Les échanges surface-atmosphère du mercure gazeux dans l'écosystème lac Ontario/fleuve Saint-Laurent

La volatilisation du mercure des surfaces vers l'atmosphère et les dépôts atmosphériques du mercure sont des phénomènes importants dans la dynamique globale du mercure. Les échanges surface-atmosphère du mercure gazeux dans l'écosystème lac Ontario/fleuve Saint-Laurent sont variables dans le temps et dans l'espace. Bien que le modèle de la double couche montre que la grande partie des écosystèmes aquatiques sont en sursaturation par rapport à la constante d'Henry, des observations in situ, à l'aide de techniques de chambre à flux, montrent que des dépôts gazeux sont également possibles. Les dépôts gazeux du mercure dans l'écosystème lac Ontario/fleuve Saint-Laurent oscillent entre 0 et 4,66 ng/m2/h alors que les valeurs de volatilisation varient entre 0 et 9,28 ng/m2/h. Globalement, la volatilisation médiane du mercure est de 0,77 ng/m2/h alors que le dépôt gazeux médian est d'environ un ordre de grandeur inférieur (0,075 ng/m2/h). En été, l'ensemble des dépôts atmosphériques du mercure semble être mis à contribution lors de la volatilisation du mercure au-dessus des sols. Il semble que la majeure partie de cette volatilisation serait en fait de la ré-émission du mercure vers l'atmosphère. En hiver, seule la portion gazeuse des dépôts de mercure semble être ré-émise vers l'atmosphère. Plusieurs observations dans un marécage fluvial du lac Saint-Pierre (baie Saint-François) montrent que les flux de volatilisation du mercure sont supérieurs en période sèche qu'en période inondée (0,83 vs. 0,52 ng/m2/h). Ainsi, en période d'inondation le mercure réactif disponible pour la volatilisation serait en compétition avec les mécanismes responsables pour la méthylation du mercure (bio-disponible) et/ou la formation du sulfure de mercure (inerte sous forme de cinabre). Cet article a pour objectifs de présenter et discuter les échanges surface-atmosphère du mercure gazeux dans l'écosystème lac Ontario/fleuve Saint-Laurent.This paper presents and discusses mercury surface-atmosphere gas exchange in Lake Ontario/St. Lawrence River ecosystem. Atmospheric sources are recognised to be significant in the cycling of global mercury. Being volatile in its elemental and dimethylated forms, mercury is distributed worldwide. The dominant form of mercury in the atmosphere is gaseous elemental mercury (Hg°) (~ 98%). Cycling of atmospheric mercury proceeds by gas exchange, particle settling or by rain scavenging. Wet and particle Hg deposition mainly involves the oxidised form, i.e. the Hg(II) species, which is relatively immobile. Chemical, photolytic or biological reduction to the elemental form can increase the mobility of mercury.Transport of mercury from bodies of water to the atmosphere (volatilisation) and atmospheric deposition are significant components for mercury budgets in lakes and rivers. The large majority of aquatic ecosystems studied so far have been found to contain dissolved gaseous mercury at concentrations that were supersaturated relative to the equilibrium values predicted by Henry's law. Evasion of elemental mercury was suggested to occur over the ocean and from inland waters but was only measured directly in a few cases. A few instances of net deposition were observed over inland waters. The dynamic aspect of mercury exchange has to be explored for a better understanding of mercury behaviour in the environment. Part of this understanding can be achieved by quantifying the rate of exchange or fluxes between compartments.Until recently, mercury fluxes were quantified by estimations using mathematical models or by measuring the mercury accumulation in biological, soil and sediment samples. It is only in the last few years that technical improvements have allowed a more or less direct measurement of mercury fluxes between air/soil and air/water compartments. One of these methods is the dynamic flux chamber, which is a simple and relatively reliable technique. Total Gaseous Mercury (TGM) analysis in this study was achieved with an automatic analyser (Tekranâ 2537A). Briefly, the analytical train of this instrument is based on amalgamation of mercury onto a pure gold surface followed by a thermo-desorption step and analysis by Cold Vapour Atomic Fluorescence Spectrophotometry (CVAFS) (l=253.7 nm). Dual cartridge designs allowed alternate sampling and desorption, resulting in continuous measurements of mercury in the air stream. Both modelling and dynamic flux chamber methods are reported in this paper. The former technique was applied along cruises on Lake Ontario and the Upper St. Lawrence River whereas the latter was applied at various stationary locations along the St. Lawrence River (e.g., pasture, water, wetlands and snow surfaces). The dynamic flux chamber used was built in our laboratory. The chamber consists of a hemispheric stainless steel bowl coated with Teflon®. The open area of the chamber is 0.13 m2 and its volume is 10 L. The flow rate into the chamber is 0.09 m3/h. The measurement of mercury in the inlet and outlet air sample ports is achieved by the mercury analyser. A peripheral device using a solenoid valve directs the sample to a specific cartridge of the analyser. Hence, the analyser does sequential measurement of the ports. The mercury gas exchange fluxes across the interfaces (surface-atmosphere) (ng/m2/h) are computed using the mass balance of mercury within the flux chamber.Mercury flux across the water surface was modelled using a two-layer model. The two-layer model is a convenient but not necessarily a mechanistically accurate model, which depends on empirical relationships reported for other chemicals. The model is based on the saturation of mercury within the layers with respect to Henry's law and the overall mass transfer coefficient (air and water). Since Henry's law for mercury is high, most of the resistance to gas exchange lies in the water film (> 99%). There are two main conditions required to apply the model: (1) the chemical does not undergo any reaction within the layers; and (2) the concentrations at the boundaries of the layers are kept constant long enough that the concentration profile reaches a steady state. The model was applied to estimate the mercury flux (ng/m2/h) during cruises on Lake Ontario and the St. Lawrence River. Mercury surface-atmosphere gas exchanges in Lake Ontario/St. Lawrence River ecosystem vary in space and time. Gaseous mercury deposition in Lake Ontario/St. Lawrence River ecosystem varied between 0 and 4.66 ng/m2/h whereas mercury evasion varied between 0 and 9.28 ng/m2/h. Overall, the median mercury evasion value is 0.77 ng/m2/h which is one order magnitude larger than median deposition (0.075 ng/m2/h). In summertime, total deposition flux over soil surface is counterbalanced by mercury re-emission flux. However, during wintertime, only dry deposition over snow surface is counterbalanced by volatilisation. Hence, mercury snow deposition during wintertime might have a huge impact on the ecosystem especially during the springtime through the influence of the melt water on aquatic biota. Many mercury gas exchange observations in fluvial wetlands in the Lake Saint-Pierre (baie Saint-François) suggested larger emissions over dry wetland than flooded wetland (0.83 vs. 0.52 ng/m2/h). Hence, flooded wetlands offered conditions that contributed to competition between mercury volatilisation and methyl mercury formation or immobilisation as mercury sulphide (cinnabar)

Impact de la variation du niveau d'eau d'un marais du lac Saint-Pierre (Québec, Canada) sur les concentrations et les flux d'hydrogène, monoxyde de carbone, méthane et dioxyde de carbone

Le but de la présente étude était d'étudier l'impact de la variation des niveaux d'eau d'un marais d'eau douce (Baie Saint-François, Québec) sur l'évolution des concentrations et des flux d'hydrogène, monoxyde de carbone, méthane et dioxyde de carbone. Une approche originale impliquant l'association d'un gradient de concentration de ces composés sur un profil vertical de 1,5 m au transfert de flux turbulent micrométéorologique fut utilisée pour la détermination des flux. L'étude démontre qu'une hausse du niveau d'eau d'un bassin versant alimentant une zone humide influence les flux de méthane, de monoxyde de carbone d'hydrogène et de dioxyde de carbone. En conditions submergées, le marais émettait du méthane et du monoxyde de carbone et consommait moins d'hydrogène troposphérique. Ainsi, cette étude démontre que des mesures in situ peuvent servir à inférer des scénarios d'impacts possibles des changements climatiques et des variations des niveaux d'eau sur les émissions des gaz à effets de serre dans l'écosystème du fleuve Saint-Laurent.Wetlands are known for their great biodiversity and the important carbon reservoir that they represent. Moreover, in the global warming context, these ecosystems represent net sources or sinks for different greenhouse gases depending of their conditions. For instance, flooded conditions favour methane production whereas they prevent hydrogen and carbon monoxide soil consumption. Baie Saint-François is a freshwater wetland that opens onto Lake Saint-Pierre (St. Lawrence River) where water levels are subject to important fluctuations due to natural processes and human activities (hydroelectricity and navigation). This study was done in order to assess the impact of the Lake Saint-Pierre water level variations on the tropospheric methane, carbon monoxide, hydrogen and carbon dioxide dynamics over the wetland. Knowledge of these dynamics should provide indications about the possible effects of the decreasing or increasing water level associated with the global warming on the production or consumption of these trace gases.Studies were carried out between June and August 2003 in Baie Saint-François where soil was subjected to successions of flooded and dry conditions. Water and carbon dioxide fluxes were obtained with a Bowen ratio micrometeorological station including a high frequency single infrared gas analyser. Hydrogen, carbon monoxide and methane fluxes were estimated with the modified Bowen method, their vertical concentration gradients (1.5 m) were measured over the plant canopy. The Bowen Ratio station was equipped with different probes to measure parameters such as net radiations, soil heat fluxes and vertical temperature gradients. The turbulent transfer coefficient (k) obtained every 20 min was assumed equal for heat, water vapour and trace gases. Hence, fluxes calculations were done by the multiplication of the turbulent transfer coefficients with the vertical concentration gradients of hydrogen, carbon monoxide and methane.The instrument used to detect hydrogen, carbon monoxide and methane was a RGA5. This analyser has two detectors: the reductive gas detector (RGD) for hydrogen and carbon monoxide and a flame ionisation detector (FID) for methane. The RGD contains an HgO bed wherein oxygen reacts with reductive gases resulting in Hg° releases detectable by differential UV absorbance. Chemicals were detected continuously in 10 min cycles with an analytical reproducibility of ±0.2, 0.3 and 2% for hydrogen, carbon monoxide and methane. Generally, vertical concentration gradients measured were greater than these limits. A calibration gas containing hydrogen, carbon monoxide and methane at 4940, 1000 and 1000 ppbv respectively in nitrogen was analysed daily to verify calibration. To ensure data integrity, linearity of the instrument was assayed by several dilutions of the standard gas and the integration of the curves gave a correction factor for hydrogen (18%) and carbon monoxide (13%). An intercomparison with NOAA (National Oceanic and Atmospheric Administration) was done to corroborate these correction factors.Background carbon monoxide, methane and carbon dioxide levels were in agreement with literature values. However, hydrogen was low, as observed by other investigators in summertime, since this season is related to minimal concentrations. Methane followed a diurnal cycle where maximum levels were observed during nighttime. In wet conditions, these nocturnal peaks reached occasionally 4000 ppbv and could be explained by specific production mechanisms and diurnal changes of vertical mixing in the boundary layer. Sensitivity of the processes responsible for methane and carbon monoxide cycling was seen between July 21st and 26th where a rain episode (total precipitation of 33.2 mm) increased their background concentrations. It seems that this precipitation was enough to favour methanogenesis and inhibit tropospheric CO and CH4 consumptions by a reduction of the diffusion of these chemicals into the soil.Our results demonstrated that four to eleven days following a variation of the Lake Saint-Pierre water level, a change in the tropospheric hydrogen, carbon monoxide and methane concentrations was observed. This lag might be explained by the distance between the lake and the research station (about 1.5 km) and the required time for the adaptation of soil microorganisms to the disruption of their environment. The concentration variations of these chemicals resulted from the inhibition of the processes responsible for their consumption or the activation of the processes accountable for their production.In June, the wetland was flooded and the CO2 median flux was -56.5 g m-2 d-1. Fluxes increased significantly (Mann-Whitney, α=0.01) in July to 5.30 g m-2 d-1, possibly due to dry conditions. Indeed, absence of water favours the activity of soil aerobic microorganisms which might produce more carbon dioxide than the quantity used by plants during photosynthesis.Methane was produced in June where the median flux was 54 mg m-2 d-1. These emissions were caused by the presence of water which maintained anaerobic conditions in the sediments, a suitable environment for methanogenic microorganisms. July was characterised by dry conditions, which generated aerobic environments in soils, an unfavourable microniche for methanogens. Therefore, methane median fluxes decreased significantly (Mann-Whitney, α=0.05) to 0.011 mg m-2 d-1 in July. In August, before the end of the investigation period, water levels had increased but methane fluxes were not significantly higher than in July. Moreover, in this period, methane concentrations tended to increase, showing that after an augmentation of the Lake Saint-Pierre water level, Baie Saint-François flooding area could represent a methane source.During summer 2003, Baie Saint-François acted as a net source of carbon monoxide. In June, the median flux was 21 µg m-2 d-1 due to presence of water which inhibited consumption by soil. Emissions were significantly (Mann-Whitney, α=0.05) lower in July (15 µg m-2 d-1) due to the absence of water, which represented a suitable environment for microorganisms consuming tropospheric carbon monoxide. In August, the median carbon monoxide flux attained 65 µg m-2 d-1 due to an increase of the Lake Saint-Pierre water level. Net carbon monoxide emissions observed in wet and dry conditions might be due to the high organic content in soil and water in addition to the presence of plants since all of these are subjected to photooxidation, generating this pollutant. Therefore, an increase of the Lake Saint-Pierre water level is associated with an augmentation of tropospheric carbon monoxide due to the inhibition of the processes responsible of its consumption.A decline in the water level might result in the activation of the soil microorganisms (or abiotic hydrogenases) able to consume tropospheric hydrogen. At the beginning of the campaign (June), the median hydrogen flux was weak (-1.37 g m-2 d-1) due to the presence of water. However, a net soil consumption was seen in July, where the median hydrogen flux decreased to -125 g m-2 d-1. The Lake Saint-Pierre water level increase observed in August was associated with a significant (Mann-Whitney, α=0.05) augmentation of the hydrogen median flux to 299 g m-2 d-1. Consequently, a rise in the Lake Saint-Pierre water levels induced an inhibition of the processes responsible of the tropospheric hydrogen consumption.This study illustrated that the water level fluctuations of the Lake Saint-Pierre have an impact on the H2, CO, CH4 and CO2 dynamics over the surrounding wetlands. When the Lake Saint-Pierre water level decreased, the wetlands acted as a carbon monoxide and carbon dioxide source, but as a consumer of tropospheric hydrogen and a minor source of methane

Evolutionary quantitative genetics of juvenile body size in a population of feral horses reveals sexually antagonistic selection

This is the author accepted manuscript. The final version is available from Springer via the DOI in this record.Inter-individual variation in juvenile body size can have important consequences for individual fitness, population dynamics, and adaptive evolution. In wild vertebrate populations, larger juvenile size is usually expected to be selected for. However, understanding how such selection may translate into adaptive evolution requires an understanding of the genetic underpinnings of early development and the factors modulating selection. In this study, we characterised the genetic basis of and selection pressures acting upon juvenile body size in a large insular population of feral horses on Sable Island, Canada, to gain insights into the evolution of juvenile body size in wild vertebrate populations. We used pedigree-based quantitative genetic ‘animal models’ to quantify the sources of phenotypic variation in withers-knee length, and assessed the influence of maternal age, sex, and temporal (birth year) and spatial environmental heterogeneity in modulating overwinter survival selection. We found that withers-knee length is moderately heritable and that there was a significant positive genetic correlation between males and females. There was no indication of directional selection in a pooled-sex analysis, but we did find evidence for significant sexually antagonistic selection, with a tendency for smaller body size to be favoured in males and larger body size to be favoured in females. These results suggest that juvenile body size has the potential to evolve in this population, and that selection on juvenile size may play an important role in modulating sex-specific contributions to population dynamics. However, our results also suggest that there is unlikely to be evolutionary change in the mean body size of Sable Island foals.Natural Sciences and Engineering Research Council of CanadaCanada Foundation for InnovationRoyal SocietyUniversity of Exete

Island tameness and the repeatability of flight initiation distance in a large herbivore

This is the author accepted manuscript. The final version is available from NRC Research Press via the DOI in this record.Antipredator behaviours can be lost relatively quickly in populations that are relieved of predation, as is known for several species inhabiting islands. Flight initiation distance (FID) is often studied in the context of island tameness; however, little is known about the factors that influence and maintain FID variation in predation-free populations. Here, we studied FID in foals of an isolated predator-free population of feral horses (Equus caballus L., 1758) on Sable Island, Canada, to determine if FID could be used for research on consistent individual differences in risk aversion and island tameness. In addition to testing for temporal, spatial, and sex effects on FID, we compared repeatability estimates at two temporal scales (within and among days). Similar FID for measurements obtained on the same day and for males and females indicated an absence of short-term desensitization and sex effects. In contrast, FID decreased for measurements made on subsequent days and from east to west, which could reflect habituation to human presence and (or) other temporal and spatial processes. Repeatability was high (0.42 ± 0.06), but tended to decrease with increasing time intervals. This study highlights the potential of FID for individual-based research on the ecology and evolutionary dynamics of risk aversion in predation-free populations.Funding was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC Discovery Grant No. 371535-2009 to P.D.M.), the Canada Foundation for Innovation (Leaders Opportunity Grant No. 25046 to P.D.M.), and a Royal Society International Exchange grant (J.P. and P.D.M.). D.A. was supported by an NSERC Ph.D. scholarship. D.C. received support from the University of Exeter M.Sc. program in Evolutionary and Behavioural Ecology. J.P. was supported by a Leverhulme Trust Early Career Research Fellowship

Synergizing expectation and execution for stroke communities of practice innovations

<p>Abstract</p> <p>Background</p> <p>Regional networks have been recognized as an interesting model to support interdisciplinary and inter-organizational interactions that lead to meaningful care improvements. Existing communities of practice within the a regional network, the Montreal Stroke Network (MSN) offers a compelling structure to better manage the exponential growth of knowledge and to support care providers to better manage the complex cases they must deal with in their practices. This research project proposes to examine internal and external factors that influence individual and organisational readiness to adopt national stroke best practices and to assess the impact of an e-collaborative platform in facilitating knowledge translation activities.</p> <p>Methods</p> <p>We will develop an e-collaborative platform that will include various social networking and collaborative tools. We propose to create online brainstorming sessions ('jams') around each best practice recommendation. Jam postings will be analysed to identify emergent themes. Syntheses of these analyses will be provided to members to help them identify priority areas for practice change. Discussions will be moderated by clinical leaders, whose role will be to accelerate crystallizing of ideas around 'how to' implement selected best practices. All clinicians (~200) involved in stroke care among the MSN will be asked to participate. Activities during face-to-face meetings and on the e-collaborative platform will be documented. Content analysis of all activities will be performed using an observation grid that will use as outcome indicators key elements of communities of practice and of the knowledge creation cycle developed by Nonaka. Semi-structured interviews will be conducted among users of the e-collaborative platform to collect information on variables of the knowledge-to-action framework. All participants will be asked to complete three questionnaires: the typology questionnaire, which classifies individuals into one of four mutually exclusive categories of information seeking; the e-health state of readiness, which covers ten domains of the readiness to change; and a community of practice evaluation survey.</p> <p>Summary</p> <p>This project is expected to enhance our understanding of collaborative work across disciplines and organisations in accelerating implementation of best practices along the continuum of care, and how e-technologies influence access, sharing, creation, and application of knowledge.</p

Estimation and Mapping of Wet and Dry Mercury Deposition Across Northeastern North America

Whereas many ecosystem characteristics and processes influence mercury accumulation in higher trophic-level organisms, the mercury flux from the atmosphere to a lake and its watershed is a likely factor in potential risk to biota. Atmospheric deposition clearly affects mercury accumulation in soils and lake sediments. Thus, knowledge of spatial patterns in atmospheric deposition may provide information for assessing the relative risk for ecosystems to exhibit excessive biotic mercury contamination. Atmospheric mercury concentrations in aerosol, vapor, and liquid phases from four observation networks were used to estimate regional surface concentration fields. Statistical models were developed to relate sparsely measured mercury vapor and aerosol concentrations to the more commonly measured mercury concentration in precipitation. High spatial resolution deposition velocities for different phases (precipitation, cloud droplets, aerosols, and reactive gaseous mercury (RGM)) were computed using inferential models. An empirical model was developed to estimate gaseous elemental mercury (GEM) deposition. Spatial patterns of estimated total mercury deposition were complex. Generally, deposition was higher in the southwest and lower in the northeast. Elevation, land cover, and proximity to urban areas modified the general pattern. The estimated net GEM and RGM fluxes were each greater than or equal to wet deposition in many areas. Mercury assimilation by plant foliage may provide a substantial input of methyl-mercury (MeHg) to ecosystems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44443/1/10646_2004_Article_6259.pd

Instant availability of patient records, but diminished availability of patient information: A multi-method study of GP's use of electronic patient records

<p>Abstract</p> <p>Background</p> <p>In spite of succesful adoption of electronic patient records (EPR) by Norwegian GPs, what constitutes the actual benefits and effects of the use of EPRs in the perspective of the GPs and patients has not been fully characterized. We wanted to study primary care physicians' use of electronic patient record (EPR) systems in terms of use of different EPR functions and the time spent on using the records, as well as the potential effects of EPR systems on the clinician-patient relationship.</p> <p>Methods</p> <p>A combined qualitative and quantitative study that uses data collected from focus groups, observations of primary care encounters and a questionnaire survey of a random sample of general practitioners to describe their use of EPR in primary care.</p> <p>Results</p> <p>The overall availability of individual patient records had improved, but the availability of the information within each EPR was not satisfactory. GPs' use of EPRs were efficient and comprehensive, but have resulted in transfer of administrative work from secretaries to physicians. We found no indications of disturbance of the clinician-patient relationship by use of computers in this study.</p> <p>Conclusion</p> <p>Although GPs are generally satisfied with their EPRs systems, there are still unmet needs and functionality to be covered. It is urgent to find methods that can make a better representation of information in large patient records as well as prevent EPRs from contributing to increased administrative workload of physicians.</p

Does electronic clinical microbiology results reporting influence medical decision making: a pre- and post-interview study of medical specialists

Background: Clinicians view the accuracy of test results and the turnaround time as the two most important service aspects of the clinical microbiology laboratory. Because of the time needed for the culturing of infectious agents, final hardcopy culture results will often be available too late to have a significant impact on early antimicrobial therapy decisions, vital in infectious disease management. The clinical microbiologist therefore reports to the clinician clinically relevant preliminary results at any moment during the diagnostic process, mostly by telephone. Telephone reporting is error prone, however. Electronic reporting of culture results instead of reporting on paper may shorten the turnaround time and may ensure correct communication of results. The purpose of this study was to assess the impact of the implementation of electronic reporting of final microbiology results on medical decision making. Methods. In a pre- and post-interview study using a semi-structured design we asked medical specialists in our hospital about their use and appreciation of clinical microbiology results reporting before and after the implementation of an electronic reporting system. Results: Electronic reporting was highly appreciated by all interviewed clinicians. Major advantages were reduction of hardcopy handling and the possibility to review results in relation to other patient data. Use and meaning of microbiology reports differ significantly between medical specialties. Most clinicians need preliminary results for therapy decisions quickly. Therefore, after the implementation of electronic reporting, telephone consultation between clinician and microbiologist remained the key means of communication. Conclusions: Overall, electronic reporting increased the workflow efficiency of the medical specialists, but did not have an impact on their decision-making