A new sediment budget for the Congo River Basin reveals underestimated tributary contributions and large-scale deposition

Abstract. Sediment yields from fluvial networks to the global oceans impact land carbon and nutrient cycles and are susceptible to climate, population, and vegetation changes. The Congo River Basin is a frontier for population and land use change, but sediment yield dynamics are poorly constrained within its basin, in particular within its largest tributary, the Kasaï River. To address this, we aimed to (1) introduce a spatially flexible methodology for estimating sediment yield from remote sensing monitoring, (2) establish a budget for the Congo and Kasaï river basins from both major and secondary tributaries, and (3) better constrain depositional losses of sediment during transit in the mainstem. A random forest model was calibrated on Landsat-8 spectral data, and total suspended sediment was accurately predicted (measured vs. predicted R² = 0.79), though predictions degraded in highly turbid waters due to spectral saturation. A sediment budget of the Congo River revealed that 33.0 Tg yr⁻¹ are exported to the coastal ocean. Most sediment is derived from Congo River headwaters, the Kasaï River, the Oubangui River, and the Aruwimi River, whereas lower-order tributaries contributed 10 % of all sediment inputs. Meanwhile, major contributors to the Kasaï budget (export = 11.1 Tg yr⁻¹) were the Kasaï headwaters, Sankuru, and Kwango-Kwilu rivers. Finally, we found the Cuvette Centrale, a peatland-dominated depression, to be a depositional hotspot, and we estimated its net sediment deposition to be between 5.96 Tg yr⁻¹ and 9.4 Tg yr⁻¹. By monitoring Congo River Basin sediment transport, we aim to provide a better understanding of the Earth-surface processes occurring in a globally significant and rapidly changing watershed that lacks crucial baseline information on its sediment and carbon cycles.