Bassin forestier (Cameroun)

Des traceurs chimiques naturels ont permis de mettre en évidence les interactions entre les eaux souterraines, les marécages de la forêt tropicale et le cours d'eau dans le bassin versant tropical de Nsimi. L'étude a montré que la circulation des eaux souterraines influe fortement sur les transferts d'eau et de solutés, tandis que l'altération chimique du socle cristallin contribue de manière significative à l'exportation d'éléments dissous.

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Situation: bassin du Nyong, Cameroun

Altitude: 670 - 700 m

Géologie: socle cristallin (granite)

Type d'aquifère: aquifère cristallin fracturé

Question scientifique: "« Est-ce la zone humide ou l'aquifère qui stocke l'eau dans les bassins versants tropicaux ? »

Nsimi fait partie de l'Observatoire M-TROPICS et de l'infrastructure de recherche OZCAR

Location map

Key Findings

Groundwater is a major component of the hydrological functioning of the tropical watershed, linking the weathered basement, wetlands and stream network.
Natural chemical tracers reveal contrasting groundwater flow paths and allow the contribution of different hydrological compartments to the headwater stream to be identified.
The rainforest headwater swamp acts as an important hydrological regulator, controlling the transfer of water from the groundwater system toward the stream.
Chemical weathering is a major control on dissolved-element fluxes from the tropical crystalline-rock watershed, linking groundwater circulation, weathering and stream chemistry. The work also quantified elemental weathering fluxes and saprolite production rates.
The weathering profile is therefore not simply a passive geological layer: it is an active component of the hydrological and geochemical functioning of the watershed.

Hydrogeological model

Picture Gallery

The Multiscale TROPIcal Catchments critical zone observatory M-TROPICS dataset I: The Nyong River Basin, Cameroon

Stephane Audry, Henriette Ateba Bessa, Jean-Pierre Bedimo Bedimo, Jean-Loup Boeglin, Laurie Boithias, Jean-Jacques Braun, Bernard Dupre, Mikael Faucheux, Christelle Lagane, Jean-Christophe Marechal, Jules Remy Ndam-Ngoupayou, Bernadette Nka Nnomo, Justin Nlozoa, Jean-Claude Ntonga, Olivier Ribolzi, Jean Riotte, Emma Rochelle-Newall, Laurent Ruiz

Hydrological Processes, vol. 35, 2021

Elemental weathering fluxes and saprolite production rate in a Central African lateritic terrain (Nsimi, South Cameroon)

Jean-Jacques Braun, Jean-Christophe Maréchal, Jean Riotte, Jean-Loup Boeglin, Jean-Pierre {Bedimo Bedimo}, Jules Remy {Ndam Ngoupayou}, Brunot Nyeck, Henri Robain, M. Sekhar, Stéphane Audry, Jérôme Viers

Geochimica et Cosmochimica Acta, vol. 99, 2012, pp. 243-270