Erosion mécanique des sols et transferts géochimiques dans le bassin Adour-Garonne

L’érosion hydrique des sols résulte de processus naturels modifiés par la pression anthropique et contribue aux transferts de matières en suspension (MES) entre le continent et l’océan ainsi que du carbone organique (CO) et des éléments traces métalliques (ETM) associés. Sur la base d’une banque de données haute résolution temporelle (horaire à journalier et couverture pluriannuelle) de concentrations en MES et de débits sur des rivières contrastées du bassin Adour-Garonne, nous définissons par simulation numérique des fréquences d’échantillonnage adaptées à la typologie des bassins et les incertitudes associées. Des approches alternatives utilisant des relations MES-débit permettent de modéliser les flux annuels en MES. De plus, l’ajustement des régressions statistiques de type MES=aQ^b reflète les typologies avec une correspondance directe entre les coefficients et l’indice de sensibilité à l’érosion. Les taux d’érosion des bassins représentatifs du système Adour- Garonne montrent une large gamme comprise entre 5 et 180 t.km^-2.an^-1 et une forte variabilité interannuelle. L’étude à haute résolution des transferts de la Nivelle (représentative des petites rivières montagneuses pyrénéennes et cantabriques) a permis de quantifier précisément le flux spécifique annuel de CO particulaire (5,3 t.km^-2.an^-1), provenant pour 55% du sol, 40% de la litière et 5% de la production autochtone et de montrer la forte contribution de ces petits systèmes (70% des apports totaux) aux apports dans le Golfe de Gascogne. De même, le Congo (Zaïre), système diamétralement opposé, montre de fortes variabilités saisonnières des concentrations en CO en fonction de l’hydrologie. L’essentiel des transferts se font sous forme dissoute (>75%), en raison des faibles taux d’érosion (~9 t.km^-2.an^-1) contrairement à ceux des petites rivières montagneuses (~75 t.km^-2.an^-1). Les rapports élémentaires (As/Th, Cd/Th, Zn/Cd) établis lors de la crue cinquantennale du Lot échantillonnée à très haute résolution sont utilisés pour différencier et quantifier les zones sources de MES (235 000 t du Lot amont, 185 000 t de la remobilisation des barrages, 8000 t par le Riou Mort). Les variations temporelles en ETM reflètent la succession de dominance de source de l’aval vers l’amont et permettent de proposer une nouvelle explication de la baisse du coefficient de partition (Kd) avec des concentrations en MES croissantes (phénomène pce). Le suivi haute résolution spatiale et temporelle durant une année d’un bassin expérimental hétérogène fortement anthropisé (Decazeville) couvrant une large gamme de conditions hydrologiques (étiage prononcé – crue centennale) a démontré des différences spatiales des taux d’érosion. Des signatures géochimiques sont utilisées pour comprendre le fonctionnement hydrologique du bassin versant permettant d’interpréter les variations temporelles en ETM dissous et particulaires. Une source additionnelle souterraine est localisée contribuant à 60% et 38% du bilan annuel de Cd dissous et particulaire du Riou Mort. L’établissement du bruit de fond géochimique du bassin de Decazeville suggère que 93% et 99% des apports annuels en Zn et Cd sont d’origine anthropique.Soil erosion due to natural and anthropogenic processes controls transport of suspended particulate matter (SPM), organic carbon (OC) and associated trace elements from continent to ocean. We define sampling frequencies adapted to watershed typology and related uncertainties by using numerical simulation based on a long-term high resolution database on SPM concentrations and water discharge (Q). Alternative approaches using mathematical relations between SPM concentrations and discharge aim to develop models for annual SPM flux estimates. Moreover, statistical relations (type SPM=aQ^b) reflect watershed properties attributing distinct a and b coefficients to lithology and soil erosion sensitivity index. Representative watersheds of the Adour- Garonne River system cover a large range of annual SPM yields (5 to 180 t.km^-2.yr^-1) and show high interannual variability. High resolution data on particulate OC in the Nivelle River, a typical Pyrenean mountainous watershed, indicates high specific annual POC yields (5.3 t.km^-2.yr^-1), attributed to soil (55%), litter (40%) and autochthonous production (5%), highlighting the important contribution (70%) of small river systems to OC export into the Bay of Biscay. Despite of strongly contrasted properties, compared to the small Pyrenean rivers, also the Congo River shows seasonal OC variations related to hydrology. However, OC is essentially exported in the dissolved phase (>75%) due to the flat relief and very low SPM yields (~9 t.km^-2.yr^-1) compared to mountainous rivers (~75 t.km^-2.yr^-1). High resolution sampling during a major regional flood event in the Lot River provides geochemical signatures (e.g. As/Th, Cd/Th, Zn/Cd) for SPM, attributed to successive dominance of water masses transporting material from different sources (~235,000 t from the upstream Lot River, ~185,000 t from remobilisation of riverbed sediments and ~8,000 t from the Riou Mort River). Decreasing partition coefficients (Kd) with increasing SPM concentrations during the flood (particle concentration effectpce) are attributed to source-related variations rather than colloidal influence or changed grain size composition of SPM, suggesting a third possible explanation for the commonly observed pce. The high resolution observation network in the heterogeneous experimental Riou Mort watershed reveals important spatial and temporal variability of erosion during contrasted hydrological situations. Moreover, we identify an additional yet unknown underground point source contributing 60% and 38% to annual dissolved and particulate Cd fluxes, respectively. The determination of natural background values of heavy metal in the Riou Mort watershed suggests 93% and 99% of annual particulate Zn (73 t) and Cd (2,4 t) fluxes are of anthropogenic origin

KẾT QUẢ BƯỚC ĐẦU VỀ HÀM LƯỢNG CÁC KIM LOẠI NẶNG TRONG NƯỚC SÔNG HỒNG TẠI TRẠM THỦY VĂN SƠN TÂY

This study  is  based  on the  experimental  results  obtained  from  analysis  of suspended  and  dissolved  heavy  metal concentrations (V, Cr, Co, Ni, Cu, Zn, As, Mo, Cd, Sb, Pb and Th) in the Red River at the SonTay station during 2011. The results showed that for the dissolved phase, heavy metal concentrations were relatively stable, whatever the water discharges.  In  contrast,  the  concentration  of  suspended  heavy  metals  tended  to  decrease  with  increasing  of  water discharge. Moreover, the results indicated also that the transfert of heavy metals by the Red River was mainly in the suspended phase (up to 99 %). If the water quality of the Red River can be classified as good (column A - QCVN08: 2008/BTNMT) in term of dissolved heavy metal concentrations; the suspended heavy metal concentrations were higher than  the  ecological  indicators  PEC  (Probable  Effect  Concentration),  suggesting  the  effect  of  this  heavy  metal contamination on the ecology and environment in the Red River basin is extremely high (over 50% ). Finally, this study estimated the contribution of the Red River on the global flux from 0.1 to 0.4% for dissolved phase and from 0.4% to 2.2  for suspended phase.ReferencesBerg M., Stengel C., Trang P.T.K., Pham H.V., Sampton M.L., and Leng M., 2007. Magnitude of arsenic pollution in the Mékong and Red River Deltas-Cambodia and Vietnam, Science of the Total Environment 327, 413-425. Blake, W.H., Walsh, R.P.D., Barnsley, M.J., Palmer, G., Dyrynda, P., James, J.G., 2003. Heavy metal concentrations during storm events in a rehabilitated catchment. Hydrol. 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Assessment of arsenic contamination in the Red River: high resolution monitoring coupled with spatial analysis by GIS. Journal of Sciences and Technology, 51, 779-788. Eiche E., Neumann T., Berg M., Weinman B., van Geen A., Norra S., Berner Z., Stüben, D., 2008. Geochemical processes underlying a sharp contrast in groundwater arsenic concentrations in a village on the Red River delta, Vietnam. Applied Geochemistry 23, 3143-3154. Horowitz A.J., Meybeck M., Idlafkih Z., and Biger E., 1999. Variations in trace element geochemistry in the Seine River Basin based on floodplain deposits and bed sediments, Hydrological Processes 13, 1329-1340. Horowitz AJ, Elrick KA, Smith JJ., 2001. Annual suspended sediment and trace element fluxes in the Mississippi, Columbia, Colorado, and Rio Grande drainage basins. Hydrolog Process 15, 1169-1207. Huang X., Sillanpa M., Duo B. and Gjessing ET., 2008. Water quality in the Tibetan Plateau: Metal contents of four selected rivers. Environmental Pollution 156, 270-277. MacDonald DD., CG. Ingersoll, TA. Berger., 2000. Development and Evaluation of Consensus-Based Sediment Quality Guidelines for Freshwater Ecosystems. Arch. Environ. Contam. Toxicol. 39, 20-31. Masson M., 2007. Sources et transferts métalliques dans le basin versant de la Gironde-Réactivité et mécanismes géochimiques dans l’estuaire fluvial de la Gironde. Thèse doctorat de l’Université Bordeaux 1, 344 pp. Meybeck M., 1998. Man and river interface multiple impacts on water and particulates chemistry illustrated in the Seine River Basin, Hydrobiologia 373, 1-20. Osman, A.E. and Maha, A.A., 2005. Contribution of some trace elements from an Egyptian huge drain to the Mediterranean sea, west of Alexandria. Egypetian journal of aquatic research 31, 120-129. Schäfer J. , G. Blanc, S. Audry, D. Cossa C. Bossy., 2006. Mercury in the Lot-Garonne River system (France): Sources, fluxes and anthropogenic component. Applied Geochemistry 21, 515-527. Singh P., 2010. Geochemistry and provenance of stream sediments of the Ganga River and its major tributaries in the Himalayan region, India. Chemical Geology 269, 220-236. Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution. Blackwell, Oxford, 312 pp. Viers J., Dupréa B., and Gaillardet J., 2009. Chemical composition of suspended sediments in World Rivers:  New insights from a new database. Science of the total environment 407, 853-868. Zhang J., W.W. Huang, R. Letolle, C. Jusserand, 1995. Major element chemistry of the Huanghe (Yellow River), China - weathering processes and chemical fluxes. Journal of Hydrology 168, 173-203. This study  is  based  on the  experimental  results  obtained  from  analysis  of suspended  and  dissolved  heavy  metal concentrations (V, Cr, Co, Ni, Cu, Zn, As, Mo, Cd, Sb, Pb and Th) in the Red River at the SonTay station during 2011. The results showed that for the dissolved phase, heavy metal concentrations were relatively stable, whatever the water discharges.  In  contrast,  the  concentration  of  suspended  heavy  metals  tended  to  decrease  with  increasing  of  water discharge. Moreover, the results indicated also that the transfert of heavy metals by the Red River was mainly in the suspended phase (up to 99 %). If the water quality of the Red River can be classified as good (column A - QCVN08: 2008/BTNMT) in term of dissolved heavy metal concentrations; the suspended heavy metal concentrations were higher than  the  ecological  indicators  PEC  (Probable  Effect  Concentration),  suggesting  the  effect  of  this  heavy  metal contamination on the ecology and environment in the Red River basin is extremely high (over 50% ). Finally, this study estimated the contribution of the Red River on the global flux from 0.1 to 0.4% for dissolved phase and from 0.4% to 2.2  for suspended phase

Thermal Storage Unit Using the Triple Point of Hydrogen

Presented at the 16th International Cryocooler Conference, held May 17-20, 2008 in Atlanta, Georgia.The French space agency (CNES) has co-funded a Research and Technology program and CEA/SBT has developed a 14 K thermal storage unit using the triple point of hydrogen. The development unit is able to store 10 J at 14 K. The unit has been tested at various peak loads in order to validate the energy stored and to measure the temperature stability. This thermal buffer could be used in a cryogenic space mission subject to variable heat loads. The design of the unit will be described and the thermal results will be presented

Services rendus par les foraminifères benthiques dans l’étude de l’influence des forçages naturels (e.g. changement climatique) et anthropiques sur l’écosystème estuarien. Exemple de la Loire.

Due to its intermediate position between ocean and continent, estuary is located in the heart of the economic, social and cultural activities. Awareness of the need to manage this vulnerable environment, has led in recent years, to an increase in surveillance activities of the environmental quality. Physico-chemical methods, although dominant and indispensable, reach their limits as a tool for environmental management. This is why other ways are being explored, such as evaluating the environmental quality by bio-indicators. It is in this perspective that SEMHABEL project is subscribed (Suivi Environnemental des Micro-HAbitats Benthiques de l’Estuaire de la Loire - Plan Loire Grandeur Nature 2007-2013 - FEDER). This is the first study in the Loire incorporating the use of benthic foraminifera as a new biological approach. Following a sampling cruise in September 2012, 320 samples of surface sediments were collected from Nantes to de Saint-Gildas. The data obtained allowed to represent and analyze the spatial distribution of communities of benthic foraminifera, along the upstream-downstream continuum and following geochemical and sedimentary evolutions. These results are the first support for the establishment of a database that will allow a better understanding of the actual functioning of this ecosystem. Ultimately, we hope to assess the evolution of the estuarine ecosystem according to climate change and catchment area management and to develop a biotic index for routine monitoring of the health of the estuary

Recognition memory performance can be estimated based on brain activation networks

Recognition memory is an essential ability for functioning in everyday life. Establishing robust brain networks linked to recognition memory performance can help to understand the neural basis of recognition memory itself and the interindividual differences in recognition memory performance.; We analysed behavioural and whole-brain fMRI data from 1'410 healthy young adults during the testing phase of a picture-recognition task. Using independent component analysis (ICA), we decomposed the fMRI contrast for previously seen vs. new (old-new) pictures into networks of brain activity. This was done in two independent samples (training sample: N = 645, replication sample: N = 665). Next, we investigated the relationship between the identified brain networks and interindividual differences in recognition memory performance by conducting a prediction analysis. We estimated the prediction accuracy in a third independent sample (test sample: N = 100).; We identified 12 robust and replicable brain networks using two independent samples. Based on the activity of those networks we could successfully estimate interindividual differences in recognition memory performance with high accuracy in a third independent sample (r = 0.5, p = 1.29 × 10; -07; ).; Given the robustness of the ICA decomposition as well as the high prediction estimate, the identified brain networks may be considered as potential biomarkers of recognition memory performance in healthy young adults and can be further investigated in the context of health and disease

Development of 15 K Pulse Tube Cold Fingers for Space Applications at CEA/SBT

Presented at the 16th International Cryocooler Conference, held May 17-20, 2008 in Atlanta, Georgia.Pulse tube coolers for space applications have been developed for many years at CEA/SBT. After successful developments of products in the 50 – 80 K range, our focus has changed to temperature below 20 K. Our work is based on compressors delivering about 100 W of mechanical input power to the cold fingers with a goal of several hundred milliwatts of cooling power. Most of the work performed to achieve such low temperature is based on an intercepted configuration, which permits us to focus our research on the low temperature stage. A review of the different phase shifting methods (including active phase shift and cold inertance) and the associated measured performances are presented. In parallel, studies on tube configuration and temperature at warm end have been undertaken. Experimental results are presented on a pulse tube cooler with minimum temperature below 15 K

Relations entre qualité du substrat, flux de matières et activités humaines. Connaissance pour la gestion des ressources en eau de la Région Aquitaine

Les résultats de ce travail de recherche, confirment une fois de plus l'absence de déterminisme apparent entre qualité du substrat et occupation des sols. Ils montrent qu'il n'y a pas de variables prépondérantes ou explicatives de facteurs sociaux ou physiques qui soient responsables des variations affectant les milieux étudiés. Cependant, les analyses régressives des rapports entre homme et milieu montrent les liens étroits entre habitat et types de sol. L'action humaine a des effets sur la couverture végétale, sur les sols et sur l'hydraulique qui avec le climat et la topographie constituent les principaux facteurs d'érosion

Human cerebellum and corticocerebellar connections involved in emotional memory enhancement

Emotional information is better remembered than neutral information. Extensive evidence indicates that the amygdala and its interactions with other cerebral regions play an important role in the memory-enhancing effect of emotional arousal. While the cerebellum has been found to be involved in fear conditioning, its role in emotional enhancement of episodic memory is less clear. To address this issue, we used a whole-brain functional MRI approach in 1,418 healthy participants. First, we identified clusters significantly activated during enhanced memory encoding of negative and positive emotional pictures. In addition to the well-known emotional memory-related cerebral regions, we identified a cluster in the cerebellum. We then used dynamic causal modeling and identified several cerebellar connections with increased connection strength corresponding to enhanced emotional memory, including one to a cluster covering the amygdala and hippocampus, and bidirectional connections with a cluster covering the anterior cingulate cortex. The present findings indicate that the cerebellum is an integral part of a network involved in emotional enhancement of episodic memory