The groundwater geochemistry of the Saloum delta aquifer: Importance of silicate weathering, recharge and mixing processes

Abstract

The physical-chemical and isotopic characteristics of the groundwater in the Saloum detrital aquifer system obtained from a network of 74 sampling points have indicated the likely geochemical reactions and defined the groundwater flow regime in the context of a semi-arid region. The main geochemical zones with distinct water types and isotopic contents displayed through this investigation are the results of ion exchange reactions, both congruent and incongruent reactions of carbonate, silicate minerals combined with effects of recharge/ discharge by evaporation and salinization processes in the vicinity of the estuary system. Use of minor and trace elements against the conservative ions of Cl and Br supports the highly weathering processes of the aquifer matrix which seem even to affect by incongruent reactions the oxide and hydroxide minerals under aerobic conditions. In this region, recharge is highly heterogeneous and recent recharged waters as well as preferential flow paths have been evidenced using stable isotopes of ¹⁸O and ²H together with radioactive 3H.

Key words: Hydrochemistry, stable isotopes, radioactive isotope, groundwater recharge, salinization.