The Yongding River groundwater system in Beijing plain is located in western Beijing. Precipitation samples of a hydrological year in Beijing plain were collected, and D and 18O components of these samples were analyzed. A set of groundwater samples in the Yongding River groundwater system were also collected during the arid season, and components of eight ions, D and 1so, concentrations of Sr, and ratios of 87Sr/86Sr of these samples were analyzed. On such a basis, some conclusions have been reached: the hydrochemical types of groundwater in the study area are comparatively simple; the groundwater in the study area is derived mainly from infiltration of local precipitation, and is affected by different degrees of evaporation during the process; Sr and Ca elements in groundwater share a similar hydrogeochemical process; values and variation range of 87Sr/86Sr ratios are small,which implies that Sr element in groundwater comes from carbonate rock. The results obtained by the authors will provide a practical basis for further understanding the groundwater system of the study area and the water sources.%北京平原区永定河地下水系统位于北京市的西部.在该区采集了一个水文年的大气降水样,并对其中的D和18O组成作了分析;于旱季在该地下水系统中采集了大量地下水样,并对其中的八大离子浓度、D和18O组成、Sr浓度以及87Sr/86Sr比值作了分析.研究结果表明,研究区地下水的水化学类型较为单一;研究区地下水主要来源于大气降水入渗补给,并且在补给过程中经历了不同程度的蒸发作用的影响;地下水中的Sr和Ca元素经历了较为相似的水文地球化学过程;地下水中的87Sr/86Sr比值普遍较小且变幅也很小,据此判断Sr均为碳酸盐岩来源.这些分析结果将为进一步识别研究区的地下水系统及地下水来源提供依据.
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