Spatial and seasonal dynamics of total suspended sediment and organic carbon species in the Congo River

Abstract

[1] The Congo (Zaire) River, the world's second largest river in terms both of water discharges and of drainage area after the Amazon River, has remained to date in a near-pristine state. For a period between 2 and 6 years, the mainstream near the river mouth (Brazzaville/Kinshasa station) and some of the major and minor tributaries (the Oubangui, Mpoko, and Ngoko-Sangha) were monitored every month for total suspended sediment (TSS), particulate organic carbon (POC), and dissolved organic carbon (DOC). In this large but relatively flat equatorial basin, TSS levels are very low and organic carbon is essentially exported as DOC: from 74% of TOC for the tributaries flowing in savannah regions and 86% for those flowing in the rain forest. The seasonal patterns of TSS, POC, and DOC show clockwise hysteresis in relation to river discharges, with maximum levels recorded 2 to 4 months before peak flows. At the Kinshasa/Brazzaville station, the DOC distribution is largely influenced by the input from the tributaries draining the large marshy forest area located in the center of the basin. There is a marked difference between specific fluxes, threefold higher in the forest basins than in the savannah basins. The computation of inputs to the Atlantic Ocean demonstrates that the Congo is responsible for 14.4 Â 10 6 t/yr of TOC of which 12.4 Â 10 6 t/yr is DOC and 2 Â 10 6 t/yr is POC. The three biggest tropical rivers (the Amazon, the Congo, and the Orinoco), with only 10% of the exoreic world area drained to world oceans, contribute $4% of its TSS inputs but 15-18% of its organic carbon inputs. These proportions may double when considering only world rivers discharging into the open ocean.Citation: Coynel, A., P. Seyler, H. Etcheber, M. Meybeck, and D. Orange (2005), Spatial and seasonal dynamics of total suspended sediment and organic carbon species in the Congo River, Global Biogeochem. Cycles, 19, GB4019,

Biogeochemical contrast between different latitudes and the effect of human activity on spatio-temporal carbon cycle change in Asian river systems

“…25 Table. 3 shows the comparison of annual runoff and carbon flux in three types of river data in West Siberian Lowland (including Ob River basin) and Mekong River basin. The simulated results are generally in the range of previous data (Schlunz and Schneider, 2000;Coynel et al, 2005;Alin et al, 2011;Dai et al, 2012;Long et al, 2015), as evaluated in the author's previous studies (Fig. A2 in Appendix A) (Nakayama, 2017a(Nakayama, , 2017b.…”

“…The model further clarified that these mechanisms are closely related to the slight increase in DIC and the decrease in POC in nighttime in three rivers. (Nakayama, 2017a(Nakayama, , 2017b in order to estimate the carbon cycle both in vertical flux such as CO2 evasion to the atmosphere and sediment storage, and in horizontal transport such as TOC, DOC, POC, DIC-flux to the ocean in previous data of these rivers (Schlunz and Schneider, 2000;Coynel et al, 2005;Rasera et al, 2008;Dubois et al, 2010;Alin et al, 2011;Butman and Raymond, 2011;Dai et al, 2012;10 Striegl et al, 2012;Abril et al, 2015;Lauerwald et al, 2015;Long et al, 2015). There are no data about CO2 evasion but only pCO2 and average efflux data in Mekong River Long et al, 2015), the author estimated CO2 evasion by multiplying the average efflux (gC/m 2 /yr) and water area (km 2 ).…”

“…These trends imply the predominance of the seasonality in in-stream respiration of organic carbon fixed originally on land and along river margins and mobilized into flowing waters, as suggested 10 by the previous observed data (Richey et al, 2002;Rudorff et al, 2011). (Schlunz and Schneider, 2000;Coynel et al, 2005;Aufdenkampe et al, 2011;Dai et al, 2012;Raymond et al, 2013;Hartman 15 et al, 2014;Borges et al, 2015) in order to estimate CO2 evasion to the atmosphere, sediment storage, and TOC, DOC, POC, DIC-flux to the ocean in previous data. Because the new model can simulate both horizontal transport to the ocean and vertical fluxes and includes aquatic metabolism and terrestrially derived carbon together in major rivers, the result implied that there is active interplay between inorganic and organic carbon (DOC, POC, DIC, pCO2, etc.)…”

Fluvial organic carbon losses from a Bornean blackwater river

“…The relationship in this study shows the opposite and may be attributed to the "flushing effect" whereby water with a high DOC concentration (due to long residence time in the soil/peat layer throughout the dry season) is washed into the rivers by the rising water level during the onset of the wet season (Pearce et al, 1986;Hornberger et al, 1994). A strong positive correlation between DOC concentration and discharge was also reported from the Congo basin which comprises evergreen forest, savannah and swamp forest (Coynel et al, 2005). The "flushing" process is enhanced when the previously dry or stagnant upper limits of the river bed/bank are inundated with large amounts of water as discharge rates increase (Casey and Farr, 1982).…”

Remote Sensing Observation of Particulate Organic Carbon in the Pearl River Estuary

“…High intensity rainfall over monsoon regions in the wet season can lead to severe terrestrial erosion, resulting in an increase in TSM in rivers. When the TSM concentration is high, primary production of phytoplankton can decrease due to light limitation [34]. Thus, allochthonous POC becomes the major source of POC, and POC(%TSM) will decrease.…”