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Orientador: César Augusto Moreira / Resumo: Aterros sanitários de resíduos sólidos são a forma de disposição final adequada mais utilizada no mundo devido a suas vantagens operacionais. O processo de instalação, no entanto, exige o desenvolvimento de diversos sistemas tecnológicos a fim de garantir uma disposição de resíduos segura em termos ambientais e de saúde pública. Ainda assim, a contaminação do ambiente subterrâneo pelos produtos da degradação dos resíduos sólidos (chorume) é recorrente. Diante dessas ocorrências, é necessário investigar a área com o objetivo de encontrar as falhas nos sistemas do aterro responsáveis pela contaminação; propor projetos de remediação e monitoramento. Este trabalho aplicou o método geofísico da eletrorresistividade em uma vala de resíduos de um aterro sanitário de pequeno porte com o intuito de diagnosticar a presença de chorume no aquífero e detectar possíveis imperfeições no sistema de impermeabilização. Adicionalmente, por meio de um monitoramento temporal do parâmetro resistividade, entender a dinâmica da geração e fluxo do chorume na área do aterro. Para tanto, o levantamento geofísico contou com 12 linhas de tomografia elétrica, adquiridas durante um período de 3 anos (2016, 2017 e 2018). Para complementar os resultados o método do potencial espontâneo foi aplicado na área no ano de 2018 com o objetivo de adicionar informações a respeito do estágio de degradação dos resíduos sólidos. Os resultados do parâmetro resistividade elétrica são apresentados em seções 2D e modelos de... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Landfills are the most widely used destination in the world for municipal solid waste due to their operational advantages. The installation, however, requires the development of several technological systems in order to ensure a safe and environmentally correct disposal of waste. Nevertheless, the contamination of the subsurface by leachate is recurrent. In view of these occurrences, it is necessary to investigate the area in order to find the faults in the landfill systems responsible for the contamination; propose projects for remediation and monitoring of the area. Therefore, this project predicted the application of the resistivity method in order to diagnose the sources of contamination and to detect possible point of percolation through the geomembrane. By means of a temporal monitoring the present project aimed to understand the leachate generation and flow in the landfill area. For this purpose, the geophysical survey consisted of 12 electrical tomography lines, acquired during a three-year acquisition period (2016, 2017 and 2018). To complement the results, the self-potential method was applied in the area in the year 2018 with the purpose of adding information about the solid waste degradation stage. The results of the resistivity parameter are presented in 2D sections and 3D visualization models with discussions for the superficial level of acquisition, for the geomembrane level (-4m) and for the aquifer level (-10m). The analysis over the years allowed the identif... (Complete abstract click electronic access below) / Doutor

Anomalias de potencial espontâneo com amplitudes de dezenas a centenas de milivolts são observadas em plumas de contaminação apesar de não serem explicadas por modelos de geobateria normalmente utilizados na geofísica de exploração. Modelos recentemente propostos, denominados de biogeobateria, assumem que estruturas orgânicas produzidas por micro- organismos assumem a função de condução eletrônica que os minerais condutivos exercem no modelo clássico de geobateria. O modelo de biogeobateria, por outro lado, se assemelha com o que se denomina sistemas bioeletroquímicos ou células de combustível microbianas em áreas da biotecnologia (bioenergia). O presente trabalho explora esta semelhança para desenvolver um experimento de laboratório que utiliza um sistema bioeletroquímico como modelo análogo de biogeobateria para mostrar que este modelo é capaz de explicar o sinal de potencial espontâneo observado em campo. Os resultados experimentais e de modelagem numérica mostram que a amplitude do potencial elétrico depende: da área do catodo, da resistência interna da biogeobateria, da existência de um fluxo adicional de cátions do anodo para o catodo, da resistividade elétrica do meio e da separação do anodo com o catodo. Os resultados experimentais mostraram-se compatíveis com observações de campo obtidas na caracterização hidrogeofísica de uma pluma de contaminação, proveniente de um aterro de resíduos (lixão). A pluma de contaminação se estende por dois níveis em profundidade, comprometendo a qualidade do aquífero livre e certamente do aquífero confinado. A ano- malia de potencial espontâneo alcança amplitude de 70mV sobre o aquífero livre, sendo praticamente desprezível sobre o aquífero confinado, tal como se observa em laboratório em modelos correspondentes. O experimento com biogeobateria mostra também que as reações químicas desencadeadas no anodo oxidam o substrato orgânico, reduzindo a demanda química de oxigênio em 10 % no experimento considerado. Este resultado mostra que sinais de potencial espontâneo em áreas contaminadas podem ser considerados como indicativos de processos oxidativos ocorrendo em um substrato orgânico sendo, pois, de relevância para o reconhecimento de processos de atenuação natural em terrenos com contaminantes orgânicos. / Self-potential anomalies with amplitudes of tens to hundreds of millivolts are observed in contaminated plumes despite not fully explained by geobattery models commonly used in geophysical exploration. Recently proposed models, termed as biogeobattery, assume that organic structures produced by microorganisms act as electronic conductors, as it is done by conductive minerals in standard geobattery models. The biogeobattery model in addition resembles what is termed as bioelectrochemical system or microbial fuel cell in fields of the research in biotechnology (bioenergy). This study explores this similarity to develop a laboratory experiment using a bioelectrochemical system as an analog model for a biogeobattery, to show that this model is able to explain the spontaneous potential signals observed in many geophysical surveys over contaminated sites. Experimental and modeling results show that the amplitude of the electric potential from a biogeobattery depends on: the area of ? the cathode, its internal resistance, the existence of an additional flow of cations (from the anode to the cathode), the electrical resistivity of the medium and the separation of anode to the cathode. In general, the experimental results were compatible with field observations at a contamination plume produced by a landfill. The contamination plume extends over two levels deep, degrading the quality of the unconfined and confined aquifers. The amplitude of the self-potential anomaly reaches 70mV over the unconfined aquifer and is negligible over the confined aquifer, as observed in the corresponding models of the laboratory experiment. The biogeobattery experiment also shows that chemical reactions at the system anode were able do oxidize the organic substrate, reducing in 10% its chemical oxygen demand. This result shows that self-potential signals in contaminated areas can be regarded as indicative of oxidative processes taking of buried organic matter and, as such, a proxy of biodegradation processes leading to natural attenuation of organic ontaminants.

Anomalias de potencial espontâneo com amplitudes de dezenas a centenas de milivolts são observadas em plumas de contaminação apesar de não serem explicadas por modelos de geobateria normalmente utilizados na geofísica de exploração. Modelos recentemente propostos, denominados de biogeobateria, assumem que estruturas orgânicas produzidas por micro- organismos assumem a função de condução eletrônica que os minerais condutivos exercem no modelo clássico de geobateria. O modelo de biogeobateria, por outro lado, se assemelha com o que se denomina sistemas bioeletroquímicos ou células de combustível microbianas em áreas da biotecnologia (bioenergia). O presente trabalho explora esta semelhança para desenvolver um experimento de laboratório que utiliza um sistema bioeletroquímico como modelo análogo de biogeobateria para mostrar que este modelo é capaz de explicar o sinal de potencial espontâneo observado em campo. Os resultados experimentais e de modelagem numérica mostram que a amplitude do potencial elétrico depende: da área do catodo, da resistência interna da biogeobateria, da existência de um fluxo adicional de cátions do anodo para o catodo, da resistividade elétrica do meio e da separação do anodo com o catodo. Os resultados experimentais mostraram-se compatíveis com observações de campo obtidas na caracterização hidrogeofísica de uma pluma de contaminação, proveniente de um aterro de resíduos (lixão). A pluma de contaminação se estende por dois níveis em profundidade, comprometendo a qualidade do aquífero livre e certamente do aquífero confinado. A ano- malia de potencial espontâneo alcança amplitude de 70mV sobre o aquífero livre, sendo praticamente desprezível sobre o aquífero confinado, tal como se observa em laboratório em modelos correspondentes. O experimento com biogeobateria mostra também que as reações químicas desencadeadas no anodo oxidam o substrato orgânico, reduzindo a demanda química de oxigênio em 10 % no experimento considerado. Este resultado mostra que sinais de potencial espontâneo em áreas contaminadas podem ser considerados como indicativos de processos oxidativos ocorrendo em um substrato orgânico sendo, pois, de relevância para o reconhecimento de processos de atenuação natural em terrenos com contaminantes orgânicos. / Self-potential anomalies with amplitudes of tens to hundreds of millivolts are observed in contaminated plumes despite not fully explained by geobattery models commonly used in geophysical exploration. Recently proposed models, termed as biogeobattery, assume that organic structures produced by microorganisms act as electronic conductors, as it is done by conductive minerals in standard geobattery models. The biogeobattery model in addition resembles what is termed as bioelectrochemical system or microbial fuel cell in fields of the research in biotechnology (bioenergy). This study explores this similarity to develop a laboratory experiment using a bioelectrochemical system as an analog model for a biogeobattery, to show that this model is able to explain the spontaneous potential signals observed in many geophysical surveys over contaminated sites. Experimental and modeling results show that the amplitude of the electric potential from a biogeobattery depends on: the area of ? the cathode, its internal resistance, the existence of an additional flow of cations (from the anode to the cathode), the electrical resistivity of the medium and the separation of anode to the cathode. In general, the experimental results were compatible with field observations at a contamination plume produced by a landfill. The contamination plume extends over two levels deep, degrading the quality of the unconfined and confined aquifers. The amplitude of the self-potential anomaly reaches 70mV over the unconfined aquifer and is negligible over the confined aquifer, as observed in the corresponding models of the laboratory experiment. The biogeobattery experiment also shows that chemical reactions at the system anode were able do oxidize the organic substrate, reducing in 10% its chemical oxygen demand. This result shows that self-potential signals in contaminated areas can be regarded as indicative of oxidative processes taking of buried organic matter and, as such, a proxy of biodegradation processes leading to natural attenuation of organic ontaminants.

For the protection of wetland and water resources it would be beneficial to understand when collapse conduits function as recharge points to the underlying aquifer. Inexpensive, noninvasive methods to detect recharge are desirable. Previous studies show negative self-potential (SP) anomalies over sinkholes that correspond to the expected electrokinetic effects of groundwater flowing downward through a conduit. SP surveys are less labor-intensive than high-resolution 3D GPR and resistivity, and continuous long-term monitoring is possible. However, before SP surveys can be reliable indicators of flow, SP contributions from ET, conductivity changes, redox reactions, thermoelectric effects, cultural noise, and lateral flow must be understood. A year of continuous SP monitoring was combined with high-resolution 3-D GPR surveys, and intermittent water table monitoring over two small covered-karst sinkholes in Tampa, Florida. Positive and negative SP anomalies episodically manifested over conduits, suggesting that conduit flow is dynamic, not static. Three distinct SP flow regimes in the conduits are postulated: fast flow open to the aquifer, slow flow open to the confining layer through the collapse conduit walls, and a conduit, plugged high enough to behave like the rest of the confining layer. SP responses after rain events also appear to measure the effects of two moving Gaussian wetting front curves, one striking the monitoring electrode, one the reference. viii The wetting front volumes are differently dispersed by traveling different distances. By comparing curve shapes for all possible pairs of electrodes, it may be possible to establish surficial infiltration and flow patterns. Temporal SP response clearly shows SP is also affected by soil conductivity, rainfall history, and cultural noise. Ultimately, SP changes too frequently to rely on measurements many hours or days apart. Over the course of the year, the electrodes became less responsive to rainfall and more erratic. Extremely wet and dry conditions seemed to affect responses. The porous faces of the electrodes or the bentonite clay gel used to enhance contact may decline. It appears a better design for electrodes and electrode contact needs to be developed. To test the intermittent behavior hypothesis, more conduits need to be studied, and moisture and SP must be studied concurrently. Several reference electrodes placed in various topographic, vegetative, geologic, and climatic settings could help distinguish groundwater flow from other SP sources. SP is a valuable research tool; however external complexities such as cultural noise, sinkhole lithology, and the state of the unsaturated zone make SP data difficult to interpret without ancillary information.

Les méthodes géophysiques non intrusives sont requises pour caractériser la zone vadose, les réservoirs d’hydrocarbures, ou les sites de stockages de CO₂. Nous analysons l’impact d’une injection de CO₂ gazeux sur la conductivité électrique et les propriétés électrocinétiques des roches carbonatées partiellement ou totalement saturées grâce aux méthodes de polarisations provoquée et spontanée. Les données sont analysées au regard au regard de mesures effectuées sur une roche chimiquement neutre, vis-à-vis du CO₂, c’est-à-dire , un grès de Fontainebleau. Nous comparons également nos résultats aux données de la littérature. Le coefficient de couplage électrocinétique est un paramètre clé, dont nous allons étudier la dépendance vis-à-vis de la saturation, sujet hautement débattu de nos jours. En utilisant la méthode de polarisation spontanée, nous étudions les relations entre le coefficient de couplage électrocinétique, la pression capillaire ainsi que la perméabilité relative au sein des roches carbonatées. Un système expérimental a été élaboré pour mesurer simultanément la perméabilité relative, l’indice de resistivité et le coefficient de couplage électrocinétique en écoulement diphasique de type eau-gaz, en fonction de la saturation en azote ou en dioxyde de carbone. Les résultats sont comparés à des modèles théoriques basés sur les approches de Brooks et Corey et van Genuchten, dont les exposants nous permettent d’ajuster les données avec les modèles de pression capillaire avec succès. Les échantillons sont saturés avec des saumures de différentes compositions, dont les ions sont mono- ou divalents et pour lesquelles la force ionique est comprise entre 10⁻⁴ et 10⁰ Mol L⁻¹. La valeur absolue du coefficient de couplage électrocinétique augmente lorsque la force ionique de la solution diminue, ce qui a déjà été observé dans les roches gréseuses. Le potentiel zêta a été calculé en utilisant une version modifiée de l’équation d’Helmholtz-Smoluchowski, qui prend en compte les effets liés à la conductivité de surface. Comme pour le coefficient de couplage, la valeur absolue du potentiel zêta chute lorsque la force ionique augmente. Nous nous intéressons également aux effets liés à une injection de CO₂ et à la dissolution de la calcite sur la valeur de ce potentiel zêta. Enfin, nous utilisons la méthode de polarisation provoquée pour déterminer l’influence de conductivité de l’eau porale sur la conductivité électrique complexe, la chargeabilité normalisée ainsi que le temps de relaxation en milieu carbonaté non saturé. Nous montrons que ces paramètres peuvent être considérés comme des paramètres de polarisation de la double couche électrique lorsque la conductivité de l’eau porale est comprise entre 10⁻³ et 10⁰ S m⁻¹. / Minimally intrusive geophysical methods are required to characterize both the vadose zone of the Earth, hydrocarbon reservoirs and CO₂ sequestration. We investigate the impact of gaseous CO₂ on both electrical conductivity and electrokinetic properties of limestones under saturated and unsaturated conditions, using the spectral induced polarization and the self-potential methods. These data are contrasted with measurements performed on a Fontainebleau sandstone and data from the literature. That said, the dependence of a key parameter, the streaming coupling coefficient, with the saturation remains highly debated. Using the self-potential method, we explore the relationship between the streaming potential coupling coefficient, the capillary pressure curves and the permeability in carbonate rocks characterized by distinct textures. A new core flooding system is used to measure simultaneously both the relative permeability, the resistivity index and the streaming potential coupling coefficient in steady-state two-phase flow conditions as a function of the saturation with CO₂ or N₂. The results are compared with a recently developed theoretical model, which can accommodate either the Brooks and Corey or the van Genuchten models for the capillary pressure curves. Saturation was achieved with monovalent and divalent brines with ionic strength ranging from 1x10⁻³ Mol L⁻¹ to 1x10⁰ Mol L⁻¹. The magnitude of the coupling coefficient increases with decreasing ionic strength similarly to the trend observed for sandstones. The zeta potential has been calculated at full saturation using a modified version of the Helmholtz-Smoluchowski equation that accounts for surface electrical conductivity. Under atmospheric conditions, the magnitude of the zeta potential is decreasing with the increase of the ionic strength. We also investigate the effects of a CO₂ release and the calcite dissolution on the magnitude of the zeta potential. Finally, we use the spectral induced polarization method to determine the pore water conductivity effects on the complex electrical conductivity, the normalized chargeability and the main relaxation time during drainage in a clay free limestone. We also show evidences that these parameters could be considered as polarization parameters of the electrical double layer in the pore water conductivity range 10⁻³ - 10⁰ S m⁻¹.

Résumé : Au Québec, les ouvrages hydrauliques représentent une source indéniable pour la production d’énergie et la gestion hydraulique, et par conséquent un moteur nécessaire pour le développement socioéconomique. De ce fait, une conception adéquate et des inspections continues sont nécessaires pour assurer la stabilité et la sécurité de ces ouvrages. Ainsi, les anomalies dans les barrages doivent être localisées dans le plus court délai. L’érosion interne est la cause principale de la rupture des ouvrages en remblai. En conséquence, l’infiltration de l’eau dans les barrages, qui engendre le phénomène d’érosion interhe, doit être détectée. Quelques méthodes non destructives ont été développées pour ausculter ces ouvrages et déterminer le niveau piézométrique dans les ouvrages en remblai. Dans le cadre de ce projet, la méthode de la polarisation spontanée a été adoptée. Cette méthode consiste à mesurer de façon passive un champ électrique généré à la surface des particules du sol par électrofiltration. Le phénomène d’électrofiltration est défini par la circulation hydrique dans la matrice poreuse d ’un matériau qui engendre un champ électrique mesurable à la surface du sol. Des essais au laboratoire de l’Université de Sherbrooke ont été réalisés pour déterminer l’effet de la circulation de l’eau sur les propriétés électriques de différents matériaux. Un dispositif d’essai a été développé et utilisé pour les essais et le modèle théorique est celui de Helmholtz-Smoluchowski. Durant les essais, l’influence de la charge hydraulique, de la température et de la granulométrie sur les propriétés électriques des matériaux ont été vérifiées. Les expériences ont pour objectif primaire de déterminer le rapport entre le coefficient de couplage et le potentiel zêta en utilisant la méthode de la polarisation spontanée. Les résultats expérimentaux obtenus ont été comparés avec des valeurs tirées de la littérature pour tester le modèle et le protocole utilisés. Étant donné que les données expérimentales correspondent avec les valeurs acceptées dans la communauté scientifique, le modèle expérimental adopté peut être considéré fiable. Ce projet est un préalable pour une recherche future qui permettra de développer un algorithme d’inversion pour déterminer et localiser les anomalies dans les ouvrages en remblai. Les études expérimentales ont démontrées que la charge hydraulique a eu un effet considérable sur les propriétés électriques des différents matériaux. Le coefficient de couplage et le potentiel zêta varie proportionnellement avec la charge hydraulique. De plus, les propriétés électriques ont subi une variation en fonction de la température du fluide. Enfin, le coefficient de couplage et le potentiel zêta des différents matériaux ont subi des variations proportionnelles à l’uniformité de chacun des matériaux. Pour un matériau plus uniforme, le coefficient de couplage est plus faible et le potentiel zêta est plus élevé. // Abstract : In Quebec, hydraulic represents an undeniable source for energy production and therefore needed an engine for economie development. Therefore, proper design and ongoing inspections are necessary to ensure the stability and safety of these structures. Thus, abnormaiities in embankment dams should be located in the shortest time. The internai erosion is the main cause of the failure of embankment dams. Consequently, the infiltration of water in dams, which generates the internai erosion, should be detected. Several non-destructive methods have been developed to auscultate these structures and determine the groundwater level in the embankment works. In this project, the self-potential (SP) method was adopted. This method consists in measuring a passive electric field at the surface of the soil. The phenomenon is defined by the electrofiltration circulation water into the porous matrix of a material which generates a measurable electric current to the ground surface. Laboratory tests at the Université de Sherbrooke were performed to determine the effect of water flow on the electrical properties for different materials. Plexiglas pipe was used for testing and the theoretical model is the Helmholtz-Smoluchowski. During the tests, the influence of hydraulic loading and temperature on the electrical properties of the materials has been checked. The experiments aim at determining the primary relationship between the coupling coefficient and zeta potential using the self-potential (SP) method. The experimental results were compared with values from the literature to confirm the model and protocol used. Thus since that the experimental data are consequent with those theoretical, experimental model adopted can be considered as reliable. This project is a prerequisite for future research that will develop an inversion algorithm to identify and locate anomalies in the embankment dams. Experimental studies have demonstrated that the hydraulic load had a significant effect on the electrical properties of different materials. The coupling coefficient and the zeta potential vary proportionally to the hydraulic load. In addition, the electrical properties underwent change depending on the fluid temperature. Finally, the coupling coefficient and zeta potential of different materials have fluctuated proportionally to the uniformity of each material. For a more uniform material, the coupling coefficient is lower and the zeta potential is higher.

La contamination par les hydrocarbures peut altérer les propriétés physicochimiques et biologiques du sous-sol, par conséquent le diagnostic et l’évolution des contaminants peuvent être surveillés en couplant les analyses géochimiques et les techniques géophysiques. Dans ce travail, différentes méthodes géophysiques de sub-surface telles que la tomographie de résistivité électrique, la polarisation induite, le géoradar et le potentiel spontané ont été utilisées d’une manière combinée pour localiser les zones impactées par les hydrocarbures du site de l’ancienne raffinerie de Petit Couronne. Les investigations géophysiques par la tomographie de résistivité électrique en 2D ont révélés la présence des anomalies de fortes valeurs de conductivité et chargeabilité électrique associés aux zones contaminées de l’aquifère. Les résultats obtenus avec les profils d’ERT et IP indiquent que la contamination a modifié les parties capacitives et ohmiques de la conduction électrique dans les sédiments contaminés. Cette signature très conductrice des zones contaminées est due aux processus de biodégradation des hydrocarbures qui minéralisent les eaux de l’aquifère. Les panaches d’hydrocarbures ont été identifiés sur les profils de géoradar par une forte atténuation des amplitudes de signaux électromagnétiques. Les profils de potentiel spontané ont aussi fourni une cartographie spatiale des zones contaminées par leurs signatures électriques négatives qui est associées aux processus d'oxydoréduction et biodégradation à l’interface entre la zone non saturée et saturée. Une carte de potentiel redox a été reconstruite à partir de l'inversion des données résiduelles de potentiel spontané grâce au calcul des composantes de la densité du courant électrique. La contribution redox dans l'aquifère contaminé s'explique par des dipôles verticaux répartis sur la frange capillaire juste au-dessus de la nappe phréatique, en favorisant le mécanisme de la biogéobatterie sur ce site. L’ensemble de ces résultats ont été confirmés par les mesures géochimiques menées au niveau des forages. L'étude a montré que les altérations biologiques des hydrocarbures ont modifié les propriétés chimiques de l'eau porale et que l'étendue de la contamination des eaux souterraines peut être délimitée à partir du contraste géophysique observé entre les zones contaminées et les zones non contaminées. La combinaison des différentes méthodes géophysiques avec des analyses géochimiques ponctuelles au niveau des forages ont permis de mieux comprendre les différents processus qui sont à l’origine de modifications des propriétés biogéochimiques dans les sols et les eaux souterraines. / The presence of hydrocarbon contamination in the subsurface can modify the physiochemical and biological properties of soil and groundwater. The sensitivity of geophysical methods to biogeochemical changes occurring in contaminated media can be used to monitor hydrocarbon contamination in a fast and inexpensive way. As such, geophysical methods including, electrical resistivity tomography, induced polarization, ground penetrating radar, self-potential and magnetic susceptibility were used in this work to characterize the hydrocarbon contamination and investigate its effects on the soil and groundwater geophysical and geochemical properties at a site impacted by an aged hydrocarbon plume. The geophysical response to hydrocarbon contamination varies according to factors related to the contaminant in question and to the contaminated environment. Therefore, to achieve a better interpretation, the field geophysical data were constrained by geochemical soil boring data which showed that biodegradation is occurring in the site. This was shown through observing elevated total dissolved solids concentrations, elevated groundwater electrical conductivity values, negative redox potential values and depleted terminal electron acceptors concentrations in the contaminated locations. Throughout the investigation, the geophysical measurements supported the conductive model and consistently recorded low resistivity anomalies, high chargeability values and attenuated GPR reflections in the contaminated zones. Additionally, significant negative self-potential anomalies associated with oxidation-reduction processes coupled to the biodegradation of hydrocarbons were recorded in the groundwater contaminated zone. Based on this observation, a redox potential map of the contaminated site was constructed by the inversion of the field self potential data. Throughout the process, a groundwater model was first calibrated to remove the electrokinetic component from the SP signal. Then, the obtained residual self potential data was inverted for the electrical current density by using an inversion algorithm which includes minimizing a cost function with a data misfit contribution and a regularizer. As a result, the obtained current density was used to construct a map of redox potential showing the borders and the redox front of the contaminant plume. The redox contribution was explained by vertical dipoles distributed across the capillary fringe, supporting further the mechanism of bio-geo-battery which was created due to the existence of a strong redox potential gradient between the highly reducing conditions within the plume and the oxidizing conditions outside the plume. Furthermore, elevated magnetic susceptibility values were recorded in the biologically active transition zone where bio-precipitation of iron minerals is occurring. Given these results, this study showed that biological alterations of hydrocarbons induced subtle changes in the pore water biogeochemistry, which consequently modified the geophysical properties of the contaminated sediments. The extent of groundwater contamination was delineated according to the geophysical contrast between the contaminated and clean zones. Moreover, the combination of the different geophysical methods, constrained by the geochemical point measurements, provided insight on the different processes which might have modified the soil and groundwater biogeochemical properties at the contaminated site.

Les bassins versants anthropisés sont soumis à des forçages qui évoluent rapidement et déséquilibrent les écosystèmes. Les écosystèmes côtiers et en particulier lagunaires sont très sensibles à la qualité et à la quantité de la source biogène d’origine continentale. La lagune d’Arcachon (Sud Ouest de la France) est alimentée par un bassin versant de 3.000 km2 dont l’occupation des sols est dominée par la forêt depuis plus de 150 ans. La maïsiculture s’est fortement développée depuis les années 1970 et un centre de stockage de déchets ménagers et industriels (CSDU) a été aménagé à moins de 3 km du littoral. Cette thèse se propose d’évaluer la dynamique des éléments biogènes dans le continuum fluvio-estuarien du bassin versant. L’analyse de l’occupation des sols par SIG, une mission d’observation de deux ans, et des études ponctuelles de crues et du continuum fluvial ont permis d’évaluer précisément le flux biogène d’origine continentale et de construire les bases d’un modèle de transport : les taux d’exportation dépendent de l’occupation des sols avec 45, 93, 2.850 et 61 kg N-Nitrate km-2 an-1 calculés pour les parcelles forestières, déforestées, agricoles et urbaines respectivement. L’exportation a lieu préférentiellement en tout début de crue mais le lessivage est rapidement limité. En revanche, les eaux souterraines peuvent contribuer significativement au flux annuel pour les bassins versants les plus agricoles. On a pu démontrer qu’une réduction de 10 % des apports d’engrais azotés réduirait de plus de 50 % le flux d’azote vers la lagune. Une étude approfondie intégrant hydrologie, biogéochimie et géophysique a permis de comprendre les mécanismes de dispersion et d’atténuation d’un panache de pollution issu du CSDU. Celui-ci s’écoule vers la lagune avec l’aquifère superficiel à une vitesse de 23 m an-1 pour l’ammonium et environ 50 m an-1 pour le chlorure mettant en évidence une forte atténuation de l’ammonium dans l’aquifère par sorption et nitrification. Actuellement, le panache n’a pas atteint le littoral et seul le drainage par la rivière permet une exportation rapide jusqu’à la lagune. Ce drainage favorise une très forte nitrification dans la zone hyporhéique et dans la rivière, ce qui limite le flux d’ammonium vers la lagune. Dans ces conditions, le temps de résidence de l’ammonium dans l’aquifère est entre 7 et 18 ans. L’intégration des processus biogéochimiques estuariens dans la dynamique des flux biogènes vers la lagune est une nouveauté. L’étude des éléments biogènes et de la matière organique particulaire permet de démontrer que les estuaires de la lagune sont autotrophes à l’échelle de l’année et permettent un abattement d’environ 30 % du flux de nitrate continental. Saisonnièrement toutefois, les processus de reminéralisation peuvent dominer. Les estuaires ont peu d’impact sur la biogéochimie du phosphore contrairement au sédiment de la lagune. / The anthropized watersheds shift quickly and may disturb the ecosystems. Coastal ecosystems and coastal lagoons are highly sensitive to the amount and the quality of biogenic material originating from continents. The Arcachon lagoon (France South West) raises continental waters originating from a watershed of 3,000 km2 . Pine forestry cover the main surface area of the watershed since 150 years. Cornfields are appeared since 1970 and quickly increase. A solid waste disposal has been created near the littoral. The purpose of this PhD is to assess the global cycle of biogenic materials through the riverine and estuarine continuum. Land-use analyze by GIS, two years of monitoring and some studies of flood events and river continuum have permit to assess the flux of biogenic material and to build a transport model. The export rates depend of land-use and we assess the annual export rate to 45, 93, 2,850, and 61 kg N-Nitrate km-2 year -1 in forested parcel, deforested parcel, agricultural parcel and urban parcel respectively. The export is more efficiency at the beginning of flood events. However the groundwater may supply high amount of nitrogen in highly agricultural watershed. We have shown that a decrease of 10 % in fertilizer input to farming areas would probably reduce the annual flux of more than 50 %. A study based on hydrology, biogeochemistry and geophysics permit to understand the behavior of a contaminated plume originating from the waste disposal. The ammonium plume flows towards the lagoon at a velocity of 23 m year -1 whereas the chloride plume should flows at 50 m year -1. It highlights an efficiency attenuation of ammonium dispersion due to sorption in soil and nitrification. The plume needs about 100 years to reach the lagoon and nowadays the only way of dispersion is the drainage of contaminated groundwater by the river. This way permits an efficiency nitrification in the hyporheic zone and limits the flux of ammonium. Considering that the input of ammonium from the landfill is balanced by the present day output via the river, the residence time of ammonium in the aquifer is between 7 and 18 years. The integration of estuarine biogeochemistry has been realized for the first time. The survey of biogenic materials and organic matter emphasizes that estuaries are autotrophic at annual scale and decrease the nitrogen continental flux of about 30 %. But in autumn, the mineralization and nutrient recycling is observed. In the Arcachon lagoon, the estuaries have a negligible impact on phosphorus biogeochemistry contrary to the sediment.

La caractérisation des circulations thermo-convectives dans les milieux naturels est particulièrement étudiée pour ses applications industrielles, notamment en géothermie. Cette caractérisation correspond à deux enjeux liés à (i) la détection des remontées hydrothermales et (ii) la quantification de l'énergie évacuée par le système actif. La méthodologie proposée par cette thèse comporte ainsi deux volets. Le premier volet vise la localisation des systèmes actifs par caractérisation géophysique de sub-surface. Les techniques de prospection mises en œuvre sont la tomographie de résistivité électrique (TRE), la mesure in situ de température et la mesure de polarisation spontanée (PS). L'objet étudié dans cette thèse est la remontée hydrothermale située au niveau de la limite supérieure de l'effondrement de Rina Grande, au sommet du volcan Stromboli. L'approche géophysique de sub-surface comprend une cartographie spatiale (à l’échelle métrique) en TRE, PS et température et un suivi temporel des signaux PS et thermique. La cartographie spatiale nous renseigne sur l'extension spatiale du système hydrothermal (TRE) et le caractère actif des circulations (PS et température). Le modèle de résistivité électrique a été amélioré en tenant compte de la topographie, issue d'un Modèle Numérique de Terrain généré par photogrammétrie. Le traitement des données de surveillance montre qu'une relation linéaire lie le signal thermique et le signal PS, une relation qui ne peut être purement thermo-électrique. Le jeu de données temporel met l'accent sur la dynamique du système convectif et notamment la probable dépendance de la vigueur du système convectif avec les variations saisonnières de température atmosphérique. Le second volet vise à quantifier l'énergie évacuée par des systèmes thermo-convectifs à l'aide d'une approche numérique. L'approche géophysique met en évidence le fait que les zones endommagées telles que des limites structurales favorisent la circulation des fluides hydrothermaux. Ceci s'explique par le fait que fractures, failles ouvertes, zones d'altération etc. changent à petite échelle la perméabilité du milieu. L'approche numérique est donc vouée à la simulation 3D de l'écoulement et du transfert de chaleur dans des milieux poreux fracturés. Le travail s'est basé sur un code d'écoulement en milieux poreux fracturé pré-existant. Ce code a été adapté afin de résoudre le problème thermique. L'étude théorique vise à quantifier l'influence des paramètres du réseau de fractures sur l'énergie dissipée. L'influence de la densité de fractures, de la transmissivité de fractures et l'anisotropie du réseau de fractures sont évaluées. L'étude compare également les flux de chaleur dégagés par des modèles où les fractures sont insérées de manière discrète avec des modèles homogènes et de même propriétés macroscopiques (approche effective). Les résultats montrent que la validité de l'approche effective est fortement dépendante des paramètres du réseau de fracture. / The characterization of thermo-convective circulations in natural environments is particularly studied especially for geothermal applications. This characterization corresponds to two issues related to (i) the detection of the hydrothermal flows(ii) the quantification of the energy discharged by the active system. The methodology proposed by this thesis thus comprises two parts. The first component aims at locating active systems with geophysical methods. The prospecting techniques used are electrical resistivity tomography (ERT), in situ temperature measurement and self potential (SP) measurements. The object studied in this thesis is the hydrothermal system located at the upper limit of the Rina Grande sector collapse, at the top of the Stromboli volcano. The sub-surface geophysical approach includes spatial (metric) mapping in ERT, SP and temperature, and monitoring of SP and thermal signals. Spatial mapping informs us about the spatial extension of the hydrothermal system (ERT) and the active character of the circulations (SP and temperature). The model of electrical resistivity has been improved taking into account the topography, resulting from a Digital Elevation Model generated by photogrammetry. The treatment of the monitoring data shows that a linear relationship links the thermal and the PS signals, a relationship that can not be entirely due to thermoelectric effect. The temporal dataset focuses on the dynamics of the convective system and in particular the probable dependence of the vigor of the convective system on seasonal variations in atmospheric temperature.The second part aims at quantifying the energy released by thermo-convective systemsusing a numerical approach. The geophysical approach highlights the fact that damaged areas such as structural boundaries favor the circulation of hydrothermal fluids. This is due to the fact that fractures, open faults, alteration zones, etc. change the permeability of the medium on a small scale. The numerical approach is therefore dedicated to the 3D simulation of the flow and heat transfer in fractured porous media. The work is based on a pre-existing code in fracturing porous media, able to solve the flow problem. This code has been adapted to solve the thermal problem also. The theoretical study aims to quantify the influence of fracture network parameters on the released energy. The influence of fracture density, fracture transmissivity and fracture network anisotropy are evaluated. The study also compares the heat fluxes generated by models where the fractures are discretely inserted with homogeneous models with the same macroscopic properties (effective approach). The results show that the validity of the effective approach is highly dependent on the parameters of the fracture network.