OZCAR-RI AgrHyS Environmental Research Observatory - France

The soil horizons whose total thickness may be highly variable at the scale of the catchment (from 35 to roughly 5 m) comprise a large number of secondary mineral phases including illite, smectite, kaolinite, various Fe-oxides and Fe-oxi-hydroxides (hematite, goethite,...) and Mn oxides. The soils are organized following the topography with well-drained ?Luvisols? in the upland areas while in bottomlands poorly-drained domains consist of ´Luvisols ?Redoxisols´ and ´Luvisols ? Redoxisols dégradés´ resulting from an increasing development of hydromorphy and degradation in originally well-drained horizons due to an excess of water of topographical origin. These soils are acid (pH from 5 to 7 in surface, from 4.6 to 6.7 in the regolith). The content of organic matter varies from 2.5-6.5% in the upper layers to 0.3-2% in deeper zones and in the regolith. Organic layers are 30-40 cm deep. The hydraulic conductivity is around 10-5 m/s in upslope soils to 10-6 m/s in bottolands. The weathered zone is 1 to more than 30 m deep and its hydraulic conductivity is between 4.10-5 and 2.10-6 m/s. The conductivity of the geological bedrock is estimated around 3.5 10-6 m/s (Pauwels et al., 1996).