Investigation of chemical evolution of groundwater through water stable isotopes and hydrochemical characteristics in Soubré and Gagnoa counties, Côte d'Ivoire

Groundwater is an important source of water for many people around the world, enabling them to meet their diverse needs. The main objectives of this study are to identify the sources and processes of groundwater mineralization, as well as the groundwater recharge mechanism. For that, the hydrogeochemical, statistical and isotopic approaches were investigated to get a thorough understanding of the many processes involved in mineralization. The results show that groundwater is acidic, fresh and good (TDS < 1000 mg/l; 5.22 < pH< 6.84). Na+ and HCO3- are the dominant cation and anion, respectively. The high values of NO3-N and SO42- observed in some samples are the consequence of human influences. Piper diagram shows that hydrogen carbonate types are the most abundant in the area representing more than half of the samples. The simultaneous analysis of Gibbs and Modified-Gibbs diagrams indicate carbonate and silicate weathering as major processes involved in groundwater mineralisation. In addition to previous processes, there are also the presence of gypsum dissolution characterised by a significant correlation between Ca2+ and SO42- (r = 0.81) and the cation exchange that dominates on groundwater samples with respect to the reverse one.As for isotopic measurements, they are performed on 2H and 18O of the water molecule. From their δ2H-H2O and δ18O-H2O ratios, a good linear relationship is established (δ2H = 7.28δ18O + 8.58) representing the groundwater line (GwL). The comparison with the global and local lines would suggest as recharge mechanism in groundwater the precipitation process.