Paleoenvironmental legacies and groundwater salinity in arid inland basins: A synthesis review with evidence from Southern Africa

Abstract

Makgadikgadi–Okavango–Zambezi Basin (MOZB) Groundwater salinization is a widespread and persistent environmental challenge, particularly in water-scarce regions. In inland arid and semi-arid basins, salinity commonly reflects long-term paleoenvironmental legacies, yet the interactions among drivers such as climate shifts, sedimentation, hydrogeochemistry, and groundwater dynamics remains poorly constrained. This synthesis review integrates sedimentological, tectonic, hydrochemical, and hydrological evidence from the Makgadikgadi–Okavango–Zambezi Basin (MOZB) to elucidate the controls on groundwater salinity evolution for water security. The basin exhibits a pronounced concentric hydrogeochemical zonation, with highly saline chloride-dominated groundwater in the central paleo-lake region, transitioning outward through sulphate-rich waters to calcium–bicarbonate groundwater at basin margins. This pattern reflects the spatial distribution of paleo-evaporites combined with restricted lateral groundwater flow in a hydrologically closed system. Sedimentary sediment ages exceeding 300 ka are decoupled from groundwater ages younger than 30 ka, indicating that although the sedimentary framework and evaporitic sources are ancient, groundwater has been partially replenished during later humid climatic phases. Groundwater salinity in the MOZB represents a paleoenvironmental legacy, shaped by Late Pleistocene Lake desiccation and evaporite formation, modulated by subsequent pluvial recharge events, and maintained by the basin’s endorheic hydrological configuration. Consequently, groundwater management strategies cannot rely on natural dilution but should prioritize targeted deep-aquifer exploration and conjunctive use of surface water and groundwater to enhance long-term water security. • Paleoenvironmental legacies influence on inland groundwater salinity. • Groundwater salinity reflects tectonics, evaporite formation and limited flushing. • MOZB climate sensitivity may amplify future groundwater salinity risks. • MAR, conjunctive water use, and aquifer mapping must be explored. • Prioritize high-resolution age dating, deep aquifer study and transport modelling.