Identification of the water source and groundwater recharge in a paddy field using stable hydrogen and oxygen isotopes

Abstract

AbstractThe stable isotopes of oxygen-18 and deuterium were utilized to identify different water sources mixing in the soil layer that recharged to groundwater of a paddy field during the growth season in 2014. Based on the measurements of deuterium and oxygen-18 in soil water, rainwater and groundwater in the paddy field of Chianan Plain in Southwest Taiwan in the wet season was collected, and the relationship between δD and δ18O in soil water and groundwater recharge was investigated in this study. The soil water in the paddy field of Chianan plain was collected with suction lysimeters for the identification of different sources of subsurface flow. The isotopic compositions of hydrogen and oxygen in different water bodies were used to evaluate the groundwater recharge sources in the paddy field. The intensity of rainfall and evaporation influenced the saturation conditions of pore water present in the soil layer. In general, transiently intense rainfall tended to be difficult in recharging groundwater. The results show the use of stable isotopes in water bodies can be used to monitor or identify the source/sink of soil layer and their respective contributions to groundwater recharge. In this research, the isotopic compositions of hydrogen and oxygen in the soil water at different depths before and after event water were identified. The top soil layer (<30 cm depth) in the presence of the isotope depleted soil water was probably subjected to evaporation. The soil water has more depleted isotope composition that was observed in shallow soil layers. More depleted fraction of isotopes in groundwater was similar to rainwater, which suggested that the groundwater was primarily from rainfall. In addition, the isotopic compositions of hydrogen and oxygen in groundwater slightly deviated from the local meteoric water line in southern Taiwan.