Érosion du pergélisol, transport fluvial et sédimentation marine, côte est de la baie d'Hudson, Nunavik, Canada

Cette thèse présente une étude du système érosion-transport-sédimentation en milieu de thermokarst dans un contexte de réchauffement climatique. La zone d’étude comprend le bassin versant de la rivière Sheldrake, 5 km au nord du village Umiujaq au Nunavik, ainsi qu’une zone de 15 km2 au large de son embouchure, dans le Passage de Nastapoka, en baie d’Hudson. Trois axes majeurs sont considérés: 1- l’étude des conditions de pergélisol et l’estimation quantitative des masses et volumes de sédiments et de carbone érodés à l’échelle du bassin versant ; 2- la mesure du régime hydrologique et sédimentaire du principal vecteur de transport, la rivière Sheldrake ; 3- la bathymétrie, la sédimentologie et la mesure des apports sédimentaires et organiques dans le milieu marin côtier au large de l’embouchure de la rivière. Dans le bassin versant de la rivière Sheldrake, le pergélisol s’est considérablement dégradé au cours des 50 dernières années, particulièrement dans la toundra forestière. La subsidence des lithalses, des palses, des plateaux de pergélisol et des plateaux palsiques engendre la formation de mares de thermokarst. De nombreux glissements de terrain et des ravins d’érosion sont également actifs et favorisent le rejet de sédiments dans le réseau fluvial. Avec la dégradation du pergélisol, la connectivité hydrologique augmente, ce qui facilite l’évacuation des sédiments et du carbone via le cours d’eau principal. Dans cet environnement thermokarstique, la charge sédimentaire fluviale en suspension est plus importante en été alors que les températures élevées de l’air commandent le dégel des sols, favorisant l’activation des ostioles et le déclenchement des glissements de terrain. Les pluies estivales permettent le transport et l’évacuation des sédiments en baie d’Hudson. Parvenus en mer, les sédiments et le carbone transportés en suspension subissent une forte dispersion à cause de l’intensité des courants marins du Passage de Nastapoka. Il en résulte l’absence d’une augmentation mesurable du taux de sédimentation. En revanche, la composition isotopique du carbone sédimentaire montre que la fraction terrigène a augmenté depuis le Petit Âge Glaciaire et que ce phénomène s’est considérablement accéléré vers la fin du 20ème siècle. Il est suggéré que la dégradation du pergélisol contribue à cette augmentation, quoique ce ne soit pas le seul facteur qu’on puisse invoquer.This thesis studies the system erosion-transport-sedimentation in a thermokastic area, in a context of warming climate. The study area encompasses the catchment of the Sheldrake River, 5 km north of the village Umiujaq, Nunavik, and a 15 km2 area off its mouth, in the Nastapoka Sound, in Hudson Bay. Three main axes are considered: 1- study of permafrost conditions and quantitative estimate of the volumes and masses of eroded sediment and organic carbon at the scale of the catchment; 2- measurements of the hydrological and sedimentary regime of the main vector of transport, the Sheldrake River; 3- bathymetry, sedimentology and measurements of mineral and organic inputs in the coastal marine environment, off the river mouth. In the Sheldrake River catchment, permafrost has considerably degraded during the last 50 years, particularly in the forested tundra. Subsidence of lithalsas, palsas, permafrost plateaus and peat plateaus leads to the formation of thermokarst ponds. Many landslides and erosion gullies are also active and favor inputs of sediments in the fluvial network. Because of permafrost decay, hydrological connectivity increases, facilitating evacuation of sediment and carbon through the river. In this thermokarstic environment, the fluvial sedimentary load in suspension is more important during summer when high air temperatures provoke soils thawing, favoring frostboils activation and triggering of landslides. Summer rainfalls allow sediment transport and evacuation in Hudson Bay. Once in the sea, the sediments and carbon in suspension are dispersed because of the intensity of the marine currents in the Nastapoka Sounds. This results in an absence of a measurable increase of sedimentation rates. However, the isotopic composition of sedimentary carbon shows that the terrestrial fraction has increased since the Little Ice Age and that this trend has significantly accelerated since the end of the 20th century. It is suggested that permafrost decay contributes to this increase, although it is not the only proposed source

Daily Eastern News: March 03, 2017

https://thekeep.eiu.edu/den_2017_mar/1002/thumbnail.jp

Enjeux et impacts des barrages de Diama (Mauritanie) et Arzal (France) : des contextes socio-économiques et environnementaux différents pour de mêmes conséquences

The similar dams of Arzal (Vilaine, France) and Diama (Mauritania-Senegal frontier) have same strategic functions for the regions and countries where they are built as fresh waters storage. They also had similar consequences over the ecosystems and local and regional activities. The imperfect results of the belated remediations also had as disastrous induced effects and leave the populations and ecosystems in a fragile and vulnerable situation if confronted with any environmental (drought, flood…), socio-economical or political (relations between Mauritania and Senegal) crisis

Enjeux et impacts des barrages de Diama (Mauritanie) et Arzal (France) : des contextes socio-économiques et environnementaux différents pour de mêmes conséquences

Les barrages d’Arzal sur la Vilaine (France) et de Diama sur le fleuve Sénégal à la frontière mauritano-sénégalaise, ont les mêmes fonctions principales, stratégiques pour les régions et pays où ils ont été bâtis, puisqu’ils permettent de constituer d’énormes réserves d’eaux douces en zones estuariennes, et ceci malgré des contextes environnementaux et socio-économiques très différents. S’ils ont favorisé l’émergence d’autres atouts, ils ont aussi eu des conséquences importantes sur les écosystèmes et les activités traditionnelles locales et régionales. Les actions de remédiation mises en œuvre tardivement, et qui auraient sans doute pu être plus ambitieuses, ont eu des résultats mitigés dont les effets induits laissent les populations et les écosystèmes dans une situation de fragilité et de vulnérabilité face à toute crise environnementale (sécheresse, crue/inondation, etc.), socio-économique ou encore politique, comme on a pu le constater par exemple lorsque les relations mauritano-sénégalaises se sont dégradées.The similar dams of Arzal (Vilaine, France) and Diama (Mauritania-Senegal frontier) have same strategic functions for the regions and countries where they are built as fresh waters storage. They also had similar consequences over the ecosystems and local and regional activities. The imperfect results of the belated remediations also had as disastrous induced effects and leave the populations and ecosystems in a fragile and vulnerable situation if confronted with any environmental (drought, flood…), socio-economical or political (relations between Mauritania and Senegal) crisis

A Novel Model of Mixed Vascular Dementia Incorporating Hypertension in a Rat Model of Alzheimer's Disease.

Alzheimer's disease (AD) and mixed dementia (MxD) comprise the majority of dementia cases in the growing global aging population. MxD describes the coexistence of AD pathology with vascular pathology, including cerebral small vessel disease (SVD). Cardiovascular disease increases risk for AD and MxD, but mechanistic synergisms between the coexisting pathologies affecting dementia risk, progression and the ultimate clinical manifestations remain elusive. To explore the additive or synergistic interactions between AD and chronic hypertension, we developed a rat model of MxD, produced by breeding APPswe/PS1ΔE9 transgenes into the stroke-prone spontaneously hypertensive rat (SHRSP) background, resulting in the SHRSP/FAD model and three control groups (FAD, SHRSP and non-hypertensive WKY rats, n = 8-11, both sexes, 16-18 months of age). After behavioral testing, rats were euthanized, and tissue assessed for vascular, neuroinflammatory and AD pathology. Hypertension was preserved in the SHRSP/FAD cross. Results showed that SHRSP increased FAD-dependent neuroinflammation (microglia and astrocytes) and tau pathology, but plaque pathology changes were subtle, including fewer plaques with compact cores and slightly reduced plaque burden. Evidence for vascular pathology included a change in the distribution of astrocytic end-foot protein aquaporin-4, normally distributed in microvessels, but in SHRSP/FAD rats largely dissociated from vessels, appearing disorganized or redistributed into neuropil. Other evidence of SVD-like pathology included increased collagen IV staining in cerebral vessels and PECAM1 levels. We identified a plasma biomarker in SHRSP/FAD rats that was the only group to show increased Aqp-4 in plasma exosomes. Evidence of neuron damage in SHRSP/FAD rats included increased caspase-cleaved actin, loss of myelin and reduced calbindin staining in neurons. Further, there were mitochondrial deficits specific to SHRSP/FAD, notably the loss of complex II, accompanying FAD-dependent loss of mitochondrial complex I. Cognitive deficits exhibited by FAD rats were not exacerbated by the introduction of the SHRSP phenotype, nor was the hyperactivity phenotype associated with SHRSP altered by the FAD transgene. This novel rat model of MxD, encompassing an amyloidogenic transgene with a hypertensive phenotype, exhibits several features associated with human vascular or "mixed" dementia and may be a useful tool in delineating the pathophysiology of MxD and development of therapeutics

TGFβ promotes low IL10-producing ILC2 with profibrotic ability involved in skin fibrosis in systemic sclerosis

Objective : Innate lymphoid cells-2 (ILC2) were shown to be involved in the development of lung or hepatic fibrosis. We sought to explore the functional and phenotypic heterogeneity of ILC2 in skin fibrosis within systemic sclerosis (SSc). Methods : Blood samples and skin biopsies from healthy donor or patients with SSc were analysed by immunostaining techniques. The fibrotic role of sorted ILC2 was studied in vitro on dermal fibroblast and further explored by transcriptomic approach. Finally, the efficacy of a new treatment against fibrosis was assessed with a mouse model of SSc. Results : We found that ILC2 numbers were increased in the skin of patients with SSc and correlated with the extent of skin fibrosis. In SSc skin, KLRG1− ILC2 (natural ILC2) were dominating over KLRG1+ ILC2 (inflammatory ILC2). The cytokine transforming growth factor-β (TGFβ), whose activity is increased in SSc, favoured the expansion of KLRG1- ILC2 simultaneously decreasing their production of interleukin 10 (IL10), which regulates negatively collagen production by dermal fibroblasts. TGFβ-stimulated ILC2 also increased myofibroblast differentiation. Thus, human KLRG1- ILC2 had an enhanced profibrotic activity. In a mouse model of SSc, therapeutic intervention-combining pirfenidone with the administration of IL10 was required to reduce the numbers of skin infiltrating ILC2, enhancing their expression of KLRG1 and strongly alleviating skin fibrosis. Conclusion : Our results demonstrate a novel role for natural ILC2 and highlight their inter-relationships with TGFβ and IL10 in the development of skin fibrosis, thereby opening up new therapeutic approaches in SSc

High methylmercury in Arctic and subarctic ponds is related to nutrient levels in the warming eastern Canadian Arctic

Permafrost thaw ponds are ubiquitous in the eastern Canadian Arctic, yet little information exists on their potential as sources of methylmercury (MeHg) to freshwaters. They are microbially active and conducive to methylation of inorganic mercury, and are also affected by Arctic warming. This multiyear study investigated thaw ponds in a discontinuous permafrost region in the Subarctic taiga (Kuujjuarapik-Whapmagoostui, QC) and a continuous permafrost region in the Arctic tundra (Bylot Island, NU). MeHg concentrations in thaw ponds were well above levels measured in most freshwater ecosystems in the Canadian Arctic (>0.1 ng L−1). On Bylot, ice-wedge trough ponds showed significantly higher MeHg (0.3−2.2 ng L−1) than polygonal ponds (0.1−0.3 ng L−1) or lakes (<0.1 ng L−1). High MeHg was measured in the bottom waters of Subarctic thaw ponds near Kuujjuarapik (0.1−3.1 ng L−1). High water MeHg concentrations in thaw ponds were strongly correlated with variables associated with high inputs of organic matter (DOC, a320, Fe), nutrients (TP, TN), and microbial activity (dissolved CO2 and CH4). Thawing permafrost due to Arctic warming will continue to release nutrients and organic carbon into these systems and increase ponding in some regions, likely stimulating higher water concentrations of MeHg. Greater hydrological connectivity from permafrost thawing may potentially increase transport of MeHg from thaw ponds to neighboring aquatic ecosystems

Novel oral targeted therapies in inflammatory bowel disease

Background: There is a great unmet clinical need for efficacious, tolerable, economical and orally administrated drugs for the treatment of inflammatory bowel disease (IBD). New therapeutic avenues have become possible including the development of medications that target specific genetic pathways found to be relevant in other immune mediated diseases. Aims: To provide an overview of recent clinical trials for new generation oral targeted medications that may have a future role in IBD management. Methods: Pubmed and Medline searches were performed up to 01/03/18 using keywords: ‘IBD’, ‘UC’, ‘CD’, ‘inflammatory bowel disease’ ‘ulcerative colitis’, Crohn’s disease’ in combination with ‘phase’, ‘study’, ‘trial’, and ‘oral’. A manual search of the clinical trial register, article reference lists, abstracts from meetings of Digestive Disease Week, United European Gastroenterology Week and ECCO congress were also conducted. Results: In randomised controlled trials primary efficacy endpoints were met for tofacitinib (JAK 1/3 inhibitor-phase III), upadacitinib (JAK 1 inhibitor-phase II) and AJM-300 (α4-integrin antagonist-phase II) in ulcerative colitis. Ozanimod (S1P receptor agonist-phase II) also demonstrated clinical remission. For Crohn’s disease, filgotinib (JAK1 inhibitor-phase II) met primary endpoints and laquinimod (quinolone-3-carboxide small molecule-phase II) was also efficacious. Trials using mongersen (SMAD7 inhibitor) and vidofludimus (dihydroorotate dehydrogenase inhibitor) have been halted. Conclusions: This is potentially the start of an exciting new era in which multiple therapeutic options are at the disposal of physicians to treat IBD on an individualised basis. Head-to-head studies with existing treatments and longer term safety data are needed for this to be possible