Silver behaviour along the salinity gradient of the Gironde Estuary
Dissolved and particulate Ag concentrations (Ag D and Ag P , respectively) were measured in surface water and suspended particulate matter (SPM) along the salinity gradient of the Gironde Estuary, South West France, during three cruises (2008-2009) covering contrasting hydrological conditions, i.e. two cruises during intermediate and one during high freshwater discharge (~740 and~2,300 m 3 /s). Silver distribution reflected non-conservative behaviour with 60-70 % of Ag P in freshwater particles being desorbed by chlorocomplexation. The amount of Ag P desorbed was similar to the so-called reactive, potentially bioavailable Ag P fraction (60±4 %) extracted from river SPM by 1 M HCl. Both Ag P (0.22±0.05 mg/kg) and Ag P /Th P (0.025-0.028) in the residual fraction of fluvial and estuarine SPM were similar to those in SPM from the estuary mouth and in coastal sediments from the shelf off the Gironde Estuary, indicating that chlorocomplexation desorbs the reactive Ag P. The data show that desorption of reactive Ag P mainly occurs inside the estuary during low and intermediate discharge, whereas expulsion of partially Ag P-depleted SPM (Ag P /Th P 0.040) during the flood implies ongoing desorption in the coastal ocean, e.g. in the nearby oyster production areas (Marennes-Oléron Bay). The highest Ag D levels (6-8 ng/ L) occurred in the mid-salinity range (15-20) of the Gironde Estuary and were decoupled from freshwater discharge. In the maximum turbidity zone, Ag D were at minimum, showing that high SPM concentrations (a) induce Ag D adsorption in estuarine freshwater and (b) counterbalance Ag P desorp-tion in the low salinity range (1-3). Accordingly, Ag behaviour in turbid estuaries appears to be controlled by the balance between salinity and SPM levels. The first estimates of daily Ag D net fluxes for the Gironde Estuary (Boyle's method) showed relatively stable theoretical Ag D at zero salinity (Ag D 0 0 25-30 ng/L) for the contrasting hydrological situations. Accordingly, Ag D net fluxes were very similar for the situations with intermediate discharge (1.7 and 1.6 g/day) and clearly higher during the flood (5.0 g/day) despite incomplete desorption. Applying Ag D 0 to the annual freshwater inputs provided an annual net Ag D flux (0.64-0.89 t/year in 2008 and 0.56-0.77 t/year in 2009) that was 12-50 times greater than the Ag D gross flux. This estimate was consistent with net Ag D flux estimates obtained from gross Ag P flux considering 60 % desorption in the estuarine salinity gradient.
(Environmental Science and Pollution Research. vol. 20, n° 0944-1344, pp. 1352-1366, 01/03/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
MMHg production and export from intertidal sediments to the water column of a tidal lagoon (Arcachon Bay, France)
Hg cycling in biologically productive coastal areas is of special importance given the potential for bioaccumulation of monomethylmercury (MMHg) into aquatic organisms. Field experiments were performed during three different seasons in Arcachon Bay, a mesotidal lagoon (SW France), to assess the variability of the water column concentrations, sediment-water exchanges and potential formation and degradation of MMHg. The objectives were to evaluate the contribution of intertidal mudflats to MMHg production and the various pathways of Hg species export. Dissolved and bulk concentrations of Hg species in the water column downstream of tidal flats were measured throughout several tidal cycles. The Hg benthic fluxes at the sediment-water interface were determined by means of benthic chambers for three different stations. Hg methylation and demethylation potentials were determined in surficial sediments and the water column using isotopic tracers. The tidal surveys demonstrated that benthic remobilization of Hg occurs primarily in association with sediment erosion and advection during ebb tide. However, elevated dissolved Hg concentrations observed at low tide were found to be caused by a combination of pore-waters seeping, benthic fluxes and methylation in the water column. Benthic fluxes were more intense during late winter conditions (median MMHg and inorganic Hg (IHg) fluxes: 64 and 179 pmol m-2 h-1, respectively) and subsequently decreased in spring (median 0.7 and -5 pmol m-2 h-1, respectively) and fall (median -0.4 and -1.3 pmol m-2 h-1, respectively). The trends in methylation and demethylation potentials were at the opposite of the fluxes, two times lower during winter than for spring or fall conditions. In this tidal environment, MMHg production in surface sediments and its subsequent release is estimated to be the major source of MMHg to the water column during winter and spring time. However, during the more productive summer period, the Hg methylation extent in the water column may be very significant and equivalent to the sediment contribution.
(Biogeochemistry. vol. 114, n° 0168-2563, pp. 341-358, 26/02/2013)
LCABIE, UPPA, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UBO EPE
Comparative effects of two water-accommodated fractions from light and heavy crude oils on early life stage of zebrafish Danio rerio
Session: Aquatic ecotoxicology AT16 Comparative effects of two water-accommodated fractions from light and heavy crude oils on early life stage of zebrafish Danio rerio.
(pp. 82, 11/02/2013)
IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS, LPGP, INRA, Biosit : Biologie - Santé - Innovation Technologique
Late Quaternary megaturbidites of the Indus Fan: Origin and stratigraphic significance
The Indus sedimentary basin forms one of the largest "source-to-sink" systems of the Quaternary and extends over 106 km2 offshore. It is characterized by a complex tectonic setting marked by the Himalayan active orogenic belt in the source area, and the active strike-slip India-Arabia plate boundary (Owen Fracture Zone; OFZ) in its distal reaches. This paper focuses on a Late Quaternary channel-levee system from the Indus Fan captured by the recent opening of the 20°N pull-apart basin, located at 850 km off the present-day Indus Delta, along the OFZ. In this area the channel-mouth deposits consist of a set of up to 23 m thick megaturbidites trapped in the basin. These deposits form "ponded" lobe deposits in a tectonically-active confined basin. Age determination from radiocarbon dating and extrapolation of local deformation rates show that the older deposits observed on the seismic profiles are up to 358 ka BP old (MIS 10). The origin of these Late Quaternary deposits are investigated in the context of the Indus "source-to-sink" system and their significance is placed in a sequence stratigraphic framework. Integration of the stratigraphic architecture of the 20°N Basin megaturbidites with previous work in the area suggests that the Indus Fan evolved from a delta-fed turbidite system with several active canyons and channel-levee during the forced regressive conditions of the last falling stage of sea-level (122-25 ka BP), to a point source turbidite system during the sea-level lowstand (Last Glacial Maximum) and early transgressive stages (25-12 ka BP). This work sheds new light on the recent evolution of the Indus sedimentary system and illustrates the importance of the delta/river evolution during the fall of sea-level (e.g., incised valley formation) on the timing of sedimentary transfer and sediment distribution at the basin-scale.
(Marine Geology. vol. 336, n° 0025-3227, pp. 10-23, 01/02/2013)
UWA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, iSTeP, UPMC, CNRS, LGENS, INSU - CNRS, CNRS, ENS-PSL, PSL, SHOM, LDO, INSU - CNRS, UBO EPE, CNRS
A mesocosm study of fate and effects of CuO nanoparticles on endobenthic species (Scrobicularia plana, Hediste diversicolor)
The fate and effects of CuO nanoparticles (CuO NPs) were examined in endobenthic species (Scrobicularia plana, Hediste diversicolor), under environmentally realistic conditions in outdoor mesocosms (exposure to Cu at 10 μg L−1 in particulate (CuO NPs) or soluble salt (CuNO3) forms) for 21 days. Labile Cu was determined in water and sediment by using diffusive gradient in thin films. No labile Cu being detected from CuO NPs; the observed effects in invertebrates exposed to CuO NPs were mainly attributed to the toxicity of nanoparticulate rather than dissolved Cu toxicity. Bioaccumulation of CuO NPs was observed in both species. Biomarkers were examined at different levels of biological organization: biochemical markers of defense and damage, biomarkers of genotoxicity (comet assay), and behavioral biomarkers (feeding and burrowing). Behavioral biomarkers, antioxidant defenses (catalase, glutathion S-transferase, metallothionein), and genotoxicity are the most sensitive tools to highlight the effect of soluble or nanoparticulate metal forms. Concerning other biomarkers of defense (superoxide dismutase, lactate dehydrogenase, laccase) and damage (thiobarbituric acid reactive substances, acetylcholinesterase, acid phosphatase), no significant effects were detected. This experiment shows the suitability of mesocosms for studying the environmental effects of nanoparticles.
(Environmental Science and Technology. vol. 47, n° 0013-936X, pp. 1620-1628, 01/02/2013)
MMS, UM, UN UFR ST, UN, UFR SPB, UN, LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BE, IFREMER, ECOMERS, UNS, CNRS, UniCA, NHM, MMS UCO, UCO, UNAM
A three-year time series of mineral dust deposits on the West African margin: Sedimentological and geochemical signatures and implications for interpretation of marine paleo-dust records
Mineral dust deposits in the Northeastern Tropical Atlantic Ocean (NETAO) are an important contribution for reconstructing paleoenvironments and paleoclimates of West Africa. However, the interpretation of the changes in the sedimentological and geochemical characteristics of the dust deposits recorded in the marine sediments from the NETAO remains incomplete. In order to improve our understanding of dust proxies, in particular its mineralogical and geochemical provenance tracers, present-day dust deposition has been monitored at Mbour (∼80 km south of Dakar) on the Senegalese margin. Here we report a multi-proxy investigation of a unique three-year continuous time series of mineral dust deposits collected at a weekly (or better) temporal resolution over the March 2006–March 2009 period. Mass deposition flux and mean modal grain size display marked but reverse seasonal features, with higher flux during the winter/spring seasons and coarser grain size mode in summer when flux is minimal, reflecting contrasting transport patterns throughout the year. Similarly, clay mineralogy, the illite/kaolinite ratio in particular, shows seasonal fluctuations, manifesting the latitudinal displacement of the contributing domains of provenance in response to the seasonal migration of the ITCZ position and the associated wind systems. Our three-year record also reveals the occurrence of major deposition events superimposed on the seasonal pattern, generally during the winter/spring dry seasons and most frequently during the month of March. Our study shows that these major events, which contribute a large fraction of the total annual deposition flux, all originate from the western Sahara–Sahel (a major area of emission in the region beside the Bodele Depression, stretching from the Mauritanian and Western Saharan coasts to the Hoggar Mountains). Combined with air mass tri-dimensional back-trajectories and satellite images, the mineralogical and Sr–Nd isotopic compositions of these large dust events enable us to identify several mineralogically and geochemically distinct provenance sectors within this vast western area. Unlike the background dust deposits, the 87Sr/86Sr and the εNd isotopic signatures of the major dry events closely match that of the NETAO Late Holocene sediments, supporting the hypothesis that these events account for most of the aeolian terrigenous supply reaching the ocean floor. Although this database needs to be expanded, our results already provide useful constraints for the interpretation of the dust proxies' variations in marine sedimentary archives off Mauritania/Senegal in terms of changes in wind regimes and aridity over West Africa.
(Earth and Planetary Science Letters. vol. 364, n° 0012-821X, pp. 145-156, 01/02/2013)
LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], CNRS, MPIC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMAGO, IRD
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