Les transformations microbiennes de l’azote dans les grandes rivières

Les rivières reçoivent de l'azote de leurs bassins versants et elles constituent les derniers sites de transformations des nutriments avant leur livraison aux zones côtières. Les transformations de l’azote inorganique dissous en azote gazeux sont très variables et peuvent avoir un impact à la fois sur l’eutrophisation des côtes et les émissions de gaz à effet de serre à l’échelle globale. Avec l’augmentation de la charge en azote d’origine anthropique vers les écosystèmes aquatiques, les modèles d’émissions de gaz à effet de serre prédisent une augmentation des émissions d’oxyde nitreux (N2O) dans les rivières. Les mesures directes de N2O dans le Lac Saint-Pierre (LSP), un élargissement du Fleuve Saint-Laurent (SLR) indiquent que bien qu’étant une source nette de N2O vers l'atmosphère, les flux de N2O dans LSP sont faibles comparés à ceux des autres grandes rivières et fleuves du monde. Les émissions varient saisonnièrement et inter-annuellement à cause des changements hydrologiques. Les ratios d’émissions N2O: N2 sont également influencés par l’hydrologie et de faibles ratios sont observés dans des conditions de débit d'eau plus élevée et de charge en N élevé. Dans une analyse effectuée sur plusieurs grandes rivières, la charge hydraulique des systèmes semble moduler la relation entre les flux de N2O annuels et les concentrations de nitrate dans les rivières. Dans SLR, des tapis de cyanobactéries colonisant les zones à faible concentration de nitrate sont une source nette d’azote grâce à leur capacité de fixer l’azote atmosphérique (N2). Étant donné que la fixation a lieu pendant le jour alors que les concentrations d'oxygène dans la colonne d'eau sont sursaturées, nous supposons que la fixation de l’azote est effectuée dans des micro-zones d’anoxie et/ou possiblement par des diazotrophes hétérotrophes. La fixation de N dans les tapis explique le remplacement de près de 33 % de la perte de N par dénitrification dans tout l'écosystème au cours de la période d'étude. Dans la portion du fleuve Hudson soumis à la marée, la dénitrification et la production de N2 est très variable selon le type de végétation. La dénitrification est associée à la dynamique en oxygène dissous particulière à chaque espèce durant la marée descendante. La production de N2 est extrêmement élevée dans les zones occupées par les plantes envahissantes à feuilles flottantes (Trapa natans) mais elle est négligeable dans la végétation indigène submergée. Une estimation de la production de N2 dans les lits de Trapa durant l’été, suggère que ces lits représentent une zone très active d’élimination de l’azote. En effet, les grands lits de Trapa ne représentent que 2,7% de la superficie totale de la portion de fleuve étudiée, mais ils éliminent entre 70 et 100% de l'azote total retenu dans cette section pendant les mois d'été et contribuent à près de 25% de l’élimination annuelle d’azote.Rivers receive nitrogen (N) from their watershed and are the final sites of nutrient processing before delivery to coastal waters. Transformations of dissolved inorganic N (DIN) to gaseous N are highly variable and can impact both coastal eutrophication and greenhouse gas emissions. With anthropogenic N loading to aquatic ecosystems on the rise, nitrous oxide (N2O) emission from rivers should increase. Direct measurements of N2O from lake St. Pierre (LSP), an enlargement of the St. Lawrence River (SLR) indicate that although LSP is a net atmospheric source of N2O to the atmosphere fluxes are low compared to others rivers. Emissions are seasonally and inter-annually highly variable due to changes in hydrological conditions. N2O: N2 is also influenced by hydrology and lower ratios are observed in conditions of higher water discharge and elevated N charge into the ecosystem. In a cross system analysis, hydraulic load mitigates the relation between annual N2O flux and nitrate concentrations in rivers. In SLR, cyanobacterial mats colonizing low nitrate areas are a net source of N with high negative di-nitrogen (N2) fluxes. Given that fixation occurred during daylight and that oxygen concentrations in the water column were supersaturated, we hypothesize that N2 fixation is performed by the dominant cyanobacteria in anoxic micro-zone of the mat and/ or possibly by heterotrophic diazotrophs. Our estimates indicate that N fixation in the mats account for the replacement of up to 33% of the N loss via denitrification in the entire ecosystem during the study period. In the tidal Hudson River N2 production is highly variable between vegetated shallows and was associated with species-driven differences in dissolved oxygen (DO) dynamics during the ebb tide. N2 production was extremely high in invasive floating-leaved plants (Trapa natans) but was insignificant in submersed native vegetation. An estimate of summertime N2 production in Trapa beds suggests that these beds are a major seasonal hotspot for N removal. Large Trapa beds represent only 2.7% of the total area of the tidal Hudson but they remove between 70 and 100% of the total N retained in this section of the river during summer months and contribute to as much as 25% of the annual N removal

Effect of extracranial lesion severity on outcome of endovascular thrombectomy in patients with anterior circulation tandem occlusion: analysis of the TITAN registry

Introduction Endovascular treatment (EVT) for tandem occlusion (TO) of the anterior circulation is complex but effective. The effect of extracranial internal carotid artery (EICA) lesion severity on the outcomes of EVT is unknown. In this study we investigated the effect of EICA lesion severity on the outcomes of tandem occlusion EVT. Methods A multicenter retrospective TITAN (Thrombectomy In TANdem lesions) study that included 18 international endovascular capable centers was performed. Patients who received EVT for atherosclerotic TO with or without EICA lesion intervention were included. Patients were divided into two groups based on the EICA lesion severity (high-grade stenosis (>= 90% North American Symptomatic Carotid Endarterectomy Trial) vs complete occlusion). Outcome measures included the 90-day clinical outcome (modified Rankin Scale score (mRS)), angiographic reperfusion (modified Thrombolysis In Cerebral Ischemia (mTICI) at the end of the procedure), procedural complications, and intracranial hemorrhage at 24 hours follow-up. Results A total of 305 patients were included in the study, of whom 135 had complete EICA occlusion and 170 had severe EICA stenosis. The EICA occlusion group had shorter mean onset-to-groin time (259 +/- 120 min vs 305 +/- 202 min;p=0.037), more patients with diabetes, and fewer with hyperlipidemia. With respect to the outcome, mTICI 2b-3 reperfusion was lower in the EICA occlusion group (70% vs 81%;p=0.03). The favorable outcome (90-day mRS 0-2), intracerebral hemorrhage and procedural complications were similar in both groups. Conclusion Atherosclerotic occlusion of the EICA in acute tandem strokes was associated with a lower rate of mTICI 2b-3 reperfusion but similar functional and safety outcomes when compared with high-grade EICA stenosis

School Meals Case Study: Senegal

This school meals case study forms part of a collection led by the Research Consortium for School Health and Nutrition’s "Good Examples" Community of Practice. Developed by Sidy Toukara and Seyni Kébé, the School Meals Case Study of Senegal serves to document how the national school meals programme is organized, funded, and monitored throughout the country. The objectives of this case study include presenting an introduction to the country profile, outlining the design and implementation of school feeding programmes, describing their monitoring and evaluation processes, and highlighting lessons learned, best practices, and challenges. This case study is written as a working paper, and can be updated to reflect evolving circumstances. The ‘Good Examples’ Community of Practice supports the evidence generation of the Research Consortium for School Health and Nutrition, the evidence-generating arm of the School Meals Coalition. The Research Consortium’s objective is to carry out independent research across diverse sectors and generate solid, compelling, and actionable evidence regarding the benefits of school food programs to inform evidence-based decision-making on school health and nutrition policies and practices

Estimates of carbon stocks in sandy soils cultivated under local management practices in Senegal’s groundnut basin

Soil organic carbon (SOC) is essential for the productivity of agroecosystems and for mitigating climate change. Because the SOC contents of sandy soils are usually small, the effects of agricultural management upon SOC stocks in such soils have been insufficiently studied. In West sub-arid Africa, the coarse-textured soils (mostly Arenosols) are diversely managed by smallholders. In this study, we aimed to quantify SOC stocks in cultivated soils of that region, in a context where agricultural practices rely mainly upon organic inputs derived from various integrated crop-livestock systems. SOC stocks were estimated for the 0-30 cm depth in 1,813 plots in Senegal's groundnut basin. We found that SOC stocks in farmers' fields varied between 2.3 and 59.8 Mg C ha(-1) (mean +/- standard deviation, 14.6 +/- 0.14 Mg C ha(-1)). SOC stocks were influenced slightly by soil type, but were only weakly correlated to soils' clay and silt contents. SOC stocks differed significantly among the three studied village territories due to contrasting livestock-raising systems. Average stocks were significantly higher in plots close to housings (home-fields), which receive larger amounts of organic inputs, than in plots farther from the village (out-fields). Thus, the organic inputs to home-fields improves soil C stocks of these sandy soils in the short term. Innovative agricultural practices in the studied area probably need to target options for managing all fields optimally. Those options will require continuous application of organic products-a measure that will in turn require solutions for improving availability or management of local organic resources

Cholesteryl ester transfer protein modulates the effect of liver X receptor agonists on cholesterol transport and excretion in the mouse

International audienceHuman plasma, unlike mouse plasma, contains the cholesteryl ester transfer protein (CETP) that may influence the reverse cholesterol transport. Liver X receptor (LXR), an oxysterol-activated nuclear receptor induces CETP transcription via a direct repeat 4 element in the CETP gene promoter. The aim of the study was to assess in vivo the impact of LXR activation on CETP expression and its consequences on plasma lipid metabolism and hepatic and bile lipid content. Wild-type and humanized mice expressing CETP were treated for five days with T0901317 LXR agonist. This treatment produced marked rises in both hepatic CETP mRNA and plasma CETP activity levels. Interestingly, the LXR agonist-mediated, 2-fold rise in both total and HDL cholesterol levels in treated wild-type mice was not observed in CETPTg mice, and the accumulation of cholesterol in the liver of CETPTg mice was reversed by LXR agonist treatment. Moreover, LXR activation induced a 2-fold increase in hepatic LDL-receptor expression in wild-type and CETPTg mice, and it produced a significantly greater rise in biliary cholesterol concentration in CETPTg mice as compared with wild-type mice. In conclusion, induction of CETP constitutes a major determinant of the effect of LXR agonists on cholesterol transport and excretion