Subsurface Hydrodynamics of the Southeastern Taoudéni Basin (West Africa) through Hydrogeochemistry and Isotopy

Abstract

The Taoudéni Basin, spanning 20% of Burkina Faso, holds vital aquifers for the Sahel’s water security and development. However, limited understanding of these aquifers’ hydrodynamics, including the flow patterns, mineralization processes, and renewal rates, hinders sustainable management practices in this arid region. Therefore, this study aims to investigate the aquifer hydrodynamics, mineralization processes and groundwater renewal in the transboundary Taoudéni Basin. Through a combination of hydrogeochemical and isotopic analyses, alongside existing data, this study examines 347 physicochemical samples, 149 stable isotope samples, and 71 tritium samples collected from 2013 to 2022. The findings reveal mineralization and stable isotopes (δ18O, δ2H) spatially aligned with the groundwater flow direction, validating this and indicating potentially multiple independent aquifers. The predominant mineralization mechanisms involve silicate hydrolysis and carbonate dissolution, supplemented by minor processes like evaporitic dissolution and cation exchange. The anthropogenic influence suggests potential groundwater recharge with potential pollution in the “SAC1”, “SAC2”, “GFR”, “GGQ”, and “GKS” geological formations. The stable isotopes (δ18O, δ2H) indicate recharge occurred over 4.5 kyr B.P., while tritium (3H) analysis confirms the presence of old, mixed waters, indicating slow renewal. Overall, this study highlights the minimal recent recharge and limited renewal rates, questions tritium’s efficacy for old water detection, and emphasizes the need for sustainable management.