Afin de mieux comprendre et évaluer l'impact du changement climatique sur les stocks de carbone organique du sol (COS) et les flux de carbone, et en particulier la respiration hétérotrophe du sol (RS), il est nécessaire d'étudier la sensibilité de la RS à la température. Plusieurs études sur les facteurs contrôlant la dépendance de la RS à la température ont été faites antérieurement et montrent que la sensibilité de la RS à la température diminue avec la température. Ces études ont suggéré que cette diminution de sensibilité de la RS à la température était liée à la modification de la disponibilité en substrat. D'autres études ont suggéré que cette diminution est liée à l'adaptation de la communauté microbienne aux températures élevées. La sensibilité de la RS à la température est plus particulièrement critique dans les régions semi-arides, comme le Nord Ouest de la Tunisie où le stock de COS est faible. Il est nécessaire de connaître l'effet de la disponibilité en substrat sur la sensibilité de la RS à la température. Dans cette étude, les échantillons de sol ont été incubés pendant 28 jours après une période de 28 jours de pré-incubation. Les pré-incubations et incubations ont été réalisées à 20, 30, 40 et 50°C. Pour tester l'effet de la disponibilité en substrat sur la sensibilité de la RS à la température, du glucose a été ajouté au sol au début de la période d'incubation. L'analyse des résultats a montré que les températures élevées de pré-incubation réduisent la sensibilité de la RS à la température d'incubation. L'addition de glucose réduit l'effet de températures élevées de pré-incubation sur la réponse de la RS. Il apparaît ainsi que la diminution de la sensibilité de la RS après un mois de pré-incubation aux fortes températures est due à la diminution de la disponibilité en substrat. Elle semble aussi liée à une diminution de la biomasse microbienne. Puisque, le sol utilisé pour cette étude est un Cambi sol Calco-magnésimorphe, une deuxième expérimentation a été réalisée afin de déterminer la part de CO2 provenant des carbonates et la part de CO2 provenant du COS. Cette étude a été réalisée par des mesures des signatures isotopiques (δ13C) du COS, des carbonates et du CO2 émis. Après 28 jours d'incubation, 23±9% de CO2 provient des carbonates. Cette contribution est faible par rapport à la teneur initiale élevée de C-CaCO3 dans le sol (4,3%) et est indépendante de la température d'incubation. Cette étude a montré que la réduction de la sensibilité de la RS aux fortes températures est surtout liée à une réduction de la disponibilité en substrat organique et de la biomasse microbienne aux fortes températures. / To better understand and assess the impact of climate change on the stocks of soil organic carbon (SOC) and carbon fluxes, and particularly heterotrophic soil respiration (SR), it is necessary to study the sensitivity of SR to temperature. Several studies have been achieved to improve the understanding of factors controlling the temperature dependence of SR and showed that the temperature sensitivity of SR decreases with temperature. These studies suggested that this decrease in temperature sensitivity of SR was related to change in substrate availability. Other studies presented microbial adaptation to warmed conditions. The temperature sensitivity of SR is especially critical in semi-arid regions, such as North West Tunisia, where the SOC stock is low. It is necessary to know the influence of substrate availability on the sensitivity of SR to temperature. In this study, soil samples were incubated for 28 days after a 28-day pre-incubation per iod. Pre-incubation and incubation were carried out at 20, 30, 40 and 50°C. To test the substrate availability effect on the temperature sensitivity of SR, glucose was added to soil at the beginning of the incubation period. Results showed that the highest pre-incubation temperature reduced the temperature sensitivity of SR during the subsequent incubation period. Glucose addition reduced the effect of high pre-incubation temperature on SR response. Thus, it appears that the observed decrease in SR sensitivity to temperature after one month pre-incubation at high temperature was due to a reduce in substrate availability and to a decrease in microbial biomass. Since the soil used in this study is a Calcari-Leptic Cambisol, a second experiment was also performed to determine the amount of CO2 from carbonates and the amount of CO2 from SOC. This study was carried out by measurements of the isotopic signatures (δ13C) of SOC, carbonates and emitted CO2. After 28 days of inc ubation, 23±9% of CO2 came from carbonates. This contribution was low compared to the high initial C-CaCO3 content in soil (4.3%), and it was independent to the incubation temperature. This study showed that reduce in the sensitivity of SR to high temperatures was probably due to a reduction in the substrate availability and to a decrease in microbial biomass.

Le cycle du carbone (C) est, depuis la révolution industrielle, déstabilisé par l’introduction dans l’atmosphère de C autrefois fossilisé. Certaines mesures de mitigation prometteuses impliquent la séquestration accrue du CO2 atmosphérique dans les sols via le développement du réseau racinaire des arbres. Ce projet de recherche visait à : 1) quantifier la biomasse racinaire ligneuse produite annuellement par unité de surface par le Salix miyabeana cultivé en régie intensive à courtes rotations, 2) doser la concentration en C et en N des racines de saule en fonction de leur profondeur et de leur diamètre et 3) déterminer l’influence des propriétés pédoclimatiques du milieu sur la séquestration du carbone organique (Corg) par les racines. Pour y arriver, six souches de saules ont été excavées à partir de huit sites (n=48) et neuf carottes de recolonisation ont été implantées à cinq sites (n=45) pour évaluer la productivité racinaire fine. Les échantillons séchés ont été pesés pour quantifier la biomasse racinaire produite, et ont été analysés pour le C et le N. La productivité en biomasse racinaire ligneuse du saule en plantation pour tout le réseau d'échantillonnage varie de 0,7 – 1,8 Mg/ha/an. La proportion de C dans la biomasse racinaire s’étend de 31,3% à 50,4% et sa variance dans les tissus est expliquée par le diamètre racinaire et par les conditions environnementales des sites de provenance. Les conditions climatiques constituent la principale influence sur la production de biomasse racinaire. La variance de la biomasse racinaire est significativement contrôlée (p :0,004) par la quantité de précipitation de l’été et de l’année qui contrôlent ensemble 83,4 % du r2 ajusté. La précipitation de l’été est inversement liée à la productivité racinaire puisque les protéines expansines des racines sont stimulées par les carences hydriques du sol. La production de racines fines des plantations (1,2 à 2,4 Mg/ha/an) est, elle, plus fortement contrôlée par les conditions pédologiques du site qui expliquent 36,5% de la variance de productivité des racines fines contre 37,5% de la variance expliquée par les facteurs pédoclimatiques. Le P et le N du sol ont des rôles prépondérants sur la production de racines fines. Une disponibilité en P accrue dans le sol stimule la biomasse racinaire fine alors qu’une quantité supérieure de N dans le sol limite la croissance racinaire tout en favorisant la croissance des parties aériennes de la plante. Ce projet a permis d’améliorer notre compréhension des conditions pédologiques et climatiques qui engendrent, au Québec méridional, une productivité et une séquestration en Corg accrue dans le réseau racinaire du saule. / The carbon cycle has gone through notable changes since the industrial revolution, with the introduction of once fossilized C into the atmosphere. A number of promising mitigation solutions have been explored, including enhanced sequestration of atmospheric CO2 into soils by promoting the development of shrub trees’ root system. This research aims at: 1) quantifying total root biomass produced per unit surface per year from the short rotation coppice (SRC) of shrub willow (Salix Miyabeana), 2) obtaining the C and N concentration of roots according to diameter and depth and 3) determining the influence of pedoclimatic properties on underground C productivity. In order to achieve these goals, six willow trunks were excavated by hand from eight sites (n=45) and nine ingrowth cores were installed at five sites (n=45) to evaluate fine root productivity. The dried samples were weighted to quantify their total biomass and analyzed, for C and N content. Measured coarse root productivity at the sites varies from 0.7 to 1.8 Mg/ha/an. The C stock in the coarse root biomass varies (31.26% - 50.35%) and its variance is mainly explained by root diameter and the environmental caracteristics of the site of origin. Climatic constraints are the main influence over coarse root biomass production. Its variance is controlled (significant p: 0.004) by yearly and summer precipitations, controlling together 83.4% of the adjusted r2. Summer precipitation is negatively correlated to coarse root growth because the expansin protein content and activity within the roots is stimulated in dry environments. Fine root productivity (1.2 to 2.4 Mg/ha/year) is, however, controlled by a mix of climatic constraints and pedological constraints. There is 36.5% of the variance that is attributable to the pedological constraints and 37.5% of the variance explained by pedoclimatic constraints. The soil P and N contents have critical roles in the determination of fine root productivity. A large soil P stock stimulates fine root growth, whereas a large soil N stock limits the growth of the roots and stimulate aboveground biomass growth. This research allowed a better understanding of the conditions leading to enhanced productivity for willow SRC in the southern region of Quebec.

As crescentes preocupações com a mitigação das mudanças do clima levaram à criação de mecanismos de mercado que recompensassem financeiramente ações adicionais de remoção de gases do efeito estufa da atmosfera através de projetos voltados ao mercado de carbono. Embora, no âmbito do Protocolo de Kyoto, apenas atividades florestais de florestamento e reflorestamento sejam consideradas elegíveis, a maturação do mercado voluntário de carbono levou regimes de mercado como o Verified Carbon Standard (VCS) a aceitaram, entre outras, atividades de projeto envolvendo a melhoria do manejo florestal, incluindo a conversão da exploração madeireira convencional (EC) para o manejo florestal com exploração de impacto reduzido (MF-EIR), atividade esta que, muito provavelmente, estará inclusa no escopo de um futuro programa florestal de mitigação das mudanças do clima, o REDD+ (redução de emissões do desmatamento e degradação florestal mais os benefícios do seqüestro de carbono através de melhorias do manejo florestal). Utilizando uma série histórica de 16 anos de dados de uma área florestal explorada através da EC e do MFEIR em Paragominas, Estado do Pará, estimou-se os impactos dos tratamentos na dinâmica do carbono ao longo do tempo, sob a perspectiva de um projeto florestal de crédito de carbono envolvendo a conversão da EC para o MF-EIR. A comparação entre os tratamento MF-EIR e EC em relação às taxas de regeneração dos estoques de carbono apontou diferenças estatísticas significativas (P < 0,001). O tratamento MF-EIR apresentou um incremento médio observado de 12,30 Mg C ha-1 ano-1 e estimado de 13,01 Mg C ha-1 ano-1, enquanto que o tratamento EC apresentou um incremento médio observado de 5,42 Mg C ha-1 ano-1 e estimado de 5,43 Mg C ha-1 ano-1. O volume de créditos de carbono estimado para o projeto envolvendo a conversão da EC para o MFEIR foi de 61,81 VCUs ha-1. Considerando um buffer de créditos da ordem de 15%, o volume dos créditos passível de comercialização passou para 52,54 VCUs ha-1. A análise econômica realizada, considerando cenários distintos envolvendo a área do projeto (500; 1.000; 5.000; e 10.000 ha) e o preço do crédito de carbono (US$ 5,00; US$ 7,50; e US$ 10,00 unidade-1), resultou em uma matriz de resultados onde apenas projetos com área superior a 1.000 ha seriam possivelmente viáveis economicamente à atividade de projeto de carbono em questão. Por fim, o valor mínimo estimado do crédito de carbono para que não haja prejuízo financeiro aos madeireiros pela postergação do início do segundo ciclo de corte na área do projeto, tempo necessário para que os estoques de carbono da biomassa arbórea viva atinjam seu valor inicial pré-exploração, foi de US$ 5,33 por unidade, estando dentro da faixa de preços praticados pelo mercado de carbono apontada pela literatura. / Growing concerns over global climate change led to the development of market mechanisms that financially compensate additional retention or sequestration of greenhouse gases (GHGs). While under the Kyoto Protocol only forest activities related to afforestation and reforestation are eligible for compensation, maturation of voluntary carbon markets led to schemes such as the Verified Carbon Standard (VCS) to accept other sorts of forest-based offsets, such as the conversion from conventional logging (CL) to reduced-impact logging (RIL). It is anticipated that this sort of activity will also be included in the scope of the future REDD+ program (reduced emissions from deforestation and forest degradation plus the carbon sequestration benefits of improved forest management). Carbon dynamics over a16 year period after CL and RIL in Paragominas, Pará State, Brazil was assessed. The observed and estimated mean annual increments in carbon stocks after RIL were 12.30 Mg C ha-1 yr-1 and 13.01 Mg C ha-1 yr-1. After CL, in contrast, the annual increments in carbon stocks (observed and estimated) were only 5.42 Mg Cha-1 yr-1 and 5.43 Mg C ha-1 yr-1, respectively. The amount of carbon credits estimated for the project involving the conversion from CL to RIL was 61.81 VCUs ha-1. Assuming buffer credits of 15%, tradable carbon was reduced to 52.54 VCUs ha-1. The economic analysis performed, considering different scenarios involving the project area (500; 1,000; 5,000 and 10,000 ha) and carbon credit prices (USD 5.00; USD 7.00 and USD 10.00 unit-1), resulted in an array of results where only projects >1,000 ha would likely be economically viable. Finally, the minimum estimated carbon credit price that would imply in no financial loss to loggers by delaying the start of the second cutting cycle, that is, the, time required for the live carbon stocks to reach their pre-logging values, was USD 5.33 per unit, which is within the range of prices observed on the current carbon market.

La biodiversité des forêts tropicales humides (FTH) est inégalement répartie dans les trois principales régions des tropiques : les Néotropiques, l’Asie du sud-est et l’Afrique tropical. Même si les forêts africaines contiennent une diversité en espèces végétales et un endémisme importants, leur richesse spécifique reste faible par rapport aux autres massifs forestiers tropicaux. Cette disparité serait liée à l’impact négatif d’événements d’extinction durant le Cénozoïque plus intenses dans les forêts africaines. A l’échelle du bassin du Congo, les niveaux de diversité important et l’endémisme des forêts africaines seraient liés à l’hypothèse d’existence de forêts refuges du passé. Cette hypothèse suggère une contraction des forêts en ‘refuges’ durant les événements climatiques du Dernier Maximum Glacier (DMG, entre 24’000 et 12’000 Ans).L’objectif principal de cette thèse est d’étudier l’évolution des forêts africaines en réponse aux changements climatiques sur des pas de temps anciens (millions d’années) et plus récent (milliers d’années). Pour cela nous étudions deux groupes de palmiers Africains : les rotins de la sous-tribu des Ancistrophyllinae et le genre de sous-bois des FTH d’Afrique Centrale Podococcus composé de deux espèces P. barteri et P. acaulis. Le premier groupe nous renseigne sur les événements d’extinctions anciens durant le Cénozoïque, alors que le second permet d’étudier la réponse des FTH face aux changements climatiques du Pléistocène. L’approche utilisée dans cette thèse consiste à 1) reconstruire l’histoire évolutive des rotins, et 2) inférer la dynamique évolutive des deux espèces de Podococcus dans le temps. Cinq objectifs spécifiques structurant deux grandes parties de la thèse ont été retenus. Première partie : (i) reconstruire les relations phylogénétiques chez les Ancistrophyllinae à l’aide de marqueurs chloroplastiques et nucléaires, (ii) estimer les âges de divergences puis tester l’impact des événements d’extinction chez les Ancistrophyllinae. Seconde partie : (iii) construire les modèles de niches écologiques et inférer les zones de stabilité écologique des deux espèces de Podococcus depuis le DMG, (iv) reconstruire les relations phylogéographiques chez Podococcus à partir de plastomes entier obtenus avec du Séquençage Nouvelle Génération ‘NGS’ et (v) évaluer la concordance entre la diversité génétique et la stabilité écologique des populations de Podococcus.Les résultats suggèrent que les espèces d’Ancistrophyllinae se sont probablement diversifiées de manière constante mais avec un taux d’extinction assez élevé ponctué par un ou plusieurs événements d'extinction sévères au cours du Cénozoïque. Les Ancistrophyllinae ont divergé durant l’Eocène et la plupart des espèces sont apparues après 10 Ma durant la fin du Miocène et du début du Pliocène. Chez le genre Podococcus, une corrélation significative entre la diversité génétique unique et la stabilité écologique a été démontré appuyant l’hypothèse des forêts refuges. Les populations écologiquement stables et diversifiées sont principalement localisées dans les zones montagneuses comme les Monts de Cristal et les Monts Doudou au Gabon, mais aussi dans les forêts littorales atlantiques au Gabon et au Cameroun. Par contre la plupart des populations datent d’avant le DMG ce qui traduit une réponse des espèces sur plusieurs cycles glaciers. Les résultats de cette thèse montrent que les changements climatiques anciens et plus récents ont fortement influencé l’évolution et la dynamique des espèces forestières d’Afrique Centrale. De plus, nos résultats ont permis d’identifiés les forêts côtières comme prioritaires pour la conservation de la diversité en Afrique Centrale. / Tropical rain forests (TRF) biodiversity is not equally distributed between the three main tropical regions: Neotropics, South East Asia and tropical Africa. Even though African rain forests display high levels of diversity and endemism, this diversity is low compared to that of the other tropical regions. One of the main hypotheses advanced to explain this lower species diversity is that the African flora has undergone higher extinction rates during the Cenozoic. Across the Congo basin, high levels of species diversity and endemism is thought to be linked to the hypothesis of forest refugia. This hypothesis suggests a contraction of rain forests in 'refugia' during the Last Glacial Maximum (LGM, between 24’000 and 12’000 Years).The aim of this thesis is to study the evolution of African rain forests in response to climate change on ancient (million years) and more recent (thousands of years) time scales. For this we study two groups of African palms: the rattans of the sub-tribe Ancistrophyllinae and the understory genus of Central African TRF Podococcus with two species P. barteri and P. acaulis. The first group provides information about ancient extinctions events during the Cenozoic, while the second is used to study the response of TRF during Pleistocene climate change in Central Africa. The approach used in this thesis is to 1) reconstruct the evolutionary history of African rattans, and 2) to infer the evolutionary dynamics of the two species of Podococcus through time. The five specific objectives structuring two main parts of the thesis are: First part: (i) reconstruct phylogenetic relationships among Ancistrophyllinae using plastid and nuclear markers, (ii) estimate divergence times and test the impact of extinction events on Ancistrophyllinae. Second part: (iii) build ecological niche models and infer the areas of habitat stability of the two species of Podococcus from the LGM, (iv) reconstruct phylogeographic relationships of populations of Podococcus from whole plastomes obtained using Next Generation Sequencing and (v) assess the correlation between genetic diversity and ecological niche stability of all populations of Podococcus.Results suggest that Ancistrophyllinae has possibly undergone a constant diversification with a relatively high extinction rate punctuated by one or more severe extinction events during the Cenozoic. Ancistrophyllinae diverged during the Eocene with most species originating to the Late Miocene after 10 Ma. In the genus Podococcus, a significant correlation between the unique genetic diversity and habitat stability was demonstrated supporting the hypothesis of forests refugia in Central Africa. Ecologically stable and diverse populations are mainly located in mountainous areas such as Monts de Cristal and Monts Doudou in Gabon, but also in the Atlantic coastal forests in Gabon and Cameroon. In contrast, most of the populations predate the LGM reflecting that species respond over several glacial cycles. Results of this thesis highlight that ancient and recent climate changes have strongly influenced the evolution and dynamics of Central African forests. In addition, our results allowed the identification of African Atlantic coastal forests as an important conservation priority.

El CO2 es una variable clave que afecta tanto al desarrollo como a la fisiología de las plantas, por lo que los incrementos derivados del cambio climático afectarán al crecimiento de los cultivos. Muchas de las respuestas fisiológicas observadas frente al aumento del CO2 están influenciadas por su interacción con otros estreses, como por ejemplo la salinidad, debido al creciente aumento de las áreas afectadas por la salinidad y su impacto sobre la masa vegetal. Por ello, en esta Tesis, se expone como la agricultura desarrolla una función muy importante en la lucha contra el cambio climático debido a su papel como secuestradores de CO2 atmosférico. Las conclusiones de este trabajo ayudarán a clarificar aspectos esenciales para elegir las soluciones más efectivas en este ámbito junto con otras problemáticas dadas en nuestras tierras de cultivos como son el estrés salino, el cual se verá implementado por dicho cambio climático. / CO2 is a variable key that affects both development and the plant physiology, so that the increases resulting from climate change will affect crop growth. Many of the observed physiological responses to increased CO2 in front are influenced by its interaction with other stresses, such as salinity, due to the increasing of the areas affected by the salinity and its impact on the vegetation. Therefore, in this thesis agriculture is exposed as a very important place in the fight against climate change due to its role as kidnappers of atmospheric CO2. The conclusions of this work help clarify what is essential to choose the best solutions effective in this area along with other issues given in our crop lands such as salt stress, which will be implemented by the climate change

Ph.d.-afhandling. Københavns Universitet, 2002. / Haves også i trykt udg.

Geological sequestration of CO₂ in deep saline reservoirs is one of the ways to reduce its continuous emission into the atmosphere to mitigate the greenhouse effect. The effectiveness of any CO₂ sequestration operation depends on pore volume and the sequestration efficiency of the reservoir. Sequestration efficiency is defined here as the maximum storage with minimum risk of leakage to the overlying formations or to the surface. This can be characterized using three risk parameters i) the time the plume takes to reach the top seal; ii) maximum lateral extent of the plume and iii) the percentage of mobile CO₂ present at any time. The selection among prospective saline reservoirs can be expedited by developing some semi-analytical correlations for these risk parameters which can be used in place of reservoir simulation study for each and every saline reservoir. Such correlations can reduce the cost and time for commissioning a geological site for CO₂ sequestration. To develop such correlations, a database has been created from a large number of compositional reservoir simulations for different elementary reservoir parameters including porosity, permeability, permeability anisotropy, reservoir depth, thickness, dip, perforation interval and constant pressure far boundary condition. This database is used to formulate different correlations that relate the sequestration efficiency to reservoir properties and operating conditions. The various elementary reservoir parameters are grouped together to generate different variants of gravity number used in the correlations. We update a previously reported correlation for time to hit the top seal and develop new correlations for other two parameters using the newly created database. A correlation for percentage of trapped CO₂ is also developed using a previously created similar database. We find that normalizing all risk parameters with their respective characteristic values yields reasonable correlations with different variants of gravity number. All correlations confirm the physics behind plume movement in a reservoir. The correlations reproduce almost all simulation results within a factor of two, and this is adequate for rapid ranking or screening of prospective storage reservoirs. CO₂ injection in saline reservoirs on the scale of tens of millions of tonnes may result in fracturing, fault activation and leakage of brine along conductive pathways. Critical contour of overpressure (CoP) is a convenient proxy to determine the risk associated with pressure buildup at different location and time in the reservoir. The location of this contour varies depending on the target aquifer properties (porosity, permeability etc.) and the geology (presence and conductivity of faults). The CoP location also depends on relative permeability, and we extend the three-region injection model to derive analytical expressions for a specific CoP as a function of time. We consider two boundary conditions at the aquifer drainage radius, constant pressure or an infinite aquifer. The model provides a quick tool for estimating pressure profiles. Such tools are valuable for screening and ranking sequestration targets. Relative permeability curves measured on samples from seven potential storage formations are used to illustrate the effect on the CoPs. In the case of a constant pressure boundary and constant rate injection scenario, the CoP for small overpressures is time-invariant and independent of relative permeability. Depending on the relative values of overall mobilities of two-phase region and of brine region, the risk due to a critical CoP which lies in the two-phase region can either increase or decrease with time. In contrast, the risk due to a CoP in the drying region always decreases with time. The assumption of constant pressure boundaries is optimistic in the sense that CoPs extend the least distance from the injection well. We extend the analytical model to infinite-acting aquifers to get a more widely applicable estimate of risk. An analytical expression for pressure profile is developed by adapting water influx models from traditional reservoir engineering to the "three-region" saturation distribution. For infinite-acting boundary condition, the CoP trends depend on same factors as in the constant pressure case, and also depend upon the rate of change of aquifer boundary pressure with time. Commercial reservoir simulators are used to verify the analytical model for the constant pressure boundary condition. The CoP trends from the analytical solution and simulation results show a good match. To achieve safe and secure CO₂ storage in underground reservoirs several state and national government agencies are working to develop regulatory frameworks to estimate various risks associated with CO₂ injection in saline aquifers. Certification Framework (CF), developed by Oldenburg et al (2007) is a similar kind of regulatory approach to certify the safety and effectiveness of geologic carbon sequestration sites. CF is a simple risk assessment approach for evaluating CO₂ and brine leakage risk associated only with subsurface processes and excludes compression, transportation, and injection-well leakage risk. Certification framework is applied to several reservoirs in different geologic settings. These include In Salah CO₂ storage project Krechba, Algeria, Aquistore CO₂ storage project Saskatchewan, Canada and WESTCARB CO₂ storage project, Solano County, California. Compositional reservoir simulations in CMG-GEM are performed for CO₂ injection in each storage reservoir to predict pressure build up risk and CO₂ leakage risk. CO₂ leakage risk is also estimated using the catalog of pre-computed reservoir simulation results. Post combustion CO₂ capture is required to restrict the continuous increase of carbon content in the atmosphere. Coal fired electricity generating stations are the dominant players contributing to the continuous emissions of CO₂ into the atmosphere. U.S. government has planned to install post combustion CO₂ capture facility in many coal fired power plants including W.A. Parish electricity generating station in south Texas. Installing a CO₂ capture facility in a coal fired power plant increases the capital cost of installation and operating cost to regenerate the turbine solvent (steam or natural gas) to maintain the stripper power requirement. If a coal-fired power plant with CO₂ capture is situated over a viable source for geothermal heat, it may be desirable to use this heat source in the stripper. Geothermal brine can be used to replace steam or natural gas which in turn reduces the operating cost of the CO₂ capture facility. High temperature brine can be produced from the underground geothermal brine reservoir and can be injected back to the reservoir after the heat from the hot brine is extracted. This will maintain the reservoir pressure and provide a long-term supply of hot brine to the stripper. Simulations were performed to supply CO₂ capture facility equivalent to 60 MWe electric unit to capture 90% of the incoming CO₂ in WA Parish electricity generating station. A reservoir simulation study in CMG-GEM is performed to evaluate the feasibility to recycle the required geothermal brine for 30 years time. This pilot study is scaled up to 15 times of the original capacity to generate 900 MWe stripping system to capture CO₂ at surface. / text

The intracontinental endorheic Aral Sea, remote from oceanic influences, represents an excellent sedimentary archive in Central Asia that can be used for high-resolution palaeoclimate studies. We performed palynological, microfacies and geochemical analyses on sediment cores retrieved from Chernyshov Bay, in the NW part of the modern Large Aral Sea. The most complete sedimentary sequence, whose total length is 11 m, covers approximately the past 2000 years of the late Holocene. High-resolution palynological analyses, conducted on both dinoflagellate cysts assemblages and pollen grains, evidenced prominent environmental change in the Aral Sea and in the catchment area. The diversity and the distribution of dinoflagellate cysts within the assemblages characterized the sequence of salinity and lake-level changes during the past 2000 years. Due to the strong dependence of the Aral Sea hydrology to inputs from its tributaries, the lake levels are ultimately linked to fluctuations in meltwater discharges during spring. As the amplitude of glacial meltwater inputs is largely controlled by temperature variations in the Tien Shan and Pamir Mountains during the melting season, salinity and lake-level changes of the Aral Sea reflect temperature fluctuations in the high catchment area during the past 2000 years. Dinoflagellate cyst assemblages document lake lowstands and hypersaline conditions during ca. 0–425 AD, 920–1230 AD, 1500 AD, 1600–1650 AD, 1800 AD and since the 1960s, whereas oligosaline conditions and higher lake levels prevailed during the intervening periods. Besides, reworked dinoflagellate cysts from Palaeogene and Neogene deposits happened to be a valuable proxy for extreme sheet-wash events, when precipitation is enhanced over the Aral Sea Basin as during 1230–1450 AD. We propose that the recorded environmental changes are related primarily to climate, but may have been possibly amplified during extreme conditions by human-controlled irrigation activities or military conflicts. Additionally, salinity levels and variations in solar activity show striking similarities over the past millennium, as during 1000–1300 AD, 1450–1550 and 1600–1700 AD when low lake levels match well with an increase in solar activity thus suggesting that an increase in the net radiative forcing reinforced past Aral Sea’s regressions. On the other hand, we used pollen analyses to quantify changes in moisture conditions in the Aral Sea Basin. High-resolution reconstruction of precipitation (mean annual) and temperature (mean annual, coldest versus warmest month) parameters are performed using the “probability mutual climatic spheres” method, providing the sequence of climate change for the past 2000 years in western Central Asia. Cold and arid conditions prevailed during ca. 0–400 AD, 900–1150 AD and 1500–1650 AD with the extension of xeric vegetation dominated by steppe elements. Conversely, warmer and less arid conditions occurred during ca. 400–900 AD and 1150–1450 AD, where steppe vegetation was enriched in plants requiring moister conditions. Change in the precipitation pattern over the Aral Sea Basin is shown to be predominantly controlled by the Eastern Mediterranean (EM) cyclonic system, which provides humidity to the Middle East and western Central Asia during winter and early spring. As the EM is significantly regulated by pressure modulations of the North Atlantic Oscillation (NAO) when the system is in a negative phase, a relationship between humidity over western Central Asia and the NAO is proposed. Besides, laminated sediments record shifts in sedimentary processes during the late Holocene that reflect pronounced changes in taphonomic dynamics. In Central Asia, the frequency of dust storms occurring during spring when the continent is heating up is mostly controlled by the intensity and the position of the Siberian High (SH) Pressure System. Using titanium (Ti) content in laminated sediments as a proxy for aeolian detrital inputs, changes in wind dynamics over Central Asia is documented for the past 1500 years, offering the longest reconstruction of SH variability to date. Based on high Ti content, stronger wind dynamics are reported from 450–700 AD, 1210–1265 AD, 1350–1750 AD and 1800–1975 AD, reporting a stronger SH during spring. In contrast, lower Ti content from 1750–1800 AD and 1980–1985 AD reflect a diminished influence of the SH and a reduced atmospheric circulation. During 1180–1210 AD and 1265–1310 AD, considerably weakened atmospheric circulation is evidenced. As a whole, though climate dynamics controlled environmental changes and ultimately modulated changes in the western Central Asia’s climate system, it is likely that changes in solar activity also had an impact by influencing to some extent the Aral Sea’s hydrology balance and also regional temperature patterns in the past. <hr> The appendix of the thesis is provided via the HTML document as ZIP download. / Der Aralsee ist ein intrakontinental gelegenes endorheisches Gewässer fernab von ozeanischen Einflüssen, welches ein exzellentes sedimentäres Archiv für hochauflösende Paläoklimastudien in Zentralasien darstellt. In der vorliegenden Studie wurden umfangreiche palynologische, mikrofazielle und geochemische Analysen anhand von mehreren Bohrkernen aus der Chernyshov-Bucht im NW des heutigen Großen Aralsees durchgeführt. Die vollständigste der erbohrten Sequenzen weist dabei eine Länge von 11 m auf und beinhaltet näherungsweise die letzten 2000 Jahre des Holozän. Die hochauflösenden palynologischen Analysen der Studie, welche sowohl die Untersuchung von Dinoflagellatenzysten als auch Pollen beinhaltet, zeugen von einschneidenden Umweltveränderungen im Aralsee und seinem Einzugsgebiet. Die Untersuchung von Diversität und räumlicher Verbreitung der fossilen Dinoflagellatenzysten vermittelt dabei ein genaues Bild von den Salinitäts- und Seespiegeländerungen der letzten 2000 Jahre. Aufgrund der weitgehenden Abhängigkeit der hydrologischen Verhältnisse des Aralsees von der Wasserführung seinen tributären Flüsse, hängt sein Seespiegel unmittelbar von den Schmelzwasserzuflüssen im Frühjahr ab. Da der Schmelzwasserzufluss seinerseits mit den Temperaturveränderungen im Tien Shan und Pamir während der Schneeschmelze in Verbindung steht, spiegeln die Paläo-Salinität und der Paläo-Seespiegel des Aralsees folglich die Temperaturveränderungen im hochgelegenen Einzugsgebiet des Aralsees wider. Die Untersuchung der fossilen Dinoflagellatenzysten belegt besonders niedrige Seestände und hypersaline Bedingungen während der Perioden 0–425 AD, 920–1230 AD, 1500 AD, 1600 AD, 1800 AD und seit 1960, wohingegen oligohaline Bedingungen und höhere Seestände zwischen diesen Phasen dokumentiert sind. Ferner stellen umgelagerte Dinoflagellatenzysten aus Paläogenen und Neogenen Ablagerungen wertvolle Proxies für den Beleg von extremen Flächenspülereignissen dar, wie sie beispielsweise 1230–1450 AD aufgetreten und durch sehr hohe Niederschläge dokumentiert sind. Anhand der in der Studie erarbeiteten Daten ist davon auszugehen, dass die am Aralsee nachgewiesenen Umweltveränderungen im Wesentlichen von klimatischen Änderungen induziert wurden, durch historischen Bewässerungsfeldbau oder militärischen Konflikten jedoch noch verstärkt werden konnten. Darüber hinaus zeigen die Seestandsveränderungen eine sehr hohe Korrelation mit der Sonnenaktivität im letzten Jahrtausend, wie etwa während den Perioden 1000–1300 AD, 1450–1550 und 1600–1700 AD. Komplementär zu der Untersuchung von Dinoflagellatenzysten liefert die Pollenanalyse wertvolle Klimadaten für das Becken des Aralsees. Verschiedene Temperatur- (Jahresmittel, kältester gegen wärmster Monat) und Niederschlagsparameter wurden mit Hilfe der Methode der „probability mutual climatic spheres“ quantitative ausgewertet, womit die Klimaentwicklung im westlichen Zentralasien der letzten 2000 Jahre nachvollzogen werden konnte. Kalte und aride Bedingungen wiesen demnach die durch trockenangepasste Vegetation und Steppenelementen geprägten Perioden 0–400 AD, 900–1150 AD und 1500–1650 AD auf. Andererseits traten warme und weniger aride Klimabedingungen in den durch niederschlagsbedürftigere Pflanzen gekennzeichneten Zeiträumen 400–900 AD and 1150–1450 AD in den Vordergrund. Die Studie zeigt für das Becken des Aralsees, dass die Veränderungen im Niederschlagsmuster hauptsächlich vom zyklonalen System des östlichen Mittelmeergebietes (EM) gesteuert werden, welches den nahen Osten und das westliche Zentralasien mit Feuchtigkeit im Winter und Frühjahr versorgt. Da seinerseits das EM maßgeblich von Luftdruckänderungen der Nordatlantischen Oszillation (NAO) während seiner negativen Phase reguliert wird, ist ein Zusammenhang zwischen der Feuchtigkeit im westlichen Zentralasien und dem NAO anzunehmen. Außerdem belegen die laminierten Sedimente Veränderungen in den Sedimentationsprozessen während des späten Holozän, sowie ausgeprägte Änderungen im taphonomischen Verhalten. In Zentralasien hängt die Häufigkeit der im Frühjahr auftretenden Staubstürme hauptsächlich von der Intensität und der Position des Sibirienhochs (SH) ab. Der Gehalt an Titanium (Ti) als Proxy für äolischen Eintrag in den laminierten Sedimenten erlaubt die Rekonstruktion von winddynamischen Veränderungen in Zentralasien in den letzten 1500 Jahren. Die Studie beinhaltet daher die bislang längste Analyse der Variabilität des SH. Hohe Titaniumwerte sprechen für eine stärkere Winddynamik während den Perioden 450–700 AD, 1210–1265 AD, 1350–1750 AD und 1800–1975 AD, und dokumentieren demzufolge eine stärker ausgeprägtes SH während des Frühjahrs. Umgekehrt belegen geringe Titaniumwerte für die Zeit von 1180–1210 AD, 1265–1310 AD, 1750–1800 AD und 1980–1985 AD einen reduzierten Einfluss des SH.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Les domaines subalpin et jurassien sont constitués de nombreux systèmes karstiques de dimension et de surface réduites qui peuvent représenter localement l'unique ressource des communes. Les bassins d'alimentation de ces systèmes sont essentiellement composés de forêts et de pâturages et ne présentent qu'une urbanisation limitée. Les systèmes karstiques sont des milieux de transferts rapides assez mal connus dans la région. L'objectif principal de cette thèse s'attache à étudier les relations entre le fonctionnement et la vulnérabilité des systèmes karstiques de moyenne montagne. La vulnérabilité est abordée selon trois approches : intrinsèque, anthropique et climatique. Pour cela huit sites de nature différente et complémentaire (sources karstiques, galerie karstique et rivières) ont été étudiés.La vulnérabilité intrinsèque est étudiée par l'application de la méthode PaPRIKa. Cette analyse se fonde sur la superposition par pondération de cartes des bassins d'alimentation réalisées en fonction des critères Roche, Infiltration, Protection et Karstification. Elle permet de spatialiser les degrés de vulnérabilité sur le bassin d'alimentation d’un système karstique. Bien que les systèmes étudiés présentent des fonctionnements hydrodynamiques et une occupation des sols relativement similaires, les degrés de vulnérabilité diffèrent en fonction des sites.La vulnérabilité anthropique est étudiée, dans le cadre du programme Interreg Alpeau, sous l'angle de la remobilisation des sols suite à des travaux de sylviculture programmés sur les bassins d'alimentation. La recherche s'est concentrée sur la matière organique dissoute et en suspension et plus particulièrement sur la matière organique fluorescente. Ce travail a d’abord nécessité la réalisation d’un état des lieux sur les transferts associés au fonctionnement hydrodynamique des sites d’étude sur un cycle hydrologique. Pendant ou à la suite des travaux, les eaux des systèmes karstiques présentent des pics de turbidité ainsi que des venues en matières organiques fluorescentes du type humique et protéique, en azote total et en carbone organique total beaucoup plus importants (entre 5 et 10 fois plus). Cependant, tous les sites ne présentent pas d’augmentation significative des apports en matières en suspension et dissoutes, malgré l'ampleur des travaux réalisés.Enfin la vulnérabilité climatique est approchée par l'étude de chroniques historiques sur plus de 60 ans. Les précipitations et les températures de trois stations météorologiques ainsi que les débits de deux sources et une rivière ont été analysés afin d'extraire les grandes tendances. En plus de l'augmentation de la température ambiante de +1.5°C en 50 ans, les précipitations présentent une tendance à la baisse des cumuls annuels depuis 1980. La baisse des cumuls est plus particulièrement marquée à partir de 2003. Cette baisse de précipitations et l'augmentation des températures ont une répercussion quantitative sur les eaux de surface et souterraines. Les tendances observées sur les débits moyens annuels des systèmes étudiés sont en corrélation avec les précipitations. Malgré une tendance à la fonte des neiges de plus en plus précoce, les étiages basés sur les VCN10 ne montrent pas de réelle tendance à l’augmentation sur la période 1960-2011. Basées sur les données du GIEC 2007, les débits des sources subalpines ont été estimés pour les années 2030, 2050 et 2080. Les résultats montrent une diminution importante de la ressource en eau qui pourrait atteindre des baisses de l'ordre de 46% à l'horizon 2080. / The subalpine and jura middle mountains are composed of a many karstic systems characterized by small size and area. For local towns, these systems can represent the only water resource. The catchment areas are mainly composed of forests and pastures and have a limited urbanisation. Local karst systems have quick flow transfer and are not really known in the region. The main goal of this thesis is the study of the relationship between functioning and vulnerability of middle mountains karst systems. The vulnerabilities are analysed with three approaches: intrinsic, anthropogenic and climatic, applied on eight sites with variable natures (karst spring, karst conduit and rivers) which are additional. The intrinsic vulnerability is studied by the use of PaPRIKa method. This method is based on the overlaying by weighting catchment area maps. Each map is represented by one criterion. Criteria used to carry out a final map are: Rock, Infiltration, Protection and karstification. The method allows the characterization of the vulnerability degrees on the catchment area. Although the study systems have hydrodynamic functioning and similar soil occupation, the vulnerability degrees change for each site. Within the ALPEAU program, the soil remobilization due to sylvicultural activities is used as an anthropogenic vulnerability factor on the catchment area. The study is focused on dissolved and suspended organic matter, especially the fluorescent organic matter. This work has begun with the study of the organic matter transfers during hydrological cycle in natural conditions (without anthropogenic activities). During or after sylvicultural activities, karst waters can show turbidity peaks associated with concentration increasing of humic like, protein like, total nitrogenous and total organic carbon. However, all sites don't show a significant increase in spite of the intensity of sylvicultural activities. The climatic vulnerability is approached with the study of historical data since 60 years. The temporal evolution of precipitation, discharge and temperature have been analysed in order to extract global trends. Besides temperature increase (+15°C) since 50 years, the quantity of precipitations shows a decrease from 1980. This decrease is particularly accentuated since 2003. The decrease of precipitation and the increase of temperature lead an impact on the ground and fresh water quantity. Trends observed on mean annual discharge are correlated with the variation of precipitations. Despite an early snowmelt, low flow periods, defined by the VCN10, don't show significant increase on the period 1960-2011.