Le projet de thèse a eu pour but l’étude de la formation et de l’élimination du N2O par des catalyseurs cuivre-zéolithe ou fer-zéolithe, utilisés pour le procédé de réduction catalytique sélective des NOx par l'ammoniac (NH3-SCR). Dans ce processus de réduction des NOx, les principales voies de formation de N2O sont la décomposition du nitrate d’ammonium (NH4NO3) et l’oxydation de NH3. L’étude bibliographique a montré une contribution plus importante de la décomposition du nitrate d’ammonium. La recherche s’est donc focalisée dans l’étude de la décomposition du nitrate d’ammonium en empruntant deux axes : la décomposition du NH4NO3 commercial et la formation in situ suivi de la décomposition du nitrate d’ammonium.Les catalyseurs, utilisés pour cette étude, ont été, tout d'abord, amplement caractérises par différentes techniques d’analyse physico-chimique afin de connaitre particulièrement la concentration et forme de déposition des métaux, l’acidité et la taille des cristaux.Après avoir abordé la décomposition du NH4NO3 commercial sans catalyseur, l'étude s'est orientée sur l'effet de l'interaction avec un catalyseur. La nature du gaz vecteur, les conditions hydrodynamiques et la quantité de NH4NO3 ont aussi été évaluées.La décomposition sous conditions statiques, i.e. sans entrainement du NH4NO3 liquide, conduit principalement le N2O. En revanche, les chemins réactionnels suivis sous conditions dynamiques dépendent du mode de déposition du nitrate d’ammonium. Les agrégats solides de nitrate d'ammonium en contact avec la surface externe du catalyseur se décomposent directement en N2O, surtout quand le nitrate d’ammonium liquide ne peut pas être entrainé par le gaz vecteur. L’absence de catalyseur favorise la décomposition vers l’azote par l’interaction entre le NH3 et du HNO3 libérés lors de la dissociation du NH4NO3. D’autre part, en présence d’un catalyseur, le NH3 formé tend à s’adsorber et à s’oxyder à plus haute température. La variation du gaz vecteur n'engendre pas d'effet significatif sur la décomposition du NH4NO3.La décomposition du nitrate d’ammonium formé in situ a été réalisée dans le but de se rapprocher des conditions du procédé NH3-SCR, où le nitrate d’ammonium se forme par l’interaction entre le NH3 et le NO2. La méthode expérimentale a été conçue pour maximiser la formation du nitrate d’ammonium selon les deux cas extrêmes pouvant être trouvés dans un système SCR : la saturation préalable du catalyseur en NH3 puis en NO2 (« NH3 experiment ») et l’inverse, saturation en NO2 puis NH3 (« NO2 experiment »). Dans ce cas plusieurs catalyseurs ont été préparés afin d’isoler certaines caractéristiques et évaluer leur impact. Les effets de la teneur en cuivre, du type de métal (Cu ou Fe), de la structure de la zéolite (CHA ou FER), de la méthode de préparation, de l’atmosphère de calcination et du gaz vecteur pendant la décomposition ont été étudiés. Les effets obtenus ont été corrélés avec les résultats de la caractérisation physicochimique des catalyseurs afin de déterminer les paramètres prépondérants des différences observées.La formation du N2O lors du « NH3 experiment » est toujours plus importante que celle obtenue dans le « NO2 experiment » et dépend fortement de la concentration en sites acides de Brönsted quelle que soit la structure de la zéolithe. En revanche, dans le « NO2 experiment », ce sont plutôt les espèces métalliques et sa localisation qui influencent la décomposition du nitrate d’ammonium. La taille des cristaux a aussi une influence. La méthode de préparation et l’atmosphère de calcination n’ont pas un effet très significatif. Le gaz vecteur influence seulement les émissions à haute température : la formation du N2O est plus importante en présence d’oxygène. / The thesis project focused on the study of the formation and elimination of N2O by copper-zeolite or iron-zeolite catalysts, used for selective catalytic reduction of NOx with ammonia (NH3-SCR). In the NOx reduction process the main N2O formation routes are the decomposition of the ammonium nitrate (NH4NO3) and the NH3 oxidation. Still, a literature review showed a more important contribution from the decomposition of ammonium nitrate. Therefore, the study was then concentrated on the decomposition of the ammonium nitrate in two axes: the decomposition of commercial NH4NO3 and the in situ formation followed by decomposition of ammonium nitrate.Besides, the catalysts used for this study, have been thoroughly characterized by different physicochemical techniques in order to, particularly, assess the concentration and deposition form of metals, the acidity and the size of the crystals.After performing the decomposition of commercial NH4NO3 without catalyst, the study has focused on the effect of interaction with a catalyst. The effect of the carrier gas, the hydrodynamic conditions and concentration of NH4NO3 were also studied.Under static conditions, i.e. without liquid NH4NO3 entrainment, the decomposition of the commercial ammonium nitrate mostly leads to N2O. In contrast, the reaction pathway under dynamic conditions depends on the deposition method of ammonium nitrate onto the catalyst. The solid aggregates in the outer surface of the catalyst decompose directly to N2O, especially when the liquid ammonium nitrate cannot be entrained by the carrier gas. The absence of a catalyst promotes the decomposition into nitrogen, formed by the interaction between the NH3 and HNO3 released upon the dissociation of NH4NO3. On the other hand, in the presence of a catalyst NH3 tends to adsorb and to be oxidized at higher temperatures. The carrier gas composition did not have a significant effect in the decomposition of NH4NO3.The decomposition of ammonium nitrate formed in situ was performed in order to get closer from what happens under SCR conditions, where the ammonium nitrate is formed by the interaction between NH3 and NO2. The experimental method was designed to maximize the formation of ammonium nitrate according to the two extreme conditions that may be found in a SCR system: firstly catalyst saturation by NH3 and then by NO2 (“NH3 experiment”) and then the reverse, saturation by NO2 and then by NH3 (“NO2 experiment”). In this study several catalysts were prepared in order to isolate certain characteristics and assess their impact. The effects of the copper loading, the type of metal (Cu and Fe), the structure of the zeolite (CHA or FER), the method of preparation, the calcination atmosphere and the carrier gas during decomposition were studied. These effects were correlated to the results of the physico-chemical characterization of the catalysts with the purpose of find the cause of the faced differences.The formation of N2O during the “NH3 experiment” is always greater than that obtained on the “NO2 experiment”, and strongly depends on the concentration of the Brönsted acid sites, regardless the zeolite structure. However, on the “NO2 experiment”, it is rather the metal species and its location that influence the decomposition of ammonium nitrate. The size of the crystals also has an influence. The preparation method and the calcination atmosphere do not have a significant effect. The carrier gas impacts on the high temperature emission: the formation of N2O is greater in the presence of oxygen.

Nitrogen (N)-fixing trees can both mitigate climate change, by relieving N limitation of plant growth which promotes carbon dioxide (CO²) sequestration in plant biomass, and exacerbate climate change, by stimulating nitrification and denitrification which promotes nitrous oxide (N²O) emissions from soils. The balance between the negative radiative forcing (CO² sequestration in plant biomass) and positive radiative forcing (N²O emissions from soils) of N-fixing trees is unresolved. In this thesis I use a sequence of theoretical and empirical approaches to investigate the influence of N-fixing trees on CO² sequestration by forests and N²O emissions from forest soils, i.e., the net CO²-N²O effect of forests. The first chapter establishes a basis for the N²O effect of N-fixing trees with a meta-analysis, to accompany existing meta-analyses of the CO² effect of N-fixing trees. Chapter one demonstrates that N- fixing trees significantly increase N²O emissions from forest soils relative to non-fixing trees. The second chapter explores the controls and potential global importance of the net CO²-N²O effect of N-fixing trees using a theoretical ecosystem model. The third chapter explores the net CO²-N²O effect of N-fixing trees under manipulations of these controls with a field experiment paired with a modified version of the theoretical ecosystem model from the second chapter. Together, chapters two and three suggest that the net CO²-N²O effect of N-fixing trees is controlled by N limitation of plant growth and the extent to which N-fixing trees can regulate N fixation: N-fixing trees mitigate climate change relative to non-fixing trees under N limitation of plant growth, but N-fixing trees that cannot regulate N fixation exacerbate climate change relative to non-fixing trees under non-N limitation of plant growth. The fourth chapter represents the ecological mechanisms studied in chapters one, two and three in a land model: LM4.1-BNF is a novel representation of biological N fixation (BNF) and an updated representation of N cycling in the Geophysical Fluid Dynamics Laboratory Land Model 4.1 (LM4.1). LM4.1-BNF includes a mechanistic representation of asymbiotic BNF by soil microbes, the competitive dynamics between N-fixing and non-fixing plants, N limitation of plant growth, and N2O emissions from soils. Together these chapters elucidate the influence of N-fixing trees on the capacity of forests to mitigate and exacerbate climate change and establish a framework to analyse and project the trajectory of the net CO²-N²O effect of forests under global change.

Les sols agricoles représentent près de 66 % des émissions anthropiques de protoxyde d’azote (N₂O), 3ème gaz responsable de l’effet de serre additionnel. La variabilité des émissions mesurées au champ est élevée. La structure du sol impacte à la fois la production et le transport du N₂O dans le profil de sol. L’objectif de cette thèse était de comprendre le rôle de l’état structural du sol sur la variabilité spatiale des émissions de N₂O. La démarche utilisée associe deux types d’expérimentations en laboratoire - à l’échelle d’un bac de 0,3 m² x 0,1 m et sur une maquette de parcelle agricole de 10 m² x 0,3 m en sol nu - à un travail de modélisation intégrant des processus physiques, chimiques et biologiques dans le profil de sol et le ruissellement, le tout à une résolution temporelle fine. Ce travail a mis en évidence une hiérarchie entre les processus de production et de transport, qui évolue avec le temps et les conditions environnementales : dans des conditions favorables à la dénitrification, la production de N₂O augmente avec la masse volumique en lien avec une augmentation de la part de porosité remplie d’eau, jusqu’à une certaine limite. Le modèle déterministe a montré que la dynamique de la pluie et du ruissellement associé modifie l’intensité et la dynamique des émissions de N₂O, celles-ci étant plus tardives dans les zones avales recevant du ruissellement. Enfin, ce travail a confirmé la complexité du déterminisme des émissions de N₂O et a permis de souligner l’intérêt de caractériser la structure du sol et les émissions à une haute résolution spatiale pour améliorer la qualité des modèles prédictifs. / Agricultural soils account for 66 % of anthropogenic nitrous oxide emissions (N₂O), the 3rd greenhouse gas emitted from anthropogenic activities. N₂O emissions variability measured in-situ is quite high. Soil structure affects both N₂O production processes and N₂O movements through the soil profile. The main goal of this work was to understand the part of soil structure in soil N₂O spatial variability. Two kinds of laboratory experiments were designed: rainfall experiments on soil trays of 0.3 m² x 0.1 m and on a 10 m² x 0.3 m box with a slope. A modelling approach with a short time step was combined, involving representation of physical, chemical and biological soil processes as well as a representation of surface runoff.This work highlighted a hierarchy between N₂O production and N₂O transportation processes, which evolve with time and environmental conditions: under conditions that favor denitrification, N₂O production increases with soil bulk density due to an increase in the water-filled pore space, until a threshold limit. The deterministic modelling approach showed that rainfall dynamic and resulting runoff affect soil N₂O emissions, those emissions occurring later downslope. Finally, this work highlighted the complexity of soil N₂O emissions determinism and we pointed out that the description of soil structure at a high spatial resolution would be useful to improve modelling quality.

No description available.

付記する学位プログラム名: グローバル生存学大学院連携プログラム / 京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21465号 / 農博第2308号 / 新制||農||1064(附属図書館) / 学位論文||H31||N5160(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 舟川 晋也, 教授 間藤 徹, 教授 縄田 栄治 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Bakgrund: Lustgas har konstaterats vara ett mycket bra alternativ för smärtlindring av barn vid kortvarig procedurrelaterad smärta. Lustgasen har snabbt insättande effekt och biverkningar av lustgas är få eller av mild karaktär. Lustgas påverkar miljön negativt men en del av detta kan avhjälpas med effektiva ventilationssystem. Sjukvårdspersonal som exponeras för lustgas regelbundet utsätts för hälsorisker, dessa risker är dock inte helt kartlagda i nuläget. Sjuksköterskor som administrerar lustgas ställs inför en komplex situation med många faktorer att ta hänsyn till. Lustgasens betydelse i vården har studerats ur ett patient-, hälso- och miljöperspektiv. Enligt vår kännedom saknas studier som fokuserat på specialistsjuksköterskans eller blivande specialistsjuksköterskors upplevelser av lustgasadministrering till barn. Syfte: Att undersöka specialistsjuksköterskors och sjuksköterskor under pågående specialistutbildnings upplevelser av att administrera lustgas till barn i samband med procedursmärta på akutmottagning. Metod: En kvalitativ deskriptiv intervjustudie med induktiv design tillämpades. Strukturerade intervjuer genomfördes med tio specialistsjuksköterskor och blivande specialistsjuksköterskor på ett medelstort sjukhus i Sverige. Intervjuerna transkriberades och analyserades därefter genom kvalitativ innehållsanalys. Resultat: Analysen resulterade i tre huvudkategorier; Sjuksköterskans strategier vid lustgasadministrering, Utmaningar i samband med lustgasadministrering och Lustgasens begränsningar och möjligheter. Vidare abstraherades 11 underkategorier. Övervägande positiva erfarenheter av lustgasadministrering till barn framkom under intervjuerna. I resultaten framkom att sjuksköterskan behöver kunna anpassa sig efter barnets förutsättningar. Även betydelsen av ett välfungerande teamarbete, hur arbetsmiljön påverkar lustgasadministrering och betydelsen av tydliga riktlinjer framträdde. Upplevelser av trötthet och det känslomässiga engagemanget vid lustgasadministrering beskrevs. Diskussion: Teamarbetets framgång kopplas till god kommunikation. Resultaten tyder på att hög arbetsbelastning påverkar hur väl riktlinjer följs och i förlängningen skulle detta kunna innebära att patientsäkerheten påverkas negativt. Lokala skillnader kan ha gått förlorade då studien utgår från ett sjukhus, skillnader mellan olika verksamheter skulle kunna ha bidragit med viktig information. För att belysa sjuksköterskors personliga erfarenheter användes strukturerade intervjuer. Det är möjligt att frågorna styrt svaren och att ämnen som inte togs upp kunnat ge värdefullt information. Slutsats: Sjuksköterskors upplevelser av att administrera lustgas är övervägande positiva och det finns en önskan om att utöka användandet av lustgas inom barnsjukvård. Välfungerande teamarbete och tydliga riktlinjer framträder som väsentligt för att framgångsrikt kunna administrera lustgas till barn inom akutsjukvård. Vidare forskning bör inkludera flera sjukhus för att identifiera viktig information om likheter och skillnader i användandet av lustgas samt jämföra upplevelserna hos dem som administrerar lustgasen.

No description available.

The consequence of climate change will be more flooding in some areas and problems with sea-level rise. Drained wetlands and lakes that today are used for agriculture in the future may need to be rewetted because it might be unsustainable to continue to drain them. Rewetting these lands will have many positive effects like for instance decreased greenhouse gas emissions since these lands due to their high organic matter content are emitting a lot of CO2 and N2O. In this study two sites that could become candidates for rewetting have been studied and compared for their CO2 and N2O emissions. This was done by using a method for sampling gases both from a closed chamber and directly from soil. The emission rates were higher for Ramsjön compared to Vesan for both gases that could probably be an effect of season. A strong covariation between the two gases was shown for Ramsjön and the relationship was fairly strong for Vesan this indicates a common process for releasing the two gases. Rewetting these areas would probably have a high potential for saving greenhouse gas emissions and possibly also serve as flood adaptation areas with a high biodiversity and recreational value.

Nitrous oxide (N2O) emisison from paddy soil via the soil nitrification and denitrification processes makes an important contribution to atmospheric greenhouse gas concentrations. The soil N2O emission processes are controlled not only by biological, physical and chemical factors but also by farming practices. In recent years, modeling approach has become popular to predict and estimate greenhouse gas fluxes from field studies. In this study, the DeNitrification–DeComposition (DNDC) model were calibrated and tested by incorporating experimental data with the local climate, soil properties and farming management, for its simulation applicability for the irrigated rice system in Duy Xuyen district, a delta lowland area of Vu Gia-Thu Bon River Basin regions. The revised DNDC was then used to quantitatively estimate N2O emissions from rice fields under a range of three management farming practices (water management, crop residue incorporation and nitrogen fertilizer application rate). Results from the simulations indicated that (1) N2O emissions were significantly affected by water management practices; (2) increases in temperature, total fertilizer N input substantially increased N2O emissions. Finally, five 50-year scenarios were simulated with DNDC to predict their long-term impacts on crop yield and N2O emissions. The modelled results suggested that implementation of manure amendment or crop residue incorporation instead of increased nitrogen fertilizer application rates would more efficiently mitigate N2O emissions from the tested rice-based system. / Phát thải nitơ ôxít (N2O) từ canh tác lúa nước (thông qua quá trình nitrat hóa và phản nitrat hóa) đóng góp đáng kể vào tổng lượng khí nhà kính có nguồn gốc từ sản xuất nông nghiệp. Quá trình phát thải N2O là không chỉ phụ thuộc vào các yếu tố sinh-lý-hóa học mà còn phụ thuộc các phương pháp canh tác. Trong những năm gần đây, việc ứng dụng mô hình hóa nhằm tính toán và ước lượng sự phát thải khí nhà kính ngày càng trở lên phổ biến. Trong nghiên cứu này, số liệu quan trắc từ thí nghiệm đồng ruộng và dữ liệu về đất đai, khí hậu, biện pháp canh tác được sử dụng để kiểm nghiệm và phân tích độ nhạy của mô hình DNDC (mô hình sinh địa hóa). Sau đó, mô hình được sử dụng để tính toán lượng N2O phát thải trong canh tác lúa nước dưới các phương thức canh tác khác nhau (về chế độ tưới, mức độ vùi phụ phẩm, bón phân hữu cơ, phân đạm) tại huyện Duy Xuyên, thuộc vùng đồng bằng thấp của lưu vực sông Vu Gia-Thu Bồn. Kết quả kiểm định chỉ ra rằng (1) sự phát thải N2O bị ảnh hưởng đáng kể do sự thay đổi chế độ tưới; (2) nhiệt độ tăng và lượng phân bón N tăng sẽ làm tăng phát thải N2O. Kết quả mô phỏng về tác động lâu dài (trong 50 năm) của các yếu tố đến năng suất cây trồng và phát thải N2O cho thấy: Việc sử dụng phân hữu cơ và phụ phẩm nông nghiệp thay thế cho việc bón phân đạm sẽ giúp giảm phát thải N2O đáng kể.

Nitrous oxide (N2O) is a greenhouse gas (GHG) with 300 times the radiative forcing in the atmosphere of carbon dioxide (CO2), and has recently become a subject of great concern because the nitrogen (N) fertilizers which have been necessary to increase agricultural productivity have also dramatically increased N2O emissions from agroecosystems. Many N control practices have been suggested and implemented in agroecosystems, but their ability to simultaneously remove reactive N from the environment and prevent the production of N2O is, at best poorly understood. The goal of this work is to characterize environmental controls on production of N2O in denitrifying bioreactors. The review portion of this work first discusses the geologic history of the N cycle, how its past and present processes differ, and how it is being affected by human activity. It then explores the N cycle's biochemical pathways, reviews the controls for each of its steps, and discusses the environmental drivers of these controls. The review closes with a discussion of environmental N management strategies. The experimental portion of this work further explores these concepts by observing how biochar amendment and the modification of pH affect N2O production in the denitrification pathway in denitrifying bioreactors. Both pH and biochar have previously been shown to affect N2O production and many N management practices utilize biochar or manipulate pH to increase N retention. The objectives of the experiment were to: 1) Examine headspace N2O concentration in sealed, biochar-amended, denitrifying bioreactors; 2) Determine if the effects of pH on N2O production differ in biochar-amended systems versus controls (under acidic, unbuffered, and buffered conditions); 3) Quantify key denitrification genes (nirK, nirS, nosZ) in each treatment combination. Experimental results showed biochar treatment to significantly increase N2O emissions, a result which runs contrary to most, but not all studies regarding its effects on N2O production. Differences between treatments decreased with increasing pH levels. Biochar did not exhibit significant effects on individual denitrification genes, but it did show influence on the ratios of their populations. On the other hand, pH was found to have significant effects on nirS and nosZ populations. Differences in N2O production between biochar and controls were thus explained by biochar's chemical effects, likely its ability to increase denitrification activity. Developing an understanding of the mechanisms behind these differences will require using a combination of isotope tracing, enzyme assays, and mass balance approaches. Future microbial work in biochar-amended systems should attempt to characterize differences in gene expression, overall community structure, and long-term population trends in the genes of interest. The combination of these approaches should allow researchers to better predict where N2O production will occur and develop strategies to mitigate it while simultaneously increasing food production to meet the demands of a growing population. / Master of Science