Two catchments amended with snow fences were paired with unaltered controls to investigate the influences of increased snow accumulation on the hydrology, soil thermal regime, and nutrient fluxes from High Arctic headwater catchments, representative of polar desert and mid-moisture vegetative classes at the Cape Bounty Arctic Watershed Observatory (CBAWO). The impact of augmented snow accumulation on the winter soil thermal regime was highly variable during the period studied. Soil temperatures were 8-9°C warmer beneath a drift 54 cm deep compared to ambient snow (10 cm) in the winter of 2006-2007, whereas soil temperatures were not significantly warmer beneath drifts (88 and 50 cm) compared to ambient snow (18 and 35 cm) in the winter of 2007-2008. Departures between air and ground surface temperatures suggest that snow accumulation was insufficient to insulate soils before February 2007-2008 due to late snow accumulation, compared to earlier snow accumulation in September in the winter of 2006-2007. The augmented snow accumulation did not significantly impact the timing of soil thaw in spring or active layer thickness at this site. Greater snow accumulation in the amended catchments altered runoff characteristics, including an extended duration of runoff by 30-80%, a delay in peak flow of ~5 days, and increased runoff ratios. Augmented snow accumulation, resulted in greater fluxes of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved inorganic carbon (DIC), nitrate (NO3-), ammonium (NH4+) and total inorganic solutes (TIS) in amended catchments relative to control sites. The seasonality of solute fluxes were also affected, with a greater proportion of inorganic solute fluxes occurring in the later portion of the runoff season compared to the controls. Snow accumulation was strong factor in determining total specific solute fluxes, with the magnitude of DOC and DON fluxes also strongly dependent on vegetative class. An active layer detachment that occurred in one of the amended catchments may have contributed to changes in nutrient fluxes, but the precise influence of the active layer detachment could not be differentiated from the combined impact of the disturbance and increased snow accumulation. / Thesis (Master, Geography) -- Queen's University, 2010-09-23 10:36:11.833

Abstract Knowledge of the thermal conditions in the lithosphere is based on theoretical models of heat transfer constrained by geological and geophysical data. The present dissertation focuses on the uncertainties of calculated temperature and heat flow density results and on how they depend on the uncertainties of thermal properties of rocks, as well as on the relevant boundary conditions. Due to the high number of involved variables of typical models, the random simulation technique was chosen as the applied tool in the analysis. Further, the random simulation technique was applied in inverse Monte Carlo solutions of geothermal models. In addition to modelling technique development, new measurements on thermal conductivity and diffusivity of middle and lower crustal rocks in elevated pressure and temperature were carried out. In the uncertainty analysis it was found that a temperature uncertainty of 50 K at the Moho level, which is at a 50 km's depth in the layered model, is produced by an uncertainty of only 0.5 W m-1 K-1 in thermal conductivity values or 0.2 orders of magnitude uncertainty in heat production rate (mW m-3). Similar uncertainties are obtained in Moho temperature, given that the lower boundary condition varies by ± 115 K in temperature (nominal value 1373 K) or ± 1.7 mW m-2 in mantle heat-flow density (nominal value 13.2 mW m-2). Temperature and pressure dependencies of thermal conductivity are minor in comparison to the previous effects. The inversion results indicated that the Monte Carlo technique is a powerful tool in geothermal modelling. When only surface heat-flow density data are used as a fitting object, temperatures at the depth of 200 km can be inverted with an uncertainty of 120 - 170 K. When petrological temperature-depth (pressure) data on kimberlite-hosted mantle xenoliths were used also as a fitting object, the uncertainty was reduced to 60 - 130 K. The inversion does not remove the ambiguity of the models completely, but it reduces significantly the uncertainty of the temperature results.

Groundwater is an important source of baseflow. Baseflow supports minimum flows and living area through dry periods, and moderates surface water temperature. The reductions in baseflow after urbanization can cause degradation of the stream ecosystem. The purpose of this study was to investigate the groundwater-surface water interaction and thermal regime of Clythe Creek, Guelph to illustrate the importance of groundwater/streamflow interaction in determining the health of a stream ecosystem. Piezometers were used to quantify vertical and lateral groundwater flow direction, and surface water temperature measurements were used to characterize and quantify the thermal regime. Groundwater-surface water interaction varied both temporally and spatially between the two geomorphic units. Average summer surface water temperatures were consistently cooler in the downstream portion of the study reach. The importance of groundwater-surface water interactions in supporting stream ecosystems was concluded from this study, and restoration strategies to address threats from urbanization were made. / Ontario Research Fund (ORF)

Ces travaux de thèse se focalisent sur la modélisation numérique de la réponse thermique des glaciers froids aux variations climatiques. La prise en compte du forçage climatique par la modification des conditions de surface des glaciers est l'un des points clefs de cette étude. On montre l'importance des processus de fusion/regel en zone d'accumulation froide ainsi que de l'épaisseur de la couverture de neige et névé autour de la ligne d'équilibre. Les modèles développés dans cette thèse s'appliquent à des cas concrets sur trois glaciers du massif du Mont Blanc (Alpes françaises). Ces études permettent d'analyser des situations à risque et de reconstituer le climat passé à haute altitude. Le jeu de données très complet acquis sur le site du Col du Dôme (4250 m) comprend des mesures profondes de températures et de densités ainsi que des mesures d'accumulation et de vitesses de surface. Il a permis de valider et développer un modèle à trois dimensions de régime thermique couplé à un modèle d'écoulement et forcé par des données climatiques. Ce modèle permet d'étudier en détail la réponse thermique des zones d'accumulation froides aux changements climatiques. Il peut aussi être utilisé pour la prédiction du réchauffement futur des glaciers suspendus présentant un risque comme le glacier de Taconnaz dont une analyse préliminaire est effectuée ici. Le réchauffement basal jusqu'au point de fusion pourrait conduire à la déstabilisation de ce type de glacier. Le site du glacier de Tête Rousse ( environ 3200 m) a permis d'établir clairement l'influence de la couverture de neige et de névé sur le régime thermique des glaciers autour de la ligne d'équilibre. Les résultats obtenus à partir du couplage d'un modèle de neige (CROCUS) avec un modèle de régime thermique sont en excellent accord avec les observations de températures réalisées dans le glacier. On explique ainsi les causes de la structure thermique particulière du glacier de Tête Rousse responsable de la formation d'une poche présentant un risque pour la commune à l'aval. Dans le futur, les simulations indiquent que le glacier va continuer de se refroidir, limitant ainsi le risque de formation de poche d'eau. Dans le dernier chapitre, nous avons développé une nouvelle méthode inverse pour reconstituer les températures du passé à partir de profils de températures observées dans la glace. Elle est basée sur l'inversion simultanée de plusieurs profils de températures provenant de différents sites de forage ayant subi le même forçage climatique. La méthode permet de s'affranchir de l'impact des processus de fonte/regel en surface pour reconstruire les variations passées des températures de l'air. Les résultats obtenus sur le Col du Dôme montrent que le réchauffement climatique sur le site à 4250 m est similaire à celui observé à basse altitude. Ces résultats tendent à montrer que le réchauffement climatique n'est pas amplifié avec l'altitude. / This thesis focuses on the numerical modeling of the thermal response of glaciers to climate changes. The change in surface conditions related to climate forcing is one of the key point of this study. We point out the crucial role of the meltwater refreezing in cold accumulation zone and the thickness of the snow and firn cover around the equilibrium line. The models are developed from the study of specific cases of three glaciers in Mont Blanc range ( French Alps). These studies allow us to analyze the risk related to hanging glaciers and to reconstruct the past temperaures at high altitude from observede nglacial temperatures. The very extensive dataset obtained at the site of the Col du Dôme (4250 m) includes measurements of deep temperatures and density profiles as well as measurements of snow accumulation and surface velocities. These observations allow us to develop and validate a three-dimensional thermal regime model coupled with a flow model and forced by meteorological data. This model is used to perform a thorough study of the thermal response of cold accumulation zone to climate change. It can also be used for the prediction of future glacial hazard related to hanging glaciers warming. A preliminary analysis has been carried out on the hanging glacier of Taconnaz. The warming could have a major impact on the stability of this kind of glaciers frozen to their beds if the melting point is reached. The study performed on Tête Rousse glacier (about 3200 m) shows clearly the influence of the snowpack and firn cover on the thermal regime of glaciers around the equilibrium line. The results obtained from coupling of a snow model (CROCUS) with a model of thermal regime reveal a very good agreement with the observed ice temperatures. This study provides insights into the thermal processes responsible for water storage inside a small almost static glacier, which can lead to catastrophic outburst floods. In the future, according to atmospheric temperature increase scenarios for the coming century, most of the glacier will become cold which will reduce the risk of water filled cavity formation. Finally, a new inverse method has been developed to reconstruct temperatures in the past from observed englacial temperatures. The method is based on the simultaneous inversion of several temperature profiles coming from different drilling sites with the same climate forcing. The method overcomes the impact of refreezing meltwater to reconstruct past air temperatures variations. This is similar to the observed regional low altitude trend. The results obtained on the Col du Dome shows that climate warming on the site at 4250 m is similar to the observed regional low altitude trend in the northwestern Alps, suggesting that air temperature trends are not altitude dependent.

Dans les industries de procédés, les opérations de pompage et de transformation sont fondamentales et omniprésentes. Durant ces opérations unitaires (incluant des transferts de chaleur, de matière et de quantités de mouvement), les produits évoluent (réactions chimiques et biochimiques, croissances microbiennes, traitements thermiques, etc.) induisant dans de nombreux cas des phénomènes d'encrassement avec des cinétiques et des intensités variables. Les recherches issues de l’INRA ont conduit à la mise au point d’un capteur d’encrassement basé sur une analyse thermique différentielle et locale. Ce dernier permet le contrôle en continu et en ligne du niveau d’encrassement d’un équipement et a été protégé par brevet. L’entreprise Neosens a acquis une licence d’exploitation exclusive sur ce brevet afin de développer et commercialiser le produit dont les limites sont maintenant connues.Dans ce travail, nous visons à atteindre deux objectifs majeurs en vue de répondre aux nouvelles problématiques posées. Le premier doit permettre la mise au jour d’un capteur d’encrassement en utilisant les technologies microsystèmes. Le second vise la validation d’un nouveau mode de fonctionnement et d’une méthode pour le contrôle de l’encrassement. Ce travail s'appuie naturellement sur les travaux antérieurs et les principales phases de recherche ont porté sur la conception, la réalisation et l'intégration d'éléments sensibles sur les bases technologiques des microsystèmes, l'intégration des régimes thermiques permanent et périodique associés au traitement en ligne du signal et à la validation expérimentale aux échelles laboratoire, pilote et industrielles des géométries et configurations nouvelles.Les travaux de recherche ont permis de fiabiliser et d’améliorer considérablement les performances métrologiques. Le microsystème réalisé apparaît comme complémentaire du capteur existant en termes de limites de détection et de quantification. / In industrial processes including agro and bioprocess, fouling is considered to be a complex and misunderstood phenomenon. Unit operations (including heat, mass and momentum transfers) are carried out in continuous, batch or fed-batch processes. During these operations, the products may evolve (chemical and biochemical reactions, microorganisms growth and activity, etc.) and fouling may occur with a wide range of kinetics from minutes up to years and dimensions from micrometers up to centimeters. Research issued from INRA led to develop a fouling sensor based on local differential thermal analysis and to patent this system. The device enables on-line and continuous monitoring of fouling propensity. Neosens company acquired an exclusive licence and develop and commercialize the sensor whose operating limits are known. In this work, our scientific and technological objectives are to break new locks through: (i) the realization of a fouling sensor based on microsystems technologies, (ii) the investigation and validation of an alternative thermal working mode and a method for fouling monitoring. Based on the previous work, our research deals with conception, realisation and integration of components based on microsystems technologies, integration of permanent and periodic thermal regimes with on-line data treatment and experimental validation at laboratory, pilot-plant and industrial scales for new geometries and configurations.This work led to metrology improvement and reliability. The resulting microsensor seems to be a complement of previous sensor regarding detection and quantification limits

This study has as main purpose to evaluate the influence of different color profiles on the cultivation related to temperature and dissolved oxygen concentration in the nutrient solution in the growing of rocket over two growing seasons in hydroponic system NFT. The experiment was conducted in the period of April to August 2012, in protected ambient counting with three production benches each comprised of eight profiles for the conduct of the plants evaluated, having four black and four white painted with plastic paint. The two colors of profile were arranged alternately and, to surround effect, a profile was installed on each edge of the bench. During the experiment, the temperature was recorded and the concentration of dissolved oxygen in the nutrient solution in the profiles three times per day, at 9:00, 15:00 and 21:00. In each reading recorded the temperature and concentration of oxygen at the beginning and end of two profiles of each color. For growth analysis, assessments were performed every four days in two growing seasons, autumn and winter, and the variables were evaluated: leaf dry matter, stem dry mass and root dry mass; plant height; root length; number of leaves and leaf area index. The results were analyzed separately and show that the different colors and profile stations modify the temperature and oxygen concentration of the nutrient solution. The black color profile increased the temperature of the circulating nutrient solution. Changes in temperature affected the concentration of dissolved oxygen in the nutrient solution. The different colors and seasons interfered with the growth of rocket. Plants grown in white profile showed higher leaf dry matter, stem dry mass and root dry mass, as well as increased root length and increased leaf area index. / O trabalho teve como objetivo avaliar a influência de diferentes cores de perfis de cultivo sobre a temperatura e concentração de oxigênio dissolvido na solução nutritiva no cultivo de rúcula ao longo de duas estações de cultivo em sistema hidropônico NFT. O experimento foi realizado no período de abril a agosto de 2012, em ambiente protegido contando com três bancadas de produção cada qual composta por oito perfis para a condução das plantas avaliadas sendo, quatro de cor preta e quatro pintados com tinta plástica branca. As duas cores de perfil foram dispostas alternadamente e, para efeito de bordadura foi instalado um perfil em cada borda da bancada. Durante a condução do experimento, foi registrada a temperatura e concentração de oxigênio dissolvido na solução nutritiva nos perfis três vezes por dia, sendo às 9:00h, 15:00h e 21:00h. Em cada leitura registrava-se a temperatura e concentração de oxigênio no início e final de dois perfis de cada cor. Para a análise de crescimento, as avaliações foram realizadas a cada quatro dias em duas estações de cultivo, outono e inverno, e as variáveis avaliadas foram: massa de folha seca, massa de caule seco e massa de raiz seca; altura de planta; comprimento de raiz; número de folhas e índice de área foliar. Os resultados obtidos foram analisados separadamente e demonstram que as diferentes cores de perfil e estações do ano modificaram a temperatura e concentração de oxigênio da solução nutritiva. A cor preta do perfil aumentou temperatura da solução nutritiva circulante. Mudanças na temperatura influenciaram na concentração de oxigênio dissolvido na solução nutritiva. As diferentes cores de perfil e estações do ano interferiram no crescimento da rúcula. As plantas cultivadas no perfil branco apresentaram maior massa de folha seca, massa de caule seco e massa de raiz seca, bem como maior comprimento de raiz e maior índice de área foliar.

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2018-08-24T19:38:47Z No. of bitstreams: 1 2016 - Daniela Augusto Chaves.pdf: 7459629 bytes, checksum: db78e044349231645bd60b6c5fb4c66e (MD5) / Made available in DSpace on 2018-08-24T19:38:47Z (GMT). No. of bitstreams: 1 2016 - Daniela Augusto Chaves.pdf: 7459629 bytes, checksum: db78e044349231645bd60b6c5fb4c66e (MD5) Previous issue date: 2016-02-25 / CAPES / The monitoring of soil thermal regime in periglacial environment is critical to identify the presence of permafrost and the thickness of the active layer. This study was conducted to identify factors that influence the soil thermal regime in Keller Peninsula, from 02/2011 to 02/2015. For such monitoring were installed air temperature sensors (Tar) and soil (Ts) and soil moisture at different depths and sites in Keller Peninsula. Preliminary analyzes of the data were based on the monthly average, annual; maximum and minimum averages and seasonal averages of Tar; Ts and soil moisture at different depths in the monitoring sites Ipanema Ref?gio II, Punta and site soil with Standard. After these analyzes identified the days of freezing, thawing, isothermal and freezing / thawing for each depth; the frequency distribution of temperature and temperature fluctuation during the period studied. The analyzes were carried out: the cross-correlation between the AAO series (Antarctic Oscillation Index), SOI (Southern Oscillation Index), Tar and Ts; linar simple regression between the annual average temperatures and the highest average maximum and annual minimum; Multiple linear regression between moisture apparent soil thermal difuvividade (DTA); N_fator the rate of freezing and its relationship with DTA and; the harmonic analysis of the AAO series, SOI, MEI (multivariate ENSO index), Tar and Ts. The highest and lowest Tar annual average in the four years and four sites studied was 1.7 ?C on site Ref?gio II and 4.8 ?C in place with Standard Solo, respectively. The period in which the soil has more time under the active layer system was Ipanema and Ref?gio II. The highest and the lowest sum of degree days of thawing and freezing were 154.6 and 263.3, respectively Ref?gio II In cross-correlation analysis the delay phase between the waves of Tar and Ts was less than one month in all sites. The correlation between the AAO x Tar Tar and SOI x occurs up to 5 months delay between the phases. Simple linear regression analysis indicated that in Ipanema and Ref?gio II, the soil thermal regime restricted the active layer. On site soil with Standard and Punta Plaza thermal regime presented reached the permafrost before the layer of 0.80 and 1.00 m deep respectively. In the frequency histograms showed predominance of temperatures around 0 ?C and the first difference graph shown that temperature variations are stronger in summer. Multiple linear regrass?o analysis showed that the moisture influence on the DTA in most cases. The freezing N_fator was inversely proportional to close DTA the surface, but when compared with the DTA in depth the relationship approaches. The harmonic analysis identified that climate variability in ways that influenced the Tar these sites between the years 2011-2014, were the AAO and SOI indices. In general, the thermal insulation provided by covering the thickest snow in places Punta Plaza and Solo with Standard allowed the permafrost were found at depths less when compared to the Ref?gio II and Ipanema sites that were less thick blanket of snow. / O monitoramento do regime t?rmico do solo em ambiente periglacial ? fundamental para identificar a presen?a do permafrost e a espessura da camada ativa. Este estudo foi realizado para identificar os fatores que influenciam no regime t?rmico do solo na Pen?nsula Keller, entre 02/2011 a 02/2015. Para tal monitoramento foram instalados sensores de temperatura do ar (Tar) e do solo (Ts) e umidade do solo em diferentes profundidades e s?tios na Pen?nsula de Keller. As an?lises preliminares dos dados foram realizadas com base nas m?dias mensais, anuais; m?dias m?ximas e m?nimas e m?dias sazonais de Tar, Ts e umidade do solo em diferentes profundidades nos s?tios de monitoramento Ipanema, Ref?gio II, Punta e s?tio Solo com Padr?o. Ap?s essas an?lises foram identificados os dias de congelamento, descongelamento, isot?rmicos e congelamento/descongelamento para cada profundidade; as frequ?ncias de distribui??o das temperaturas e oscila??o de temperatura durante o per?odo estudado. As an?lises realizadas foram: a de correla??o cruzada entre as s?ries de AAO (Antarctic Oscillation Index), SOI (Southern Oscillation Index), Tar e Ts; a regress?o linar simples entre as temperaturas m?dias anuais e a maior m?dia m?xima e m?nima anuais; a regress?o linear m?ltipla entre umidade a difuvividade t?rmica aparente do solo (DTA); o ?ndice N_fator de congelamento e sua rela??o com a DTA e; a an?lise harm?nica das s?ries AAO, SOI, MEI (multivariate ENSO index), Tar e Ts. A maior e a menor Tar m?dia anual nos quatro anos e nos quatro s?tios estudados foi de -1,7 ?C no s?tio Ref?gio II e de ?4,8 ?C no s?tio Solo com Padr?o, respectivamente. O per?odo em que o solo apresentou mais tempo sob o regime de camada ativa foi Ipanema e Ref?gio II. A maior e a menor soma de graus dias de descongelamento e congelamento foram de 154,6 e ?263,3, respectivamente em Ref?gio II. Na an?lise de correla??o cruzada o atraso de fases entre as ondas de Tar e Ts foi inferior a um m?s em todos os s?tios. A correla??o entre a AAO x Tar e SOI x Tar ocorre com at? cinco meses de atraso entre as fases. A an?lise de regress?o linear simples indicou que, em Ipanema e em Ref?gio II, o regime t?rmico do solo se restringe a camada ativa. No s?tio Solo com Padr?o e Punta Plaza o regime t?rmico apresentado alcan?ou o permafrost antes da camada de 0,80 e 1,00 m de profundidade respectivamente. Os histogramas de frequ?ncia apresentaram predomin?ncia de temperaturas em torno de 0 ?C e o gr?fico de primeira diferen?a mostrou que as varia??es da temperatura foram mais fortes no ver?o. A an?lise de regrass?o linear m?ltipla mostrou que a umidade influencia na DTA na maior parte dos casos. O N_fator de congelamento foi inversamente proporcional a DTA pr?xima a superf?cie, por?m quando o compara com a DTA em profundidade essa rela??o se aproxima. A an?lise harm?nica permitiu identificar que os modos de variabilidade clim?tica que influenciaram a Tar nesses s?tios, entre os anos de 2011 a 2014, foram os ?ndices AAO e SOI. De maneira geral, o isolamento t?rmico proporcionado por cobertura da neve mais espessa nos s?tios Punta Plaza e Solo com Padr?o, permitiu que o permafrost fosse encontrado a profundidades menores quando comparado com os s?tios Ref?gio II e Ipanema, que obtiveram cobertura da neve menos espessa.

Les poissons vivant au sein d’une rivière sont soumis à des variations circadiennes de température pouvant influencer la croissance, la digestion et le métabolisme standard. Les modèles bioénergétiques utilisant les fonctions métaboliques pour déterminer la croissance d’un poisson ont souvent été élaborés avec des poissons acclimatés à des températures constantes. Ces modèles pourraient sous-estimer l’énergie dépensée par un poisson soumis à des températures fluctuantes. En utilisant la respirométrie par débit intermittent, les objectifs de ce travail étaient : (1) de quantifier les différences entre les taux métaboliques standards de poissons acclimatés à une température constante (20.2 oC ± 0.5 oC) et à des fluctuations circadiennes de température (19.8 oC ± 2.0 oC; 19.5 oC ± 3.0 oC) et (2) comparer deux méthodologies pour calculer les taux métaboliques standards de poissons sujets aux fluctuations circadiennes de températures : respirométrie (a) en température constante ou (b) en température fluctuante. Les poissons acclimatés à des fluctuations circadiennes de température ont des taux métaboliques standards plus élevés que des poissons acclimatés à une température constante. À 20.2 oC ± 0.5 oC, les taux métabolique standards ont été de 25% à 32% plus bas pour des poissons maintenus à une température constante que pour des poissons gardés sous des fluctuations circadiennes de température. Les méthodologies utilisées pour estimer les taux métaboliques standards de poissons sujets aux fluctuations de température offrent des résultats similaires. / Fish that inhabits river are subjected to circadian fluctuations in water temperature. These fluctuations can influence growth, digestion and metabolic processes. Bioenergetic models are traditionally modeled using data recorded from fish kept at constant water temperatures. These models could underestimate the energy spent by fish subjected to fluctuating temperatures. Thus, with intermittent-flow respirometry, the objectives of this study were to: (1) quantify the differences between standard metabolic rates of fish acclimatized to a constant temperature (20.2 oC ± 0.5 oC) and two circadian fluctuating temperatures (19.8 oC ± 2.0 oC; 19.5 oC ± 3.0 oC) and (2) compare two methodology for calculate standard metabolic rates of fish subjected to circadian fluctuating temperatures: intermittent-flow respirometry with (a) constant temperature or (b) fluctuating temperatures. Fish held at circadian fluctuating temperatures have higher standard metabolic rates than fish acclimatized to a constant temperature. At 20.2 oC ± 0.5 oC, standard metabolic rates was 25% to 32% lower for fish held at constant temperature than for fish held under circadian fluctuations. However, results of the two different strategies used to calculate standard metabolic rates of fish subjected to circadian fluctuating temperatures did not differ.

Les poissons vivant au sein d’une rivière sont soumis à des variations circadiennes de température pouvant influencer la croissance, la digestion et le métabolisme standard. Les modèles bioénergétiques utilisant les fonctions métaboliques pour déterminer la croissance d’un poisson ont souvent été élaborés avec des poissons acclimatés à des températures constantes. Ces modèles pourraient sous-estimer l’énergie dépensée par un poisson soumis à des températures fluctuantes. En utilisant la respirométrie par débit intermittent, les objectifs de ce travail étaient : (1) de quantifier les différences entre les taux métaboliques standards de poissons acclimatés à une température constante (20.2 oC ± 0.5 oC) et à des fluctuations circadiennes de température (19.8 oC ± 2.0 oC; 19.5 oC ± 3.0 oC) et (2) comparer deux méthodologies pour calculer les taux métaboliques standards de poissons sujets aux fluctuations circadiennes de températures : respirométrie (a) en température constante ou (b) en température fluctuante. Les poissons acclimatés à des fluctuations circadiennes de température ont des taux métaboliques standards plus élevés que des poissons acclimatés à une température constante. À 20.2 oC ± 0.5 oC, les taux métabolique standards ont été de 25% à 32% plus bas pour des poissons maintenus à une température constante que pour des poissons gardés sous des fluctuations circadiennes de température. Les méthodologies utilisées pour estimer les taux métaboliques standards de poissons sujets aux fluctuations de température offrent des résultats similaires. / Fish that inhabits river are subjected to circadian fluctuations in water temperature. These fluctuations can influence growth, digestion and metabolic processes. Bioenergetic models are traditionally modeled using data recorded from fish kept at constant water temperatures. These models could underestimate the energy spent by fish subjected to fluctuating temperatures. Thus, with intermittent-flow respirometry, the objectives of this study were to: (1) quantify the differences between standard metabolic rates of fish acclimatized to a constant temperature (20.2 oC ± 0.5 oC) and two circadian fluctuating temperatures (19.8 oC ± 2.0 oC; 19.5 oC ± 3.0 oC) and (2) compare two methodology for calculate standard metabolic rates of fish subjected to circadian fluctuating temperatures: intermittent-flow respirometry with (a) constant temperature or (b) fluctuating temperatures. Fish held at circadian fluctuating temperatures have higher standard metabolic rates than fish acclimatized to a constant temperature. At 20.2 oC ± 0.5 oC, standard metabolic rates was 25% to 32% lower for fish held at constant temperature than for fish held under circadian fluctuations. However, results of the two different strategies used to calculate standard metabolic rates of fish subjected to circadian fluctuating temperatures did not differ.

En général, le métabolisme des poissons est estimé à des valeurs de température constantes, mais les effets de fluctuations journalières de température similaires à celles retrouvées en milieu naturel semblent peu connus. Les objectifs du présent mémoire sont de quantifier les effets de la température moyenne d’acclimatation et d’évaluer les effets de l’historique thermique des individus, sur les réponses métaboliques de tacons de saumon Atlantique (Salmo salar) aux fluctuations journalières de la température. Des tacons provenant de deux rivières, une fraîche et une chaude, ont été acclimatés à un maximum de quatre régimes thermiques (constant 15 °C ou 20 °C, fluctuant 15 °C ± 2.5 °C ou 20 °C ± 2.5 °C) et leur taux métabolique standard estimés par respirométrie par débit-intermittent. Les fluctuations journalières de température (15 °C ± 2.5 °C) près de l’optimum thermique pour cette espèce (16 °C) n’affectent pas le taux métabolique standard. À l’opposé, les fluctuations journalières de température plus chaudes (20 °C ± 2.5 °C) augmentent de 35.4% le taux métabolique standard des tacons de la rivière plus chaude, mais pas ceux des poissons de la rivière fraîche. Ainsi, la température moyenne à laquelle sont acclimatés les poissons peut affecter leur réponse métabolique aux fluctuations journalières de température, mais cette réponse peut varier entre populations provenant de rivières présentant des régimes thermiques différents. Enfin, grâce aux données de métabolisme précédemment estimées, un modèle de métabolisme standard a été développé pour des tacons de saumon Atlantique soumis à des fluctuations journalières de température. / Usually, fish metabolism is evaluated under constant values of temperature, but the effects of daily temperature fluctuations similar to those found in natural environment on metabolism seems to be much less understood. The goals of this study are to quantify the effects of the mean acclimation temperature and to assess the effects of the thermal history on the metabolic response of Atlantic salmon (Salmo salar) parr to daily fluctuations of water temperature. Atlantic salmon parr originating from two rivers, one cool and one relatively warm, were acclimated to up to four thermal regimes (constant 15 °C or 20 °C, daily fluctuating 15 °C ± 2.5 °C or 20 °C ± 2.5 °C) and their standard metabolic rate was estimated using intermittent-flow respirometry. Daily temperature fluctuations (15 °C ± 2.5 °C) near this species’ thermal optimum (16 °C) do not influence standard metabolic rate. In contrast, daily fluctuations of higher temperature (20 °C ± 2.5 °C) do increase standard metabolic rate by 35.4% for fish from the warmer river, but not for fish from the cooler river. Therefore, the mean temperature to which fish are acclimated may affect their responses to daily fluctuations of water temperature, but this response may vary between populations originating from rivers having different thermal regimes. Using standard metabolic rates previously estimated, a standard metabolic rate model was developed for Atlantic salmon parr exposed to daily fluctuations of temperature.