Abstract
Methods to determine the recharge elevation of groundwater using the altitude effect of δD and δ 18 O have been extensively applied in hydrogeological investigations. The secondary parameter d-excess has also been used as a groundwater tracer. In this study, to examine the usefulness of these tracers along with 17 O-excess, ~160 groundwater samples were collected from a humid region at the foot of Mt. Fuji, Japan. The sampling area covered 40 × 45 km, with most sampling sites located below 1,000 m above sea level. The relatively low elevation and small scale of the basin allowed for examination of the elevation-dependence of groundwater isotopes. Using high-precision isotope analyses, a low lapse rate but clear elevation-dependence in spring waters was observed for d-excess (0.18‰·100 m −1 ). The recharge elevation determined by d-excess correlated with those by δD and δ 18 O, indicating that d-excess has high potential as a groundwater tracer for the determination of recharge elevation. On the other hand, 17 O-excess in groundwater held small spatial variation, with an average of 25 per meg in the horizontal direction and a lapse rate of 0.6 per meg·100 m −1 . The low lapse rate compared to the analysis error inhibits its usefulness as a tracer. The fact that the recharge elevation determined by δD, δ 18 O, and d-excess were similar indicates that the combination of these tracers could increase the reliability of the results.