Analyses directionnelles multivariées de la qualité des précipitations sur la région de Québec

La question des précipitations acides est devenue une des principales préoccupations environnementales de ce siècle. Les dommages engendrés touchent l'ensemble des composantes atmosphérique, aquatique et terrestre de notre écosystème. Dans cet article, l'intérêt est tourné vers le transport des substances polluantes en faisant intervenir le vecteur des précipitations acides: le vent. Il existe une croyance populaire, largement répandue dans l'est du Canada, consistant à admettre que les vents d'est ou du nord sont associés à des précipitations faiblement chargées en éléments acides, contrairement aux vents du sud-ouest qui transporteraient les charges plus contaminées des industries situées dans le Midwest nord-américain. Une confirmation expérimentale de la réalité du phénomène est présentée ici.Une analyse factorielle des correspondances permet de mettre en évidence des relations entre la direction des vents et la composition chimique des précipitations. Des analyses de variance permettent ensuite de montrer la signification de l'effet de la direction des vents sur les concentrations de sulfates et de nitrates, en plus de mettre en évidence un effet saisonnier significatif pour ces deux variables. Les concentrations de nitrates et de sulfates associées aux vents de l'ouest sont respec- tivement de 0,33 mg/l-¹ et 1,73 mg/l-¹ comparativement à 0,24 mg/l-¹ et 1,48 mg/l-¹ pour les vents provenant de l'est. En ce qui concerne l'effet saisonnier, les concentrations moyennes de nitrates sont plus élevées durant les mois de janvier et de mars alors que les concentrations de sulfates sont plus elevées durant les mois d'été.The problem of acidic precipitation has become an important environmental concern; related damages can affect atmospheric, terrestrial and aquatic components of our ecosystem. This paper focuses on wind-driven atmospheric transport of contaminants, notably niirates and sulfates. Conventional wisdom in eastern Canada holds that winds originating from the east bring precipitation less loaded with acidic components than winds originating from the southwest; the latter carry contarninants generated by industries located in the American Midwest.An experimental confirmation of this phenomenon is presented here. SPERBER (1987) showed that hourly series of piecipitation content and wind direction, measured at a reception site are adequate to represent the lagrangian history of precipitating systems (New York City region). Following this result, we suppose that the northesastern continental atmospheric system is homogeneous enough so that winds measured at our reception site (Québec City region) are representative of the whole system. Thus, our experiment is performed in eulerian coordinates.The data bank used in the statistic alana|yses contains 10 time series: the weekly concentrations of 9 compounds found in the precipitation (H, Ca, Cl, K, Mg, Na, NO3, NH4 and SO4) gathered at the local Montmorency site and a s:ries ofweekly prevailing winds measured at the nearby Québec City airport. The time series contain 312 observations covering a full six year period (December 1981 to December 1987). As the original data bank of corcentrations is episodic, i.e. an obsercvation is available for each day with a significant precipitation event, volumes and loadings are used to derive the average weekly values of concentrations. In contrast, hourly series of direction (projected in 36 directions) and velocity of the prevailing winds are used to build, via a vectorial addition, a weekly series of wind direitions projected on a 12 point wind rose where directions corespond to the nind origin and not its destination.Classic statistical methods are used to deal with this data bank. Principal component analysis studies relationships between series of concentrations in the precipitations, while correspondence analysis highrights the relationships betwlen tile series of precipitation content and the series ofwind direction. The final statistical method, analysis of variance, is used to test the signilïcance of relationships higtrlighted by the correspondence analysis.The principal component analysis shows that all variables were positively correlated with the first component which reflects the fact that a higtrly loaded precipitation event will show high concentrations for each ofthe nine variables. The second component discriminates two groups of variables: one includes NO3, NH4 and SO4, the other Ca, Mg and Cl. The acidity variable, H, is nearer to the acid ion group (NO3, NH4 and SO4) than to the other ion group (Ca, Mg and Cl).The correspondence analysis shows that high concentrations of acidic compounds (NO3, NH4 and SO4) are highly rerated to winds from the W and WSW directions; conversely lower concentrations of the same compounds are associated with winds from the E and ENE directions. The elements Ca, Mg and Cl, reputed to be of oceanic origin, show high functional relationships between high concentrations and E, ENE winds and also between low concentrations and W, WSW winds. These results support the popular belief initially presented that acid precipitation is largely associated with winds from the southwest.The analyses of variance show that precipitation concentrations (NO3 and SO4) are significantly different according to the wind directions. Nitrate and sulfate concentrations associated with winds originating from the west are respectively 0.33-mg.l-l and 1.73 mg.l-l compared, to 0.24 mg.l-l and 1.48 mg.l-l for winds originating from the east. The analyses ofvariance also indicate a significant seasonal effect where mean monthly concentrations in nitrates are hilhest for winter months and early spring whereas sulfate concentrations are highest for the summer months

Metabolic engineering of Escherichia coli for the production of coenzyme Q10

Coenzyme Q10 is required for respiratory electron transport and protects biological membranes against oxidative damage. As coenzyme Q10 supplements are used to treat or to alleviate symptoms associated with an increasing number of health conditions, there is growing interest in the development of bioprocesses for its production. The biosynthesis of coenzyme Q10 involves the condensation of an isoprenoid, decaprenyl diphosphate, with an aromatic compound, para-hydroxybenzoate, followed by a series of modifications of the aromatic moiety of the molecule via the ubiquinone pathway. Escherichia coli naturally produces coenzyme Q8, but replacement of its octaprenyl diphosphate synthase by a decaprenyl diphosphate synthase is sufficient to eliminate the production of coenzyme Q8 and favor the synthesis of coenzyme Q10. A rational genetic engineering approach was used to create a strain of E. coli capable of producing high levels of coenzyme Q10. First, the endogenous octaprenyl diphosphate synthase gene was deleted and functionally replaced by a decaprenyl diphosphate synthase-encoding gene derived from Sphingomonas baekryungensis. Additionally, this strain was engineered to produce elevated levels of para-hydroxybenzoate by over-expressing genes encoding enzymes of the E. coli shikimate pathway. The production of isoprenoid was increased by introducing a heterologous mevalonate pathway. Decaprenyl diphosphate and para-hydroxybenzoate were further directed toward the ubiquinone pathway by overexpressing a para-hydroxybenzoate prenyltransferase. The resulting recombinant strain was capable of producing elevated levels of coenzyme Q10. In order to further enhance production of this antioxidant, an investigation into the interplay between coenzyme Q10 biosynthesis and primary metabolism was conducted. This investigation revealed a link between sorbitol catabolism and coenzyme Q10 production in the engineered strain. Moreover, abrogating carbon flux to acetate by selected gene knock-outs also enhanced coenzyme Q10 accumulation. However, the engineered strains developed through this research were found to be highly unstable, leading to high variability in coenzyme Q10 production. This instability was hypothesized to result from the burden exerted by the engineered aromatic and foreign mevalonate pathways on primary metabolism. As a result, further optimization of these engineered strains of E. coli will be required in order to develop a suitable platform for coenzyme Q10 production

Multi-time-scale hydroclimate dynamics of a regional watershed and links to large-scale atmospheric circulation:Application to the Seine river catchment, France

(IF 3.73; Q1)International audienceIn the present context of global changes, considerable efforts have been deployed by the hydrological scientific community to improve our understanding of the impacts of climate fluctuations on water resources. Both observational and modeling studies have been extensively employed to characterize hydrological changes and trends, assess the impact of climate variability or provide future scenarios of water resources. In the aim of a better understanding of hydrological changes, it is of crucial importance to determine how and to what extent trends and long-term oscillations detectable in hydrological variables are linked to global climate oscillations.In this work, we develop an approach associating correlation between large and local scales, empirical statistical downscaling and wavelet multiresolution decomposition of monthly precipitation and streamflow over the Seine river watershed, and the North Atlantic sea level pressure (SLP) in order to gain additional insights on the atmospheric patterns associated with the regional hydrology. We hypothesized that: (i) atmospheric patterns may change according to the different temporal wavelengths defining the variability of the signals; and (ii) definition of those hydrological/circulation relationships for each temporal wavelength may improve the determination of large-scale predictors of local variations.The results showed that the links between large and local scales were not necessarily constant according to time-scale (i.e. for the different frequencies characterizing the signals), resulting in changing spatial patterns across scales. This was then taken into account by developing an empirical statistical downscaling (ESD) modeling approach, which integrated discrete wavelet multiresolution analysis for reconstructing monthly regional hydrometeorological processes (predictand: precipitation and streamflow on the Seine river catchment) based on a large-scale predictor (SLP over the Euro-Atlantic sector). This approach basically consisted in three steps: 1 – decomposing large-scale climate and hydrological signals (SLP field, precipitation or streamflow) using discrete wavelet multiresolution analysis, 2 – generating a statistical downscaling model per time-scale, 3 – summing up all scale-dependent models in order to obtain a final reconstruction of the predictand. The results obtained revealed a significant improvement of the reconstructions for both precipitation and streamflow when using the multiresolution ESD model instead of basic ESD. In particular, the multiresolution ESD model handled very well the significant changes in variance through time observed in either precipitation or streamflow. For instance, the post-1980 period, which had been characterized by particularly high amplitudes in interannual-to-interdecadal variability associated with alternating flood and extremely low-flow/drought periods (e.g., winter/spring 2001, summer 2003), could not be reconstructed without integrating wavelet multiresolution analysis into the model. In accordance with previous studies, the wavelet components detected in SLP, precipitation and streamflow on interannual to interdecadal time-scales could be interpreted in terms of influence of the Gulf-Stream oceanic front on atmospheric circulation

Généralisation du test de tendance de Foster et Stuart à des échantillons Markoviens courts.

Foster et Stuart (1954) ont développé sur des chroniques longues et indépendantes un test non-paramétrique progressif basé sur la répugnance des séries stationnaires à battre les records établis quand leur longueur augmente: la somme et la différence du nombre des records inférieurs et supérieurs permettent de tester la stationnarité en moyenne et en variance. Leurs résultats théoriques sont étendus aux séries courtes; puis des séries Markoviennes (N = 10 ... 300; P = 0 ... 0.95) sont générées par simulation de Monte-Carlo pour établir les valeurs moyennes et la dispersion des statistiques; la puissance des tests en pourcentage de détection est calculée pour des tendances linéaires variées. L'apparition répétée de nouveaux records historiques, dans une série de concentrations, constitue un indice de tendance plus apparent que le calcul progressif d'un paramètre de tendance centrale. La généralisation présentée permet, après caractérisation de la persistance avant tendance, d'exploiter pratiquement cette approche originale