High denitrification potential but low nitrous oxide emission in a constructed wetland treating nitrate-polluted agricultural run-off

Acknowledgements The study was conducted within the framework of several scientific projects: “Efficacité des Zones Tampons” by OFB (French Office for Biodiversity, and technical group “Zones Tampons “), and HydroGES (financed by the Agency for the Environment and Mastery of Energy, ADEME). The travel was supported by two French–Estonian Parrot RTD projects “Ecological engineering for nutrient control in rural catchments” and “Process-based approach and enhanced technologies of treatment wetlands” (2014–2016). The PIREN-Seine programme and the Fédération Ile-de-France de Recherche pour l'Environnement (FIRE) are also acknowledged for their support. The authors also thank AQUI'Brie association for their support and stakeholders' involvement. This study was also supported by the Estonian Research Council (grants IUT2 16, PRG352 and MOBERC20) and by the EU through the European Regional Development Fund (Centres of Excellence ENVIRON and EcolChange, and MOBTP101 returning researcher grant by the Mobilitas Pluss programme).Peer reviewedPostprin

Variação temporal da descarga sólida em suspensão e identificação de minerais a partir de aperfeiçoamento de método de amostragem automática no Córrego Riacho Fundo, Brasília, Distrito Federal

Este estudo buscou contribuir com informações sedimentométricas sobre o Córrego Riacho Fundo (CRF), afluente do Lago Paranoá, Brasília, Distrito Federal, historicamente o principal transportador de sedimentos da bacia. Utilizamos método acústico com o equipamento River Surveyour M9 da Sontek, para levantamento de vazão, e amostrador automático ISCO 6712, para amostragem de água e sedimentos, com coleta em ponto fixo em relação ao leito do córrego e coleta com adaptação para amostragem a 40 cm de profundidade da superfície d’água. A mineralogia de uma seleção de amostras de sedimentos coletados foi determinada por difratometria de raios X. Além disso, a turbidez das águas foi medida por meio de sonda multiparamétrica flutuando a 40 cm da superfície. Os resultados obtidos permitiram elaborar uma nova curva-chave do CRF, com vazões medidas em cotas nunca registradas. O novo método de coleta implantado possibilitou obter informações em cotas que não haviam sido amostradas antes e permitiu também diminuir a dispersão dos dados entre concentração e cota. Assim, comparando os dois métodos, com o método fixo obteve-se R2 = 0,28, e com o método com flutuabilidade, R2 = 0,45. A adaptação com flutuação também favoreceu uma boa correlação entre turbidez e concentração, apresentando R2 = 0,92. A análise de histerese mostrou que a maioria dos eventos ocorre no sentido anti-horário. A quantidade total de sedimentos suspensos por evento de chuva variou entre 43 e 1.258 t com o método adaptado, e entre 47 e 10.142 t com o método de coleta fixa. A mineralogia dos sedimentos é composta por saponita, vermiculita, ilita, muscovita, caolinita, gibbsita, diásporo, quartzo, rutilo e hematita. O uso do amostrador automático permitiu identificar maior número de minerais quando comparados outros estudos na região.This work aimed to contribute in the sedimentometric study of the Riacho Fundo stream, affluent of Lake Paranoá, Brasília, Federal District, and historically the main sediments exporter for the entire basin. For this purpose, the flow was measured by the acoustic method with the Sontek River Surveyour M9 equipment and an automatic sampler ISCO 6712 was used for water and sediment sampling, with collection at a fixed point and varying according to the height, in a water depth of 40 cm. The mineralogy of chosen sediment samples was assessed by X-ray diffraction. Also, simultaneous monitoring of the turbidity was carried out, with a floating multiparameter probe, likewise. The results are useful data for the location, since there is lack of data for reservoir sedimentation planning. Furthermore, the improved sampling method (floating probe) showed a better coefficient of determination (R2 = 0,45) than the fixed sampling method (R2 = 0,28). Thus, a good correlation could be reached between turbidity and concentration (R2 = 0.92). Hysteresis was generally counterclockwise. The use of the automatic sampler allowed the identification of minerals in the suspended sediments, which are not identified in other studies in the region.

A map and a database for flint-bearing formations in Southern France: A tool for Petroarchaeology

Une carte des principales formations à silex du sud de la France est en cours de réalisation. Elle propose, à tous les préhistoriens, une base nécessaire au développement d’études interrégionales sur la circulation des silex. Elle est le fruit d’une collaboration entre des acteurs impliqués dans la problématique de caractérisation de la provenance des silex. Elle regroupe les résultats de leurs prospections systématiques ou ciblées dans six régions (Aquitaine, Auvergne, Languedoc-Roussillon, Midi-Pyrénées, Provence-Alpes-Côte-d’Azur, Rhône-Alpes). Elle intègre, en plus, le dépouillement d’un grand nombre de documents : i) les principaux articles et thèses traitant des formations à silex du sud de la France ; ii) plus de 200 fiches issues de la base de données du sous-sol BSS du BRGM, qui permettent de visualiser des logs ou des documents scannés ; iii) 529 cartes géologiques à 1/50 000 et leurs notices. La carte est organisée en trois couches de données superposables : une carte des affleurements ou gîtes primaires, une carte des altérites et des formations superficielles remaniées et une carte des formations alluviales. La carte existera dans deux versions numériques aisément actualisables : une version dans un format PDF et une version sous la forme d’un SIG. C’est l’ensemble de la formation contenant le ou les même(s) type(s) de silex qui est prise en compte, le terme de formation désignant un terrain possédant des caractères communs et qui constitue un ensemble cartographiable. Chacune des formations recensées fait l’objet d’une notice simplifiée qui décrit l’encaissant et - le ou les - type(s) de silex présent(s). Ces notices descriptives et explicatives contiennent des photos à toutes les échelles (de la formation à l’échelle microscopique). Des références bibliographiques géologiques et archéologiques complèteront chaque notice. La version définitive de ces notices constituera un atlas. Les archéologues et géologues disposeront ainsi de fiches descriptives pour chaque type de silex et son encaissant. Elles serviront aux diagnoses analytiques (structures, textures et compositions minéralogiques).A map of the main flint bearing formations in the South of France is under construction. It will provide an essential basis to develop interregional studies about flint procurements and travels. It results from collaboration between actors involved in topic flint sourcing. It includes results of their systematic surveys and studies in six regions (Aquitaine, Auvergne, Languedoc-Roussillon, Midi-Pyrenees, Provence-Alpes - Côte d’Azur, Rhône-Alpes). Moreover, it includes a large number of associated data : i) The main papers and those dealing with flint bearing formations of southern France, ii) more than 200 records from the under-soil database BSS BRGM, which give access to logs or scanned documents iii) 529 geological maps at 1/50 000 and their leaflets. The map is organized in three superimposed layers : a map of outcrops or primary deposits, a map of surficial weathered formation and a revised map of alluvial formations. The map is available in two versions which are easily updatable : a PDF version and an interactive GIS version. In this document, every formation containing the same type (s) (s) of flint is taken into account and forms a mappable entity. Every listed formation is linked to a text which describes the parent rock and/or the type(s) of flint(s). These records contain descriptive and explanatory pictures at different scale (naked eye to microscopic scale). Geological and archaeological references complement every record. The final version will constitute an atlas. Archaeologists and geologists will find description sheets of every type of flint and bearing rock. They will help for analytical diagnoses (structure, texture and mineralogical composition)

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Summary Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung’s disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung’s disease) from 264 hospitals (89 in high-income countries, 166 in middleincome countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030

Fontes e dinâmica do cromo nos solos ultramáficos de Niquelândia, Brasil

Tese (doutorado)—Universidade de Brasília/Université Paris-Sud, Faculte des Sciences D'Orsay, 2008.RÉSUMÉLa disponibilité et la mobilité du chrome ont été étudiées sur quatre sols développés sur le complexe ultramafique de Niquelândia (état du Goiàs, Brésil), à l’aide d’expérimentations en laboratoire et in situ. La teneur totale en chrome de ces sols est particulièrement élevée, et sa compartimentation évolue avec la position dans la toposéquence et la profondeur du sol. La majorité du chrome est associée aux oxydes de fer bien cristallisés qui constituent la matrice solide des sols. Il est également présent au sein des chromites, et de phases mineurs silicatées. La quantité de chrome extractible est importante et majoritairement sous sa forme toxique (CrVI). Cette fraction atteint 1000 mg kg-1 soit plus de 10% du chrome total; ces teneurs sont dix fois supérieures à celles observées en Nouvelle-Calédonie. Des cinétiques d’échange isotopique du chromate ont confirmé la labilité de cette fraction. Elles ont également mis en évidence une vitesse d’échange rapide entre les phases porteuses et la solution, ainsi qu’une capacité élevée de ces sols à maintenir une importante concentration de chromate en solution. L’ensemble des résultats indique que le Cr(VI) labile est désorbé depuis la fraction fine composée d’oxydes de fer qui contrôle ainsi sa disponibilité et sa mobilité. Les résultats suggèrent que le chromate labile est faiblement adsorbé aux phases porteuses. La disponibilité du chrome est très hétérogène à des échelles décimétrique et décamétrique. L’étude des eaux du sol et de surface à l’échelle du bassin versant a mis en évidence une mobilité importante du Cr(VI) et des concentrations en chromate supérieures aux teneurs considérées comme toxiques, suggérant un impact sur les organismes vivants du complexe et également les écosystèmes environnants. D’autre part, l’analyse des solutions du sol a confirmé la faible teneur en nutriments, le rapport défavorable Ca:Mg et la disponibilité de certains métaux (Cr, Ni) typiques de ces milieux. Ces trois caractéristiques sont souvent considérés comme responsable de la faible fertilité de ce type de sol et du particularisme de ces écosystèmes. Enfin, les résultats suggèrent que la disponibilité en Cr(VI) de ces sols résulte de leur capacité d’échange anionique et non d’oxydation du Cr(III). __________________________________________________________________________________ ABSTRACTChromium availability and mobility were studied on four soils developed on the complex ultramafic of Niquelândia (Goias state, Brazil), using laboratories and in situ experiments. Total chromium content is particularly high, and its partitioning evolves according to landscape position and depth. Chromium is mainly associated to well crystallized iron oxides, forming the soil matrix. However, extractable chromium is important, and mainly under the toxic form (CrVI). It reached 1,000 mg kg-1 (more than 10% of total chromium), those contents are ten times higher than those observed in New Caledonia. Results indicate that Cr (VI) in solution is released from the fine fraction composed by iron-oxides, which consequently control the Cr(VI) availability and mobility. Isotopic exchange kinetics of chromate has confirmed the exchange between the bearing phases and solution. They also highlighted a rapid exchange between the Cr-bearing phases and the solution, and the important Cr(VI) buffer capacity of these soils. They also suggest that the chromate is slightly adsorbed on iron-oxides. The chromate concentrations in soil solutions are important, higher than the usual hazardous contents. The chromate lability is very heterogeneous with the locality at a centimetric and metric scale. The soil solution and surface water study on the catchment area has highlighted an important Cr(VI) mobility at soil and complex scale, suggesting an impact on organisms of the complex and surrounding ecosystems. Moreover, the soil solutions analysis show the low nutrients content, the imbalance Ca:Mg and the metals (Cr, Ni) availability, often considered responsible to the low fertility of those soils and the specificity of ultramafic ecosystems. Finally, results suggest that the Cr(VI) availability of those soils results from their anionic exchange capacity and not from their capacity to oxidize Cr (III). ___________________________________________________________________________________ RESUMOOs solos ou as coberturas de alteração constituem um dos principais compartimentos dos ecossistemas continentais. Estes ecossistemas são situados na interface entre a litosfera, a atmosfera, a hidrosfera e a biosfera (Robert, 1996). O solo é, por sua vez, fonte e sistema acumulador de contaminantes, de origem geoquímica ou de atividades antrópicas. Numerosas reações de transformação, mobilização e de transferência de elementos químicos para as águas e as plantas, sob intervenção ou não dos organismos vivos, têm lugar dentro dos solos e contribuem assim, para considerá-los como «reatores biogeoquímicos» (Bourrelier et Berthelin, 1998). Como conseqüência, os solos têm um papel fundamental no funcionamento dos ciclos biogeoquímicos e sobre a qualidade da água subterrânea. Assim, os solos têm importância crucial na transferência de contaminantes para a cadeia trófica. Dada a capacidade limitada de acumulação, retenção e depuração de poluentes, os solos constituem um ambiente muito sensível à poluição, exigindo melhor conhecimento sobre eles com o objetivo de minimizar os impactos da poluição no espaço e no tempo (Bourrelier et Berthelin, 1998). Os elementos-traço (ET), dos quais o cromo faz parte, estão presentes naturalmente nas rochas magmáticas, sedimentares e metamórficas, por vezes, em concentrações importantes, como nas rochas ultramáficas. A alteração química destas rochas, portadoras naturais dos metais, conduz à liberação e à redistribuição de ET nos solos. Os processos de dissolução, precipitação, sorção e desorção são responsáveis pela dinâmica dos ET nos solos e consequentemente dos riscos ecotoxicológicos (Brown et al., 1999). Entretanto, não é somente a presença de ET que induz o impacto sobre o ecossistema, mas sua biodisponibilidade. Esta é condicionada pela mobilidade e interação dos ET com soluções e organismos vivos. A estabilidade geológica dos crátons das zonas intertropicais, assim como o clima quente e úmido favorecem a alteração das rochas e permitem o desenvolvimento de espessos mantos de alteração laterítica podendo atingir mais de cem metros de espessura (Pedro, 1968; Tardy, 1993). Estes mantos de alteração representam os importantes jazimentos metálicos, como nos ambientes ultramáficos (Ni, Co, Pt) e abrigam ecossistemas particulares. A extração mineral coloca em risco esses ecossistemas, como no caso de Niquelândia. Torna-se então fundamental conhecer melhor tais ecossistemas e seu funcionamento, para melhor conservar e protegê-los. A região de Niquelândia é uma área de estudo excepcional interessando ao «desenvolvimento da explotação mineira, preservação do meio natural e restauração ecológica». As rochas ultramáficas são rochas mantélicas que afloram sob condições tectônicas particulares. Os solos desenvolvidos sobre estas rochas são conhecidos por serem muito ricos em metais e mais particularmente em níquel e cromo. As características químicas particulares destes solos favorecem o desenvolvimento de ecossistemas específicos, fortemente endêmico, adaptados aos metais e à baixa fertilidade dos solos (Jaffre, 1980). Neste ambiente, o estudo do cromo e da dinâmica dos solos implica na abordagem dos diferentes compartimentos do solo, i.e. a matriz sólida, a solução e os organismos. No meio natural, o cromo está presente sob duas valências: o cromo trivalente [Cr(III)] e o cromo hexavalente [Cr(VI)]; este ultimo conhecido por sua forte toxidez e os problemas ambientais que acarreta (Barlett et James, 1996). Assim, o estudo dos solos do maciço ultramáfico de Niquelândia (Goiás, Brasil), nesta tese visa a: i) conhecer as fontes e compreender a variabilidade dos teores de cromo; ii) caracterizar a ocorrência do cromo, os mecanismos de fixação e as soluções do solo, iii) quantificar e caracterizar a biodisponibilidade e a mobilidade do cromo sobre água-soloplanta, a fim de avaliar os riscos potenciais de mobilização. Apos expor o estado da arte, apresentar a área de estudo e os métodos utilizados, este estudo se direciona para dois grandes eixos. O primeiro trata mais particularmente do compartimento sólido dos solos. No primeiro momento, foi feito o estudo mineralógico a fim de conhecer a natureza (composição química e mineralógica) e os principais processos pedológicos. A segunda parte apresenta os resultados do conjunto das investigações focadas na solução do solo. Com objetivo de quantificar e caracterizar o cromo lábil, diferentes abordagens foram utilizadas no estudo da disponibilidade e mobilidade do cromo nos solos. Por fim, a conclusão geral discute o conjunto dos resultados, propõe um modelo sobre a dinâmica do cromo na escala do solo e da topossequência e expõe os principais conhecimentos trazidos por este estudo sobre os processos que regem a mobilidade e a disponibilidade do cromo nos solos de Niquelândia

Using DET and DGT probes (ferrihydrite and titanium dioxide) to investigate arsenic concentrations in soil porewater of an arsenic-contaminated paddy field in Bangladesh

International audienceArsenic concentration in the pore water of paddy fields (C-soln) irrigated with arsenic-rich groundwater is a key parameter in arsenic uptake by rice. Pore water extracts from cores and in situ deployment of DET and DGT probes were used to measure the arsenic concentration in the porewater. Ferrihydrite (Fe) and titaniumdioxide (Ti) were used as DGT binding agents. Six sampling events during different growing stages of the rice, inducing different biogeochemical conditions, were performed in one rice field. A time series of DGT experiments allow the determination of an in situ arsenic diffusion coefficient in the diffusive gel (3.34 x 10(-6) cm(2) s(-1)) needed to calculate the so-called C-DGT(Fe) and C-DGT(Ti) concentrations. Over 3 days of a given sampling event and for cores sampled at intervals smaller than 50 cm, great variability in arsenic C-soln concentrations between vertical profiles was observed, with maxima of concentrations varying from 690 to 2800 mu g L-1. Comparisons between arsenic measured C-sol and C-DET and calculated C-DGT(Fe) and C-DGT(Ti) concentrations show either, in a few cases, roughly similar vertical profiles, or in other cases, significantly different profiles. An established iron oxyhydroxide precipitation in the DET gel may explain why measured arsenic C-DET concentrations occasionally exceeded C-soln. The large spread in results suggests limitations to the use of DET and type of DGT probes used here for similarly representing the spatio-temporal variations of arsenic content in soil pore water in specific environmental such as paddy soils. (C) 2015 Elsevier B.V. All rights reserved

Sources et dynamique du chrome dans les sols ultramafiques de Niquelandia, Brésil

La disponibilité et la mobilité du chrome ont été étudiées sur quatre sols développés sur le complexe ultramafique de Niquelândia (état du Goiàs, Brésil), à l aide d expérimentations en laboratoire et in situ. La teneur totale en chrome de ces sols est particulièrement élevée, et sa compartimentation évolue avec la position dans la toposéquence et la profondeur du sol. La majorité du chrome est associée aux oxydes de fer bien cristallisés qui constituent la matrice solide des sols. Il est également présent au sein des chromites, et de phases mineurs silicatées. La quantité de chrome extractibles est importante et majoritairement sous sa forme toxique (CrVI). Cette fraction atteint 1000 mg kg-1 soit plus de 10% du chrome total ; ces teneurs sont dix fois supérieures à celles observées en Nouvelle-Calédonie. Des cinétiques d échange isotopique du chromate ont confirmé la labilité de cette fraction. Elles ont également mis en évidence une vitesse d échange rapide entre les phases porteuses et la solution, ainsi qu une capacité élevée de ces sols à maintenir une importante concentration de chromate en solution. L ensemble des résultats indique que le Cr(VI) labile est désorbé depuis la fraction fine composée d oxydes de fer qui contrôle ainsi sa disponibilité et sa mobilité. Les résultats suggèrent que le chromate labile est faiblement adsorbé aux phases porteuses. La disponibilité du chrome est très hétérogène à des échelles décimétrique et décamétrique. L étude des eaux du sol et de surface à l échelle du bassin versant a mis en évidence une mobilité importante du Cr(VI) et des concentrations en chromate supérieures aux teneurs considérées comme toxiques, suggérant un impact sur les organismes vivants du complexe et également les écosystèmes environnants. D autre part, l analyse des solutions du sol a confirmé la faible teneur en nutriments, le rapport défavorable Ca:Mg et la disponibilité de certains métaux (Cr, Ni) typiques de ces milieux. Ces trois caractéristiques sont souvent considérés comme responsable de la faible fertilité de ce type de sol et du particularisme de ces écosystèmes. Enfin, les résultats suggèrent que la disponibilité en Cr(VI) de ces sols résulte de leur capacité d échange anionique et non d oxydation du Cr(III).Chromium availability and mobility were studied on four soils developed on the complex ultramafic of Niquelândia (Goias state, Brazil), using laboratories and in situ experiments. Total chromium content is particularly high, and its partitioning evolves according to landscape position and depth. Chromium is mainly associated to well crystallized iron oxides, forming the soil matrix. However, extractable chromium is important, and mainly under the toxic form (CrVI). It reached 1,000 mg kg-1 (more than 10 % of total chromium), those contents are ten times higher than those observed in New Caledonia. Results indicate that Cr (VI) in solution is released from the fine fraction composed by iron-oxides, which consequently control the Cr(VI) availability and mobility. Isotopic exchange kinetics of chromate has confirmed the exchange between the bearing phases and solution. They also highlighted a rapid exchange between the Cr-bearing phases and the solution, and the important Cr(VI) buffer capacity of these soils. They also suggest that the chromate is slightly absorbed on iron-oxides. The chromate concentrations in soil solutions are important, higher than the usual hazardous contents. The chromate labibily is very heterogeneous with the locality at a centimetric and metric scale. The soil solution and surface water study on the catchment area has highlighted an important Cr(VI) mobility at soil and complex scale, suggesting an impact on organisms of the complex and surrounding ecosystems. Moreover, the soil solutions analysis show the low nutrients content, the imbalance Ca:Mg and the metals (Cr, Ni) availability, often considered responsible to the low fertility of those soils and the specificity of ultramafic ecosystems. Finally, results suggest that the Cr(VI) availability of those results from their anionic exchange capacity and not from their capacity to oxidize Cr (III).ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Design ab-initio de matériaux micro et nanostructurés pour l'émission thermique cohérente en champ proche et en champ lointain

L émission thermique à partir d un corps chaud a été longtemps considérée comme étant large bande et quasi-isotrope. Aujourd hui nous savons que ce paradigme est faux et de nombreux matériaux micro et nanostructurés ont été développés pour rayonner dans des bandes spectrales étroites et autour de certaines directions d espace. Les techniques modernes de dépôt permettent maintenant de concevoir des structures complexes à base de matériaux métalliques, polaires ou diélectriques à l échelle nanométrique. Ces avancées soulèvent la question de la meilleure structure possible pour obtenir des propriétés radiatives désirées et pour augmenter le degré de cohérence d une source. Cependant, jusqu à présent, seules des stratégies heuristiques basées sur une approche de type essai-erreur ont été suivies pour concevoir des sources thermiques. Dans ce travail de thèse, nous présentons une méthode générale pour le design ab-initio de sources thermiques cohérentes en champ lointain et en champ proche. Le cadre de ce travail est celui de la théorie des matrices de diffusion et de l électrodynamique fluctuationnelle. De nouveaux effets de champ proche sont prédits théoriquement pour les matériaux nanostructurés multicouches. Ils ouvrent de nouvelles opportunités pour améliorer de façon significative les performances des technologies modernes de conversion d énergie.Emission of thermal light from a hot body has been considered during long time as broadband and quasi-isotropic. Today we know this paradigm is wrong and it has been shown that many micro and nanostructured materials are able to radiate in narrow spectral bands and around specific directions of space. The ability to artificially grow in a controllable manner, from modern deposition techniques, complex structural configurations of metallic, polar and dielectric materials raises now the issue of the best achievable inner structures to tailor the radiative properties of a nanostructured thermal source in a prescribed manner and to enhance the coherence degree of its emission. However, so far, only heuristic strategies based on trial-and-error have been followed for engineering such sources. In this thesis we present a general method for the ab initio design of coherent thermal sources both in far field and near field. The framework of this thesis is the scattering matrix theory and the fluctuational electrodynamic. New near-field effects are theoretically predicted for nanostructured materials. They open new opportunities to significantly improve the performances of new energy conversion technologies.NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocSudocFranceF

Assessment of chromate availability in tropical ultramafic soils

International audienc

The millimetre-scale distribution of 2,4-D and its degraders drives the fate of 2,4-D at the soil core scale

The biodegradation of organic compounds in soil is a key process that has major implications for different ecosystem services such as soil fertility, air and water quality, and climate regulation. Due to the complexity of soil, the distributions of organic compounds and microorganisms are heterogeneous on sub-cm scales, and biodegradation is therefore partly controlled by the respective localizations of organic substrates and degraders. If they are not co-localized, transfer processes become crucial for the accessibility and availability of the substrate to degraders. This spatial interaction is still poorly understood, leading to poor predictions of organic compound dynamics in soils. The objectives of this work were to better understand how the mm-scale distribution of a model pesticide, 2,4-dichlorophenoxyacetic acid (2,4-D), and its degraders drives the fate of 2,4-D at the cm soil core scale. We constructed cm-scale soil cores combining sterilized and “natural” soil aggregates in which we controlled the initial distributions of 2,4-D and soil microorganisms with the following spatial distributions: i) a homogeneous distribution of microorganisms and 2,4-D at the core-scale, ii) a co-localized distribution of microorganisms and 2,4-D in a single spot (360 mm3) and iii) a disjoint localization of microorganisms and 2,4-D in 2 soil spots (360 mm3) separated by 2 cm. Two sets of experiments were performed: one used radiolabeled 14C-2,4-D to study the fate of 2,4-D, and the other used 12C-2,4-D to follow the dynamics of degraders. Microcosms were incubated at 20 °C and at field capacity (−31.6 kPa). At the core scale, we followed 2,4-D mineralization over time. On three dates, soil cores with microorganisms and 2,4-D localized in soil spots, were cut out in slices and then in 360 mm3 soil cubes. The individual soil cubes were then independently analysed for extractable and non-extractable 14C and for degraders (quantitative PCR of tfd A genes). Knowing the initial position of each soil cube allowed us to establish 3D maps of 2,4-D residues and degraders in soil. The results indicated that microorganisms and pesticide localizations in soil are major driving factors of i) pesticide biodegradation, by regulating the accessibility of 2,4-D to degrading microorganisms (by diffusion); and ii) the formation of non-extractable residues (NER). These results also emphasized the dominant role of microorganisms in the formation and localization of biogenic NER at a mm-scale. To conclude, these results demonstrate the importance of considering micro-scale processes to better understand the fate of pesticides and more generally of soil organic substrates at upper scales in soil and suggest that such spatial heterogeneity should not be neglected when predicting the fate of organic compounds in soils