Cycle des nutriments dans les mares d’une tourbière ombrotrophe du sud du Québec

Les mares sont abondantes dans les tourbières nordiques mais aucune recherche ne s’est penchée spécifiquement sur les cycles des nutriments dans ces environnements. Ce mémoire vise donc à comprendre les cycles de l’azote (N), du phosphore (P) et du carbone (C) dans les mares d’une tourbière ombrotrophe du sud du Québec, et à déterminer quels facteurs environnementaux contrôlent ces cycles. Pour ce faire, les relations entre la chimie des mares et leurs caractéristiques physiques et biologiques ont été étudiées. Les caractéristiques des mares expliquaient 28.2% de la variation dans la chimie de l’eau entre les mares. De cette variation, 81.9% et 14.8% étaient expliqués respectivement par la profondeur et le type de végétation entourant les mares. Les mares les moins profondes présentaient des concentrations en C et en N beaucoup plus élevées que les mares les plus profondes. Le C organique des mares où la végétation était dominée par des conifères était en outre plus récalcitrant à la décomposition que celui des mares où la végétation était composée majoritairement de mousses. L’influence de la profondeur a été confirmée par un suivi saisonnier de mares de tailles différentes. Au cours de la saison de croissance 2016, la biogéochimie des mares de faible profondeur et des mares les plus profondes a évolué de façon significativement différente. Les concentrations en P étaient minimes dans toutes les mares et tout au long de l’été, confirmant l’aspect limitatif de cet élément dans ces environnements. Mes travaux ont démontré que la chimie d’une tourbière ombrotrophe n’est pas seulement dictée par les intrants atmosphériques, mais aussi par des processus biogéochimiques internes. Cette étude a donc permis de mettre en lumière la complexité de ces environnements.Open-water pools are common features in northern peatlands but their nutrient biogeochemistry has seldom been studied. The goal of this thesis is to understand the nitrogen (N), phosphorus (P) and carbon (C) cycles in pools of an ombrotrophic peatland located in southern Québec and to determine the environmental factors controlling such cycles. The relationship between pool water chemistry and their physical and biological characteristics were studied. Pool characteristics significantly explained 28.2% of the variation in water chemistry. Of this, 81.9% and 14.8% were respectively explained by pool depth and the dominant vegetation type surrounding the pools. Shallow pools had higher C and N concentrations than deep pools. Organic C (OC) from pools where vegetation was dominated by coniferous trees was also more recalcitrant to decomposition than OC from pools where vegetation was mainly composed of mosses. The influence of depth on pool biogeochemistry was confirmed by a seasonal survey of pools of different sizes. Over the course of the 2016 growing season, nutrient biogeochemistry from shallow and deep pools significantly evolved differently. All summer long, P concentrations were low in all pools, indicating that ombrotrophic peatland pools are P-limited. My work has shown that water chemistry in a rain-fed peatland is not only determined by atmospheric inputs, but also by internal biogeochemical processes. This study highlights the complexity of these environments

La géographie et la biogéochimie des mares de tourbières tempérées : patrons et processus à l’interface eau-tourbe

Les écosystèmes aquatiques sont de plus en plus reconnus pour leur rôle dans les cycles biogéochimiques locaux et globaux en raison de leur grand potentiel réactif. Les tourbières sont quant à elles des environnements relativement stables, mais qui participent aussi largement aux cycles biogéochimiques car elles accumulent de grandes quantités de carbone (C) et d’autres éléments dans leurs sols. À l’intérieur de certaines tourbières tempérées, de petites étendues d’eau se développent par la décomposition de la matière organique qui compose leur matrice, mais de larges pans de leur fonctionnement biogéochimique sont ignorés. La structure et la géographie de ces mares de tourbières, particulièrement l’interface eau-tourbe qui les caractérise, pourraient d’ailleurs en faire des écosystèmes d’un dynamisme peu commun. Le but de cette thèse est de déterminer en quoi la géographie particulière des mares de tourbières, à commencer par celle des régions tempérées, influence leurs patrons et processus biogéochimiques. Les résultats démontrent que les mares de tourbières sont des écosystèmes sans commune mesure parmi les milieux aquatiques. Les mares sont biogéochimiquement distinctes des autres milieux lentiques en raison de la structure du paysage qui les entoure, faisant d’elles des environnements où les concentrations en C organique dissous (DOC) sont plusieurs fois plus élevées et où le pH est 100 fois plus acide que dans les lacs. La biogéochimie des mares est par contre variable dans le temps et l’espace en fonction de paramètres morphologiques et climatiques. Par exemple, les concentrations en DOC sont plus élevées dans les mares les moins profondes et sous un climat moins humide, mais ces concentrations fluctuent rapidement au cours des saisons en fonction de variations météorologiques, faisant d’elles des sentinelles climatiques. Les patrons biogéochimiques observés dans les mares de tourbières semblent tirer leur origine de leur structure plutôt que d’une influence allochtone à plus grande échelle comme c’est le cas pour la plupart des lacs. Une expérience menée dans une tourbière ombrotrophe du sud du Québec montre ainsi que les processus de décomposition de la matière organique qui caractérisent les mares de tourbières varient spatialement en fonction de la profondeur des mares et de la composition chimique du matériel à décomposer. Au final, les résultats de la thèse démontrent que les patrons et processus biogéochimiques observés dans les mares de tourbières tempérées sont effectivement dirigés par leur géographie particulière, où les mécanismes fonctionnels sont en partie dictés par l’interface eau-tourbe.Aquatic ecosystems are increasingly recognized for their contribution to local and global biogeochemical cycles because of their high reactivity potential. Peatlands are relatively stable ecosystems but that nonetheless play a large role in biogeochemical cycles because they sequester large amounts of carbon (C) and other elements. Within temperate peatlands, waterbodies may develop by the decomposition of the organic matter that forms the soil but their biogeochemical functioning remain largely ignored. Their structure and their geography, especially the water-peat interface, may thus make peatland pools ecosystems that are more dynamic than other aquatic environments. The goal of this thesis is to determine how the geography of temperate peatland pools influences their biogeochemical patterns and processes. Results show that peatland pools are biogeochemically distinct from other aquatic environments because of the structure of the landscape in which they develop, with dissolved organic C (DOC) concentrations being severalfold higher and pH being 100-fold more acidic than lakes. The biogeochemistry of peatland pools is, however, variable in both space and time in relation to morphological and climatic parameters. For example, DOC concentrations are higher in shallower pools and in arid climates, but these concentrations rapidly vary within and across seasons in relation to changes in temperatures and precipitation, highlighting their potential to act as climate sentinel. The observed biogeochemical patterns in peatland pools originate from their internal structure rather than from a broader-scale allochthonous influence like lakes. The influence of pool internal structure was revealed in an experiment we conducted in an ombrotrophic peatland of southern Québec that showed that organic matter decomposition processes vary spatially in relation to pool depth and to the chemical composition of the organic matter. Overall, the results demonstrate that temperate peatland pool biogeochemical patterns and processes are indeed controlled by their unique geography, and where functional mechanisms are partly driven by the water-peat interface

DHA Improves Cognition and Prevents Dysfunction of Entorhinal Cortex Neurons in 3xTg-AD Mice

Defects in neuronal activity of the entorhinal cortex (EC) are suspected to underlie the symptoms of Alzheimer's disease (AD). Whereas neuroprotective effects of docosahexaenoic acid (DHA) have been described, the effects of DHA on the physiology of EC neurons remain unexplored in animal models of AD. Here, we show that DHA consumption improved object recognition (↑12%), preventing deficits observed in old 3xTg-AD mice (↓12%). Moreover, 3xTg-AD mice displayed seizure-like akinetic episodes, not detected in NonTg littermates and partly prevented by DHA (↓50%). Patch-clamp recording revealed that 3xTg-AD EC neurons displayed (i) loss of cell capacitance (CC), suggesting reduced membrane surface area; (ii) increase of firing rate versus injected current (F-I) curve associated with modified action potentials, and (iii) overactivation of glutamatergic synapses, without changes in synaptophysin levels. DHA consumption increased CC (↑12%) and decreased F-I slopes (↓21%), thereby preventing the opposite alterations observed in 3xTg-AD mice. Our results indicate that cognitive performance and basic physiology of EC neurons depend on DHA intake in a mouse model of AD

Spatial and temporal variability in summertime dissolved carbon dioxide and methane in temperate ponds and shallow lakes

Small waterbodies have potentially high greenhouse gas emissions relative to their small footprint on the landscape, although there is high uncertainty in model estimates. Scaling their carbon dioxide (CO2) and methane (CH4) exchange with the atmosphere remains challenging due to an incomplete understanding and characterization of spatial and temporal variability in CO2 and CH4. Here, we measured partial pressures of CO2 (pCO2) and CH4 (pCH4) across 30 ponds and shallow lakes during summer in temperate regions of Europe and North America. We sampled each waterbody in three locations at three times during the growing season, and tested which physical, chemical, and biological characteristics related to the means and variability of pCO2 and pCH4 in space and time. Summer means of pCO2 and pCH4 were inversely related to waterbody size and positively related to floating vegetative cover; pCO2 was also positively related to dissolved phosphorus. Temporal variability in partial pressure in both gases weas greater than spatial variability. Although sampling on a single date was likely to misestimate mean seasonal pCO2 by up to 26%, mean seasonal pCH4 could be misestimated by up to 64.5%. Shallower systems displayed the most temporal variability in pCH4 and waterbodies with more vegetation cover had lower temporal variability. Inland waters remain one of the most uncertain components of the global carbon budget; understanding spatial and temporal variability will ultimately help us to constrain our estimates and inform research priorities

N-3 polyunsaturated fatty acid and neuroinflammation in aging and Alzheimer's disease

The innate immune system of the brain is mainly composed of microglial cells, which play a key role in the maintenance of synapses and the protection of neurons against noxious agents or lesions owing to their phagocytic activity. In the healthy brain, microglia are highly motile and strongly interact with neurons either by physical contact, induction of oxidative stress or through specific mediators, such as chemokines and cytokines. In response to inflammatory insult however, microglial cells get activated and produce inflammatory cytokines. The action of cytokines on specific receptors expressed in the brain triggers the development of sickness behavior and altered cognitive and emotional processes. The effects are acute and reversible as normal behavior is restored once the synthesis of inflammatory brain cytokines returns to baseline after a few hours. However, in pathological situations, these cytokines may reach toxic levels and have irreversible consequences such as neuronal death, as observed in neurodegenerative disorders such as Alzheimer’s disease. Omega-3 (n-3) polyunsaturated fatty acids (PUFAs) are essential nutrients and fundamental components of neuronal and glial cell membranes. They accumulate in the brain during the perinatal period in a dietary supply-dependent fashion. Their brain levels may diminish with age, but can be increased by diets enriched in n-3 PUFAs. Changes in the immune profile have been associated with n-3 PUFAs intake in humans and animal models. Therefore, the increasing exposure of the population to diets low in n-3 PUFAs could contribute to the deleterious effects of the chronic activation of microglia in the brain

The environmental footprint of academic and student mobility in a large research-oriented university

Academic mobility for field work, research dissemination and global outreach is increasingly recognized as an important contributor to the overall environmental footprint of research institutions. Student mobility, while less studied, also contributes to universities’ environmental footprint. Université de Montréal (UdeM) is the largest university in Montréal, Canada. It has a research budget of 450M$, employs 1426 full-time professors, and has a total student population of 33 125 undergraduate and 12 505 graduate students. To assess the footprint of academic mobility at UdeM, we surveyed the research community ( n  = 703; including professors, research professionals and graduate students) about their travel habits. We also measured the contribution from travel undertaken by sports teams and international students as well as students engaged in study abroad and internships programs using data provided by the university. While the average distance travelled for work and research purposes by the UdeM community is around 8525 km/person, professors travel more than 33 000 km/person per year. We also estimated that the 5785 international students or students enroled in study abroad programs travel annually around 12 600 km/person. UdeM’s per capita annual travel-related C and N footprints vary, with international students generating for example 3.85 T CO _2 and 0.53 kg N while professors generate 10.76 T CO _2 and 2.19 kg N. Air travel emissions are the main contributors to these footprints. We provide insights into the distribution of travel-related environmental footprint within the university, the main reasons for travelling, the most frequent destinations, and the factors preventing researchers from reducing their travel-related environmental impact

Interactions et trajectoires d’insertion des immigrants dans les régions du Québec

Au printemps 2019, l’Équipe de recherche en partenariat sur la diversité culturelle et l’immigration dans la région de Québec (ÉDIQ) a tenu un colloque lors du 87e congrès de l’ACFAS, intitulé « Interactions et trajectoires d’insertion dans les régions du Québec : stratégies des immigrants et des institutions ». Regrouper dans ce colloque des acteurs issus des milieux de pratique (santé et services sociaux, emploi et éducation) et des chercheurs nous a permis d’engager un dialogue entre les savoirs des praticiens et ceux issus de divers horizons universitaires (travail social, géographie, psychologie, relations industrielles, ethnologie, sages-femmes), permettant du même coup l’émergence d’un regard transversal et multidisciplinaire sur des enjeux complexes. À cet égard, la mise en relation des stratégies élaborées par les institutions et les structures locales d’accueil des nouveaux arrivants avec celles déployées par ces derniers cherchait à favoriser l’élaboration de recommandations en matière de politiques sociales, de pratiques d’intervention et de services, en adéquation avec les besoins spécifiques et changeants de la population. Ce numéro se compose de six articles issus des présentations offertes lors du colloque

Biogeochemical Distinctiveness of Peatland Ponds, Thermokarst Waterbodies, and Lakes

Small lentic freshwater ecosystems play a disproportionate role in global biogeochemical cycles by processing large amounts of carbon (C), nitrogen (N), and phosphorus (P), but it is unlikely that they behave as one homogenous group for the purpose of extrapolation. Here, we synthesize biogeochemical data from >12,000 geographically distinct freshwater systems: lakes, peatland ponds, and thermokarst waterbodies. We show that peatland ponds are biogeochemically distinct from the more widely studied lake systems, while thermokarst waterbodies share characteristics with peatland ponds, lakes, or both. For any given size or depth, peatland ponds tend to have dissolved organic carbon concentrations several-fold higher and are 100-fold more acidic than lakes because of the organic matter-rich settings in which they develop. The biogeochemical distinctiveness of freshwater ecosystems highlights the need to account for the fundamental differences in sources and processing of organic matter to understand and predict their role in global biogeochemical cycles