Bilan des connaissances de la dynamique de l’érosion des côtes du Québec maritime laurentien

Un bilan des connaissances de la dynamique de l’érosion côtière dans l’estuaire et le golfe du Saint-Laurent montre que le recul du littoral dans les formations meubles est très important, variant généralement entre 0,5 et 2 m/an. Les données indiquent une accélération récente du phénomène, ce qui va dans le sens de la tendance mondiale appréhendée dans le contexte des changements climatiques. Il semble que les côtes à marais maritimes soient les plus sensibles, certains schorres supérieurs ayant déjà disparu au cours de la dernière décennie. Cela s’explique par le fait que, dans les régions froides, les marais maritimes sont affectés par un grand nombre de processus, dont le sapement par les vagues et les courants de marée, l’affouillement et l’arrachement par les glaces littorales, les processus cryogéniques, la dessiccation et les activités anthropiques et biologiques. Si l’action des vagues pendant les marées de vive eau et les tempêtes conditionne, dans une large mesure, le recul des falaises sableuses, les processus cryogéniques et hydrogéologiques sont les principaux responsables de la réactivation et de l’érosion des falaises à base argileuse et silteuse des complexes deltaïques. À l’échelle du Québec maritime, des études quantitatives saisonnières sont nécessaires pour bien comprendre la répartition spatio-temporelle des processus et surtout, les facteurs et les causes qui régissent l’érosion côtière dans les régions tempérées froides.A review of coastal erosion dynamics in the St. Lawrence maritime Estuary and Gulf demonstrates that shoreline retreat in unconsolidated formations varies between 0.5 and 2.0 m/yr. The data indicate a recent acceleration of coastal erosion that corresponds with the anticipated global trend resulting from climatic change. Saltmarshes are the most sensitive to coastal erosion, with some upper marshes having already disappeared in the last decade. In cold regions saltmarshes are affected by numerous processes such as undercutting by waves and tidal currents, ice foot scouring, freeze-thaw processes, wetting and drying processes, biologic processes and anthropogenic activities. Wave action during spring tides or storm surges is an important factor causing shoreline retreat in sandy cliffs, whereas cryogenic and hydrogeological processes are mainly responsible for reactivation and erosion of silt and clay-based cliffs in deltaic environments. In maritime Québec, quantitative seasonal studies are needed to develop a better understanding of spatio-temporal process distribution and to better assess the causes that regulate coastal erosion in mid-latitude cold regions

Géomorphologie et diversité végétale des marais du Cap Marteau et de l’Isle-Verte, estuaire du Saint-Laurent, Québec

Cet article traite de l’influence des caractéristiques géomorphologiques et sédimentologiques sur la diversité végétale de trois marais de l’estuaire maritime du Saint-Laurent soumis aux mêmes conditions marégraphiques, mais situés à des degrés contrastés d’exposition aux processus marins. Des inventaires biophysiques de plus de 1 500 quadrats de 1,5 m x 1,5 m et une cartographie morphosédimentologique ont été effectués dans ces marais. Les résultats indiquent que la diversité végétale des marais actuels est fortement influencée par la combinaison des types de substrat et de la topographie découlant de la morphosédimentologie quaternaire et récente. L’équilibre entre les processus d’érosion et de sédimentation, contrôlés en partie par le degré d’exposition des marais aux processus marins, joue également un rôle important sur la diversité végétale des marais. Celle-ci, exprimée par l’indice de Shannon et la richesse végétale, atteint des valeurs maximales sur le schorre supérieur. Comme cette partie du marais est particulièrement sensible aux changements pouvant survenir dans le régime sédimentaire, la diversité végétale constitue un indicateur de l’état d’équilibre hydrosédimentaire des marais.The objective of this paper is to examine the relationship between the plant diversity and the morphosedimentological characteristics of three tidal marshes of the Lower St. Lawrence estuary. These marshes are subject to similar tidal conditions, but are exposed to contrasted degrees of exposure to marine processes. Plant inventory and detailed mapping of 1 500 plots have been realised in the marshes. The analysis of the vegetation diversity and the geomorphological characteristics (topography, substratum) suggest that the plant diversity is strongly linked to the geodiversity. This is explained by the combination of the types of substratum and the topography which derive from the Quaternary and recent morphosedimentology. The processes of erosion and sedimentation, controlled by the degree of exposure, also play a role in the plant diversity of the marshes. It appears that the plant diversity (Shannon index and species richness) peaks within the upper marsh. Because this region is highly sensitive to changes in the sedimentary budget, our results suggest that the plant diversity is a good indicator of the hydrosedimentary state of the marsh

La terrasse Mitis à la pointe de Mille-Vaches (péninsule de Portneuf), rive nord de l’estuaire maritime du Saint-Laurent : nature des dépôts et évolution du niveau marin relatif à l’holocène

La basse terrasse à l’extrémité sud-ouest de la péninsule de Portneuf, sur la Haute Côte-Nord du Saint-Laurent, correspond à la terrasse Mitis présente dans quelques autres localités de la rive nord de l’estuaire. Entièrement composée de matériaux meubles détritiques, elle comprend plusieurs unités, la plupart sableuses, d’une épaisseur supérieure à 3 m. Mises en place en milieu littoral et intertidal, ces unités reposent sur un dépôt de sable fin gris, infratidal, lui-même susjacent au substrat limono-argileux déposé dans la Mer de Goldthwait, il y a >9,5 ka. Un dépôt de limon sableux, gris, laminé, contenant des débris de plantes en place correspondant à un faciès de schorre inférieur, coiffe la séquence sableuse. Par endroits, ce dépôt est lui-même recouvert d’une couche de tourbe de 25‑30 cm d’épaisseur. L’unité à la base de la falaise active a été mise en place entre 1990 ± 60 et 2740 ± 70 BP. Les unités sableuses au-dessus datent de 1570 ± 60 à 1880 ± 90 BP, alors que l’unité limoneuse à faciès de schorre inférieur a donné un âge au 14C allant de 1570 ± 50 à 1970 ± 70 BP. L’âge médian de la terrasse Mitis est de 1880 ± 90 BP, alors que si on prend en compte uniquement les dates pour l’unité limoneuse à faciès de schorre inférieur, il est de 1830 ± 60 BP. L’édification de la terrasse Mitis à la pointe de Mille-Vaches est donc contemporaine de la plupart des sites des deux rives de l’estuaire. Le substrat argileux de la vaste batture en face de la terrasse, qui se prolonge sous celle-ci, a été érodé lors d’un bas niveau marin pendant l’Holocène moyen qui fut suivi d’une remontée du niveau de quelques mètres. Un glissement de terrain historique, survenu vraisemblablement lors du séisme de 1663, caractérise la partie supérieure de l’estran en face de la falaise active.The low terrace at the SW extremity of the Portneuf Peninsula, on the north shore of the Lower St. Lawrence estuary, is an equivalent of the Mitis terrace occurring at a few other localities. The terrace is entirely made of detritic sediments. The various units, mostly fine to coarse sand deposited in the shore zone, are over 3 m in thickness. These sediments appear to unconformably overlie a subtidal dark grey fine sand resting on a surface eroded into a Goldthwait Sea clay deposit older than 9.5 ka. At the surface of the terrace, there is a grey, laminated sandy silt deposit with plant remains in situ (a lower marsh facies), locally covered by a thin (25‑30 cm) layer of peat. The sand unit at the base of the studied exposure has been dated 1990 ± 60 to 2740 ± 70 BP. The overlying sandy units are dated 1570 ± 60 to 1880 ± 90 BP, whereas the silt unit at the surface is dated 1570 ± 50 to 1970 ± 70 BP. The median age of the terrace is 1880 ± 90 BP, whereas if we use only the 14C dates for the silt unit, it is 1830 ± 60 BP. At Pointe de Mille-Vaches, the Mitis terrace is thus contemporaneous with most localities on both shores of the estuary. The substrate of the wide tidal flat in front of the Mitis terrace (an erosion surface underlying the terrace) was cut into the marine clay during a mid-Holocene lowstand, which was followed by a rising sea level of a few meters. An historical landslide, which possibly occurred during the 1663 seismic event, characterizes the upper part of the tidal zone in front of the active cliff

Targeting Endothelial Dysfunction in Vascular Complications Associated with Diabetes

Cardiovascular complications associated with diabetes remain a significant health issue in westernized societies. Overwhelming evidence from clinical and laboratory investigations have demonstrated that these cardiovascular complications are initiated by a dysfunctional vascular endothelium. Indeed, endothelial dysfunction is one of the key events that occur during diabetes, leading to the acceleration of cardiovascular mortality and morbidity. In a diabetic milieu, endothelial dysfunction occurs as a result of attenuated production of endothelial derived nitric oxide (EDNO) and augmented levels of reactive oxygen species (ROS). Thus, in this review, we discuss novel therapeutic targets that either upregulate EDNO production or increase antioxidant enzyme capacity in an effort to limit oxidative stress and restore endothelial function. In particular, endogenous signaling molecules that positively modulate EDNO synthesis and mimetics of endogenous antioxidant enzymes will be highlighted. Consequently, manipulation of these unique targets, either alone or in combination, may represent a novel strategy to confer vascular protection, with the ultimate goal of improved outcomes for diabetes-associated vascular complications

Deciphering lifelong thermal niche using otolith δ18O thermometry within supplemented lake trout (Salvelinus namaycush) populations

1. The selection of thermal habitat by fish is strongly regulated by physiology and behaviour. However, delineation of a species lifelong thermal niche remains tech-nically challenging. Lake trout (Salvelinus namaycush) survival and productivity are recognised as being tightly linked to a somewhat restricted thermal habitat. The factors guiding temperature selection during each life stage remain poorly understood. 2. In this study, we tested the significant factors controlling the realised thermal niche of lake trout from two southern Quebec small boreal lakes that experienced supplementation stocking during the last 20 years. We used oxygen stable isotope (δ18O) thermometry of otolith calcium carbonates (aragonite) using secondary-ion mass spectrometry to estimate experienced lifelong temperatures. We investi-gated the thermal habitat of lake trout with known genotypes (local, hybrid, and stocked). 3. Ontogeny and genetic origin influenced temperature selection in both studied lake trout populations. Young-of-the-year consistently used warmer, shallower habitats (10.7 ± 2.6°C, 7.5 m depth) prior to a juvenile transition to colder and deeper waters (8.5 ± 3.3°C, 10 m depth). Stocked lake trout, originating from a genetically distinct ecotype, exhibited a more variable thermal niche, with some individuals consistently using warmer habitat (10.4 ± 1°C) than local fish. Their hybrid progeny also occupied a warmer thermal niche, intermediate to the paren-tal strains. We propose that increased fat content and genetic origin are potential explanatory factors for warmer temperature use. 4. This study reiterates that high-resolution otolith δ18O thermometry is a uniquely well-suited approach for unravelling the multiple factors that influence lifelong temperature selection in fish. Our results illustrate that the realised thermal niche is influenced by a genetic–environment interaction

Sea ice increases benthic community heterogeneity in a seagrass landscape

Sea ice plays an important role in subpolar seagrass meadows. It protects meadows against wave action and extreme temperatures. On the other hand, sea ice destroys seagrass leaves and removes plots of sediments and organics debris, leaving long-lasting ice-made tidal pools of various shapes and sizes within the meadow. The present study aimed at investigating the effect of sea ice on benthic community structure and biogeochemical processes in a subpolar seagrass meadow. Vegetated areas (V), artificially-created (aTP), and natural (nTP) tidal pools were sampled from April to October 2018 in a seagrass meadow located at Manicouagan Peninsula (Québec; 49°5′36″N, 68°12′44″W). aTP and nTP showed similar sediment characteristics with coarser sediment and lower particulate organic carbon and total nitrogen content but also lower NOx and higher NH4+ and PO43− porewater concentrations as compared to V. Benthic macrofauna communities showed a strong seasonality with very reduced total density, biomass and species richness during wintertime (from December to April) relatively to summertime (from June to September). Benthic macrofauna communities were also more diversified and abundant in V than in aTP and nTP. Species assemblages in aTP and nTP represented a subset of species assemblages in V with any species found exclusively in tidal pools. However, total biomass was similar among treatments, suggesting that tidal pools sheltered larger individuals than vegetated areas. These results underline the importance of considering the spatial heterogeneity of seagrass meadows when assessing the functioning of these ecosystems. -- Keywords : Biodiversity ; Macrofauna ; Biogeochemistry ; Zostera marina ; Subpolar environment ; Tidal pools

Remote sensing of coastal vegetation phenology in a cold temperate intertidal system: Implications for classification of coastal habitats

Intertidal vegetation provides important ecological functions, such as food and shelter for wildlife and ecological services with increased coastline protection from erosion. In cold temperate and subarctic environments, the short growing season has a significant impact on the phenological response of the different vegetation types, which must be considered for their mapping using satellite remote sensing technologies. This study focuses on the effect of the phenology of vegetation in the intertidal ecosystems on remote sensing outputs. The studied sites were dominated by eelgrass (Zostera marina L.), saltmarsh cordgrass (Spartina alterniflora), creeping saltbush (Atriplex prostrata), macroalgae (Ascophyllum nodosum, and Fucus vesiculosus) attached to scattered boulders. In situ data were collected on ten occasions from May through October 2019 and included biophysical properties (e.g., leaf area index) and hyperspectral reflectance spectra (Rrs(λ)). The results indicate that even when substantial vegetation growth is observed, the variation in Rrs(λ) is not significant at the beginning of the growing season, limiting the spectral separability using multispectral imagery. The spectral separability between vegetation types was maximum at the beginning of the season (early June) when the vegetation had not reached its maximum growth. Seasonal time series of the normalized difference vegetation index (NDVI) values were derived from multispectral sensors (Sentinel-2 multispectral instrument (MSI) and PlanetScope) and were validated using in situ-derived NDVI. The results indicate that the phenology of intertidal vegetation can be monitored by satellite if the number of observations obtained at a low tide is sufficient, which helps to discriminate plant species and, therefore, the mapping of vegetation. The optimal period for vegetation mapping was September for the study area

The role of ecotype‐environment interactions in intraspecific trophic niche partitioning subsequent to stocking

Worldwide, stocking of fish represents a valuable tool for conservation and maintenance of species exploited by recreational fishing. Releases of hatchery-reared fish are more and more recognized to have numerous demographic, ecological, and genetic impacts on wild populations. However, consequences on intraspecific trophic relationships have rarely been investigated. In this study, we assessed the impacts of supplementation stocking and resulting introgressive hybridization on the trophic niches occupied by stocked, local, and hybrid lake trout (Salvelinus namaycush) within populations of piscivorous and planktivorous ecotypes stocked from a wild piscivorous source population. We compared trophic niches using stable isotope analysis (δ13C and δ15N) and trophic position among the three genetic origins. Putative genetic effects were tested with phenotype–genotype association of “life history” ecological traits (body size, growth rate, condition index, and trophic niche) and genotypes (RADseq SNP markers) using redundant discriminant analysis (RDA). Results showed that sympatry resulting from the stocking of contrasting ecotypes is a risk factor for niche partitioning. Planktivorous populations are more susceptible to niche partitioning, by competitive exclusion of the local fish from a littoral niche to an alternative pelagic/profundal niche. Observed niche partitioning is probably a manifestation of competitive interactions between ecotypes. Our results emphasize that ecotypic variation should be considered for more efficient management and conservation practices and in order to mitigate negative impact of supplementation stocking

Supplementation stocking of Lake Trout (Salvelinus namaycush) in small boreal lakes : Ecotypes influence on growth and condition

Supplementation stocking is a commonly used management tool to sustain exploited fish populations. Possible negative consequences of supplementation on local stocks are a concern for the conservation of wild fish populations. However, the direct impacts of supplementation on life history traits of local populations have rarely been investigated. In addition, intraspecific hybridization between contrasting ecotypes (planktivorous and piscivorous) has been seldom considered in supplementation plans. Here, we combined genetic (genotype-by-sequencing analysis) and life history traits to document the effects of supplementation on maximum length, growth rates, body condition and genetic admixture in stocked populations of two Lake Trout ecotypes from small boreal lakes in Quebec and Ontario, Canada. In both ecotypes, the length of stocked individuals was greater than local individuals and, in planktivorous-stocked populations, most stocked fish exhibited a planktivorous-like growth while 20% of fish exhibited piscivorous-like growth. The body condition index was positively related to the proportion of local genetic background, but this pattern was only observed in stocked planktivorous populations. We conclude that interactions and hybridization between contrasting ecotypes is a risk that could result in deleterious impacts and possible outbreeding depression. We discuss the implications of these findings for supplementation stocking

Identification of Golgi-localized acyl transferases that palmitoylate and regulate endothelial nitric oxide synthase

Lipid modifications mediate the subcellular localization and biological activity of many proteins, including endothelial nitric oxide synthase (eNOS). This enzyme resides on the cytoplasmic aspect of the Golgi apparatus and in caveolae and is dually acylated by both N-myristoylation and S-palmitoylation. Palmitoylation-deficient mutants of eNOS release less nitric oxide (NO). We identify enzymes that palmitoylate eNOS in vivo. Transfection of human embryonic kidney 293 cells with the complementary DNA (cDNA) for eNOS and 23 cDNA clones encoding the Asp-His-His-Cys motif (DHHC) palmitoyl transferase family members showed that five clones (2, 3, 7, 8, and 21) enhanced incorporation of [3H]-palmitate into eNOS. Human endothelial cells express all five of these enzymes, which colocalize with eNOS in the Golgi and plasma membrane and interact with eNOS. Importantly, inhibition of DHHC-21 palmitoyl transferase, but not DHHC-3, in human endothelial cells reduces eNOS palmitoylation, eNOS targeting, and stimulated NO production. Collectively, our data describe five new Golgi-targeted DHHC enzymes in human endothelial cells and suggest a regulatory role of DHHC-21 in governing eNOS localization and function