Parameter uncertainty and sensitivity analysis in sediment flux calculation

International audienceThis paper examines uncertainties in the calculation of annual sediment budgets at the outlet of rivers. Emphasis is put on the sensitivity of power-law rating curves to degradations of the available discharge-concentration data. The main purpose is to determine how predictions arising from usual or modified power laws resist to the infrequence of concentration data and to relative uncertainties affecting source data. This study identifies cases in which the error on the estimated sediment fluxes remains of the same order of magnitude or even inferior to these in source data, provided the number of concentration data is high enough. The exposed mathematical framework allows considering all limitations at once in further detailed investigations. It is applied here to bound the error on sediment budgets for the major French rivers to the sea

Climate change impacts on fish reproduction are mediated at multiple levels of the brain-pituitary-gonad axis

Anthropogenic emissions of carbon dioxide in the atmosphere have generated rapid variations in atmospheric composition which drives major climate changes. Climate change related effects include changes in physicochemical proprieties of sea and freshwater, such as variations in water temperature, salinity, pH/pCO(2) and oxygen content, which can impact fish critical physiological functions including reproduction. In this context, the main aim of the present review is to discuss how climate change related effects (variation in water temperature and salinity, increases in duration and frequency of hypoxia events, water acidification) would impact reproduction by affecting the neuroendocrine axis (brain-pituitary-gonad axis). Variations in temperature and photoperiod regimes are known to strongly affect sex differentiation and the timing and phenology of spawning period in several fish species. Temperature mainly acts at the level of gonad by interfering with steroidogenesis, (notably on gonadal aromatase activity) and gametogenesis. Temperature is also directly involved in the quality of released gametes and embryos development. Changes in salinity or water acidification are especially associated with reduction of sperm quality and reproductive output. Hypoxia events are able to interact with gonad steroidogenesis by acting on the steroids precursor cholesterol availability or directly on aromatase action, with an impact on the quality of gametes and reproductive success. Climate change related effects on water parameters likely influence also the reproductive behavior of fish. Although the precise mechanisms underlying the regulation of these effects are not always understood, in this review we discuss different hypothesis and propose future research perspectives.info:eu-repo/semantics/publishedVersio

A role for More Axillary Growth1 (MAX1) in evolutionary diversity in strigolactone signaling upstream of MAX2

Strigolactones (SLs) are carotenoid-derived phytohormones with diverse roles. They are secreted from roots as attractants for arbuscular mycorrhizal fungi and have a wide range of endogenous functions, such as regulation of root and shoot system architecture. To date, six genes associated with SL synthesis and signaling have been molecularly identified using the shoot-branching mutants more axillary growth (max) of Arabidopsis (Arabidopsis thaliana) and dwarf (d) of rice (Oryza sativa). Here, we present a phylogenetic analysis of the MAX/D genes to clarify the relationships of each gene with its wider family and to allow the correlation of events in the evolution of the genes with the evolution of SL function. Our analysis suggests that the notion of a distinct SL pathway is inappropriate. Instead, there may be a diversity of SL-like compounds, the response to which requires a D14/D14-like protein. This ancestral system could have been refined toward distinct ligand-specific pathways channeled through MAX2, the most downstream known component of SL signaling. MAX2 is tightly conserved among land plants and is more diverged from its nearest sister clade than any other SL-related gene, suggesting a pivotal role in the evolution of SL signaling. By contrast, the evidence suggests much greater flexibility upstream of MAX2. The MAX1 gene is a particularly strong candidate for contributing to diversification of inputs upstream of MAX2. Our functional analysis of the MAX1 family demonstrates the early origin of its catalytic function and both redundancy and functional diversification associated with its duplication in angiosperm lineages

Evaluer les émissions de gaz à effet de serre d'un système d'assainissement, quels outils et quelles expériences ?

National audienceLa lutte contre le réchauffement climatique est aujourd'hui une priorité nationale et l'objectif de division par 4 des émissions de gaz à effet de serre de la France à horizon 2050 ne pourra être atteint si les collectivités ne disposent pas d'un état des lieux de l'impact actuel sur le changement climatique de l'ensemble des services publics locaux qu'elles gèrent, ainsi que d'outils leur permettant d'apprécier l'impact environnemental de leurs décisions sur les évolutions du fonctionnement de ces services. Ainsi, bien que les services d'assainissement ne comptent pas parmi les services publics locaux les plus contributeurs aux émissions de gaz à effet de serre, la prise en compte de leur impact sur le changement climatique, comme plus généralement sur l'ensemble des composantes de l'environnement autres que l'eau et les sols, est un élément d'aide à la décision de plus en plus pris en considération lors du choix de nouvelles filières pour le traitement des eaux et des boues. A cet effet, l'emploi des méthodologies existantes (approche ACV, Bilan carbone) semble appelé à s'étendre dans l'avenir, de manière à fournir à toutes les collectivités sans distinction de taille de nouveaux outils d'aide à la décision. Ceci suppose toutefois de disposer d'une vision partagée sur les méthodologies à adopter, ce qui n'est pas encore le cas aujourd'hui, et de disposer de connaissances plus précises sur les différents facteurs d'émission de gaz à effet de serre liés à l'activité des services d'assainissement

Spéciation et flux des métaux-trace dans une station d'épuration importante : impact des traitements successifs

International audienceSeven metals (Cd, Co, Cr, Cu, Fe, Ni and Pb) were monitored at the Seine-Aval wastewater treatment plant during 6 sampling campaigns in April 2004. Particulate and dissolved metals have been measured in 24 h composite samples at each treatment stage (primary settling, secondary activated sludge and tertiary flocculation by FeCl3). In addition, the diffusive gradient in thin film technique (DGT) was used to determine the dissolved inert and labile metal fraction. Although all treatment stages were able to decrease particulate metals concentrations in wastewater, most dissolved metals concentrations were mainly affected during primary settling. This unexpected result was attributed to tertiary sludge filtrate recirculation. Metals added via the FeCl3 reagent at the tertiary treatment were shown to lower the overall Cr removal from wastewater and to enrich Ni in effluents. The plant operating conditions (recirculation and reagent addition) appear therefore as important as treatment processes for the metals removal. Total metal fluxes were highly decreased by the whole treatment plant for Cd, Cr, Cu and Pb and to a lesser extend for Co and Ni. However, the labile metal fluxes were poorly decreased for Cu (18%), not significantly decreased for Ni and increased for Fe. The labile fraction of Cd, Co and Cr was not detectable at any stage of the plant. Discharged labile fluxes, at least for Ni, were potentially significant compared to the labile metal fluxes in the river measured downstream the plant. Treated urban wastewater discharges should be carefully considered as a possible source of bioavailable trace metals

Caractérisation de la matière organique dissoute des rejets d'une importante station d'épuration et influence sur la biodisponibilité du cuivre

National audienceLa matière organique dissoute [MaO) joue un rôle important dans la spéciation et la biodisponibilité des métaux traces. Cependant aucune information n'est actuellement disponible quant à l'influence des Mao issues du rejet de station d'épuration sur la biodisponibilité du cuivre. Une procédure d'extraction et de fractionnement de la MOD sur résines [DAX-8 et XAD-41 a été mise en place afin d'extraire la MaO urbaine dans son intégralité avec un minimum de perte et d'altération. Trois fractions: hydrophobe (HPa], transphiLique (TPHI et hydrophile lHPIl représentant respectivement 34 %, 20 % et 46 % du carbone ont ainsi été isolées d'une eau de sortie de station d'épuration [STEP]. Cette distribution montre l'importance en milieu anthropisé de la fraction HPI souvent négligée de par sa difficile extraction. Différentes techniques analytiques (élémentaires, spectroscopiques: UV, IR] ont permis de caractériser ces fractions mettant ainsi en évidence: une MaO urbaine peu humifiée, des fractions HPO et TPH de nature chimique proche et une fraction HPI différente, notamment de par sa très faible aromaticité. La biodisponibilité du cuivre en présence de chacune de ces trois fractions de MaO a été évaluée à l'aide d'un biotest de toxicité aigüe sur Daphnia magna. Les résultats montrent qu'à l'instar des substances humiques, la MaO issue de rejets traités de STEP, bien que moins humifiée, conserve un pouvoir limitant la toxicité du cuivre