Details

Autor(en) / Beteiligte

• Emvoutou, Huguette C.
• Estelle Ndomè, E.-P.
• Diongue, Djim M.L.
• Ndam, Jules R.
• Stumpp, Christine
• Ketchemen-T., Béatrice
• Ekodeck, Georges E.
• Travi, Yves
• Faye, Serigne

Titel

Hydrochemical and isotopic studies providing a new functional model for the coastal aquifers in Douala Coastal Sedimentary Basin (DCSB)/Cameroon

Ist Teil von

• The Science of the total environment, 2024-02, Vol.912, p.169412-169412, Article 169412

Ort / Verlag

Netherlands: Elsevier B.V

Erscheinungsjahr

2024

Quelle

Access via ScienceDirect (Elsevier)

Beschreibungen/Notizen

• A new conceptual model of the hydrogeological systems in Cameroon's Douala Coastal Sedimentary Basin (DCSB) was constructed. The model is based upon the basin's known geology, plus data from recent field campaigns that allowed the collection of rainwater and groundwater samples for analyses of stable isotopes (δ2H, δ18O, δ13C), radiogenic isotopes (3H, 14C), and water chemistry. Aquifer characteristics that were thereby deciphered include recharge, isotopic distributions, residence times, and mixing processes. Rainfall samples (mean δ18O = −2.0 ‰; mean δ2H = −6.80 ‰; weighted mean = −2.4 ‰ δ18O, −9.85 ‰ δ2H) scatter along two distinct lines, thus indicating that local rainfall events undergo processes during convective events, variability in humidity, amount effects, and seasonal variations. Stable isotope values of river water samples are close to the weighted mean of local precipitation, with some downstream enrichment. The Quaternary/Mio-Pliocene superficial aquifer system (depth < 70 m) and the intermediate Oligocene/Upper Eocene aquifer system (depth: 70 to 200 m) exhibit evidence of similar fractionation processes through an enrichment gradient of δ-values. The enrichment is more pronounced at the top of the superficial aquifer, which is very exposed to direct rainfall water infiltration, evaporation, and amount effects. The depth profiles of δ-values coupled to water chemistry and tritium contents, evidence leakage between (i) the superficial system's Quaternary alluvium sands and Mio-Pliocene sands; and (ii) the superficial and intermediate systems. Thus, the aquifers that contain modern, post nuclear groundwater are characterized by flow exchanges and direct recharge from rainfall events. In contrast, the Upper Eocene system has depleted δ-values and lower bicarbonate contents, suggesting not only that this system was recharged by rapid infiltration (with limited effect of evaporation), but that this recharge occurred during a cooler time in the past. The residence times (computed from 14C dates) indicate uncorrected ages ranging from hundreds to thousands of years. [Display omitted] •Precipitation in the study area shows non-equilibrium conditions and d-excess points to oceanic and continental sources.•Chemical data reveal vertical, lateral, and hydraulic links between the superficial system and to deep Oligocene formation.•Environmental isotopes and radiocarbon trace origin, recharge, and age of groundwaters in the two aquifer systems.