Effect of a freshwater pulse on mesoscale circulation and phytoplankton distribution in the lower St. Lawrence Estuary

As part of a multidisciplinary program to study the physical-biological interactions regulating carbon flows in the lower St. Lawrence Estuary (LSLE), three cruises were conducted in June–July 1990 during a neap-spring tidal cycle when biological production was expected to be maximal. Nutrient (nitrates and silicates), phytoplankton biomass (chlorophyll), oxygen, temperature, salinity, and current fields were used to elucidate the effect of a freshwater pulse produced by the discharge of the St. Lawrence and Saguenay rivers on the current fields and the biological variability and productivity of the LSLE. A simple Rossby adjustment model is presented to explain the temporal (3–5 days) and spatial (40–50 km) scales of motion in our study region (impact of the freshwater pulse on the circulation). Prior to the passage of the pulse during the neap tide, the circulation was dominated by a downstream outflow and phytoplankton blooms were limited to areas of weak baroclinic currents downstream and along the south shore. The arrival of the pulse during the tidal transition led to the intensification of a transverse current that most likely reduced flushing and allowed phytoplankton biomass to develop further upstream and toward the north shore. During the spring tide, lower salinity waters and the bloom spread along the north shore as the transverse current weakened. Based on these observations, a new conceptual model of mesoscale physical-biological interactions in the LSLE is presented that emphasizes the importance of transverse motions in regulating mesoscale patterns in phytoplankton blooms

Etude de la repartition spatio-temporelle des activites biologiques de part et d'autre du front liguro-provencal. Caracterisation de la fonction de puits pour le CO2 produit par l'activite respiratoire des microorganismes planctoniques

SIGLEINIST T 74374 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

A new modeling approach to define marine ecosystems food-web status with uncertainty assessment

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASAREInternational audienceEcosystem models are currently one of the most powerful approaches used to predict and analyse the consequences of anthropogenic and climate-driven changes in food web structure and function. The modeling community is however still lacking techniques for taking microbial processes properly into account and assessing flow uncertainty explicitly. A linear inverse model of the Bay of Biscay continental shelf was built using a Monte Carlo method coupled with a Markov Chain (LIMMCMC) to characterize the system's trophic food-web status and its associated structural and functional properties. By taking into account the natural variability of ecosystems (and their associated flows) and the lack of data on these environments, this innovative approach enabled the quantification of uncertainties for both estimated flows and derived food-web indices. This uncertainty assessment constituted a real improvement on the existing Ecopath model for the same area and both models results were compared. Our results suggested a food web characterized by main flows at the basis of the food web and a high contribution of primary producers and detritus to the entire system input flows. The developmental stage of the ecosystem was characterized using estimated Ecological Network Analysis (ENA) indices; the LIM-MCMC produced a higher estimate of flow specialization (than the estimate from Ecopath) owing to better consideration of bacterial processes. The results also pointed to a detritus-based food-web with a web-like structure and an intermediate level of internal flow complexity, confirming the results of previous studies. Other current research on ecosystem model comparability is also presented

Dissolved organic carbon in the Gulf of St. Lawrence

Dissolved organic carbon in the Gulf of St. Lawrence was measured throughout the water column by high-temperature catalytic oxidation during and after the 1994 spring phytoplankton bloom. DOC ranged from 28 to 111 μM. Except for the waters near the Magdalen Islands, the DOC in the euphotic zone was higher after the bloom (84.2-99.1 μM) than during the bloom (81-83 μM). Lowest euphotic zone DOC occurred near the Magdalen Islands (49 μM) where it was nearly as low as the deep-water DOC (35-50 μM) in the Anticosti Channel and Cabot Strait. In the deep water below 150 m the DOC levels in the inner regions of the Gulf were higher during the bloom than after it. These results along with the results of phytoplankton, bacteria, and ocean chemistry analyses were subjected to multiple regression, Spearman Rank, and principal component analyses to elucidate the role of DOC in transferring carbon between planktonic components of the Gulf of St. Lawrence pelagic ecosystem. The analyses showed a relationship between DOC and phytoplankton primary production in the euphotic zone during the bloom and a relationship between DOC and bacterial production in the euphotic zone after the bloom. A diel study showing DOC production in the morning and DOC degradation in the evening implicated phytoplankton in generating DOC during the dayThis study was carried out as a contribution to the Canadian JGOFS program with the financial support from both the Natural Science and Engineering Research Council of Canada and the Department of Fisheries and Oceans, Canada. We thank P.J. Wangersky for his encouragement, M.L. Dubé and A. Gagné for their analytical support, and two anonymous reviewers for their helpful comment

Le concept d’approche écosystémique appliqué à l’estuaire du Saint-Laurent (Canada)

Depuis plusieurs années, le concept d’approche écosystémique est avancé mondialement comme une solution possible aux problématiques de gestion liées à la détérioration des écosystèmes marins et de leurs ressources découlant de l’activité humaine, incluant les pêches, le développement industriel, l’aquaculture, etc. Au Canada, le ministère des Pêches et des Océans a développé en 2007 plusieurs initiatives scientifiques régionales afin de tester différents modèles pour l’application d’une telle approche au soutien de la gestion intégrée de diverses activités humaines qui menacent l’intégrité d’un écosystème. L’estuaire maritime du Saint-Laurent, dans l’est canadien, a constitué le cadre d’une de ces initiatives de recherche écosystémique (IRÉ) qui s’est déroulée de 2007 à 2012. L’estuaire est une région de forte production biologique exposée à une vaste gamme de pressions et d’activités humaines pouvant avoir un impact dommageable sur son intégrité et son utilisation durable. Lors d’ateliers de consultations incluant la participation à la fois de scientifiques et des principaux gestionnaires de cette région, deux priorités communes ont été retenues pour la mise en oeuvre de cette IRÉ, soit : (1) espèces fourragères responsables de la présence du rorqual bleu dans l’estuaire maritime du Saint-Laurent et (2) caractérisation des habitats fréquentés par le béluga du Saint-Laurent. L’objectif général de l’IRÉ de l’estuaire du Saint-Laurent était de développer un cadre opérationnel pour la coordination et l’intégration de projets existants ou des suivis en cours avec des nouveaux projets afin de fournir des informations et des avis scientifiques intégrés (application de l’approche écosystémique) reliés aux deux priorités choisies. Les deux thèmes ont abouti à une évaluation scientifique intégrée documentée dans des avis à caractère écosystémique sur plusieurs enjeux de gestion et objectifs de conservation à l’échelle de l’écosystème. Les résultats ont généré de l’information très pertinente à la gestion du parc marin Saguenay–Saint-Laurent, la mise en oeuvre de plans de rétablissement d’espèces en péril (béluga, rorqual bleu) et l’établissement attendu d’une zone de protection marine dans la région. L’objectif du manuscrit est de décrire les éléments qui ont justifié le choix de l’estuaire maritime du Saint-Laurent comme aire d’étude et de présenter la mise en œuvre et certains résultats intégrateurs de l’initiative de recherche écosystémique dans cette région.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients

International audienceThe aim of this study was to estimate the incidence of COVID-19 disease in the French national population of dialysis patients, their course of illness and to identify the risk factors associated with mortality. Our study included all patients on dialysis recorded in the French REIN Registry in April 2020. Clinical characteristics at last follow-up and the evolution of COVID-19 illness severity over time were recorded for diagnosed cases (either suspicious clinical symptoms, characteristic signs on the chest scan or a positive reverse transcription polymerase chain reaction) for SARS-CoV-2. A total of 1,621 infected patients were reported on the REIN registry from March 16th, 2020 to May 4th, 2020. Of these, 344 died. The prevalence of COVID-19 patients varied from less than 1% to 10% between regions. The probability of being a case was higher in males, patients with diabetes, those in need of assistance for transfer or treated at a self-care unit. Dialysis at home was associated with a lower probability of being infected as was being a smoker, a former smoker, having an active malignancy, or peripheral vascular disease. Mortality in diagnosed cases (21%) was associated with the same causes as in the general population. Higher age, hypoalbuminemia and the presence of an ischemic heart disease were statistically independently associated with a higher risk of death. Being treated at a selfcare unit was associated with a lower risk. Thus, our study showed a relatively low frequency of COVID-19 among dialysis patients contrary to what might have been assumed