Éditeur(s) : Gauthier-Villars
Résumé : The three main sources of organic matter in oceanic basins are marine plankton, terrestrial higher plants and undifferentiated residual organic matter which has been highly degraded in subaerial environments. The time and areal distribution of marine organic matter is mainly controlled by the conditions of preservation. In deep oceans accumulation occurs mainly in confined anoxic basins, and also in open ocean, where local conditions generate a surplus of supply over bacterial degradation. Moderately degraded terrestrial organic matter is derived from land plants and carried away by rivers and currents. It is mainly deposited in sediments of the river fans. Residual organic matter has been highly degraded in subaerial conditions prior to transportation, and may consist of contemporaneous and/or recycled material. It cannot be degraded any more and may be spread over wide areas, regardless of the local environments.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1981

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00246/35680/34188.pdf
http://archimer.ifremer.fr/doc/00246/35680/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Evidence of a changing environment in the catchment area of a small pond (Lansquenet, Lorraine, France) during the last millennium was provided by coupling palynology data and organic ratios [terrestrial to aquatic ratio: TAR(HC); the C29 vs. C27 sterols, C29/C27(ST); average chain length, ACL and aquatic/macrophytes ratio, Paq]. The depositional and alteration conditions of organic matter (OM) were provided by the 5α(H)-stanols/Δ5-sterols ratio. This study shows that quite simple organic ratios clearly allow identification of the different evolution steps of a watershed, from a swamp to the progressive settlement of a pond. During the swampy period, the C/N(at) (ca. 11.1), TAR(HC) (ca. 36.8), C29/C27(ST) (ca. 8.7) and Paq (<0.3) show a high contribution of allochthonous OM associated with the presence of particular aquatic and mesohygrophilous species. A woody level dated to the XIIIth century reflects the period of the settlement of the pond in a more oxic environment [5α(H)-stanol/Δ5sterol ratio <0.2]. Then, the progressive increase in aquatic input and the development of submerged and floating macrophytes are evidenced by low C/N(at) (<7.6), TAR(HC) (ca. 2.7), C29/C27(ST) (ca. 2) and high Paq (ca. 0.5), suggesting an increase in the water level and eutrophication of the pond. A second oxic event [5α(H)-stanols/Δ5sterols ratio averaging 0.16], associated with extensive OM degradation, corresponds to the most recent dredging in 2002 and reflects an important disturbance of sediments due to pond management.
ISSN: 0146-6380

hal-00758066
https://hal.archives-ouvertes.fr/hal-00758066
DOI : 10.1016/j.orggeochem.2012.06.004

Éditeur(s) : Estuaries Research Federation
Résumé : Estuarine systems are complex environments where seasonal and spatial variations occur in concentrations of suspended particulate matter, in primary constituents, and in organic matter content. This study investigated in the laboratory the flocculation potential of estuarine-suspended particulate matter throughout the year in order to better identify the controlling factors and their hierarchy. Kinetic experiments were performed in the lab with a "video in lab" device, based on a jar test technique, using suspended sediments sampled every 2 months over a 14-month period at three stations in the Seine estuary (France). These sampling stations are representative of (1) the upper estuary, dominated by freshwater, and (2) the middle estuary, characterized by a strong salinity gradient and the presence of an estuarine turbidity maximum. Experiments were performed at a constant low turbulent shear stress characteristic of slack water periods (i.e., a Kolmogorov microscale > 1,000 A mu m). Flocculation processes were estimated using three parameters: flocculation efficiency, flocculation speed, and flocculation time. Results showed that the flocculation that occurred at the three stations was mainly influenced by the concentration of the suspended particulate matter: maximum floc size was observed for concentrations above 0.1 g l(-1) while no flocculation was observed for concentrations below 0.004 g l(-1). Diatom blooms strongly enhanced flocculation speed and, to a lesser extent, flocculation efficiency. During this period, the maximum flocculation speed of 6 A mu m min(-1) corresponded to a flocculation time of less than 20 min. Salinity did not appear to automatically enhance flocculation, which depended on the constituents of suspended sediments and on the content and concentration of organic matter. Examination of the variability of 2D fractal dimension during flocculation experiments revealed restructuring of flocs during aggregation. This was observed as a rapid decrease in the floc fractal dimension from 2 to 1.4 during the first minutes of the flocculation stage, followed by a slight increase up to 1.8. Deflocculation experiments enabled determination of the influence of turbulent structures on flocculation processes and confirmed that turbulent intensity is one of the main determining factors of maximum floc size.
Estuaries and coasts : Journal of the Estuarine Research Federation (1559-2723) (Estuaries Research Federation), 2009-07 , Vol. 32 , N. 4 , P. 678-693

Droits : 2009 Springer
http://archimer.ifremer.fr/doc/2009/publication-6631.pdf
DOI:10.1007/s12237-009-9160-1
http://archimer.ifremer.fr/doc/00000/6631/

Éditeur(s) : Public Library Science
Résumé : Subsurface sediments of the Sonora Margin (Guaymas Basin), located in proximity of active cold seep sites were explored. The taxonomic and functional diversity of bacterial and archaeal communities were investigated from 1 to 10 meters below the seafloor. Microbial community structure and abundance and distribution of dominant populations were assessed using complementary molecular approaches (Ribosomal Intergenic Spacer Analysis, 16S rRNA libraries and quantitative PCR with an extensive primers set) and correlated to comprehensive geochemical data. Moreover the metabolic potentials and functional traits of the microbial community were also identified using the GeoChip functional gene microarray and metabolic rates. The active microbial community structure in the Sonora Margin sediments was related to deep subsurface ecosystems (Marine Benthic Groups B and D, Miscellaneous Crenarchaeotal Group, Chloroflexi and Candidate divisions) and remained relatively similar throughout the sediment section, despite defined biogeochemical gradients. However, relative abundances of bacterial and archaeal dominant lineages were significantly correlated with organic carbon quantity and origin. Consistently, metabolic pathways for the degradation and assimilation of this organic carbon as well as genetic potentials for the transformation of detrital organic matters, hydrocarbons and recalcitrant substrates were detected, suggesting that chemoorganotrophic microorganisms may dominate the microbial community of the Sonora Margin subsurface sediments.
Plos One (1932-6203) (Public Library Science), 2014-08 , Vol. 9 , N. 8 , P. e104427

Droits : This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
http://archimer.ifremer.fr/doc/00203/31408/29801.pdf
DOI:10.1371/journal.pone.0104427
http://archimer.ifremer.fr/doc/00203/31408/

Éditeur(s) : Gauthier-Villars
Résumé : Five particle traps were deployed at depths of 4 400 to 4 900 rn at two stations on the Demerara abyssal plain and one station on the Cape Verde abyssal plain (tropical Atlantic). At the same time, an intensive sampling of superficial sediments was carried out using a 0,25 m2 box corer. The total particle flux varied from 372 to 87,7 mg dry weightfm2/day. The average concentration of organic carbon was 40 mg/g of material collected. ln the surface sediment this was only 4 mg/g. A direct relationship existed between the intensity of the flux of organic matter and the richness of the organic matter of the deposited sediment. According to our calculations, more than 90% of the organic matter arriving at the bottom is consumed by the abyssal benthos and only 1% is lost to permanent sediment deposits. For 100 calories consumed by the benthos, 99 are utilized by the infauna and flora, 0, 7 by the holothurian egafauna and 0,3 by near-bottom fisches. The biochemical composition of the particles is characterized at ali stations by a predominance of "humic" material in the total organic matter (more than 55%). The part of the molecules unaltered form living material varied from on station to another: for the most oceanic station the protein dominated, composing 20% of the total energy. At the station onder the influence of the continent the lipid fraction grew and was almost equal to that of the protein. ln this case, the carbohydrate fraction was very weak (7% of the organic matter). Finally the preference of the animais which feed on the particles is principally for the most energetic (lipid) and the most easily hydrolysable (labile protein) molecules: the other molecules, such as the humic matter, are less preferred, although they still contribute to about half of the energy consumed by the abyssal benthic animais.
Cinq pièges à particules ont été déployés à des profondeurs comprises entre 4400 et 4 900 rn sur deux stations dans la plaine abyssale de Demerara et une station dans la plaine abyssale du Cap Vert (Atlantique tropical). Dans le même temps, un échantillonnage intensif du sédiment superficiel a été réalisé à l'aide d'un carottier de 0,25 m2 d'ouverture. Le flux particulaire total mesuré varie de 372 mg de matière sèche/m2/jour à 87,7 mg/m2/g de matériel récolté. Dans les sédiments superficiels, elle n'est plus que d'environ 4 mg/g. Il existe une relation directe entre l'intensité du flux organique et la richesse en composés organiques du sédiment. D'après nos estimations, plus de 90% du matériel organique arrivant sur le fond sont consommés par les organismes benthiques abyssaux et seulement 1% est perdu dans la sédimentation permanente. Pour 100 calories consommées par le benthos, 99 le sont par la petite faune et la flore vivant dans le sédiment, 0, 7 calories sont utilisées par les holothuries (mégafaune) et 0,3 calories par les poissons. La composition biochimique des particules se caractérise, à toutes les stations, par la prédominance des composés organiques transformées néobiogéniques ( « humus ») dans la matière organique totale (plus de 55%). La part des molécules de la matière vivante varie d'une station à l'autre: à la station la plus océanique, les protéines dominent et composent 200/o de l'énergie totale des apports. Dans la station plus soumise aux influences continentales, la concentration en lipides augmente et peut égaler celle des protéines. Dans ce cas, le taux de glucides des particules est très faible (7% des apports organiques). Enfin, les préférences nutritionnelles des animaux qui s'alimentent sur ces particules se portent principalement sur les molécules les plus énergétiques (lipides) et les plus facilement hydrolysables (protéines labiles) : les autres molécules, comme les composés néobiogéniques sont moins recherchés bien qu'ils contribuent pour moitié à l'énergie consommée par les animaux benthiques abyssaux
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1985 , Vol. 8 , N. 3 , P. 293-301

Droits : Gauthier-Villars
http://archimer.ifremer.fr/doc/00112/22318/19991.pdf
http://archimer.ifremer.fr/doc/00112/22318/

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : We report rare earth element (REE) and neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n=25), estuaries (n=18), open-ocean settings (n=15), and cold seeps (n=12). Sedimentary Organic Matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2 – 0.02M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H202 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases. The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with ΣREE = 109 ± 86 ppm (mean ± s; n=58). The organic fractions leached from cold seep sediments display even higher concentration levels (285 ± 150 ppm; mean ± s; n=12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea- water). The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display εNd values that typically range between the εNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit εNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition. Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation.
Geochimica Et Cosmochimica Acta (0016-7037) (Pergamon-elsevier Science Ltd), 2014-09 , Vol. 140 , P. 177-198

Droits : 2014 Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00191/30250/28682.pdf
DOI:10.1016/j.gca.2014.05.016
http://archimer.ifremer.fr/doc/00191/30250/

Éditeur(s) : Elsevier
Résumé : Dissolved and particulate Hg fluxes in the Lot-Garonne-Gironde fluvial-estuarine system were obtained from observation of daily discharge and suspended particulate matter (SPM) concentrations. In addition to the measurements of the total dissolved (< 0.45 gm) and particulate Hg (> 0.45 gm), called HgTD and HgTp respectively, the dissolved inorganic Hg species (HgRD) were determined monthly. Geochemical background values for HgTp in sediments and SPM were similar to crustal values and to typical concentrations in SPM of non-contaminated river systems, respectively. The Riou Mort watershed already known as the origin of important historical polymetallic (e.g., Cd, Zn) pollution was identified as an important Hg point source. In the downstream Lot River, Hg concentrations were clearly higher than those in other moderately contaminated systems. The mean relative contribution of HgRD to HgTD in the Lot River and in the Garonne River was close to 25% and 50%, respectively, and showed no correlation with water discharge or SPM concentration. Depending on the origin and nature of SPM, HgTp concentrations were correlated or not with particulate organic C (POC). Maximum HgTp concentrations were measured in samples containing low POC concentrations and were attributed to sediment resuspension. In contrast, high POC concentrations (6-17%) during algal blooms were associated with low/moderate HgTp concentrations (< 0.5 mg kg(-1)) at different sites, suggesting that Hg concentrations in fluvial phytoplankton may be limited by bioavailability of dissolved Hg and/or physiologically controlled Hg accumulation. Mercury was mostly (up to 98%) transported in the particulate phase with estimated annual Hg fluxes at the outlet of the Lot River system ranging from 35 to 530 kg a(-1) for the past decade. The minimum anthropogenic component (58-84% of total Hg fluxes) could not be explained by present Riou Mort point source contributions, suggesting important Hg release from contaminated sediment as a major source and from downstream point sources (e.g., coal-fired power plants and/or metal processing industries). HgTp concentrations and fluxes were strongly related to hydrologic variations and were clearly increased by riverbed dredging during lock construction. Therefore, the estimated Hg stocks in the Lot River sediment (5-13 tons) represent an important potential Hg source for the downstream fluvial-estuarine system.
Applied Geochemistry (0883-2927) (Elsevier), 2006-03 , Vol. 21 , N. 3 , P. 515-527

Droits : 2006 Elsevier Ltd All rights reserved
http://archimer.ifremer.fr/doc/2006/publication-1343.pdf
DOI:10.1016/j.apgeochem.2005.12.004
http://archimer.ifremer.fr/doc/00000/1343/

Éditeur(s) : Gauthier-Villars
Résumé : The analysis of humic compounds by elemental analysis, PY-GC-MS and HPLC techniques permitted determination of the origin of organic inputs, essentially terrestrial, and the effects of environmental conditions in the deposits along a north-south transect through the Rhone delta, from the river mouth to the open sea. In the prodelta the sedimentation of fine particles enriches the sediments in organic matter. The humic compound contents were relatively low in sediments, perhaps due to a rapid burying of organic matter which leads to anoxic conditions. In sediments fulvic acids are more abundant than humic acids. Elemental analysis indicated that fulvic acids were enriched in hydrogen and nitrogen as compared to humic acids. Furthermore, H/C and N/C ratios increased in the fulvic and humic acids towards the open sea, related to a more marine character. Pyrolysis analysis showed some differences between the chemical composition of fulvic acids which correspond to low molecular weights enriched in carbohydrates, and that of humic acids, high molecular weight compounds which are enriched in phenols and aromatic hydrocarbons. The pyrolysis-derived phenols were abundant near the river mouth, decreasing towards the open sea as nitrogen-containing-compounds increased. Near the river mouth, the abundance of phenolic aldehydes demonstrated by HPLC emphasized the existence of fresh organic matter. On the other hand, off the mouth, an increase in phenolic acids could indicate a more degraded organic material. The fractionation of humic acids in various classes of molecular weight species using ultrafiltration (Amicon membranes) and their analysis showed that, close to the river mouth, the large proportion of the high molecular weight humic compounds observed was enriched in phenols and carbohydrates, probably inherited from the terrestrial ligno-cellulosic complex. This process seemed to be superimposed on the increase of molecular weights which is usually observed as the environment becomes purely marine. These humic compounds would derived either from organic matter from terrestrial soils swept along by the river flow, after deposition on its bed or, more probably, from high molecular weight compounds which, associated with the mineral phase, flocculated when reaching the fluvio-marine front. Generally, the low molecular weight fractions were enriched in hydrogen and nitrogen. Near the river mouth, nitrogen-containing compounds were concentrated in the low molecular weight classes which correspond to organic molecules regarded as humic precursors. Off the mouth, they were incorporated into the high molecular weight complexes, certainly of marine origin.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 1 , P. 61-74

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00101/21187/18804.pdf
http://archimer.ifremer.fr/doc/00101/21187/

Éditeur(s) : Elsevier
Résumé : This study was carried out in shrimp ponds from New Caledonia, in order to determine the cause of the exceptional proportion of abnormal tests (FAI) (often >50%, sometimes >80%). FAI was positively correlated to the quantity of easily oxidized material (EOM) deposited on the bottom of the ponds and to the sediment oxygen demand, and negatively correlated to redox. These results suggest that a very high FAI is a potential indicator for great accumulations of native organic matter, leading to a high sediment oxygen demand. When studying ancient sediments in core samples, exceptional abundances of abnormal tests may indicate periods of high accumulation of EOM, and therefore of oxygen depletion. This finding should help in better management of aquaculture ponds, but should also allow new insight into the interpretation of sedimentary records, providing a useful proxy for paleoenvironmental reconstructions.
Marine Pollution Bulletin (0025-326X) (Elsevier), 2009-09 , Vol. 59 , N. 8-12 , P. 323-335

Droits : 2009 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6955.pdf
DOI:10.1016/j.marpolbul.2009.08.012
http://archimer.ifremer.fr/doc/00000/6955/

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

Éditeur(s) : Université d'Angers
Résumé : In oyster farming areas, organic matter fluxes toward sediment is increased. Pacific oysters (Crassostrea gigas) reject organic-rich faeces and pseudofaeces as a result of filtration process. Organic matter can be consumed by benthic fauna, but in excess it can entails the reduction of benthic faunal species richness, abundance and biomass. Organic matter degradation also induces hypoxic (or anoxic) conditions in the sediment, and production of ammonia and sulfides in toxic concentrations. The main objective of this study is to assess the effects of oyster farming on benthic intertidal ecosystems in the Pertuis Charentais. Benthic macrofauna, living (stained) foraminifera, and physicochemical characteristics of the water column and sediment were used as indicators to evaluate these effects. A multidisciplinary approach was conducted across the Pertuis Charentais at 3 different spatial scales: an oyster trestle (micro-scale), an oyster culture area (meso-scale) and various sites across the Pertuis Charentais (macro-scale). The study was also realised at 4 different temporal scales: some months for the spatial micro-scale, every two weeks for 2 years at meso-scale and once per season during one year at macro-scale. In this study, I found that oyster farming enriches sediment in fine particles, organic matter (up to 12 %), particulate organic carbon (15-20 µg mg 1) and leads to high microphytobenthic biomass. Moreover, the association of seasonnal warming (during spring and summer), remineralisation of accumulated organic matter and short-term hypoxic conditions leads to sulfides and ammonium production. Consequently, the benthic biodiversity decreases and the population dynamic is disturbed. The population dynamic disturbance is characterised by fast abundance rises followed by high mortality rates. In these conditions, tolerant benthic macrofaunal (Cirratulidae, Spionidae and Capitellidae) and foraminiferal (Ammonia tepida and Cribroelphidium gunteri) species are promoted. AMBI index confirms "medium" ecological quality of oyster farming areas. On the contrary, across the control sites, sensible species are maintained (Amphipods, Rosalina cf. vilardeboana). Comparison of oyster farming techniques shows that on-bottom culture is less disturbing for benthic ecosystem than off-bottom culture. Axial tomodensitometry, an innovative method, was used to describe in 3D the sedimentary column organisation. I show that oyster farming modifies the sedimentary column functioning. Indeed, the macrofaunal diversity decrease leads to the modification of the functional diversity of assemblages. Thus, the vertical distribution of living foraminifera is limited in oyster farming areas, because their distribution is tightly related to macrofaunal bioturbating modes.
Dans les zones ostréicoles, les flux de matière organique sont importants, l'huître Crasssotrea gigas rejetant sous forme de pseudo-fécès et de fécès de grandes quantités de matière organique. De ce fait, bien que cette matière organique puisse être consommée par la faune benthique, sa surabondance peut provoquer une réduction de la richesse spécifique, de l'abondance et de la biomasse et provoquer sur le plan des processus biogéochimiques des déplétions en oxygène et l'apparition de substances comme l'ammonium et les sulfures dont les concentrations peuvent devenir toxiques. L'objectif principal de cette étude était donc de déterminer l'impact de l'ostréiculture, grâce à plusieurs indicateurs, sur le compartiment benthique d'un écosystème littoral comme les pertuis charentais. Pour évaluer ces effets, la macrofaune benthique et les foraminifères vivants benthiques ont été utilisés en association avec des mesures des paramètres physico-chimiques de la colonne d'eau et du sédiment. Une approche pluridisciplinaire a ainsi été menée dans les pertuis charentais à trois échelles spatiales différentes : à l'échelle d'une table ostréicole (micro-échelle), à l'échelle d'un site ostréicole (méso-échelle) et à l'échelle des pertuis charentais (macro-échelle). Dans les trois cas, un suivi dans le temps a été associé à une étude de distribution spatiale, quelques mois à micro-échelle, tous les quinze jours pendant deux années à méso-échelle et une fois par saison pendant une année à macro-échelle. Ces différentes approches ont permis d'avoir une vision pertinente de la dynamique et de la réponse fonctionnelle de la faune benthique aux changements induits par la présence de l'ostréiculture. La présence des cultures ostréicoles dans les pertuis charentais enrichit les sédiments en particules fines, en matière organique (12 %), en carbone organique particulaire (15-20 µg mg-1) et favorise une production microphytobenthique élevée. Pendant la période chaude de l'année printemps-été, la reminéralisation de la matière organique accumulée associée à des hypoxies temporaires a favorisé la production de sulfures et d'ammonium. Dans les stations soumises à l'ostréiculture, la diversité des assemblages diminue. La dynamique des espèces est caractérisée par des augmentations rapides des abondances suivies d'épisodes de mortalité. Les espèces tolérantes de la macrofaune benthique (Cirratulidae, Spionidae et Capitellidae) et des foraminifères vivants benthiques (Ammonia tepida et Cribroelphidium gunteri) sont favorisées. Le calcul de l'indice AMBI confirme la qualité écologique moyenne de ces sites. Au contraire, dans la station témoin, les espèces sensibles sont favorisées (Amphipodes, Rosalina cf. vilardeboana). La comparaison de la technique de culture sur table et de culture à plat a montré que la culture des huîtres à plat est moins perturbante pour le milieu. L'étude de la bioturbation a montré l'influence qui existe entre le mode de bioturbation des différents groupes de la macrofaune et la répartition verticale des foraminifères vivants dans la colonne sédimentaire. La diminution de la diversité des assemblages de la macrofaune dans les zones soumises à l'ostréiculture modifient la diversité fonctionnelle de ces assemblages et affectent le fonctionnement de la colonne sédimentaire, limitant la répartition verticale des foraminifères dans ces zones.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2007/these-2582.pdf
http://archimer.ifremer.fr/doc/00000/2582/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
PurposeMarine mangrove sediments in the Manche-à-Eau lagoon (Guadeloupe, Caribbean Sea) harbor locally extensive, white microbial mats. These mats cover the surface of reduced sediments near the roots of red mangrove trees, Rhizophora mangle, and are mainly composed of sulfur-oxidizing bacteria belonging to the Beggiatoaceae family, with some filamentous cyanobacteria. The goal of this study was to investigate the possible influence of sediment characteristics on the presence of these microbial mats.Materials and methodsFour push cores were collected in April 2013, two from zones with microbial mats and two from zones without mats. Sediment characteristics (grain-size distribution, mineralogy, total organic carbon (TOC) and total nitrogen (TN) contents, atomic TOC/TN ratios, and organic matter (OM) δ13C values) were compared for all four cores.Results and discussionSignificant differences were observed between sediments below microbial mats and those without mats. Sediments with microbial mats contained greater amounts of clay, and higher TOC, TN, and TOC/TN ratios, with lower total carbonate content and δ13C values. The higher clay content most likely results from lower fluid flow velocity near to mangrove roots, while higher TOC/TN ratios and lower δ13C values indicate higher inputs of OM from mangrove trees. These results are consistent with the fact that microbial mats were observed near the roots of mangrove trees, which trap OM from terrestrial vegetation and fine sediments.ConclusionsThe grain-size distribution of sediment particles, the total carbonate content, and the δ13C values are the main parameters discriminating between zones with microbial mats and those without mats. Variations in total carbonate content, which is mainly of biogenic origin, result from conditions that are more favorable for benthic organisms in zones without microbial mats. Variations of the TOC/TN ratios are controlled by the presence of a non-negligible amount of inorganic nitrogen bound to surface clay mineral particles and/or by microbial processes.
ISSN: 1439-0108

hal-01545903
https://hal.archives-ouvertes.fr/hal-01545903
DOI : 10.1007/s11368-016-1555-6

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Benthic cyanobacterial mats (BCMs) are impacting coral reefs worldwide. However, the factors and mechanisms driving their proliferation are unclear. We conducted a multi-year survey around the Caribbean island of Curaçao, which revealed highest BCM abundance on sheltered reefs close to urbanised areas. Reefs with high BCM abundance were also characterised by high benthic cover of macroalgae and low cover of corals. Nutrient concentrations in the water-column were consistently low, but markedly increased just above substrata (both sandy and hard) covered with BCMs. This was true for sites with both high and low BCM coverage, suggesting that BCM growth is stimulated by a localised, sub-strate-linked release of nutrients from the microbial degradation of organic matter. This hypothesis was supported by a higher organic content in sediments on reefs with high BCM coverage, and by an in situ experiment which showed that BCMs grew within days on sediments enriched with organic matter (Spirulina). We propose that nutrient runoff from urban-ised areas stimulates phototrophic blooms and enhances organic matter concentrations on the reef. This organic matter is transported by currents and settles on the seabed at sites with low hydrodynamics. Subsequently, nutrients released from the organic matter degradation fuel the growth of BCMs. Improved management of nutrients generated on land should lower organic loading of sediments and other benthos (e.g. turf and macroalgae) to reduce BCM proliferation on coral reefs.
ISSN: 1932-6203

hal-01159626
https://hal-univ-perp.archives-ouvertes.fr/hal-01159626
https://hal-univ-perp.archives-ouvertes.fr/hal-01159626/document
https://hal-univ-perp.archives-ouvertes.fr/hal-01159626/file/journal.pone.0125445.pdf
DOI : 10.1371/journal.pone.0125445

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : Sites of monomethylmercury (MMHg) production in Amazonian regions have been identified in hydraulic reservoirs, lake sediments and wetlands, but tailings ponds have not yet received sufficient attention for this purpose. This work evidenced high MMHg production within the water column and the interstitial water of two tailings ponds of French Guiana Au mines located; (i) in a small scale exploitation (Combat) where Hg was used for Au amalgamation, and (ii) in an industrial on-going Au mine (Yaoni) processing without Hg. The (MMHg)(D) maximum (2.5 ng L-1) occurred in the oxic water column above the sediment-water interface (SWI) of the most recent tailings pond (Combat), where the substrate was fresh, the redox transition was sharp and the pool of total Hg was large. In the Yaoni pond, the (MMHg)(D) maximum concentration (1.4 ng L-1) was located at the SWI where suboxic conditions prevailed. Using the (MMHg)(D) concentration as a proxy for Hg methylation rates, the present results show that Hg methylation may occur in various redox conditions in tailings ponds, and are favored in areas where the organic matter regeneration is more active. A 3-month long laboratory experiment was performed in oxic and anoxic boxes filled with high turbidity waters from the Combat Au mine to simulate tailings ponds. Slaked lime was added in an experimental set (2 mg L-1)and appeared to be very efficient for the reduction of suspended particulate matter (SPM) to environmentally acceptable concentrations. However, at the end of the experiment, large (MMHg)(D) concentrations were monitored under treated anoxic conditions with the (MMHg)(D) maximum located at the SWI above the Fe-reducing zones. No (MMHg)(D) was detected in oxic experiments. The use of slaked lime for SPM decantation appears to be an efficient and non-onerous process for Au miners to avoid Hg methylation in tailings ponds when it is combined with rapid drainage of the mine waters. A subsequent human intervention is however necessary for the recovery of soil structure through the cover of dried ponds with organic rich materials and reforestation to avoid the stagnation of rain waters and the occurrence of anoxia. (C) 2010 Elsevier Ltd. All rights reserved.
Applied Geochemistry (0883-2927) (Pergamon-elsevier Science Ltd), 2011-02 , Vol. 26 , N. 2 , P. 222-229

Droits : 2010 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/00030/14117/12133.pdf
DOI:10.1016/j.apgeochem.2010.11.022
http://archimer.ifremer.fr/doc/00030/14117/

Résumé : Bacteriological study of abyssal sediments: During the Demeraby mission of the N/O Jean Charcot in the western Atlantic Ocean, a study of the microflora of the digestive tracts of echinoderms (Holothuroidea of various genera, Asteroidea, Echinoidea) was compared with that of the surrounding sediment. The bacterial concentration observed in the digestive tracts of all the animals studied is higher than that in the surrounding sediments. The largest numbers were always found in the most anterior part of the digestive tracts of the holothurians. In some cases, the increase is considerable (7.10 versus 5.2. 10 cells per millilitre): It indicates a proliferation of bacterial cells in the anterior part of the digestive tract. As the sediment moves through the digestive tract, the bacterial level progressively decreases. In the most posterior part, the concentration is, however, always clearly greater than that in the surrounding sediment. In the case of the holothurian of the genus Deima, analysis according to the Adamsonian principle of comparison shows that the microflora isolated from the various parts of the digestive tract is composed of taxonomic groups showing little resemblance to those isolated from the sediment. In the case of the holothurian of the genus Pseudostichopus, no specialisation of the microflora from digestive tract contents appears with respect to that of the ingested sediment. Examination of metabolic activities suggests a juxtaposition of two types of communities: Free sediment - sediment in transit that complement one other in their enzymatic and nutritional behaviour Indeed, the strains of free sediment seem to be rather suitable for hydrolysing and using carbohydrates, while those of enteric communities prefer the hydrolysis of lipids and proteins and the assimilation of fatty acids, dicarboxylic acids, hydroxylic acids and certain amino acids. Moreover, the enteric microflorae possess a greater nutritional versatility that, linked with its total numbers, has a sizeable catabolic potential. .../... -2- Measurements of heterotrophic activity done by means of 14 C glucose tracers make it possible to show that the metabolic activities of the bacterial communities of superficial abyssal sediments vary according to zones. In the Amazon Cone, a clear glucose mineralization gradient over a distance of a few kilometres can be observed. In the abyssal plain of Demerara heterotrophic activities are slowed in relation to those of the superficial sediments of the Cone of the Amazon, even though the bacterial numbers and the depths are of the same order of magnitude in the two zones. The abundant microflorae associated with the various divisions of digestive tract contents of the Deima abyssal holothurian manifest little metabolic activity as regards the glucose. However, the bacterial communities of Pseudostichopus and Psychropotes manifest very strong heterotrophic activities, increasing from the oesophagus towards the cloaca. Current results are too fragmentary to allow us to observe possible physiological specialisation of enteric bacterial communities enabling the facilitation of digestion processes in the host. Conclusion: In the abyssal environment, characterised by poorly developed bacterial communities, microflorae associated with the digestive tract contents of echinoderms have considerably greater cellular concentrations. By means of their enzymatic equipment, these enteric communities, which complement those of the free microflorae of superficial sediments, can participate in the transformation of organic matter in the abyssal area. Study of the dynamics of microbial communities and their heterotrophic activities in shellfish farms: From experiments done on the water in the Arcachon basin, trials to quantify and describe the reactivity potential of bacterial communities were performed. Bacterial communities were defined by direct counts, counts after setting them up for cultivation, structure and diversity of these communities, dosage of AMP, ADP, ATP. Two opposite ecological conditions were considered: Autumn conditions (high temperature) and a winter conditions (low temperature). Tubs of sea water of 6 and 60 litres were enriched either with ammonium chloride or a mixture of amino acids, at about 500 uAtg N.L. The experiments lasted 24 hours, with sampling every 3 hours. The autumn community reacted rapidly (6 hours), the response to the enrichment in organic nitrogen being the highest. The structure of the community has unstable immature stages. On the contrary, during the winter experiment, no response could be perceived. This may mean that the latency phase is greater than 24 hours. The structure of this community has mature stages. In conclusion, bacterial communities react in the same way as macroscopic communities. Stable communities are diversified and correspond to mature stages of the ecosystem; the immature stages are unstable and less diversified. This type of experiment has made it possible to bring to light the rapidity of response of bacterial populations, and can be used to define the stability of a bacterial community in a precise biotope.
ETUDE BACTERIOLOGIQUE DES SEDIMENTS ABYSSAUX RESUME Au cours de la mission DEMERABY du n/o Jean CHARCOT en atlantique occidental , une étude de la microflore des tractus digestifs d'Echinodermes (Holothurides de différents genres, Astérides, Echinides) a été comparée à celle du sédiment environnant. La concentration bactérienne observée dans les tractus digestifs de tous les animaux étudiés est supérieure à celle des sédiments environnants. Les effectifs les plus importants sont toujours observés dans la partie la plus antérieure des tractus digestifs des holothuries. Dans certains cas, l'accroissement est considérable (7.10 contre 5,2. 10 cellules/ml) : il indique une prolifération des cellules bactériennes dans la partie antérieure du tractus digestif. Au.cours de la progression du sédiment dans le tractus digestif, la charge bactérienne décroit progressivement. Dans la partie la plus postérieure, la concentration est cependant toujours nettement supérieure à celle du sédiment environnant-. Dans le cas d'une holothurie du genre Deima, l'analyse selon le principe adansonien de comparaison montre que la microflore isolée des différentes parties du tractus digestif est constituée de groupes taxonomiques présentant peu de ressemblance avec ceux isolés du sédiment. Dans le cas d'une holothurie du genre Pseudostichopus il n'apparait pas de spécialisation de la microflore du contenu du tractus digestif par rapport à celle du sédiment ingéré. ¿ ¿ . L'étude des activités métaboliques suggère une juxtaposition de deux types de communautés : sédiment libre-sédiment en transit qui se complètent dans leur comportement enzymatique et nutritionnel. En effet les souches du sédiment libre semblent être plutôt aptes à hydrolyser et à utiliser les glucides, tandis que celles des communautés entériques portent leur préférence sur l'hydrolyse des lipides et protéines et 1'assimilation des acides gras, acides dicarboxyl iques, hydro'xy-acides et certains acides aminés. D'autre part les microflores entériques possèdent une versatilité nutritionnelle plus importante qui, liée à leurs effectifs, offre une potentialité catabolique non négligeable. .../... -2- Les mesures d'activité hétérotrophe effectuées au moyen de traceurs glucose 14 C permettent de montrer que les activités métaboliques des communautés bactériennes des sédiments abyssaux superficiels varient selon les zones. Dans le Cone de l'Amazone on observe un net gradient de minéralisation du glucose sur une distance de quelques kilomètres. Dans la plaine abyssale de Demerara les activités hétérotrophessont ralenties par rapport à celles des sédiments superficiels du Cone de l'Amazone, bien que les effectifs bactériens et les profondeurs soient du même ordre de grandeur dans ces deux zones. Les abondantes microflores associées aux différentes fractions du contenu du tractus digestif de l'holothurie abyssale Deima ne manifestent que peu d'activités métaboliques vis à vis du glucose. Par contre les communautés . bactériennes de Pseudostichopus et P syahropotes manifestent des activités hétérotrophes très fortes, croissant de 1'oesophage vers le cloaque. Les résultats actuels sont trop fragmentaires pour permettre d'observer une éventuelle spécialisation physiologique des communautés bactériennes entëriques permettant de faciliter les processus de digestion chez l'hôte. Conclusion: dans le milieu abyssal, caractérisé par des communautés bactériennes faiblement développées, les microflores associées aux contenus de tractus digestif des Echinodermes présentent des concentrations cellulaires considérablement plus importantes. Par leurs équipements enzymâtiques ces communautés entëriques complémentaires de ceux des microflores libres des sédiments superficiels, peuvent participer à la transformation des matières organiques du domaine abyssal. ETUDE DE LA DYNAMIQUE DES COMMUNAUTES MICROBIENNES ET DE LEURS ACTIVITES HETEROTROPHES DANS LES PARCS CONCHYLICOLES RESUME A partir d'expérimentations effectuées sur l'eau du bassin d'Arcachon, des essais de quantification et qualification du potentiel de réactivité des communautés bactériennes ont été effectuées. Les communautés bactériennes ont été définies par comptage directs, comptages après mise en culture, structure et diversité de ces communautés, dosage des AMP, ADP, ATP. Deux situations écologiques opposées ont étées considérées . Une situation automnale (température élevée) et une situation hivernale (température faible). Des bacs d'eau de mer de 6 et 60 litres ont été enrichis , soit avec du chlorure d'ammonium, soit avec un mélange d'acides aminés, à environ 500 uAtg N.l" . Les expériences ont duré 24 heures, avec des prélèvements toutes les 3 heures. La communauté automnale réagit rapidement (6 heures), la ' réponse à l'enrichissement en azote organique étant la plus importante. La structure de la communauté présente des stades immatures instables. Au contraire, au cours de l'expérimentation hivernale, aucune réponse n'a pu être perçue. Ceci peut signifier que la phase de latence est supérieure à 24 heures. La structure . de cette communauté présente des stades matures. En Conclusion, les communautés bactériennes réagissent de la même façon que les communautés macroscopiques. Les communautés stables sont diversifiées et correspondent à des stades matures de l'écosystème, les stades immatures sont instables et moins diversifiés. Ce type d'expérience a permi de mettre en évidence la rapidité de réponse des populations bactériennes, et peut être utilisé pour définir la stabilité d'une communauté bactérienne dans un biotope précis.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/1981/rapport-1926.pdf
http://archimer.ifremer.fr/doc/00000/1926/

Éditeur(s) : HAL CCSD Oldendorf/Luhe
Résumé : International audience
Large filamentous sulfur-oxidizing bacteria belonging to the Beggiatoacae family can cover large portions of shallow marine sediments surrounding mangroves in Guadeloupe (French West Indies). In order to assess the importance of Beggiatoa mats as an infaunal food source, observations were conducted of the area within mats and at increasing distances from mats. We used natural isotopic compositions and a C-13 enrichment study. Both revealed an ingestion of bacterial mats by associated meiofauna, dominated by rotifers and to a smaller extent by small polychaetes and nematodes. Compared to adjacent sites, sediment covered by bacterial mats presented a higher abundance of diatoms, whereas the total biomass of bacteria did not vary. This constant bacterial abundance suggests that the proportion of organic matter represented by sulfur bacteria is limited compared to the fraction of total bacteria. There was no significant difference in infaunal abundance in mats, suggesting that the availability of this chemosynthetic food resource had a limited local effect. Grazers presented a delta C-13 value increasing with distance from the mat. However, isotopic composition of phospholipid-derived fatty acids specific for diatoms and bacteria revealed that this change is related to modifications of delta C-13 dietary components rather than to changes in diet composition. These complementary methods revealed that the occurrence of sulfur-oxidizing bacterial mats does not necessarily affect grazer abundance and importance of bacteria in their diet. Despite its wide occurrence, Beggiatoa mats would consequently have a minor influence on the structure of the mangrove food web.
ISSN: 0171-8630

hal-01545912
https://hal.archives-ouvertes.fr/hal-01545912
DOI : 10.3354/meps11035

Éditeur(s) : Elsevier
Résumé : The accumulation of nine heavy metals in fine-grained sediments from the mangrove fringed coast of French Guiana is evaluated. The dynamic features of the South American tropical coastline, from the Amazon to the Orinoco Rivers, result in mangrove sediments being alternately submitted to phases of erosion and net sedimentation a few tens of years long. This process influences the distribution of the heavy metals associated with these frequently re-mobilized deposits. Sedimentary cores and mangrove plant samples were collected, at different seasons, in various swamps characterized by different properties (content of sedimentary organic matter, distance from sea water and fresh water). The ranges of measured concentrations expressed in mu mol g(-1) were the following: Cu (0.06 to 0.61), Co (0.12 to 0.68), Pb (0.08 to 0.18), Ni (0.32 to 0.76), Cr (0.61 to 1.40), Zn (1.25 to 5.94), Mn (4.36 to 45.4) and Fe (441 to 1128). No differences were found between sediments from mangroves developing upstream and downstream of urban areas, i.e. Cayenne and Kourou. This suggests that the content of mangrove sediments in heavy metals along the coastline of French Guiana is essentially the result of the continuous alternation of accumulation and transport phases occurring upstream after departing from the Amazon watershed. The sources of this heavy metals content are thus difficult to identify. However it is well known that the alluvium produced by the natural erosion of the Amazonian soils is naturally enriched in mercury. Also, the run-off from gold mining activities is known to contribute to mercury pollution. Ranges in total Hg were between 0.15 and 2.57 nmol g(-1), with mean values close to 0.41 nmol g(-1), and were clearly correlated with total organic carbon except for some outstanding high values, which may be a result of rapid geochemical changes. Heavy metal concentrations showed variations with depth. The redox conditions and the decay processes affecting the organic matter control the cycling of iron and manganese, which in turn control the concentrations and associations of heavy metals. These preliminary results suggest that the variations in heavy metal content with depth or between mangrove areas result largely from diagenetic processes rather than changes in metal input resulting from local human activities. (c) 2005 Elsevier B.V. All rights reserved.
Marine Chemistry (0304-4203) (Elsevier), 2006 , Vol. 98 , N. 1 , P. 1-17

Droits : 2005 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2006/publication-1041.pdf
DOI:10.1016/j.marchem.2005.06.001
http://archimer.ifremer.fr/doc/00000/1041/

Résumé : After a period of rapid development of the sites (an increase in both reared surface area and production), tropical shrimp aquaculture is currently being faced with critical problems due to economical and ecological constraints. In many countries with favourable conditions for shrimp aquaculture such as indonesia or Vietnam, sites are often badly selected and/or over-exploited. This conducts to sorne extent to decreases or collapses in the production due to the difficulty in predicting the maximum production capacity of the sites. Furthermore, it appears that production sustainability depends on many factors among which socio-economy and ecolo gy are of prime importance. The STD3 project titled « Assessment of tropical shrimp aquaculture impact on the environment in tropical countries using hydrobiology, ecology and remote sensing as helping tools for diagnosis )) was initiated in 1994, with the aim to study the sustainability of marine shrimp aquaculture in tropical areas, main! y Indonesia and Vietnam, through the following tasks: (i) improve site selection and study the impact of aquaculture on marine environments presenting a variable sensitivity to organic sewage, (ii) analyse the socio-economical aspects and profitability of the aquaculture industry and of common resources (iii) use remote sensing and geographical data bases for diagnosis and monitoring of site degradation (iv) reinforce the capacity of Asian scientists through training. Severa! aquaculture sites have been investigated in the Lampung region (South Sumatra, Indonesia), the Mekong delta (Vietnam) and on the West coast of New-Caledonia, providing a large range of typical ecosystems encountered in Asia and in the Pacifie, from coralline sites to coastal plains with mangrove and deltaic areas. The study concerned the spatial structure and seasonal influence of these ecosystems, the temporal variation during the course of the project (3 years) and the relation between the ecological structure and farm productions. Remote sensing provides a synoptic vision over large land expanses. Severa! scenes were processed for landuse mapping using conventional classification techniques. Concerning water quality assessment, a general relation for the Java sea was found between image and field data in terms of total suspended matter. Applying this relation to a new site in Sumatra has provided an initial approach to water type and, together with land use mapping, a preliminary assessment of the suitability of the area to shrimp aquaculture development. Socio-economic research has been focused on the identification ofneeds for collective action, including public policy, in the perspective of shrimp farming sustainability. The main concern is in the regulation of shrimp farming intensification and extensification at the scale of coastal ecosystemic entities in a common property resource management perspective. The common considered here is coastal water quality. Comparing the local development profiles and the institutional grounds for the design and implementation of collective management rules shows that variables such as land tenure system, farm owner socio-economic profile, social homogeneity or heterogeneity of the farmers are key factors to analyse the potential for sustainability. The defmition of water quality and the possible means to ensure its collective management are discussed. The main conclusion is that the economie incentives to farming development are strong but there is no significant difference among traditional, semi-intensive and intensive systems in terms of economie efficiency or wealth distribution. The description of the functioning of the different kinds of ecosystems make it possible to give an advice concerning the positioning of the activity inside the ecosystem, and furthermore to have a reference state in order to determine the impact of the activity on the coastal environnement. This impact can be summarized as an increase in the concentration of total suspended matt€?r, of particulate organic matter and of sulfate reducing bacterias. This organic ma~.er is either issued from rearing activities or from telluric origine, due to mangrove eradication when building the ponds. An evaluation of the relationship existing between productivity and characteristics of each ecosystem bas been conducted by correlating ecological indicators data (concentration of total suspended matter, particulate organic matter, chlorophyll, percentage of pheopigments in total pigments and cyanobacteria and sulfatereducing bacteria in water and sediments) with the average production of the farms. This comparison lead to the compilation of a scale of observed production integrating the range of these environmental parameters with shrimp production levels, bound to facilitate the positioning of shrimp farming in relation with the confmement leve! of each ecosystem. Lastly, ali geographie data originated from the various compartments of the study have been geo-referenced and loaded into a geographical information system. This allows to display any query made on spatial variables and their related statistical data, including the ir variations over the last few years and to reveal patterns and phenomena otherwise not obvious.
Le programme mis en oeuvre par la DRV (Paris, CREMA-L'Houmeau, DELIAO Brest, COP Tahiti, GIE/RA Nouvelle Calédonie), dans le cadre d'un projet européen STD3 «(Sciences et Technique au Service du Développement», en collaboration avec l'Université de Montpellier II, l'Ecole Nationale d'Agronomie de Rennes, l'ITC (Hollande), l'Institut Océanographique de Nha Trang (Vietnam), le BADC de Jepara et le BPPT de Jakarta (Indonésie), avait pour but la mise au point de méthodes permettant d'améliorer la sélection des sites ainsi que le suivi du développement et de l'impact de l'aquaculture des crevettes Péneides en milieu tropical pour éviter la surexploitation. Quatre axes de recherche ont été défmis : a) identifier la nature et quantifier les rejets de déchets issus de ce type d'aquaculture, b) définir les caractéristiques écologiques des écosystèmes susceptibles d'accueillir l'activité aquacole et suivre leur évolution sous l'influence des rejets, c) déterminer l'influence de la gestion des fermes et des ressources (aspects économiques) sur les performances de productivité, d) déterminer la capacité de la télédétection comme outil de diagnostic d'impact à l'échelle de la région, e) mener un programme de formation d'étudiants et jeunes chercheurs Vietnamiens et Indonésiens.

Droits : 1998 Ifremer
http://archimer.ifremer.fr/doc/00132/24357/22357.pdf
http://archimer.ifremer.fr/doc/00132/24357/

Éditeur(s) : Gauthier-Villars
Résumé : Mud fields located In the inner part of shelves in front of large estuaries are preferential environments for the investigation of the mechanisms and evolution in time of the supply of such sedimentary bodies. The study of different constituents of the particulate organic matter trapped in the sediments of the West Gironde mud patch contributes to the knowledge of the input origins. This study was carried out with different techniques, including pyrolysis-gas chromatography-mass spectrometry and high performance liquid chromatography, on samples from a core collected in the centre of the mud field. At the bottom of the core, the increase of sugars, amino-sugars and some aromatic hydrocarbons may indicate a more marine character of organic components. The same appears to be the case at the top of the core, where, despite a finer sedimentation, biochemical characteristics could show a more pronounced marine influence than in the middle part. In the middle part of the core, on the other hand, the increase in phenols could result from an increase in lignin-derived. terrestrial inputs. The increase in pyrolysis-derived cyclopentenone may indicate the same terrestrial influence, because this component has its origin in aliphatic polycarboxylic acids resulting from sail leaching. The continental character of the sedimentation is also reflected in the increase of the silt-clay fractions representative of suspended matter originating in the Gironde estuary, associated with a slight carbonate decrease. The taxonomic significance of some phenols is noteworthy: this is especially the case of the cinnamyls which, in the middle part of the core, emphasize the input of herbaceous debris and of the hydroxybenzyls which, at the bottom, provide evidence of the algal origin of part of the organic material. Thus, by means of pyrolysis results and HPLC phenol analysis, it is possible to establish the more or less continental signature of organic components trapped in the ''Ouest-Gironde'' mud patch. This study of organic matter, which confirms earlier sedimentological and micropaleontological data, constitutes a new approach, adapted to the identification of the origin of carbon sources.
Oceanolica Acta (0399-1784) (Gauthier-Villars), 1997 , Vol. 20 , N. 5 , P. 687-695

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00093/20426/18093.pdf
http://archimer.ifremer.fr/doc/00093/20426/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Trace metals (Cd, U, Co, Ni, Cu, Ba, Fe, Mn), total organic carbon (TOC) and C and N stable isotope signatures (delta C-313 and delta N-15) were determined in short sediments cores from the inner and outer shelf off Concepcion, Chile (similar to 36 degrees S). The objectives were to establish the effect of environmental conditions on trace metal distributions at two shelf sites, one affected by seasonal oxygenation and the other by permanent low oxygen conditions due to the presence of the oxygen minimum zone (OMZ). We evaluate trace metals as proxies of past changes in primary productivity and the bottom water oxygen regime. Concentrations of pore water sulfides and NH4+ were also measured as indicators of the main diagenetic pathways at each site. Our results for the inner shelf (seasonal suboxia) suggest that the oxidative state of the sediments responds to seasonal pulses of organic matter and that seasonal oxygenation develops during high and low primary productivity in the water column. Here, positive fluxes (to the water column) estimated from pore water concentrations of several elements were observed (Ba, Co, Ni, Fe and Mn). The less reduced environment at this site produces authigenic enrichment of Cu associated with the formation of oxides in the oxic surface sediment layer, and the reduction of U within deeper sediment sections occur consistently with negative estimated pore water fluxes. In the outer shelf sediments (permanent suboxia, OMZ site), negative fluxes (to the sediment) were estimated for all elements, but these sediments showed authigenic enrichments only for Cd, Cu and U. The short oxygenation period during the winter season did not affect the accumulation of these metals on the shelf. The distribution of Cu, Cd and U have been preserved within the sediments and the authigenic accumulation rates estimated showed a decrease from the deep sections of the core to the surface sediments. This could be explained by a gradual decrease in the strength of the OMZ in the last 100 years, in combination with periods of strong oxygenations during El Nino events. (C) 2011 Elsevier Ltd. All rights reserved.
ISSN: 0278-4343

hal-00745672
https://hal.archives-ouvertes.fr/hal-00745672
DOI : 10.1016/j.csr.2011.11.006