Long term nitrogen budget modelling in a small agricultural watershed: hydrological control assessment of nitrogen losses with semi-distributed (SWAT) and distributed (TNT2) models

Nitrogen exports in catchments are known to be greatly variable because nitrogen cycle in watershed is controlled by different factors such as landuse, farm management practices, climate, soil type and hydrological setting. Our aim is to study the relative importance of the processes controlling nitrogen losses at catchment scale in the long term using a modelling approach constrained by a long term record of observations. The study area is a catchment of 330 ha with 95 % of intensive agriculture in a hilly shallow soil context, in the south west of France. Historical field rotation and nitrogen river load data have been collected for a 20 year period. Two process-based and spatially distributed models have been chosen to simulate nitrogen transfer and transformation in the whole catchment. The first one is the fully distributed TNT2 model, developed and validated in a different context (farming systems in north-western France). The second one is the widely used, semi-distributed SWAT model, used and recognizedto be realistic in many studies on nitrogen transfer in river. This comparative modelling approach was used to evaluate the effect of different modelling approaches on the identification of controlling factors, and the ability of both models to simulate alternative scenarios. The discharge, especially during storm flow, is well simulated by the curve number approach and the semi-distributed hydrological parameter description used SWAT, while the Topmodel-derived approach used in TNT2 tends to underestimate some peak discharges. Nitrogen dynamic simulations are considered to be acceptable for both models for a long time period but the use of both models allows to exhibit their respective capacity and limits. TNT2 has higher potentiality to test the impact of complex agricultural scenarios because the description of management practices and the simulation of crops to management options is more detailed. It permits the assessment of spatial interactions and focussed spatial management, like the set up of grass or tree strips. SWAT can then be used to scale up change scenarios from TNT2 small catchment results to large catchments

Understanding nitrogen transfer dynamics in a small agricultural catchment: Comparison of a distributed (TNT2) and a semi distributed (SWAT) modeling approaches

The coupling of an hydrological and a crop model is an efficient approach to study the impact of the interactions between agricultural practices and catchment physical characteristics on stream water quality. We analyzed the consequences of using different modeling approaches of the processes controlling the nitrogen (N) dynamics in a small agricultural catchment monitored for 15 years. Two agro-hydrological models were applied: the fully distributed model TNT2 and the semi-distributed SWAT model. Using the same input dataset, the calibration process aimed at reproducing the same annual water and N balance in both models, to compare the spatial and temporal variability of the main N processes. The models simulated different seasonal cycles for soil N. The main processes involved were N mineralization and denitrification. TNT2 simulated marked seasonal variations with a net increase of mineralization in autumn, after a transient immobilization phase due to the burying of the straw with low C:N ratio. SWAT predicted a steady humus mineralization with an increase when straws are buried and a decrease afterwards. Denitrification was mainly occuring in autumn in TNT2 because of the dynamics of N availability in soil and of the climatic and hydrological conditions. SWAT predicts denitrification in winter, when mineral N is available in soil layers. The spatial distribution of these two processes was different as well: less denitrification in bottom land and close to ditches in TNT2, as a result of N transfer dynamics. Both models simulate correctly global trend and inter-annual variability of N losses in small agricultural catchment when a sufficient amount data is available for calibration. However, N processes and their spatial interactions are simulated very differently, in particular soil mineralization and denitrification. The use of such tools for prediction must be considered with care, unless a proper calibration and validation of the different N processes is carried out

Nanoscale electrical analyses of axial-junction GaAsP nanowires for solar cell applications

Axial p-n and p-i-n junctions in GaAs0.7P0.3 nanowires are demonstrated and analyzed using electron beam induced current microscopy. Organized self-catalyzed nanowire arrays are grown by molecular beam epitaxy on nanopatterned Si substrates. The nanowires are doped using Be and Si impurities to obtain p- and n-type conductivity, respectively. A method to determine the doping type by analyzing the induced current in the vicinity of a Schottky contact is proposed. It is demonstrated that for the applied growth conditions using Ga as a catalyst, Si doping induces an n-type conductivity contrary to the GaAs self-catalyzed nanowire case, where Si was reported to yield a p-type doping. Active axial nanowire p-n junctions having a homogeneous composition along the axis are synthesized and the carrier concentration and minority carrier diffusion lengths are measured. To the best of our knowledge, this is the first report of axial p-n junctions in self-catalyzed GaAsP nanowires

Quantum Confinement and Electronic Structure at the Surface of van der Waals Ferroelectric {\alpha}-In2_{2}Se3_{3}

Two-dimensional (2D) ferroelectric (FE) materials are promising compounds for next-generation nonvolatile memories, due to their low energy consumption and high endurance. Among them, {\alpha}-In$_{2}$Se$_{3}$ has drawn particular attention due to its in- and out-of-plane ferroelectricity, whose robustness has been demonstrated down to the monolayer limit. This is a relatively uncommon behavior since most bulk FE materials lose their ferroelectric character at the 2D limit due to depolarization field. Using angle resolved photoemission spectroscopy (ARPES), we unveil another unusual 2D phenomena appearing in 2H \alpha-In$_{2}$Se$_{3}$ single crystals, the occurrence of a highly metallic two-dimensional electron gas (2DEG) at the surface of vacuum-cleaved crystals. This 2DEG exhibits two confined states which correspond to an electron density of approximatively 10$^{13}$ electrons/cm$^{3}$, also confirmed by thermoelectric measurements. Combination of ARPES and density functional theory (DFT) calculations reveals a direct band gap of energy equal to 1.3 +/- 0.1 eV, with the bottom of the conduction band localized at the center of the Brillouin zone, just below the Fermi level. Such strong n-type doping further supports the quantum confinement of electrons and the formation of the 2DEG.Comment: 20 pages, 12 figure

Discutindo a educação ambiental no cotidiano escolar: desenvolvimento de projetos na escola formação inicial e continuada de professores

A presente pesquisa buscou discutir como a Educação Ambiental (EA) vem sendo trabalhada, no Ensino Fundamental e como os docentes desta escola compreendem e vem inserindo a EA no cotidiano escolar., em uma escola estadual do município de Tangará da Serra/MT, Brasil. Para tanto, realizou-se entrevistas com os professores que fazem parte de um projeto interdisciplinar de EA na escola pesquisada. Verificou-se que o projeto da escola não vem conseguindo alcançar os objetivos propostos por: desconhecimento do mesmo, pelos professores; formação deficiente dos professores, não entendimento da EA como processo de ensino-aprendizagem, falta de recursos didáticos, planejamento inadequado das atividades. A partir dessa constatação, procurou-se debater a impossibilidade de tratar do tema fora do trabalho interdisciplinar, bem como, e principalmente, a importância de um estudo mais aprofundado de EA, vinculando teoria e prática, tanto na formação docente, como em projetos escolares, a fim de fugir do tradicional vínculo “EA e ecologia, lixo e horta”.Facultad de Humanidades y Ciencias de la Educació

Les déstabilisations de flanc des volcans de l'Ile de La Réunion (Océan Indien): Mise en évidence, implications et origines

Composition du jury de thèse: Olivier Merle, Président, Université Blaise Pascal, Clermont II Christine Deplus, Examinateur, Institut de Physique du Globe de Paris Patrick Bachèlery, Rapporteur, Université de La Réunion Bruno Savoye, Rapporteur, IFREMER -- La version de la thèse déposée en ligne est une version basse résolution. Pour une version haute résolution, me contacter à: [email protected] joint study of the emerged and submerged parts of Reunion Island (Indian Ocean), based on the evaluation of marine multibeam data collected these last 20 years and confronted with previous geological and geophysical works, demonstrates the considerable importance of flank landslide processes in the evolution of this volcanic oceanic system. Fifty or so mass-wasting events recurrently dismantled Piton des Neiges, Les Alizés, and Piton de La Fournaise volcanoes during the last 2 million years at least. They are multi-scale, primary or secondary, and of aerial, coastal or submarine origin. Most correspond to instantaneous and catastrophic phenomena of debris avalanche type. Their deposits are mainly accumulated at sea, within four gigantic topographic bulges named "Reliefs Sous-Marins", located to the east, north, west and south of the island. These fans are 20-30 km wide at the coastline and 100-150 km wide at their end, 70-80 km offshore. They were built gradually by the superimposition and/or the juxtaposition of products displaced during landslide episodes implying up to several hundreds of km3 of materials. A very small proportion is recognized on land, in Piton des Neiges central part or at its littoral edges, and constitutes the proximal facies of the deposits recognized offshore. The main structural features of Reunion sub-aerial morphology are interpreted as (1) relatively recent landslide scars, often remodelled by erosion and/or filled by subsequent volcanic activity, or (2) remnants of old debris avalanches amphitheatres whose border faults could have been reactivated by volcano-tectonics (caldera collapses, gravitational spreading, Piton des Neiges hypovolcanic complex subsidence,...) and/or during younger landslide events. These faults have probably guided the mass-wasting of the edifice by erosion, thus facilitating the digging of Piton des Neiges central depressions (the three Mafate, Salazie, Cilaos cirques and the Marsouins paleo-cirque) and of the main valleys of the island. The study of Mount Haddington volcano (James Ross Island, Antarctica) and analogue experiments show that the ductile deformation of low strength layers existing within shield volcanoes, and in particular of volcanoclastic deltas, made up mostly of debris avalanche deposits, is a key for the generation of rotational slides and subsequent debris avalanches. This model is privileged for Reunion volcanoes, considering a predominant role of gravitational processes in flank landslides triggering.L'étude conjointe des parties immergée et émergée de l'Ile de La Réunion (Océan Indien), basée sur la valorisation des données marines multifaisceaux acquises ces 20 dernières années et confrontée à l'ensemble des connaissances géologiques et géophysiques, démontre l'importance considérable des processus de déstabilisations de flanc dans l'évolution des édifices de ce système volcanique océanique. Au total, une cinquantaine d'événements multi-échelles, primaires ou secondaires, d'origine aérienne, côtière ou sous-marine, ont démantelé de façon récurrente les volcans du Piton des Neiges, des Alizés et du Piton de La Fournaise au cours des 2 derniers millions d'années au moins. La plupart correspondent à des phénomènes instantanés et catastrophiques de type avalanche de débris. Leurs dépôts sont principalement accumulés en mer, au sein de quatre gigantesques excroissances topographiques, les Reliefs Sous-Marins, localisés à l'est, au nord, à l'ouest et au sud de l'île. Ces éperons triangulaires, de 20-30 km de large au niveau de la côte et 100-150 km à leur extrémité, à 70-80 km du littoral, se sont construits progressivement par la superposition et la juxtaposition des produits déplacés dans des épisodes de déstabilisation pouvant impliquer plusieurs centaines de km3 de matériaux. Une très faible proportion est retrouvée à terre, au cœur et en bordure littorale du massif du Piton des Neiges et constitue le faciès proximal des dépôts immergés. Les principales structures de la morphologie sub-aérienne de l'île sont interprétées comme (1) les zones sources de déstabilisations relativement récentes, souvent remodelées par l'érosion et/ou comblées par l'activité volcanique ultérieure, ou (2) les traces rémanentes d'amphithéâtres d'avalanches de débris anciens dont les failles bordières ont pu être réactivées dans des processus volcano-tectoniques (effondrements caldériques, étalement gravitaire, subsidence du complexe hypovolcanique du Piton des Neiges,...) et/ou lors d'épisodes ultérieurs de déstabilisation. Ces failles ont probablement guidé le démantèlement par érosion des massifs et ainsi facilité le creusement des dépressions centrales du Piton des Neiges (les trois cirques de Mafate, Salazie, Cilaos et le paléo-cirque des Marsouins) et des principales vallées de l'île. L'étude du volcan Mount Haddington (Ile de James Ross, Antarctique) et les expériences analogiques montrent que la déformation ductile d'horizons de faible résistance inclus dans la structure des volcans boucliers, et en particulier de deltas volcanoclastiques essentiellement constitués de dépôts d'avalanches de débris, est un élément clé dans la génération de glissements rotationnels et d'avalanches de débris ultérieures. Ce modèle est privilégié à La Réunion, en considérant un rôle prépondérant des processus gravitaires dans le déclenchement des déstabilisations des volcans de l'île

Growth and collapse of the Reunion Island volcanoes

International audienceThis work presents the first exhaustive study of the entire surface of the Reunion Island volcanic system. The focus is on the submarine part, for which a compilation of all multibeam data collected during the last 20 years has been made. Different types of submarine features have been identified: a coastal shelf, debris avalanches and sedimentary deposits, erosion canyons, volcanic constructions near the coast, and seamounts offshore. Criteria have been defined to differentiate the types of surfaces and to establish their relative chronology where possible. Debris avalanche deposits are by far the most extensive and voluminous formations in the submarine domain. They have built four huge Submarine Bulges to the east, north, west, and south of the island. They form fans 20–30 km wide at the coastline and 100–150 km wide at their ends, 70–80 km offshore. They were built gradually by the superimposition and/or juxtaposition of products moved during landslide episodes, involving up to several hundred cubic kilometers of material. About 50 individual events deposits can be recognized at the surface. The landslides have recurrently dismantled Piton des Neiges, Les Alizés, and Piton de La Fournaise volcanoes since 2 Ma. About one third are interpreted as secondary landslides, affecting previously emplaced debris avalanche deposits. On land, landslide deposits are observed in the extensively eroded central area of Piton des Neiges and in its coastal areas. Analysis of the present-day topography and of geology allows us to identify presumed faults and scars of previous large landslides. The Submarine Bulges are dissected and bound by canyons up to 200 m deep and 40 km long, filled with coarse-grained sediments, and generally connected to streams onshore. A large zone of sedimentary accumulation exists to the north–east of the island. It covers a zone 20 km in width, extending up to 15 km offshore. Volcanic constructions are observed near the coast on both Piton des Neiges and Piton de la Fournaise volcanoes and are continuations of subaerial structures. Individual seamounts are present on the submarine flanks and the surrounding ocean floor. A few seem to be young volcanoes, but the majority are probably old, eroded seamounts. This study suggests a larger scale and frequency of mass-wasting events on Reunion Island compared to similar islands. The virtual absence of downward flexure of the lithosphere beneath the island probably contributes to this feature. The increased number of known flank–failure events has to be taken into consideration when assessing hazards from future landslides, in particular, the probability of landslide-generated tsunamis

Comparison of global geomagnetic field models and evaluation using marine datasets in the north-eastern Atlantic Ocean and western Mediterranean Sea

Abstract Many models describing the Earth’s magnetic field exist and are maintained by international research organizations. However, no clear general overview of the cross-compared quality of these models is available. An evaluation of the internal component and of the anomaly field as estimated by a selection of nine geomagnetic models with global coverage is presented here. Anomaly field models are also compared with an external, independently processed marine dataset extracted from Shom’s (the French Hydrographic and Oceanographic Service) geophysical database. The comparative study shows that internal geomagnetic fields computed outside the provisional domain, up to degrees 12 or 13 of spherical harmonics (SH), can be considered as equivalent. Relative amplitude differences with the World Magnetic Model 2015 (WMM2015) and the 12th generation of the International Geomagnetic Reference Field (IGRF-12) taken as references are lower than 10 nT. For an extent reduced to the north-eastern Atlantic Ocean and western Mediterranean Sea, anomaly field models up to SH degree 720 and the 3rd version of the Earth Magnetic Anomaly Grid (EMAG2v3) at the equivalent 0.5° resolution are the closest models to the filtered marine data. However, they are significant spatial discrepancies and standard deviations of differences between models and data are about 65 nT. The 3-arc-minute World Digital Magnetic Anomaly Map (WDMAM) best reflects the unfiltered marine data, but with significant standard deviations of about 70 nT. Results demonstrate that any model can be used with insignificant errors to compute raw anomalies from total field measurements by removing the internal component of the Earth’s magnetic field. In addition, they suggest that the priority should be given to WDMAM for levelling and evaluating marine datasets and for computing enhanced high-resolution regional magnetic maps