Spatial distributions of oxygen and hydrogen isotopes in multi-level groundwater across South Korea: A case study of mountainous regions

Abstract

This study presents the spatial distributions of stable isotopes for groundwater according to well depth and spring water across South Korea, using an interpolation model to provide baseline information for hydrological studies. In total, 888 groundwater and 108 spring water samples were collected across South Korea; their oxygen and hydrogen isotopic compositions (δ¹⁸O and δ²H) were analyzed. δ¹⁸O and δ²H values biased toward the summer local meteoric water line and low d-excess values indicate that summer precipitation is important for groundwater recharge. The δ¹⁸O and δ²H values for groundwater and spring water decrease progressively from the southwest to the northeast on the Korean Peninsula. Based on eight hydrological regions, the average δ¹⁸O values of groundwater and spring water are negatively correlated with latitude, but they are positively correlated with temperature. This result indicates that the spatial distributions of groundwater isotopic values in South Korea are significantly influenced by latitude and altitude effects associated with the movement of the North Pacific air mass in summer. Spring waters showed a negative correlation between δ¹⁸O and d-excess, with more depleted ¹⁸O values than groundwater, indicating that local recharge and flow within mountainous areas is dominant. Considering that the correlation in multi-level groundwater located in northern regions is similar to that of spring water, the contribution of regional groundwater flow, which is recharged in mountainous areas, is considered to be higher in the northern regions. The spatial distribution of δ¹⁸O in groundwater gradually approached the spatial distribution of spring water with increasing well depth, indicating that the contribution of regional groundwater flow may be greater in deep groundwater. Our results provide estimates for data-poor regions, supporting the investigation of links between groundwater and other hydrological factors.

Keywords: Multi-level groundwater; Spatial distribution; Spring water; Stable isotope; Well depth.