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See detailVariability of methane in the epilimnion of Lake Kivu
Borges, Alberto ULg; Abril, Gwenael; Delille, Bruno ULg et al

Poster (2011, July 11)

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See detail5.04 - Carbon Dioxide and Methane Dynamics in Estuaries
Borges, Alberto ULg; Abril, Gwenaël

in Wolanski, Eric; McLusky, Donald (Eds.) Treatise on Estuarine and Coastal Science, Volume 5: Biogeochemistry (2011)

Estuaries profoundly transform the large amounts of carbon delivered from rivers before their transfer to the adjacent coastal zone. As a consequence of the complex biogeochemical reworking of ... [more ▼]

Estuaries profoundly transform the large amounts of carbon delivered from rivers before their transfer to the adjacent coastal zone. As a consequence of the complex biogeochemical reworking of allochthonous carbon in the sediments and the water column, CO2 and CH4 are emitted into the atmosphere. We attempt to synthesize available knowledge on biogeochemical cycling of CO2 and CH4 in estuarine environments, with a particular emphasis on the exchange with the atmosphere. Unlike CH4, the global emission of CO2 to the atmosphere from estuaries is significant compared to other components of the global carbon cycle [less ▲]

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See detailDiffusive methane emissions to the atmosphere from Lake Kivu (Eastern Africa)
Borges, Alberto ULg; Abril, Gwenaël; Delille, Bruno ULg et al

in Journal of Geophysical Research. Biogeosciences (2011), 116(G03032),

We report a data-set of methane (CH4) concentrations in the surface waters of Lake Kivu obtained during four cruises (March 2007, September 2007, June 2008, April 2009) covering the two main seasons ... [more ▼]

We report a data-set of methane (CH4) concentrations in the surface waters of Lake Kivu obtained during four cruises (March 2007, September 2007, June 2008, April 2009) covering the two main seasons, rainy (October to May) and dry (June to September). Spatial gradients of CH4 concentrations were modest in the surface waters of the main basin. In Kabuno Bay (a small sub-basin), CH4 concentrations in surface waters were significantly higher than in the main basin. Seasonal variations of CH4 in the main basin were strongly driven by deepening of the mixolimnion and mixing of surface waters with deeper waters rich in CH4. On an annual basis, both Kabuno Bay and the main basin of Lake Kivu were over-saturated in CH4 with respect to atmospheric equilibrium (7330% and 2510%, respectively), and emitted CH4 to the atmosphere (39 mmol m-2 yr-1 and 13 mmol m-2 yr-1, respectively). The source of CH4 to atmosphere was two orders of magnitude lower than the CH4 upward flux. The source of CH4 to the atmosphere from Lake Kivu corresponded to ~60% of the terrestrial sink of atmospheric CH4 over the lake’s catchment. A global cross-system comparison of CH4 in surface waters of lakes shows that both Kabuno Bay and the main basin are at the lower end of values in lakes globally, despite the huge amounts of CH4 in the deeper layers of the lake. This is related to the strongly meromictic nature of the lake that promotes an intense removal of CH4 by bacterial oxidation. [less ▲]

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See detailIn vitro simulation of oxic/suboxic diagenesis in an estuarine fluid mud subjected to redox oscillations
Abril, Gwenael; Commarieu, Marc-Vincent ULg; Etcheber, Henri et al

in Estuarine Coastal And Shelf Science (2010), 88(2), 279-291

Estuarine turbidity maxima (ETMs) are sites of intense mineralisation of land-derived particulate organic matter (OM), which occurs under oxic/suboxic oscillating conditions owing to repetitive ... [more ▼]

Estuarine turbidity maxima (ETMs) are sites of intense mineralisation of land-derived particulate organic matter (OM), which occurs under oxic/suboxic oscillating conditions owing to repetitive sedimentation and resuspension cycles at tidal and neap-spring time scales. To investigate the biogeochemical processes involved in OM mineralisation in ETMs, an experimental set up was developed to simulate in vitro oxic/anoxic oscillations in turbid waters and to follow the short timescale changes in oxygen, carbon, nitrogen, and manganese concentration and speciation. We present here the results of a 27-day experiment (three oxic periods and two anoxic periods) with an estuarine fluid mud from the Gironde estuary. Time courses of chemical species throughout the experiment evidenced the occurrence of four distinct characteristic periods with very different properties. Steady oxic conditions were characterised by oxygen consumption rates between 10 and 40 mu mol L-1 h(-1), dissolved inorganic carbon (DIC) production of 9-12 mu mol L-1 h(-1), very low NE4+ and Mn2+ concentrations, and constant NO3 production rates (0.4 - 0.7 mu mol L-1 h(-1)) due to coupled ammonification and nitrification. The beginning of anoxic periods (24 h following oxic to anoxic switches) showed DIC production rates of 2.5-8.6 mu mol L-1 h(-1) and very fast NO consumption (5.6-6.3 mu mol L-1 h(-1)) and NH4+ production (1.4-1.5 mu mol L-1 h(-1)). The latter rates were positively correlated to NO concentration and were apparently caused by the predominance of denitrification and dissimilatory nitrate reduction to ammonia. Steady anoxic periods were characterised by constant and low NO3- concentrations and DIG and NH4+ productions of less than 1.3 and 0.1 mu mol L-1 h(-1), respectively. Mn2+ and CH4 were produced at constant rates (respectively 0.3 and 0.015 mu mol L-1 h(-1)) throughout the whole anoxic periods and in the presence of nitrate. Finally, reoxidation periods (24-36 h following anoxic to oxic switches) showed rapid NH4+ and Mn2+ decreases to zero (1.6 and 0.8-2 mu mol L-1 h(-1), respectively) and very fast NO production (3 mu mol L-1 h(-1)). This NO3- production, together with marked transient peaks of dissolved organic carbon a few hours after anoxic to oxic switches, suggested that particulate OM mineralisation was enhanced during these transient reoxidation periods. An analysis based on C and N mass balance suggested that redox oscillation on short time scales (day to week) enhanced OM mineralisation relative to both steady oxic and steady anoxic conditions, making ETMs efficient biogeochemical reactors for the mineralisation of refractory terrestrial OM at the land-sea interface. (C) 2010 Elsevier Ltd. All rights reserved. [less ▲]

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See detailCarbon cycling in the mixolimnion of Lake Kivu : results from the CAKI project
Borges, Alberto ULg; Descy, Jean-Pierre; Delille, Bruno ULg et al

Conference (2009, January 19)

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See detailSeasonal Variability of Carbon Dioxide in the Rivers and Lagoons of Ivory Coast (West Africa)
Koné, Yéfanlan José-Mathieu; Abril, Gwenaël; Kouadio, K. N. et al

in Estuaries and Coasts (2009), 32

We report partial pressure of CO2 (pCO2) and ancillary data in three rivers (Bia, Tanoé, and Comoé) and five lagoons (Tendo, Aby, Ebrié, Potou, and Grand-Lahou) in Ivory Coast (West Africa), during four ... [more ▼]

We report partial pressure of CO2 (pCO2) and ancillary data in three rivers (Bia, Tanoé, and Comoé) and five lagoons (Tendo, Aby, Ebrié, Potou, and Grand-Lahou) in Ivory Coast (West Africa), during four cruises covering the main climatic seasons. The three rivers were oversaturated in CO2 with respect to atmospheric equilibrium, and the seasonal variability of pCO2 was due to dilution during the flooding period. Surface waters of the Potou, Ebrié, and Grand-Lahou lagoons were oversaturated in CO2 during all seasons. These lagoons behaved similarly to the oligohaline regions of macrotidal estuaries that are CO2 sources to the atmosphere due to net ecosystem heterotrophy and inputs of riverine CO2 rich waters. The Aby and Tendo lagoons were undersaturated in CO2 with respect to the atmosphere because of their permanent haline stratification (unlike the other lagoons) that seemed to lead to higher phytoplankton production and export of organic carbon below the pycnocline. [less ▲]

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See detailThe impact of lateral carbon fluxes on the European carbon balance
Ciais, P.; Borges, Alberto ULg; Abril, Gwenaël et al

in Biogeosciences (2008), 5

To date, little is known about the impact of processes which cause lateral carbon fluxes over continents, and from continents to oceans on the CO2 – and carbon budgets at local, regional and continental ... [more ▼]

To date, little is known about the impact of processes which cause lateral carbon fluxes over continents, and from continents to oceans on the CO2 – and carbon budgets at local, regional and continental scales. Lateral carbon fluxes contribute to regional carbon budgets as follows: Ecosystem CO2 sink=Ecosystem carbon accumulation+Lateral carbon fluxes. We estimated the contribution of wood and food product trade, of emission and oxidation of reduced carbon species, and of river erosion and transport as lateral carbon fluxes to the carbon balance of Europe (EU-25). The analysis is completed by new estimates of the carbon fluxes of coastal seas. We estimated that lateral transport (all processes combined) is a flux of 165 Tg C yr−1 at the scale of EU-25. The magnitude of lateral transport is thus comparable to current estimates of carbon accumulation in European forests. The main process contributing to the total lateral flux out of Europe is the flux of reduced carbon compounds, corresponding to the sum of non-CO2 gaseous species (CH4, CO, hydrocarbons, . . . ) emitted by ecosystems and exported out of the European boundary layer by the large scale atmospheric circulation. [less ▲]

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See detailEmission of CO2 and CH4 to the atmosphere by sediments and open waters in two Tanzanian mangrove forests
Kristensen, Erik; Flindt, Mogens R.; Ulomi, Shadrack et al

in Marine Ecology. Progress Series (2008)

Carbon gas balance was evaluated in an anthropogenically impacted (Mtoni) and a pristine (Ras Dege) mangrove forest in Tanzania. Exchange of carbon dioxide (CO2) was measured for inundated and air-exposed ... [more ▼]

Carbon gas balance was evaluated in an anthropogenically impacted (Mtoni) and a pristine (Ras Dege) mangrove forest in Tanzania. Exchange of carbon dioxide (CO2) was measured for inundated and air-exposed sediments during day and night using in situ and laboratory incubations. In situ methane (CH4) emissions were measured in the dark during air exposure only. Emission of CO2 and CH4 from open waters (e.g. creeks) was estimated from diurnal measurements of CO2, partial pressure (pCO2) and CH4 concentrations. CO2 emission from darkened sediments devoid of biogenic structures was comparable during inundation and air exposure (28 to 115 mmol m–2 d–1) with no differences between mangrove forests. Benthic primary production was low with only occasional net uptake of CO2 by the sediments. Emissions of CH4 from air-exposed sediment were generally 3 orders of magnitude lower than for CO2. Presence of pneumatophores and crab burrows increased low tide emissions several fold. Emissions from open waters were dependent on tidal level and wind speed. Lowest emission occurred during high tide (1 to 6 mmol CO2 m–2 d–1; 10 to 80 μmol CH4 m–2 d–1) and highest during low tide (30 to 80 mmol CO2 m–2 d–1; 100 to 350 μmol CH4 m–2 d–1) when supersaturated runoff from the forest floor and porewater seepage reached the creek water. Based on global average primary production and measured gas emissions, the carbon gas balance of the 2 mangrove forests was estimated. The densely vegetated Ras Dege forest appears to be an efficient sink of greenhouse carbon gases, while extensive clear-cutting at the Mtoni forest apparently has reduced its capacity to absorb CO2, although it is seemingly still a net sink for atmospheric CO2. [less ▲]

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See detailCarbon dioxide fluxes in Lake Kivu
Borges, Alberto ULg; Delille, Bruno ULg; Descy, Jean-Pierre et al

Conference (2007, June 12)

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See detailImportance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania)
Bouillon, Steven; Middelburg, Jack J.; Dehairs, Frank et al

in Biogeosciences (2007), 4

We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and ... [more ▼]

We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and biological driving forces. Since the creek has no upstream freshwater inputs, highest salinity was observed at low tide, due to evaporation effects and porewater seepage. Total suspended matter (TSM) and particulate organic carbon (POC) showed distinct maxima at periods of highest water flow, indicating that erosion of surface sediments and/or resuspension of bottom sediments were an important source of particulate material. Dissolved organic carbon (DOC), in contrast, varied in phase with water height and was highest at low tide. Stable isotope data of POC and DOC displayed large variations in both pools, and similarly followed the variations in water height. Although the variation of 13CDOC (−23.8 to −13.8‰) was higher than that of 13CPOC (−26.2 to −20.5‰), due to the different endmember pool sizes, the 13C signatures of both pools differed only slightly at low tide, but up to 9‰ at high tide. Thus, at low tide both DOC and POC originated from mangrove production. At high tide, however, the DOC pool had signatures consistent with a high contribution of seagrass-derived material, whereas the POC pool was dominated by marine phytoplankton. Daily variations in CH4, and partial pressure of CO2 (pCO2) were similarly governed by tidal influence and were up to 7- and 10-fold higher at low tide, which stresses the importance of exchange of porewater and diffusive fluxes to the water column. When assuming that the high dissolved inorganic carbon (DIC) levels in the upper parts of the creek (i.e. at low tide) are due to inputs from mineralization, 13C data on DIC indicate that the organic matter source for mineralization had a signature of −22.4‰. Hence, imported POC and DOC from the marine environment contributes strongly to overall mineralization within the mangrove system. Our data demonstrate how biogeochemical processes in the intertidal zone appear to be prominent drivers of element concentrations and isotope signatures in the water column, and how pathways of dissolved and particulate matter transport are fundamentally different. [less ▲]

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See detailDynamics of organic and inorganic carbon across contiguous mangrove and seagrass systems (Gazi bay, Kenya)
Bouillon, Steven; Dehairs, Frank; Velimirov, Branko et al

in Journal of Geophysical Research. Biogeosciences (2007), 112(G02018),

We report on the water column biogeochemistry in adjacent mangrove and seagrass systems in Gazi Bay (Kenya), with a focus on assessing the sources and cycling of organic and inorganic carbon. Mangrove and ... [more ▼]

We report on the water column biogeochemistry in adjacent mangrove and seagrass systems in Gazi Bay (Kenya), with a focus on assessing the sources and cycling of organic and inorganic carbon. Mangrove and seagrass-derived material was found to be the dominant organic carbon sources in the water column, and could be distinguished on the basis of their d13C signatures and particulate organic carbon:total suspended matter (POC/TSM) ratios. Spatially, a distinct boundary existed whereby the dominance of mangrove-derived material decreased sharply close to the interface between the mangrove forest and the dense seagrass beds. The latter is consistent with the reported export of mangrove-derived material, which is efficiently trapped in the adjacent seagrass beds. There were significant net inputs of POC and dissolved organic carbon (DOC) along the Kidogoweni salinity gradient, for which the d13CPOC signatures were consistent with those of mangroves. DOC was the dominant form of organic carbon in both mangrove and seagrass beds, with DOC/POC ratios typically between 3 and 15. Dynamics of dissolved inorganic carbon in the creeks were strongly influenced by diagenetic C degradation in the intertidal mangrove areas, resulting in significant CO2 emission from the water column to the atmosphere. Although highest partial pressure of CO2 (pCO2) values and areal CO2 flux rates were observed in the mangrove creeks, and the water column above the seagrass beds was in some locations a net sink of CO2, most of the ecosystems’ emission of CO2 to the atmosphere occurred in the seagrass beds adjacent to the mangrove forest. The presence of dense seagrass beds thus had a strong effect on the aquatic biogeochemistry, and resulted in trapping and further mineralization of mangrove-derived POC, intense O2 production and CO2 uptake. The adjacent seagrass beds provide a large area with conditions favorable to exchange of CO2 with the atmosphere, thereby limiting export of mangrove-derived organic and inorganic carbon toward the coastal ocean. [less ▲]

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See detailCarbon dioxide in European coastal waters
Borges, Alberto ULg; Schiettecatte, L. S.; Abril, Gwenaël et al

in Estuarine Coastal & Shelf Science (2006), 70(3), 375-387

We compiled from literature annually integrated air-water fluxes of carbon dioxide (CO2) computed from field measurements, in 20 coastal European environments that were gathered into 3 main ecosystems ... [more ▼]

We compiled from literature annually integrated air-water fluxes of carbon dioxide (CO2) computed from field measurements, in 20 coastal European environments that were gathered into 3 main ecosystems: inner estuaries, upwelling continental shelves and non-upwelling continental shelves. The comparison of annual cycles of the partial pressure of CO2 (pCO(2)) in 5 contrasting continental shelves provided insights into the biogeochemical drivers of the CO2 fluxes. The latter were also investigated by comparing CO2 fluxes to net ecosystem (NEP) and net community production (NCP) in 3 contrasted coastal ecosystems. Air-water CO2 fluxes were scaled at European regional level and compared to fluxes of atmospheric CO2 in other aquatic and terrestrial compartments. Continental shelves are significant sinks for atmospheric CO2 at an average rate of -1.9 molC m(-2) yr(-1) that scaled at European level corresponds to an absorption of atmospheric CO2 of -68.1 TgC yr(-1). This sink is equivalent to the one reported for the terrestrial biosphere of -66.1 TgC yr(-1), based on carbon-stock change models. Estuaries are significant sources of CO2 to the atmosphere at an average rate of 49.9 molC m(-2) yr(-1) that is higher than the CO2 emission to the atmosphere from rivers, streams and lakes. The scaled emission of CO2 to the atmosphere from inner estuaries of about 67.0 TgC yr(-1) would almost fully balance the sink of atmospheric CO2 computed for continental shelves. However, the scaled emission of CO2 from estuaries to the atmosphere is inconsistent with the potential emission of CO2 based on the fate of river organic carbon during estuarine transit. This discrepancy is most probably due to the poorly constrained surface area estimate of inner estuaries. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailGas transfer velocities of CO2 in three European estuaries (Randers Fjord, Scheldt and Thames)
Borges, Alberto ULg; Delille, Bruno ULg; Schiettecatte, Laure-Sophie et al

in Limnology & Oceanography (2004), 49(5), 1630-1641

We measured the flux of CO2 across the air–water interface using the floating chamber method in three European estuaries with contrasting physical characteristics (Randers Fjord, Scheldt, and Thames). We ... [more ▼]

We measured the flux of CO2 across the air–water interface using the floating chamber method in three European estuaries with contrasting physical characteristics (Randers Fjord, Scheldt, and Thames). We computed the gas transfer velocity of CO2 (k) from the CO2 flux and concomitant measurements of the air–water gradient of the partial pressure of CO2 (pCO2). There was a significant linear relationship between k and wind speed for each of the three estuaries. The differences of the y-intercept and the slope between the three sites are related to differences in the contribution of tidal currents to water turbulence at the interface and fetch limitation. The contribution to k from turbulence generated by tidal currents is negligible in microtidal estuaries such as Randers Fjord but is substantial, at low to moderate wind speeds, in macrotidal estuaries such as the Scheldt and the Thames. Our results clearly show that in estuaries a simple parameterization of k as a function of wind speed is site specific and strongly suggest that the y-intercept of the linear relationship is mostly influenced by the contribution of tidal currents, whereas the slope is influenced by fetch limitation. This implies that substantial errors in flux computations are incurred if generic relationships of the gas transfer velocity as a function of wind speed are employed in estuarine environments for the purpose of biogas air–water flux budgets and ecosystem metabolic studies. [less ▲]

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See detailInorganic and organic carbon biogeochemistry in the Gautami Godavari estuary (Andhra Pradesh, India) during pre-monsoon : the local impact of extensive mangrove forests
Bouillon, Steven; Frankignoulle, Michel; Dehairs, Frank et al

in Global Biogeochemical Cycles (2003), 17(4),

[1] The distribution and sources of organic and inorganic carbon were studied in the Gautami Godavari estuary (Andhra Pradesh, India) and in a mangrove ecosystem in its delta during pre-monsoon. In the ... [more ▼]

[1] The distribution and sources of organic and inorganic carbon were studied in the Gautami Godavari estuary (Andhra Pradesh, India) and in a mangrove ecosystem in its delta during pre-monsoon. In the oligohaline and mesohaline section (salinity 0–15) of the estuary, internal production of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) was recorded, and the d13CDIC profile suggests that carbonate dissolution may be an important process determining the DIC dynamics in this section of the Godavari. The partial pressure of CO2 (pCO2) was fairly low along the entire salinity gradient, (293–500 ppm), but much higher and more variable (1375–6437 ppm) in the network of tidal mangrove creeks in the delta. Here, variations in the concentration and d13C of the DIC pool were shown to result largely from the mineralization of organic matter. The present study clearly identifies the mangrove creeks as an active site of mineralization and CO2 efflux to the atmosphere, but shows that these changes in the aquatic biogeochemistry are a localized feature, rapidly fading in the adjacent Kakinada Bay. Our data indicate that mineralization of dissolved organic carbon (DOC) of mangrove origin, and its subsequent efflux as CO2 to the atmosphere may represent an important fate for mangrove carbon. Although further quantification of this process in a variety of systems is required, we suggest that some of the current ideas on the role of mangroves in the carbon budget of the coastal zone may need to be reconsidered. [less ▲]

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See detailCarbonate dissolution in the turbid and eutrophic Loire estuary
Abril, Gwenaël; Etcheber, Henri; Delille, Bruno ULg et al

in Marine Ecology. Progress Series (2003), 259

We measured particulate and dissolved organic carbon (POC and DOC), chlorophyll, oxygen, partial pressure of Co-2, pH, total alkalinity (TAlk) and particulate inorganic carbon (PIC) during a late summer ... [more ▼]

We measured particulate and dissolved organic carbon (POC and DOC), chlorophyll, oxygen, partial pressure of Co-2, pH, total alkalinity (TAlk) and particulate inorganic carbon (PIC) during a late summer cruise in the eutrophic Loire estuary. These parameters reveal an intense mineralisation of organic matter in the estuarine maximum turbidity zone (MTZ) that results in oxygen deficits (down to 20% of the saturation level) and high CO2 oversaturations (pCO(2) up to 2900 muatm). Several facts revealed the occurrence of carbonate dissolution in the Loire MTZ: large amounts of alkalinity were produced in the upper estuary, increasing its transfer to the ocean by 30%; the calculated saturation index showed a net undersaturation for aragonite and a slight undersaturation for calcite in the MTZ; and PIC decreased from 2.1% (% dry weight) in riverine suspension to 0.4% in the MTZ. A stoichiometric approach is used to assess the coupling between aerobic respiration and carbonate dissolution, where apparent oxygen utilisation, excess CO2, TAlk and dissolved inorganic carbon are compared quantitatively. About 20%, of the CO2 generated by respiration was involved in carbonate dissolution. The loss of PIC at the river-estuary transition quantitatively corresponds to the amount of authigenic calcite precipitated upstream in the highly eutrophic river. This suggests that CO2 exchange with the atmosphere along the eutrophic river-estuary continuum is buffered by carbonate precipitation in the autotrophic river and its dissolution in the heterotrophic estuary. [less ▲]

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See detailExcess atmospheric carbon dioxide transported by rivers into the Scheldt Estuary
Abril, Gwenaël; Etcheber, Henri; Borges, Alberto ULg et al

in Comptes Rendus de l'Académie des Sciences de Paris (2000), 330

The transport of excess atmospheric CO2 (defined as the fraction of dissolved inorganic carbon (DIC) that can escape as CO2 to the atmosphere due to water-air equilibration), by the five rivers entering ... [more ▼]

The transport of excess atmospheric CO2 (defined as the fraction of dissolved inorganic carbon (DIC) that can escape as CO2 to the atmosphere due to water-air equilibration), by the five rivers entering the Scheldt estuary is investigated. Excess CO2 originates from both respiration in the soil and the river and represents 10 % of the DIC and 6 % of the total carbon input into the estuary. The ventilation of this CO2 in the estuary is however a minor contribution (10 %) to the total estuarine emission to the atmosphere, compared to heterotrophic activity and acidification due to nitrification within the estuarine zone. [less ▲]

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See detailCarbon Dioxide Emission from European Estuaries
Frankignoulle, Michel; Abril, Gwenaël; Borges, Alberto ULg et al

in Science (1998), 282(5388), 434-6

The partial pressure of carbon dioxide (pCO2) in surface waters and related atmospheric exchanges were measured in nine European estuaries. Averaged fluxes over the entire estuaries are usually in the ... [more ▼]

The partial pressure of carbon dioxide (pCO2) in surface waters and related atmospheric exchanges were measured in nine European estuaries. Averaged fluxes over the entire estuaries are usually in the range of 0.1 to 0.5 mole of CO2 per square meter per day. For wide estuaries, net daily fluxes to the atmosphere amount to several hundred tons of carbon (up to 790 tons of carbon per day in the Scheldt estuary). European estuaries emit between 30 and 60 million tons of carbon per year to the atmosphere, representing 5 to 10% of present anthropogenic CO2 emissions for Western Europe. [less ▲]

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