Evaluation of the recent morphological evolution of the Gironde estuary through the use of some preliminary synthetic indicators
Drastic evolution of the physical coastal environment are expected in the future under the effect of climate change. They make necessary to better understand the past morphology evolution, especially considering areas that are the habitat for some specific ecosystems. Moreover, because the context of the water framework directive (WFD), EU members need to generate indicators to evaluate the status of estuarine water masses. To satisfy these two obectives, the recent evolution of the Gironde estuary has been studied by the analysis of bathymetry with GIS. The Gironde is the largest estuary of western Europe, and one of the most turbid. In this study, the analysis extents from 1962 to 1994. Results show that the zone of maximum volume of deposited sediment has migrated continuously towards the upstream portion of the estuary, which is coherent with the decrease of summer river flow and the upstream shift of the turbidity maximum toward the riverine sections. In addition, zones with relative stable and unstable morphology were identified, showing rythmic distribution similarly to those previously recognized through the evolution over 160 years (18251984). This seems to be independent from the fluvial regime, but rather related to the interaction between tidal co-oscillations and estuarine morphology, which is not elucidated yet. Finally, some hydro-morpho-sediemntary (HMS) indicators useful to the WFD have been described : distribution of depths, changes on cross section areas, changes of intertidal areas. They are discussed to discriminate the "natural" and "anthropogenic" contribution to morphological changes observed.
(Journal of Coastal Research. vol. 165, n° 0749-0208, pp. 1224-1229, 01/04/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Refining benthic foraminiferal Mg/Ca-temperature calibrations using core-tops from the western tropical Atlantic: Implication for paleotemperature estimation
[1] Benthic foraminiferal Mg/Ca has been shown to have great potential as a proxy for reconstructing deep water temperatures. However, the exact relationship between Mg uptake in benthic foraminifera and temperature is still ambiguous, and further exploration and refinement is much needed to reduce uncertainties associated with the method. Here, we present new core-top Mg/Ca data from benthic foraminiferal species from the lower part of the thermocline in the western tropical Atlantic (northern Brazilian margin). This area is unusual in that the changes in carbonate chemistry along the transect are very small, making it an ideal region for isolating and studying the role of temperature in the incorporation of Mg into the benthic shells. Our results show that benthic foraminiferal Mg/Ca largely reflects temperature in this area. Our data are combined with previously published data to produce new and improved Mg/Ca calibration equations for a number of benthic foraminiferal species within the Atlantic Ocean. Our study provides the first C. wuellerstorfi Mg/Ca data for the 4-6 °C temperature range and indicates that C. wuellerstorfi Mg/Ca is strongly controlled by temperature. As a result, the newly established C. wuellerstorfi calibration over the entire 0-6 °C temperature range is significantly improved with respect to previously published C. wuellerstorfi calibrations limited to the coldest part between 0 and 4 °C. Other benthic species (Cibicidoides kullenbergi, Globocassidulina subglobosa, Uvigerina peregrina, and Oridorsalis umbonatus) have also been studied, although these results are less conclusive.
(Geochemistry, Geophysics, Geosystems. vol. 14, pp. 929-946, 01/04/2013)
UiB, BCCR, BIO / UiB, UiB, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS
Longshore sediment flux hindcast and potential impact of future wave climate change along the Gironde/Landes Coast, SW France
The West-facing Gironde/Landes Coast, SW France, comprises about 230 km of high-energy, nonengineered, sandy beaches. It extends from the Gironde estuary to the North, and to the Adour estuary to the South. Overall, the coast erodes at a rate of about 1 to 2 m/yr, with localized areas with stronger erosion or with a stable or slow accretive trend. The gradients in longshore sediment transport and the sediment budgets are presumably the most important factor controlling decadal scale evolution of the shoreline along the Gironde/Landes Coast. It is established that the net longshore drift, which is only disturbed at the tidal inlet system of the Arcachon Lagoon and shoreward of the Capbreton Canyon, is oriented southward (Michel, 1997). However, its intensity and longshore variability, as well as how it will evolve in the framework of climate change, are still a matter of debate. This important issue is addressed in this contribution. First, longshore sediment fluxes are hindcasted over the period 1958-2002, using an ERA-40 wind forced wave modelling and the most commonly used empirical longshore drift formulae (Charles et al, 2012). Results are (1) discussed with respect to the existing estimations based on smaller periods and using different datasets; (2) compared the shoreline evolution measured during this period and (3) further analyzed to address the respective contributions of the different representative wave classes (e.g. swell, storm waves, wind waves) to the total longshore drift. Wave projections, based on wind fields from one climate model (ARPEGE-Climat) for several emission scenarios (A2, A1B and B1), are carried out to estimate possible wave climate change in 2061-2100 (compared to a so-called REF scenario covering the 1961-2000 period). It shows that, for instance for the A2 scenario and the summer season, the modal significant wave height is likely to decrease together with a 5° northward rotation of incoming wave incidence. Based on the wave model outputs, longshore sediment fluxes along the Aquitanian coast are computed for the four scenarios. The analysis of the relative sediment flux evolution (A2, A1B and B1 scenarios with respect to present day REF scenario) shows an overall decrease of the southerly longshore drift magnitude. A thorough analysis of the wave components evolution responsible for this decreasing trend is done, as well as an analysis of the longshore drift gradients along the Aquitanian coast. The potential impact of longshore drift evolution on the shoreline evolution at the 2061-20100 is discussed.
(Journal of Coastal Research. vol. 65 (Special Issue), n° 0749-0208, pp. pp. 1785-1790, 01/04/2013)
BRGM, CSIRO, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Live (stained) benthic foraminifera from the Cap-Ferret Canyon (Bay of Biscay, NE Atlantic): A comparison between the canyon axis and the surrounding areas
(Deep Sea Research Part I: Oceanographic Research Papers. vol. 74, n° 0967-0637, pp. 98-114, 01/04/2013)
BIAF, UA, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CEFREM, UPVD, INSU - CNRS, CNRS, CEFREM, UPVD, INSU - CNRS, CNRS, CEMAGREF
Réserve Naturelle Nationale des prés salés d'Arès et de Lège-Cap Ferret (33) : connaissance et suivi des peuplements benthiques, supra-benthiques, ichtyologiques et des fonctions écologiques du compartiment tidal (programme de recherche Biamar 2012)
Les objectifs de cette étude étaient : • Le développement et l’expérimentation de méthodes réplicables pour l’étude du «couple» benthos/poissons, dans une optique à la fois de connaissance, de suivi et de gestion/conservation • La caractérisation des peuplements étudiés, en termes de richesses spécifiques, d’abondances relatives et de biomasses • L’étude de la dynamique spatio-temporelle (habitats/saisons) des peuplements étudiés • L’identification et la caractérisation des fonctions écologiques jouées par ces marais maritimes pour les poissons amphihalins.
(pp. 1, 28/03/2013)
IRSTEA, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR EPBX, IRSTEA, IRSTEA
Relative potency of PCB126 to TCDD for sublethal embryotoxicity in the mummichog (Fundulus heteroclitus).
The relative potency (ReP) of 3,3',4,4',5-pentachlorobiphenyl (PCB126) to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for sublethal responses was assessed in Fundulus heteroclitus embryos. Eggs were treated with intravitelline injections of graded sublethal doses of PCB126 (312-5000 pg g(-1) wet weight, ww) or TCDD (5-1280 pg g(-1) ww). At 16 days post-fertilization (DPF), craniofacial deformities were observed in larvae hatched from eggs treated with the two highest doses of PCB126 (2500-5000 pg g(-1) ww). Both compounds caused a dose-responsive reduction of larval growth and prey capture ability (at ≥1250 pg g(-1) ww), and induction of ethoxyresorufin-O-deethylase (EROD) activity (at ≥80 pg g(-1) ww). The dose-response relationships for EROD activity for PCB126 and TCDD had similar slopes and the ReP of PCB126 to TCDD for EROD activity was estimated at 0.71. This is 140-fold higher than the World Health Organization (WHO) TCDD equivalency factor (TEF) of PCB126 for fish (0.005), which is based on rainbow trout (Oncorhynchus mykiss) embryolethality data. The slope of the dose-response relationship for prey capture ability for PCB126 was steeper than for TCDD, suggesting different mechanisms of action. Expression levels of several genes were also studied by quantitative real-time polymerase chain reaction (qPCR) following exposure to single doses of TCDD or PCB126 (1280 and 1250 pg g(-1) ww, respectively) causing similar EROD induction. A different pattern of responses was observed between PCB126 and TCDD: PCB126 appeared to induce antioxidant responses by inducing sod2 expression, while TCDD did not. These results suggest that relative potencies are species-specific and that the current ReP for PCB126 underestimates its toxicity for some fish species. It is recommended to develop species-specific RePs for a variety of sublethal endpoints and at environmentally relevant doses.
(Aquatic Toxicology. vol. 128-129, n° 0166-445X, pp. 203-14, 15/03/2013)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Disentangling the effects of water and nutrients for studying the outcome of plant interactions in sand dune ecosystems
Questions What is the relative role of water vs nutrients in driving changes in plant interactions in a dry and nutrient-poor dune system, where facilitation has been shown to highly contribute to the diversity and composition of plant communities? Location Atlantic coastal sand dune system, Aquitaine region, France. Methods We manipulated water (water addition) and nutrient (fertilizer addition) availabilities in a full-factorial experiment that lasted from September 2005 to September 2006. The responses of plants to neighbours were assessed through transplanting six target species within each experimental plot in the presence or absence (removal procedure) of the dominant shrub Helichrysum stoechas. We also measured changes in H. stoechas biomass among treatments. Results Watering mainly affected survival of the target species without neighbours and the direction of their responses to the shrub, whereas fertilization strongly increased the biomass of the shrub and intensity of the responses of the targets to the effects of the shrub. We did not observe any occurrence of biotic interactions (either positive or negative) for most of the target species in the unfertilized plots. In contrast, three of the six species exhibited significant facilitation in fertilized and un-watered plots, and significant competition in fertilized and watered plots. Conclusions Our results highlight the co-limitation of water and nutrients in coastal sand dunes. Nutrient availability mainly drove the neighbour effect of the shrub, whereas water availability affected the responses of the target species. Although further measurements of resource modifications by the shrub are needed to firmly conclude neighbour effects, our results provide new insights to the contrasting results in the literature on plant–plant interactions in unproductive communities. We propose that, depending on the system, changes in a given direct stress factor may either induce a collapse of interactions by decreasing neighbour performances and their effects, or a shift in the direction of interactions by affecting target species responses.
(Journal of Vegetation Science. vol. 24, n° 1100-9233, pp. 375-383, 01/03/2013)
ECODIV, UNIROUEN, NU, BioGeCo, INRA, UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
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