Éditeur(s) : OMICS Publishing Group
Résumé : Coastal tropical shrimp farming may impact the adjacent ecosystems through the release of large quantities of effluents rich in nutrients. In New Caledonia, mangroves are considered as a natural biofilter to reduce impacts on the surrounding World Heritage listed lagoon. Our main objective was to understand the influence of effluent discharge on the biogeochemistry of mangrove sediments. A monitoring of the physico-chemical parameters of mangrove sediments was carried out during a whole year, including active and non active periods of the farm. The parameters studied were: i) benthic primary production (Chl-a concentrations), ii) physico-chemical parameters of sediments (redox potential, pH, salinity, TOC, TN, TS, δ13C and δ15N), iii) concentrations of dissolved nitrogen, iron and phosphorus. A mangrove developing in the same physiographic conditions, presenting the same zonation, and free of anthropogenic input was used as reference. The concentration of benthic Chl-a measured at sediment surface in the effluent receiving mangrove was twice to three times that measured in the control zone whatever the season. We thus suggest that nutrients inputs significantly increased the phytobenthic production in the effluent receiving mangrove during the whole year, even after the cessation of discharges and because of natural seasonal dynamic of phytobenthos. Although the flow of surface OM was increased, the OM content at depth was not higher than in the control mangrove. However, the contribution of mangrove detritus to the sedimentary organic pool was higher probably as a result of higher density and much greater individual size of the mangrove trees. Unlike the control mangrove sediment, the effluent receiving mangrove sediment was not stratified, redox potential values were high and presence of Fe3+ was detected down to 50 cm depth, probably as a result of a larger root system, allowing a better sediment oxygenation and accentuated OM decomposition processes, and thus limiting ecosystem saturation.
Journal of Aquaculture Research & Development (21559546) (OMICS Publishing Group), 2014-07-03 , Vol. 5 , N. 5 , P. 1-13

Droits : 2014 Marchand C, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
http://archimer.ifremer.fr/doc/00251/36253/34801.pdf
DOI:10.4172/2155-9546.1000262
http://archimer.ifremer.fr/doc/00251/36253/

Éditeur(s) : Elsevier Sci Ltd
Résumé : This study analyses the impact on the oceanic mean state of the evolution of the oceanic component (NEMO) of the climate model developed at Institut Pierre Simon Laplace (IPSL-CM), from the version IPSL-CM4, used for third phase of the Coupled Model Intercomparison Project (CMIP3), to IPSL-CM5A, used for CMIP5. Several modifications have been implemented between these two versions, in particular an interactive coupling with a biogeochemical module, a 3-band model for the penetration of the solar radiation, partial steps at the bottom of the ocean and a set of physical parameterisations to improve the representation of the impact of turbulent and tidal mixing. A set of forced and coupled experiments is used to single out the effect of each of these modifications and more generally the evolution of the oceanic component on the IPSL coupled models family. Major improvements are located in the Southern Ocean, where physical parameterisations such as partial steps and tidal mixing reinforce the barotropic transport of water mass, in particular in the Antarctic Circumpolar Current) and ensure a better representation of Antarctic bottom water masses. However, our analysis highlights that modifications, which substantially improve ocean dynamics in forced configuration, can yield or amplify biases in coupled configuration. In particular, the activation of radiative biophysical coupling between biogeochemical cycle and ocean dynamics results in a cooling of the ocean mean state. This illustrates the difficulty to improve and tune coupled climate models, given the large number of degrees of freedom and the potential compensating effects masking some biases.
Ocean Modelling (1463-5003) (Elsevier Sci Ltd), 2013-12 , Vol. 72 , P. 167-184

Droits : 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00170/28102/26612.pdf
DOI:10.1016/j.ocemod.2013.09.001
http://archimer.ifremer.fr/doc/00170/28102/

Éditeur(s) : Amer Geophysical Union
Résumé : Large rivers are key hydrologic components in oceanography, particularly regarding air-sea and land-sea exchanges and biogeochemistry. We enter now in a new era of Sea Surface Salinity (SSS) observing system from Space with the recent launches of the ESA Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius/Sac-D missions. With these new sensors, we are now in an excellent position to revisit SSS and ocean color investigations in the tropical northwest Atlantic using multi-year remote sensing time series and concurrent in situ observations. The Amazon is the world's largest river in terms of discharge. In its plume, SSS and upper water column optical properties such as the absorption coefficient of colored detrital matter (acdm) are strongly negatively correlated (<-0.7). Local quasi-linear relationships between SSS and acdm are derived for these plume waters over the period of 2010-2013 using new spaceborne SSS and ocean color measurements. Results allow unprecedented spatial and temporal resolution of this coupling. These relationships are then used to estimate SSS in the Amazon plume based on ocean color satellite data. This new product is validated against SMOS and in situ data and compared with previously developed SSS retrieval models. We demonstrate the potential to estimate tropical Atlantic SSS for the extended period from 1998 to 2010, prior to spaceborne SSS data collection.
Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2015-05 , Vol. 120 , N. 5 , P. 3177-3192

Droits : 2015. American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00255/36610/35742.pdf
DOI:10.1002/2014JC010109
http://archimer.ifremer.fr/doc/00255/36610/

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Forest ecosystems have integral roles in climate stability, biodiversity and economic development. Soil stewardship is essential for sustainable forest management. Organic matter (OM) removal and soil compaction are key disturbances associated with forest harvesting, but their impacts on forest ecosystems are not well understood. Because microbiological processes regulate soil ecology and biogeochemistry, microbial community structure might serve as indicator of forest ecosystem status, revealing changes in nutrient and energy flow patterns before they have irreversible effects on long-term soil productivity. We applied massively parallel pyrosequencing of over 4.6 million ribosomal marker sequences to assess the impact of OM removal and soil compaction on bacterial and fungal communities in a field experiment replicated at six forest sites in British Columbia, Canada. More than a decade after harvesting, diversity and structure of soil bacterial and fungal communities remained significantly altered by harvesting disturbances, with individual taxonomic groups responding differentially to varied levels of the disturbances. Plant symbionts, like ectomycorrhizal fungi, and saprobic taxa, such as ascomycetes and actinomycetes, were among the most sensitive to harvesting disturbances. Given their significant ecological roles in forest development, the fate of these taxa might be critical for sustainability of forest ecosystems. Although abundant bacterial populations were ubiquitous, abundant fungal populations often revealed a patchy distribution, consistent with their higher sensitivity to the examined soil disturbances. These results establish a comprehensive inventory of bacterial and fungal community composition in northern coniferous forests and demonstrate the long-term response of their structure to key disturbances associated with forest harvesting. The ISME Journal (2012) 6, 2199-2218; doi:10.1038/ismej.2012.84; published online 2 August 2012
ISSN: 1751-7362

hal-01546179
https://hal.archives-ouvertes.fr/hal-01546179
DOI : 10.1038/ismej.2012.84

Éditeur(s) : Actes de colloques. Ifremer Brest [ACTES COLLOQ. IFREMER.]. 1986
Résumé : Seawater samples taken from shallow suspended particle maxima (20-57m) at or near the base of the surface mixed layer in various oceanic areas were tested for their potential to produce hydrogen (H sub(2)) gas. Results suggest that hydrogen can be bacterially produced through a fermentative process in microanaerobic niches within particulate matter. The organisms responsible for this process are ubiquitous within the temperate and tropical waters sampled. Enumeration of potential H sub(2)-producing bacteria using fluorescent antibody techniques yielded a maximum at the base of the surface mixed layer, the same depth where the greatest H sub(2) gas production potential was observed. Hydrogen-producing bacteria comprised up to 15% of the total bacterial direct count (AODC). Findings indicate that bacteria associated with shallow nepheloid layers are capable of producing gas and thus contributing to the observed supersaturated gas concentration in the marine environment.
Des échantillons d'eau de mer contenant des particules en suspension ont été prélevés en zone peu profonde (20 à 57 m) sur ou près de la couche brassée de surface en différents points de l'océan et ont été testés pour leur potentiel de production d'H2. Les résultats suggèrent que l'hydrogène peut être produit, par les bactéries, lors d'un processus fermentatif dans des microniches anaérobies de la matière particulaire. Les organismes responsables de ce processus sont ubiquistes dans les échantillons provenant des eaux tempérées el tropicales. Les numérations maximales de bactéries potentiellement productrices d'hydrocele, faites par des techniques d'anticorps fluorescents, sont obtenues à la base de la couche brassée de surface ; à cette même profondeur est observé le potentiel de production d'hydrogène le plus important. Les bactéries productrices d'hydrogène constituent jusqu'à 15 % des numérations bactériennes totales, effectuées par comptage direct (AODC). Ces observations indiquent que les bactéries associées aux couches nephéloïdes peu profondes sont capables de produire de l'hydrogène et contribuent ainsi à la sursaturation en gaz observée dans le milieu marin.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/1984/acte-962.pdf
http://archimer.ifremer.fr/doc/00000/962/

Résumé : This report synthesises the knowledge on the biogeochemical cycle, bioconcentration processes and ecotoxicity of lead in the marine environment. Man induced changes on the lead cycle, especially along the French coasts are reviewed. Concentration levels, mechanisms and fluxes between geochemical reservoirs are assessed. Emphasis is given on sublethal effects and toxicity mechanisms. Quality standards used in European Community countries are listed. Conclusions and recommendations for environmental management and research are given.
Le présent document constitue une synthèse des connaissances sur le cycle biogéochimique, la bioconcentration et l'écotoxicité du plomb en milieu marin. Il fait état des perturbations du cycle du plomb par l'action de l'homme, en particulier dans le milieu littoral français. Les niveaux de concentration et les quantités échangées entre les réservoirs géochimiques sont évalués. L'accent est mis sur les effets sublétaux et les mécanismes de toxicité vis-à-vis du biotope marin. Les réglementations relatives en milieu marin actuellement en vigueur dans les pays de la Communauté européenne sont répertoriées. Avec les conclusions quelques recommandations en matière de gestion et de recherche sont faites.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/1993/rapport-1449.pdf
http://archimer.ifremer.fr/doc/00000/1449/

Éditeur(s) : MDPI AG
Résumé : In mangrove ecosystems, strong reciprocal interactions exist between plant and substrate. Under semi-arid climate, Rhizophora spp. are usually predominant, colonizing the seashore, and Avicennia marina develops at the edge of salt-flats, which is the highest zone in the intertidal range. Along this zonation, distribution and speciation of C, Fe, S, N, and P in sediments and pore-waters were investigated. From the land-side to the sea-side of the mangrove, sediments were characterized by I/ increase in: (i) water content; (ii) TOC; (iii) mangrove-derived OM; II/ and decrease in: (i) salinity; (ii) redox; (iii) pH; (iv) solid Fe and solid P. Beneath Avicennia and Rhizophora, TS accumulated at depth, probably as a result of reduction of iron oxides and sulfate. The loss of total Fe observed towards the sea-side may be related to sulfur oxidation and to more intense tidal flushing of dissolved components. Except the organic forms, dissolved N and P concentrations were very low beneath Avicennia and Rhizophora stands, probably as a result of their uptake by the root systems. However, in the unvegetated salt-flat, NH4+ can accumulate in organic rich and anoxic layers. This study shows: (i) the evolution of mangrove sediment biogeochemistry along the intertidal zone as a result of the different duration of tidal inundation and organic enrichment; and (ii) the strong links between the distribution and speciation of the different elements.
Journal of Marine Science and Engineering (2077-1312) (MDPI AG), 2015-02-10 , Vol. 3 , N. 1 , P. 52-72

Droits : 2015 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/).
http://archimer.ifremer.fr/doc/00251/36252/34802.pdf
DOI:10.3390/jmse3010052
http://archimer.ifremer.fr/doc/00251/36252/

Résumé : Arsenic levels of in the marine environment are high in comparison with other contaminants. Over the past twenty years, a large number of arsenic organic compounds have been identified in the water, sediments and living species. This document constitutes a synthesis of current knowledge on arsenic sources, and contamination levels, on its biogeochemical cycle as well as its toxic effects on human and marine fauna. This paper highlights in particular the effects of phosynthesis on arsenic speciation and its distribution throughout the marine environment. Problems of toxicity in the case of certain phyto- and zooplankton species are identified. Bioaccumulation in seaweeds, molluscs and fishes is documented as well, with special attention to the species encountered in the French coastal waters.
Les niveaux de présence de l'arsenic en milieu marin sont élevés comparativement à d'autres contaminants. Depuis une vingtaine d'années, de nombreux composés organiques de l'arsenic ont été identifiés dans l'eau, les sédiments et les espèces vivantes. Le présent document constitue une synthèse des connaissances sur les sources et les niveaux de contamination, le cycle biogéochimique, les effets toxiques pour l'homme et les espèces marines. L'accent est mis notamment sur les effets de la photosynthèse sur la spéciation de cet élément et sur sa distribution dans le milieu. Les problèmes de toxicité pour certaines espèces phyto- et zooplanctonniques sont identifiés. La bioaccumulation chez les algues, les mollusques et les poissons est bien documentée, avec une attention particulière pour les espèces présentes dans les eaux côtières françaises.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/1993/rapport-1448.pdf
http://archimer.ifremer.fr/doc/00000/1448/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The biogeochemistry of sulfur and carbon during early-diagenetic processes within organic-rich marine mangrove sediments was studied in the “Manche à Eau” lagoon, Guadeloupe, West Indies. These sediments are characterized by a total organic carbon content (TOC) mostly above 11 wt%, δ13CTOC below − 25‰ VPDB and C/Nmolar ratios exceeding 15. Rates of mangrove-derived organic carbon accumulation vary between ~ 200 and 400 gOC·m− 2·yr− 1, with highest rates at the shore of the lagoon. On the lagoon border, where colorless filamentous sulfur-oxidizing bacteria colonize the sediments, active sulfate reduction within the upper 20 cm, with a net removal rate of ~ 0.5 μmol·cm− 3·d− 1, is assumed to be essentially driven by organic carbon oxidation. This is expressed by relatively low apparent sulfur isotope fractionation (34εnet = − 33‰) and a gentle δ18O/δ34Ssulfate apparent slope of 0.36 ± 0.03 (2s). Further inside the lagoon, in the absence of sulfur-oxidizing bacteria, higher apparent sulfur isotope fractionation and a steeper δ18O/δ34Ssulfate slope (0.67 ± 0.20) suggest an overall lower sulfate removal rate that may be coupled to minor sulfur disproportionation. Spatial and vertical variation in sulfur cycling, reflected by oxygen and sulfur isotopic characteristics, seem to be mainly controlled by unsteady to relatively steady organic matter deposition and its reactivity. In all sediments, δ34S values of pyrite are positively correlated with the TOC/TS ratio and negatively correlated with δ13CTOC; suggesting a primary control of the quantity and quality of organic matter on the pyrite isotope records, despite potential iron-limiting conditions for the most active sites. Our results provide insights into the role of organic carbon input on sulfur cycling; stimulating sulfate reduction and in turn the presence of sulfur-oxidizing microbial mats, resulting in an intense cycling of both carbon and sulfur in these marine mangrove sediments.
ISSN: 0009-2541

hal-01507696
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01507696
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01507696/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01507696/file/Cr%C3%A9mi%C3%A8re%20et%20al.%20-%20Sulfur%20diagenesis%20under%20rapid%20accumulation%20of%20orga.pdf
DOI : 10.1016/j.chemgeo.2017.02.017