Hydro-geochemical processes in the Complexe Terminal aquifer of southern Tunisia: An integrated investigation based on geochemical and multivariate statistical methods

Abstract

Hydrochemical data from a total of 104 groundwater samples were used to investigate the main factors and mechanisms that control the chemistry of groundwaters in the Complexe Terminal (CT) aquifer of Chott region in southern Tunisia. Multivariate statistical techniques combining Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) were applied to the dataset of 12 physicochemical parameters (i.e. pH, T°, depth, Na+, K+, Ca2+, Mg2+, HCO3−, NO3−, Cl−, SO42−, and TDS). The HCA using Ward’s method and squared Euclidean distance classified the parameters into four clusters based on their dissimilarities. The application of PCA resulted in two factors explaining 64.25% variance. Geochemical methods combined with HCA and PCA confirm that groundwater chemistry is not controlled by the different lithological facies of the aquifer, but by the presence of evaporates randomly distributed in the basin.Although stable isotope data (2H and 18O) of some groundwater are consistent with a slight modern recharge, CT groundwaters are mostly depleted bearing witness to the recharge of the aquifer system occurred under different climatic conditions than present. The stable isotopic composition of these paleowaters which all lie to the right of the local meteoric water line also indicates more pronounced evaporation of rainfall during the recharge process than during present-day conditions.