Geochemical evolution and tracing of groundwater salinization using different ionic ratios, multivariate statistical and geochemical modeling approaches in a typical semi-arid basin

摘要

The vulnerability of semi-arid basin aquifers to long-term salinization due to the dissolution of groundwater chemical constituents is a major global problem. Despite this, resilient techniques of tracing the sources of groundwater salinization in semi-arid basin aquifers are still evolving due to the aquifer complexities. This study proves the effectiveness of the use of different ionic ratios, multivariate statistical, and geochemical modeling approaches to understand groundwater evolution and trace salinization in the semi-arid Pru Basin of Ghana. The basin is homogeneously composed of argillaceous sediments of the Oti/Pendjari Group of the Voltaian Supergroup. A total of 81 samples from hand-dug wells and boreholes within the Pru Formation of the Oti/Pendjari Group in the basin were collected for this study. Quantitative analysis of the data shows that the abundance of major ions follows the order: Na+ - Ca2+ - Mg2+ - K+ and Cl- - HCO3 - SO42-. The groundwater evolved from Na-HCO3, Na-HCO3-Cl, Na-Ca-HCO3 to Na-Mg-HCO3 water types in a decreasing order of abundance. Calculated meteoric genesis index (r2) indicates the dominance of deep meteoric water percolation effects on groundwater chemistry. Groundwater chemistry is principally controlled by water-rock interaction, ion exchange reactions, weathering (carbonate and silicate), salinization, and anthropogenic activities. Different ionic ratio plots and spatial distribution maps reveal the prevalence of salinization in the aquifer system, especially around the southwestern part of the basin. Revelle index assessment of the groundwater salinization level indicates that about 19.8% of the groundwater samples with RI values 0.5 is influenced by salinization. The groundwater salinization results from saline water intrusion from adjacent aquifers, mixing effects, ion exchange reactions, water-rock interaction, and anthropogenic activities. The geochemical modeling involving thermodynamic calculation of mineral saturation indices in PHREEQC indicates that groundwater is largely saturated with respect to majority of the carbonate and silicate mineral phases.