Traçage minéralogique de l’origine des sédiments aux confluents de cours d’eau

Traçage minéralogique de l'origine des sédiments aux confluents de cours d'eau. La dynamique sédimentaire des confluents de cours d'eau peut s'étudier par l'intermédiaire de traceurs marquant l'origine des particules. La connaissance de la source sédimentaire est essentielle pour comprendre les processus de mélange des sédiments du lit et établir des relations causales entre les sources de contamination et la dynamique des sites contaminés liés à l'arrivée d'un tributaire. On a examiné les particules du lit d'un confluent naturel sablonneux où la minéralogie des sédiments composant les bassins-versants est différenciée. En raison de leurs forme et densité, les feldspaths K s'avèrent des traceurs efficaces et indiquent qu'à la jonction étudiée le mélange des apports sédimentaires est presque complété à une distance de mélange de 2,1 (distance à partir de l'apex/largeur du confluent). Par contre, les micas et le pourcentage de minéraux lourds, sensibles au tri hydraulique, ne révèlent pas la provenance des particules. La méthode a aussi été employée pour déterminer le patron de dispersion des particules à un confluent du Saint-Laurent. Ici la minéralogie des particules diffère peu entre les bassins-versants. Toutefois, les variations spatiales du pourcentage de minéraux lourds sont directement liées à la morphologie du lit caractérisée par un banc d'accumulation se terminant par un abrupt à l'entrée du tributaire. Les faibles teneurs en minéraux lourds sur la pente de l'abrupt démontrent que le fluide est peu compétent à l'abri de la construction sédimentaire. Par contre, à son pied et à son sommet, le fluide effectue un tri hydraulique efficace, ce qui entraîne une concentration des particules lourdes. Ces variations des teneurs en minéraux lourds sont indicatrices du tri hydraulique plutôt que de la source sédimentaire.Sedimentary dynamics of river channel confluences may be studied through the use of natural tracers. The information supplied by tracers is of crucial interest to understand the mixing processes of bed material from the confluent channels and of potential zones of accumulation of contaminated sediments. We examined the bed material of a confluence where the mineralogy of the sediments of the tributary watershed differs from that of the main channel. The potential of two tracers (K feldspars and micas) and the heavy mineral concentrations is assessed. Due to its shape and density, K feldspars is the most efficient tracer to reveal the mixing between the sediment loads coming from the upstream channels. The spatial distribution of the tracer suggests a very rapid mixing of the loads: at a distance equivalent to 2.1 channel width, mixing is nearly completed. Micas and heavy mineral concentrations are less reliable indicators of the sedimentary dynamics. The technique was also applied at a confluence along the St. Lawrence River. In this case, clear mineralogical differences between the sediments of the watersheds are absent. The spatial pattern of heavy mineral concentrations is controlled by the main morphological feature of the confluence, that is, the avalanche face at the edge of a tributary mouth bar prograding within the St. Lawrence. Low heavy mineral concentrations are located on the avalanche face itself while higher concentrationms are found at the foot and top of the face. This pattern reflects variations in sorting regime rather than origin of particles.Die Sediment-Dynamik der Zusammenflusse von Wasserlàufen kann mit Hilfe von Aufspùrern, welche die Herkunft der Teilchen markieren, studiert werden. Die Kenntnis der Sedimentquelle ist unerlâsslich fur das Verstàndnis der Mischprozesse der Flussbettsedimente und die Herstellung von kausalen Beziehungen zwischen den Quellen der Verunreinigung und der Dynamik der verunreinigten Plàtze aufgrund eines tributàren Zuflusses. Man hat die Teilchen des Bettes eines natùrlichen sandigen Zusammenflusses untersucht, wo die Minéralogie der die Flussbecken bildenden Sedimente unterschiedlich ist. Wegen ihrer Form und Dichte erweisen sich die K-Feldspate als erfolgreiche Aufspiirer und sie zeigen, dass am untersuchten Zusammenfluss die Mischung der Sedimentzufuhr in einer Mischungsentfernung von 2,1 (Entfemung vom Scheitel/ von der Breite des Zusammenflusses) fast vollstândig ist. Dieselbe Méthode wurde auch verwendet, urn das Dispersionsmuster der Teilchen an einem Zusammenfluss des Sankt-Lorenz zu bestimmen. Hier unterscheidet sich die Minéralogie der Teilchen zwischen den Flussbecken wenig. Dennoch sind die râumlichen Abweichungen des Prozentsatzes schwerer Minérale direkt mit der Morphologie des Flusses verbunden, welche sich durch eine Aufschûttungsbank charakterisiert, die mit einem Abbruch am tributàren Zufluss endet. Der geringe Anteil von schweren Mineralen am Gefàlle des Abbruchs zeigt, dass die Flùssigkeit im Schutz des Sedimentbaus wenig Einfluss hat. Jedoch bewirkt die Flùssigkeit an seinem Fuss und seiner Spitze ein erfolgreiches hydraulisches Sortieren, was zu einer Konzentration der schweren Teilchen fùhrt. Dièse Abweichungen im Gehalt an schweren Mineralen spiegeln eher das hydraulische Sortieren als die Sedimentherkunft

Exposure to excessive heat and impacts on labour productivity linked to cumulative CO2 emissions

Cumulative CO2 emissions are a robust predictor of mean temperature increase. However, many societal impacts are driven by exposure to extreme weather conditions. Here, we show that cumulative emissions can be robustly linked to regional changes of a heat exposure indicator, as well as the resulting socioeconomic impacts associated with labour productivity loss in vulnerable economic sectors. We estimate historical and future increases in heat exposure using simulations from eight Earth System Models. Both the global intensity and spatial pattern of heat exposure evolve linearly with cumulative emissions across scenarios (1% CO2, RCP4.5 and RCP8.5). The pattern of heat exposure at a given level of global temperature increase is strongly affected by non-CO2 forcing. Global non-CO2 greenhouse gas emissions amplify heat exposure, while high local emissions of aerosols could moderate exposure. Considering CO2 forcing only, we commit ourselves to an additional annual loss of labour productivity of about 2% of total GDP per unit of trillion tonne of carbon emitted. This loss doubles when adding non-CO2 forcing of the RCP8.5 scenario. This represents an additional economic loss of about 4,400 G$every year (i.e. 0.59$/tCO2), varying across countries with generally higher impact in lower-income countries

Exposure to excessive heat and impacts on labour productivity linked to cumulative CO2 emissions

Cumulative CO2 emissions are a robust predictor of mean temperature increase. However, many societal impacts are driven by exposure to extreme weather conditions. Here, we show that cumulative emissions can be robustly linked to regional changes of a heat exposure indicator, as well as the resulting socioeconomic impacts associated with labour productivity loss in vulnerable economic sectors. We estimate historical and future increases in heat exposure using simulations from eight Earth System Models. Both the global intensity and spatial pattern of heat exposure evolve linearly with cumulative emissions across scenarios (1% CO2, RCP4.5 and RCP8.5). The pattern of heat exposure at a given level of global temperature increase is strongly affected by non-CO2 forcing. Global non-CO2 greenhouse gas emissions amplify heat exposure, while high local emissions of aerosols could moderate exposure. Considering CO2 forcing only, we commit ourselves to an additional annual loss of labour productivity of about 2% of total GDP per unit of trillion tonne of carbon emitted. This loss doubles when adding non-CO2 forcing of the RCP8.5 scenario. This represents an additional economic loss of about 4,400 G$every year (i.e. 0.59$/tCO2), varying across countries with generally higher impact in lower-income countries

The Canadian Urban Environmental Health Research Consortium - A protocol for building a national environmental exposure data platform for integrated analyses of urban form and health

Background: Multiple external environmental exposures related to residential location and urban form including, air pollutants, noise, greenness, and walkability have been linked to health impacts or benefits. The Canadian Urban Environmental Health Research Consortium (CANUE) was established to facilitate the linkage of extensive geospatial exposure data to existing Canadian cohorts and administrative health data holdings. We hypothesize that this linkage will enable investigators to test a variety of their own hypotheses related to the interdependent associations of built environment features with diverse health outcomes encompassed by the cohorts and administrative data. Methods: We developed a protocol for compiling measures of built environment features that quantify exposure; vary spatially on the urban and suburban scale; and can be modified through changes in policy or individual behaviour to benefit health. These measures fall into six domains: air quality, noise, greenness, weather/climate, and transportation and neighbourhood factors; and will be indexed to six-digit postal codes to facilitate merging with health databases. Initial efforts focus on existing data and include estimates of air pollutants, greenness, temperature extremes, and neighbourhood walkability and socioeconomic characteristics. Key gaps will be addressed for noise exposure, with a new national model being developed, and for transportation-related exposures, with detailed estimates of truck volumes and diesel emissions now underway in selected cities. Improvements to existing exposure estimates are planned, primarily by increasing temporal and/or spatial resolution given new satellite-based sensors and more detailed national air quality modelling. Novel metrics are also planned for walkability and food environments, green space access and function and life-long climate-related exposures based on local climate zones. Critical challenges exist, for example, the quantity and quality of input data to many of the models and metrics has changed over time, making it difficult to develop and validate historical exposures. Discussion: CANUE represents a unique effort to coordinate and leverage substantial research investments and will enable a more focused effort on filling gaps in exposure information, improving the range of exposures quantified, their precision and mechanistic relevance to health. Epidemiological studies may be better able to explore the common theme of urban form and health in an integrated manner, ultimately contributing new knowledge informing policies that enhance healthy urban living

Correction of air freezing index for pavement frost protection design to consider future climate changes

In cold regions, climate affects flexible pavement performance, such as frost heave. In the context of a changing climate, air freezing index can no longer be considered as fixed for pavement design. Climate simulations were performed for Quebec conditions in order to determine the evolution of the air freezing index over the coming decades. Using a relationship between average frost heave and the yearly roughness deterioration rate and a proposed method to consider decreasing air freezing index, the effect of climate change was quantified with respect to the 1971-2000 conditions. Thinner pavement structures are obtained with the calculation approach, and its effect was quantified in terms of materials and pavement life. It was shown that a reduction of 100 mm could be considered for pavements built on frost sensitive soils. In addition, the proposed method showed an increase of pavement life, quantified with roughness, for most of the cases considered.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Climatic drivers

Contributing authors : Carl Barrette, Diane Chaumont, Chris Derksen, James Hamilton, Stephen Howell, Thomas Ingeman-Nielsen, Thomas James, Diane Lavoie, Sergey Marchenko, Steffen M. Olsen, Christian B. Rodehacke, Martin Sharp, Sharon L. Smith, Martin Stendel, Rasmus T. Tonbo