References of "Borges, Alberto"
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See detailWetlands influencing river biogeochemistry: the case study of the Zambezi and the Kafue Rivers
Teodoru, CR; Nyoni, FC; Nyambe, I et al

Conference (2014)

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See detailCarbon Cycling of Lake Kivu (East Africa): Net Autotrophy in the Epilimnion and Emission of CO2 to the Atmosphere Sustained by Geogenic Inputs
Borges, Alberto ULg; Morana, C; Bouillon, S et al

in PLoS ONE (2014), 9(10), 109500

We report organic and inorganic carbon distributions and fluxes in a large (>2000 km2) oligotrophic, tropical lake (Lake Kivu, East Africa), acquired during four field surveys, that captured the seasonal ... [more ▼]

We report organic and inorganic carbon distributions and fluxes in a large (>2000 km2) oligotrophic, tropical lake (Lake Kivu, East Africa), acquired during four field surveys, that captured the seasonal variations (March 2007–mid rainy season, September 2007–late dry season, June 2008–early dry season, and April 2009–late rainy season). The partial pressure of CO2 (pCO2) in surface waters of the main basin of Lake Kivu showed modest spatial (coefficient of variation between 3% and 6%), and seasonal variations with an amplitude of 163 ppm (between 579±23 ppm on average in March 2007 and 742±28 ppm on average in September 2007). The most prominent spatial feature of the pCO2 distribution was the very high pCO2 values in Kabuno Bay (a small sub-basin with little connection to the main lake) ranging between 11213 ppm and 14213 ppm (between 18 and 26 times higher than in the main basin). Surface waters of the main basin of Lake Kivu were a net source of CO2 to the atmosphere at an average rate of 10.8 mmol m−2 d−1, which is lower than the global average reported for freshwater, saline, and volcanic lakes. In Kabuno Bay, the CO2 emission to the atmosphere was on average 500.7 mmol m−2 d−1 (~46 times higher than in the main basin). Based on whole-lake mass balance of dissolved inorganic carbon (DIC) bulk concentrations and of its stable carbon isotope composition, we show that the epilimnion of Lake Kivu was net autotrophic. This is due to the modest river inputs of organic carbon owing to the small ratio of catchment area to lake surface area (2.15). The carbon budget implies that the CO2 emission to the atmosphere must be sustained by DIC inputs of geogenic origin from deep geothermal springs. [less ▲]

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See detailNew Insights into Iron-Based Photosynthesis
Thompson, K; Lliros, M; Borrego, C et al

Conference (2014)

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See detailDisproportionate contribution of riparian inputs to organic carbon pools in freshwater systems
Marwick, T.R.; Borges, Alberto ULg; Van Acker, K. et al

in Ecosystems (2014), 17

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See detailContrasting biogeochemical characteristics of the Oubangui River and tributaries (Congo River basin)
Bouillon, Steven; Yambélé, Athanase; Gillikin, David P. et al

in Scientific Reports (2014), 4

The Oubangui is a major tributary of the Congo River. We describe the biogeochemistry of contrasting tributaries within its central catchment, with watershed vegetation ranging from wooded savannahs to ... [more ▼]

The Oubangui is a major tributary of the Congo River. We describe the biogeochemistry of contrasting tributaries within its central catchment, with watershed vegetation ranging from wooded savannahs to humid rainforest. Compared to a 2-year monitoring record on the mainstem Oubangui, these tributaries show a wide range of biogeochemical signatures, from highly diluted blackwaters (low turbidity, pH, conductivity, and total alkalinity) in rainforests to those more typical for savannah systems. Spectral analyses of chromophoric dissolved organic matter showed wide temporal variations in the Oubangui compared to spatio-temporal variations in the tributaries, and confirm that different pools of dissolved organic carbon are mobilized during different hydrological stages. d13C of dissolved inorganic carbon ranged between -28.1 per mil and -25.8 per mil, and was strongly correlated to both partial pressure of CO2 and to the estimated contribution of carbonate weathering to total alkalinity, suggesting an important control of the weathering regime on CO2 fluxes. All tributaries were oversaturated in dissolved greenhouse gases (CH4, N2O, CO2), with highest levels in rivers draining rainforest. The high diversity observed underscores the importance of sampling that covers the variability in subcatchment characteristics, to improve our understanding of biogeochemical cycling in the Congo Basin. [less ▲]

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See detailCurrent systematic carbon-cycle observations and the need for implementing a policy-relevant carbon observing system
Ciais, P.; Dolman, A. J.; Bombelli, A. et al

in Biogeosciences (2014), 11(13), 3547--3602

A globally integrated carbon observation and analysis system is needed to improve the fundamental understanding of the global carbon cycle, to improve our ability to project future changes, and to verify ... [more ▼]

A globally integrated carbon observation and analysis system is needed to improve the fundamental understanding of the global carbon cycle, to improve our ability to project future changes, and to verify the effectiveness of policies aiming to reduce greenhouse gas emissions and increase carbon sequestration. Building an integrated carbon observation system requires transformational advances from the existing sparse, exploratory framework towards a dense, robust, and sustained system in all components: anthropogenic emissions, the atmosphere, the ocean, and the terrestrial biosphere. The paper is addressed to scientists, policymakers, and funding agencies who need to have a global picture of the current state of the (diverse) carbon observations.We identify the current state of carbon observations, and the needs and notional requirements for a global integrated carbon observation system that can be built in the next decade. A key conclusion is the substantial expansion of the ground-based observation networks required to reach the high spatial resolution for CO2 and CH4 fluxes, and for carbon stocks for addressing policy-relevant objectives, and attributing flux changes to underlying processes in each region. In order to establish flux and stock diagnostics over areas such as the southern oceans, tropical forests, and the Arctic, in situ observations will have to be complemented with remote-sensing measurements. Remote sensing offers the advantage of dense spatial coverage and frequent revisit. A key challenge is to bring remote-sensing measurements to a level of long-term consistency and accuracy so that they can be efficiently combined in models to reduce uncertainties, in synergy with groundbased data. Bringing tight observational constraints on fossil fuel and land use change emissions will be the biggest challenge for deployment of a policy-relevant integrated carbon observation system. This will require in situ and remotely sensed data at much higher resolution and density than currently achieved for natural fluxes, although over a small land area (cities, industrial sites, power plants), as well as the inclusion of fossil fuel CO2 proxy measurements such as radiocarbon in CO2 and carbon-fuel combustion tracers. Additionally, a policy-relevant carbon monitoring system should also provide mechanisms for reconciling regional top-down (atmosphere-based) and bottom-up (surface-based) flux estimates across the range of spatial and temporal scales relevant to mitigation policies. In addition, uncertainties for each observation data-stream should be assessed. The success of the system will rely on long-term commitments to monitoring, on improved international collaboration to fill gaps in the current observations, on sustained efforts to improve access to the different data streams and make databases interoperable, and on the calibration of each component of the system to agreed-upon international scales. [less ▲]

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See detailProduction of dissolved organic matter by phytoplankton and its uptake by heterotrophic prokaryotes in large tropical lakes
Morana, Cédric; Sarmento, Hugo; Descy, Jean-Pierre et al

in Limnology & Oceanography (2014), 59(4), 1364-1375

In pelagic ecosystems, phytoplankton extracellular release can extensively subsidize the heterotrophic prokaryotic carbon demand. Time-course experiments were carried out to quantify primary production ... [more ▼]

In pelagic ecosystems, phytoplankton extracellular release can extensively subsidize the heterotrophic prokaryotic carbon demand. Time-course experiments were carried out to quantify primary production, phytoplankton excretion, and the microbial uptake of freshly released dissolved organic carbon (DOC) derived from phytoplankton extracellular release (DOCp) in four large tropical lakes distributed along a productivity gradient: Kivu, Edward, Albert, and Victoria. The contributions of the major heterotrophic bacterial groups to the uptake of DOCp was also analyzed in Lake Kivu, using microautoradiography coupled to catalyzed reporter deposition fluorescent in situ hybridization. The percentage of extracellular release (PER) varied across the productivity gradient, with higher values at low productivity. Furthermore, PER was significantly related to high light and low phosphate concentrations in the mixed layer and was comparatively higher in oligotrophic tropical lakes than in their temperate counterparts. Both observations suggest that environmental factors play a key role in the control of phytoplankton excretion. Standing stocks of DOCp were small and generally contributed less than 1% to the total DOC because it was rapidly assimilated by prokaryotes. In other words, there was a tight coupling between the production and the heterotrophic consumption of DOCp. None of the major phylogenetic bacterial groups that were investigated differed in their ability to take up DOCp, in contrast with earlier results reported for standard labeled single-molecule substrates (leucine, glucose, adenosine triphosphate). It supports the idea that the metabolic ability to use DOCp is widespread among heterotrophic prokaryotes. Overall, these results highlight the importance of carbon transfer between phytoplankton and bacterioplankton in large African lakes. [less ▲]

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See detailIncrease in dimethylsulfide (DMS) emissions due to eutrophication of coastal waters offsets their reduction due to ocean acidification
Gypens, N; Borges, Alberto ULg

in Frontiers in Marine Science - Marine Ecosystem Ecology (2014), 1(4),

Available information from manipulative experiments suggested that the emission of dimethylsulfide (DMS) would decrease in response to the accumulation of anthropogenic CO2 in the ocean (ocean ... [more ▼]

Available information from manipulative experiments suggested that the emission of dimethylsulfide (DMS) would decrease in response to the accumulation of anthropogenic CO2 in the ocean (ocean acidification). However, in coastal environments, the carbonate chemistry of surface waters was also strongly modified by eutrophication and related changes in biological activity (increased primary production and change in phytoplankton dominance) during the last 50 years. Here, we tested the hypothesis that DMS emissions in marine coastal environments also strongly responded to eutrophication in addition to ocean acidification at decadal timescales. We used the R-MIRO-BIOGAS model in the eutrophied Southern Bight of the North Sea characterized by intense blooms of Phaeocystis that are high producers of dimethylsulfoniopropionate (DMSP), the precursor of DMS. We showed that, for the period from 1951 to 2007, eutrophication actually led to an increase of DMS emissions much stronger than the response of DMS emissions to ocean acidification. [less ▲]

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See detailAir-Sea Interactions of Natural Long-Lived Greenhouse Gases (CO2, N2O, CH4) in a Changing Climate
Bakker, Dorothee C. E.; Bange, Hermann W.; Gruber, Nicolas et al

in Ocean-Atmosphere Interactions of Gases and Particles (2014)

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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 detailThe Dimethylsulfide Cycle in the Eutrophied Southern North Sea: A Model Study Integrating Phytoplankton and Bacterial Processes
Gypens, N; Borges, Alberto ULg; Speeckaert, Gaëlle ULg et al

in Plos One (2014), 9(1)(e85862 DOI: 10.1371/journal.pone.0085862),

We developed a module describing the dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) dynamics, including biological transformations by phytoplankton and bacteria, and physico-chemical ... [more ▼]

We developed a module describing the dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) dynamics, including biological transformations by phytoplankton and bacteria, and physico-chemical processes (including DMS air-sea exchange). This module was integrated in the MIRO ecological model and applied in a 0D frame in the Southern North Sea (SNS). The DMS(P) module is built on parameterizations derived from available knowledge on DMS(P) sources, transformations and sinks, and provides an explicit representation of bacterial activity in contrast to most of existing models that only include phytoplankton process (and abiotic transformations). The model is tested in a highly productive coastal ecosystem (the Belgian coastal zone, BCZ) dominated by diatoms and the Haptophyceae Phaeocystis, respectively low and high DMSP producers. On an annual basis, the particulate DMSP (DMSPp) production simulated in 1989 is mainly related to Phaeocystis colonies (78%) rather than diatoms (13%) and nanoflagellates (9%). Accordingly, sensitivity analysis shows that the model responds more to changes in the sulfur:carbon (S:C) quota and lyase yield of Phaeocystis. DMS originates equally from phytoplankton and bacterial DMSP-lyase activity and only 3% of the DMS is emitted to the atmosphere. Model analysis demonstrates the sensitivity of DMS emission towards the atmosphere to the description and parameterization of biological processes emphasizing the need of adequately representing in models both phytoplankton and bacterial processes affecting DMS(P) dynamics. This is particularly important in eutrophied coastal environments such as the SNS dominated by high non-diatom blooms and where empirical models developed from data-sets biased towards open ocean conditions do not satisfactorily predict the timing and amplitude of the DMS seasonal cycle. In order to predict future feedbacks of DMS emissions on climate, it is needed to account for hotspots of DMS emissions from coastal environments that, if eutrophied, are dominated not only by diatoms. [less ▲]

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See detailSources, transport et transformation du carbone, de l’azote et du phosphore dans le fleuve Niger : résultats après 2 années d’observations à Niamey
Alhou, Bassirou; Darchambeau, François ULg; Bouillon, Steven et al

Conference (2013, December 05)

Le fleuve Niger est le troisième plus important fleuve d'Afrique et draine une superficie d'environ 2 120 000 km². Il englobe six régions hydrographiques caractéristiques des écosystèmes de l’Afrique ... [more ▼]

Le fleuve Niger est le troisième plus important fleuve d'Afrique et draine une superficie d'environ 2 120 000 km². Il englobe six régions hydrographiques caractéristiques des écosystèmes de l’Afrique occidentale. Nonobstant l’importance de ce fleuve à l’échelle régionale et continentale, peu de données ont été récemment collectées sur la biogéochimie du fleuve et en particulier sur son rôle dans le transport et la transformation de la matière, dont le carbone, l’azote et le phosphore. La présente communication traite des résultats d’un suivi sur deux années, d’avril 2011 à mars 2013 dans le Niger moyen, en amont de la ville de Niamey (Niger) [2.01° E, 13.57° N], selon une fréquence d’observation bihebdomadaire. Les variables mesurées sont la température, la conductivité, l’oxygène dissous, le pH, la matière en suspension (MES), l’alcalinité totale (TA), les différentes formes du carbone (C), de l’azote (N) et du phosphore (P) inorganiques dissous, le C, l’N et le P organiques particulaires, ainsi que la composition isotopique de ces éléments. Une attention particulière est portée aux concentrations des gaz à effet de serre (GES) que sont le dioxyde de carbone (CO2), le méthane (CH4) et l’hémioxide d’azote (N2O). Les débits journaliers du fleuve proviennent de la station de mesure hydrologique de l’autorité du Bassin du Niger (ABN) à Niamey. Les flux annuels ont été calculés par la méthode de Beale pour les régimes stratifiés (Gumleaf v0.1) à partir des débits quotidiens et des concentrations observées. La situation hydrologique a été fort contrastée entre les 2 années d’étude puisque le débit moyen sur la première année était de seulement 674 m3 s-1, soit un des débits les plus faibles enregistrés sur le fleuve à Niamey depuis 1940, et de 1096 m3 s-1, soit une valeur médiane, lors de la deuxième année. Nos résultats montrent que la MES, le carbone organique particulaire, le carbone organique dissous et le carbone inorganique dissous sont principalement transportés lors de la crue locale, engendrée par les précipitations de la mousson en juillet-août. La seconde crue, ou crue guinéenne, qui a lieu de novembre à janvier, est caractérisée par une chute des températures et des eaux claires. Les flux annuels des différentes espèces transportées étaient en relation directe avec les différences de régime hydrologique. [less ▲]

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See detailContribution to the description of the nitrogen cycle in Lake Kivu
Roland, Fleur ULg; Borges, Alberto ULg; Crowe, Sean et al

Poster (2013, November 12)

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See detailLake Kivu: food web structure and energy flows
Descy, J-P; Sarmento, H; Isumbisho, P et al

Conference (2013, August 04)

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See detailCoccolithophore blooms in the Bay of Biscay: Results from the PEACE project
Harlay, Jérôme ULg; Chou, Lei; Sabbe, Koen et al

Conference (2013, May 15)

Pelagic and benthic processes were determined in the nothern Bay of Biscay when coccolithophores blooms occured between 2006 and 2008. Here we present a synthesis of pelagic primary production ... [more ▼]

Pelagic and benthic processes were determined in the nothern Bay of Biscay when coccolithophores blooms occured between 2006 and 2008. Here we present a synthesis of pelagic primary production, calcification and respiration and benthic respiration and dissolution of CaCO3. Or results suggest that CaCO3 dissolution in the surface sediments is small (~1%) compared to integrated pelagic calcification. Benthic respiration increases with the organic load of the sediment and represents ~8% of the integrated pelagic respiration. The relationship between dissolution and respiration rates suggests a metabolic driven dissolution in waters supersaturated with respect to calcite (omega>3.5). We address a mass balance of the described processes and associated CO2 fluxes in the water column. [less ▲]

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