soil water movement in recent years, and its accuracy and sensitivity was higher than traditional research methods. Based on hydrogen and oxygen isotope techniques, there was analyzing the stable hydrogen and oxygen isotopic characteristics of precipitation,throughfall and stem flow, and then analyzing the characteristics of soil water,surface water and groundwater of four stand types(arboreal forest, shrub forest,waste-grassland and non-forest land) in water source area of Yuanyang terrace.Combined with analysis and processing method such as multivariate statistical analysis, linear regression and description statistics and then conclude some results.The main results showed that:(1) The annual precipitation was 1469 mm on 2014 in water source area of Yuanyang terrace, and the precipitation of rainy season constitute around 89.04% of annual rainfall. The LMWL was δD = 6.8384δ18O-5.6921(R2= 0.8787, n=20), with smaller slope and intercept compared with GMWL. This phenomenon indicated that there might have re-evaporation in the process of local precipitation and suffered by regional vapor evaporation.(2) Soil water recharge in the water source area of Yuanyang Terrace was not only from precipitation, but also may related with other permanent recharge source.The relationship between δD and δ18O of soil water of four stand types(arboreal forest, shrub forest, waste-grassland and non-forest land) was δD=7.6578δ18O+5.255(R2=0.9075, n=143).The δD and δ18O mean values was-104‰ and-14.3‰respectively, these values were substantially below the mean values of precipitation.It was indicated that soil water not just from precipitation during the study, it was a mixture of the original soil water and seasonal precipitation. Moreover, the hydrogen and oxygen isotopic values of soil water were obviously negative compared with precipitation, it suggested that soil water was more come from antecedent precipitation.(3) The trend of hydrogen and oxygen isotope of soil water in four different stands types had large difference between shallow layer and deep layer, and soil water in deep layer had extremely weak interference by outside environment,whereas shallow layer had larger. In the four different forest types, the δ18O values on the soil profile surface changed greatly. To a certain extent, it reflected the soilevaporation isotope fractionation effect. With the increase of soil depth, the fluctuation change of δ18O values was more and more small, especially, it was most obvious in the 80-100 cm soil layer, and it tended to be stable. The results showed that the shallow soil water was easily affected by precipitation and evaporation mixing effects, the isotopic composition changed greatly. But the deep soil water accepted finite precipitation recharge, then the precipitation and soil water was mixed evenly, so the changes of the isotopic composition was small.(4) In the arboreal forest and waste-grassland, the δ18O values in the surface soil was higher than in the deep soil water. While for the shrub forest and non-forest land,the variation trend was just the opposite, which was showed that in the study area precipitation infiltration process had two kinds of characteristics of infiltration. Clear soil water infiltration mechanism of the research area had great significance for revealing the mechanism of water cycle and its sustainable development in water source area in Yuanyang terrace. |
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