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

Influence of ground surface characteristics on the mean radiant temperature in urban areas

The effect of variations in land cover on mean radiant surface temperature (Tmrt) is explored through a simple scheme developed within the radiation model SOLWEIG. Outgoing longwave radiation is parameterised using surface temperature observations on a grass and an asphalt surface, whereas outgoing shortwave radiation is modelled through variations in albedo for the different surfaces. The influence of surface materials on Tmrt is small compared to the effects of shadowing. Nevertheless, altering ground surface materials could contribute to a reduction on Tmrt to reduce the radiant load during heat-wave episodes in locations where shadowing is not an option. Evaluation of the new scheme suggests that despite its simplicity it can simulate the outgoing fluxes well, especially during sunny conditions. However, it underestimates at night and in shadowed locations. One grass surface used to develop the parameterisation, with very different characteristics compared to an evaluation grass site, caused Tmrt to be underestimated. The implications of using high resolution (e.g. 15 minutes) temporal forcing data under partly cloudy conditions are demonstrated even for fairly proximal sites

Light Plays an Essential Role in Intracellular Distribution of Auxin Efflux Carrier PIN2 in Arabidopsis thaliana

BACKGROUND: Light plays a key role in multiple plant developmental processes. It has been shown that root development is modulated by shoot-localized light signaling and requires shoot-derived transport of the plant hormone, auxin. However, the mechanism by which light regulates root development is not largely understood. In plants, the endogenous auxin, indole-3-acetic acid, is directionally transported by plasma-membrane (PM)-localized auxin influx and efflux carriers in transporting cells. Remarkably, the auxin efflux carrier PIN proteins exhibit asymmetric PM localization, determining the polarity of auxin transport. Similar to PM-resident receptors and transporters in animal and yeast cells, PIN proteins undergo constitutive cycling between the PM and endosomal compartments. Auxin plays multiple roles in PIN protein intracellular trafficking, inhibiting PIN2 endocytosis at some concentrations and promoting PIN2 degradation at others. However, how PIN proteins are turned over in plant cells is yet to be addressed. METHODOLOGY AND PRINCIPLE FINDINGS: Using laser confocal scanning microscopy, and physiological and molecular genetic approaches, here, we show that in dark-grown seedlings, the PM localization of auxin efflux carrier PIN2 was largely reduced, and, in addition, PIN2 signal was detected in vacuolar compartments. This is in contrast to light-grown seedlings where PIN2 was predominantly PM-localized. In light-grown plants after shift to dark or to continuous red or far-red light, PIN2 also accumulated in vacuolar compartments. We show that PIN2 vacuolar targeting was derived from the PM via endocytic trafficking and inhibited by HY5-dependent light signaling. In addition, the ubiquitin 26S proteasome is involved in the process, since its inhibition by mutations in COP9 and a proteasome inhibitor MG132 impaired the process. CONCLUSIONS AND SIGNIFICANCE: Collectively, our data indicate that light plays an essential role in PIN2 intracellular trafficking, promoting PM-localization in the presence of light and, on the other hand, vacuolar targeting for protein degradation in the absence of light. Based on these results, we postulate that light regulation of root development is mediated at least in part by changes in the intracellular distribution of auxin efflux carriers, PIN proteins, in response to the light environment

The Arabidopsis transcription factor HY5 integrates light and hormone signaling pathways

The role of the Arabidopsis transcription factor LONG HYPOCOTYL 5 (HY5) in promoting photomorphogenic development has been extensively characterized. Although the current model for HY5 action largely explains its role in this process, it does not adequately address the root phenotype observed in hy5 mutants. In our search for common mechanisms underlying all hy5 traits, we found that they are partly the result of an altered balance of signaling through the plant hormones auxin and cytokinin. hy5 mutants are resistant to cytokinin application, and double mutant analyses indicate that a decrease in auxin signaling moderates hy5 phenotypes. Microarray analyses and semiquantitative RT-PCR indicate that two negative regulators of auxin signaling, AUXIN RESISTANT 2 (AXR2)/INDOLE ACETIC ACID 7 (IAA7) and SOLITARY ROOT (SLR)/IAA14, are underexpressed in hy5 mutants. The promoters of these genes contain a putative HY5 binding site, and in line with this observation, HY5 can bind to the promoter of AXR2 in vitro. Increased AXR2 expression in a hy5 background partially rescues the elongated hypocotyl phenotype. In summary, it appears that auxin signaling is elevated in hy5 mutants because HY5 promotes the expression of negative regulators of auxin signaling, thereby linking hormone and light signaling pathways

Multivariate directional analysis of precipitation content in the Quebec region

International audienceThe 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 nitrates and sulphates. 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 contaminants generated by industries located in the American Midwest. An experimental confirmation of this phenomenon is presented here. SPERBER (1987) showed that hourly series of precipitation 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 north-eastern continental atmospheric system is homogeneous enough so that winds measured at tour 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 statistical analyses 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 series of weekly prevailing winds measured at the nearby Quebec City airport. The time series contain 312 observations covering a full six years period (December 1981 to December 1987). As the original data bank of concentrations is episodic, i.e. an observation 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 directions projected on a 12 points wind rose where directions correspond to the wind 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 highlights the relationships between the series of precipitation content and the series of wind direction. The final statistical method, analysis of variance, is used to test the significance of relationships highlighted by the correspondence analysis. The principal component analysis showed that all variables were positively correlated with the first component, which reflects the fact that a highly loaded precipitation event will show high concentrations for each of the nine variables. The second component discriminates two groups of variables: one includes NO3, SO4 and NH4, the other Ca, Mg, and Cl. The acidity variable, H, is nearer to the acid ion group (NO3, SO4, NH4) than the other ion group (Ca, Mg and Cl). The correspondence analysis shows that high concentrations of acidic compounds (NO3, SO4 and NH4) are highly related 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 an 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 sulphate concentrations associated with winds originating from the west are respectively 0,33 mg.l-1 and 1,73mg.l-1 compared to 0,24 mg.l-1 and 1,48 mg.l-1 for winds originating from the east. The analyses of variance also indicate a significant seasonal effect, where mean monthly concentrations in nitrates are highest for winter months and early spring, whereas sulphate concentrations are highest for the summer months

Multivariate directional analysis of precipitation content in the Quebec region

International audienceThe 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 nitrates and sulphates. 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 contaminants generated by industries located in the American Midwest. An experimental confirmation of this phenomenon is presented here. SPERBER (1987) showed that hourly series of precipitation 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 north-eastern continental atmospheric system is homogeneous enough so that winds measured at tour 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 statistical analyses 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 series of weekly prevailing winds measured at the nearby Quebec City airport. The time series contain 312 observations covering a full six years period (December 1981 to December 1987). As the original data bank of concentrations is episodic, i.e. an observation 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 directions projected on a 12 points wind rose where directions correspond to the wind 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 highlights the relationships between the series of precipitation content and the series of wind direction. The final statistical method, analysis of variance, is used to test the significance of relationships highlighted by the correspondence analysis. The principal component analysis showed that all variables were positively correlated with the first component, which reflects the fact that a highly loaded precipitation event will show high concentrations for each of the nine variables. The second component discriminates two groups of variables: one includes NO3, SO4 and NH4, the other Ca, Mg, and Cl. The acidity variable, H, is nearer to the acid ion group (NO3, SO4, NH4) than the other ion group (Ca, Mg and Cl). The correspondence analysis shows that high concentrations of acidic compounds (NO3, SO4 and NH4) are highly related 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 an 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 sulphate concentrations associated with winds originating from the west are respectively 0,33 mg.l-1 and 1,73mg.l-1 compared to 0,24 mg.l-1 and 1,48 mg.l-1 for winds originating from the east. The analyses of variance also indicate a significant seasonal effect, where mean monthly concentrations in nitrates are highest for winter months and early spring, whereas sulphate concentrations are highest for the summer months