Evolution of groundwater in volcanic aquifer of Axum, Ethiopia: Isotopic and hydrochemical evidence

Hydrochemical and isotopic data are used to examine the decisive processes controlling groundwater chemistry and to reveal sources of groundwater. Groundwater from Axum area shows distinctive chemical and isotopic variation suggesting spatial diversity of the aquifer and different geochemical evolution. Individual compositions appear to be controlled by the type of host rock and intensity of water-rock interaction. Weathering of silicates and to lesser extent of calcite containing veins as well as ion-exchange explains most of the observed spatial variability in groundwater composition. The δ²H_VSMOW and δ¹⁸O_VSMOW values of the groundwaters indicate a meteoric origin. The δ¹³C_VPDB values of dissolved inorganic carbon (DIC) range from −12 to +1‰ revealing magmatic CO₂ and soil CO₂ as predominant sources for DIC.