Abstract
In this study, the stable isotope values of oxygen and hydrogen were used to identify the seasonal contribution ratios of precipitation to groundwater recharge in the Hualien River basin of eastern Taiwan. The differences and correlations of isotopes in various water bodies were examined to evaluate the groundwater recharge sources for the Hualian River basin and the interrelations between groundwater and surface water. Proportions of recharge sources were calculated based on the results of the mass balance analysis of the isotope composition of hydrogen and oxygen in the basin. Mountain river water accounted for 83% and plain rainfall accounted for 17% of the groundwater recharge in the Huanlian River basin. Using the mean d-values, a comparison of d-values of precipitation and groundwater indicates the groundwater consists of 75.5% wet seasonal sources and 24.5% dry seasonal sources, representing a distinct seasonal variation of groundwater recharge in the study area. Comparisons between hydrogen and oxygen isotopes in rainwater showed that differences in the amount of rainfall resulted in depleted oxygen and hydrogen isotopes for precipitation in wet seasons as compared to dry seasons. The river water contained more depleted hydrogen and oxygen isotopes than was the case for precipitation, implying that the river water mainly came from the upstream catchment. In addition, the hydrogen and oxygen isotopes in the groundwater slightly deviated from the hydrogen and oxygen isotopic meteoric water line in Huanlian. Therefore, the groundwater in this basin might be a mixture of river water and precipitation, resulting in the effect of the river water recharge being greater than that of rainfall infiltration.
Highlights
Oxygen and hydrogen isotopes of water are widely used as tracers to understand hydrogeological processes such as precipitation, groundwater recharge, groundwater-surface water interactions, and basin hydrology [1,2,3,4,5,6]
According to the results of the groundwater budget in the Hualian River basin, 27% of the infiltration is direct rainfall, 18% of the recharge is the lateral flow of boundary, and 55% of the groundwater recharge comes from river water
The present study examined the stable isotopic composition of precipitation, river water, and groundwater in the Hualian River basin
Summary
Oxygen and hydrogen isotopes of water are widely used as tracers to understand hydrogeological processes such as precipitation, groundwater recharge, groundwater-surface water interactions, and basin hydrology [1,2,3,4,5,6]. In the process of oceanic water evaporation becoming inland rainfall, a sequence of isotope fractionations causes variations in the composition of the isotope values of oxygen and hydrogen in continental meteoric water. The empirical equation was found by Craig [13] when he used a linear regression method to analyze the composition of the isotopes of oxygen and hydrogen in samples of precipitation, snow water, and river water from all over the world His finding is known as the Global Meteoric Water Line (GMWL): δD = 8 δ18O + 10. In the meteoric water line of oxygen and hydrogen isotopes, the slope represents the ratio of the temperature relationship between δD and δ18O when condensation occurs; the value of the intercept is based on the evaporative conditions in the water source region. The results provide useful information about hydrological processes, such as the interaction of precipitation, river water, and groundwater
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