Tracing groundwater recharge sources beneath a reservoir on a mountain-front plain using hydrochemistry and stable isotopes

Mountain-front recharge, including mountain block recharge and stream seepage, is important for basin aquifers. With the construction of reservoirs in mountainous areas and the recurrent seepage problems of dams, reservoir seepage might become another type of mountain-front recharge. This study identified the recharge sources of groundwater beneath Huangbizhuang Reservoir on the North China Plain (NCP). Hydrochemical data and the stable isotopic compositions ( δ 18 O and δ D) of water were employed to determine the occurrence of Huangbizhuang Reservoir seepage recharge to groundwater in the mountain-front area. Then, the relative percentages of ‘reservoir seepage’ to total recharge were quantified using end-member mixing analysis (EMMA). The results suggest that the recharge sources beneath the reservoir are mountain block recharge, local precipitation and reservoir seepage. Using D and δ 18 O values, EMMA revealed that the mean contribution ratio of reservoir seepage to groundwater beneath the reservoir is 36% ± 4%, while that of mountain block recharge is 33% ± 11% in consideration of the uncertainty. Reservoir seepage accounts for a large proportion of mountain-front recharge and should be included in the calculations of mountain-front recharge on the NCP which was ignored currently.