The Effect of Organic Matter on Chemical Weathering: Study of a Small Tropical Watershed: Nsimi-Zoétélé Site, Cameroon

B. Dupré
1998 Mineralogical magazine  
The effect of organic matter during soil/water interaction is still a debated issue on the control of chemical weathering in a tropical environment (Schwartzman and volk, 1989; Chin and Mills, 1991; Heyes and Moore, 1992; Drever, 1994) . In order to study this effect in detail, we focused on the weathering processes occurring in a small tropical watershed (Nsimi/Zo+t+l+, South Cameroon).The Nsimi basin is a pilot site of the PEGI program (programme d'Environnement de la G6osph~re
more » ... h~re Intertropicale, ORSTOM-CNRS) and it offers a unique opportunity to study weathering mechanisms in a lateritic system within a small basin by coupling soil and water chemistry. The lateritic cover in this site can reach up to 40 m in depth and show two pedological distinct zones: 1) slope soils on the hills or elevated areas had 2) hydromorphic soils in the swamp zone which represent 20% of the basin surface. The first results obtained from this program (Viers et al., 1997) show strong chemical differences between waters located in slope zones (depleted in organic matter) and those ponded in swamp zones (enriched in organic matter). The study was performed on waters samples taken from piezometric wells and springs in slope areas, and from piezometric wells and marsh waters in the swamp zones, between 1994-1997. Soil samples analysed in this study were collected during a well drilling in December 1996. Water samples were analysed by high pressure liquid chromatography (HPLC ; major cations and anions) and inductively-coupled plasma mass spectrometry (ICP-MS; trace elements). Dissolved organic carbon was measured by low temperature 6 0 -$0-40-2 0 -1 0 -C3 D O C I A i + F e 9 N a + M g + K + Ca m H 4 S i 0 4 FIG. 1. Stacked diagrams showing the relative importance of major elements in the <0.2gin phases. 405
doi:10.1180/minmag.1998.62a.1.214 fatcat:6pw646makjg6lnwqgvz7p56ol4