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See detailCarbon dioxide evasion from the Seine River: Drivers analysis and spatiotemporal reconstruction
Marescaux, A; Thieu, v; Borges, Alberto ULiege et al

Conference (2017, February 26)

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See detailHow phosphorus limitation can control climate-active gas sources and sinks
Gypens, Nathalie; Borges, Alberto ULiege; Ghyoot, Caroline

in Journal of Marine Systems (2017), 170

Since the 1950's, anthropogenic activities have increased nutrient river loads to European coastal areas. Subsequent implementation of nutrient reduction policies have led to considerably reduction of ... [more ▼]

Since the 1950's, anthropogenic activities have increased nutrient river loads to European coastal areas. Subsequent implementation of nutrient reduction policies have led to considerably reduction of phosphorus (P) loads from the mid-1980's, while nitrogen (N) loads were maintained, inducing a P limitation of phytoplankton growth in many eutrophied coastal areas such as the Southern Bight f the North Sea (SBNS). When dissolved inorganic phosphorus (DIP) is limiting, most phytoplankton organisms are able to indirectly acquire P from dissolved organic P (DOP). We investigate the impact of DOP use on phytoplankton production and atmospheric fluxes of CO2 and dimethylsulfide (DMS) in the SBNS from 1951 to 2007 using an extended version of the RMIRO-BIOGAS model. This model includes a description of the ability of phytoplankton organisms to use DOP as a source of P. Results show that primary production can increase up to 30% due to DOP uptake under limiting DIP conditions. Consequently, simulated DMS emissions also increase proportionally while CO2 emissions to the atmosphere decrease, relative to the reference simulation without DOP uptake [less ▲]

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See detailDynamics and emissions of N2O in groundwater: A review
Jurado Elices, Anna ULiege; Borges, Alberto ULiege; Brouyère, Serge ULiege

in Science of the Total Environment (2017), 584-585C

This work reviews the concentrations, the dynamics and the emissions of nitrous oxide (N2O) in groundwater. N2O is an important greenhouse gas (GHG) and the primary stratospheric ozone depleting substance ... [more ▼]

This work reviews the concentrations, the dynamics and the emissions of nitrous oxide (N2O) in groundwater. N2O is an important greenhouse gas (GHG) and the primary stratospheric ozone depleting substance. The major anthropogenic source that contributes to N2O generation in aquifers is agriculture because the use of fertilizers has led to the widespread groundwater contamination by inorganic nitrogen (N) (mainly nitrate, NO3−). Once in the aquifer, this inorganic N is transported and affected by several geochemical processes that produce and consume N2O. An inventory of dissolved N2O concentrations is presented and the highest dissolved concentration is about 18.000 times higher than air-equilibrated water (up to 4004 μg N L-1). The accumulation of N2O in groundwater is mainly due to denitrification and to lesser extent to nitrification. Their occurrence depend on the geochemical (e.g., NO3−, dissolved oxygen, ammonium and dissolved organic carbon) as well as hydrogeological parameters (e.g., groundwater table fluctuations and aquifer permeability). The coupled understanding of both parameters is necessary to gain insight on the dynamics and the emissions of N2O in groundwater. Overall, groundwater indirect N2O emissions seem to be a minor component of N2O emissions to the atmosphere. Further research might be devoted to evaluate the groundwater contribution to the indirect emissions of N2O because this will help to better constraint the N2O global budget and, consequently, the N budget. [less ▲]

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See detailShifts in the carbon dynamics in a tropical lowland river system (Tana River, Kenya) during flooded and non-flooded conditions
Geeraert, N.; Omengo, F. O.; Borges, Alberto ULiege et al

in Biogeochemistry (2017), 132(1-2), 141-163

Rivers transport sediment and carbon (C) from the continents to the ocean, whereby the magnitude and timing of these fluxes depend on the hydrological regime. We studied the sediment and carbon dynamics ... [more ▼]

Rivers transport sediment and carbon (C) from the continents to the ocean, whereby the magnitude and timing of these fluxes depend on the hydrological regime. We studied the sediment and carbon dynamics of a tropical river system at two sites along the lower Tana River (Kenya), separated by a 385 km stretch characterized by extensive floodplains, to understand how the river regime affects within-river C processing as well as the C exchange between floodplain and river. Sampling took place during three different wet seasons (2012–2014), with extensive flooding during one of the campaigns. We measured the suspended sediment concentration, the concentration and stable isotope signature of three different carbon species (particulate and dissolved organic carbon, POC and DOC, and dissolved inorganic carbon, DIC) and other auxiliary parameters. During non-flooded conditions, the total C flux was dominated by POC (57–72%) and there was a downstream decrease of the total C flux. DIC was dominating during the flooded season (56–67%) and the flux of DIC and DOC coming from the inundated floodplains resulted in a downstream increase of the total carbon flux. Our data allowed us to construct a conceptual framework for the C dynamics in river systems, whereby nine major fluxes were identified. The application of this framework highlighted the dominance of POC during non-flooded conditions and the significant CO2 emissions during the flooded season. Furthermore, it identified the exchange of POC with the floodplain as an important factor to close the C budget of the river. © 2017, Springer International Publishing Switzerland. [less ▲]

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See detailCalibration of hydroclimate proxies in freshwater bivalve shells from Central and West Africa
Kelemen, Z.; Gillikin, D. P.; Graniero, L. E. et al

in Geochimica et Cosmochimica Acta (2017), 208

Freshwater bivalve shell oxygen and carbon stable isotope ratios (δ18O, δ13C) may act as recorders of hydroclimate (e.g., precipitation-evaporation balance, discharge) and aquatic biogeochemistry. We ... [more ▼]

Freshwater bivalve shell oxygen and carbon stable isotope ratios (δ18O, δ13C) may act as recorders of hydroclimate (e.g., precipitation-evaporation balance, discharge) and aquatic biogeochemistry. We investigate the potential of these hydroclimate proxies measured along the growth axis of shells collected from the Oubangui River (Bangui, Central African Republic) and the Niger River (Niamey, Niger). Biweekly water samples and in situ measurements collected over several years, along with daily discharge data from both sites allowed a direct comparison with proxies recorded in the shells. Data from a total of 14 unionid shells, including three species (Chambardia wissmanni, Aspatharia dahomeyensis, and Aspatharia chaiziana), confirmed that shells precipitate carbonate in oxygen isotope equilibrium with ambient water. Because water temperature variations were small, shell δ18O values (δ18Oshell) also accurately record the seasonality and the range observed in water δ18O (δ18Ow) values when calculated using an average temperature. Calculated δ18Owvalues were in good agreement over the entire record of measured δ18Owvalues, thus δ18Oshellrecords can be reliably used to reconstruct past δ18Owvalues. Discharge and δ18Owvalues from both rivers fit a logarithmic relationship, which was used to attempt reconstruction of past hydrological conditions, after calculating δ18Owvalues from δ18Oshellvalues. A comparison with measured discharge data suggests that for the two rivers considered, δ18Oshelldata are good proxies for recording discharge conditions during low(er) discharge levels, but that high discharge values cannot be accurately reconstructed due to the large scatter in the discharge-δ18Owrelationship. Moreover, periods of bivalve shell growth cessation due to high turbidity or air exposure should be taken into account. While δ13C values of dissolved inorganic carbon in both rivers showed clear seasonality and correlated well with discharge, most of the shells analyzed did not record these variations adequately, likely due to the complication of vital effects including the variable contribution of metabolic CO2. Thus, tropical African unionid δ18Oshellvalues can be used to reconstruct δ18Owvalues with high confidence to provide insight on past hydroclimate such as precipitation-evaporation balance and periods of low discharge. © 2017 Elsevier Ltd [less ▲]

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See detailEmission and oxidation of methane in a meromictic, eutrophic and temperate lake (Dendre, Belgium)
Roland, Fleur ULiege; Darchambeau, François ULiege; Morana, Cédric ULiege et al

in Chemosphere (2017)

We sampled the water column of the Dendre stone pit lake (Belgium) in spring, summer, autumn and winter. Depth profiles of several physico-chemical variables, nutrients, dissolved gases (CO2, CH4, N2O ... [more ▼]

We sampled the water column of the Dendre stone pit lake (Belgium) in spring, summer, autumn and winter. Depth profiles of several physico-chemical variables, nutrients, dissolved gases (CO2, CH4, N2O), sulfate, sulfide, iron and manganese concentrations and d13C-CH4 were determined. We performed incubation experiments to quantify CH4 oxidation rates, with a focus on anaerobic CH4 oxidation (AOM), without and with an inhibitor of sulfate reduction (molybdate). The evolution of nitrate and sulfate concentrations during the incubations was monitored. The water column was anoxic below 20 m throughout the year, and was thermally stratified in summer and autumn. High partial pressure of CO2 and CH4 and high concentrations of ammonium and phosphate were observed in anoxic waters. Important nitrous oxide and nitrate concentration maxima were also observed (up to 440 nmol L- 1 and 80 mmol L -1, respectively). Vertical profiles of d13C-CH4 unambiguously showed the occurrence of AOM. Important AOM rates (up to 14 mmol L -1 d- 1) were observed and often co-occurred with nitrate consumption peaks, suggesting the occurrence of AOM coupled with nitrate reduction. AOM coupled with sulfate reduction also occurred, since AOM rates tended to be lower when molybdate was added. CH4 oxidation was mostly aerobic (~80% of total oxidation) in spring and winter, and almost exclusively anaerobic in summer and autumn. Despite important CH4 oxidation rates, the estimated CH4 fluxes from the water surface to the atmosphere were high (mean of 732 mmol m- 2 d- 1 in spring, summer and autumn, and up to 12,482 mmol m- 2 d- 1 in winter). [less ▲]

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See detailIron-dependent nitrogen cycling in a ferruginous lake and the nutrient status of Proterozoic oceans
Michiels, Celine C.; Darchambeau, François ULiege; Roland, Fleur ULiege et al

in Nature Geoscience (2017), advance online publication

Nitrogen limitation during the Proterozoic has been inferred from the great expanse of ocean anoxia under low-O2 atmospheres, which could have promoted NO3- reduction to N2 and fixed N loss from the ocean ... [more ▼]

Nitrogen limitation during the Proterozoic has been inferred from the great expanse of ocean anoxia under low-O2 atmospheres, which could have promoted NO3- reduction to N2 and fixed N loss from the ocean. The deep oceans were Fe rich (ferruginous) during much of this time, yet the dynamics of N cycling under such conditions remain entirely conceptual, as analogue environments are rare today. Here we use incubation experiments to show that a modern ferruginous basin, Kabuno Bay in East Africa, supports high rates of NO3- reduction. Although 60 of this NO3- is reduced to N2 through canonical denitrification, a large fraction (40\%) is reduced to NH4+, leading to N retention rather than loss. We also find that NO3- reduction is Fe dependent, demonstrating that such reactions occur in natural ferruginous water columns. Numerical modelling of ferruginous upwelling systems, informed by our results from Kabuno Bay, demonstrates that NO3- reduction to NH4+ could have enhanced biological production, fuelling sulfate reduction and the development of mid-water euxinia overlying ferruginous deep oceans. This NO3- reduction to NH4+ could also have partly offset a negative feedback on biological production that accompanies oxygenation of the surface ocean. Our results indicate that N loss in ferruginous upwelling systems may not have kept pace with global N fixation at marine phosphorous concentrations (0.04-0.13[thinsp][mu]M) indicated by the rock record. We therefore suggest that global marine biological production under ferruginous ocean conditions in the Proterozoic eon may thus have been P not N limited. [less ▲]

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See detailProductivity and temperature as drivers of seasonal and spatial variations of dissolved methane in the Southern Bight of the North Sea
Borges, Alberto ULiege; Speeckaert, Gaëlle ULiege; Champenois, Willy ULiege et al

in Ecosystems (2017), doi:10.1007/s10021-017-0171-7

Dissolved CH4 concentrations in the Belgian coastal zone (North Sea) ranged between 670 nmol L-1 near-shore and 4 nmol L-1 off-shore. Spatial variations of CH4 were related to sediment organic matter (OM ... [more ▼]

Dissolved CH4 concentrations in the Belgian coastal zone (North Sea) ranged between 670 nmol L-1 near-shore and 4 nmol L-1 off-shore. Spatial variations of CH4 were related to sediment organic matter (OM) content and gassy sediments. In near-shore stations with fine sand or muddy sediments, the CH4 seasonal cycle followed water temperature, suggesting methanogenesis control by temperature in these OM rich sediments. In off-shore stations with permeable sediments, the CH4 seasonal cycle showed a yearly peak following the Chlorophyll-a spring peak, suggesting that in these OM poor sediments, methanogenesis depended on freshly produced OM delivery. This does not exclude the possibility that some CH4 might originate from dimethylsulfide (DMS) or dimethylsulfoniopropionate (DMSP) or methylphosphonate transformations in the most off-shore stations. Yet, the average seasonal CH4 cycle was unrelated to those of DMS(P), very abundant during the Phaeocystis bloom. The annual average CH4 emission was 126 mmol m-2 yr-1 in the most near-shore stations (~4 km from the coast) and 28 mmol m-2 yr-1 in the most off-shore stations (~23 km from the coast), 1,260 to 280 times higher than the open ocean average value (0.1 mmol m-2 yr-1). The strong control of CH4 by sediment OM content and by temperature suggests that marine coastal CH4 emissions, in particular in shallow areas, should respond to future eutrophication and warming of climate. This is supported by the comparison of CH4 concentrations at five stations obtained in March 1990 and 2016, showing a decreasing trend consistent with alleviation of eutrophication in the area. [less ▲]

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See detailDimethylsulfonopropionate would be a reactive oxygen species scavenger for phytoplankton cell
Royer, Colin ULiege; Borges, Alberto ULiege; Gypens, Nathalie

Diverse speeche and writing (2017)

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See detailEffects of human land use on the terrestrial and aquatic sources of fluvial organic matter in a temperate river basin (The Meuse River, Belgium)
Lambert, Thibault; Bouillon, Steven; Darchambeau, François et al

in Biogeochemistry (2017)

The impact of human activities on the concentrations and composition of dissolved organic matter (DOM) and particulate organic matter (POM) was investigated in the Walloon Region of the Meuse River basin ... [more ▼]

The impact of human activities on the concentrations and composition of dissolved organic matter (DOM) and particulate organic matter (POM) was investigated in the Walloon Region of the Meuse River basin (Belgium). Water samples were collected at different hydrological periods along a gradient of human disturbance (50 sampling sites ranging from 8.0 to 20,407 km2) and during a 1.5 year monitoring of the Meuse River at the city of Liège. This dataset was completed by the characterization of the DOM pool in groundwaters. The composition of DOM and POM was investigated through elemental (C:N ratios), isotopic ($\delta$13C) and optical measurements including excitation emission matrix fluorescence with parallel factor analysis (EEM--PARAFAC). Land use was a major driver on fluvial OM composition at the regional scale of the Meuse Basin, the composition of both fluvial DOM and POM pools showing a shift toward a more microbial/algal and less plant/soil-derived character as human disturbance increased. The comparison of DOM composition between surface and groundwaters demonstrated that this pattern can be attributed in part to the transformation of terrestrial sources by agricultural practices that promote the decomposition of soil organic matter in agricultural lands and subsequent microbial inputs in terrestrial sources. In parallel, human land had contrasting effects on the autochthonous production of DOM and POM. While the in-stream generation of fresh DOM through biological activity was promoted in urban areas, summer autochthonous POM production was not influenced by land use. Finally, soil erosion by agricultural management practices favored the transfer of terrestrial organic matter via the particulate phase. Stable isotope data suggest that the hydrological transfer of terrestrial DOM and POM in human-impacted catchment are not subject to the same controls, and that physical exchange between these two pools of organic matter is limited. [less ▲]

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See detailMethane in the South China Sea and the Western Philippine Sea
Tseng, Hsiao-Chun; Chen, Chen-Tung Arthur; Borges, Alberto ULiege et al

in Continental Shelf Research (2017), 135

Approximately 700 water samples from the South China Sea (SCS) and 300 water samples from the western Philippine Sea (wPS) were collected during eight cruises from August 2003 to July 2007 to determine ... [more ▼]

Approximately 700 water samples from the South China Sea (SCS) and 300 water samples from the western Philippine Sea (wPS) were collected during eight cruises from August 2003 to July 2007 to determine methane (CH4) distributions from the surface to a depth of 4250 m. The surface CH4 concentrations exceeded atmospheric equilibrium, both in the SCS and the wPS, and the concentrations were 4.5±3.6 and 3.0±1.2 nmol L−1, respectively. The sea-to-air fluxes were calculated, and the SCS and the wPS were found to emit CH4 to the atmosphere at 8.6±6.4 µmol m−2 d−1 and 4.9±4.9 µmol m−2 d−1, respectively. In the SCS, CH4 emissions were higher over the continental shelf (11.0±7.4 µmol m−2 d−1) than over the deep ocean (6.1±6.0 µmol m−2 d−1), owing to greater biological productivity and closer coupling with the sediments on the continental shelf. The SCS emitted 30.1×106 mol d−1 CH4 to the atmosphere and exported 1.82×106 mol d−1 CH4 to the wPS. The concentrations of both CH4 and chlorophyll a were high in the 150 m surface layer of the wPS, but were not significantly correlated with each other. CH4 concentrations generally declined with increasing depth below the euphotic zone but remained constant below 1,000 m, both in the SCS and the wPS. Some high CH4 concentrations were observed at mid-depths and bottom waters in the SCS, and were most likely caused by the release of CH4 from gas hydrates or gas seepage. [less ▲]

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See detailHIPE: Human impacts on ecosystem health and resources of Lake Edward; exploring a poorly known ichthyofaunal
Decru, E; Van Steenberge, M; Bouillon, S et al

Poster (2016, December 16)

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See detailCopper toxicity on coral holobiont photosynthetic processes
Georges, Nadège; Richir, Jonathan ULiege; Batigny, Antoine et al

Poster (2016, December 16)

Copper (Cu), an essential micronutrient to organisms, may become toxic when present at too high environmental concentrations. This metal remains an aquatic contaminant of concern, notably because of its ... [more ▼]

Copper (Cu), an essential micronutrient to organisms, may become toxic when present at too high environmental concentrations. This metal remains an aquatic contaminant of concern, notably because of its recent re-use as biocide in metal-based antifouling paints. The aim of this study was to monitor the physiological alterations in a zooxanthellate coral species and its endosymbionts (i.e. the coral holobiont) exposed to increasing Cu concentrations. Nubbins of Seriatopora hystrix were exposed for 8 days in 1 L intermittent respirometers to 5 nominal Cu concentrations: 0-2-5-15-50 ppb. Respirometers were maintained at 25.0±0.2°C with successive open/close cycles of 30 min. A 12/12 hours day-night light regime was applied with constant daylight intensity of 200 μmol photons m-2 s-1. Water renewal rate during the 30 min open cycles was 15 mL.min-1. The photosynthetic performances of coral endosymbionts were assessed daily with a fluorescence imaging system (imaging-PAM). At the end of the 8-days experiment, the maximal photochemical quantum yield (FV/FM) of coral nubbins had decreased by 12% and 38%, respectively, in the 15 ppb and 50 ppb treatments. This decrease was even greater for the effective photochemical quantum yield (ɸPSII) with values dropping by 41% and 54%, respectively. Cu exposure also affected the symbiosis between the coral host and its endosymbionts. Nubbins of the 15 ppb treatment slightly lightened from day 6, whilst nubbins exposed to the 50 ppb treatment lightened from day 3, and started to bleach from day 6. The analysis of nubbins’ primary productivity did not coincide with the above observations, the oxygen production within each respirometer remaining relatively constant during the overall experiment for all treatments. This unexpected observation may be the sign of a compensation mechanism. In conclusion, Cu affected the photosynthetic processes of S. histrix within 8 days from relevant environmental concentrations of 15 ppb. The exposure of corals to toxic chemicals thus has to be considered as an additional stressor to, e.g., ocean acidification or elevated temperature, which may disturb their ecophysiology and lead to bleaching. [less ▲]

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See detailEcoNum, a research unit devoted to marine environment monitoring
Richir, Jonathan ULiege; Batigny, Antoine; Georges, Nadège et al

Conference (2016, October 27)

The monitoring of coastal environments remains a research domain of great interest and concern. Coastal ecosystems are threatened by natural and human-induced stressors and are, as transitional ... [more ▼]

The monitoring of coastal environments remains a research domain of great interest and concern. Coastal ecosystems are threatened by natural and human-induced stressors and are, as transitional environments, particularly sensitive to disturbances. EcoNum first research thematic revolves around hermatypic corals, calcifying organisms, and their adaptation potentials to environmental changes including by using original and patented chemostats. The studied organisms are grown and maintained in artificial mesocosms that simulate environmental conditions of a natural system. This infrastructure allows to perform long-term experiments, giving time to organisms to adapt to the tested conditions (e.g., increased temperature or lowered pH). Longer-term studies have demonstrated that many organisms are more resistant to environmental stressors than previously observed on the short-term. EcoNum also studies coastal plankton abundance and diversity. Plankton is particularly sensitive to physicochemical changes of water bodies. The classification and the enumeration of planktonic organisms require specialized tools in order to analyse time series of multiple samples. EcoNum has developed a software for the semi-automatic classification of planktonic organisms called Zoo/PhytoImage. This software has been used to study a 10-year time series of coastal Mediterranean zooplankton samples. The concomitant analysis of environmental parameters registered at high frequency with specific statistical tools such as the R package pastecs allows to understand the processes governing the changes observed in plankton assemblages. The use and the development of statistical tools in R (e.g., Zoo/Phytoimage, pastecs) is a priority of EcoNum to favour open access knowledge and reproductive sciences. EcoNum research topics also focus on coastal ecotoxicology. Chemicals, including trace elements, remain contaminants of concern, mainly in coastal environments that are the final sink of inland pollution sources. The chemical integrity of coastal ecosystems thus has to be accurately monitored. The partitioning of chemicals between their dissolved, particulate and sedimentary phases does not provide information on their bioavailability. EcoNum thus monitors coastal waters using bioindicator species such as seagrasses, mussels or sand worms. A global map of the contamination of the Mediterranean by trace elements has been drawn using seagrasses has bioindicator species. EcoNum also studies trace element ecology and toxicology. For instance, it has demonstrated the toxicity of copper on the coral Seriatopora hystrix and it's symbiont's photosynthetic processes, or its bioaccumulation and basipetal translocation towards rhizomes in the seagrass Posidonia oceanica as reserve nutrient for subsequent leaf growth. Finally, coastal vegetated systems are potential carbon thinks (or sources) in the global carbon cycle. Therefore, EcoNum studies the primary productivity of seagrass meadows, from the individual to the community, with measuring techniques as diverse as PAM-fluorometry or biomass production determination. To conclude, EcoNum is a research unit devoted to marine environment monitoring. It develops research thematics on major coastal communities such as coral reefs, seagrass beds or plankton assemblages and studies their natural dynamics and the effects of stressors on their global functioning. [less ▲]

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See detailDiversity, dynamics and trophic ecology of animal communities associated to Posidonia oceanica (L.) Delile macrophytodetrital accumulation: synthesis of a ten year study
Lepoint, Gilles ULiege; Borges, Alberto ULiege; Champenois, Willy ULiege et al

Poster (2016, October 17)

In the Mediterranean, Neptune grass Posidonia oceanica, produces a huge quantity of detrital biomass. These macrophytodetritus may accumulate in shallow waters, forming litter accumulations colonised by ... [more ▼]

In the Mediterranean, Neptune grass Posidonia oceanica, produces a huge quantity of detrital biomass. These macrophytodetritus may accumulate in shallow waters, forming litter accumulations colonised by abundant, yet understudied, animal communities. These accumulations are especially foraged by juvenile and adult fishes. Here, we aim to synthesize results obtained over the last ten years regarding diversity, dynamics and trophic ecology of associated meio- and macrofauna. Accumulations are found throughout the year but important seasonal and short-term variability in composition, quantity and physico-chemical parameters inside the accumulation is observed. Accumulations are dominated by respiration (litter degradation), however, primary production occurs at exposed surfaces (epiphytic production). Meio- and macrofauna have distinct traits in comparison to adjacent habitats (seagrass meadows or epilithic algae communities). A physico-chemical gradient occurs inside accumulations which partially defines assemblage composition and distribution. Meiofauna, in particular harpacticoid copepods, is diverse, abundant and composed of species from seagrass meadows, water column and sediment. In contrast, macrofaunal assemblages are simplified compared to the ones occurring in the seagrass meadows and are dominated by amphipods. Litter accumulations display a lower macrofaunal diversity than do seagrass meadows, but a higher abundance and animal biomass. Meio- and macrofauna show a high trophic diversity, dominated by ingestion and assimilation of epiphytes (macroalgae and, probably, detrivorous microbiota). Moreover, direct or indirect assimilation of carbon originating from seagrass detritus is demonstrated for many species. Although diverse trophic niches were observed, the assemblage showed a simplified trophic web structure compared to the seagrass meadows. Detritivorous organisms dominate this assemblage and are more abundant in the litter than in the living meadows. Consequently, according to its abundance and the fact it consumes directly and indirectly seagrass material, fauna associated to litter accumulation may play a significant role in the degradation and transfer to higher trophic level of detrital seagrass carbon. [less ▲]

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See detailShift in the chemical composition of dissolved organic matter in the Congo River network
Lambert, Thibault ULiege; Bouillon, S.; Darchambeau, François ULiege et al

in Biogeosciences (2016), 13(18), 5405-5420

The processing of terrestrially derived dissolved organic matter (DOM) during downstream transport in fluvial networks is poorly understood. Here, we report a dataset of dissolved organic carbon (DOC ... [more ▼]

The processing of terrestrially derived dissolved organic matter (DOM) during downstream transport in fluvial networks is poorly understood. Here, we report a dataset of dissolved organic carbon (DOC) concentrations and DOM composition (stable carbon isotope ratios, absorption and fluorescence properties) acquired along a 1700 km transect in the middle reach of the Congo River Basin. Samples were collected in the mainstem and its tributaries during high water (HW) and falling water (FW) periods. DOC concentrations and DOM composition along the mainstem were found to differ between the two periods, because of a reduced lateral mixing between the central water masses of the Congo River and DOM-rich waters from tributaries and also likely because of a greater photodegradation during FW as water residence time (WRT) increased. Although the Cuvette Centrale wetland (one of the world’s largest flooded forest) continuously releases highly aromatic DOM in streams and rivers of the Congo Basin, the downstream transport of DOM was found to result in an along stream gradient from aromatic to aliphatic compounds. The characterization of DOM through parallel factor analysis (PARAFAC) suggests that this transition results from (1) the losses of aromatic compounds by photodegradation and (2) the production of aliphatic compounds by biological reworking of terrestrial DOM. Finally, this study highlights the critical importance of the river-floodplain connectivity in tropical rivers in controlling DOM biogeochemistry at large spatial scale and suggests that the degree of DOM processing during downstream transport is a function of landscape characteristics and WRT [less ▲]

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See detailOccurrence of greenhouse gases (CO2, N2O and CH4) in groundwater of the Walloon Region (Belgium)
Jurado Elices, Anna ULiege; Borges, Alberto ULiege; Hakoun, Vivien et al

Conference (2016, September 27)

Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) can be indirectly transferred to the atmosphere through groundwater discharge into surface water bodies such as rivers. However, these emissions ... [more ▼]

Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) can be indirectly transferred to the atmosphere through groundwater discharge into surface water bodies such as rivers. However, these emissions are poorly evaluated and highly uncertain. The aim of this work is identify the hydrogeological contexts (alluvial, sandstone, chalk and limestone aquifers) and in situ conditions which are most conducive to the generation and occurrence of GHGs in groundwater at a regional scale. To this end, CO2, CH4 and N2O concentrations as well as major and minor elements were monitored (n=37 samples) in two field campaigns (09/2014 and 03/2015) in 15 groundwater bodies of the Walloon Region (Belgium). This preliminary work, which was presented in the 42st IAH conference (Rome, Italy), shown that GHG concentrations range from 5,160 to 47,544 ppm from the partial pressure of CO2 and from 0 to 1,064 nmol/L and 1 to 5,637 nmol/L for CH4 and N2O respectively. Overall, groundwater was supersaturated in GHGs with respect to atmospheric equilibrium, suggesting that groundwater contribute to the atmospheric GHGs budget. A third sampling campaign is carried out in 2016 including around 60 new groundwater samples. The combination of the results of the three campaigns allows: (1) reducing the uncertainties related to indirect emissions of GHG through groundwater-surface water interaction and (2) contributing to a better understanding of the occurrence of GHGs in aquifers. New results will be presented and discussed in detail in the presentation. [less ▲]

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See detailMassive marine methane emissions from near-shore shallow coastal areas
Borges, Alberto ULiege; Champenois, Willy ULiege; Gypens, N et al

in Scientific Reports (2016), 6

Methane is the second most important greenhouse gas contributing to climate warming. The open ocean is a minor source of methane to the atmosphere. We report intense methane emissions from the near-shore ... [more ▼]

Methane is the second most important greenhouse gas contributing to climate warming. The open ocean is a minor source of methane to the atmosphere. We report intense methane emissions from the near-shore southern region of the North Sea characterized by the presence of extensive areas with gassy sediments. The average flux intensities (~130 μmol m−2 d−1) are one order of magnitude higher than values characteristic of continental shelves (~30 μmol m−2 d−1) and three orders of magnitude higher than values characteristic of the open ocean (~0.4 μmol m−2 d−1). The high methane concentrations (up to 1,128 nmol L−1) that sustain these fluxes are related to the shallow and well-mixed water column that allows an efficient transfer of methane from the seafloor to surface waters. This differs from deeper and stratified seep areas where there is a large decrease of methane between bottom and surface by microbial oxidation or physical transport. Shallow well-mixed continental shelves represent about 33% of the total continental shelf area, so that marine coastal methane emissions are probably under-estimated. Near-shore and shallow seep areas are hot spots of methane emission, and our data also suggest that emissions could increase in response to warming of surface waters. [less ▲]

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