90 research outputs found
Resource competition affects plankton community structure; evidence from trait-based modeling
Understanding the phenology of phytoplankton species is a challenge and despite a lot of theoretical work on competition for resources, this process is under-represented in deterministic models. To study the main driver of the species selection, we used a trait-based model that keeps phenotypic variability through physiological trait parameterization. Next, we validated the results by using the toxic dinoflagellate Alexandrium minutum which is a toxic species. Due to their monitoring, we show that harmful algae are ideal models for studying ecological niches and for contributing to this more global challenge. As a first step, a dimensionless model of an estuary (France) was built with water temperature and water exchanges deduced from a hydro-dynamic model. The biological parametrization takes into account the size (from pico- to microphytoplankton) and the type of assimilation. The results show that temperature, competition for nutrients and dilution are important factors regulating the community structure and Alexandrium minutum dynamics (more especially the bloom initiation and magnitude). These drivers contribute to the determination of the ecological niche of A. minutum, influence the shape of its blooms and provide potential explanations of its interannual variability. This approach makes the community structure more flexible in order to study how environmental forcings could drive its evolution
Long-term evolution (1988-2008) of Zostera spp. meadows in Arcachon Bay (Bay of Biscay)
The spatial variability of seagrass meadows in Arcachon Bay, was studied between 1988 and 2008 using a combination of mapping techniques based on aerial photographs for intertidal dwarf-grass (Zostera noltti) beds and acoustic sonar for permanently submerged eelgrass (Zostera marina) populations. The results show a severe decline over the period for both species, as well as an acceleration of the decline since 2005 for Z. noltii. The total surface regression over the studied period is estimated to be 22.8 km(2) for Z. noltii and 2.7 km(2) for Z. marina, which represent declines of 33 and 74% respectively. Environmental data time series spanning the same period were investigated in order to seek the causes for such a decline. The calculated inter-annual trends for temperature, salinity, nitrate plus nitrite, ammonia, suspended sediment and chlorophyll a did not identify any clear environmental change capable of explaining the observed seagrass regression. For instance, no evident sign of eutrophication was observed over the study period. On the other hand, we suggest that the observed variations of ammonia in the inner part of the lagoon are a symptom of the seagrasses' disappearance and thus, a first sign indicating a change of the Arcachon Bay ecosystem towards more instability and vulnerability. Several hypotheses to explain the observed seagrass decay are proposed. (C) 2010 Elsevier Ltd. All rights reserved
Proceedings of the 4th International Conference on Transport, Atmosphere and Climate
The "4th International Conference on Transport, Atmosphere and Climate (TAC-4)" held in Bad
Kohlgrub (Germany), 2015, was organised with the objective of updating our knowledge on the impacts
of transport on the composition of the atmosphere and on climate, three years after the TAC-3
conference in Prien am Chiemsee (Germany).
The TAC-4 conference covered all aspects of the impact of the different modes of transport (aviation,
road transport, shipping etc.) on atmospheric chemistry, microphysics, radiation and climate,
in particular
Desired weight loss and its association with health, health behaviors and perceptions in an adult population with weight excess: One-year follow-up
Background: Metabolic syndrome (MetS) worsens quality of life and increases mortality. Dissatisfaction with weight in patients with MetS may modify the effect of lifestyle interventions to achieve changes in health-related behaviors. Objective: To assess 1-year changes in cardiovascular risk scores, self-perceived general health and health-related behaviors according to observed changes in desired weight loss during the first year of intervention in a large cardiovascular prevention trial. Design: Prospective analysis of the PREDIMED-PLUS trial, including 5,499 adults (55-75 years old) with overweight or obesity at baseline. Methods: The desired weight loss was the difference between ideal and measured weight. Tertiles of change in desired weight loss (1 year vs. baseline) were defined by the following cut-off points: >= 0.0 kg (T1, n = 1,638); 0.0 to -4.0 kg (T2, n = 1,903); <=-4.0 kg (T3, n = 1,958). A food frequency questionnaire assessed diet and the Minnesota-REGICOR questionnaire assessed physical activity. The Framingham equation assessed cardiovascular risks. The changes in the severity of MetS were also assessed. The Beck Depression Inventory assessed depressive symptoms and the SF-36 assessed health-related quality of life. Data were analyzed using general linear models. Results: BMI decreased at T2 and T3 (T1: 0.3, T2: -0.7, T3: -1.9). The most significant improvement in diet quality was observed at T3. Cardiovascular risk decreased at T2 and T3. Mean reductions in MetS severity score were: -0.02 at T1, -0.39 at T2 and -0.78 at T3. The perception of physical health increases in successive tertiles. Conclusions: In older adults with MetS, more ambitious desired weight loss goals were associated with improvements in diet, cardiovascular health and perceived physical health during the first year of a healthy lifestyle intervention programme. Weight dissatisfaction needs to be considered by health professionals
Recommended from our members
Synthetic and Mechanistic Studies into the Reductive Functionalization of Nitro Compounds Catalyzed by an Iron(salen) Complex
Publication status: PublishedWe report on the use of a simple, bench-stable [FeÂ(salen)2]-ÎŒ-oxo precatalyst in the reduction of nitro compounds. The reaction proceeds at room temperature across a range of substrates, including nitro aromatics and aliphatics. By changing the reducing agent from pinacol borane (HBpin) to phenyl silane (H3SiPh), we can chemoselectively reduce nitro compounds while retaining carbonyl functionality. Our mechanistic studies, which include kinetics, electron paramagnetic resonance (EPR), mass spectrometry, and quantum chemistry, indicate the presence of a nitroso intermediate and the generation of an on-cycle iron hydride as a key catalytic intermediate. Based on this mechanistic insight, we were able to extend the chemistry to hydroamination and identified a simple substrate feature (alkene lowest unoccupied molecular orbital (LUMO) energy) that could be used to predict which alkenes would result in productive catalysis
Rapport Alex Breizh. Impact des contrĂŽles environnementaux sur la dynamique des efflorescences de lâalgue toxique Alexandrium minutum en Rade de Brest. ModĂ©lisation en compĂ©tition interspĂ©cifique.
Depuis 2012, la rade de Brest a Ă©tĂ© lâobjet de fermetures administratives de commercialisation de coquillages et de ramassage en raison des toxicitĂ©s induites par le dĂ©veloppement de la microalgue nuisible Alexandrium minutum. Le suivi terrain existant depuis 2009 Ă la Pointe du chĂąteau (estuaire de la Mignonne, Daoulas) a Ă©tĂ© renforcĂ© en 2016 dans le cadre de ce projet (AlexBreizh) afin de cerner la dynamique de croissance de cette microalgue en lien avec les facteurs environnementaux et la dynamique des autres espĂšces phytoplanctoniques. Ce suivi hebdomadaire de 12 annĂ©es a permis de comprendre la dynamique saisonniĂšre de cet environnement et sa variabilitĂ© interannuelle. Alexandrium minutum est observĂ© uniquement dans la pĂ©riode qui sâĂ©tend dâavril Ă septembre et les maximums dâabondance sont en juin et juillet. Selon les annĂ©es, le bloom dĂ©marre en mai (printemps chauds comme en 2014) ou juin (2013, printemps froid). La tempĂ©rature de 15°C est lâindicateur du dĂ©marrage possible dâun bloom, ce qui a Ă©tĂ© aussi vĂ©rifiĂ© sur dâautres sites bretons. Les maximas sont liĂ©s aux conditions estivales de dĂ©bits, de forts dĂ©bits entrainant des apports consĂ©quents en nitrates et phosphates qui stimulent la croissance dâA. minutum et lui permettent de dominer la flore phytoplanctonique. Ce fut le cas en 2012 oĂč lâĂ©tĂ© a Ă©tĂ© exceptionnellement pluvieux. La communautĂ© phytoplanctonique en hiver est au repos. A partir de mars on observe une succession Ă©cologique avec dâabord un dĂ©veloppement du microphytoplancton alors que les concentrations en azote et phosphore du milieu sont Ă©levĂ©es (dĂ©bits hivernaux forts) suivi par le nanophytoplancton puis le picophytoplancton en Ă©tĂ©. A lâoccasion de crues estivales, câest Ă nouveau le microphytoplancton qui se dĂ©veloppe. Ces mesures de lâensemble de la communautĂ© phytoplanctonique ont pu ĂȘtre rĂ©alisĂ©es dans AlexBreizh par lâutilisation de la cytomĂ©trie in situ. Lâensemble des donnĂ©es mesurĂ©es, intĂ©grĂ© dans la base Quadrige2 et consultable par tous, a permis de tester diffĂ©rentes analyses afin de mettre en Ă©vidence des liens entre paramĂštres environnementaux et dĂ©veloppement dâAlexandrium minutum. Les analyses de niche Ă©cologique montrent une prĂ©fĂ©rence dâAlexandrium minutum pour les conditions estivales (tempĂ©rature et lumiĂšre Ă©levĂ©es) avec une tolĂ©rance pour des conditions plus estuariennes ainsi que des conditions environnementales plus favorables en Bretagne pour le dĂ©veloppement dâA. minutum. Lâanalyse fonctionnelle sur les taxons de microphytoplancton a mis en Ă©vidence 3 pĂ©riodes 2009 â 2011, 2011 â 2015 et 2015 â 2018. La premiĂšre est associĂ©e Ă la dominance de Chaetoceros qui dĂ©cline ensuite, la deuxiĂšme est reprĂ©sentĂ©e par la dominance dâA. minutum et la troisiĂšme correspond au dĂ©clin dâA. minutum ainsi quâĂ une plus grande prĂ©cocitĂ© des blooms de microphytoplancton. AppliquĂ© Ă lâestuaire de Daoulas, un modĂšle numĂ©rique de dynamique dâA. minutum en compĂ©tition avec 72 autres phĂ©notypes de phytoplancton a mis en Ă©vidence et hiĂ©rarchisĂ© les facteurs de contrĂŽle dâA. minutum. Ce dernier est contrĂŽlĂ© dâabord par la tempĂ©rature puis par les phosphates et enfin par les nitrates en Ă©tĂ©. Ce modĂšle adimensionnel simule les 10 annĂ©es mesurĂ©es et reproduit la variabilitĂ© saisonniĂšre et interannuelle dâA. minutum et de lâensemble de la communautĂ© phytoplanctonique mais sous-estime les concentrations de phosphate en Ă©tĂ© et donc les abondances du microphytoplancton, fortement limitĂ©es par les phosphates. Ce biais rĂ©duit sa capacitĂ© Ă simuler des scĂ©narios de rĂ©duction des apports en azote et phosphore, le phosphore Ă©tant largement plus limitant que lâazote. Il met nĂ©anmoins en Ă©vidence le fort dĂ©sĂ©quilibre trophique existant dans les milieux du fond de la rade de Brest oĂč les apports excessifs dâazote par les fleuves Mignonne et Aulne (et les autres aussi) provoquent des rapports azote/phosphore extrĂȘmement Ă©levĂ©s. Plusieurs pistes dâĂ©volution du modĂšle ont Ă©tĂ© testĂ©es comme la prise en compte des kystes (phase de dormance dâA. minutum et dâautres espĂšces), la mixotrophie (capacitĂ© Ă assimiler de la matiĂšre organique en plus de la photosynthĂšse) ou lâapport de cellules venant de la rade. Ces travaux nâont pas amĂ©liorĂ© le modĂšle et il est ainsi possible dâaffirmer que le bloom dâA. minutum est essentiellement liĂ© Ă sa capacitĂ© photosynthĂ©tique et de dĂ©veloppement local. Lâextension du modĂšle Ă lâensemble de la rade est en cours mais compliquĂ©e du fait de la gestion des frontiĂšres ouvertes avec la Mer dâIroise ce qui suppose plus dâinformations sur les 72 phĂ©notypes simulĂ©s. La comparaison du suivi de la Pointe du ChĂąteau avec les suivis existant en rade, centre Rade (LanvĂ©oc) et entrĂ©e de la rade (Ste Anne) montre lâaspect particulier de lâestuaire de Daoulas avec un dĂ©veloppement local et des abondances de nanophytoplancton, picophytoplancton et A. minutum bien supĂ©rieures au centre et entrĂ©e de la rade. Enfin, un systĂšme dâalerte est testĂ© sur les 12 annĂ©es, basĂ© sur le suivi journalier des dĂ©bits, tempĂ©rature et coefficient de marĂ©e. Il est une ouverture vers un systĂšme plus robuste Ă perfectionner et une mise en place opĂ©rationnelle possible
Recommended from our members
CoreâShell Nanorods as Ultraviolet Light-Emitting Diodes
Existing barriers to efficient deep ultraviolet (UV) light-emitting diodes (LEDs) may be reduced or overcome by moving away from conventional planar growth and toward three-dimensional nanostructuring. Nanorods have the potential for enhanced doping, reduced dislocation densities, improved light extraction efficiency, and quantum wells free from the quantum-confined Stark effect. Here, we demonstrate a hybrid top-down/bottom-up approach to creating highly uniform AlGaN coreâshell nanorods on sapphire repeatable on wafer scales. Our GaN-free design avoids self-absorption of the quantum well emission while preserving electrical functionality. The effective junctions formed by doping of both the n-type cores and p-type caps were studied using nanoprobing experiments, where we find low turn-on voltages, strongly rectifying behaviors and significant electron-beam-induced currents. Time-resolved cathodoluminescence measurements find short carrier liftetimes consistent with reduced polarization fields. Our results show nanostructuring to be a promising route to deep-UV-emitting LEDs, achievable using commercially compatible methods
- âŠ