Spatiotemporal variability of hydrogen stable isotopes at a local scale in shallow groundwater during the warm season in Tottori Prefecture, Japan

Abstract

Oxygen and hydrogen stable isotopes are key hydrological tracers for identifying groundwater flow paths, groundwater recharge sources, and related hydrogeological processes. This study aims to identify the spatiotemporal variability in isotopic compositions of hydrogen (δ²H) measured in shallow groundwater, river water, paddy water, and precipitation collected from two catchments in Tottori Prefecture, Japan. A total of 613 surface water and groundwater samples were collected from 45 sites (wells) in five different landscapes during a two-year survey. The enriched groundwater δ²H values were in the range –52‰ to −36‰, and large isotopic variations were observed in the coastal regions of the study area. The lower groundwater δ²H compositions were in the range −61‰ to −53‰ in high elevation areas. Our study shows that the spatial variation in groundwater δ²H (23‰) was larger than the temporal variation (12‰) within the 3,500 km² total area of Tottori Prefecture. At this scale, clear correspondence between the temporal standard deviations of the δ²H values and landscape characteristics was not found, suggesting that spatial scales should be considered carefully when analyzing the temporal evolution of hydrological tracers.