A variabilidade das propriedades físicas do solo apresenta impacto sobre o desempenho das atividades de produção agrícola. Métodos indiretos para obtenção de informações sobre as propriedades do solo com interesse agronômico são utilizados com o intuito de favorecer o uso de insumos de modo mais adequado. A condutividade elétrica aparente do solo (CEa) é influenciada por diversas propriedades, muitas delas interrelacionadas e com variabilidade em curta distância, sendo difícil a separação dos diversos fatores. As medidas de CEa são usualmente tomadas em superfície com arranjos de eletrodos para prospecção de um volume de solo proporcional à distância entre eles. Neste trabalho foi utilizada uma metodologia que permitiu identificar algumas das propriedades com maior impacto sobre a CEa, merecendo destaque aquelas relacionadas ao espaço poroso do solo. A caracterização detalhada da variação da CEa ao longo do perfil do solo e sua comparação com aquela obtida a partir da sondagem elétrica vertical permitiram identificar algumas limitações desta técnica. A presença de camadas com variação de diversas propriedades físicas e de umidade no perfil do solo alterou os valores observados em superfície. A relação entre a distância de separação dos eletrodos no arranjo com quatro pontas igualmente espaçadas, e a profundidade de prospecção, coeficiente k, oscilou entre 0,35 e 0,70 para os solos LVd, LAd e PVe avaliados. A sondagem elétrica empregada na caracterização de variabilidade espacial na horizontal e em profundidade em uma área com teores de argila oscilando entre 150 e 379 g kg-1 na camada 0 a 0,2 m e entre 225 e 326 g kg-1 na camada 0,6 a 0,8 m apresentou resultado satisfatório. / The variability of soil physical properties has an impact on the performance of agricultural production activities. Indirect methods for obtaining information on the soil properties with agronomic interest are used to allow the use of inputs more appropriately. The apparent soil electrical conductivity ( ECa ) is influenced by several properties , many of them interrelated and presenting variability in short distances, being difficult to separate the various factors. ECa measures are usually taken in surface, using electrode arrangements for prospecting a soil volume proportional to the distance between them. In this work, a methodology was used that identified some of the properties with the greatest impact on the ECa, with emphasis to those related to soil porous space. The detailed characterization of the variation of ECw throughout the soil profile and its comparison with that obtained from the vertical electrical sounding was carried to identify certain limitations of this technique. The presence of several layers with varying physical properties and moisture in the soil profile changed values obtained from surface sounding. The relationship between the separation of the electrodes in the array with four points equally spaced, the Wenner array, and the depth of exploration, coefficient k, ranged between 0.35 and 0.70 for the soils LVd , LAd PVe and evaluated. A survey was done for the ECa characterization of spatial variability in the horizontal and along soil profile in an area with clay content ranging from 150 to 379 g kg - 1 in the layer from 0 to 0.2 m and between 225 and 326 g kg - 1 in layer 0, 6 to 0.8 m. The use of ECa for characterizing this variability showed satisfactory results.

A variabilidade das propriedades físicas do solo apresenta impacto sobre o desempenho das atividades de produção agrícola. Métodos indiretos para obtenção de informações sobre as propriedades do solo com interesse agronômico são utilizados com o intuito de favorecer o uso de insumos de modo mais adequado. A condutividade elétrica aparente do solo (CEa) é influenciada por diversas propriedades, muitas delas interrelacionadas e com variabilidade em curta distância, sendo difícil a separação dos diversos fatores. As medidas de CEa são usualmente tomadas em superfície com arranjos de eletrodos para prospecção de um volume de solo proporcional à distância entre eles. Neste trabalho foi utilizada uma metodologia que permitiu identificar algumas das propriedades com maior impacto sobre a CEa, merecendo destaque aquelas relacionadas ao espaço poroso do solo. A caracterização detalhada da variação da CEa ao longo do perfil do solo e sua comparação com aquela obtida a partir da sondagem elétrica vertical permitiram identificar algumas limitações desta técnica. A presença de camadas com variação de diversas propriedades físicas e de umidade no perfil do solo alterou os valores observados em superfície. A relação entre a distância de separação dos eletrodos no arranjo com quatro pontas igualmente espaçadas, e a profundidade de prospecção, coeficiente k, oscilou entre 0,35 e 0,70 para os solos LVd, LAd e PVe avaliados. A sondagem elétrica empregada na caracterização de variabilidade espacial na horizontal e em profundidade em uma área com teores de argila oscilando entre 150 e 379 g kg-1 na camada 0 a 0,2 m e entre 225 e 326 g kg-1 na camada 0,6 a 0,8 m apresentou resultado satisfatório. / The variability of soil physical properties has an impact on the performance of agricultural production activities. Indirect methods for obtaining information on the soil properties with agronomic interest are used to allow the use of inputs more appropriately. The apparent soil electrical conductivity ( ECa ) is influenced by several properties , many of them interrelated and presenting variability in short distances, being difficult to separate the various factors. ECa measures are usually taken in surface, using electrode arrangements for prospecting a soil volume proportional to the distance between them. In this work, a methodology was used that identified some of the properties with the greatest impact on the ECa, with emphasis to those related to soil porous space. The detailed characterization of the variation of ECw throughout the soil profile and its comparison with that obtained from the vertical electrical sounding was carried to identify certain limitations of this technique. The presence of several layers with varying physical properties and moisture in the soil profile changed values obtained from surface sounding. The relationship between the separation of the electrodes in the array with four points equally spaced, the Wenner array, and the depth of exploration, coefficient k, ranged between 0.35 and 0.70 for the soils LVd , LAd PVe and evaluated. A survey was done for the ECa characterization of spatial variability in the horizontal and along soil profile in an area with clay content ranging from 150 to 379 g kg - 1 in the layer from 0 to 0.2 m and between 225 and 326 g kg - 1 in layer 0, 6 to 0.8 m. The use of ECa for characterizing this variability showed satisfactory results.

An integrated use of radio magnetotelluric (RMT) and controlled source tensor magnetotelluric (CSTMT) measurements, the so-called CSRMT method, has been employed in environmental and resource exploration studies. A number of case histories, including a groundwater investigation in glacial deposits, a study of fracture zones for geotechnical purposes and a mining exploration study of a copper deposit, are presented in this thesis in order to illustrate the usefulness and capability of the CSRMT method. The resolutions of the estimated models using various types of data are studied. Magnetotelluric transfer functions are used to analyze the dimensionality, the near surface resistivity distortions and the near field effects in the case of CSTMT data analysis. The near field effects in CSTMT data have also been identified by performing 2½D forward modelling. Data analysis, dimensionality tests and forward modelling show that at the lowest frequencies used the CSTMT transfer functions are generally distorted by source effects, except when the source-receiver distances are sufficient large compared with the penetration depth. Regarding CSTMT transfer functions, apparent resistivities are generally less distorted than phases. TM mode transfer functions are more affected by the sources than TE mode, while tipper vectors generally contain source signatures at all frequencies. Based on the analysis of dimensionality and source effects 2D inverse modelling of CSTMT and RMT data, as well as their combination, have been performed under the plane wave assumption. The RMT method proved to be a powerful tool for imaging the upper 50 m near-surface, but their penetration depth reduces as a conductive layer structures cover the targets at depth. The penetration depth can be increased by including the CSTMT data in the modelling if the measurements are in the far field range. The resolution of the deeper parts of the models may be improved by performing a joint inversion of TE and TM modes, if the strike direction is well-defined. Alternatively, inversion of determinant data can be performed, since the determinant data are less affected by 3D structures and source effects. However the resolution of the determinant models is somewhat degraded compared to the models inverted from combined TE and TM modes.

La qualité des eaux des lacs et le risque d’eutrophisation peuvent être évalués par une étude des composés biogènes. Les sources et les puits de nutriments qui déterminent les processus biogéochimiques peuvent être quantifiés avec un bilan de masse de matière. L’objectif de la thèse était de réaliser ce bilan de masse pour les nutriments dans les deux grands lacs côtiers médocains, Lacanau et Carcans-Hourtin (SW France). Pour cela, j'ai réalisé un suivi de la concentration en nutriments et des paramètres associés des eaux de pluie, des rivières, des canaux, des eaux des lacs et des eaux souterraines au cours de deux cycles hydrologiques en 2014 et 2015. Les processus biogéochimiques à l’interface eau-sédiment et les flux benthiques ont été déterminés à partir de carottes sédimentaires prélevées saisonnièrement et la construction d’une carte sédimentaire des deux lacs. Le bilan hydrologique a pu être réalisé à partir des données de débit et de hauteur d'eau, des mesures géophysiques et des mesures de 222Rn. Nos résultats ont permis de faire un bilan de masse complet de l'azote, du phosphore, de la silice, du fer et de l'alcalinité. Nous avons déterminé les principales sources et les puits de matière et leur évolution au cours de l’année. Les principaux résultats de la thèse sont avant tout la création d’un jeu de données original et riche qui permet pour la première fois d’avoir une vue d’ensemble de la biogéochimique des lacs aquitains. Nous montrons que l’impact des flux souterrains est faible. Les flux benthiques jouent un rôle majeur pour l’azote. L’export de composés biogènes à la sortie des lacs vers le milieu côtier a été quantifié et comparé aux apports par le bassin versant, ce qui a permis d’évaluer la capacité de séquestration des nutriments dans les sédiments. Nous montrons que ces lacs sont pauvres en phosphore, ce qui limite la productivité biologique. Nous avons aussi défini les conditions et les conséquences de la stratification transitoire des eaux des lacs en été. Cet ensemble de données a également permis d'apporter des connaissances supplémentaires sur la dynamique du mercure dans les lacs aquitains. Nous montrons le rôle que jouent les apports en sulfate du bassin versant sur la production de méthylmercure dans les sédiments. / To evaluate water quality and the risk of eutrophication of lakes, the dynamics of biogenic compounds must be studied. Sources and sinks of nutrients that define lake biogeochemical processes can be assessed from a mass balance approach and the study of internal reactions. The objective of the thesis was to realize a mass balance for nutrients in two coastal lakes: Lacanau and Carcans-Hourtin (SW France). For this purpose, I conducted a monitoring of rainwater, rivers, canals, lakes and groundwater concentration of nutrients and associate parameters during the two hydrological cycles of 2014 and 2015. Biogeochemical processes at the sediment water interface and benthic fluxes were determined from sediment cores collected at each season, and from the drafting of a new sediment map. The water balance was obtained from water level and discharge measurements, geophysical prospection and 222Rn measurements. Our results allowed us to make a full mass balance of nitrogen, phosphorus, silica, iron and alkalinity. We have identified the main sources and sinks of nutrients and their evolution along the year. The main results of the thesis is that groundwater discharge is not a significant contribution of nutrients; benthic fluxes supply high amount of dissolved nitrogen and most of the nutrient are sequester in the lake sediments. Total export of nutrient at the outlet of lakes has been quantified and compared to inputs from the watershed. We point out that phosphorus limits lake productivity. We also show the dynamics of transient lake stratification in summer and its impact on biogeochemical processes. This set of data has also provided additional insight into the dynamics of mercury in Aquitaine lakes. We show the role of sulphate inputs from the watershed in the production of methylmercury in lake sediments. All these results give for the first time an overall view of Aquitaine lake biogeochemistry.

Cette thèse s'attache à la compréhension des phénomènes de couplages sismo-électromagnétiques survenant dans des milieux poreux contenant des fluides, ainsi qu'au développement de méthodes d'imagerie géophysique basées sur ces conversions. Deux axes de travail sont investigués. Le premier concerne le traitement des données sismo-électromagnétiques et notamment l'extraction des réponses interfaciales, qui peuvent renseigner sur le sous-sol en profondeur. Nous comparons l'impact de plusieurs méthodes de filtrage sur les amplitudes et les formes d'onde de ces réponses, dont une nouvelle technique de filtrage en domaine des curvelets, qui s'appuie sur les similarités entre les données sismiques et cosismiques. D'autre part, nous étendons la théorie de la propagation couplée des ondes sismiques et électromagnétiques à des milieux partiellement saturés pour le cas d'un mélange air/eau. Nous adaptons un programme de simulation numérique des ondes sismo-électromagnétiques à ces conditions. / This thesis aims to improve our understanding of seismo-electromagnetic coupling phenomena occuring in fluid-containing porous media and to develop geophysical imaging techniques based on conversions.Two areas of work are explored. The first encompasses seismoelectromagnetic data processing, especially the extraction of interface responses, which may provide information about the subsurface at depth. We compare the influence of several filtering techniques on the amplitudes and waveforms of the interface responses, among which a new filtering technique in the curvelet domain, taking advantage of the similarity between seismic and coseismic data. Furthermore, we extend the theory for the coupled propagation of seismic and electromagnetic waves here to partially saturated media for the case of a water/air mixture. We adapt a seismoelectromagnetic wave modelling program to these conditions.

Made available in DSpace on 2015-02-24T19:48:45Z (GMT). No. of bitstreams: 1 WashingtonLET_TESE.pdf: 9876489 bytes, checksum: b0b53c16cdf88ab9e63cb1b22c08ab0f (MD5) Previous issue date: 2013-06-17 / The monitoring of Earth dam makes use of visual inspection and instrumentation to identify and characterize the deterioration that compromises the security of earth dams and associated structures. The visual inspection is subjective and can lead to misinterpretation or omission of important information and, some problems are detected too late. The instrumentation are efficient but certain technical or operational issues can cause restrictions. Thereby, visual inspections and instrumentation can lead to a lack of information. Geophysics offers consolidated, low-cost methods that are non-invasive, non-destructive and low cost. They have a strong potential and can be used assisting instrumentation. In the case that a visual inspection and strumentation does not provide all the necessary information, geophysical methods would provide more complete and relevant information. In order to test these theories, geophysical acquisitions were performed using Georadar (GPR), Electric resistivity, Seismic refraction, and Refraction Microtremor (ReMi) on the dike of the dam in Sant Lloren? de Montgai, located in the province of Lleida, 145 km from Barcelona, Catalonia. The results confirmed that the geophysical methods used each responded satisfactorily to the conditions of the earth dike, the anomalies present and the geological features found, such as alluvium and carbonate and evaporite rocks. It has also been confirmed that these methods, when used in an integrated manner, are able to reduce the ambiguities in individual interpretations. They facilitate improved imaging of the interior dikes and of major geological features, thus inspecting the massif and its foundation. Consequently, the results obtained in this study demonstrated that these geophysical methods are sufficiently effective for inspecting earth dams and they are an important tool in the instrumentation and visual inspection of the security of the dams / O monitoramento do comportamento de barragens de terra faz uso da inspe??o visual e da instrumenta??o para identificar e caracterizar danos no barramento ou estruturas auxiliares. A primeira ? subjetiva possibilitando erros de interpreta??o ou omiss?o, mesmo assim, alguns problemas s? podem ser detectados tardiamente. A instrumenta??o tem se mostrado satisfat?ria, mas pode apresentar restri??es por quest?es t?cnicas ou operacionais. Assim, pode existir defici?ncia nas informa??es produzidas pela inspe??o visual e pela instrumenta??o. A Geof?sica disp?e de m?todos consolidados, n?o invasivos, n?o destrutivos, e de baixo custo, com forte potencial para atuar auxiliando a instrumenta??o convencional, podendo, no caso de inexist?ncia ou falha geral desta, fornecer informa??es mais completas e relevantes que a inspe??o visual. Para fundamentar essas afirma??es, foram realizadas aquisi??es geof?sicas de Resistividade El?trica, Georadar (GPR), S?smica de refra??o, e Refraction Microtremor (ReMi) no dique da barragem de Sant Lloren? de Montgai, localizada na prov?ncia de Lleida, a 145 Km de Barcelona Catalunha. Os resultados obtidos confirmaram que os m?todos geof?sicos utilizados respondem individualmente de forma satisfat?ria ?s condi??es construtivas do dique de terra, ?s anomalias presentes, e ? geologia encontrada (aluvi?o, rochas carbon?ticas e evapor?ticas). Pode se afirmar ainda que esses m?todos, quando utilizados de forma integrada, s?o capazes de diminuir as ambiguidades nas interpreta??es individuais e permitem o imageamento satisfat?rio do interior do dique e das principais fei??es geol?gicas e dessa forma inspecionar o maci?o e sua funda??o. Dessa forma, os resultados apresentados por essa pesquisa demonstram que os m?todos geof?sicos constituem uma importante ferramenta que pode ser utilizada na verifica??o das condi??es do maci?o de uma barragem de terra