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Keywords:

  • Congo River;
  • Orinoco River;
  • material fluxes;
  • suspended sediment;
  • dissolved solids;
  • dissolved organic carbon

Abstract

This study compares the total suspended sediment (TSS), total dissolved solids (TDS), and dissolved organic carbon (DOC) dynamics of two major inter-tropical rivers, the Congo in Central Africa and the Orinoco in South America, focusing on sampling undertaken during the period 2006–2010. Both rivers are characterized by similar mean annual discharges into the Atlantic Ocean, on its eastern and western margins, respectively. For both rivers, the results presented are placed in the context of the available longer-term hydrological time series (Congo: 1903–2010; Orinoco: 1926–2010). The key features of the recent records of material flux for both rivers were established and compared with other published data from the 20th century. The available discharge time series show that the rivers are characterized by similar maximum monthly discharges (Congo: 75 500 m3 s-1; Orinoco: 85 500 m3 s-1) and similar inter-annual variability (Congo: 1.69; Orinoco: 1.66). However, contrasts in low-flow regime (minimum low flows: Congo: 23 000 m3 s-1; Orinoco: 2300 m3 s-1) and seasonal variability (Congo: 3.3; Orinoco: 37.2), as well as in material fluxes were identified. Specific suspended sediment yields for the Orinoco (89 t km-2 yr-1) were very significantly higher than those for the Congo (9.4 t km-2 yr-1). These differences are mainly explained by contrasts in the physiographic characteristics of the two river basins, such as their contrasting relief. The differences between the TSS fluxes calculated for the Orinoco in this study and those indicated by published data from the second half of the 20th century can be explained by the impact of the hydroelectric dams built in the foothills of the Andean Cordillera. Changes in the TSS fluxes of the Congo are mainly explained by the impact of climatic change on total runoff. Copyright © 2013 John Wiley & Sons, Ltd.