Abstract
This study used stable hydrogen and oxygen isotopes as natural tracers to investigate their isotopic composition in precipitation, and in shallow and deep groundwater in the Penghu Islands in the Taiwan Strait. We aimed to understand the differences and relationships in isotope compositions within various water bodies and to evaluate the source of groundwater recharge. The hydrogen and oxygen isotopic compositions of sampled groundwater are mainly distributed along the meteoric water line in the Penghu Islands, the variations in the distribution range being minor (the δD values are distributed from −48.2‰ to −37.7‰, with a mean value of −43.14 ± 2.4‰; the δ18O values are distributed from −6.96‰ to −5.46‰, with a mean value of −6.34 ± 0.34‰). The data suggest that the groundwater is sourced mainly from local precipitation. In addition, a comparison of the hydrogen and oxygen isotopic compositions of groundwater and precipitation in Taiwan shows that the δ values for groundwater are distributed between those for precipitation during the northeast monsoon and the southwest monsoon seasons. However, some of the δ values trends towards the isotopic composition of the precipitation during the southwest monsoon season. Thus, the source of groundwater may have a closer association with precipitation during this time.
Highlights
Previous studies have found that hydrogen and oxygen isotopes are not affected by the environment and degradation of water quality [1]
The results results of their study showed that there are no signs of seawater in deep groundwater, some of their study showed that there are no signs of seawater in deep groundwater, some shallow shallow groundwater has heavier isotopic compositions
The results show that the H and O isotopic compositions of all samples were distributed along the meteoric water line (Figure 4), indicating that the meteoric source of shallow groundwaters in the Penghu Islands is from meteoric water
Summary
Previous studies have found that hydrogen and oxygen isotopes are not affected by the environment and degradation of water quality [1]. The generation and composition of these isotopes are controlled by different stages in the water cycle, and are associated with the movement of water bodies and hydrological processes, with low temporal variation. These stable isotopes can be used to investigate the behavior of water body movement in the stratum and the mutual relationships between various water bodies. The stable isotopes of hydrogen and oxygen were generally used to evaluate hydrological environments [2]. Isotopic studies can be used to monitor groundwater flow in unsaturated porous layers [8] and to understand preferential flow pathways [9]
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