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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 detailThe age of river-transported carbon: A global perspective
Marwick, Trent R.; Tamooh, Fredrick; Teodoru, Cristian R. et al

in Global Biogeochemical Cycles (2015), 29(2), 122--137

The role played by river networks in regional and global carbon (C) budgets is receiving increasing attention. Despite the potential of radiocarbon measurements (Δ14C) to elucidate sources and cycling of ... [more ▼]

The role played by river networks in regional and global carbon (C) budgets is receiving increasing attention. Despite the potential of radiocarbon measurements (Δ14C) to elucidate sources and cycling of different riverine C pools, there remain large regions for which no data are available and no comprehensive attempts to synthesize the available information and examine global patterns in the 14C content of different riverine C pools. Here we present new 14C data on particulate and dissolved organic C (POC and DOC) from six river basins in tropical and subtropical Africa and compiled >1400 literature Δ14C data and ancillary parameters from rivers globally. Our analysis reveals a consistent pattern whereby POC is progressively older in systems carrying higher sediment loads, coinciding with a lower organic carbon content. At the global scale, this pattern leads to a proposed global median Δ14C signature of −203‰, corresponding to an age of ~1800 years B.P. For DOC exported to the coastal zone, we predict a modern (decadal) age (Δ14C = +22 to +46‰), and paired data sets confirm that riverine DOC is generally more recent in origin than POC—in contrast to the situation in ocean environments. Weathering regimes complicate the interpretation of 14C ages of dissolved inorganic carbon, but the available data favor the hypothesis that in most cases, more recent organic C is preferentially mineralized. [less ▲]

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See detailTechnical Note: Large overestimation of pCO2 calculated from pH and alkalinity in acidic, organic-rich freshwaters
Abril, G; Bouillon, S; Darchambeau, François ULg et al

in Biogeosciences (2015), 12(1), 67-78

Inland waters have been recognized as a significant source of carbon dioxide (CO2) to the atmosphere at the global scale. Fluxes of CO2 between aquatic systems and the atmosphere are calculated from the ... [more ▼]

Inland waters have been recognized as a significant source of carbon dioxide (CO2) to the atmosphere at the global scale. Fluxes of CO2 between aquatic systems and the atmosphere are calculated from the gas transfer velocity and the water–air gradient of the partial pressure of CO2 (pCO2). Currently, direct measurements of water pCO2 remain scarce in freshwaters, and most published pCO2 data are calculated from temperature, pH and total alkalinity (TA). Here, we compare calculated (pH and TA) and measured (equilibrator and headspace) water pCO2 in a large array of temperate and tropical freshwaters. The 761 data points cover a wide range of values for TA (0 to 14 200 μmol L􀀀1), pH (3.94 to 9.17), measured pCO2 (36 to 23 000 ppmv), and dissolved organic carbon (DOC) (29 to 3970 μmol L􀀀1). Calculated pCO2 were >10% higher than measured pCO2 in 60% of the samples (with a median overestimation of calculated pCO2 compared to measured pCO2 of 2560 ppmv) and were >100% higher in the 25% most organic-rich and acidic samples (with a median overestimation of 9080 ppmv). We suggest these large overestimations of calculated pCO2 with respect to measured pCO2 are due to the combination of two cumulative effects: (1) a more significant contribution of organic acids anions to TA in waters with low carbonate alkalinity and high DOC concentrations; (2) a lower buffering capacity of the carbonate system at low pH, which increases the sensitivity of calculated pCO2 to TA in acidic and organicrich waters. No empirical relationship could be derived from our data set in order to correct calculated pCO2 for this bias. Owing to the widespread distribution of acidic, organic-rich freshwaters, we conclude that regional and global estimates of CO2 outgassing from freshwaters based on pH and TA data only are most likely overestimated, although the magnitude of the overestimation needs further quantitative analysis. Direct measurements of pCO2 are recommended in inland waters in general, and in particular in acidic, poorly buffered freshwaters [less ▲]

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See detailBacterial Community Composition in Three Freshwater Reservoirs of Different Alkalinity and Trophic Status
Llirós, Marc; Inceoğlu, Özgul; García-Armisen, Tamara et al

in PLoS ONE (2014)

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See detailThe effects of Triclosan on the metabolism of developing Sheepshead minnow (Cyprinodon variegatus) larvae
Lallemand, Lise; Voisin, Anne-Sophie; Darchambeau, François ULg et al

Poster (2014, December)

The aquatic environment represents the final sink for many chemicals, including bactericidal agents. Among them Triclosan (TCS) has been shown to affect the thyroid system of teleost. Thyroid hormones are ... [more ▼]

The aquatic environment represents the final sink for many chemicals, including bactericidal agents. Among them Triclosan (TCS) has been shown to affect the thyroid system of teleost. Thyroid hormones are involved in the control of metabolism, so changes in hormone levels induced by triclosan may affect respiratory rates and antioxidant stress in exposed fish. Couples of three females and two males were placed in breeding chambers designed for this experiment. Eggs were collected and maintained in seawater. Embryos were selected under a dissection microscope, randomly assigned to each of five treatment groups: Control, DMSO control, 20 μg/L TCS, 50 μg/L TCS and 100 μg/L TCS and placed in incubation dishes (50 per dish) at 25°C. On day 6, embryos hatched and larvae were transferred to 1L dishes. The larvae were fed on artemias and on flaked fish food till day 15 and 30 post hatching when the fish were analyzed. Respiratory rate measurements were carried out by respirometry and assays of antioxidant enzymes, Glutathionreductase (GR), glutathione peroxidase (GPx) and glutathione-S-transferase (GST) were conducted to determine the presence of oxidative stress. Respirometry showed that TCS exposed fish exhibited decreased the metabolism at 15 dph, whereas no differences in respiration rate could be observed between control and exposed larvae at 30 dph. At 15 dph no difference was observed for any of the antioxidant enzymes, whereas at 30 dph a sharp increase in the activity of GR was observed between the control and TCS exposed fish. The activity of GST and Gpx remained stable. Thyroid hormones are major factors controlling the metabolic rate related to respiration and oxidative stress. TCS reduced the metabolism at 15 dph that corresponds to the moment where larvae to juvenile transition of Sheepshead minnows occur. Previous experiments showed that TCS induces an increase in thyroid hormone concentrations and hyperthyroidism induces oxidative stress. So our observed increase of antioxidant protection mechanisms could be a way to compensate oxidative stress. On the other hand, the changes in GR activity observed at 30 dph, may also be related to the reduced metabolism at 15 dph. [less ▲]

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See detailTurnover rates of carbon and nitrogen stable isotopes in the amphipod Gammarus aequicauda: insights for trophic studies of Mediterranean macrophytodetritus accumulation.
Remy, François ULg; Melchior, Aurélie; Darchambeau, François ULg et al

Conference (2014, August 04)

A quite diverse and abundant macrofauna assemblage is found in the Mediterranean Sea in exported Posidonia oceanica macrophytodétritus accumulations along with meiofauna, microalgae, fungi and bacteria ... [more ▼]

A quite diverse and abundant macrofauna assemblage is found in the Mediterranean Sea in exported Posidonia oceanica macrophytodétritus accumulations along with meiofauna, microalgae, fungi and bacteria. This study focused on a dominant vagile macroinvertebrate species living and feeding in exported dead P.oceanica leaves litter from Calvi Bay (Corsica, France): Gammarus aequicauda. Results of gut content observations and stable isotope analysis (SIAR data) showed clearly that G. aequicauda is the most important dead P. oceanica consumer with up to 50% of dead leaves contribution. An isotopic turnover experiment was conducted with 3 controlled simultaneous treatments: 1. amphipod feeding for 43 days, 2. Green algae feeding for 30 days and 3. Posidonia oceanica litter feeding for 30 days. Individuals (n = 12 to 16) have been sampled every 7 days and whole individual stable isotope analysis have been conducted. An exponential decay regression model and calculations resulted in half-lives for C ranging from 11.72 days (treatment 1) to 51.62 days (treatment 3). Treatment 2 data did not allow us to fit a curve, consequence of a potentially very low turnover rate. For N, no significant increase or decrease of the δ15N values have been observed, and we thus concluded that δ15N was at the equilibrium from the beginning to the end of the experiment. It appears that amphipods feeding on low quality food (high to very high C/N ratio) like algae and Neptune grass dead leaves, show a lower turnover rate for C than amphipods feeding on a high quality animal food (low C/N ratio). Carbon and Nitrogen stable isotope “Trophic Enrichment Factor” (TEF) were calculated for treatments where δ13C or δ15N were at the equilibrium at the end of the experiment. Calculated TEF for nitrogen ranged from 0.53‰ ± 0.439 to 0.96‰ ± 0.424 for treatment 2 and 3 (consistent with detritus-feeder invertebrate values) and was 2.91‰ ± 0.558 for treatment 1 (consistent with predator invertebrate values). For C calculations, a TEF of 0,81‰± 0.39 for treatment 1 and a TEF of 1.19‰ ± 0.824 for treatment 3 were calculated. [less ▲]

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See detailAnaerobic methane oxidation in two tropical freshwater systems
Roland, Fleur ULg; Darchambeau, François ULg; Crowe, SA et al

Poster (2014, May 05)

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See detailAmmonia Oxidising Archaea in the OMZ of a freshwater African Lake
Lliros, M; Ingeoglu, O; Garcia-Armisen, T et al

Poster (2014, May 05)

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See detailRates of microbial sulfur oxidation in low oxygen environments
Crowe, SA; Canfield, DE; Sturm, A et al

Poster (2014, May 05)

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See detailAnaerobic methane oxidation in two tropical freshwater systems
Roland, Fleur ULg; Darchambeau, François ULg; Crowe, SA et al

Poster (2014, April 27)

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See detailProduction of dissolved organic matter by phytoplankton and its uptake by heterotrophic prokaryotes in large tropical lakes
Morana, C; Sarmento, H; Descy, J-P et al

Poster (2014, April 27)

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See detailTemporal variability and spatial distribution of suspended matter and organic C pool in the Zambezi River
Teodoru, C; Bouillon, S; Borges, Alberto ULg et al

Poster (2014, April 27)

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