Éditeur(s) : HAL CCSD Wiley
Résumé : Proper estimates of decomposition are essential for tropical forests, given their key role in the global carbon (C) cycle. However, the current paradigm for litter decomposition is insufficient to account for recent observations and may limit model predictions for highly diverse tropical ecosystems. In light of recent findings from a nutrient-poor Amazonian rainforest, we revisit the commonly held views that: litter traits are a mere legacy of live leaf traits; nitrogen (N) and lignin are the key litter traits controlling decomposition; and favourable climatic conditions result in rapid decomposition in tropical forests. Substantial interspecific variation in litter phosphorus (P) was found to be unrelated to variation in green leaves. Litter nutrients explained no variation in decomposition, which instead was controlled primarily by nonlignin litter C compounds at low concentrations with important soil fauna effects. Despite near-optimal climatic conditions, tropical litter decomposition proceeded more slowly than in a climatically less favourable temperate forest. We suggest that slow decomposition in the studied rainforest results from a syndrome of poor litter C quality beyond a simple lignin control, enforcing energy starvation of decomposers. We hypothesize that the litter trait syndrome in nutrient-poor tropical rainforests may have evolved to increase plant access to limiting nutrients via mycorrhizal associations.
ISSN: 0028-646X

hal-01032400
https://hal.archives-ouvertes.fr/hal-01032400
DOI : 10.1111/j.1469-8137.2010.03483.x

Éditeur(s) : Université de Pau et des Pays de l'Adour
Résumé : In a context of decline of European eel (Anguilla anguilla L.) and search for biological markers of habitat use and quality, a multidisciplinary approach was engaged on the Adour estuary and its associated wetlands. Two axes were developed. The first axe aimed at highlighting the successive presence of the species in different ecosystems based on the otolith elemental composition. The second aimed at the evaluation of the chemical pressure underwent by eels based on the contaminant bioconcentration in soft tissues and the early molecular response to the chemical stress. With a view to the analyses of otolith elemental composition taking into account the 3D structure, the low elemental concentration in the matrix and keeping the finest spatial resolution, four micro sampling strategies and multi elemental analyses using femtosecond laser ablation ICP-MS were tested (crater, 1D scan, 2D scan, flash ablation). The strategy showing the best compromise according to the objectives (continuous recording, multi elemental approach) was applied on otolith of yellow eels from the Adour. The simultaneous use of Sr and Ba profiles, after validation, represents a new tool, easy, fast and reliable for the reconstruction of freshwater and brackish ecosystems use by eel avoiding misinterpretation due to vaterite inclusions. Three major behaviors were highlighted on the Adour: a residency in brackish water, a residency in freshwater and nomad behavior. The last one is illustrated by a shift to brackish water after three to four years spent in freshwater. Simultaneously, the study of inorganic and organic contamination of eel soft tissues showed that sampled wetlands are moderately contaminated. These results were confirmed by the first estimation, in wild conditions, of the early response to the chemical stress using the hepatic expression of CYP1A1 gene measured by real time RT-PCR. Conversely, in the downstream part of the Adour estuary, Hg loads in eels, especially methyl mercury, and PCBs analyses indicate values that need further investigations considering the European norms of consumption. The comparison of the different markers used (heavy metal and organochlorinated compounds contamination of soft tissues, condition index) support a lower quality of the estuary despite higher eel growth rate on this site. This study supports the use of numerous markers in integrated studies in order to understand and specify the relationships between eels and their continental growth zones.
Dans un contexte de déclin de l'anguille européenne (Anguilla anguilla L.) et de recherche de marqueurs biologiques retraçant la fréquentation des divers habitats et renseignant sur la qualité de ceux-ci, une approche pluridisciplinaire a été mise en place sur l'estuaire de l'Adour et ses zones humides. Deux axes ont été privilégiés. Le premier cherchait à visualiser la présence successive de l'espèce dans différents écosystèmes en se basant sur la composition élémentaire des otolithes. Le deuxième avait pour but d'évaluer la pression chimique inorganique et organique subie par l'anguille dans les zones d'études en s'appuyant sur la bioconcentration des contaminants dans les tissus mous et la réponse moléculaire précoce au stress chimique. En vue des analyses de la composition élémentaire des otolithes et pour répondre au mieux à la structure en trois dimensions, à la faible concentration des éléments dans la matrice tout en conservant une résolution spatiale la plus fine possible, quatre stratégies de micro-échantillonnage et d'analyses multiélémentaires par ablation laser femtoseconde ICP-MS ont été testées (cratère, scan 1D, scan 2D, ablation flash). La méthodologie présentant le meilleur compromis par rapport aux objectifs fixés (enregistrement continu, approche multiélémentaire) a ensuite été appliquée sur les otolithes d'anguilles jaunes du Bas-Adour. L'utilisation simultanée des profils continus de Sr et de Ba, après validation, constitue un outil facile d'utilisation, rapide et fiable pour reconstruire les historiques de fréquentation des différents écosystèmes estuariens et dulçaquicoles par l'anguille tout en s'affranchissant des problèmes potentiels liés aux inclusions de vatérite, un polymorphe du carbonate de calcium. Trois grands types de comportement ont pu être mis en évidence sur l'Adour : résidence en eau saumâtre, résidence en eau douce et nomadisme. Ce dernier est plus particulièrement illustré par un mouvement marqué vers l'eau saumâtre pour des individus ayant passé de trois à quatre ans dans l'eau douce. Parallèlement, l'étude de la contamination organique et inorganique des tissus mous de l'anguille a permis de déduire à la faible contamination des zones humides échantillonnées. La première estimation en condition naturelle de la réponse précoce au stress chimique par évaluation de l'expression hépatique du gène CYP1A1 par RT-PCR en temps réel confirme ces résultats. En revanche, dans la partie estuarienne aval de l'Adour, les niveaux en Hg, présent en majorité sous sa forme méthylée dans les anguilles, et l'analyse des PCBs indiquent des valeurs qui suscitent un examen plus approfondi au regard des normes européennes en vigueur. La confrontation des différents descripteurs (contamination des tissus mous par les métaux lourds et organochlorés, indice de condition) utilisés conforte la qualité moindre de la zone estuarienne malgré des performances de croissance de l'anguille favorisées sur ces sites. Ainsi, cette étude supporte l'intérêt de la mise en oeuvre de descripteurs multiples utilisés (niveaux de métaux lourds et organochlorés dans les tissus mous, réponse moléculaire au stress chimique, microchimie de l'otolithe, indice de condition, taux de croissance) dans des approches intégrées pour comprendre et préciser les relations existantes entre l'anguille et ses zones de croissance continentales.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2009/these-7381.pdf
http://archimer.ifremer.fr/doc/00000/7381/

Éditeur(s) : HAL CCSD Elsevier
Résumé : Detailed sedimentological investigations on numerous outcrops and drill-core sections in the 2.1-Ga-old Franceville basin, Gabon, provide evidence for a large-scale injectite network. The injectites were formed by the injection of sands through a thickness of about 150 m of the FB1 Member, and now cover a minimum area of 70 km2 corresponding to the Bangombé plateau, but are also recognized close to Franceville 35 km farther south-east. The injectite lithology corresponds to a mud- or carbonate-supported sandstone characterized by a loose and uncompacted fabric contrasting with the host-rock. Because the injectites are often parallel to subparallel to the stratification, they were misinterpreted as depositional beds by previous authors. At outcrop, the injectite bodies exhibit sill, dyke, wing and protrusive geometries emplaced during early burial within poorly compacted material, with partial wall erosion and dissociation. The source of the sand material is attributed to a channel-levee turbidite depositional system located in the lower part of the FB1 Member. These deposits were buried by a thick biochemical muddy cap deposited during a starvation phase, which increased the seal capacity of the system. This type of architecture has a high potential to develop compaction disequilibrium during burial. Moreover, in the case of the Francevillian injectites, the abundance of microbial organic matter favoured early methane degassing and lateral charging of the sand reservoir. The overpressure in the channels was periodically released during early burial, through the effect of rapid sedimentary and tectonic loading, and possible seismic activity. The fluidized sand was injected according to a symmetrical wing pattern. Thus, the injected masses caused a local decrease in the grade of the lateritic manganese ore deposit of the Bangombé plateau.
ISSN: 0301-9268

hal-01667217
https://hal.archives-ouvertes.fr/hal-01667217
DOI : 10.1016/j.precamres.2017.09.022

Éditeur(s) : HAL CCSD MDPI
Résumé : International audience
AbstractThis review provides a global overview of microporous silica based membranes for desalination via pervaporation with a focus on membrane synthesis and processing, transport mechanisms and current state of the art membrane performance. Most importantly, the recent development and novel concepts for improving the hydro-stability and separating performance of silica membranes for desalination are critically examined. Research into silica based membranes for desalination has focussed on three primary methods for improving the hydro-stability. These include incorporating carbon templates into the microporous silica both as surfactants and hybrid organic-inorganic structures and incorporation of metal oxide nanoparticles into the silica matrix. The literature examined identified that only metal oxide silica membranes have demonstrated high salt rejections under a variety of feed concentrations, reasonable fluxes and unaltered performance over long-term operation. As this is an embryonic field of research several target areas for researchers were discussed including further improvement of the membrane materials, but also regarding the necessity of integrating waste or solar heat sources into the final process design to ensure cost competitiveness with conventional reverse osmosis processes. © 2012 by the authors.
ISSN: 2073-4441

hal-01683200
https://hal.univ-antilles.fr/hal-01683200
DOI : 10.3390/w4030629

Éditeur(s) : Public Library Science
Résumé : The blue mussel, Mytilus edulis, is a commercially important species, with production based on both fisheries and aquaculture. Dynamic Energy Budget (DEB) models have been extensively applied to study its energetics but such applications require a deep understanding of its nutrition, from filtration to assimilation. Being filter feeders, mussels show multiple responses to temporal fluctuations in their food and environment, raising questions that can be investigated by modeling. To provide a better insight into mussel–environment interactions, an experiment was conducted in one of the main French growing zones (Utah Beach, Normandy). Mussel growth was monitored monthly for 18 months, with a large number of environmental descriptors measured in parallel. Food proxies such as chlorophyll a, particulate organic carbon and phytoplankton were also sampled, in addition to non-nutritious particles. High-frequency physical data recording (e.g., water temperature, immersion duration) completed the habitat description. Measures revealed an increase in dry flesh mass during the first year, followed by a high mass loss, which could not be completely explained by the DEB model using raw external signals. We propose two methods that reconstruct food from shell length and dry flesh mass variations. The former depends on the inversion of the growth equation while the latter is based on iterative simulations. Assemblages of food proxies are then related to reconstructed food input, with a special focus on plankton species. A characteristic contribution is attributed to these sources to estimate nutritional values for mussels. M. edulis shows no preference between most plankton life history traits. Selection is based on the size of the ingested particles, which is modified by the volume and social behavior of plankton species. This finding reveals the importance of diet diversity and both passive and active selections, and confirms the need to adjust DEB models to different populations and sites.
Plos One (1932-6203) (Public Library Science), 2014-10 , Vol. 9 , N. 10 , P. 1-13

Droits : 2014 Picoche 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/00218/32895/31380.pdf
http://archimer.ifremer.fr/doc/00218/32895/31381.pdf
http://archimer.ifremer.fr/doc/00218/32895/31382.pdf
http://archimer.ifremer.fr/doc/00218/32895/31383.pdf
http://archimer.ifremer.fr/doc/00218/32895/31384.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : URL de l'article : http://www.sciencedirect.com/science/article/B6WPN-4XY3KDK-2/2/fd8508af63d82e29b4f9829c65194e26
The impact of climatic changes that occurred during the last glacial maximum and the Holocene on vegetation changes in the Amazon Basin and the Guiana Shield are still widely debated. The aim of our study was to investigate whether major changes in vegetation (i.e. transitions between rainforests and C4 savannas) occurred in northern French Guiana during the Holocene. We measured variations in the δ13C of soil organic matter at eight sites now occupied by forest or savannah. The forest sites were selected to cover two regions (forest refugia and peneplains) which are thought to have experienced different intensities of disturbance during the latest Pleistocene and the Holocene. We found that none of the forest sites underwent major disturbances during the Holocene, i.e. they were not replaced by C4 savannahs or C4 forest savannahs for long periods. Our results thus suggest that tropical rainforests in northern French Guiana were resilient to drier climatic conditions during the Holocene. Nevertheless, geographical and vertical variations in the 13C of SOM were compatible with minor changes in vegetation, variations in soil processes or in soil physical properties.
ISSN: 0033-5894

halshs-00551758
https://halshs.archives-ouvertes.fr/halshs-00551758
DOI : 10.1016/j.yqres.2009.11.007

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Tropical forests determine global biogeochemical cycles to a large extent, but control factors for key ecosystem processes such as decomposition remain poorly understood. With a full-factorial C (cellulose), N (urea), and P (phosphate) fertilization experiment, we tested the relative importance of C and nutrient limitation on litter decomposition in a mature lowland moist forest of French Guiana. Despite the previously demonstrated litter C quality control over decomposition and the very low soil P content (0.1 mg g(-1) of soil) at our study site, fertilization with C or P alone did not increase the decomposition of a wide range of litter types (N:P ratios between 20 and 80). Nitrogen fertilization alone also had no effect on decomposition. However, the combined fertilization with N and P resulted in up to 33.5% more initial litter mass lost, with an increasing effect with wider litter N:P ratios. Soil fauna strongly stimulated litter mass loss and enhanced nutrient fertilization effects. Moreover, nutrient effects on decomposition increased with additional C fertilization in the presence of fauna. Our results suggest that increased N availability is required for a positive P effect on decomposition in the studied P-poor tropical forest. Further stimulation of decomposition by C amendment through priming indicates energy limitation of decomposers that is co-determined by nutrient availability. The demonstrated intricate control of the key resources C, N, and P on decomposition calls for an intensified research effort on multiple resource limitation on key processes in tropical forests and how they change under multiple human impacts.
ISSN: 1432-9840

hal-01032414
https://hal.archives-ouvertes.fr/hal-01032414
DOI : 10.1007/s10021-012-9564-9