Present weathering rates in a humid tropical watershed: Nsimi, South Cameroon

Braun, Jean‐Jacques; Ngoupayou, Jules Rémy Ndam; Viers, Jérôme; Dupré, Bernard; Bedimo, Jean-Pierre Bedimo; Boeglin, Jean-Loup; Robain, Henri; Nyeck, Brunot; Freydier, Rémi; Nkamdjou, Luc Sigha; Rouiller, J.; Müller, Jean‐Pierre

doi:10.1016/j.gca.2004.06.022

Cited by 163 publications

(121 citation statements)

References 69 publications

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“…4) (Kuitcha, 2002;Tienjo, 2007). It should be recall that the DOC concentrations measured in the soil by Braun et al (2005) have been found also to be decreasing with depth. This can show the link between moisture and chemical transfer (Ndam, 1997).…”

Section: Resultsmentioning

confidence: 91%

Transfer of moisture through the unsaturated zone in the tropical forest using the neutron probe

Fouepe

Kengni

Rao

et al. 2009

Int. J. Environ. Sci. Technol.

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ABSTRACT:Knowledge of moisture content is crucial in assessing spatial and temporal movement of water through the unsaturated zone. Moisture storage is also important for monitoring the soil water balance and for validation of water balance models. The purpose of this work was to determine and analyse moisture content profiles at point locations in the unsaturated zone of a lateritic soil around Nsimi, south of Cameroon. Neutron probe has been connected to a set of tensiometers in an area of 60 ha. A comparative study between a site covered with vegetation and a site uncovered was conducted to assess the influence of vegetation in the process of moisture transfers. The results showed that the spatial distribution of moisture profiles varied according to the site and the texture of the soil, with in general increasing of moisture from the surface horizon toward the deeper layers. The mean values of moisture varied from θ m = 0,397 cm 3 /cm 3 on barren site, against θ m = 0,429 cm 3 /cm 3 in vegetation. Values of suction were generally strong in surface and at depth, but weak in the intermediate layers.

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Section: Resultsmentioning

confidence: 91%

Transfer of moisture through the unsaturated zone in the tropical forest using the neutron probe

Fouepe

Kengni

Rao

et al. 2009

Int. J. Environ. Sci. Technol.

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“…The detailed calculations are indicated in the discussion part. Braun et al, 2005).The hillside recharge R hill , the discharge Q hill and Q base are also indicated.…”

Section: Settingsmentioning

confidence: 99%

“…In the composite parent rock, the distribution of major elements in the primary minerals is, in decreasing order: Grain size distribution, bulk and grain densities and major elements (in wt.%) are from Braun et al (2005).…”

Section: Elemental Distribution In Bedrock and Weathering Productsmentioning

confidence: 99%

“…They have to be considered as both palaeoclimatic records and feed-through reactors and representative of optimal conditions for chemical weathering (Kisakurek et al, 2004;Braun et al, 2005;West et al, 2005;Anderson et al, 2007;Wimpenny et al, 2007). In such regions, (Godderis et al, 2008) determined that silicate weathering in the warm humid tropical belt is five times less sensitive to continental runoff than in mid-latitude temperate climate due to the shield effect of the deep mature weathering profiles.…”

Section: Introductionmentioning

confidence: 99%

“…The mineralogy and geochemistry of the solid phases (i.e. lateritic products) and the water chemistry have been extensively studied within both systems (Viers et al, 1997;Oliva et al, 1999;Braun et al, 2005). The contribution of phytoliths to the suspended load of biogenic silica was also investigated (Cary et al, 2005), whilst isotopic fractionation of Nd, Fe and Zn in the different reservoirs of the system were discussed by (Viers and Wasserburg, 2004;Viers et al, 2007;Poitrasson et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

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

Braun

Maréchal

Riotte

et al. 2012

Geochimica et Cosmochimica Acta

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International audienceThe comparison between contemporary and long-term weathering has been carried out in the Small Experimental Watershed (SEW) of Nsimi, South Cameroon in order to quantify the export fluxes of major and trace elements and the residence time of the lateritic weathering cover. We focus on the hillside system composed of a thick lateritic weathering cover topped by a soil layer. This study is built on the recent improvements of the hillside hydrological functioning and on the analyses of major and trace elements. The mass balance calculation at the weathering horizon scale performed with the parent rock as reference indicates (i) strong depletion profiles for alkalis (Na, K, Rb) and alkaline earths (Mg, Ca, Sr, Ba), (ii) moderate depletion profiles for Si, P, Cd, Cu, Zn, Ni and Co, (iii) depletion/enrichment profiles for Al, Ga, Ge, Sn, Pb, LREE, HREE, Y, U, Fe, V, Cr, Mn. It is noteworthy that (i) Mn and Ce are not significantly redistributed according to oxidative processes as it is the case for Fe, V and Cr, and (ii) Ge is fractionated compared to silica with enrichment in Fe-rich horizons. The calculations performed for the topsoil with iron crust as parent material reference reveal that the degradation of the iron crust is accompanied by the loss of most of the constituting elements, among which are those specifically accumulated as the redox sensitive elements (Fe, V, Cr) and iron oxide related elements like Th. The overall current elemental fluxes from the hillside system at the springs and the seepage zones are extremely low due to the inert lateritic mineralogy. 94% of the whole Na flux generated from the hillside corrected from atmospheric deposits (77 mol/ha/yr) represents the current weathering rates of plagioclase (oligoclase) in the system, the other remaining 6% may be attributed to the dissolution of hornblende. The silica hillside flux is 300 mol/ha/yr and can be mostly attributed to the plagioclase and kaolinite dissolution. Al and Ga are exported from the lateritic regolith and maybe due to the dissolution of kaolinite crystals. Compared to the other immobile elements (Zr, Hf, Nb and Th), Ti is significantly exported. Among redox-sensitive elements (Fe, V, Cr, Mn, Ce), only Ce and Mn are exported out of the hillside system. The other elements (Fe, V, Cr) are likely able to be mobilized but over a short distance only. Rb , Sr, Ba, Ni, Cu, Zn are affected by export processes. LREE and Y are exported but in very low amounts (in the range from µmol/ha/yr to mmol/ha/yr) while HREE and U are exported in negligible quantities. A first attempt is carried out to compare the mature ridge top profile from Nsimi SEW with the immature ridge top weathering profile from the Mule Hole SEW (South India), developed on similar granodioritic basement, in order to get deeper insight into (i) the contemporary saprolite production rates and (ii) the combined effect of precipitation (in terms of Mean Annual Rainfall, MAR) and evapotranspiration on the aggressiveness of the draining solutions. Consider...

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