Biogeohydrodynamic in the forested humid tropical environment: the case study of the Nsimi small experimental watershed (south Cameroon)

摘要: This paper summarizes a six-year study of the Nsimi Small Experimental Watershed (SEW), considered as model for South Cameroon humid tropical ecosystem. When this small watershed was set up, no similar survey input/output hydrobiogeochemical fluxes in granitoid rocks stable cratonic environment available, to our knowledge, on any site close Equator. Moreover, is first attempt, world-wide, combine different approaches hydrology, (bio)geochemistry, mineralogy, crystallography, microbiology, geophysics and pedology. Research based (1) regular surveys various water reservoirs SEW ecosystem (atmospheric deposits, groundwater stream), (2) related either organisation composition superficial layers (basement rocks, saprolite, soils) or hydrological, biological geochemical processes. These aim at finding main parameters involved chemical physical erosion processes ecosystem, understanding source particular rivers, (3) documenting accurately exportation elements soil (4) investigating possible relation between biodegradation organic matter leaching metals (especially iron) (5) comparing long short term weathering rates using mass balance calculations. Another important objective provide new scientific engineering database future development Cameroon, which still nowadays relatively preserved ecosystem. One major results essential role played by cycle (vegetation matter) fractionation, storage environments. Moreover we are able propose current from obtained mineralogy basement layers, geochemistry soluble colloidal phases waters hydrology within hydrosystem. has been confirmed extended regional scale (Nyong river basin). It emphasized behaviour (Fe, Al, Si), nutrients (C, Ca, Mg, K, Sr) specific tracers with strong mobility (Cl, Na) contrary an extremely low (Zr, Th, REEs). On scale, contrast occurs zones flooding hill slope lateritic profiles, front (interface saprolite rocks), swampy zone Mengong brook flows. High DOC contents (15 mg/L) but also high Fe, Zr characterize waters. Na Si have mainly deep origin (exfiltration), REEs strongly linked located upper horizons swamp. Fe much more complex due its change redox state can be independent complexation. Concerning base cations, their constrained (storage leaching). K typically influenced cycle. During floods, Cl same K: it one most striking points study. However, annual budget balanced. These characteristics understood consequence minerals present (kaolinite, goethite, zircon, Th-oxide). allows cations Al Fe. demonstrated that microbial populations play mobilization transition (e.g. Fe). point out humic acids transport usually immobile Zr, Fe). It must mentioned worldwide even Nyong network among least concentrated means if plays some zone, action limited cation scale. The reason invoked directly pedological history geomorphology watershed. presence thick composed latosol hillsides hydromorphic soils constant lead isolating bedrock. residence time preserving parent rock hydro-chemical outputs. topsoil stabilized vegetation cover, limits mechanical erosion. should taken into account carbon calculation because wide areas shields concerned ecosystems. comparison short-term us suggest paleo-climatic conditions did not since Miocene (6-20 Ma) part world.