Using stable isotopes and mean residence time to characterize the groundwater system in the Tatun Volcanic Group, Taiwan

Stable isotopes, δ²H and δ¹⁸O, of precipitation and groundwater in two adjacent catchments, the north, and south, in the Tatun Volcanic Group, Taiwan were used to characterize the regional groundwater. The results show that the isotopic composition of precipitation exhibits seasonal variations, which suggests different sources of moisture generation for the rainfall in the study area. In general, the north catchment shows more enriched isotopic characteristics than that of the south one.  

The seasonal variations of precipitation, with lighter in summer, arise from changes in isotopic water vapor composition associated with the seasonal activity of the Asian monsoon which was used in estimating the mean residence time (MRT) of groundwater in the region. The preliminary results show that the average MRT of the study area ranges from 180 to 500 days in the north catchment while it is 180 to 900 days in the south catchment.