• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 104
  • 82
  • 43
  • 21
  • 6
  • 6
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 306
  • 68
  • 54
  • 45
  • 43
  • 41
  • 37
  • 36
  • 34
  • 32
  • 32
  • 30
  • 29
  • 28
  • 25
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
201

Coupled flow and geomechanics modeling for fractured poroelastic reservoirs

Singh, Gurpreet, 1984- 16 February 2015 (has links)
Tight gas and shale oil play an important role in energy security and in meeting an increasing energy demand. Hydraulic fracturing is a widely used technology for recovering these resources. The design and evaluation of hydraulic fracture operation is critical for efficient production from tight gas and shale plays. The efficiency of fracturing jobs depends on the interaction between hydraulic (induced) and naturally occurring discrete fractures. In this work, a coupled reservoir-fracture flow model is described which accounts for varying reservoir geometries and complexities including non-planar fractures. Different flow models such as Darcy flow and Reynold's lubrication equation for fractures and reservoir, respectively are utilized to capture flow physics accurately. Furthermore, the geomechanics effects have been included by considering a multiphase Biot's model. An accurate modeling of solid deformations necessitates a better estimation of fluid pressure inside the fracture. The fractures and reservoir are modeled explicitly allowing accurate representation of contrasting physical descriptions associated with each of the two. The approach presented here is in contrast with existing averaging approaches such as dual and discrete-dual porosity models where the effects of fractures are averaged out. A fracture connected to an injection well shows significant width variations as compared to natural fractures where these changes are negligible. The capillary pressure contrast between the fracture and the reservoir is accounted for by utilizing different capillary pressure curves for the two features. Additionally, a quantitative assessment of hydraulic fracturing jobs relies upon accurate predictions of fracture growth during slick water injection for single and multistage fracturing scenarios. It is also important to consistently model the underlying physical processes from hydraulic fracturing to long-term production. A recently introduced thermodynamically consistent phase-field approach for pressurized fractures in porous medium is utilized which captures several characteristic features of crack propagation such as joining, branching and non-planar propagation in heterogeneous porous media. The phase-field approach captures both the fracture-width evolution and the fracture-length propagation. In this work, the phase-field fracture propagation model is briefly discussed followed by a technique for coupling this to a fractured poroelastic reservoir simulator. We also present a general compositional formulation using multipoint flux mixed finite element (MFMFE) method on general hexahedral grids with a future prospect of treating energized fractures. The mixed finite element framework allows for local mass conservation, accurate flux approximation and a more general treatment of boundary conditions. The multipoint flux inherent in MFMFE scheme allows the usage of a full permeability tensor. An accurate treatment of diffusive/dispersive fluxes owing to additional velocity degrees of freedom is also presented. The applications areas of interest include gas flooding, CO₂ sequestration, contaminant removal and groundwater remediation. / text
202

Turbulent Fluxes of CO2, H2O and Energy in the Atmospheric Boundary Layer above Tropical Vegetation investigated by Eddy-Covariance Measurements / Turbulente Flüsse von CO2, H2O und Energie in der Atmosphärischen Grenzschicht untersucht mittels Eddy-Kovarianz Messungen

Falk, Ulrike 20 February 2004 (has links)
No description available.
203

LAND USE IMPACT ON SOIL GAS AND SOIL WATER TRANSPORT PROPERTIES

Kreba, Sleem 01 January 2013 (has links)
The consequences of land use choices on soil water and gas transport properties are significant for gas and water flux in agricultural environments. Spatial and temporal patterns and associations of soil water and soil gas characteristics and processes in different land uses are not well understood. The objectives of this study were to 1) characterize soil structure under crop and grass systems, 2) quantify spatial patterns and associations of soil physical characteristics in crop and grass systems, and 3) quantify spatial and temporal patterns and associations of CO2 and N2O fluxes. The research was conducted in a 60 by 80 m field divided into grass and crop systems. Sixty sampling points were distributed in four transects with 5- and 1-m spatial intervals between measurement points. Gas fluxes were measured, at two-week time intervals, 22 times during a year. Pore size distribution was more homogeneous and more continuous pores were found in the grass than in the crop system. The spatial variability of most selected soil physical characteristics was more structured in the crop than in the grass system, which reflected the impact of land use and soil structure on their spatial patterns. CO2 flux was dependent for a longer distance in the grass than in the crop system, however, the two land-use systems exhibited similar spatial ranges of N2O flux. Gas fluxes were temporally dependent for a longer period in the grass than in the crop system. The spatial associations between CO2 and N2O fluxes and selected biochemical and physical factors depended on the flux sampling season and land use. Soil temperature was the dominant controlling factor on the temporal variability of CO2 and N2O fluxes but not on the spatial behavior. Considering the spatial and temporal ranges and dependency strength of soil variables helps identify efficient sampling designs that can result in better time and resource management. Spatial and temporal relationships between the selected soil variables also improve understanding soil management and sampling soil variables. This study provides the baseline and recommendations for future investigations specifically for sampling designs, soil management, and predictions of different soil processes related to gas fluxes.
204

Non-dimensional gradient functions for water vapor and carbon dioxide in the marine boundary layer / Dimensionslösa gradientfunktioner för vattenånga och koldioxid i det marina gränsskiktet

Vahlberg, Caroline January 2015 (has links)
A better understanding of the exchange processes taking place over the oceans is of great importance since the oceans cover about 70 % of the Earth’s surface. With better knowledge the turbulent fluxes can be more accurate parameterized, which is essential in order to improve the weather- and climate models. In this study, the non-dimensional gradient functions for water vapor (Φq) and carbon dioxide (Φc) in the marine boundary layer have principally been studied. The quality of the instrumentation used in the study has also been evaluated. The study is mainly based on tower measurements of turbulent fluxes and vertical profiles of water vapor and carbon dioxide, taken from the Östergarnsholm Island located in the Baltic Sea. The measurements have been shown to represent open-sea conditions for most situations when the winds are coming from the east-south sector, even though the measurements are obtained over land. It was found that the best fitting non-dimensional gradient functions for water vapor during unstable conditions were Φq = 2(1–18z/L)–1/2 and Φq = 1.2(1–14z/L) –1/2 at the 10 and 26 m level on the tower, respectively. No unique relationship could be established for Φq during stable conditions. Φq showed a dependence with wind direction and could for winds coming from the sector 80°– 160° be described with the relationship Φq = 1.2 + 10.7z/L during stable conditions. For the wind sector 50°– 80° the relationship for Φq was found to be Φq = 1.8 + 7.1z/L during stable conditions. A high degree of scatter was apparent in the calculated values of Φc during both stable and unstable conditions and did not seem to show any Monin-Obukhov similarity behaviour. The results indicate that there might be measurement problems with the instruments measuring the turbulent fluxes of carbon dioxide, but further studies are needed in order to draw a firm conclusion about the quality of the instruments. The profile measurements of water vapor seem to work fine, but more studies of carbon dioxide are needed before a statement can be made regarding the quality of the profile measurements of carbon dioxide. / Skiktet närmast marken kallas det atmosfäriska gränsskiktet och karaktäriseras av turbulens, dvs. oregelbundna virvelrörelser av olika storlekar som uppstår av vindens friktion mot jordytan (land eller hav) eller av luftens uppvärmning av jordytan. Genom turbulens kan utbyte av värme, vattenånga, momentum, koldioxid och andra gaser ske mellan jordytan och atmosfären. Turbulenta utbytesprocesser i det atmosfäriska gränsskiktet är viktiga att studera för att kunna beräkna ett turbulent flöde från en yta i väder- och klimatmodeller. Genom en ökad förståelse av flödena kan dessa bli mer noggrant parametriserade (dvs. en fysikalisk process som sker på en mindre skala eller är för komplex för att kunna beskrivas i en modell förenklas genom att beskriva processen med hjälp av ett antal kända parametrar som kan upplösas i modellen), vilket är grundläggande för att kunna förbättra modellerna. Flödena beräknas med hjälp av de s.k. dimensionslösa gradientfunktionerna, vilka relaterar flödet av en viss turbulent kvantitet, t.ex. värme, momentum, vattenånga, koldioxid etc., till dess vertikala gradient. Enligt Monin-Obukhovs similaritetsteori ska funktionerna vara universella och endast bero på den atmosfäriska stabiliteten. I denna studie har de dimensionslösa gradientfunktionerna för vattenånga (Φq) och koldioxid (Φc) i det marina gränsskiktet huvudsakligen analyserats. Kvaliteten på de instrument som har använts i studien har också utvärderats. I studien har främst data av turbulenta flöden och vertikala profiler av vattenånga och koldioxid använts som erhållits från ett torn på ön Östergarnsholm i Östersjön. Även om mätningarna sker över land har det visat sig att de för de flesta situationer när vinden blåser från sektorn ost-syd representerar likvärdiga förhållanden som gäller över öppet hav. Resultaten visade på att uttrycken Φq = 2(1–18z/L)–1/2 respektive Φq = 1.2(1–14z/L)–1/2 bäst beskriver de dimensionslösa gradientfunktionerna för vattenånga under instabila förhållanden på mäthöjderna 10 respektive 26 m. Något unikt uttryck för Φq under stabila förhållanden kunde inte fastställas. Φq visade ett beroende av vindriktning och kunde under stabila förhållanden beskrivas med uttrycket Φq = 1.2 + 10.7z/L för vindsektorn 80°– 160°. För vindar i sektorn 50°– 80° kunde Φq beskrivas enligt Φq = 1.8 + 7.1z/L under stabila förhållanden. En stor spridning syntes i de beräknade värdena av Φc under både stabila och instabila förhållanden och verkade inte följa Monin-Obukhov’s similaritetsteori. Resultatet tyder på att det kan vara mätproblem med de instrument som mäter de turbulenta flödena av koldioxid, men fler studier behövs för att kunna dra en definitiv slutsats om instrumentens kvalitet. Profilmätningarna av vattenånga verkar fungera bra, men fler studier om koldioxid måste utföras innan ett uttalande angående kvaliteten på profilmätningarna av koldioxid kan göras.
205

Soil organic carbon (SOC) now and in the future. Effect of soil characteristics and agricultural management on SOC and model initialisation methods using recent SOC data

Nemoto, Rie 19 December 2013 (has links) (PDF)
Soil organic carbon (SOC) concentrations and greenhouse gas (GHG) emissions are not uniform across the landscape, but assemble in "hotspots" in specific areas. These differences are mainly driven by human-induced activities such as agricultural management. 40-50% of the Earth's land surface is under agricultural land-use, for instance cropland, managed grassland and permanent crops including agro-forestry and bio-energy crops. Furthermore, 62% of the global soil C stock is SOC and the soil stores more than 3 times more C than the atmosphere. Thus, C sequestration in agricultural soil has a potentially important role in increasing SOC storage and GHG mitigation, and there is considerable interest in understanding the effects of agricultural management on SOC and GHG fluxes in both grasslands and croplands, in order to better assess the uncertainty and vulnerability of terrestrial SOC reservoirs. For the sake of discovering the agricultural management practices relating to the effective and sustainable C sequestration in agricultural lands in Europe, simulating future terrestrial C stocks and GHG budgets under varied agricultural management systems in major European ecosystems is essential. Using models is a useful method with the purpose of this and abundant studies have carried out. However, many model results have not been validated with reliable observed long-term data, while other studies have reported a strong impact of model initialisation on model result. Nevertheless, predictions of annual to decadal variability in the European terrestrial C and GHG ressources largely rely on model results. Consequently, finding the most appropriate and comprehensive model initialisation method for obtaining reliable model simulations became important, especially for process-based ecosystem models. In recent years, Zimmermann et al. (2007) have succeed in initialising the Rothamsted Carbon model (RothC) using a physical and chemical soil fractionation method. For that reason, we hypothesised that measured detailed SOC data would be useful to initialise ecosystem models, and this hypothesis should be tested for different process-based models and agricultural land-use and management. (...)
206

In situ remediation of contaminated sediments using thin-layer capping : efficiency in contaminant retention and ecological implications

Samuelsson, Göran S. January 2013 (has links)
Hydrophobic organic contaminants (HOCs) often reside in sediments sorbed to particles, most tightly to particles with high content of organic carbon. If persistent, such pollutants can accumulate in the sediment for many years and constitute a contamination risk for sediment-living organisms and organisms at higher trophic levels, including humans. Since traditional remediation techniques are associated with complications (e.g. release of contaminants during dredging operations, disturbance of benthic faunal communities), or constraints (handling of large amounts of contaminated sediment and water, limitations due to depth and size of the area, high costs), there is a need for new alternative methods. In situ remediation through thin-layer capping (a few centimeter cover) with a sorbing material such as activated carbon (AC) has been proposed as an alternative remediation method. Compared to traditional remediation techniques, AC amendment in a thin layer means less material handling and lower costs and is assumed to be less disruptive to benthic communities. The objectives of this thesis were to investigate the ecological effects from thin layer capping as well as the efficiency in contaminant retention. Thin layer capping amended with AC proved to reduce availability of HOCs to the tested organisms, the gastropod Nassarius nitidus (Paper II), the clam Abra nitida (Paper III) and to polychaete worms  (Paper II and III). The remediation technique also decreased the sediment-to-water fluxes of the contaminants (Paper II and III). However, AC amended thin-layer capping was also found to cause negative biological effects. In laboratory studies with only a few species the negative effects were minor, or difficult to discern with the endpoints used (Paper II and III). In a larger multi-species mesocosm (boxcore) study, on the other hand, the negative effects were more prominent (Paper I) and in a large scale field study the benthic community was found to be profoundly disturbed by the AC amendment, with the effects persisting or even worsening ca one year (14 months) post amendment (Paper IV). / <p>At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 3: Manuscript; Paper 4: Manuscript.</p> / Carbocap / Opticap / Thinc
207

An evaluation of regional sustainability by analysing energy and carbon flows – A study of Jämtland, Sweden

Skytt, Torbjörn January 2018 (has links)
Models showing the anthropogenic and natural flows of two sustainability indicators; carbon based GHG and energy (as work energy) have been made for the Swedish region Jämtland. The methodology used was inspired by the study sustainability analysis conducted on the small Danish island Samsø using the above two indicators. The aim was to upscale the methodology used for Samsø and make necessary adaptations for Jämtland in order to be able to evaluate sustainability in terms of global warming. We also wanted to study the linkages between research, education and regional sustainability initiatives. Working at a regional level has advantages compared to working at a national or global level, as socio-ecological processes can be covered more extensively to reach a deeper understanding of practical aspects. In parallel to this we have also been participating in local and regional sustainability activities to increase our understanding of practical approaches and human behaviour. Studies of the energy flows in Jämtland show that 46,000 TJ (88% renewable) flows into the region and about 31,000 TJ is exported. The remaining 15,000 TJ (63% renewable) drives ‘the machine Jämtland’. Added to this is about 4000TJ as matter. The total global warming potential (GWP20) impact of Jämtland (as carbon dioxide equivalents, CO 2eq ) indicating influence on the global mean temperature as radiative forcing) is an annual uptake of 2.4 Mton. The total regional emissions, as CO 2eq, from anthropogenic activities, including consumption, are 1500 kton. The region has large emissions of methane, 80kton (6700 kton CO 2eq ), mainly from mires, lakes and animals but also large uptakes of CO2 from assimilation in woody biomass. Jämtland can be regarded as relatively sustainable from several perspectives, but taking the large forests and a population of only 127,000 inhabitants into consideration, the total uptake of CO 2eq is not very large and of the 15,000 TJ driving Jämtland, 37% comes from non-renewable sources. From a national (and global) perspective Jämtland needs to perform better, in view of its considerable reserves of natural resources. How to increase long-term sustainability in the region is a complex issue that requires penetration from many perspectives. Modelling results presented here needs to be interpreted in a broader sustainability context, together with regional stakeholders, to serve as a base for future knowledge development and sustainability activities. / Två modeller har utvecklats för att studera antropogena och naturliga flöden av energi (exergi) och kolbaserade växthusgasflöden i Jämtland. Metodiken har inspirerats av en metodik för att göra hållbarhetsanalyser som genomförts för den lilla danska ön Samsø utifrån dessa båda indikatorer. Att arbeta på regional nivå har fördelar gentemot att arbeta på en nationell eller global nivå eftersom man har större möjligheter att gå ned på djupet både gällande samhälleliga processer och ekologiska processer. Kopplingen mellan siffror och faktiska skeenden blir tydligare. Parallellt med arbetet med de regionala modellerna har vi också deltagit i lokalt och regionalt arbete för att förståelsen omkring praktiska angreppssätt och mänskligt beteende. Studien av energiflöden i Jämtland visar att 46.000 TJ (varav 88% förnyelsebart) flödar in i regionen och 31.000 TJ exporteras ut och att resterande 15.000 TJ (varav 63% förnyelsebart) driver maskineriet Jämtland. Till detta kommer omkring 4000 TJ i form av material. Den totala GWP20-påverkan från Jämtland är ’kylande’ och motsvarar ett upptag av koldioxid-ekvivalenter årligen på 2.4 Mton, vilket ungefär motsvarar emissionen från225.000 genomsnittssvenskar. De totala antropogena emissionerna av CO 2eq , inklusive konsumtion, är 1500 kton. Regionen uppvisar betydande emissioner av metan, 80 kton (motsvarande 6700 kton CO 2eq ) från sjöar, myrar och våtmarker samt djur. Jämtland kan ur flera perspektiv betraktas som relativt hållbart, men tar man de enorma skogsarealerna och den i ett internationellt perspektiv blygsamma befolkningen på 127 000 personer i beaktande är hållbarheten mindre övertygande. Vidare är 37% av den energi som driver Jämtland faktiskt icke-förnyelsebar. Sett ur ett globalt perspektiv och med hänvisning till Jämtlands enorma naturresurser behöver Jämtland prestera bättre. Hur man skall kunna öka den långsiktiga hållbarheten är en komplex fråga som kräver belysning från flera olika perspektiv. Resultat som de som presenteras här måste tolkas tillsammans med regionala intressenter i ett bredare hållbarhetssammanhang för att kunna utarbeta lämpliga implementeringsstrategier. / <p>Vid tidpunkten för framläggningen av avhandlingen var följande delarbete opublicerat: delarbete 4 (manuskript).</p><p>At the time of the defence the following paper was unpublished: paper 4 (manuscript).</p>
208

Le contrôle des émissions de protoxyde d'azote par le fonctionnement hydrique des sols / The control of nitrous oxide emissions by the hydric functioning of soils

Rabot, Eva 30 October 2014 (has links)
Les sols et les activités agricoles qu’ils supportent, contribueraient à environ 2/3 des émissions globales de protoxyde d’azote (N2O), un puissant gaz à effet de serre. L’objectif de la thèse était la compréhension des déterminismes des émissions de N2O liés aux propriétés hydriques des sols. Des expérimentations de laboratoire permettant le contrôle hydrique fin d’échantillons de sol, en saturation et en désaturation, et la mesure des flux de N₂O ont été menées. Un couplage avec la tomographie par rayons-X a par ailleurs permis de caractériser la connectivité gazeuse. Enfin, une démarche de modélisation a permis de tester les hypothèses de fonctionnement émises, et de poursuivre la démarche de réflexion sur le lien entre les propriétés hydriques des sols et les émissions de N₂O. On a mis en évidence le rôle des propriétés hydriques des sols dans la variabilité des émissions de N₂O couramment observées, et la nécessité de distinguer des périodes de production/consommation de N₂O et de transport. On retiendra ainsi le fort caractère dynamique des émissions de N₂O, en lien avec la phase hydrique (saturation ou désaturation), le fonctionnement hydrodynamique des sols, le transport gazeux et la configuration spatiale de l’air et de l’eau dans le réseau de pores. Afin de décrire l’intensité et le timing des pics de N₂O, il est apparu pertinent d’observer les paramètres potentiel matriciel, coefficient de diffusion gazeuse et connectivité gazeuse, en plus de la teneur en eau. Ces observations ont des implications sur la modélisation des flux de N₂O. On recommande ainsi l’utilisation couplée de modules de transport hydrique, de transport gazeux et en solution de N₂O, en plus de modules de production microbiologique, pour prédire efficacement les émissions de N₂O. / Soils and associated agricultural activities are estimated to account for about 2/3 of the global emissions of nitrous oxide (N₂O), a potent greenhouse gas. The aim of the thesis was to understand the controls linked to soil hydric properties on N₂O emissions. Laboratory experiments were designed to control the hydric status of soil samples during wetting and drying, and to measure N₂O fluxes. Moreover, a coupling with X-ray computed tomography allowed characterizing the gaseous connectivity. Finally, a modeling approach allowed testing the hypotheses of functioning, and to further discuss the links between hydric properties and N₂O emissions. We highlighted the role of soil hydric properties on the variability of N₂O emissions which is often measured, and the need to distinguish N₂O production/consumption and transport phases. The highly dynamic nature of N₂O emissions was linked to the hydric phase (wetting or drying), soil hydrodynamic functioning, gas transport, and spatial configuration of water and air in the pore network, in addition to the water-filled pore space parameter. These observations have implications for N₂O emission modeling. We recommend thus the coupled use of hydric transport, and modules of gas and liquid transport of N₂O, in addition to microbial production modules to efficiently predict N₂O emissions.
209

Dilemas da construção do espaço público e seus vínculos com os fluxos comunicativos primários : a experiência da rádio comunitária no bairro restinga

Daniel, Maira Graciela January 2008 (has links)
Esta dissertação tem como tema a constituição da esfera pública no contexto brasileiro. Hannah Arendt e Jürgen Habermas desenvolveram análises fundamentais para a definição conceitual da esfera pública, sendo ela compreendida, nesta pesquisa, como um espaço de discussão com predominância do agir comunicativo. No Brasil, a formação dessa esfera deuse de forma problemática, havendo a prevalência de valores como patrimonialismo, paternalismo e confusão entre a esfera pública e a esfera privada. O estudo da Rádio Quilombo FM, uma rádio comunitária, localizada no bairro Restinga, periferia da cidade de Porto Alegre/RS, objetiva analisar a relação estabelecida entre os fluxos comunicativos primários e a rádio comunitária, buscando perceber de que forma a esfera pública, que pode a partir disso ser formada, colabora para o rompimento com as formas tradicionais de sua constituição, propiciando ou não a criação de uma esfera pública alternativa de caráter democrático. A metodologia proposta na pesquisa foi qualitativa com uso de observação participante e entrevistas em profundidade como técnicas de investigação. / The theme of this Master's dissertation is the constitution of the public sphere in the Brazilian context. Hannah Arendt and Jürgen Habermas developed fundamental analyses for the conceptual definition of the public sphere, understood, in this research, as a space for discussion with predominance of the communicative acting. In Brazil, the constitution of this sphere was done in a problematic way, prevailing values such as patrimonialism, paternalism and confusion between the public sphere and the private one. The objective of studying Radio Quilombo FM, a community radio in Restinga neighborhood, suburbs in the city of Porto Alegre/RS, is to analyze the relationship established between the primary communication fluxes and a community radio, trying to perceive how the public sphere contributes to the rupture with the traditional ways of its constitution, allowing or not the creation of an alternative public sphere with democratic character. The methodology proposed in this research was qualitative, with the use of participant observation and in-depth interviews as techniques of investigation.
210

Effet du type de sol sur le fonctionnement biogéochimique des écosystèmes forestiers / Influence of soil type on the biogeochemical functioning of forest ecosystems

Kirchen, Gil 18 December 2017 (has links)
Cette thèse porte sur l’impact du type de sol sur le fonctionnement biogéochimique d’un écosystème forestier typique d’Europe centrale et occidentale. Pour cette étude, un dispositif expérimental a été mis en place par l’INRA et l’ANDRA au sein d’une hêtraie (Fagus sylvatica) dans la forêt de Montiers-sur-Saulx (Meuse, France) afin de suivre les cycles biogéochimiques entre les différents compartiments de l’écosystème (l’atmosphère, la canopée, la litière et le sol). L’intérêt particulier du site expérimental de Montiers vient du contraste important entre les types de sols pour un même peuplement : rendisol, calci-brunisol et alocrisol/brunisol. Pour la première fois, les stocks et les flux de l’eau et des éléments ont été mesurés et comparés in situ et sur le long terme (entre janvier 2012 et décembre 2015) sur des sols forestiers différents, toutes les autres conditions du site égales par ailleurs (climat, apports atmosphériques, âge et structure du peuplement). Les stocks totaux et échangeables dans le sol et les stocks dans les différents compartiments de la biomasse végétale (branches, tronc, racines grosses et fines) ont été déterminés par le biais d’analyses chimiques et de modélisations. Les flux élémentaires ont été calculés à partir des prélèvements mensuels des solutions de l’écosystème (dépôt atmosphérique, pluviolessivat, écoulement de tronc, solutions libres et liées du sol) et des chutes de litière. Le modèle hydrique BILJOU© a été utilisé pour estimer les composantes du bilan hydrique de l’écosystème. Les résultats montrent que la réserve utile du sol, les stocks des éléments dans le sol, les compositions chimiques des solutions du sol, la stratégie de colonisation racinaire et la production de biomasse pérenne diffèrent fortement en fonction du type de sol. Contrairement à ce que l’on pouvait supposer compte tenu des différences marquées entre les signatures chimiques des solutions des trois sols, les compositions foliaires du peuplement et les flux des éléments hors sol en solution (échange de la canopée, apport au sol) et sous forme solide (chute de litière) ne diffèrent pas ou peu entre les trois stations expérimentales pour la majorité des éléments. La part biologique des cycles minéraux est globalement prédominante et le renouvellement des racines fines représente un flux de recyclage généralement supérieur à la chute de litière aérienne. Nous montrons également que la quantité d’eau transpirée par la canopée, directement liée à la taille de la réserve utile du sol, est le facteur de contrôle principal de la productivité du peuplement à l’échelle annuelle. Des processus d’adaptation du peuplement aux conditions physico-chimiques du sol semblent réduire, voire compenser entièrement, les facteurs secondaires de contrôle de la productivité du peuplement (notamment la disponibilité des nutriments dans le sol). Ainsi un enjeu significatif pour les gestionnaires forestiers pourrait être l’adaptation des pratiques sylvicoles à des parcelles de gestion davantage basées sur les propriétés physiques des sols, et en particulier les profondeurs d’apparition de la roche-mère et de colonisation racinaire / This thesis deals with the impact of soil type on the biogeochemical functioning of a typical forest ecosystem of Central and Western Europe. For this study, a strongly instrumented experimental site was implemented in a beech stand (Fagus sylvatica) within the state forest of Montiers-sur-Saulx (Meuse, France), in order to monitor the biogeochemical cycling between the different compartments of the ecosystem (the atmosphere, the canopy, the forest floor and the soil). The particular value of the Montiers experimental site resides in the strong contrast between soil types under the same beech stand: Rendzic Leptosol, Eutric Cambisol and Dystric Cambisol. For the first time, stocks and fluxes of water and elements were measured and compared in situ and over the long term (from January 2012 to December 2015) on different forest soil types, all other site conditions being equal (climate, atmospheric inputs, stand age and structure). Total and exchangeable pools in the soil and stocks in the different compartments of the vegetation (branches, trunk, fine and coarse roots) were determined via chemical analysis and modelisation. Fluxes of elements were calculated from monthly sampling of the ecosystem’s solutions (atmospheric deposition, throughfall, stemflow, gravitational and bound soil solutions) and of litter fall. The water balance model BILJOU© was used to estimate the different components of the water budget. The results show that the soil water holding capacity, the stocks of elements in the soil, the chemical composition of soil solutions, the rooting strategy and the perennial biomass production differ strongly between soil types. Contrary to what might have been expected in regard to the marked differences between the chemical signatures of the soils solutions in the three soils, the foliar elemental composition of the beech stand and the aboveground fluxes of elements in solution (canopy exchange, stand deposition) and in solid state (litter fall) do not differ significantly between the three experimental stations for the majority of the studied elements. The biological part of the mineral cycles is overall predominant and the recycling through fine roots turnover is generally higher than litter fall. We also show that the quantity of water transpired by the forest canopy, directly linked to the soil water holding capacity, is the primary control factor of the annual stand productivity. Stand adaptation mechanisms to physico-chemical soil properties seemed to reduce, or even entirely compensate for, secondary factors controlling the stand productivity (in particular nutrient availability in the soil). Thus a significant issue for forest managers might be to further adapt forestry practices to management units based on soil physical properties, especially depth to the bedrock and rooting depth

Page generated in 0.0713 seconds