Analysis of extreme hydrological events (river and tidal floods) in the Medoc vineyards and consequences on the metal pollution of the Gironde Estuary
The ADAPT’EAU research project (ANR CEP&S) intends to assess the vulnerability of environments and societies to the impacts of Global Change on river-estuarine environments. During the last decades, the Gironde Estuary has been affected by major storm events (e.g. Martin in 1999, Xynthia in 2010), which caused river and tidal floods that temporarily submerged urban and agricultural lands. In the context of regional environmental changes forecast (e.g. sea level rise, urbanization, changing agriculture), there are uncertainties on the frequency of extreme events (storms, floods) and their impacts on metal mobilization from temporarily submerged land surfaces, particularly from copper (Cu) contaminated vineyard soils. Based on an interdisciplinary approach coupling geochemistry, geomatics and geography, our study aims at characterizing extreme events in one of the largest areas of red wine production (Medoc; left bank of the Gironde Estuary) using the prefectural orders on natural catastrophes published in the Official Journal from 1982 to 2011 (database GASPAR; French Ministry of Ecology) associated with a weather events database. In identified flood-stricken sites, vineyard soils were collected and leached by natural waters under laboratory conditions in order to (i) simulate the effects of river floods (soil with freshwater) and tidal floods (soil with estuarine water) and (ii) investigate the physico-chemical processes of metal leaching or adsorption on soils. The parameters of the incubations (duration, temperature, salinity) were determined from the event characteristics. Our first experimentations simulating prolonged river flood (20 days) showed significant Cu desorption increasing Cu levels in freshwater by a factor 5. We discuss the potential impact of water flooding in intra-estuarine watersheds with similar land uses on the water quality of the Gironde Estuary by comparing metal mobilization to metal gross fluxes transported by the Garonne River to the coastal ocean.
(pp. 1, 11/04/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR ADBX, IRSTEA
Effects of uranium on crayfish Procambarus clarkii mitochondria and antioxidants responses after chronic exposure What have we learned?
We examined the impacts of Uranium (U) on mitochondria and on the response of antioxidants in the gills and the hepatopancreas of crayfish Procambarus clarkii after long-term exposure (30 and 60 days) to an environmentally relevant concentration (30 μg. U/L). The expression of mitochondrial genes (12s, atp6, and cox1), as well as the genes involved in oxidative stress responses (sod(Mn) and mt) were evaluated. The activities of antioxidant enzymes (SOD, CAT, GPX and GST) were also studied. U accumulation in organs induced changes in genes' expression. The evolution of these transcriptional responses and differences between gene expression levels at high and low doses of exposure were also discussed. This study demonstrated that, after long-term exposure, U caused a decrease in antioxidant activities and induced oxidative stress. A possible ROS-mediated U cytotoxic mechanism is proposed. Expression levels of the investigated genes can possibly be used as a tool to evaluate U toxicity and seem to be more sensitive than the enzymatic activities. However a multiple biomarker approach is recommended as the perturbed pathways and the mode of action of this pollutant are not completely understood. © 2011.
(Ecotoxicology and Environmental Safety. vol. 78, n° 0147-6513, pp. 218-224, 01/04/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSN/DEI/SECRE/LRE, IRSN/DEI/SECRE, IRSN
Network analysis of the planktonic food web during the spring bloom in a semi-enclosed lagoon (Arcachon, SW France)
The structure and functioning of the food web in Arcachon Bay (Bay of Biscay, Northeast Atlantic Ocean) was analyzed during the spring bloom period to evaluate the sensitivity of this ecologically and economically important ecosystem perturbation. Differences in the timing of the peaks in phytoplankton and zooplankton populations occur due to a mismatch between primary production and grazing. Using an inverse approach based on in situ experimental data, an ecological network analysis was carried out to characterize emergent properties of the food web and to estimate carbon flows. The data set was composed of rate measurements for net primary production, import and export of dissolved organic carbon, and grazing of heterotrophic nanoflagellates and ciliates by metazoan micro- and mesozooplankton. Ecological network analysis indices were calculated on the estimated fluxes and compared to values from plankton models built with exactly the same method. The largest activities in the resulting model came from the nano- and microphytoplankton. The detritivory/herbivory ratio, the recycling rates and the relative redundancy of the system were very low compared to other planktonic systems, even in similar periods of bloom. These values indicate a transitional system with poor resilience that exports a large quantity of carbon either to the benthos where it is consumed by non-planktonic consumers such as oysters, or else to systems outside of the bay (outwelling).
(Acta Oecologica. vol. 40, n° 1146-609X, pp. 40-50, 01/04/2012)
LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Cleaning of marine sediment samples for large diatom stable isotope analysis
Diatom stable isotope analysis offers considerable potential in palaeoceanography, particularly where carbonate material is scarce or absent. However, extracting pure diatom frustules free of external labile organic matter from marine sediments is an essential requirement for their applications as paleoenvironmental proxies. Here, based largely on previous work, we developed a method including physical separation and chemical oxidation steps to concentrate and clean pure large diatoms from laminated diatom mat and diatomaceous clay sediment samples for their stable isotope analysis. Using the physical separation techniques consisting of the removal of carbonate and excess organic matter, sieving, differential settling, and heavy liquid floatation, pure diatoms can be successfully isolated from the sediment samples with opal concentration more than 10%. Subsequent time oxidation experiment shows that labile organic matter coating pure diatom valves can be effectively removed with 30% H 2 O 2 at 65 ℃ for 2 h. Measurements of δ 13 C after every step of physical separation demonstrate that contaminants and lost diatoms can influence the original diatom stable isotope signal, highlighting the importance of a visual check for dominant diatom size in the initial sample and purity in the final sample. Although the protocol described here was only applied to diatom mats or diatom oozes containing large diatoms (Ethmodiscus rex), we believe that this method can be adapted to common dia-toms of general marine sediment samples. KEY WORDS: large diatom, stable isotope, physical separation, chemical oxidation, Parece Vela basin, palaeoceanography.
(Journal of Earth Science. vol. 23, n° 1674-487X, pp. 161-172, 01/04/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Reconstruction of the late-Holocene changes in the Sub-Arctic Front position at the Reykjanes Ridge, north Atlantic
Changes in the dynamics of the North Atlantic subpolar gyre are involved in the modulation of the northward salinity and heat transport in the northern North Atlantic via the North Atlantic Current (NAC). Variations in the strength of the East Greenland Current (EGC) can influence the gyre dynamics by impacting deep convection in the Labrador Sea. Oxygen isotope data of three planktonic foraminiferal species (surface water Neogloboquadrina pachyderma dextral coiling and Globigerina bulloides; thermocline recorder Globorotalia inflata) from a site located close to the present Sub-Arctic Front at the Reykjanes Ridge suggest significant strengthening or shifting of the Sub-Arctic Front throughout the late Holocene. The oxygen isotope based inferences are supported by Mg/Ca-derived temperature reconstructions from Neogloboquadrina pachyderma dextral coiling, alkenone-derived sea surface temperature and other paleoclimatic proxy data. The late-Holocene strengthening/shift of the Sub-Arctic Front appears caused by an increasingly more defined and fresher EGC. The proposed subpolar gyre changes may modulate the northward heat transport, and explain the geographically different long-term climatic trends in the North Atlantic during the late Holocene, i.e. a cooling of the EGC-influenced regions and a warming of the NAC-influenced areas from c. 4 to 5 ka. This mechanism cannot, however, explain the simultaneous occurrence of millennial-scale events at c. 5.6, 3.9, 2.7, 1.3 ka and the ‘Little Ice Age’ in both areas. Noteworthy is the steadily increasing amplitude of these cold events at the Reykjanes Ridge, likely induced by drift ice and/or EGC-influence culminating in the ‘Little Ice Age’. A widespread pronounced warming at 2.0 ka seems to represent the ‘Roman Warm Period’ and reflects the warmest period of the late Holocene.
(The Holocene. vol. 22, n° 0959-6836, pp. 877-886, 19/03/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
New data on the Silurian-Devonian palaeontology and biostratigraphy of Bolivia
In order to precisely establish the bio- and chronostratigraphic position of several levels of the Silurian-Devonian succession of Bolivia, with respect to the International Time Scale, additional Silurian and Devonian localities belonging to the Eastern Cordillera and the Interandean Zone areas have been recently revised and sampled, both for macrofossils and palynomorphs. Specifically, the localities are Nunumayani, and Muruhuta from the late Silurian-early Devonian time interval. Correlations with other fossiliferous localities are discussed, namely Huacallani and Rumicorral. A new outcrop yielding Middle Devonian tabulate corals at Pisacavina is described; its faunal content is described, and compared with the historical coral collection. As a result, it appears clearly that the Silurian-Devonian Bolivian fauna needs a thorough revision, as well as the selection of stratigraphically significant macrofossils. Besides macrofossils, the analysis of palynomorph assemblages is significant in establishment of both intra-Bolivian and international correlations before any reliable biogeographic reconstruction is done. This paper records the first discovery of a plant of the genus Protolepidodendron from the Devonian of Bolivia. An ostracod assemblage from Pisacavina is described, illustrated, and discussed for the first time; it suggests an Early Devonian or an Eifelian age. Newly described taxa include the coral Parastriatopora boliviana sp. nov., and the chonetoidean brachiopods Sanjuanetes glemareci sp. nov., and Kentronetes giae sp. nov.
(Bulletin of Geosciences. vol. 87, n° 1214-1119, pp. 269-314, 08/03/2012)
LDO, INSU - CNRS, UBO EPE, CNRS, IRSNB / RBINS, AMNH, GR, UR, INSU - CNRS, CNRS, CR2P, MNHN, UPMC, CNRS
Submarine slide initiation and evolution offshore Pointe Odden, Gabon — Analysis from annual bathymetric data (2004–2009)
Time serial bathymetric data acquired between 2004 and 2009 are used to evaluate the morphological evolution of the coastal area offshore Pointe Odden, located on the Mandji Island (Gabon). Data analysis highlights the alternation between fast sedimentation periods at shallow water depth related to intense longshore drift and catastrophic erosional events. Because of sediment overloading and slope oversteepening, small-scale instabilities are generated (successive slide scars, channel formation and growth by retrogressive erosion). However, when critical stability conditions are reached, large failures occur (2005 submarine slide). Geotechnical measurements and sedimentological analyses on the study area suggest that flow liquefaction would be the triggering mechanism of the 2005 event. Moreover, our analysis shows that the associated slide scar is rapidly filled by compensation and that failure morphology could disappear from the seafloor in about 15–20 years.
(Marine Geology. vol. 299-302, n° 0025-3227, pp. 43-50, 01/03/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to late Pliocene/early Pleistocene climate cooling
The global late Pliocene/early Pleistocene cooling (~3.0-2.0 million years ago, Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela Upwelling System (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilization in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Plio/Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0-2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to late Pliocene/early Pleistocene cooling.
(Climate of the Past Discussions [Climate of the Past Preprints]. vol. 8, n° 1814-9340, pp. 669-694, 01/03/2012)
LOCEAN, IPSL, ENS-PSL, PSL, UVSQ, UPMC, CEA, INSU - CNRS, X, IP Paris, CNES, CNRS, MNHN, IRD, UPMC, INSU - CNRS, CNRS, CAU, GEOMAR, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Silicic acid flux to the ocean from tidal permeable sediments: A modeling study
Sandy sediments of tidal beaches are poor in reactive substances because they are regularly flushed by significant flow caused by tidal forcing. This transport process may significantly affect the flux of reactive solutes to the ocean. A two dimensional model coupling the Richards equation that describes the flow in permeable sediments and the conservation equation of the silicic acid was developed to simulate the evolution of the silicic acid concentration into a variably saturated porous media submitted to tidal forcing. A detailed algorithm of drainage zone under tidal forcing and numerical methods needed to solve it are properly presented. Flux to the ocean has been estimated. The silicic acid concentration displays a permanent lens with low silicic acid concentration at the top of the tidal zone. This lens that results from the tidal forcing, presents weak variations of area during the tidal cycle. Silicic outflux to the ocean increases with increasing beach slope, hydraulic conductivity and tidal range. Simulations reveal that the total silicic acid flux to the ocean from the coastal marine sands can be considered as significant compared to the flux supplied by the rivers. These results may alter the previously published global budget of the silicic acid to the ocean.
(Computers & Geosciences. vol. 43, n° 0098-3004, pp. 52-62, 28/02/2012)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BACCHUS, Inria, UB, CNRS, IMB, UB, Bordeaux INP, CNRS, MC2, Inria, UB, CNRS
Calibration of sorption and biodegradation of micropollutants in a biokinetic model: New experimental protocol and first results
An innovative experimental strategy is proposed to calibrate sorption and biodegradation modelling parameters. The protocol was based on batch experiments simulating the different conditions occurring in a full-scale activated sludge reactor. The studied conditions were the redox condition (aerobic, anoxic) and the substrate condition (no other substrate, carbon and nitrogne substrate, only nitrogen substrate). Thanks to the monitoring of dissolved and sorbed concentrations of micropollutant, robust mass balances could be performed. We succeeded in determining easily modelling parameter values associated to each condition. An application of the strategy is presented for a beta blocker (atenolol). We will apply this procedure to the other studied substances (other pharmaceuticals, alkylphenols, polycyclic aromatic hydrocarbons and pesticides).
(pp. 1, 26/02/2012)
UR MALY, IRSTEA, UM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS