Les sols de montagne constituent un réservoir majeur de carbone stocké sous forme de matière organique (carbone organique du sol, COS), potentiellement hautement vulnérable aux changements des conditions climatiques. Afin de comprendre les répercussions des changements des conditions climatiques sur la dynamique du COS des sols de montagne, cette thèse s'appuie sur une expérimentation de transplantation altitudinale de monolithes de sol de prairie subalpine calcaire, mise en place dans le Jura Suisse en 2009. Cette expérimentation permet de simuler deux scénarios réalistes de changements climatiques attendus au cours du 21éme siècle, visant à réchauffer et assécher le climat (+2°C et +4°C ; -20% et -40% de précipitations).La démarche conceptuelle de cette thèse a été d'étudier les effets des changements des conditions climatiques (variations saisonnières et manipulation climatique) au bout de quatre années d'expérimentation sur (i) la dynamique des communautés microbiennes et de leur activité enzymatique de décomposition du COS, (ii) la dynamique de différents pools de COS qui constituent la ressource énergétique des micro-organismes décomposeurs, (iii) les interactions s'établissant entre les communautés microbiennes et leurs ressources énergétiques et (iv) les stocks de COS du sol.Nos résultats montrent une très forte dynamique saisonnière du processus de décomposition microbienne se traduisant par de fortes activités enzymatiques de décomposition, une biomasse microbienne plus importante et une structure des communautés microbienne différente lors de la saison hivernale par rapport à la saison estivale. Ces résultats sont en lien avec la dynamique observée des pools les plus labiles du COS (C organique extractible à l'eau et C organique particulaire libre), et des modèles d'équations structurelles montrent que les conditions climatiques (variations saisonnières et manipulation climatique) modifient les interactions s'établissant entre les communautés microbiennes et leurs ressources pour contrôler la décomposition enzymatique du COS.Enfin, ce travail de thèse montre une forte diminution des concentrations en COS sous l'effet de la manipulation climatique, qui ne peut être expliquée par une décomposition microbienne accrue du COS. Au contraire, nos résultats suggèrent que la diminution de la concentration en COS pourrait être due à l'accélération des processus pédologiques naturels sous les scénarios de changement climatique au sein de ces sols calcaires de prairies subalpines, avec une décarbonatation accrue favorisant la lixiviation du carbone organique dissous et le lessivage du pool de COS associé aux argiles. Ces résultats inédits offrent de nouvelles perspectives de recherche sur les effets des changements climatiques sur l'évolution des stocks de COS. / Mountain soils stocks huge quantities of carbon as soil organic matter (SOM) which may be highly vulnerable to climate change and thus alter the atmospheric greenhouse gases concentration at a decadal timescale. To understand the effect of climate conditions on the dynamics of mountain soil organic carbon (SOC), a climate change experiment was set up in October 2009 in Swiss Jura subalpine grassland soils. The climate change experiment (soil transplantation) simulated two realistic climate change scenarios, with increased air temperatures ranging between 2 °C and 4 °C and decreased precipitation ranging between 20% and 40%. These changes reflect current predictions of climate change for the 21th century in temperate mountain regions.We studied the effect of climate conditions (climate manipulation and seasonal changes) after four years of climate experiment on (i) the dynamic of microbial decomposition, microbial abundance and community structure, (ii) the dynamic soil organic matter pools with contrasted turnover rate and representing the energetic resource of microbial communities, (iii) the interactions between microbial communities and soil organic matter pools and (iv) the soil organic carbon stocks.This work shows a strong seasonal dynamics of microbial decomposition with higher enzymatic activities, higher microbial abundance and shift of microbial community structure in winter than in summer. These results were linked to the seasonal organic matter labile pools dynamics. Moreover structural equation modeling shows that climate manipulation differently influences the drivers of SOC enzymatic decomposition in summer and winter.Finally, this work shows a strong decrease of soil organic carbon concentration under the climate change manipulation which cannot be explained by an increase of microbial activities. In contrast, our results suggest that the observed climate-induced decrease in bulk soil organic C content was due a SOC decrease in the most biogeochemically stable SOM fraction associated with a decrease in clay content and a decrease of soil calcareous concentration. Thus, our results hint more so towards an effect of SOM leaching (Gavazov, 2013) to explain the climate effect on SOC content than an effect of microbial and/or plant activities.

Objetivou-se neste trabalho avaliar a variabilidade espacial e temporal do carbono no solo produzindo um mapa, sobre esse tema para toda a área da Estação Experimental de Mogi Mirim (EE Mogi Mirim), juntamente com a análise dos fluxos dos gases de efeito estufa (CO2, N2O e CH4) e a relação desses dois fenômenos com as variáveis do solo nos diferentes usos da terra. Para se alcançar objetivo proposto com relação aos estoques de carbono e avaliação das variáveis do solo foi feita a coleta e o prepara das amostras nas profundidades de 00 até 30 cm, foi feito o georreferenciamento e determinação dos teores de carbono, densidade do solo, calculo dos estoques de carbono e determinação da cor do solo. Por sua vez para o estudo e entendimento dos fluxos dos gases de efeito estufa (GEE), comparou-se um talhão considerado sem perturbação (Talhão 41) e a partir desse talhão avaliou-se comparativamente em uma seqüência com ambientes com histórico de uso da terra representativo da área com manejos. Os fluxos dos gases CO2, N2O e CH4 foram medidos utilizando-se câmaras estáticas. Nos resultados obtidos foi aplicada a estatística descritiva clássica e geoestatistica para avaliar a freqüência e distribuição dos dados. Resultados relativos as variáveis do solo mostram que praticamente a grande maioria tende a diminuir com a profundidade (Ca, soma das bases, CTC, acidez potencial e carbono). Por sua vez o pH é sempre muito alto nas 3 camadas e a saturação por bases e o magnésio são muito baixos e permanecem inalterados em todas as profundidades. A variabilidade espacial dos estoques de carbono possui características isotrópicas. Especificamente na profundidade 00 - 10 cm, o modelo teórico que melhor se ajustou foi o exponencial, na profundidade 10 - 20 cm foi o esférico e na profundidade 20 - 30 cm foi o exponencial. Os estoque de C na profundidade 00 10 cm, tiveram como média 22.8 ton C/ ha-1, sendo o maior valor de 42.9 ton C/há-1 e o menor valor de 10.3 ton C/há-1. Na profundidade 10 - 20cm, a média do estoque de carbono foi de 14.9 ton C/há-1, sendo o maior valor de 31.5 ton C/há-1 e o menor valor de 6.99 ton C/há-1. Na profundidade 20 -30 cm, a média do estoque de carbono foi de 11.45 ton C/há-1, sendo o maior valor de 25.28 ton C/há-1 e o menor valor de 6.3 ton C/há-1. Os resultados das análises dos fluxos do gás carbônico, como um todo mostra que a respiração do solo variou entre 75.3 e 164.4mgC m-2 h-1. Relativo aos fluxos de N2O os valores médios para as emissões variaram entre 8,85 e 51,94 \'mü\'gN m-2 h-1, enquanto que a absorção variou, entre -1,32 e - 4,59 \'mü\'gN m-2 h-1. Os resultados dos fluxos do gás metano médio ficaram entre 4,63 e 31,51 mgC m-2 h-1, enquanto que os valores de oxidação média ficaram entre -5,41 e -22,79 mgC m-2 h-1 / The aim here is to evaluate the spacial and transient variability of carbon in soil, producing a map about this subject for all the area of the Experimental Station of Mogi Mirim (Estação Experimental de Mogi Mirim EE Mogi Mirim), with the emissions analyzes of greenhouse gases effect (CO2, N2O e CH4), and the relation between these phenomenon with the soil variables in different uses of the land. In order to reach the proposed objective related to the carbon storages, and the variable evaluation of the soil, a sample collect and preparation were made at a depth from 00 to 30cm. It was also made the georeferencial and the carbon levels determination, density of soil, the estimate of carbon storages, and the determination of soil color. The study and understanding of the greenhouse gas emissions (GGF), a área considered without disturbing, and from it a comparative evaluation in a sequence of environments with historical land use representative of the management area. The CO2, N2O and CH4 gas emissions were measured by using static chambers. In the results obtained, it was applied the classic statistic description and geostatistics to evaluate the frequency and the distribution of data. Results related to the soil variables show that the major trend to decrease, according to the depth (Ca, sum of bases, CTC, potential acidity, and carbon). On the contrary, the pH is always very high in 3 layers, and the saturation for bases and the magnesium are very low, maintaining unchangeable in all depths. The variability of the carbon storages have isotropic characteristics. Specifically in depth 00 - 10cm, the theorical model that better adjusted was the exponential; in depth 10 - 20cm, it was the spherical, and in depth 20 - 30cm it was the exponential. The carbon storage in depth 00-10cm had as na average 22.8ton C / ha-1, being the highest value of 42.9 ton C/ha-1, and the lowest value of 10.3 ton C/ha-1. In depth 10 - 20 cm, the average of carbon storage was 14.9 ton C/ha-1, being the highest value of 31.5 ton C/ha-1, and the lower value of 6.99 ton C/ha-1. In depths of 20 - 30cm, the average of carbon storage was of 11.45 ton C/há-1, being the highest value of 25.28 ton C/ha-1, and the lowest of 6.3 ton C/ha-1 The analyze results of carbon gás emissions as a whole, shows that the soil breath varied between 75.3 e 164.4 . mgC m-2 h-1 . Regard to N2O emissions, the average values to emissions varied between 8.85 and 51.94 \'mü\'gN m-2 h-1, while the absorption varied, between -1.32 e - 4.59 \'mü\'gN m-2 h-1. The results of average methane gas were between 4.63 e 31.51 mgC m-2 h-1, while the average oxidation values were between -5.41 e -22.79 mgC m-2 h-1

The Mogale’s Gate Biodiversity Centre is a 3 060 ha reserve located within the Gauteng province. The area comprises grassland with woodland patches in valleys and lower-lying areas. To develop a scientifically based management plan a detailed vegetation study was undertaken to identify and describe the different ecosystems present. From a TWINSPAN classification twelve plant communities, which can be grouped into nine major communities, were identified. A classification and description of the plant communities, as well as, a management plan are presented. The area comprises 80% grassland and 20% woodland with 109 different plant families. The centre has a grazing capacity of 5.7 ha/LSU with a moderate to good veld condition. From the results of this study it is clear that the area makes a significant contribution towards carbon storage with a total of 0.520 tC/ha/yr stored in all the plant communities. / Environmental Sciences / M.Sc. (Environmental Management)

Doctoral thesis abstract Assessment of climate change impacts on selected ecosystem services in the Czech Republic: Application of land use scenarios MSc Eliška Lorencová Climate and land use change are recognized as the greatest global environmental problems. Both considerably impact delivery of crucial ecosystem services, such as carbon sequestration, water flow regulation, erosion control, and food and fibre production. By combining future projections of ALARM scenarios (for years 2020, 2050 and 2080) with modelling of ecosystem services, the study aims to evaluate climate change impact on selected ecosystem services (carbon storage and sequestration, erosion control and sediment retention) in the Czech Republic. This study provides quantitative as well as spatially explicit analysis of the impacts on selected ecosystem services in the Czech Republic. Performed ecosystem service assessment indicates that spatial distribution of provision of ecosystem services, such as carbon storage and sequestration, sediment retention reflects the projected future land use changes. In case of carbon sequestration, SEDG scenario shows the lowest carbon sequestration rates accounting for 37,029.6 Gg C within the period 2000-2080. Stable vegetation cover is one of the factors that play important role in amount of sediment...

Doctoral thesis abstract Assessment of climate change impacts on selected ecosystem services in the Czech Republic: Application of land use scenarios MSc Eliška Lorencová Climate and land use change are recognized as the greatest global environmental problems. Both considerably impact delivery of crucial ecosystem services, such as carbon sequestration, water flow regulation, erosion control, and food and fibre production. By combining future projections of ALARM scenarios (for years 2020, 2050 and 2080) with modelling of ecosystem services, the study aims to evaluate climate change impact on selected ecosystem services (carbon storage and sequestration, erosion control and sediment retention) in the Czech Republic. This study provides quantitative as well as spatially explicit analysis of the impacts on selected ecosystem services in the Czech Republic. Performed ecosystem service assessment indicates that spatial distribution of provision of ecosystem services, such as carbon storage and sequestration, sediment retention reflects the projected future land use changes. In case of carbon sequestration, SEDG scenario shows the lowest carbon sequestration rates accounting for 37,029.6 Gg C within the period 2000-2080. Stable vegetation cover is one of the factors that play important role in amount of sediment...

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[pt] Como solução para viabilizar a produção de óleo com alto teor de dióxido de carbono, condição característica do pré-sal brasileiro, foi escolhida a estratégia de reinjeção desse mesmo gás produzido como método de recuperação de petróleo e como instrumento de mitigação da emissão atmosférica desse tipo de GEE (Gas do Efeito Estufa). A combinação de duas técnicas de recuperação, a injeção de água e a de gás, conhecida como WAG (Water Alternated Gas) se mostrou promissora por combinar benefícios como a varredura microscópica do gás com a estabilidade e economia obtidas pela injeção de água. Este projeto tem como objetivo entender o potencial de produção para traçar uma estratégia de otimização de recuperação do óleo aliado ao armazenamento da maior quantidade de CO2 possível, por meio de simulações numéricas de fluxo contínuo por modelos composicionais. A metodologia adotada para este projeto foi a utilização de módulos comerciais de simulação de reservatórios, fornecidos pela CMG (Computer Modeling Group), para ajuste de dados PVT de um fluido com características próximas ao do pré-sal, para que este pudesse ser aplicado em dois modelos sintéticos de reservatórios, para otimização de campo e avaliação deste pós período de produção. Desta forma, o presente trabalho proporciona uma visão do comportamento do método WAG e sua influência sobre o fator de recuperação deste reservatório, além de discutir as interações envolvidas em microescala em um ambiente reativo como um reservatório carbonático na presença do CO2. A partir dos resultados obtidos com a simulação, é possível concluir que as reações químicas entre os componentes aquosos e minerais presentes na formação porosa tem como consequência o aprisionamento do carbono. / [en] The strategy of CO2 produced reinjection is a solution to enable the pre-salt oil production as a petroleum recovery method and as an instrument to mitigate atmospheric emission of this GHG (Greenhouse Gas). The combination of two recovery techniques, water and gas injection, is known as Water Alternated Gas (WAG) has shown a successful combination of benefits such as microscopic gas sweeping with the stability and economy achieved by water injection. This project aims to understand the production potential to outline an optimization strategy of oil recovery coupled with the CO2 maximum storage possible, through numerical simulations of continuous flow by compositional models. The methodology adopted for this project was the use of commercial reservoir simulation modules, provided by CMG (Computer Modeling Group), to adjust PVT data of a fluid with similar characteristics to the pre-salt oil and then it could be applied in two synthetic reservoir models for field optimization and evaluation of this postproduction period. Thus, the present work provides an insight into the behavior of the WAG method and its influence on the recovery factor of this reservoir as well as discussing the microscale interactions involved in a reactive environment as a carbonate reservoir in the presence of CO2. Findings obtained by the simulation process shows that the chemical reactions between the aqueous and mineral components present in the porous formation result in carbon entrapment.

Le stockage géologique du carbone est l’une des techniques les plus prometteuses pour réduire le taux de CO₂ dans l’atmosphère. La séquestration géologique possède la capacité et la longévité potentielles pour diminuer les émissions de CO₂ vers l’atmosphère. Dans le cadre d’injections à l’échelle industrielle, les réservoirs carbonatés peuvent faire partie des sites aptes à stocker du CO₂. Toutefois, ces injections à grandes profondeurs sont sujettes à des risques de fuites du piège géologique lui-même ou des infrastructures liés à l’exploitation du site de stockage. Ainsi, il existe principalement deux types de fuite : brutale et diffuse. Dans les deux cas, elles sont susceptibles d’entrainer des risques pour l’environnement et de mettre en danger les populations. Il est ainsi nécessaire de développer des outils capables de prévenir une fuite de CO₂ quel que soit son type. Par ailleurs, il est particulièrement indispensable de comprendre les mécanismes de transport réactif qui rentrent en jeu lors de l’arrivée de cette fuite en contexte de proche surface (zone vadose) et ainsi d’essayer d’étudier comment cette fuite peut s’amortir. Ces travaux de thèse traitent donc de la caractérisation, de la quantification et de la modélisation des processus de transferts et des interactions CO₂-H₂O-CaCO₃ dans la zone vadose en contexte de fuite à partir d’un puits de forage. Cette problématique a été d’abord abordée par une approche expérimentale sur un site pilote à Saint-Emilion. Puis, les interactions CO₂-H₂O-CaCO₃ ont été étudiées au travers d’une approche expérimentale à l’échelle de la carotte en laboratoire. L’approche expérimentale a conduit à la réalisation de deux fuites dans la zone vadose du site pilote : une fuite diffuse et une fuite ultra diffuse. Elles furent réalisées dans la continuité des expériences qui avaient déjà eu lieu auparavant. Une comparaison de l’ensemble des fuites a montré la nécessité d’utiliser des gaz nobles comme précurseurs de l’arrivée en surface du CO₂. Selon le type de fuite, l’hélium peut servir de précurseur temporel du CO₂, tandis que le krypton prévient de l’étendue du panache de gaz durant la fuite. Plus la pression d’injection du CO₂ est importante et plus le gaz migre par advection. Par ailleurs, une pression d’injection importante favorise l’existence de passage préférentiel dans la zone vadose. L’utilisation d’isotopes tels que ceux de l’hélium et du carbone permet de mettre en évidence la présence locale de phases aqueuses dans le massif et de déterminer l’origine biologique ou anthropique du CO₂. Les expériences à l’échelle de la carotte permettent d’estimer le pouvoir tampon des calcaires oligocènes en fonction du faciès de la roche. La perméabilité et la porosité de celle-ci conditionnent la dissolution des calcaires. De même, la réactivité des carbonates en contexte de fuite dépend du pH de la phase aqueuse, du débit qui traverse le réseau poreux, de la saturation en eau et des caractéristiques pétro-physiques des carbonates. / Carbon storage is one of the most encouraging methods to decrease CO₂ concentration into the atmosphere. Carbon storage provides the longevity and the capacity needed to decrease CO₂ emissions toward the atmosphere. When dealing with storage on an industrial scale, carbonated reservoirs can be among the most suitable storage sites. However, these high depth injections are subject to leakage risks from the geologic trap itself or from the framework created by the establishment of the site. Two main types of leakage exist: brutal and diffusive leakage. In both cases, they are likely to endanger the environment and the population. Therefore, it is essential to develop tools that are able to anticipate any types of CO₂ leakage. Furthermore, it is also necessary to understand the reactive transport mechanism that take place when the leakage arrives in the shallow subsurface (vadose zone)and to see how the leakage can be buffered. This work deals with the characterization, the quantification and the modelling of transfer processes and CO₂-H₂O-CaCO₃ interactions into the vadose zone in a context of a leakage from a drilling well. This issue was first dealt through field experiment on the site of Saint Emilion. Then, the CO₂-H₂O-CaCO₃ interactions were studied through an experimental approach in laboratory. Two leakage experiments were performed on the site: a diffusive leakage and an ultra-diffusive leakage. They were performed as a sequel of former experiments carried on the pilot site. A comparison of all the leakage experiments revealed the necessity to use noble gases as precursor of the CO₂ arrival at the surface. Depending of the type of the leakage, helium can be a temporal precursor while krypton can anticipate the spread of the CO₂ gas plume. The higher the injection pressure, the more the gas migrates through advective flux. Moreover, a high injection pressure favors the existence of preferential paths in the vadose zone. The use of helium and carbon isotopes makes it possible to reveal the presence of a local aqueous phase within the porous media and to identify the origin of CO₂. The core scale experiments lead to the estimation of the buffering power of Oligocene limestone according to the rock facies. The permeability and the porosity influence the dissolution of the limestone. The reactivity of carbonates during a leakage depends on the pH of the aqueous phase, the flow rate that goes through the porous media, the water saturation and petrophysical characteristics of the carbonates.

Zehn unerforschte und natürliche Moore entlang der Flüsse Baker und Pascua in der Region Aysén, im chilenischen Patagonien, wurde untersucht, um Informationen über ihre Entstehung, Hydrologie, Geomorphologie, Stratigraphie, Ökologie und Wasser- und Kohlenstoffspeichervermögen zu gewinnen. Es wurden acht verschiedene ökologische Moortypen identifiziert und fünf Moortypen unterscheidbar durch ihr geohydromorphologisches Setting mit insgesamt elf verschiedenen organischen Moorsubstraten. Die gesammelten Information erlauben erste Abschätzungen der Torf-, Süßwasser- und Kohlenstoffmengen, die in den Mooren Ayséns gespeichert sind, sowie der jährlichen Torfakkumulationsraten. Die Moortypen und die in ihnen vorkommenden organischen Substrate wurden in einem geohydromorphologischen Klassifizierungssystem zusammengefasst, welches wichtige hydrologische, geomorphologische, ökologische, bodenkundliche und landschaftliche Parameter integriert. Forschung und Kommunikation über die chilenischen Moore sollen durch diese Arbeit unterstützt werden, um angemessene Monitoring Tools und partizipative Naturschutzstrategien zu entwickeln, die für die Erhaltung dieser Ökosysteme und ihrer Kreisläufe anwendbar sind. / Ten unexplored and pristine mires along the Baker and Pascua River Basins in Aysén, Chilean Patagonia, were examined, generating information about their origin, hydrology, geomorphology, stratigraphy, ecology, and carbon and water storage capacities. Eight mire types ecologically differentiable, associated with five main mire types separable by their hydrology and geomorphology were detected, as well as eleven organic substrate types forming mire soils. The information gathered allows for a first estimation of the peat, fresh water and carbon content stored in the mires of Aysén, as well as for an average growth and annual accumulation rate of the peat. Mire types and their associated substrates are systematized in a hydrogeomorphic classification system, integrating important landscape, hydrological, geomorphical, ecological and pedological components. Research and communication about mires in the Chilean Patagonia should be further supported to generate accurate monitoring tools and participative conservation strategies that are replicable for the preservation of these ecosystems and its balance.

Negative Emissionen sind für die Zukunft unerlässlich, insbesondere um schwer vermeidbare CO₂-Quellen auszugleichen und die Dekarbonisierung zu unterstützen. Wälder spielen hierbei eine Schlüsselrolle, da sie eine vergleichsweise kostengünstige Möglichkeit bieten CO₂ aus der Atmosphäre zu filtern. Andere solche Technologien befinden sich noch in Entwicklung und lassen sich nicht in grossem Umfang einsetzen, während Aufforstung bereits in vielen Emissionszielen verankert ist. Wälder absorbieren auf natürliche Weise einen Viertel unserer jährlichen Emissionen. Doch die Ausweitung von Wäldern bringt sowohl Vorteile, wie den Schutz der Biodiversität, als auch Herausforderungen, wie lokale Klimaeffekte und Konkurrenz mit landwirtschaftlicher Produktion, mit sich. Weiter gibt es Bedenken hinsichtlich der Langlebigkeit des Kohlenstoffspeichers in Wäldern. Diese Dissertation untersucht die zusätzlichen Vorteile und Herausforderung welche Wälder in der Klimadiskussion mit sich bringen. Die Ergebnisse betonen die Bedeutung existierender tropischer Wälder für den Klimaschutz. Geeignete Gebiete für die Aufforstung sind begrenzt und äusserst heterogen verteilt. Ausserdem birgt ein zu starkes Vertrauen in die Aufforstung das Risiko, dass gebundener Kohlenstoff zu einem späteren Zeitpunkt wieder ausgestossen wird. Insgesamt sollte die Aufforstung nur zusammen mit umfassenden Emissionsreduktionen als sinnvoller Teil des Klimaschutzes betrachtet werden. / Negative emissions are vital for the future, primarily to offset hard-to-abate CO₂ sources and speed up decarbonization. Forests may play a pivotal role as they provide a cost-effective method to capture CO₂. While other negative emission technologies are in development and not yet ready to be deployed on large scales, reforestation has taken centre stage in many emission reduction strategies. Forests naturally absorb about a quarter of our annual emissions. But expanding forests brings both benefits, like supporting biodiversity, and challenges, such as affecting local climate and competing with agriculture. There are also concerns about the long-term viability of forests as carbon sinks, especially with threats from climate change and human activities leading to deforestation. This dissertation delves into the additional local and global benefits and challenges of forests used for climate change mitigation. Findings underscore the significance of existing tropical forests for climate mitigation. Further, suitable areas for reforestation are limited, and their climate benefit is heterogeneously distributed. In addition, the reliance on forest carbon carries risks, as the CO₂ stored could be released in the future. Overall, while reforestation has a role in mitigating climate change, it should be part of a broader strategy that includes drastic emission reductions.