Investigation by multivariate analysis of groundwater composition in a multilayer aquifer system from North Africa: A multi-tracer approach

• Published in: Applied geochemistry 2011-08, Vol.26 (8), p.1386-1398
• Main Author: Dassi, Lassaad
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geochemistry; Pollution, environment geology
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2011.05.012

► We investigate the hydrodynamics and hydrochemistry of a multilayer aquifer system. ► We examine the geochemical evolution, the origins and the circulation patterns of groundwater. ► The mineralization is controlled by water-rock interaction and return flow process. ► Groundwater derives from palaeoclimatic and modern end-members. ► Mixing by upward and downward leakage occurs between these two end-members. A multi-tracer approach has been carried out in the Sbeïtla multilayer aquifer system, central Tunisia, to investigate the geochemical evolution, the origin of groundwaters and their circulation patterns. It involves statistical data analysis coupled with the definition of the hydrochemical and isotopic features of the different groundwaters. Principal Components Analysis (PCA) of geochemical data used in conjunction with bivariate diagrams of major and trace elements indicate that groundwater mineralization is mainly controlled by water–rock interaction and anthropogenic processes in relation to return flow of irrigation waters. The PCA of isotopic data and bivariate conventional diagrams of stable and radiogenic isotopes i.e. δ 18O vs. δ 2H and δ 18O vs. 14C provide valuable information about the origin and the circulation patterns of the different groundwater groups. They permit classifying groundwaters into three groups. The first group is characterized by low 3H concentrations, low 14C activities and depleted stable isotope contents. It corresponds to an old end-member in relation with palaeoclimatic recharge which occurred during the Late Pleistocene and the Early Holocene humid periods. The second group is distinguished by high to moderate 3H concentrations, high 14C activities and enriched heavy isotope signatures. It corresponds to a modern end-member originating from a mixture of post-nuclear and present-day recharge in relation to return flow of irrigation waters. The third group is characterized by an average composition of stable and radiogenic isotope signatures. It provides evidence for the mixing between the upward moving palaeoclimatic end-member and the downward moving present-day end-member.