Temporal Variability of Sediments, Dissolved Solids and Dissolved Organic Matter Fluxes in the Congo River at Brazzaville/Kinshasa

For three decades, the solid and dissolved fluxes of the Congo River have been regularly monitored on a monthly basis, despite 12 years of deficiencies (1994-2005). Two programs successively carried out these follow-ups: PEGI/GBF (1987-1993) and SO HYBAM (2006-2017), upstream and downstream, respectively, of the Malebo Pool near Brazzaville, the main hydrometric station of the Congo River. The objective of this study is to examine the temporal dynamic of TSS, TDS and DOC, to explore how these descriptors change over time. Comparison with the two time programs will shed more light on how these descriptors are related to discharge. Afterward, we then find a relationship between total TSS in the water column and that measured in surface for eventual estimation of TSS by remote sensing. In the last decade, compared to the PEGI/GBF period, the discharge of the Congo River was mainly marked by a 4% increase, leading to a significant change on TDS and DOC behaviors. The TSS was quite stable (from 8.2 and 9.3 t km(-2)yr(-1)) due to the low physical erosion well known in this region. The TDS concentrations decreased slightly, by a simple dilution effect. However, the mineral dissolved fluxes (from 11.6 and 10.1 t km(-2)yr(-1)) due to the chemical weathering and atmospheric inputs still predominate over the solid fluxes. Therefore, there was no radical change in the monthly geochemical regime of Congo River Basin (CRB) during these last 30 years. Contrariwise, the DOC concentration marking the biogeochemical processes significantly increased, from 9.0+/-3.0 mg L(-1)to 12.7+/-5.0 mg L-1, due to more flooding events in the central part of the CRB. The change for the DOC fluxes is more relevant, with an increase of 45% between the two studied periods, from 11.1 x 10(6)to 16.2 x 10(6)t yr(-1). This highlights the continuous and actual importance of the "Cuvette Centrale" in the heart of the CRB for dissolved organic matter transport by the Congo River.