A review of material transport by the Congo River and its tributaries

We introduce here a model for calculating, for the first time, the annual material fluxes exported by the main tributaries of the Congo River. This model is based on a knowledge of the functioning of the main physiographic systems of the Congo River basin. For the Upper Congo, Kasai and major right-bank tributaries, we obtained a water flow values of 11·2, 10 and 8·8 l s−1 km−2 respectively, suspended matter values of 7·6, 8·9 and 5·1 t km−2 year−1 and total dissolved solid values of 16·4, 10 and 8·6 t km−2 year−1 respectively. We investigated the role played by the main physiographic units in the dynamics of material transfers within this huge concentrically structured basin. The belt of high ground covered by shrubby savanna supplies most of the suspended matter (SM = 24 mg l−1 at Mongoumba on the Ubangi River—200 km above the confluence with Congo River and 32 mg l−1 at Ouesso on the Sangha River) and of the total dissolved solids (TDS = 42 mg l−1 at Mongoumba on the Ubangi River and 41 mg l−1 at Ouesso on the Sangha River). The concentration of suspended matter is reduced by the waters of the ‘Cuvette Centrale’, a vast basin covered by rain forest (SM = 8 and TDS = 16 mg l−1 for the Likouala aux Herbes basin). Material export fluxes at the sub catchment outlets range from 4 to 9 t km−2 year−1 for suspended matter and from 11 to 31 t km−2 year−1 for total dissolved material, i.e. TDS + DOM (dissolved organic matter). The basin acts as a gigantic organic matter reservoir, which can produce 25 t km−2 year−1 of organic matter in the central flooded zone. Finally, the paper presents the first map of specific mechanical and chemical denuidation rates for the main sub catchments of the Congo basin. Copyright © 2009 John Wiley & Sons, Ltd.