A comparison of the suspended and dissolved matter dynamics of two large inter‐tropical rivers draining into the Atlantic Ocean: the Congo and the Orinoco

Laraque, Alain; Castellanos, Bartolo; Steiger, Johannes; López, José Luís; Pandi, Albert; Rodríguez, Militza; Rosales, Judith; Adèle, Georges; Perez, Jesus; Lagane, Christelle

doi:10.1002/hyp.9776

Cited by 51 publications

(50 citation statements)

References 38 publications

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“…Its tributaries cross the equatorial zone resulting in a very stable intra-annual flow regime and discharge compared to other large rivers like the Amazon (Coynel et al, 2005;Laraque et al, 2013). The river has a very low annual sediment discharge (5.5 × 10 7 t; Wetzel, 1993) that is attributed to the low overall altitude of the Congo watershed, the presence of numerous lakes and floodplains, strongly leached ferralitic soils and the extensive vegetation cover (Laraque and Olivry, 1996;Seyler et al, 2004).…”

Section: Hydrological Geological and Biogeochemical Settingsmentioning

confidence: 99%

Organic matter characterization and distribution in sediments of the terminal lobes of the Congo deep-sea fan: Evidence for the direct influence of the Congo River

et al. 2015

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International audienceThe terminal lobe complex of the Congo River submarine fan sits on the abyssal Atlantic plain, at 5000 m water depth, 760 km offshore from the river mouth estuarine area. While most rivers deliver particulate material to the continental shelf, particulate matter from the Congo River largely bypasses the shelf and is transported by turbidity currents through the Congo submarine canyon system. We determined the quantity and quality of the organic matter reaching the terminal lobe complex at five sites with marked morphological differences that may influence the distribution of organic matter. A suite of bulk geochemical (% OC, δ13Corg, δ15N, C: N), 137Cs and palynofacies analyses were done on cores collected from the terminal lobe area. These results were also compared to the composition of sediments collected upstream at the Malebo Pool (Congo River).Distal lobe complex sediments contain high amounts of terrestrial organic carbon (3–5 wt.%) that is homogeneously distributed in surficial (22 cm) and deeper sediments (580 cm) silty–clay facies. Strongly altered soil-derived organic matter with well-preserved land plant detritus from the Congo River predominates. A terrestrial soil origin for the particulate load was confirmed by the elevated 137Cs activity in lobe sediments. The vertical distribution of the 137Cs signal suggests that there has been a massive arrival of terrestrial sediments since 1963, consistent with a turbiditic origin. From the locations surveyed, we estimate a maximum accumulation of terrestrial organic carbon of ca. 1 kg OC m− 2 y− 1 for the distal lobe. However, transport modifies the organic matter both in terms of quantity and quality. Observed differences were attributed to preferential degradation of nitrogenous matter during diagenesis and to the addition of highly remineralized marine organic matter.Results from our temporal reference site (E) suggest that organic matter may be preserved in turbidite facies for thousands of years. The good preservation state of the accumulated organic matter shows that turbiditic lobe complexes should be considered as a sink for terrestrial organic carbon in the deep ocean

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Section: Hydrological Geological and Biogeochemical Settingsmentioning

confidence: 99%

Organic matter characterization and distribution in sediments of the terminal lobes of the Congo deep-sea fan: Evidence for the direct influence of the Congo River

et al. 2015

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“…Because of the marked difference in water chemistry between both typologies of river waters, there is a chemical heterogeneity between the left and right banks within the Orinoco mainstream because “whitewater” rivers flow to the left bank and “blackwater” rivers flow to the right bank. This lateral asymmetry, which has been noted by many authors (Lewis & Saunders, ; Laraque et al, ; Stallard, ), is maintained in the Orinoco from the confluence with the Guaviare River in the upper Orinoco to the river mouth due to the continuous and heterogeneous deliveries from one river bank to the other (Figure ).…”

Section: Introductionmentioning

confidence: 99%

Dynamics of dissolved major (Na, K, Ca, Mg, and Si) and trace (Al, Fe, Mn, Zn, Cu, and Cr) elements along the lower Orinoco River

Mora

Mahlknecht

Baquero

et al. 2016

Hydrological Processes

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This study addresses the changes in dissolved major and trace element concentrations along the Orinoco River, including the mixing zone between the Orinoco and Apure Rivers. Water samples from the Apure and Orinoco Rivers were collected monthly in four sectors over a period of 15 months. Auxiliary parameters (pH, dissolved oxygen, conductivity, and temperature), total suspended sediments, dissolved organic carbon (DOC), and major (Na, K, Ca, Mg, and Si) and trace (Al, Fe, Mn, Zn, Cu, and Cr) element concentrations were measured in all sectors. The relative contribution of both rivers after the Apure-Orinoco confluence was determined using Ca as a tracer.Moreover, a mixing model was developed to determine whether dissolved species exhibit a conservative behavior during mixing. The results indicate that DOC is removed from waters during the Apure-Orinoco mixing, probably due to absorption of DOC on mineral phases supplied by the Apure River. Dissolved Na, Ca, and Mg behave conservatively during the mixing processes, and their concentrations are controlled by a dilution process. The anomaly in the temporal pattern of K in the Orinoco is caused by the input of biogenic K originating from the Apure River during the high-water stage. The loss of dissolved Si during the low-water stage can be explained by the uptake of Si by diatoms. Dissolved Mn, Zn, Al, and Fe showed a non-conservative behavior during the Apure-Orinoco mixing. The removal of Mn and Zn from the dissolved phase can be explained by the formation of Mn-oxyhydroxides and the scavenging of Zn onto Mn oxides. Dissolved Fe is controlled by redox processes, although the removals of Fe and Al due to the preferential adsorption of large organometallic complexes by mineral surfaces after the Apure-Orinoco confluence can affect the mobility of both elements during transport. The conservative behavior shown by Cu and Cr can be related to the tendency of both elements to be complexed with small organic colloids, which are not preferentially adsorbed by clays. KEYWORDSmajor elements, mixing zone, organic matter, Orinoco River, trace elementsThe Orinoco River ranks third in terms of water discharge to the oceans, with an annual mean discharge of 36.000 m 3 s −1 . Like the Amazon River tributaries, the Orinoco River tributaries have been classified based on their optical appearance and their physicochemical properties in "whitewater," "clearwater," and "blackwater" rivers (Vegas-Vilarrubia, Paolini, & Miragaya, 1988 because "whitewater" rivers flow to the left bank and "blackwater" rivers flow to the right bank. This lateral asymmetry, which has been noted by many authors (Lewis & Saunders, 1984;Laraque et al., 2013;Stallard, 1987), is maintained in the Orinoco from the conflu- Therefore, the objective of this work was to investigate the temporal variation and behavior of dissolved organic carbon (DOC) and dissolved major (Na, K, Ca, Mg, and Si) and trace (Al, Fe, Mn, Zn, Cu, and Cr) elements along the lower Orinoco River mainstream. We emphasized the mixing z...

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“…Arctic rivers during the spring freshet Wickland et al, 2012), as well as in tropical catchments experiencing wet-season flushing of surface soils Laraque et al, 2013), and in small streams and headwater catchments dominated by episodic rain or snowmelt events (Carey, 2003;Wagner et al, 2008;Fellman et al, 2009;Raymond and Saiers, 2010;Jung et al, 2012;Lloret et al, 2013;Sandford et al, 2013;Pereira et al, 2014). In these scenarios, the composition of DOC is often observed to change significantly during such DOC pulses, as changing hydrologic flow paths draw upon different vegetation-and soil-derived DOC pools.…”

Section: Introductionmentioning

confidence: 99%

Spatial and temporal dynamics of biogeochemical processes in the Fraser River, Canada : a coupled organic-inorganic perspective

Voß¹

2014

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The great geologic and climatic diversity of the Fraser River basin in southwestern Canada render it an excellent location for understanding biogeochemical cycling of sediments and terrigenous organic carbon in a relatively pristine, large, temperate watershed. Sediments delivered by all tributaries have the potential to reach the ocean due to a lack of main stem lakes or impoundments, a unique feature for a river of its size. This study documents the concentrations of a suite of dissolved and particulate organic and inorganic constituents, which elucidate spatial and temporal variations in chemical weathering (including carbonate weathering in certain areas) as well as organic carbon mobilization, export, and biogeochemical transformation. Radiogenic strontium isotopes are employed as a tracer of sediment provenance based on the wide variation in bedrock age and lithology in the Fraser basin. The influence of sediments derived from the headwaters is detectable at the river mouth, however more downstream sediment sources predominate, particularly during high discharge conditions. Bulk radiocarbon analyses are used to quantify terrestrial storage timescales of organic carbon and distinguish between petrogenic and biospheric organic carbon, which is critical to assessing the role of rivers in long-term atmospheric CO 2 consumption. The estimated terrestrial residence time of biospheric organic carbon in the Fraser basin is 650 years, which is relatively short compared to other larger rivers (Amazon, Ganges-Brahmaputra) in which this assessment has been performed, and is likely related to the limited floodplain storage capacity and non-steadystate post-glacial erosion state of the Fraser River. A large portion of the dissolved inorganic carbon load of the Fraser River (>80%) is estimated to derive from remineralization of dissolved organic carbon, particularly during the annual spring freshet when organic carbon concentrations increase rapidly. This thesis establishes a baseline for carbon cycling in a largely unperturbed modern mid-latitude river system and establishes a framework for future process studies on the mechanisms of organic carbon turnover and organic matter-mineral associations in river systems.

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A comparison of the suspended and dissolved matter dynamics of two large inter‐tropical rivers draining into the Atlantic Ocean: the Congo and the Orinoco

Cited by 51 publications

References 38 publications

Organic matter characterization and distribution in sediments of the terminal lobes of the Congo deep-sea fan: Evidence for the direct influence of the Congo River

Organic matter characterization and distribution in sediments of the terminal lobes of the Congo deep-sea fan: Evidence for the direct influence of the Congo River

Dynamics of dissolved major (Na, K, Ca, Mg, and Si) and trace (Al, Fe, Mn, Zn, Cu, and Cr) elements along the lower Orinoco River

Spatial and temporal dynamics of biogeochemical processes in the Fraser River, Canada : a coupled organic-inorganic perspective

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