中文摘要：

对陕西省长武县黄土塬区降水及主要土地利用方式下0～20 m剖面土壤水进行采样和稳定同位素测定,研究了该区深层土壤水稳定同位素特征及土壤水运动机制.结果表明：长武塬区大气降水线方程为δD=7.39δ18O＋4.34（R2=0.94,n=71）,其降水稳定同位素值具有明显的冬春高、夏秋低的季节变化特征.土壤水稳定同位素值落于当地大气降水线下侧,且高于7—10月降水稳定同位素值,该区土壤主要接受同位素值偏负的夏秋降水的补给.土壤剖面上,不同土地利用方式之间土壤水同位素值随土壤深度增加而趋于一致;相同土地利用条件下,浅层土壤水同位素组成随时间推移而变化的程度剧烈,随土壤深度增加,土壤水同位素值的变化程度减弱,甚至无变化.对比降水和土壤水的稳定同位素值变化发现,在黄土塬区,活塞流和优先流并存于降水入渗过程中,但优先流入渗的发生与土地利用方式存在一定关系.通常情况下,高耗水型人工林草因水分负平衡形成的土壤干层将减小优先流发生的可能性,而农田、荒草地等土地利用方式均易发生优先流形式的降水入渗,从而对深层土壤水分或地下水形成补给.

英文摘要：

In this study,the precipitation over the Loess Tableland in Changwu County of Shaanxi Province and the soil water in 0-20 m loess profiles under different land use patterns on the Tableland were sampled,and their isotope compositions were analyzed,aimed to understand the characteristics of stable isotopes in the soil water and the mechanisms of the soil water movement.In the study area,the equation of the local meteoric water line（LMWL） was δD=7.39δ18O＋4.34（R2=0.94,n=71）,and the contents of the stable isotopes in the precipitation had an obvious seasonal variation of high in winter and spring and low in summer and autumn.The contents of the stable isotopes in the soil water were fell on the underside of the LMWL,and higher than those in the precipitation from July to October,indicating that the soil water was mainly replenished by the precipitation with lower stable isotope contents in summer and autumn.In the soil profiles of different land use patterns,the stable isotope contents in soil water tended to be the same with the increasing soil depth;while under the same land use patterns,the water＇s stable isotope composition in shallow soil layers changed greatly with time,but changed less with increasing depth.Through the comparison of the stable isotope contents in precipitation and in soil water,it was observed that the piston flow and preferential flow on the Tableland were coexisted in the process of precipitation infiltration,and the occurrence of the preferential flow had a certain relation with land use pattern.Generally,the soil desiccation caused by the negative water balance resulted from the artificial plantations of high water consumption could reduce the probability of preferential flow occurrence,whereas the precipitation infiltration in the form of preferential flow could easily occur on the farmland or natural grassland so that the soil water in deep layers or the ground water could be replenished.