Limited Consequences of Seagrass Decline on Benthic Macrofauna and Associated Biotic Indicators
Marine phanerogams are ecosystem engineers, as their presence induces major environmental changes that impact on the benthic fauna. Consequently, modifications to the structure of benthic communities would be expected to be associated with seagrass decline. Since 2005, Zostera noltii seagrass beds in Arcachon Bay (France), the largest in Europe, have undergone a severe decline. Twelve stations distributed throughout the lagoon were sampled in 2002, and all were found to be densely planted at that time. Subsequently, the same stations were revisited in 2010 and seagrass cover had drastically decreased by that time. Based on benthic macrofauna, multidimensional scaling (MDS) analysis identified four groups. Years were separated. In 2002, two groups were distinct in relation to the water body, since in 2010 separation between the two other groups was related to seagrass occurrence. When looking at community structure and dominant species there were moderate differences within and between years, independent of seagrass decline. Seagrass loss did not drastically modify the species composition as they were preserved in the remaining seagrass patches. However, there was a drop in macrofauna abundance in unvegetated muddy compared with abundance in the remaining seagrass areas. Epifauna was particularly affected by seagrass decline. Among biotic indicators based on macrofauna, multivariate indicator MISS (Macrobenthic Index in Sheltered Systems) was in agreement with the similarity of macrofauna structure among groups, while other tested indicators performed badly in relation to seagrass occurrence. However, no index detected seagrass loss, highlighting the necessity of maintaining a separate survey on seagrass cover.
(Estuaries and Coasts. vol. 36, n° 1559-2723, pp. 795-807, 29/01/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Étude de la contamination de la côte libanaise par les hydrocarbures aromatiques polycycliques (HAPs) et les éléments traces métalliques (ETMs) : archives sédimentaires et biomonitoring suite à une marée noire
Ce projet de recherche porte sur l’étude de la contamination de la côte libanaise par les composés organiques (HAP, DDE) et par les éléments-trace métalliques (Hg, Pb principalement). Les travaux sur les compartiments sédimentaires et biologiques de la côte libanaise constituent deux parties aux problématiques et aux approches distinctes autour desquelles s’articule cette thèse. Dans la première partie, l’analyse d’une carotte sédimentaire datée prélevée sur le plateau continental du Sud du Liban a permis de reconstituer l’historique de contamination dans le bassin Levantin. Les analyses de contaminants dans les sédiments de la carotte C1 combinés à la datation aux 210Pb et 137Cs ont permis d’obtenir un enregistrement fiable des variations du dépôt de mercure, de plomb et de HAP sur le plateau continental libanais, dans le bassin Levantin. Bien que les concentrations et les flux soient relativement faibles, une augmentation en deux phases des concentrations est bien mise en évidence par le profil sédimentaire de C1. Le charbon est identifié comme source principale de Pb, de Hg et de HAP dans le bassin Levantin entre la moitié du 19ème siècle et la moitié du 20ème siècle. Les résultats des ratios isotopiques du Pb et des ratios diagnostiques de HAP appuient ce constat. Les archives sédimentaires dans la carotte C1 fournissent un signal du dépôt de contaminants à l’échelle globale probablement lié aux sources d’émissions atmosphériques en provenance d’Europe Centrale et de l’Est. Dans la seconde partie, une étude de la contamination par les HAP du littoral libanais est menée suite à la marée noire résultant du conflit armé israélo-libanais en 2006. Une approche de biomonitoring sur trois ans utilisant l’espèce de moules invasives Brachidontes variabilis a été développée. Les résultats indiquent une décroissance progressive des concentrations de HAP dans l’écosystème intertidal du littoral libanais. La contamination par les HAP du fioul en zone subtidale en 2007 est nettement plus faible. Cependant la signature des HAP dans les tissus de moules prélevées trois ans après la marée noire indique toujours la présence des composés du fioul de Jiyeh. La contamination est particulièrement persistante dans certaines zones fortement touchées par la nappe de fioul en 2006. Il apparaît que l’état initial pré-marée noire n’a pas été atteint, même trois ans après la marée noire de Jiyeh. L’examen détaillé de l’évolution spatiale et temporelle de la contamination par les HAP de l’environnement intertidal est présenté dans ce volet de notre étude.
(25/01/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Live (Stained) Benthic Foraminifera Off Walvis Bay, Namibia: A Deep-Sea Ecosystem under the Influence of Bottom Nepheloid Layers
(Journal of Foraminiferal Research. vol. 43, n° 0096-1191, pp. 55-71, 22/01/2013)
BIAF, UA, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Nearshore Dynamics of Tsunami-like Undular Bores using a Fully Nonlinear Boussinesq Model.
When tsunami wave fronts reach the shore, they can evolve into a large range of bore types, from undular non-breaking bore to purely breaking bore. It is the complex competition between non-linearities, dispersive effects and energy dissipation which will govern their transformations, making the prediction of their evolution a challenging task for numerical models. In this paper we investigate the ability of a fully nonlinear Boussinesq model, SURF-WB, to predict bore dynamics in a large range of Froude numbers. The model is first applied to the formation of undular bores, and compared with laboratory data. Its ability to predict the different bore shapes is then investigated. Finally, the effects of the bore transformation on wave run-up over a sloping beach are considered.
(Journal of Coastal Research. vol. SI64, n° 0749-0208, pp. 603-607, 15/01/2013)
I3M, UM2, UM, CNRS, IMT, UT Capitole, Comue de Toulouse, INSA Toulouse, INSA, Comue de Toulouse, UT2J, Comue de Toulouse, UT3, Comue de Toulouse, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, DMA, ENS-PSL, PSL, CNRS
Longshore sediment flux hindcast: spatio-temporal variability along the SW Atlantic coast of France
The Aquitanian coast (SW France) is exposed to high-energy waves, and subject to an overall shoreline erosion of 1 to 3 m/year. Engineering practices in this area requires the knowledge of longshore sediment fluxes. The reference values of direction and variability have been estimated 33 years ago with data available at that time. More recent estimations have been done on limited area and time span. The present study aims at: (1) updating and discussing the longshore sediment flux on this coast, (2) comparing the longshore drift spatial variability with measured shoreline evolution, (3) analyzing the interannual variability, in comparison with NAO indexes. Using a recent wave hindcast spanning the period 1958–2001, and the Kamphuis (1991) formula, the obtained gradients in longshore drift appear roughly consistent with the shoreline evolution and previous estimations of residual sediment fluxes. However, the estimated northward oriented fluxes are smaller in the present study than in the 33 year old reference study. The analysis shows a strong interannual variability, slightly smaller than the longshore variability. The interannual variability is not uniform along the coast. The northern section seems to be correlated with NAO indexes. Further analyses are required to better understand the temporal variability of the longshore sediment fluxes.
(Journal of Coastal Research. vol. 165, n° 0749-0208, pp. 1785-1790, 03/01/2013)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CSIRO
Extreme winter storm versus Summer storm: morphological impact on a sandy beach
(Journal of Coastal Research. vol. 65, n° 0749-0208, pp. 648 - 653, 02/01/2013)
LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Run-out distance and erosion of debris-flows in the Nile deep-sea fan system: Evidence from lithofacies and micro-palaeontological analyses
Debrites with different volumes, depositional periods and setting are observed in the Nile deep-sea fan system. Here we present debrites from four late Quaternary environments: (i) within the Rosetta submarine channel at 1700 m; (ii) within small basins created by salt tectonics in the Eastern Province at 1300 m; (iii) on the open slope outside of channels at 2600 m; and (iv) in the distal part of the fan fringe beyond channel terminations at 3050 m water depth. The debrites comprise mud clasts in a generally ungraded muddy sand matrix. They are relatively thin (20-150 cm) in fan fringe, in channel and salt-tectonic basin settings, and somewhat thicker (>8 m) in the open slope setting. Benthic foraminiferal assemblages and variation in the planktonic/benthic foraminiferal ratios are considered as a useful tool for tentatively evaluating the origin of sediment in these debris flows and estimation of their run-out distance. Similar microfaunal contents of clast/matrix combinations document that the debrites in the Rosetta channel and salt-tectonic basin were locally sourced. The debrite from the open slope travelled farther (up to 150 km). Three separate debrites in a fan fringe core were deposited by debris flows that originated over 200 km away in water depths shallower than 1000 m. These far-travelled debris flows appear to have eroded remarkably little sediment as they travelled for ∼200 km across low (0.8-1.2°) gradient seafloor. This lack of erosion is attributed to hydroplaning or increasing pore-fluid pressure at the base of debris flows. This study confirms that remarkably mobile debris flows can travel long distances to produce thin debrites in the distal fringes of submarine fans.
(Marine and Petroleum Geology. vol. 39, n° 0264-8172, pp. 102-123, 01/01/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOAZUR 6526, IRD, UPMC, UNS, INSU - CNRS, UniCA, CNRS, ISMAR, ISMAR, CNR
Incidence of invasive macrophytes on methylmercury budget in temperate lakes: Central role of bacterial periphytic communities
Several studies demonstrated high mercury (Hg) methylation and demethylation in the periphyton associated with floating roots in tropical ecosystems. The importance of aquatic plants on methylmercury production in three temperate ecosystems from southwestern France was evaluated through Hg species concentrations, and Hg methylation/demethylation activities by using stable isotopic tracers (199 Hg(II), Me 201 Hg). Hg accumulation and high methylation and demethylation yields were detected in plant roots and periphyton, whereas results for sediment and water were low to insignificant. The presence of sulfate reducing prokaryotes was detected in all compartments (T-RFLP based on dsrAB amplified through nested PCR) and their main role in Hg methylation could be demonstrated. In turn, sulfate reduction inhibition did not affect demethylation activities. The estimation of net MeHg budgets in these ecosystems suggested that aquatic rhizosphere is the principal location for methylmercury production and may represent an important source for the contamination of the aquatic food chain.
(Environmental Pollution. vol. 172, n° 0269-7491, pp. 116 - 123, 01/01/2013)
IPREM, UPPA, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMS, UB, CNRS
Study of the optical properties of dissolved organic matter in the Seine river catchment (France)
In this study, the optical properties of dissolved organic matter (DOM) were investigated using UV/visible photometry and excitation emission matrix (EEM) fluorescence spectroscopy. Differences in quality and quantity of organic carbon were observed and highlighted discrimination of organic matter typologies between the four studied areas in the catchment of the Seine river. \textcopyright 2013 Zhejiang University Press and Springer Science+Business Media Dordrecht. All rights are reserved.
(. vol. 9789400756342, pp. 219--223, 27/10/2026)
LEESU, UPEM, ENPC, UPEC UP12, IPGP, INSU - CNRS, UPD7, UR, IPG Paris, CNRS, IPGP, INSU - CNRS, UPD7, UR, IPG Paris, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Differences in fluorescence properties between humic acid and its size fractions separated by preparative HPSEC
We applied three dimensional excitation-emission-matrix (3D-EEM) spectrofluorometry to investigate the fluorescence properties of a humic acid (HA) solution at different pH values and its size-fractions separated by preparative high performance size exclusion chromatography (HPSEC). 3D-EEM fluorescence spectra revealed peak maxima in the bulk HA which were assigned to protein-like, phenol-like and naphthol-like components. Moreover, changes of peak maxima with pH showed that phenol-like and naphthol-like molecular classes were composed of sub-components with different acidities, and, thus, different structures. The 3D-EEM spectra of three size-fractions separated by HPSEC showed similar peak maxima as for the bulk HA, with additional components, such as highly condensed aromatic systems, which had not been visible in the bulk HA. Furthermore, the fluorescence intensity of peak maxima in 3D-EEM spectra of size-fractions appeared invariably greater than that for the bulk HA. This phenomenon as well as the appearance of new maxima in size-fraction spectra is explained by the reduced self-quenching effect in the less complex and conformationally looser size-fractions. In fact, the close mutual proximity of fluorescent humic molecules in the tight supramolecular association of the bulk HA decreased or even inhibited their fluorescence quantum yield. This work shows that, due to self-quenching of humic molecules, fluorescence spectroscopy cannot be used to characterise the molecular complexity of humic matter and, thus, differentiate its environmental origin. \textcopyright 2012 Elsevier B.V.
(Journal of Geochemical Exploration. vol. 129, n° 0375-6742, pp. 23--27, 27/10/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS