Assessment of geochemical processes in the shared groundwater resources of the Taoudeni aquifer system (Sahel region, Africa)

• Published in: Hydrogeology journal Vol. 32; no. 1; pp. 167 - 188
• Main Authors: Trabelsi, Rim, Zouari, Kamel, Araguás Araguás, Luis J., Moulla, Adnane S., Sidibe, Aboubacar M., Bacar, Teis
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.02.2024; Springer Nature B.V
• Subjects: Anthropogenic factors; Aquatic Pollution; Aquifer systems; Aquifers; Calcium; Cambrian; Carbon 13; Carbon 14; Carbon isotopes; Chemical composition; Climatic conditions; Contamination; Cratons; Earth and Environmental Science; Earth Sciences; Energy budget; Fossils; Geochemistry; Geology; Geophysics/Geodesy; Groundwater; Groundwater quality; Groundwater recharge; Groundwater resources; Hydrochemicals; Hydrogeochemistry; Hydrogeology; Hydrology/Water Resources; Infiltration; Ion exchange; Ions; Isotopes; Leaching; Lithology; Livelihoods; Magnesium; Multilayers; Principal components analysis; Quaternary; Rain; Rain water; Recharge; Signatures; Stratigraphy; Surface water; Tritium; Waste Water Technology; Water analysis; Water Management; Water Pollution Control; Water quality; Water Quality/Water Pollution; Water resources; Water sampling; Weathering; Burkina Faso; Mauritania; Mali; Africa; Groundwater contamination; Arid regions; Water–rock interaction; Isotopes; Africa
• ISSN: 1431-2174; 1435-0157
• DOI: 10.1007/s10040-023-02688-5

The Taoudeni basin occupies a large portion of the West African Craton in Mauritania, Mali, SW Burkina Faso, and Algeria. The multi-layer Taoudeni aquifer system (TAS) occurs in geological formations extending in age from the Infra-Cambrian to the Quaternary. These groundwater resources support local livelihoods, maintain vital ecosystems, and strongly affect terrestrial water and energy budgets in the region. Hydrogeochemical and stable (δ 2 H, δ 13 C, δ 18 O) and radioactive ( 3 H, 14 C) isotope analyses were carried out with the aim of identifying the major geochemical processes controlling groundwater quality and the recharge mechanisms. The analyzed groundwater samples showed a wide range of chemical compositions based on major ions, with limited variability, regardless of the aquifer lithology or stratigraphy. The predominant water type, Mg–Ca–HCO 3 , was found in most geological and hydrogeological settings. A principal component analysis of the hydrochemical data revealed the two major processes governing the geochemistry of groundwaters in the TAS. These are water–rock interaction (leaching, weathering, ion exchange) and anthropogenic contamination. Environmental isotopes revealed the presence of groundwaters with heterogeneous signatures, reflecting different recharge processes and varying groundwater ages. A widespread present-day recharge by direct infiltration of rainwater and/or by surface water was highlighted by significant tritium levels in most wells and high 14 C activities occurring mainly in shallow aquifers. However, isotopically depleted δ 18 O contents with low 14 C activities were found in the confined part of the Continental Intercalaire aquifer, particularly in the Algerian part, indicating the presence of fossil groundwater, recharged under colder past climatic conditions.