References of "Darchambeau, François"
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See detailAlong-stream transport and transformation of dissolved organic matter in a large tropical river
Lambert, Thibault ULg; Teodoru, C. R.; Nyoni, F. C. et al

in Biogeosciences (2016), 13(9), 2727--2741

Large rivers transport considerable amounts of terrestrial dissolved organic matter (DOM) to the ocean. However, downstream gradients and temporal variability in DOM fluxes and characteristics are poorly ... [more ▼]

Large rivers transport considerable amounts of terrestrial dissolved organic matter (DOM) to the ocean. However, downstream gradients and temporal variability in DOM fluxes and characteristics are poorly studied at the scale of large river basins, especially in tropical areas. Here, we report longitudinal patterns in DOM content and composition based on absorbance and fluorescence measurements along the Zambezi River and its main tributary, the Kafue River, during two hydrological seasons. During high-flow periods, a greater proportion of aromatic and humic DOM was mobilized along rivers due to the hydrological connectivity with wetlands, while low-flow periods were characterized by lower DOM content of less aromaticity resulting from loss of connectivity with wetlands, more efficient degradation of terrestrial DOM and enhanced autochthonous productivity. Changes in water residence time due to contrasting water discharge were found to modulate the fate of DOM along the river continuum. Thus, high water discharge promotes the transport of terrestrial DOM downstream relative to its degradation, while low water discharge enhances the degradation of DOM during its transport. The longitudinal evolution of DOM was also strongly impacted by a hydrological buffering effect in large reservoirs in which the seasonal variability of DOM fluxes and composition was strongly reduced. [less ▲]

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See detailChemoautotrophy and anoxygenic photosynthesis within the water column of a large meromictic tropical lake (Lake Kivu, East Africa)
Morana, Cédric; Roland, Fleur ULg; Crowe, Sean A. et al

in Limnology and Oceanography (2016)

We quantified chemoautotrophic and anoxygenic photosynthetic microbial production in the water column of Lake Kivu, a permanently stratified tropical lake situated amidst volcanic activity, and aimed to ... [more ▼]

We quantified chemoautotrophic and anoxygenic photosynthetic microbial production in the water column of Lake Kivu, a permanently stratified tropical lake situated amidst volcanic activity, and aimed to identify the microorganisms involved in these processes through the analysis of their phospholipid fatty acid (PLFA) content and stable isotope (13C) labelling of PLFA in a set of incubation experiments. Data demonstrate the existence of a biogeochemically active chemoautotrophic bacterial community in the redoxcline of Lake Kivu (50–70 m). PLFA data indicate that the bacterial communities are structured vertically in the water column, with a large dissimilarity between the oxic and anoxic waters. Maximum volumetric dark CO2 fixation rates measured in Lake Kivu were in the same range as values reported from H2S-rich marine redoxclines, such as the Black and Baltic Seas, and the Cariaco Basin. Similarly, maximal chemoautotrophic activities in Lake Kivu were observed in sulfidic waters, just below the oxycline. Anoxygenic photosynthetic production was never observed in the main basin of Lake Kivu. However, anoxygenic phototrophs largely dominated CO2 fixation in the illuminated redoxcline of Kabuno Bay, a shallower ferruginous sub-basin. Overall, this study supports the idea that chemoautotrophs and/or anoxygenic photoautotrophs might play an important role in the flow of carbon and energy in permanently stratified tropical ecosystems. In Lake Kivu, these processes significantly contribute to organic matter biosynthesis and exert an indirect control on oxygenic photoautotrophs by shortcircuiting the vertical transport of nutrients to the illuminated and oxygenated surface waters. [less ▲]

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See detailNitrous oxide and methane seasonal variability in the epilimnion of a large tropical meromictic lake (Lake Kivu, East-Africa)
Roland, Fleur ULg; Darchambeau, François ULg; Morana, Cédric et al

in Aquatic Sciences (2016)

We report a data-set of monthly vertical profiles obtained from January 2012 to October 2013, from the surface to 70 m depth of nitrous oxide (N2O) and dissolved methane (CH4) in Lake Kivu, a large and ... [more ▼]

We report a data-set of monthly vertical profiles obtained from January 2012 to October 2013, from the surface to 70 m depth of nitrous oxide (N2O) and dissolved methane (CH4) in Lake Kivu, a large and deep meromictic tropical lake (East Africa). Vertical variations of N2O were modest, with ranges of 6--9 and 0--16 nmol L−1 in surface and bottom waters, respectively, and occasionally peaks of N2O (up to 58 nmol L−1) were observed at the oxic-anoxic interface. On the contrary, steep vertical gradients of CH4 were observed with values changing several orders of magnitude from surface (19--103 nmol L−1) to 70 m (113,000--520,000 nmol L−1). Seasonal variations of CH4 were caused by annual cycles of mixing and stratification, during the dry and rainy seasons, respectively. This mixing allowed the establishment of a thick oxic layer (maximum 65 m deep), leading to decreased CH4 concentrations (minimum of 8 nmol L−1), presumably due to bacterial CH4 oxidation. During the stratification period, the oxic mixed layer was thinner (minimum 25 m deep), and an increase of CH4 concentrations in surface waters was observed (maximum of 103 nmol L−1), probably due to a lower integrated CH4 oxidation on the water column. Lake Kivu seasonally alternated between a source and a sink for atmospheric N2O, but on an annual scale was a small source of N2O to the atmosphere (on average 0.43 \textmumol m−2 day−1), while it was a small source of CH4 to the atmosphere throughout the year (on average 86 \textmumol m−2 day−1). Vertical and seasonal variations of N2O are discussed in terms of nitrification and denitrification, although from the present data-set it is not possible to unambiguously identify the main drivers of N2O production. [less ▲]

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See detailNeodymium isotope constraints on past hydrological variability in the Congo Basin
Bayon, G; Schefuss, E; Dupont, L et al

Conference (2015, October 26)

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See detailDivergent biophysical controls of aquatic CO2 and CH4 in the World’s two largest rivers
Borges, Alberto ULg; Abril, G; Darchambeau, François ULg et al

in Scientific Reports (2015), 5

Carbon emissions to the atmosphere from inland waters are globally significant and mainly occur at tropical latitudes. However, processes controlling the intensity of CO2 and CH4 emissions from tropical ... [more ▼]

Carbon emissions to the atmosphere from inland waters are globally significant and mainly occur at tropical latitudes. However, processes controlling the intensity of CO2 and CH4 emissions from tropical inland waters remain poorly understood. Here, we report a data-set of concurrent measurements of the partial pressure of CO2 (pCO2) and dissolved CH4 concentrations in the Amazon (n = 136) and the Congo (n = 280) Rivers. The pCO2 values in the Amazon mainstem were significantly higher than in the Congo, contrasting with CH4 concentrations that were higher in the Congo than in the Amazon. Large-scale patterns in pCO2 across different lowland tropical basins can be apprehended with a relatively simple statistical model related to the extent of wetlands within the basin, showing that, in addition to non-flooded vegetation, wetlands also contribute to CO2 in river channels. On the other hand, dynamics of dissolved CH4 in river channels are less straightforward to predict, and are related to the way hydrology modulates the connectivity between wetlands and river channels. [less ▲]

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See detailPelagic photoferrotrophy and iron cycling in a modern ferruginous basin
Llirós, Marc; García–Armisen, Tamara; Darchambeau, François ULg et al

in Scientific Reports (2015), 5

Iron-rich (ferruginous) ocean chemistry prevailed throughout most of Earth’s early history. Before the evolution and proliferation of oxygenic photosynthesis, biological production in the ferruginous ... [more ▼]

Iron-rich (ferruginous) ocean chemistry prevailed throughout most of Earth’s early history. Before the evolution and proliferation of oxygenic photosynthesis, biological production in the ferruginous oceans was likely driven by photoferrotrophic bacteria that oxidize ferrous iron {Fe(II)} to harness energy from sunlight, and fix inorganic carbon into biomass. Photoferrotrophs may thus have fuelled Earth’s early biosphere providing energy to drive microbial growth and evolution over billions of years. Yet, photoferrotrophic activity has remained largely elusive on the modern Earth, leaving models for early biological production untested and imperative ecological context for the evolution of life missing. Here, we show that an active community of pelagic photoferrotrophs comprises up to 30% of the total microbial community in illuminated ferruginous waters of Kabuno Bay (KB), East Africa (DR Congo). These photoferrotrophs produce oxidized iron {Fe(III)} and biomass, and support a diverse pelagic microbial community including heterotrophic Fe(III)-reducers, sulfate reducers, fermenters and methanogens. At modest light levels, rates of photoferrotrophy in KB exceed those predicted for early Earth primary production, and are sufficient to generate Earth’s largest sedimentary iron ore deposits. Fe cycling, however, is efficient, and complex microbial community interactions likely regulate Fe(III) and organic matter export from the photic zone. [less ▲]

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See detailBacterial community composition in three freshwater reservoirs of di erent alkalinity and trophic status
Llirós, Marc; Inceoglu, Ozgul; Garcia-Armisen, Tamara et al

Poster (2015, August 23)

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See detailRiver geochemistry, chemical weathering, and atmospheric CO2 consumption rates in the Virunga Volcanic Province (East Africa)
Balagizi, Charles M.; Darchambeau, François ULg; Bouillon, Steven et al

in Geochemistry, Geophysics, Geosystems (2015), 16

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See detailContribution of cyanobacteria to the building of travertines in a calcareous stream
Wilmotte, Annick ULg; Golubic, Stjepko; Kleinteich, Julia et al

Poster (2015, August 03)

The ambient temperature travertine deposits of the calcareous Hoyoux River (Modave, Belgium) and several tributaries are organized and promoted by the filamentous cyanobacterium identified by its ... [more ▼]

The ambient temperature travertine deposits of the calcareous Hoyoux River (Modave, Belgium) and several tributaries are organized and promoted by the filamentous cyanobacterium identified by its morphotype and ecological properties as Phormidium cf. incrustatum. A combination of techniques was used to study this biotope: physico-chemical parameters and CO2 measurements, Scanning and Transmission Electron Microscopy, RAMAN microspectroscopy. A molecular diversity study with pyrosequencing of the cyanobacterial 16S rRNA is in progress. A potential candidate was isolated in culture. [less ▲]

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See detailGlobally significant greenhouse-gas emissions from African inland waters
Borges, Alberto ULg; Darchambeau, François ULg; Teodoru, Cristian R. et al

in Nature Geoscience (2015), advance online publication

Carbon dioxide emissions to the atmosphere from inland waters[mdash]streams, rivers, lakes and reservoirs[mdash]are nearly equivalent to ocean and land sinks globally. Inland waters can be an important ... [more ▼]

Carbon dioxide emissions to the atmosphere from inland waters[mdash]streams, rivers, lakes and reservoirs[mdash]are nearly equivalent to ocean and land sinks globally. Inland waters can be an important source of methane and nitrous oxide emissions as well, but emissions are poorly quantified, especially in Africa. Here we report dissolved carbon dioxide, methane and nitrous oxide concentrations from 12 rivers in sub-Saharan Africa, including seasonally resolved sampling at 39 sites, acquired between 2006 and 2014. Fluxes were calculated from published gas transfer velocities, and upscaled to the area of all sub-Saharan African rivers using available spatial data sets. Carbon dioxide-equivalent emissions from river channels alone were about 0.4 Pg carbon per year, equivalent to two-thirds of the overall net carbon land sink previously reported for Africa. Including emissions from wetlands of the Congo river increases the total carbon dioxide-equivalent greenhouse-gas emissions to about 0.9 Pg carbon per year, equivalent to about one quarter of the global ocean and terrestrial combined carbon sink. Riverine carbon dioxide and methane emissions increase with wetland extent and upland biomass. We therefore suggest that future changes in wetland and upland cover could strongly affect greenhouse-gas emissions from African inland waters. [less ▲]

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See detailPhytoplankton abundance and diversity in the Congo river at high and low waters
Stoyneva, MP; Descy, JP; Bouillon, S et al

Conference (2015, July 05)

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See detailLandscape Control on the Spatial and Temporal Variability of Chromophoric Dissolved Organic Matter and Dissolved Organic Carbon in Large African Rivers
Lambert, Thibault ULg; Darchambeau, François ULg; Bouillon, Steven et al

in Ecosystems (2015)

The characteristics of colored dissolved organic matter (CDOM) as well as the concentrations and stable isotope composition (d 13 C) of dissolved organic carbon (DOC) were characterized in several large ... [more ▼]

The characteristics of colored dissolved organic matter (CDOM) as well as the concentrations and stable isotope composition (d 13 C) of dissolved organic carbon (DOC) were characterized in several large rivers of Africa including the Congo, Niger, Zambezi, and Ogooué basins. We compared the spatial and temporal patterns of dissolved organic matter (DOM) quantity and quality along with various environmental gradients, including hydrology, river size, catchment vegetation, and connectivity to land. The optical proxies used include the absorption coefficient at 350 nm, the specific ultraviolet absorbance, and the spectral slope ratio (S R = 275–295-nm slope divided by 350–400-nm slope). Our results show that land cover plays a primary role in controlling both DOC concentration and optical properties of DOM in tropical freshwaters. A higher cover of dense forest in the catchment leads to a higher quantity of highly aromatic DOM in the river network, whereas an increasing savannah cover results in lower DOC concentrations and less absorptive DOM. In addition to land cover, the watershed morphology (expressed by the average slope) exerts a strong control on DOC and CDOM in tropical rivers. Our results also show that the percentage of C3 and C4 vegetation cover is not an accurate predictor for DOM and CDOM quality in rivers due to the importance of the spatial distribution of land cover within the drainage network. The comparison of our results with previously published CDOM data in temperate and high-latitude rivers highlights that DOM in tropical freshwa-ters is generally more aromatic, and shows a higher capacity for absorbing sunlight irradiance. [less ▲]

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See detailVertical Distribution of Functional Potential and Active Microbial Communities in Meromictic Lake Kivu
İnceoğlu, Özgul; Llirós, Marc; Crowe, Sean A. et al

in Microbial Ecology (2015)

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See detailApplication of stable isotopes in trophic ecology: importance of TEF and seasonal baseline for robust interpretations.
Remy, François ULg; Darchambeau, François ULg; Dauby, Patrick ULg et al

Conference (2015, April 02)

Nitrogen, carbon and sulfur stable isotopes are very powerful tools for trophic ecologists to delineate food webs of various ecosystems. More recently… the use of mixing models has exponentially increased ... [more ▼]

Nitrogen, carbon and sulfur stable isotopes are very powerful tools for trophic ecologists to delineate food webs of various ecosystems. More recently… the use of mixing models has exponentially increased to give a more specific vision of organism’s diets and trophic relationships. Two case studies will be presented to give a summary of what’s been done in Liège Oceanology Lab to improve our interpretation of stable isotopes results. First is an experimental calculation of the Trophic Enrichment Factors (TEFs) for one dominant detritivorous species of Mediterranean amphipod inhabiting seagrass detritus: Gammarus aequicauda (Martynov, 1931). This experimental study was planned after a strange result of the SAIR mixing model, giving results opposed to all observations and knowledge we had about this species. Thus, the impact of 3 very different food sources (amphipod powder, algae power, seagrass powder) on the turnover rate of C and N isotopic compositions was tested, and afterwards TEFs for C and N for each source were calculated. Animal food source showed to be the most effectively assimilated with a fast turnover rate while seagrass and algae showed very slow assimilation. TEFs calculations showed to be interesting because TEFs seem not to depend on the natural feeding type of the invertebrate but more on the type of food source. Animal source showed carnivorous TEFs values while seagrass and algae source showed typical detritivorous values. SIAR results with these new custom values gave more coherent values highlighting the major importance of TEFs values for mixing models data interpretation. Second is a simple question: are the seasonal isotopic composition variations observed for many seagrass detritus macrofauna species due to actual diet changes, or only to isotopic baseline shift of the food sources? Macrofauna and all potential food sources were sampled near STARESO Oceanographic Station (Corsica, 8°45’E; 42°35’N) in 2011-2012 at each season at two different sites. SIBER software runs with C and N isotopic data showed spatio-temporal isotopic variations at community, interspecific and intraspecific level. SIBER did not gave us information about the origin of these changes, but coupled with SIAR and our custom TEFs, species actually showing drastic changes of diet were identified, while others seem to reflect more a source baseline isotopic composition shift. Working at specific level is compulsory for fine conclusions. These two case studies highlight the importance of mixing model use and of accurate TEF values to run these models properly to draw robust and reliable conclusions using stable isotopic data. [less ▲]

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See detailInorhanic and organic carbon spatial variability in the Congo River during high waters (December 2013) and low waters (June 2014)
Borges, Alberto ULg; Bouillon, S; Teodoru, C et al

Conference (2015, February 23)

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See detailBiogeochemistry of the Congo River: annual transport fluxes and sources of carbon in the upper Congo River (Kisangani, DRC Congo)
Bouillon; Tambwe; Mambo, T et al

Conference (2015, February 22)

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See detailPlankton diversity and metabolism in the Congo River during high waters (December 2013) and low waters (June 2014)
Darchambeau, François ULg; Descy, JP; Leporcq, B et al

Poster (2015, February 22)

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See detailCyanobacteria - the constructors of travertines?
Kleinteich, Julia; Stelmach Pessi, Igor ULg; Velazquez, David et al

Conference (2015, February)

Cyanobacteria are participating in carbonate build-up and travertine formation in the Belgian river Hoyoux and its tributaries. In this study, we sampled calcareous material from travertines and oncoliths ... [more ▼]

Cyanobacteria are participating in carbonate build-up and travertine formation in the Belgian river Hoyoux and its tributaries. In this study, we sampled calcareous material from travertines and oncoliths from four sampling sites on the Hoyoux river and Triffoy brook. In addition, the water chemistry was determined. The structure of the material was analyzed by Scanning Electron Microscopy and Raman microscopy (?°. The dominant cyanobacterial species was isolated and identified on the basis of microscopic observation and amplification of the 16S-ITS fragment as Phormidium sp., likely functioning as the ‘architect’ of the travertine system. In order to describe the full diversity of the travertine system and to discriminate between the active fraction and inactive or dead organic matter, DNA as well as RNA was extracted from the travertine material, amplified using cyanobacteria specific primers and sequenced by 454 pyrosequencing. To detect seasonal changes in the biological activity, summer and winter time points were compared. This study reveals the ecology of an overlooked environment in Belgian river systems and tries to explain the build-up of travertines. [less ▲]

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See detailEast African Great Lake Ecosystem Sensitivity to changes final report
Descy, J.-P.; André, L.; Delvaux, C. et al

Report (2015)

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