Environmental controls of benthic nitrogen cycling in Lake Lugano South Basin, Switzerland – Pathways, rates, isotopic signatures and microbial communities

Nitrogen (N) is a key constituent of biomolecules required by all living organisms so understanding of its fluxes and in situ environmental availability is of crucial importance. In aquatic ecosystems, N availability regulates primary production and, to an extent, mass and energy transfer between trophic levels. Naturally, the vast reservoir of atmospheric N2 is only available to highly specialized diazotrophic microbes, but development and broad implementation of the Haber–Bosch process produces 450 million tons of nitrogen fertilizer per year from the N2 in the atmosphere, thereby changing the global N cycle entirely. Excessive loadings of reactive N (i.e., NO3-, NH4+) from fertilizer overuse have dramatically disturbed Earth ecosystems and inland waters in particular. One of the immediate consequences of P and N pollution in lakes and in the ocean is excessive biomass production, which supplies large amounts of highly labile organic matter to the sediments. Subsequent microbial degradation of this surplus organic matter quickly reduced the oxygen (O2) availability leading to proliferation of hypoxia and anoxia in bottom waters. Anaerobic respiration by microorganisms can remove significant quantities of reactive N from the system, specifically in the sediments where rates of microbial N processing are highest. Anaerobic denitrification and ammonium oxidation (anammox), which convert fixed N to N2, are globally the most important sinks for reactive N. In contrast, anaerobic dissimilatory nitrate reduction to ammonium (DNRA) hampers the removal of nitrogen and instead leads to recycling of nutrients (e.g. NH4+) in the water column. The relative partitioning between N-removal and its recycling plays a critical role in modulating eutrophication and is highly relevant for regulating the N budget of lakes and the ocean. However, our current understanding of the nitrogen cycling in lacustrine sediments, and in particular the exact biogeochemical controls on the relative partitioning between these N-transformation processes remains limited. Recent discovery of new N-transforming microorganisms with previously unknown metabolisms and unexpected links with other biogeochemical cycling (e.g. iron, manganese, sulfur and methane) implies that despite, decades of research, aquatic nitrogen cycling still hides mysteries. Lake Lugano (South Basin) is a monomictic eutrophic system, and thus an excellent model system to disentangle the relative importance of numerous microbial redox-driven transformations and identify their environmental controls. The main goal of my PhD project was to quantify the different benthic N-transformation processes and understand the potential environmental controls on their relative contribution to N reduction, and associated NO3- isotopic signatures. In addition, we investigated the microbial community’s structure and its seasonal dynamics at the surface sediments. The results highlight the overall importance of the biogeochemical controls O2, sediment reactivity, Fe2+ and H2S on the partitioning between N-loss and N-recycling, as well as on N isotopic signatures associated with NO3- reduction. Denitrification was the main anaerobic N-transformation processes in the sediments. The relative contribution of DNRA to total NO3- reduction varied from 31 to 52% depending on the season. In contrast, anammox contributed only about 1%. We demonstrated the major importance of oxygenation in controlling the fate of N in incubation experiments using natural sediments subject to fluctuating oxygen concentrations. Denitrification was favored over DNRA at relatively low oxygen concentrations (≤ 1 µM O2). In contrast N-processing via DNRA was prevalent at higher O2 levels. The O2 penetration depth was found to control the NO3- isotopic signatures in overlying water, through effects on nitrification (aerobic oxidation of NH4+ to NO3-) in particular. Finally, we showed that the availability of Fe2+ and H2S regulated the balance between denitrification and DNRA. Generally, at low Fe2+ (≤ 250 µM) and free H2S (≤ 80 µM) levels, denitrification was favored over DNRA, while DNRA was stimulated when Fe2+ concentration exceeded 700 µM. In contrast, Mn2+ did not play an important role in regulating the fate of benthic N. Among bacterial functional groups, only sulfate-reducing, sulfur-oxidizing and methanotrophic bacteria were affected by seasonally changing redox conditions at the sediment-water interface. The annual water-column turnover and subsequent oxygenation of bottom waters likely decreases Fe2+ and H2S availability in surface sediments, which may enhance NO3- removal to N2 at the oxic-anoxic interface layer. On the other hand, DNRA is less O2 sensitive than denitrification, and water-column mixing may enhance NH4+ release from the sediments. Therefore, the experimental results suggest the importance of fluctuating environmental conditions in regulating the partitioning between N-loss and N-recycling in freshwater sediments, however, it remains difficult to predict how these environmental changes act together to possibly shift the balance between the different N-cycling processes and to regulate the overall fixed N-elimination rate in lake sediments

PRISE EN COMPTE DES DISCONTINUITES DANS L'ELABORATION D'UN MODELE MECANIQUE DE MASSIF ROCHEUX. APPLICATION AU CREUSEMENT DE L'ECLUSE A BATEAUX DU BARRAGE DES TROIS GORGES (CHINE)

International audienceCet article est relatif à l'analyse de la stabilité et à l'évaluation des déformations à long terme des parois de l'écluse à bateaux du barrage des Trois Gorges en Chine. Dans un premier temps, une étude détaillée de stabilité a été réalisée avec le logiciel DEGRÉS (EMP-Centre de Géosciences) en prenant en compte les différentes caractéristiques géométriques et géologiques du massif rocheux et ses paramètres géomécaniques et hydrogéologiques. Les volumes potentiellement instables et les coefficients de sécurité correspondants ont ainsi pu être calculés conduisant à des recommandations sur le drainage et les renforcements mécaniques. Dans un second temps, une méthodologie spécifique a été mise en œuvre pour analyser le comportement mécanique du massif rocheux en réponse à l'excavation, et surtout évaluer les déplacements à long terme plusieurs années après la fin de l'excavation. Elle est basée sur la comparaison de résultats de calculs obtenus avec le logiciel FLAC (Itasca) et de données d'instrumentation obtenues alors que les travaux d'excavation de l'écluse à bateaux permanente progressaient. Plusieurs modèles de comportement, relevant en partie des techniques d'homogénéisation, mais intégrant les éléments structuraux majeurs ont ainsi été progressivement mis au point et confrontés aux données de l'instrumentation. Par ailleurs, la référence à des travaux de même nature précédemment réalisés dans le même massif (pour une écluse à bateaux provisoire) a permis de disposer de données relatives à des comportements fonction du temps, sur quelques années, et de caler des paramètres de viscosité. En conséquence, le modèle élaboré a permis de simuler numériquement l'évolution au cours du temps des déformations à long terme de l'écluse à bateaux permanente, ouvrage de près de 160 m de profondeur dans sa section la plus profonde

Debris flow hazards due to land use change above source areas in torrent catchments. The case study of Les Arcs (Savoie, France)

For a few decades, land use has changed due to developments in mountainous regions and this has resulted in new pressures on the environment. Consequently, slope instabilities could be a physical expression of such imbalance. Since the 1960s, debris flows events have occurred with an increasing frequency on Les Arcs catchment as it never happened before. At the same time, a large skiing area has been expending on the upper slopes. The study of climatic series shows that rainfall events linked to debris flow triggering were not especially intense compared to the more extreme precipitations recorded in the area for the past middle century. This observation suggests that additional factors have taken part in the debris flow triggering for the last fifty years. Following this logic, the space-time study of land use has underlined the role of winter sport resort expansion on processes such as runoff and erosion affecting torrent banks and beds, directly at the origin of debris flow generation. A complementary analysis of effects on hydrology, supported by a hydrological modelling (PCRaster Software) has been carried out as well. According to modelling results, the land use conversion is responsible for a change of annual water balance resulting in a significant increase of torrent water flow. Particularly, these effects are emphasised by the localization of converted surfaces (roads, buildings, car parks, ski runs, sport facilities...) in the catchment recharge areas above steep slopes of torrent channels, where materials are liable to be mobilized. Indeed at this interface, during rainfall events the water flow and especially the peak flow are more intense than in the past, due to water rerouting and concentrating that may activate erosive processes above debris flow source areas. At the catchment scale, the increasing number of debris flow events seems to be the answer to this change

Tunnels anciens en contexte de versant instable - Mécanismes d'instabilités et pathologies des ouvrages - Le cas du tunnel de l'Encombrouze (France).

sous presseNational audienceLes rétro-analyses de tunnels anciens en contexte de versants instables ont conduit à considérer différentes situations de tunnels entrant dans un versant : tunnel transversal au versant, oblique par rapport à celui-ci, ou le longeant sous une faible couverture. Les pathologies identifiées dans la structure de l'ouvrage varient en fonction de ces situations. Cette recherche s'intéresse à différents mécanismes d'instabilités de versant, particulièrement aux processus de fluage ainsi qu'aux désordres affectant la structure de tunnels traversant ces versants. L'analyse de la Zone d'Influence Géotechnique (ZIG) de ces ouvrages en situation de versant est un point important de cette recherche. L'étude de cas présenté correspond au tunnel ferroviaire de l'Encombrouze situé au niveau de la demi-fenêtre de l'Argentière, échancrant un anticlinal de nappes, au Nord de l'Argentière-la-Bessée (05). Cet ouvrage ancien, maçonné, est sub-parallèle au versant et situé sous une faible couverture, situation commune de nombreux ouvrages anciens lorsque les méthodes de creusement ne permettaient pas de s'enfoncer profondément dans le massif. Le contexte géologique et structural, ainsi que l'histoire géomorphologique régionale sont bien caractérisés. Ils influencent fortement le comportement local du versant ainsi que celui de l'ouvrage en son sein. Après avoir présenté l'ouvrage et ses pathologies, les différents contextes géologique, géomorphologique, hydrogéologique et sismique sont abordés dans le but de mettre en évidence leurs influences relatives sur la cinétique des mouvements du versant. Plusieurs sections du tunnel sont considérées et les pathologies associées présentées. Celles-ci, hétérogènes le long du linéaire de l'ouvrage, évolutives avec des cinétiques différentes, ne peuvent être le seul résultat du vieillissement de la structure. Elles rendent compte aussi des interactions versant instable/tunnel. Enfin, cette recherche conclura sur les mécanismes prépondérants considérés comme moteurs principaux des instabilités locales, responsables des pathologies observées dans la structure de l'ouvrage

Synthesis and Antileishmanial Activity of 1,2,4,5-Tetraoxanes against Leishmania donovani

A chemically diverse range of novel tetraoxanes was synthesized and evaluated in vitro against intramacrophage amastigote forms of Leishmania donovani. All 15 tested tetraoxanes displayed activity, with IC50 values ranging from 2 to 45 µm. The most active tetraoxane, compound LC140, exhibited an IC50 value of 2.52 ± 0.65 µm on L. donovani intramacrophage amastigotes, with a selectivity index of 13.5. This compound reduced the liver parasite burden of L. donovani-infected mice by 37% after an intraperitoneal treatment at 10 mg/kg/day for five consecutive days, whereas miltefosine, an antileishmanial drug in use, reduced it by 66%. These results provide a relevant basis for the development of further tetraoxanes as effective, safe, and cheap drugs against leishmaniasis.This research was funded by Fundação para a Ciência e a Tecnologia (FCT), and FEDER/COMPETE 2020-UE, through projects UID/Multi/04326/2019 (Centre of Marine Sciences-CCMAR) and PTDC/MAR-BIO/4132/2014.info:eu-repo/semantics/publishedVersio

Analyse de l'influence du creusement d'un tunnel au sein d'un versant instable subissant un mouvement gravitaire profond

National audienceLes rétro-analyses de tunnels anciens en contexte de versants instables ont conduit à considérer différentes situations de tunnels entrant dans un versant : tunnel transversal au versant, tunnel oblique par rapport à celui-ci, ou tunnel longeant le versant sous une faible couverture. Les pathologies identifiées dans la structure des ouvrages varient en fonction de ces situations. Cette recherche s'intéresse aux différents mécanismes d'instabilités de versant, particulièrement aux processus de fluage ainsi qu'aux désordres affectant la structure de tunnels traversant ces versants en les longeant. L'analyse de la Zone d'Influence Géotechnique (ZIG) de ces ouvrages en situation de versant est un point important de cette recherche. Au travers de simulations numériques, différents processus relatifs au vieillissement et à l'endommagement des structures des ouvrages ont été pris en compte. Il est possible de distinguer d'une part les facteurs associés aux conditions géologiques et géomorphologiques du versant et leurs évolutions dans le temps et d'autre part les facteurs correspondant aux méthodes de creusement et de construction du tunnel. L'influence des premiers facteurs sur la cinétique des mouvements et l'apparition des pathologies de l'ouvrage peut être mise en évidence en étudiant différents contextes géologiques, géomorphologiques, hydrogéologiques et sismiques. Cette étude s'intéresse à l'influence du fluage au sein du terrain encaissant comme critère aggravant les pathologies de l'ouvrage. Le creusement d'un tunnel favorise la déstabilisation du versant en provoquant un déconfinement plus ou moins important du massif encaissant suivant sa nature. Le fluage entraîne une augmentation des contraintes dans la structure et la convergence des parements au cours du temps. Au sein d'un versant, sujet au fluage et avec un tunnel proche de la surface, l'influence du fluage est mise en évidence par rapport à un modèle de base ne prenant pas en compte ce phénomène. Le fluage est un des moteurs de la déstabilisation du versant, conduisant à la localisation de bandes de cisaillement. Par ailleurs il influence le développement de pathologies dans la structure de l'ouvrage. En conclusion, des enseignements sur les méthodologies d'analyse de ces ouvrages et leur surveillance sont tirés

A Tool to Assist in the Analysis of Gaze Patterns in Upper Limb Prosthetic Use

Gaze tracking, where the point of regard of a subject is mapped onto the image of the scene the subject sees, can be employed to study the visual attention of the users of prosthetic hands. It can show whether the user is pays greater attention to the actions of their prosthetic hand as they use it to perform manipulation tasks, compared with the general population. Conventional analysis of the video data requires a human operator to identify the key areas of interest in every frame of the video data. Computer vision techniques can assist with this process, but a fully automatic systems requires large training sets. Prosthetic investigations tend to be limited in numbers. However, if the assessment task is well controlled, it is possible to make a much simpler system that uses initial input from an operator to identify the areas of interest and then the computer tracks the objects throughout the task. The tool described here, employs colour separation and edge detection on images of the visual field to identify the objects to be tracked. To simplify the computer's task further, this test uses the Southampton Hand Assessment Procedure (SHAP), to define the activity spatially and temporarily, reducing the search space for the computer. The work reported here is the development a software tool capable of identifying and tracking the Points of Regard and Areas of Interest, throughout an activity with minimum human operator input. Gaze was successfully tracked for fourteen unimpaired subjects, which was compared with the gaze of four users of myoelectric hands. The SHAP cutting task is described and the differences in attention observed with a greater number of shorter fixations by the prosthesis users compared to unimpaired subjects. There was less looking ahead to the next phase of the task by the prosthesis users

Evaluation of topography site effect in slope stability under dynamic loading

International audienceThe slope topography site effect is a phenomenon in which the seismic ground motion is amplified at the crest of the slope. This effect can damage structures and can even cause slope instabilities. The aim of this study is to explore the impact of slope geomorphology parameters on topographic site effects. A dimensionless factor, the ratio of the slope height to the seismic wavelength is identified as a critical parameter. Numerical simulations resulting in the seismic response of a uniform slope in an elastic material to excitation of vertically propagating SV waves, allowed defining the effects of these parameters to amplification factors and extension of the affected zones. In civil engineering, the knowledge of zones which will experience amplified excitation is important and essential for the structural design. In particular, the vicinity of the crest is a zone frequently affected by strong amplifications, and in some cases, earthquake-induced landslides may occur. For this reason, graphs derived from the results of numerous numerical analyses, can be useful to predicting the maximum amplification factors, the area as well as the dimension of the amplified zone in the vicinity of the crest