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See detailBelgian IPY Symposium 'The contribution of Belgian research to the achievements of the International Polar Year 2007-9
Dehairs, Frank; Decleir, Hugo; De Broyer, Claude et al

Book published by Universa Press (2010)

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See detailCarbon biogeochemistry of the Betsiboka Estuary (north-western Madagascar)
Ralison, Olivier Harifidy; Borges, Alberto ULg; Dehairs, Frank et al

in Organic Geochemistry (2008), 39

Madagascar’s largest estuary (Betsiboka) was sampled along the salinity gradient during the dry season to document the distribution and sources of particulate and dissolved organic carbon (POC, DOC) as ... [more ▼]

Madagascar’s largest estuary (Betsiboka) was sampled along the salinity gradient during the dry season to document the distribution and sources of particulate and dissolved organic carbon (POC, DOC) as well as dissolved inorganic carbon (DIC). The Betsiboka was characterized by a relatively high suspended matter load, and in line with this, low DOC/POC ratios ( 0.4–2.5). The partial pressure of CO2 (pCO2) was generally above atmospheric equilibrium (270–1530 ppm), but relatively low in comparison to other tropical and subtropical estuaries, resulting in low average CO2 emission to the atmosphere (9.1 ± 14.2 mmol m 2 d 1). Despite the fact that C4 vegetation is reported to cover >80% of the catchment area, stable isotope data on DOC and POC suggest that C4 derived material comprises only 30% of both pools in the freshwater zone, increasing to 60–70% and 50–60%, respectively, in the oligohaline zone due to additional lateral inputs. Sediments from intertidal mangroves in the estuary showed low organic carbon concentrations (<1%) and d13C values (average 19.8‰) consistent with important inputs of riverine imported C4 material. This contribution was reflected in d13C signatures of bacterial phospholipid derived fatty acids (i + a15:0), suggesting the potential importance of terrestrial organic matter sources for mineralization and secondary production in coastal ecosystems. [less ▲]

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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 detailBiogeochemistry of the Tana estuary and delta (northern Kenya)
Bouillon, Steven; Dehairs, Frank; Schiettecatte, Laure-Sophie et al

in Limnology & Oceanography (2007), 52(1), 45-59

The estuarine mixing zone of the Tana River (northern Kenya) and an extensive deltaic area just south of the estuary were sampled in April 2004 with the aim of identifying the distribution, sources, and ... [more ▼]

The estuarine mixing zone of the Tana River (northern Kenya) and an extensive deltaic area just south of the estuary were sampled in April 2004 with the aim of identifying the distribution, sources, and processing of particulate and dissolved organic carbon (POC, DOC) and inorganic carbon (DIC). C4 inputs from the catchment contributed ,50% to the POC pool in the Tana River and estuary, and in the mangrove creek water column and intertidal sediments. The d13C values of DOC, however, were typically much more negative than that of POC, indicating a substantially higher contribution by C3 and/or mangrove-derived carbon in the DOC pool. The undersaturation of O2, high pCO2, and the nonconservative nature of DIC and d13CDIC suggest a strongly heterotrophic water column, particularly in the freshwater part of the Tana and in the tidal creeks in the delta, where high additional inputs of organic matter were observed. However, some of these sites showed d18ODO signatures lower than the atmospheric equilibrium (i.e., +24.2%) indicative of significant O2 production by photosynthesis. Therefore, the heterotrophic signature in the water column is likely the result of a strong interaction with the large intertidal areas, whereby respiratory activity in sediments and in the overlying water column during tidal inundation leave a marked signature on the water column. This is confirmed by the covariation between salinity-normalized total alkalinity and DIC, whose slope indicates an important role for anaerobic diagenetic processes. If our data are representative for other large river systems in the region, current estimates are likely to underestimate suspended matter and both inorganic and organic C fluxes to the Indian Ocean from tropical east Africa. [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 detailReconstructing export production at the NE Atlantic Margin: potential and limits of the Ba proxy
Fagel, Nathalie ULg; Dehairs, Frank; Peinert, Ralf et al

in Marine Geology (2004), 204(1-2), 11-25

Barium (Ba), aluminium (Al), and zirconium (Zr) were measured in sediment trap material deployed at two margin settings of the NE Atlantic: the Bay of Biscaye at Goban Spur and the NW Iberian Margin. The ... [more ▼]

Barium (Ba), aluminium (Al), and zirconium (Zr) were measured in sediment trap material deployed at two margin settings of the NE Atlantic: the Bay of Biscaye at Goban Spur and the NW Iberian Margin. The Particulate Organic Carbon (POC)/Ba ratios of the trapped material in both margin environments are clearly higher compared to the open ocean. Although lateral advection of POC may partly explain these higher POC/Ba ratios for margin systems, it is clear that the yield of authigenic particulate Ba during organic matter degradation in the water column is lower in margin environments. In order to assess export production in margin settings we optimised transfer functions based on trapped Ba fluxes that were originally elaborated for open ocean settings. Calculations of export production based on trapped Ba flux and POC/Ba ratio were compared with calculations based on trapped POC flux only. Export production based on Ba flux show greater internal consistency amongst traps along the same mooring, suggesting that this approach has advantages over the one based on POC flux only. Estimated export productions are of the same order of magnitude as estimates of new production, but systematically fall short of the latter. This systematic discrepancy needs further investigation. (C) 2004 Elsevier B.V. All rights reserved. [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 detailCarbon and nitrogen stable isotope ratios of subtidal benthic invertebrates in an estuarine mangrove ecosystem (Andhra Pradesh, India)
Bouillon, Steven; Raman, A. V.; Dauby, Patrick ULg et al

in Estuarine Coastal and Shelf Science (2002), 54(5), 901-913

In order to assess the relative trophic importance of mangrove litterfall and aquatic primary production in the mangrove creeks of the Coringa Wildlife Sanctuary (Andhra Pradesh, India) and the adjacent ... [more ▼]

In order to assess the relative trophic importance of mangrove litterfall and aquatic primary production in the mangrove creeks of the Coringa Wildlife Sanctuary (Andhra Pradesh, India) and the adjacent semi-enclosed Kakinada Bay, carbon and nitrogen stable isotope ratios were determined in a variety of benthic invertebrate species collected at 22 sites during the pre-monsoon period (May-June) of 1997 and 1999. delta(13)C values showed little interspecific variation at any given location, but there was a distinct spatial gradient in consumer delta(13)C values of about 7parts per thousand, with more depleted values in the mangrove creeks ( - 23.6 +/- 0.6parts per thousand), and gradually increasing in the mangrove outlets ( - 21.5 +/- 0.9parts per thousand), a relatively restricted zone in the south-eastern part of Kakinada Bay adjacent to the mangroves ( - 18.8 +/- 0.8parts per thousand), and the central and northern part of the Bay ( - 16.7 +/- 1.4parts per thousand) which opens into the Bay of Bengal. This gradient is much larger than that observed during a previous study in suspended organic matter (maximum about 2.7parts per thousand) and during this study in sediment organic matter (about 1.5-2.5parts per thousand). The observed carbon stable isotope ratios thus suggest a marked selectivity of the benthic invertebrate community for pelagic and benthic microalgal food sources and indicate that mangrove-derived and other terrestrial carbon is not a significant food source for benthic invertebrate communities in this ecosystem during the pre-monsoon period. Furthermore, delta(13)C values of sediment organic matter (SOM) suggest that terrestrial carbon is not a major contributor to the SOM-pool in this ecosystem. Evidence for seaward migration of Penaeid prawns was provided by some individuals caught in the North Bay which displayed low delta(13)C values of characteristic of fauna found in the mangrove creeks or outlets. Nitrogen stable isotope ratios were found to be a useful indicator of trophic level, even though there remained some overlap between delta(15)N values of presumed low and higher trophic levels. Benthic invertebrates showed a delta(15)N gradient of about 3.2parts per thousand between the mangrove creeks and the Central and North Bay whereas sediment delta(15)N values showed a smaller spatial gradient of about 1.6parts per thousand. This gradient which is hypothesized to reflect differences in inorganic nitrogen sources and availability. (C) 2001 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailBa distribution in surface Southern Ocean sediments and export production estimates
Fagel, Nathalie ULg; Dehairs, Frank; André, Luc ULg et al

in Paleoceanography (2002), 17(2, MAR-JUN),

[1] We present excess Ba (Baxs) data (i.e., total Ba corrected for lithogenic Ba) for surface sediments from a north-south transect between the Polar Front Zone and the northern Weddell Gyre in the ... [more ▼]

[1] We present excess Ba (Baxs) data (i.e., total Ba corrected for lithogenic Ba) for surface sediments from a north-south transect between the Polar Front Zone and the northern Weddell Gyre in the Atlantic sector and between the Polar Front Zone and the Antarctic continent in the Indian sector. Focus is on two different processes that affect excess Ba accumulation in the sediments: sediment redistribution and excess Ba dissolution. The effect of these processes needs to be corrected for in order to convert accumulation rate into vertical rain rate, the flux component that can be linked to export production. In the Southern Ocean a major process affecting Ba accumulation rate is sediment focusing, which is corrected for using excess Th-230. This correction, however, may not always be straightforward because of boundary scavenging effects. A further major process affecting excess Ba accumulation is barite dissolution during exposure at the sediment-water column interface. Export production estimates derived from excess Th-230 and barite dissolution corrected Baxs accumulation rates (i.e., excess Ba vertical rain rates) are of the same magnitude but generally larger than export production estimates based on water column proxies (Th-234-deficit in the upper water column; particulate excess Ba enrichment in the mesopelagic water column). We believe export production values based on excess Ba vertical rain rate might be overestimated due to inaccurate assessment of the Baxs preservation rate. Barite dissolution has, in general, been taken into account by relating it to exposure time before burial depending on the rate of sediment accumulation. However, the observed decrease of excess Ba content with increasing water column depth (or increasing hydrostatic pressure) illustrates the dependence of barite preservation on degree of saturation in the deep water column in accordance with available thermodynamic data. Therefore correction for barite dissolution would not be appropriate by considering only exposure time of the barite to some uniformly undersaturated deep water but requires also that regional differences in degree of undersatuation be taken into account. [less ▲]

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See detailAdvective excess Ba transport as shown from sediment and trap geochemical signatures
Fagel, Nathalie ULg; André, Luc; Dehairs, Frank

in Geochimica et Cosmochimica Acta (1999), 63(16), 2353-2367

We report the results of a geochemical study of sediment and trap material. Major and trace elements (Zr, Ba, rare earth elements, and Th) were analyzed on bulk sedimentary material collected along the NE ... [more ▼]

We report the results of a geochemical study of sediment and trap material. Major and trace elements (Zr, Ba, rare earth elements, and Th) were analyzed on bulk sedimentary material collected along the NE Atlantic margin. Our aim is to test the widespread use of Ba-barite as a proxy for paleoproductivity in a continental margin area. This environment is of great interest because atmospheric-oceanic exchanges are important. In sediments, the geochemical signatures remain close to an upper crust reference, with flat shale-normalized rare earth elements patterns and constant elementary ratios. The calculated biogenic fraction of Ba or excess Pa (20-45%) remains lower than the excess Ba record in trap material (80-99%). The evolution of the geochemical signature along the margin reflects variable dilution of a detrital Post Archean Australian Shale-like component by a biogenic carbonaceous seawater-derived component. The trap material displays a wide range of variation in its trace element content (e.g., Ba similar to 150-3000 ppm, Zr similar to 2-100 ppm), except for the abyssal site, which is characterized by constant signature. In the two other sites, all of the trace element contents increase with water depth and present pronounced seasonal changes at each sampled water depth. The amount of excess Ba also increases in the deepest traps, and its evolution throughout the year mimics the change of the other analyzed trace elements. In contrast, its relationships with particulate organic carbon are not obvious. In term of fluxes, two periods of enhanced excess Ba fluxes are observed: (1) excess Pa flux increases with the detrital-like elements like Th especially during winter, and (2) excess Pa flux is enhanced without any change for the other trace elements during spring. To explain the first case, a supply through lateral advection is proposed. Such transient input of significant excess Ba flux will have a great impact on the yearly averaged estimation of the export production. Indeed, only the second case reflects a bloom in the biological productivity of the water column and must be taken into account in a mean calculation of the export production. Finally, a normalization of the excess Ba by detrital-like element like Th will help to discriminate between a real increase of the excess Ba due to local productivity change (high excess Ba and high excess Ba/Th ratio greater than or equal to 10,000) and any input due to advection process (high excess Ba but low excess Ba/Th ratio < 2000). Copyright (C) 1999 Elsevier Science Ltd. [less ▲]

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See detailBiogeochemical Studies conducted in the OMEX Area during the BELGICA cruises: Preliminary Results
Chou, Lei; Loijens, Michèle; Paucot, Hugues et al

Poster (1994, October)

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See detailDistribution of particulate trace elements in the Northeastern Atlantic
Dauby, Patrick ULg; Baeyens, Willy; Biondo, Renzo ULg et al

in Progress in Belgian Oceanographic Research (1993)

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