Investigation of the Geochemical Evolution of Groundwater Using Major Ions and Stable Isotopes Signatures: A Case Study in Transboundary Aquifers

Groundwater remains the predominant source of water supply in the Gboko area, a transboundary district of the Benue Valley, Nigeria. Studying the chemical characteristics and the mechanisms controlling the origin of groundwater are important for the sustainability of groundwater resources. This study aims to decipher the water chemical properties and the evolution of groundwater in the Gboko area, central Nigeria. A total of 50 groundwater samples were collected and analyzed for physicochemical parameters and \(\delta\) $\delta$ ²H and \(\delta\) $\delta$ ¹⁸O. Hydrochemical results revealed that the groundwater pH varied between 4.71 and 8.15, indicating that the groundwater of the area is acidic to alkaline in nature. The concentrations of the anions are in a decreasing order of \({HCO}_{3}^{-}\) ${\mathit{HCO}}_3^{-}$ > \({CO}_{3}^{2-}\) ${\mathit{CO}}_3^{2-}$ > \({NO}_{3}^{-}\) ${\mathit{NO}}_3^{-}$ > \({Cl}^{-}\) ${\mathit{Cl}}^{-}$ > \({SO}_{4}^{2-}\) ${\mathit{SO}}_4^{2-}$ > \({F}^{-}\) $F^{-}$  >  \({NO}_{2}^{-}\) ${\mathit{NO}}_2^{-}$ , while the abundance of the cations follow a decreasing magnitude of \({Ca}^{2+}\) ${\mathit{Ca}}^{2+}$ > \({Na}^{+}\) ${\mathit{Na}}^{+}$ > \({Mg}^{2+}\) ${\mathit{Mg}}^{2+}$  >  \({K}^{+}\) $K^{+}$ . Saturation indices and stable isotopes were used to interpret the chemical data. The results show the dominance of rock-water interactions and precipitation processes. Specific rock-water interaction processes include halite and calcite dissolution, basic cation exchange, and silicate weathering. Furthermore, the stable isotope data revealed that the groundwater was recharged from very recent precipitation, but with its chemical properties altered by rock-water interaction processes in a cold atmosphere. The findings of this research will provide tools that will be necessary for planning and managing the water resources of the area.