References of "Borges, Alberto"
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See detailStandard Operating Protocol: Quantification of methane and nitrous oxide via headspace equilibrium
de la Paz, M; Ferron, S; Borges, Alberto ULiege et al

in Wilson, S; Upstill-Goddard, RC (Eds.) A Best Practice Guide to Dissolved CH4 and N2O Measurements (in press)

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See detail5.1 The Meuse River basin
Descy, Jean-Pierre ULiege; Latli, A; Roland, Fleur ULiege et al

in Rivers of Europe (in press)

The Meuse is an international river that has been used by man for centuries and it is still the main source of drinking water for large cities in Belgium and the Netherlands. In fact, water quantity and ... [more ▼]

The Meuse is an international river that has been used by man for centuries and it is still the main source of drinking water for large cities in Belgium and the Netherlands. In fact, water quantity and quality have been a major issue between the various riparian countries and political regions. Many kinds of data have been generated in the past decades on various aspects of the river: (a) hydrology for the need of predicting and controlling floods; (b) water chemistry in the context of water pollution assessment and control; and (c) biology and ecology for water quality assessment and studies on aquatic biodiversity community dynamics and ecosystem function. [less ▲]

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See detailMethane paradox in tropical lakes? Sedimentary fluxes rather than pelagic production in oxic conditions sustain methanotrophy and emissions to the atmosphere
Morana, Cédric ULiege; Bouillon, S; Nolla-Ardèvol, V et al

Conference (2021, June 22)

Despite growing evidence that methane (CH4) formation could also occur in well-oxygenated surface freshwaters, its significance at the ecosystem scale is uncertain. Empirical models based on data gathered ... [more ▼]

Despite growing evidence that methane (CH4) formation could also occur in well-oxygenated surface freshwaters, its significance at the ecosystem scale is uncertain. Empirical models based on data gathered at high latitude predict that the contribution of oxic CH4 increases with lake size and should represent the majority of CH4 emissions in large lakes. However, such predictive models could not directly apply to tropical lakes which differ from their temperate counterparts in some fundamental characteristics, such as year-round elevated water temperature. We conducted stable isotope tracer experiments which revealed that oxic CH4 production is closely related to phytoplankton metabolism, and is a common feature in five contrasting African lakes. Nevertheless, methanotrophic activity in surface waters and CH4 emissions to the atmosphere were predominantly fuelled by CH4 generated in sediments and physically transported to the surface. Indeed, CH4 bubble dissolution flux and diffusive benthic CH4 flux were several orders of magnitude higher than CH4 production in surface waters. Microbial CH4 consumption dramatically decreased with increasing sunlight intensity, suggesting that the freshwater “CH4 paradox” might be also partly explained by photo-inhibition of CH4 oxidizers in the illuminated zone. Sunlight appeared as an overlooked but important factor determining the CH4 dynamics in surface waters, directly affecting its production by photoautotrophs and consumption by methanotrophs. [less ▲]

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See detailFreshwater bivalve shells as hydrologic archives in the Congo Basin
Kelemen, Z; Gillikin, DP; Borges, Alberto ULiege et al

in Geochimica et Cosmochimica Acta (2021), 308(0), 101-117

We test the applicability of bivalve shell oxygen isotope composition to reconstruct hydrological dynamics in four riverine sites in the Congo River basin. Twenty-three specimens from the Unionoida order ... [more ▼]

We test the applicability of bivalve shell oxygen isotope composition to reconstruct hydrological dynamics in four riverine sites in the Congo River basin. Twenty-three specimens from the Unionoida order were collected from locations where long-term discharge data are available, and in situ measurements and water samples were collected over several years. Due to the highly variable (species-specific) shell morphology, various sampling techniques were used to analyze the shell sections; however, every specimen recorded the seasonality of the host water oxygen stable isotope composition (δ 18 O w ) in its δ 18 O shell record. Discharge data showed an inverse relationship with δ 18 O w values, which was well described with a logarithmic fit. An exception was the Kasai River, where the δ 18 O w record shows an additional peak occurring during the high discharge period, which renders the discharge-δ 18 O w relationship more complex than in the other systems investigated. Low ratios of maximum to minimum discharge (Q max /Q min ) were found to result in a low δ 18 O w amplitude, which was reflected as low δ 18 O shell variability. The Congo and Kasai rivers had Q max /Q min ratios ~2 to 2.5, while the Oubangui showed a much higher Q max /Q min (~19). Shells correspondingly showed a large δ 18 O shell range (amplitude between 2.4 and 5.0‰) for individual Oubangui shells, and lower amplitude for other sites (1.0 to 2.2‰). Thus, shells have a high resolving power to be used to record hydrological variability, since long-term changes in precipitation pattern, discharge, land-use change, or other hydrological changes have an influence on δ 18 O w values. Shells with wide range of δ 18 O values reflect high seasonal variability in rivers, while shells with lower δ 18O amplitude correspond to sites with more steady river conditions over the year. Our study illustrates that fossil shell δ 18 O values could indicate Q max /Q min values in ancient African river systems. [less ▲]

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See detailLimnological changes in Lake Victoria since the mid-20th century
Deirmendjian, Loris ULiege; Descy, Jean-Pierre ULiege; Morana, Cédric ULiege et al

in Freshwater Biology (2021)

1. Lake Victoria experienced a strong degradation of water quality between the 1960s and the 1990s and, as a consequence of eutrophication, the dominant phytoplankton group changed from diatoms to N2 ... [more ▼]

1. Lake Victoria experienced a strong degradation of water quality between the 1960s and the 1990s and, as a consequence of eutrophication, the dominant phytoplankton group changed from diatoms to N2-fixing cyanobacteria and there was a 2- to 10-fold increase in Chlorophyll-a. The goal of this study is to determine whether the 2018-2019 physical- (light, stratification) and ecological- (nutrient, Chlorophyll-a, phytoplankton composition) conditions in Lake Victoria changed from the 1990s. 2. Samples were collected in 2018-2019 in nearshore and offshore waters (Uganda), during three contrasting seasons: heavy rains (March), low rains (October) and dry (June), which corresponded to distinct water column mixing regimes, respectively, late-stratified, early-stratified and mixed regimes. At each station (48 nearshore and 25 offshore), we measured vertical profiles of temperature, oxygen, phytoplankton biomass and composition, inorganic nutrients, and particulate organic carbon, particulate nitrogen (PN) and phosphorus. 3. Chlorophyll-a concentrations in 2018-2019 were 10.3±7.1 and 2.8±1.1 µg L-1 in the nearshore and offshore surface waters, respectively, close to those measured in the 1960s before eutrophication, but distinctly lower than those measured in the 1990s (71±100 and 14±6 µg L-1). The phytoplankton of Lake Victoria in 2018-2019 still appears dominated by diatoms and cyanobacteria, but diatoms develop better in stratified conditions whereas cyanobacteria develop better in mixing conditions in comparison with the historical observations. Accordingly, we observed more non-heterocystous filamentous and coccal/colonial cyanobacteria taxa that are better adapted to mixing conditions than gas-vacuolated heterocystous taxa, which were dominant in the 1990s. PN in 2018-2019 decreased significantly compared to the 1990s, indicative of less efficient nitrogen (N) fixation. The dissolved silica (DSi) concentrations in 2018-2019 increased significantly with the concomitant reappearance of Aulacoseira spp., which was not observed in the 1990s, presumably due to low DSi concentrations. 4. As data from long-term monitoring are missing, the reasons for the lower Chlorophyll-a concentrations in 2018-2019 compared to the 1990s are unclear. Bottom-up (nutrients) and top-down (grazing) controls on Chlorophyll-a concentrations were both unlikely. Therefore, climatic controls appear (El Niño/ La Niña conditions) as an important factor to understand the historical trend in Chlorophyll-a. Higher wind in 2018-2019 promoted vertical mixing resulting in a deeper thermocline and surface mixed layers, which eventually lowered phytoplankton production in comparison to the 1990s. In contrast, the thermocline and surface mixed layers in the 1990s were shallower, enabling phytoplankton to stay suspended in the upper well illuminated water, allowing greater productivity. The lake in 2018-2019 is still in conditions of phosphorus (P) saturation, which suggests that another episode of high Chlorophyll-a concentrations could develop if less windy conditions occur in future, as during the 1980s and the 1990s, or if continued warming of surface waters eventually overcomes the mixing from present windy conditions. 5. This study gives insights about the present ecological functioning of the lake and stresses the impacts of variations in climate on lake physics that changes the light environment for phytoplankton. We also provide a biogeochemical data set, which could contribute to a baseline survey for following the ecological changes in Lake Victoria. [less ▲]

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See detailGreenhouse gases (CO2, CH4, N2O) in the Congo River are driven by fluvial-wetland connectivity
Borges, Alberto ULiege; Allen, GH; Morana, Cédric ULiege et al

Conference (2021, May 24)

We carried out ten field expeditions between 2010 and 2015, in the lowland part of the Congo River network, to describe the spatial variations of fluvial dissolved carbon dioxide (CO2), methane (CH4), and ... [more ▼]

We carried out ten field expeditions between 2010 and 2015, in the lowland part of the Congo River network, to describe the spatial variations of fluvial dissolved carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) concentrations. We investigated the drivers of the spatial variations of dissolved CO2, CH4 and N2O concentrations by analysing co-variations with several other biogeochemical variables, aquatic metabolic processes (primary production and respiration), catchment characteristics (land cover) and wetland spatial distribution. We test the hypothesis that spatial patterns of CO2, CH4 and N2O are partly due to the connectivity with wetlands, in particular with a giant wetland of flooded forest in the core of the Congo basin, the “Cuvette Centrale Congolaise” (CCC). The integrated CO2 emission from the Congo River network (251±46 TgC yr-1) was more than three times higher than terrestrial net ecosystem exchange (NEE) on the whole catchment. It is unlikely that the fluvial CO2 emissions were sustained by the hydrological carbon export from terra firme soils (typically very small compared to terrestrial NEE), but most likely, they were sustained by wetlands (with a much higher hydrological connectivity with rivers and streams). [less ▲]

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See detailChanges in chlorophyll concentration and phenology in the North Sea in relation to de-eutrophication and sea surface warming
Desmit, X; Nohe, A; Borges, Alberto ULiege et al

Conference (2021, May 20)

At least two major drivers of phytoplankton production have changed in recent decades in the North Sea: sea surface temperature (SST) has increased by ~ 1.6°C between 1988 and 2014, and the nitrogen and ... [more ▼]

At least two major drivers of phytoplankton production have changed in recent decades in the North Sea: sea surface temperature (SST) has increased by ~ 1.6°C between 1988 and 2014, and the nitrogen and phosphorus loads from surrounding rivers have decreased from the mid-1980s onward, following reduction policies. Long time series spanning four decades (1975–2016) of nutrients, chlorophyll (Chl), and pH measurements in the Southern and Central North Sea were analyzed to assess the impact of both the warming and the de-eutrophication trends on Chl. The de-eutrophication process, detectable in the reduction of nutrient river loads to the sea, caused a decrease of nutrient concentrations in coastal waters under riverine influence. A decline in annual mean Chl was observed at 11 out of 18 sampling sites (coastal and offshore) in the period 1988–2016. Also, a shift in Chl phenology was observed around 2000, with spring bloom formation occurring earlier in the year. A long time series of pH in the Southern North Sea showed an increase until the mid-1980s followed by a rapid decrease, suggesting changes in phytoplankton production that would support the observed changes in Chl. Linear correlations, however, did not reveal significant relationships between Chl variability and winter nutrients or SST at the sampling sites. We propose that the observed changes in Chl (annual or seasonal) around 2000 are a response of phytoplankton dynamics to multiple stressors, directly or indirectly influenced by de-eutrophication and climate warming. [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, leading to a response from eutrophication and heatwaves
Borges, Alberto ULiege; Royer, Colin ULiege; Lapeyra Martin, Jon et al

Conference (2021, May 19)

Dissolved CH4 concentrations in the Belgian coastal zone (BCZ) (North Sea) ranged between 1607 nmol L-1 near-shore and 4 nmol L-1 off-shore during field cruises in 2016, 2017, 2018 and 2019. Spatial ... [more ▼]

Dissolved CH4 concentrations in the Belgian coastal zone (BCZ) (North Sea) ranged between 1607 nmol L-1 near-shore and 4 nmol L-1 off-shore during field cruises in 2016, 2017, 2018 and 2019. 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. 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. This is also supported by the response to the European heatwave of 2018 that led to record-breaking temperatures in many countries across northern and central Europe. Average seawater temperature in July was 2.5°C higher than the mean from 2004 to 2017 for same month in the BCZ. The mean dissolved CH4 concentration in surface waters in July 2018 (338 nmol L-1) was three times higher than in July 2016 (110 nmol L-1), and an extremely high dissolved CH4 concentration in surface waters (1,607 nmol L-1) was observed at one near-shore station. The high dissolved CH4 concentrations in surface waters in the BCZ in July 2018 seemed to be due to a combination of enhancement of methanogenesis and of release of CH4 from gassy sediments, both most likely related to warmer conditions. The emission of CH4 from the BCZ to the atmosphere was higher in 2018 compared to 2016 by 57% in July (599 versus 382 µmol m-2 d-1) and by 37% at annual scale (221 versus 161 µmol m-2 d-1). The European heatwave of 2018 seems to have led to a major increase of CH4 concentrations in surface waters and CH4 emissions to the atmosphere in the BCZ. [less ▲]

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See detailExperimental assessment of light decrease on the biology of Posidonia oceanica
Richir, Jonathan ULiege; Luyckx, Adrien; Champenois, Willy ULiege et al

Conference (2021, May 18)

Seagrasses have a worldwide distribution and grow from the tidal zone to more than 100 m deep. They are considered ecosystem engineers, by building structurally complex meadows. Seagrass meadows are major ... [more ▼]

Seagrasses have a worldwide distribution and grow from the tidal zone to more than 100 m deep. They are considered ecosystem engineers, by building structurally complex meadows. Seagrass meadows are major coastal ecosystems, are highly productive, provide many goods and services and have considerable environmental, financial, and heritage value. Just like any autotroph, seagrass development relies on light availability. Among the many stressors that threaten seagrasses, light deprivation is consequently a major one. Light availability can decrease because of environmental (e.g., river sediment transport) or anthropogenic (e.g., eutrophication, sediment resuspension) factors, an issue expected to worsen in the future. It is in this context that we experimentally assessed the effects of environmentally relevant shading on a keystone seagrass endemic to the Mediterranean Sea, Posidonia oceanica (Linnaeus) Delile, 1813. Screens of different transparency (nominal reduction of 15, 30 and 60% compared to control) were deployed on a healthy meadow at a depth of 15 m in Corsica, France. The experiment took place between April and August 2018, i.e., during the main annual period of productivity of the plant. Seagrass pigment contents (chlorophylls and xanthophylls), photosynthesis (rapid light curves, photosynthesis/irradiance curves and quantum yield), biometry and primary production, carbohydrates (total insoluble and soluble carbohydrates) were measured monthly. Environmental parameters light, temperature and sediment porewater chemistry (methane, nitrous oxide, sulfide, nutrients) were monitored as well. Results showed the adaptability of P. oceanica to light reduction treatments. The seagrass adapted its photosynthetic activity (RLC) and efficiency (effective quantum yield) to cope with light reduction. This improvement resulted from physiological plasticity because neither the pigment contents nor the photosynthesis/irradiance curves differed between light treatments. P. oceanica shoots further maintained their growth and biomass production despite the decrease in light, but at the expense of storing carbohydrates. Finally, the chemistry of sediment porewater, in particular toxic sulfide was not altered. Results of this work underlined the high resistance and resilience of a healthy P. oceanica meadow to five months in situ light deprivation stress. However, because of the measured decrease of storage carbohydrates, seagrass meadow perennity when exposed to longer, recurrent shading is of concern. Carbohydrates and photosynthetic activity and efficiency could further be investigated as early warning indicators in seagrasses facing light reduction stress. [less ▲]

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See detailImpact of mixing on the seasonal variations of productivity and phytoplankton communities of Lake Edward (East Africa)
Nankabirwa, A; Okello, W; Descy, Jean-Pierre ULiege et al

Conference (2021, May 17)

In this study, we conducted monthly sampling from January 2017 to October 2018 in the pelagic zone of Lake Edward, Uganda to determine seasonal variability in environmental characteristics, and changes in ... [more ▼]

In this study, we conducted monthly sampling from January 2017 to October 2018 in the pelagic zone of Lake Edward, Uganda to determine seasonal variability in environmental characteristics, and changes in phytoplankton composition and abundance expected from seasonal changes. The phytoplankton was examined using marker pigment analysis by high performance liquid chromatography (HPLC) and subsequent CHEMTAX processing for estimating abundance of phytoplankton groups. In addition, microscopy was used to identify the dominant taxa. Two mixing events were observed in the dry season (July to September) of 2017 and 2018, with temperature of about 26 – 26.5°C along a total depth of 20 m. This had a strong influence on the primary production signal of the lake with chlorophyll a (Chla) as high as 20 µg/l in 2017, with cyanobacteria ranging from 10 to 14 µg Chla /l, diatoms 4-6 µg Chla/l and green algae <3 µg Chla/l. This was also observed in the overall higher δ13C-POC and lower δ13C-DIC, showing uptake of dissolved inorganic carbon (DIC) for primary production. The relatively high C:N ratio (~10±1.9) indicate a moderate N limitation in the pelagic zone. However, these observations were only true for 2017. In the dry season of 2018 this influence was not clear with chlorophyll a barely higher than 10 µg/l despite the strong complete mixing. A multivariate analysis (RDA) was applied to identify the main environmental variables involved in the success of cyanobacteria and diatoms, broadly confirming the conclusions of a previous study in Lake Edward. [less ▲]

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See detailNet community metabolism of a Posidonia oceanica meadow
Champenois, Willy ULiege; Borges, Alberto ULiege

in Limnology and Oceanography (2021), 66(0), 2126-2140

We report a 12-yr data-set (August 2006 - October 2018) of nearly-continuous estimates (n=3275) of gross primary production (GPP), community respiration (CR), and net community production (NCP) in a ... [more ▼]

We report a 12-yr data-set (August 2006 - October 2018) of nearly-continuous estimates (n=3275) of gross primary production (GPP), community respiration (CR), and net community production (NCP) in a Posidonia oceanica seagrass meadow, computed from O2 measurements on a mooring at 10 m bottom depth in the Bay of Revellata (Corsica). Both NCP and CR were correlated to GPP and followed the leaf biomass seasonal cycle. The meadow was net autotrophic (NCP of 23±8 mol O2 m-2 yr-1, GPP (83±16 mol O2 m-2 yr-1) > -CR (-60±9 mol O2 m-2 yr-1)), in agreement with oxygen over-saturation (104% at annual scale, 101% in winter and 109% in summer). Calcification (CAL) and CaCO3 dissolution (DIS) rates were evaluated from dissolved inorganic carbon measurements in benthic chamber incubations (August 2006-2009). The meadow was found to be a net sink of CaCO3 (DIS>CAL) at an annual rate of 7 mol CaCO3 m-2 yr-1 that matched estimates of CaCO3 deposition on the meadow by sedimentation from the water column. CAL from epiphyte coralline algae was correlated to GPP, but CAL:GPP ratio (0.1) was lower than reported for coralline algae in cultures (0.6) due to the additional contribution of Posidonia to GPP. Both NCP and net DIS contributed to an annual CO2 sink of -30 mol CO2 m-2 yr-1 distinctly stronger than the estimated net air-sea CO2 flux (-1 mol CO2 m-2 yr-1). This suggests that CO2 input by vertical mixing and/or transport by horizontal advection also strongly contribute to the net atmospheric CO2 exchange. [less ▲]

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See detailHalf of global methane emissions come from highly variable aquatic ecosystem sources
Rosentreter, JA; Borges, Alberto ULiege; Deemer, BR et al

in Nature Geoscience (2021), 14(0), 225-230

Atmospheric methane is a potent greenhouse gas that plays a major role in controlling the Earth’s climate. The causes of the renewed increase of methane concentration since 2007 are uncertain given the ... [more ▼]

Atmospheric methane is a potent greenhouse gas that plays a major role in controlling the Earth’s climate. The causes of the renewed increase of methane concentration since 2007 are uncertain given the multiple sources and complex biogeochemistry. Here, we present a metadata analysis of methane fluxes from all major natural, impacted and human-made aquatic ecosystems. Our revised bottom-up global aquatic methane emissions combine diffusive, ebullitive and/or plant-mediated fluxes from 15 aquatic ecosystems. We emphasize the high variability of methane fluxes within and between aquatic ecosystems and a positively skewed distribution of empirical data, making global estimates sensitive to statistical assumptions and sampling design. We find aquatic ecosystems contribute (median) 41% or (mean) 53% of total global methane emissions from anthropogenic and natural sources. We show that methane emissions increase from natural to impacted aquatic ecosystems and from coastal to freshwater ecosystems. We argue that aquatic emissions will probably increase due to urbanization, eutrophication and positive climate feedbacks and suggest changes in land-use management as potential mitigation strategies to reduce aquatic methane emissions. [less ▲]

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See detailHalf of global methane emissions come from aquatic ecosystems - much of this is human-made
Rosentreter, J; Borges, Alberto ULiege; Poulter, B et al

Article for general public (2021)

Methane — a greenhouse gas far more potent than carbon dioxide — plays a major role in controlling the Earth’s climate. But methane concentrations in the atmosphere today are 150% higher than before the ... [more ▼]

Methane — a greenhouse gas far more potent than carbon dioxide — plays a major role in controlling the Earth’s climate. But methane concentrations in the atmosphere today are 150% higher than before the industrial revolution. In our paper published today in Nature Geoscience, we show as much as half of global methane emissions come from aquatic ecosystems. This includes natural, human-created and human-impacted aquatic ecosystems — from flooded rice paddies and aquaculture ponds to wetlands, lakes and salt marshes. [less ▲]

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See detailThe possible occurrence of iron-dependent anaerobic methane oxidation in an Ancient ocean analog
Roland, Fleur ULiege; Borges, Alberto ULiege; Darchambeau, François ULiege et al

in Scientific Reports (2021), 11(1597), 1-11

In the ferruginous and anoxic early Earth oceans, photoferrotrophy drove most of the biological production before the advent of oxygenic photosynthesis, but its association with ferric iron (Fe 3 ... [more ▼]

In the ferruginous and anoxic early Earth oceans, photoferrotrophy drove most of the biological production before the advent of oxygenic photosynthesis, but its association with ferric iron (Fe 3+) dependent anaerobic methane (CH 4) oxidation (AOM) has been poorly investigated. We studied AOM in Kabuno Bay, a modern analogue to the Archean Ocean (anoxic bottom waters and dissolved Fe concentrations > 600 µmol L −1). Aerobic and anaerobic CH 4 oxidation rates up to 0.12 ± 0.03 and 51 ± 1 µmol L −1 d −1 , respectively, were put in evidence. In the Fe oxidation-reduction zone, we observed high concentration of Bacteriochlorophyll e (biomarker of the anoxygenic photoautotrophs), which co-occurred with the maximum CH 4 oxidation peaks, and a high abundance of Candidatus Methanoperedens, which can couple AOM to Fe 3+ reduction. In addition, comparison of measured CH 4 oxidation rates with electron acceptor fluxes suggest that AOM could mainly rely on Fe 3+ produced by photoferrotrophs. Further experiments specifically targeted to investigate the interactions between photoferrotrophs and AOM would be of considerable interest. Indeed, ferric Fe 3+-driven AOM has been poorly envisaged as a possible metabolic process in the Archean ocean, but this can potentially change the conceptualization and modelling of metabolic and geochemical processes controlling climate conditions in the Early Earth. [less ▲]

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See detailDrivers of the variability of dimethylsulfonioproprionate (DMSP) and dimethylsulfoxide (DMSO) in the Southern North Sea
Royer, Colin ULiege; Borges, Alberto ULiege; Lapeyra Martin, J et al

in Continental Shelf Research (2021), 216(104360), 1-11

The influence of abiotic and biotic factors on the concentration of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) was investigated and compared during two annual cycles in 2016 and 2018 ... [more ▼]

The influence of abiotic and biotic factors on the concentration of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) was investigated and compared during two annual cycles in 2016 and 2018 in the Belgian coastal zone (BCZ) in the southern North Sea at five fixed stations. These stations covered a near-offshore gradient from stations close to the mouth of the Scheldt estuary to most offshore stations. Significant differences of Chlorophyll-a (Chl-a) concentrations were observed between the two years with higher values in early spring 2018 (due to better light and nutrient conditions coupled to colder temperatures) and in summer 2018 (due to warmer conditions) compared to 2016. Nevertheless, the seasonal and spatial DMSP and DMSO (DMS(P,O)) patterns, as well as the yearly average were nearly identical in 2016 and 2018. This can be explained by the fact that the phytoplankton groups responsible for the large differences in Chl-a in 2018 and 2016 were low DMSPproducers characterized by several diatom and dinoflagellate species, occurring in early spring and summer. Further, the Prymnesiophyceae Phaeocystis globosa, occurring in late spring and responsible of most of DMS(P,O) measured in the area, reached similar biomass both years. The DMSP:Chl-a ratio obtained from the field measurements were similar to those previously published for the main observed phytoplankton groups, but more differences were observed for the DMSO:Chl-a ratio. DMS(P,O) estimations based on Chl-a linear regressions for the whole dataset need to account on two relationships discriminating the low and high-DMSP producing species. [less ▲]

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See detailThe role of inland freshwaters in summer CO2, CH4 and N2O emissions from north-eastern Siberian Arctic tundra
Martyn Rosco, M; Dean, J; Borges, Alberto ULiege et al

Poster (2020, December)

Inland waters are an ubiquitous feature of Arctic landscapes, with carbon (C) and nutrient cycles that are closely coupled to terrestrial processes. They act as important conduits of terrestrial matter by ... [more ▼]

Inland waters are an ubiquitous feature of Arctic landscapes, with carbon (C) and nutrient cycles that are closely coupled to terrestrial processes. They act as important conduits of terrestrial matter by not only transporting but also actively storing and processing it, subsequently emitting greenhouse gases (GHG) of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)to the atmosphere. Amplified climate warming at northern high-latitudes is changing contemporary carbon and nitrogen cyclesand driving permafrost thawing which has the potential to mobilise organic matter from vast stocks stored in Arctic tundra permafrost soils. Released carbon and nitrogen becomes available to degradation producing GHGs which inland waters emit to the atmosphere, thus forming a positive feedback to climate change. GHG emissions from tundra ecosystems vary regionally with local environmental and climate factors. Dissolved GHG concentrations in collected samples from the Indigirka watershed were measured and fluxes computed during three growing seasons (2015, 2016, 2017) to provide insight into the role of each type of aquatic system in this region. Fluvial CO2 and CH4fluxes (85.7 ± 29.7 mmol C/m2/ d, 10.6 ± 27.3 mmol C/m2/ d, respectively mean ± STD) were the highest, followed by pond fluxes (30.0 ± 21.0 mmol C/m2/ d, 4.9 ± 9.4 mmol/m2/ d) and finally fluxes from lake sites (8.6 ± 7.6 mmol C/m2/ d, 0.84± 0.57 mmol/m2/ d). The aim of this study was to quantify the effect of inland water emissions on the landscape C exchange. This was done by using remote sensing information to upscale emissions and integrate them into the terrestrial C exchange of the study area. As N2O has a large warming potential and received scant attention in the Arctic biome so far its contribution to terrestrial aquatic fluxes wasalso assessed. The effect of an extensive flooding event in 2017 on the landscape GHG exchange was also evaluated since increased flooding occurrence is what climate change might hold for this region. Greater insight into these aspects will increase understanding of GHG dynamics among inland waters in the north-eastern Siberian Arctic tundra lowlands which is essential for forecasting, climate-impact-assessment and to better constrain the feedback to climate warming. [less ▲]

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See detailAquatic Ecosystems are the Most Uncertain but Potentially Largest Source of Methane on Earth
Rosentreter, JA; Borges, Alberto ULiege; Raymond, PA et al

Poster (2020, December)

Atmospheric methane is a potent greenhouse gas that has tripled in concentration since pre-industrial times. The causes of rising methane concentrations are poorly understood given its multiple sources ... [more ▼]

Atmospheric methane is a potent greenhouse gas that has tripled in concentration since pre-industrial times. The causes of rising methane concentrations are poorly understood given its multiple sources and complex biogeochemistry. Natural and human-made aquatic ecosystems, including wetlands, are potentially the largest single source of methane, but their total emissions relative to other sources have not been assessed. Based on a new synthesis of inventory, remote sensing and modeling efforts, we present a bottom-up estimate of methane emissions from streams and rivers, freshwater lakes and reservoirs, estuaries, coastal wetlands (mangroves, seagrasses, salt-marshes), intertidal flats, aquaculture ponds, continental shelves, along with recently published estimates of global methane emissions from freshwater wetlands, rice paddies, the continental slope and open ocean. Our findings emphasize the high variability of aquatic methane fluxes and a possibly skewed distribution of currently available data, making global estimates sensitive to statistical assumptions. Mean emissions make aquatic ecosystems the largest source of methane globally (53% of total global methane emissions). Median emissions are 42% of the total global methane emissions. We argue that these emissions will likely increase due to urbanization, eutrophication and climate change. [less ▲]

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See detailIdeas and perspectives: A strategic assessment of methane and nitrous oxide measurements in the marine environment
Wilson, ST; Al-Haj, AN; Bourbonnais, A et al

in Biogeosciences (2020), 17(0), 5809-5828

In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics - namely production, consumption and net emissions - is required for all biomes, especially those ... [more ▼]

In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics - namely production, consumption and net emissions - is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for a number of climate-active trace gases including methane (CH4) and nitrous oxide (N2O). The temporal and spatial distributions of CH4 and N2O are controlled by the interaction of complex biogeochemical and physical processes. To evaluate and quantify the importance of these mechanisms relevant to marine CH4 and N2O cycling requires a combination of traditional scientific disciplines including oceanography, microbiology, and numerical modeling. Fundamental to all of these efforts is ensuring that the datasets produced by independent scientists around the world are comparable and interoperable. Equally critical is transparent communication within the research community about the technical improvements required to increase our collective understanding of marine CH4 and N2O. An Ocean Carbon & Biogeochemistry (OCB) sponsored workshop was organized to enhance dialogue and collaborations pertaining to marine CH4 and N2O. Here, we summarize the outcomes from the workshop to describe the challenges and opportunities for near-future CH4 and N2O research in the marine environment. [less ▲]

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See detailVariations of dissolved greenhouse gases (CO2, CH4, N2O) in the Congo River network overwhelmingly driven by fluvial wetland connectivity
Borges, Alberto ULiege

Scientific conference (2020, November 16)

We report the spatial variations of dissolved carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) concentrations in the lowland part of the Congo River network obtained during ten field ... [more ▼]

We report the spatial variations of dissolved carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) concentrations in the lowland part of the Congo River network obtained during ten field expeditions carried out between 2010 and 2015, in the eastern part of the basin (Democratic Republic of Congo). The integrated CO2 emission from the Congo River network is more than three times higher than the estimate of terrestrial net ecosystem exchange (NEE) on the whole catchment (77 TgC yr-1). This shows that it is unlikely that the CO2 emissions from the river network were sustained by the hydrological carbon export from terra firme soils (typically very small compared to terrestrial NEE), but most likely, to a large extent, they were sustained by wetlands (with a much higher hydrological connectivity with rivers and streams). [less ▲]

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See detailMethane paradox in tropical lakes? Sedimentary fluxes rather than pelagic production in oxic conditions sustain methanotrophy and emissions to the atmosphere
Morana, Cédric ULiege; Bouillon, Steven; Nolla-Ardèvol, V et al

in Biogeosciences (2020), 17(0), 5209-5221

Despite growing evidence that methane (CH4) formation could also occur in well-oxygenated surface freshwaters, its significance at the ecosystem scale is uncertain. Empirical models based on data gathered ... [more ▼]

Despite growing evidence that methane (CH4) formation could also occur in well-oxygenated surface freshwaters, its significance at the ecosystem scale is uncertain. Empirical models based on data gathered at high latitude predict that the contribution of oxic CH4 increases with lake size and should represent the majority of CH4 emissions in large lakes. However, such predictive models could not directly apply to tropical lakes which differ from their temperate counterparts in some fundamental characteristics, such as year-round elevated water temperature. We conducted stable isotope tracer experiments which revealed that oxic CH4 production is closely related to phytoplankton metabolism, and is a common feature in five contrasting African lakes. Nevertheless, methanotrophic activity in surface waters and CH4 emissions to the atmosphere were predominantly fuelled by CH4 generated in sediments and physically transported to the surface. Indeed, CH4 bubble dissolution flux and diffusive benthic CH4 flux were several orders of magnitude higher than CH4 production in surface waters. Microbial 20 CH4 consumption dramatically decreased with increasing sunlight intensity, suggesting that the freshwater “CH4 paradox”might be also partly explained by photo-inhibition of CH4 oxidizers in the illuminated zone. Sunlight appeared as an overlooked but important factor determining the CH4 dynamics in surface waters, directly affecting its production by photoautotrophs and consumption by methanotrophs. [less ▲]

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