Hydrogeochemical controls on groundwater salinization in a coastal aquifer, SE Ghana: Implications for seawater mixing and anthropogenic influences

Abstract

Coastal aquifers across the globe are vulnerable to long-term salinization due to the attendant effects of climate change. Despite this threat to coastal aquifers, techniques for geochemical fingerprinting of the sources and factors controlling groundwater salinization are still evolving. Therefore, the purpose of this study was to assess the hydrogeochemical characteristics, identify sources of groundwater constituents, and evaluate processes and sources that contribute to groundwater salinization in the Ga West Municipality in SE Ghana by calculation of Revelle Index (RI) and Seawater Mixing Index (SMI) values, geochemical modelling, and chemometric analysis. The results indicate that sodium (Na⁺) and bicarbonate (HCO₃^-) are the dominant ions in the groundwater. The predominant water types are Na-HCO₃-Cl (24.4 %) and Na-Ca-HCO₃-Cl (17.2 %), with other mixed forms. The results of the chemometric analysis revealed that groundwater constituents are mainly derived from anthropogenic sources and salinization with limited contribution from geogenic and evaporation crystallisation processes. The groundwater shows undersaturation with respect to gypsum, calcite, aragonite, talc, halite, and quartz. The RI values range from 0.11 to 6.54 with an average value of 0.97, indicating that about 58.6 % of the boreholes in the study area are affected by salinization. Also, the SMI values indicate that 21 % of the samples show seawater intrusion as the cause of groundwater salinization. However, the groundwater salinization can also be attributed to anthropogenic activities like farming in the study area. These key findings imply that groundwater salinization in the Ga West Municipality driven by seawater mixing and human activities, poses a significant threat to agricultural productivity due to increased soil salinity. Thus, there is the need for sustainable groundwater management practices and monitoring systems to mitigate the impacts and ensure the availability of fresh water for future generations.