Isotopic and Hydrogeochemical Signatures in Evaluating Groundwater Quality in the Coastal Area of the Mekong Delta, Vietnam

Abstract

In the 21st century, fresh water scarcity is perhaps one of the biggest challenges in many coastal regions worldwide due to the rapid population growth, fast urbanization and unpredictable impacts of global climate change. Given this context, the identification of groundwater status is a crucial task for sustainable groundwater use and management practices in coastal areas around the world. This work, conducted in coastal areas of Soc Trang province, is an effort to assess groundwater quality and its controlling factors in a coastal area of the Mekong Delta, Vietnam. In this study, we investigate groundwater quality based on chemical parameters, stable isotopes ($δ$18O, $δ$2H) and saturation indices (SI). The study showed that groundwater in the study area is mainly classified into four groups: Na-Cl, Na-Mg-Ca-HCO3, Na-Mg-Ca-HCO3-SO4 and Na-HCO3-Cl. Groundwater quality might be substantially controlled by the rock-water interaction, particularly by mineral dissolution and ion-exchange process. Further, the stable isotopes and saturation indices depict the origin of salt water presenting in the aquifers because of three factors, including paleo-saline water dissolution at deeper aquifers, seawater intrusion into shallow aquifers and saline water diffusion at middle aquifers. This result suggests that the characteristics of hydrogeology, inappropriate groundwater pumping activities and change of hydrological regimes might be the main driving forces of disturbance groundwater flow systems and expansion of saline boundary in the coastal areas of the Vietnamese Mekong Delta.