References of "Bouillon, S"
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See detailDynamic seasonal nitrogen cycling in response to anthropogenic N loading in a tropical catchment, Athi–Galana–Sabaki River, Kenya
Marwick, T. R.; Tamooh, F.; Ogwoka, B. et al

in Biogeosciences (2014), 11(2), 443--460

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See detailGeochemistry of continental rivers of the Virunga Volcanic Province, East Africa
Balagizi, C; Darchambeau, François ULg; Kasereka, M et al

Conference (2013)

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See detailPhotoferrotrophy and Fe-cycling in a freshwater column
Llirós, M; Crowe, SA; García-Armisen, T et al

Conference (2013)

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See detailPhotoferrotrophy and Fe-cycling in a freshwater column
Llirós, M; Crowe, SA; García-Armisen, T et al

Poster (2013)

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See detailDynamics of dissolved inorganic carbon and aquatic metabolism in the Tana River basin, Kenya
Tamooh, F.; Borges, Alberto ULg; Meysman, F. J. R. et al

in Biogeosciences (2013), 10(11), 6911-6928

A basin-wide study was conducted in the Tana River basin (Kenya) in February 2008 (dry season), September–November 2009 (wet season) and June– July 2010 (end of the wet season) to assess the dynamics and ... [more ▼]

A basin-wide study was conducted in the Tana River basin (Kenya) in February 2008 (dry season), September–November 2009 (wet season) and June– July 2010 (end of the wet season) to assess the dynamics and sources of dissolved inorganic carbon (DIC) as well as to quantify CO2 fluxes, community respiration (R), and primary production (P). Samples were collected along the altitudinal gradient (from 3600 to 8 m) in several headwater streams, reservoirs (Kamburu and Masinga), and the Tana River mainstream. DIC concentrations ranged from 0.2 to 4.8 mmol L−1, with exceptionally high values (3.5±1.6 mmol L−1) in Nyambene Hills tributaries. The wide range of 13CDIC values (−15.0 to −2.4 ‰) indicate variable sources of DIC, with headwater streams recording more positive signatures compared to the Tana River mainstream. With with only a few exceptions, the entire riverine network was supersaturated in CO2, implying the system is a net source of CO2 to the atmosphere. pCO2 values were generally higher in the lower Tana River mainstream compared to headwater tributaries, opposite to the pattern typically observed in other river networks. This was attributed to high suspended sediment in the Tana River mainstream fuelling in-stream community respiration and net heterotrophy. This was particularly evident during the 2009 wet season campaign (median pCO2 of 1432 ppm) compared to the 2010 end of the wet season (1002 ppm) and 2008 dry season(579 ppm). First-order estimates show that in-stream community respiration was responsible for the bulk of total CO2 evasion (77 to 114 %) in the Tana River mainstream, while in the tributaries, this could only account for 5 to 68% of total CO2 evasion. This suggests that CO2 evasion in the tributaries was to a substantial degree sustained by benthic mineralisation and/or lateral inputs of CO2-oversaturated groundwater. While sediment loads increased downstream and thus light availability decreased in the water column, both chlorophyll a (0.2 to 9.6 μg L−1) and primary production (0.004 to 7.38 μmol CL−1 h−1) increased consistently downstream. Diurnal fluctuations of biogeochemical processes were examined at three different sites along the river continuum (headwater, reservoir and mainstream), and were found to be substantial only in the headwater stream, moderate in the reservoir and not detectable in the Tana River mainstream. The pronounced diurnal fluctuations observed in the headwater stream were largely regulated by periphyton as deduced from the low chlorophyll a in the water column. [less ▲]

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See detailVertical stratification and functional guilds in the bacterial community of Lake Kivu (East Africa)
Garcia-Armisen, T; Inceoglu, O; Llirós, M et al

Conference (2012, August 19)

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See detailOpening the archaeal box in a oligotrophic freshwater environment
Llirós, M; Garcia-Armisen, T; Crowe, SA et al

Poster (2012, August 19)

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See detailDynamics of dissolved inorganic carbon in the Tana River Basin, Kenya
Tamooh; Meysman, F; Van den Meersche, K et al

Conference (2012, July 08)

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See detailFirst assessment of the biogeochemistry of the upper Congo River
Darchambeau, François ULg; Bouillon, S.; Borges, Alberto ULg

Poster (2012, April 22)

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See detailVariability of methane in the epilimnion of Lake Kivu
Borges, Alberto ULg; Abril, G.; Morana, C. et al

Poster (2012, April 22)

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See detailSeasonal dynamics of organic carbon in the Tana River Basin, Kenya
Tamooh, F.; Meysman, F.; Marwick, T.R. et al

Conference (2012, April 22)

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See detailVariability of carbon dioxide and methane in the epilimnion of Lake Kivu
Borges, Alberto ULg; Bouillon, S.; Abril, G. et al

in Descy, J.-P.; Darchambeau, François; Schmid, M. (Eds.) Lake Kivu: Limnology and biogeochemistry of a tropical great lake (2012)

We report a dataset of the partial pressure of CO2 (pCO2) and me-thane concentrations (CH4) in the surface waters of Lake Kivu ob-tained during four cruises covering the two main seasons (rainy and dry ... [more ▼]

We report a dataset of the partial pressure of CO2 (pCO2) and me-thane concentrations (CH4) in the surface waters of Lake Kivu ob-tained during four cruises covering the two main seasons (rainy and dry). Spatial gradients of surface pCO2 and CH4 concentrations were modest in the main basin. In Kabuno Bay, pCO2 and CH4 concentra-tions in surface waters were higher, owing to the stronger influence of subaquatic springs from depth. Seasonal variations of pCO2 and CH4 in the main basin of Lake Kivu were strongly driven by deepen-ing of the epilimnion and the resulting entrainment of water charac-terized by higher pCO2 and CH4 concentrations. Physical and chem-ical vertical patterns in Kabuno Bay were seasonally stable, owing to a stronger stratification and smaller surface area inducing fetch limi-tation of wind driven turbulence. A global and regional cross-system comparison of pCO2 and CH4 concentrations in surface waters of lakes highlights the peculiarity of Kabuno Bay in terms of pCO2 values in surface waters. In terms of surface CH4 concentrations, both Kabuno Bay and the main basin of Lake Kivu are at the lower end of values in lakes globally, despite the huge amounts of CH4 and CO2 in the deeper layers of the lake. [less ▲]

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See detailDistribution and origin of suspended matter and organic carbon pools in the Tana River Basin, Kenya
Tamooh, F; Van den Meersche, K; Meysman, F et al

in Biogeosciences (2012), 9

We studied patterns in organic carbon pools and their origin in the Tana River Basin (Kenya), in February 2008 (dry season), September–November 2009 (wet season), and June–July 2010 (end of wet season ... [more ▼]

We studied patterns in organic carbon pools and their origin in the Tana River Basin (Kenya), in February 2008 (dry season), September–November 2009 (wet season), and June–July 2010 (end of wet season), covering the full continuum from headwater streams to lowland mainstream sites. A consistent downstream increase in total suspended matter (TSM, 0.6 to 7058 mg l−1) and particulate organic carbon (POC, 0.23 to 119.8 mg l−1) was observed during all three sampling campaigns, particularly pronounced below 1000m above sea level, indicating that most particulate matter exported towards the coastal zone originated from the mid and low altitude zones rather than from headwater regions. This indicates that the cascade of hydroelectrical reservoirs act as an extremely efficient particle trap. Although 7Be / 210Pbxs ratios/age of suspended sediment do not show clear seasonal variation, the gradual downstream increase of suspended matter during end of wet season suggests its origin is caused by inputs of older sediments from bank erosion and/or river sediment resuspension. During wet season, higher TSM concentrations correspond with relatively young suspended matter, suggesting a contribution from recently eroded material.With the exception of reservoir waters, POC was predominantly of terrestrial origin as indicated by generally high POC : chlorophyll a (POC : Chl a) ratios (up to 41 000). Stable isotope signatures of POC ( 13CPOC) ranged between −32 and −20‰and increased downstream, reflecting an increasing contribution of C4-derived carbon in combination with an expected shift in 13C for C3 vegetation towards the more semi-arid lowlands. 13C values in sediments from the main reservoir (−19.5 to −15.7 ‰) were higher than those found in any of the riverine samples, indicating selective retention of particles associated with C4 fraction. Dissolved organic carbon (DOC) concentrations were highest during the end of wet season (2.1 to 6.9 mg l−1), with stable isotope signatures generally between −28 and −22 ‰. A consistent downstream decrease in % organic carbon (%OC) was observed for soils, riverine sediments, and suspended matter. This was likely due to better preservation of the organic fraction in colder high altitude regions, with loss of carbon during downstream spiraling. 13C values for soil and sediment did not exhibit clear altitudinal patterns, but values reflect the full spectrum from C3-dominated to C4-dominated sites. Very low ratios of organic carbon to mineral surface area (OC : SA) were found in reservoir sediments and suspended matter in the lower Tana River, indicating that these are stable OC pools which have undergone extensive degradation. Overall, our study demonstrates that substantial differences occur in both the quantities and origin of suspended sediments and organic carbon along the river profile in this tropical river basin, as well as seasonal differences in the mechanisms causing such variations. [less ▲]

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See detailOrganic matter sources, fluxes and greenhouse gas exchange in the Oubangui River (Congo River basin)
Bouillon, S.; Yambélé, A.; Spencer, R.G.M. et al

in Biogeosciences (2012), 9

The Oubangui is a major tributary of the Congo River, draining an area of 500 000 km2 mainly consisting of wooded savannahs. Here, we report results of a one year long, 2-weekly sampling campaign in ... [more ▼]

The Oubangui is a major tributary of the Congo River, draining an area of 500 000 km2 mainly consisting of wooded savannahs. Here, we report results of a one year long, 2-weekly sampling campaign in Bangui (Central African Republic) since March 2010 for a suite of physicochemical and biogeochemical characteristics, including total suspended matter (TSM), bulk concentration and stable isotope composition of particulate organic carbon (POC and 13CPOC), particulate nitrogen (PN and 15NPN), dissolved organic carbon (DOC and 13CDOC), dissolved inorganic carbon (DIC and 13CDIC), dissolved greenhouse gases (CO2, CH4 and N2O), and dissolved ignin composition. 13C signatures of both POC and DOC showed strong seasonal variations −30.6 to −25.8 ‰, and −31.8 to −27.1 ‰, respectively), but their different timing indicates that the origins of POC and DOC may vary strongly over the hydrograph and are largely ncoupled, differing up to 6‰ in 13C signatures. Dissolved lignin characteristics (carbon- ormalised yields, cinnamyl:vanillyl phenol ratios, and vanillic acid to vanillin ratios) showed arked differences between high and low discharge conditions, consistent with major seasonal ariations in the sources of dissolved organic matter. We observed a strong seasonality in pCO2, ranging between 470 ± 203 ppm for Q<1000m3 s−1 (n = 10) to a maximum of 3750 pm during the first stage of the rising discharge. The low POC/PN ratios, high %POCand low and variable 13CPOC signatures during low flow conditions suggest that the majority of the POC pool during this period consists of in situ produced phytoplankton, consistent with oncurrent pCO2 (partial pressure of CO2) values only slightly above and, occasionally, below atmospheric equilibrium. Water-atmosphere CO2 fluxes estimated using two independent pproaches averaged 105 and 204 gCm−2 yr−1, i.e. more than an order of magnitude lower than current estimates for large tropical rivers globally. Although tropical rivers are often ssumed to show much higher CO2 effluxes compared to temperate systems, we show that in situ production may be high enough to dominate the particulate organic carbon pool, and lower CO2 values to near equilibrium values during low discharge conditions. The total annual flux of TSM, POC, PN, DOC and DIC are 2.33 Tg yr−1, 0.14 TgC yr−1, 0.014 TgNyr−1, 0.70 TgC yr−1, and 0.49 Tg Cyr−1, respectively. While our TSM and POC fluxes are similar to previous stimates for the Oubangui, DOC fluxes were 30% higher and bicarbonate fluxes were 35% ower than previous reports. DIC represented 58% of the total annual C flux, and under the ssumptions that carbonate weathering represents 25% of the DIC flux and that CO2 from espiration drives chemical weathering, this flux is equivalent to 50% of terrestrial-derived riverine C transport. [less ▲]

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See detailFirst assessment of the biogeochemistry of the Congo River and tributaries
Darchambeau, François ULg; Bouillon, S.; Wabakanghanzi, J. N. et al

Poster (2011, April 08)

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See detailMicrobial Diversity and Processes in Lake Kivu (East Africa)
Llirós, M.; Darchambeau, François ULg; Garcia-Armisen, T. et al

Conference (2011)

Lake Kivu is a deep meromictic and oligotrophic tropical African lake with a permanent thermal- and haline stratification with huge accumulations of dissolved CO2 and CH4 (ca. 300 km3 and 60 km3 ... [more ▼]

Lake Kivu is a deep meromictic and oligotrophic tropical African lake with a permanent thermal- and haline stratification with huge accumulations of dissolved CO2 and CH4 (ca. 300 km3 and 60 km3, respectively) in the deep anoxic monimolimnion (from 60 o 480 m depth). Although there are a wealth of information on the ecology of small eukaryotes and their trophic role on Kivu, available information on prokaryotic planktonic assemblages is scarce. Molecular analysis of archaeal and bacterial communities showed a vertical segregation imposed by the permanent redoxcline. In relation to Bacteria, Actinobacteria, Betaproteobacteria, Green Sulfur Bacteria and Bacteroidetes were the most commonly retrieved groups. For Archaea, a marked dominance of Thaumarchaeota and Crenarchaeota (75% of all archaeal OTUs) over Euryarchaeota was observed. In the anoxic hypolimnion, Euryarchaoeta (Methanosarcinales and Methanocellales) lineages together with Miscellaneous Crenarchaeotic Group phylotypes were mainly recovered. In turn, Thaumarchaeota phylotypes were recovered in oxic and suboxic waters. CARDFISH analyses over the first 100 m revealed the dominance of Bacteria (51.4% – 95.7% of DAPI-stained cells), especially Actinobacteria (epilimnion), Betaproteobacteria (oxic-anoxic interface) and Bacteroidetes (upper hypolimnion), over Archaea (1.0% – 4.5%; maximum abundances at the oxic-anoxic interface). In turn, flow cytometry evidenced the dominance of HNA cells in the euphotic layer, whereas the proportion of LNA cells increased with depth. HNA and LNA populations were still observed in the anoxic hypolimnion suggesting facultative or strict anaerobic metabolisms. The detection of distinct depth maxima of nitrate, nitrite, archaeal amoA and Marine Thaumarchaeota 16S gene copy numbers together with regularly detection of deep maxima of 3H-Thymidine uptake, and the presence of low-light adapted GSB species point towards a strong link of N, C, and S cycles in the redoxcline of Lake Kivu. [less ▲]

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