While Andosols have a proven capacity to buffer acid inputs, their long-term chemical response to elevated acid deposition remains poorly known. In this respect, the high anion retention capacity of Andosols constitutes a key parameter. Yet, the mechanisms involved in anion retention, especially sulphate, are still a matter of scientific debate. In this study, we report on the impacts of volcanogenic S and acid depositions on (i) the sulphate distribution and (ii) the processes involved in the neutralisation of the acid inputs, in two distinct soil series located downwind from Masaya volcano (Nicaragua), one of the world's largest natural source of SO2. The first series corresponds to weathered Eutric Andosols rich in allophanic constituents and the second series to weakly developed Vitric Andosols rich in volcanic glass. Long-term acid gas emission by Masaya volcano has led to important changes in the chemistry of the Andosols downwind. Sustained acid inputs have decreased the pH and exchangeable base cations contents in both Vitric and Eutric soils. These soils also show substantial S enrichment (up to 5470 mg S kg-1). However, these changes do not affect the soil acid neutralising capacity of the solid phase (ANCs) in a significant way. Despite the larger ANCs of the Vitric comparatively to the Eutric Andosols, soil pH was less in the Vitric than in the Eutric Andosols. This is related to the naturally and kinetically different mechanisms involved in the regulation of the volcanogenic acid fluxes: mineral weathering (slow kinetics) is the dominant process in Vitric Andosols, whereas cation exchange and sulphate sorption (rapid kinetics) significantly contribute to regulate proton consumption in Eutric Andosols. Formation of basic aluminium sulphate (BAS) [(K,Na)nAlx(OH)y(SO4)z] minerals in soils exposed to volcanogenic S-rich acid inputs was inferred from the results of selective extraction experiments (NH4F, KH2PO4 and oxalate). Precipitation of BAS probably constitutes the most effective inorganic SO42- retention mechanism (9-51% of total S), SO42- adsorption onto soil constituents (1-36% of total S) and occlusion into short-range ordered minerals (0-22% of total S), probably governed by ferrihydrite, constituted additional effective inorganic SO42- retention processes. Using transmission electron microscopy coupled with energy-dispersive analysis, we provide the first direct evidence of BAS minerals in soils. BAS minerals can form in these Andosols, because of the large inputs of H+ and SO2 and the availability of readily weatherable volcanic glass, which acts as an effective source of Al. Surface precipitation, i.e. two-dimensional chemisorption followed by three-dimensional nucleation and precipitation, rather than direct precipitation from solution, is likely the formation pathway of BAS particles in these soils. / Malgré une capacité importante à neutraliser les apports acides, le fonctionnement à long terme des Andosols est aussi susceptible d'être affecté par les dépôts acides. A cet égard, la capacité de rétention anionique élevée des Andosols constitue un paramètre clef. Or, les mécanismes de rétention des anions, en particulier du sulfate, demeurent un sujet controversé.Nous étudions ici les effets de dépôts acides et soufrés d'origine volcanique sur (i) la distribution du sulfate et (ii) les processus impliqués dans la neutralisation des apports acides, dans deux séries d'Andosol contrastées exposées aux émissions du volcan Masaya (Nicaragua), une des principales sources naturelles de SO2 atmosphérique. La première série comprend des Andosols Vitriques possèdant une réserve importante de minéraux altérables de nature vitreuse et la seconde est constituée d'Andosols Eutriques, plus évolués, possèdant des teneurs élevées en minéraux secondaires à organisation cristalline à courte distance. Les émissions prolongées de gaz acides provenant du volcan Masaya modifient fortement la chimie des sols exposés à ces apports. Ainsi, le pH et les teneurs en cations échangeables des Andosols Vitriques et Eutriques diminuent alors que la concentration totale en S augmente (jusqu'à 5470 mg S kg-1) en réponse aux apports d'acides. Par contre, la capacité de la phase solide de ces sols à neutraliser l'acidité (ANCs) n'est pas significativement affectée. Malgré une ANCs plus élevée dans les Andosols Vitriques comparativement aux Andosols Eutriques, le pH de ces sols est plus faible parce que les mécanismes impliqués dans la régulation des flux de protons sont différents: ceux-ci s'opèrent principalement par des réactions lentes d'altération minérale dans les Andosols Vitriques et par des réactions rapides impliquant l'échange ionique et la sorption d'anions sulfates dans les Andosols Eutriques. Sur base d'extractions sélectives (NH4F, KH2PO4 et oxalate), l'immobilisation sous forme de minéraux hydroxy-alumino-sulfatés [(K,Na)nAlx(OH)y(SO4)z] apparaît comme le mécanisme de rétention du SO42- inorganique le plus important (9-51% du S total), l'adsorption du SO42- à la surface de constituants du sol (1-36% du S total) et le piégeage du SO42- (0-22% du S total), vraisemblablement au sein d'oxydes de fer mal cristallisés, constituent également des processus efficaces de rétention du sulfate inorganique. Nous mettons en évidence par observation directe, pour la première fois, la présence de minéraux hydroxy-alumino-sulfatés dans des sols par microscopie électronique à transmission couplée à une sonde analytique EDS. La formation de ces minéraux est elle-même favorisée par l'apport considérable de sulfate d'origine volcanique et l'hydrolyse intense des verres qui libère l'aluminium en solution. La précipitation à la surface des phases adsorbantes plutôt que la précipitation directe en solution semble être le mécanisme de formation des minéraux hydroxy-alumino-sulfatés dans ces sols.

Groundwater chemistry is a function of recharge and the input chemistry of the rain, which gets transformed as it moves through the soil matrix. Apart from mineral transformations, anthropogenic activities are other external factors, which affect the groundwater chemistry. Stream – aquifer interactions alter the chemistry of groundwater in the regions nearer to the stream. A study is carried out to analyse the hydrogeochemical behavior under the influence of lithologic, precipitation and anthropogenic controls in the upper Cauvery basin. This is followed by the analysis of contributions made by the components of the hydrogeochemical cycle. A geochemical model is developed, which is used to study the spatiotemporal variations in groundwater chemistry of a silicatic rock group in a small experimental watershed. In order to study the effects of precipitation control on the groundwater chemistry the Upper Cauvery river basin (~ 10000 km2) is selected for the analysis, which stretches along three climatic zones – ‘semi-arid’ (500 – 800 mm/year rainfall), ‘sub-humid’ (1000 - 1200 mm/year) and ‘humid’ (1200 – 1500 mm/year) zones. The basin is mainly formed by granitic gneissic group of rocks with some traces of amphibolites and charnockites. Groundwater is observed to occur either in the saprolite or in the deeper hard rock zone based on the geomorphology even at the scale of a small watershed. Parts of this basin are under canal irrigation and are drained by Kabini and Cauvery Rivers. Groundwater – surface water interactions play an important role in these regions. Irrigation with different levels of intensities is practiced through groundwater in the upland areas. Observation wells considered in these three zones are classified into four classes based on the mean annual groundwater fluctuations. Wells in each of these four classes are further classified into ‘shallow’ and ‘deep’ categories based on the depth to groundwater. Analysis of the groundwater chemistry in the basin (widely spread with 120 wells in the three zones) shows a gradient in chemistry along the climatic gradient with sub-humid zone bridging between the semi-arid and humid zones. Ca/Na and Mg/Na ratios decrease from humid zone (unimodal rainfall) to semi-arid (bimodal rainfall) zone since both Na and Mg concentrations in groundwater increase along this gradient. These elements are mainly controlled by weathering reactions. Apart from the weathering of Ca, calcrete formations also play an important role in the semi-arid zone. Ion exchange process cycles between Cl and SO4 and between Ca and Na. Dissolution of CaCO3, silicate weathering and evaporation are the major mineralogical reactions. Variations in Na/Cl and Ca/Cl molar ratios indicate that shallow wells have higher molar ratios with higher variance than the deeper wells. Semi-arid zone is more silicaceous (higher Na/Cl value) than the humid zone, which has higher Ca/Cl ratio (~ 14). Effective seasonal patterns are identified using ‘recharge – discharge’ concept based on the rainfall intensity. Wells under normal scenario have low Na/Cl and Ca/Cl ratios in the ‘recharge period’ than in the corresponding ‘discharge period’ (dilution chemistry). Wells in the relatively higher pumping regions, which receive sufficient annual recharge exhibit dilution chemistry though groundwater level fluctuations are higher. However, wells in regions with insufficient recharge show ‘anti - dilution’ chemistry. Thus, the ‘recharge – discharge’ concept is useful in identifying the pumped wells from deeper wells and helps in characterizing the anthropogenic effects on the basin. Rainfall and its chemistry are to be analysed to understand the groundwater chemistry. Hence, data from various monitoring stations in India are analyzed for assessing the influence of several major factors such as, topographic location of the area, its distance from sea and annual rainfall. These stations are categorized as ‘urban’, ‘suburban’ and ‘rural’. pH, HCO3, NO3 and Mg concentrations have not changed much from coast to inland. On the other hand, SO4 and Ca concentrations changes are subjected to local emissions. Cl and Na (marine elements) originate solely from sea and a model is developed to quantify the variation in concentration of these elements under the influence of inland distance and annual rainfall. Non – linear regression model for the various categories shows that both rainfall amount and precipitation chemistry follow a power law reduction with distance from sea. Cl and Na decrease rapidly for the first 100 km distance from sea, then decrease marginally for the next 100 km and then later stabilize. Regression parameters estimated for different cases are found to be consistent (R2 ~ 0.8). Variation in one of the regression parameters accounts for the effect of urbanization. Model developed for precipitation chemistry is validated using stations from the southern peninsular region of the country. Model predictions are found to be in good correlation with observations with a relative error of ~ 5%. This relationship between the three parameters – rainfall amount, coastline distance, and concentration (in terms of Cl and Na) was validated with experiments conducted at Mule Hole SEW and Kalekere. Monthly variations in precipitation chemistry at these stations are predicted from a downscaled (in time) model and then compared with the observed data. Models developed at both annual and monthly scale are found to perform well with the field observations. Hence, this model is used for predicting the precipitation chemistry (in terms of Cl and Na) of different station points in the upper Cauvery basin. Comparative performance of alternate methods of recharge estimation i.e. Chloride mass balance (CMB) and water table fluctuation (WTF) approaches, is analyzed at various stations in the basin. Annual rainfall, Cl concentration in rain (predicted from precipitation model) and the concentration of Cl in the groundwater are the inputs for the CMB approach. Since main source of Na is from atmosphere, Na is taken as an alternative for Cl in the CMB approach and recharge is estimated using sodium mass balance (SMB) approach. Na concentrations contributed from weathering are quantified and eliminated in the analysis. Recharge estimated using SMB approach is found to be higher than CMB estimate in the semi-arid and the sub-humid zones. Water table fluctuation (WTF) method is used to compare the recharge obtained from both CMB and SMB approaches. Estimates using WTF approach are found to be higher than both CMB and SMB in the semi-arid and the sub-humid zones while SMB is found to be higher than CMB estimates. SMB and WTF estimates match well in the humid zone. An exponential relationship between recharge and annual rainfall is observed. Recharge coefficient estimated on an annual scale varied from 0.1 to 0.25 across the basin. Among CMB and SMB approaches, SMB is a better alternative for recharge estimation in semi-arid zones, where WTF approach performed poorly. Water – rock reactions are driven by the inequilibrium reactions of water with the mineral assemblage in the rock. These reactions evolve towards equilibrium with the primary minerals while a series of secondary minerals precipitate. Mass balance approach is adopted to quantify the rate at which the water – rock interactions occur in order to reach the equilibrium. Field experiments in the experimental watershed (Mule Hole SEW, ~ 4.5 km2) are carried to identify the minerals present in the region and their composition. Quartz, oligoclase, sericite, epidote and chlorite are the primary minerals while kaolinite and Fe-oxides are the secondary minerals present in this region. Percentages of oxides of different elements in each of these minerals are determined from the field experiments. Stoichiometric coefficients of different elements in each of these minerals are determined from these percentages. Long – term weathering rates are determined using these stoichiometric coefficients along with the mass fluxes of each element. Set of minerals present at different depths are found to vary among the thirteen observation wells of Mule Hole SEW. Hence, the mass balance calculations resulted in different weathering rates for a particular mineral based on the spatial location and the particular depth of the occurrence of the mineral. These weathering rates are tested for the sensitivity to carbonates with the inclusion of calcite in the mass balance calculations. With this sensitivity analysis it is observed that the presence of carbonates in the nodular form in the shallow wells has not changed the weathering reactions and their rates, and hence these wells are termed to be in the ‘silicate with secondary carbonate’ system. On the other hand, carbonates are not present in deeper wells, inclusion of which alters the equilibrium of the mass balance calculations. Thus, these wells are said to belong to the ‘silicate’ system. Anorthite present in some of the wells (MH2 and MH6) dissolves accompanied with the dissolution of carbonates. These wells are observed to belong to the third group the ‘amphibolites with primary carbonate’ system. Weathering rates of all the minerals present in these three different systems are also determined annually (short term rates). Mean of these short – term rates are observed to be the same as the long – term (over a period of 4 years) weathering rates with a minor difference of 3 – 10% in values. Thus, the weathering rates determined using mass balance approach is used to determine the quantities of concentrations of different elements contributed from the mineralogical reactions. Temporal variations in the concentrations of different chemical species in this small experimental watershed are simulated using a hydrogeochemical model. The model is developed based on a mixing cell approach, which considers the spatiotemporal variations in the recharge and the weathering inputs. Most of the weathering reactions are observed to take place in the saturated zone, which is termed as the ‘mixing zone’. This zone extends from few meters above the groundwater table to few meters below the water table. Mixing zone is discretized into series of ‘cells’ and concentrations in this zone are simulated. This group of cells is assumed to move along with the groundwater fluctuation. Sensitivity of the model is analysed subject to the variations in the recharge and the weathering fluxes. The developed model is used to simulate the concentrations of the groundwater in the three systems – ‘silicate’, ‘silicate with secondary carbonate’ and ‘amphibolites with primary carbonate’. Field data for chemical species is observed to vary in this mixing zone, boundaries of which are defined from the model simulations. Simulations corresponding to the cell at the mid depth of this mixing zone are observed to correlate well with the field data. Hence, the model developed is able to simulate the temporal variations in the groundwater chemistry. In summary, the study analyses the effects of lithological, climatic and anthropogenic factors on groundwater chemistry. The transformations in the rainwater chemistry as it reaches groundwater are analysed along different stages. A hydrogeochemical model is developed to simulate the groundwater concentrations in three different mineralogical settings over a period of three years.

Among the materials that can be treated in order to impart superhydrophobic properties are many originally hydrophilic metals. For this, they must undergo a sequential treatment, including roughening and hydrophobic coating. This contribution presents various preparation routes along with various characterization methods, such as dynamic contact angle (DCA) measurements, scanning electron microscopy (SEM) and spectroscopic techniques (FT–IRRAS, XPS, EIS). Micro-rough surfaces of pure and alloyed aluminum were generated most easily by using a modifie Sulfuric Acid Anodization under Intensifie conditions (SAAi). This produces a micro-mountain-like oxide morphology with peak-to-valley heights of 2 μm and sub-μm roughness components. Additionally, micro-embossed and micro-blasted surfaces were investigated. These micro-roughened initial states were chemically modifie with a solution of a hydrophobic compound, such as the reactive f uoroalkylsilane PFATES, the reactive alkyl group containing polymer POMA, or the polymer Teflo ® AF. Alternatively, the chemical modificatio was made by a Hot Filament Chemical Vapor Deposition (HFCVD) of a PTFE layer. The latter can form a considerably higher thickness than the wet-deposited coatings, without detrimental leveling effects being observed in comparison with the original micro-rough surface. The inherent and controllable morphology of the PTFE layers represents an important feature. The impacts of a standardized artificia weathering (WTH) on the wetting behavior and the surface-chemical properties were studied and discussed in terms of possible damage mechanisms. A very high stability of the superhydrophobicity was observed for the f uorinated wet-deposited PFATES and Teflo ® AF coatings as well as for some of the PTFE layer variants, all on SAAi-pretreated substrates. Very good results were also obtained for specimens produced by appropriate mechanical roughening and PTFE coating.

No description available.

No description available.

Exotic pine plantations are a major landuse within the coastal lowlands of southeast Queensland, extending from close to the shoreline to the hinterland ranges. These plantations are within a sub-tropical climatic zone, and in most years, the summers are appreciably wetter than the winters. This terrain, in general, has been highly weathered and the soils are poor in nutrients. Environmental factors such as the climate, topography and weathering profile (including soil) are found to be important controls on vadose zone hydrology, which, in turn, has a great impact on tree growth and consequently on the design of management practices. This research project takes a holistic approach to investigate the influence of these environmental factors at different scales, and is designed to fulfil the following objectives: (1) To build a spatial model of forest productivity for the entire Tuan Toolara State Forest (TTSF), southeast Queensland, by analysing the spatial patterns of many environmental variables that may have controls on soil water distribution. (2) To determine how some of these environmental factors are responsible for the development of water-logging and soil salinisation by examining in detail an area of low site index that is severely affected by these two processes. (3) To develop a model to assess the risks of water-logging spatially and temporally. A multiple regression model was constructed to predict the forest productivity (measured by the value of site index, the average dominant tree height at 25 years of age). The independent variables were derived from a digital elevation model (elevation, slope, curvature, hillshade, flow accumulation and distance to streams), γ-ray spectrometry (potassium, thorium and uranium), and interpolated rainfall. The model explained up to 60% of the variance in the site indices and produced predictive maps of site index for two species: P. elliottii Engelm. and Queensland hybrid, a P. elliottii × P. caribaea Morelet hybrid. The model also identified the lowest site index area at the northern Tuan State Forest (NTSF), likely due to a greater risk of water-logging and salinisation. The NTSF area is of low relief and, therefore, the focus has been on the vertical controls of deep weathering profile. The methodology included setting up a network of groundwater bores screened at different depths within the weathering profile, characterising the profile (mineralogy, EC, and pH) and the groundwaters within it (water levels, physico-chemical parameters, major and minor ions). It is found that water-logging is caused by perched groundwater formed on top of the ferricrete or mottled saprolite after prolonged rainfall. Localised salinisation is related to the discharge of brackish groundwater occurring within the mottled saprolite. The deep aquifer within the coarse saprolite is fresh and not responsible for salinisation, a situation that differs from many other settings in Australia. The ability of using the Soil and Water Assessment Tool (SWAT) computer model to simulate soil water balance and to assess the risks of water-logging was tested in a selected catchment in the TTSF. The model successfully simulated stream flow at 2 weirs for a period of 6 years; the achieved R2 were 0.752 and 0.858, respectively. Long-term simulation for a 30-year period showed that there are pronounced seasonal patterns in rainfall and evapotranspiration as well as in soil water. For mature plantation with slopes of 3-15%, the mean annual duration of water-logging ranged from 161 days in the humus podzols, to 110 days in the gleyed podzolic, and to 90 days in the yellow podzolics. The outcomes of this research suggest that forest management can be strongly supported by understanding the impacts of these environmental factors (e.g. climate, topography and weathering profile) on vadose zone hydrological processes; the selection of optimum approach will depend on the research objective or purpose. The models and analytical tools that were developed or tested here have the potential to be successfully applied elsewhere if the input data are available.

A sustainable approach to restoration of the post-mining landscape involves creating conditions where a viable growth medium can be established with the minimal amount of fertiliser inputs over a period of time. Ideally, this growth medium should comprise a combination of minerals, organic matter, and biological components with have the capacity to retain and release nutrients over time. When combined with a re-vegetation scheme appropriate to the biogeographic area, a self-sustaining ecosystem can be established. Regulatory requirements for mine restoration typically require the use of topsoil, which is often in limited supply. However, overburden is commonly present in vast quantities and has the potential to be used as a restoration substrate with appropriate amendments. There are significant gaps in our understanding of factors relating to the use and amendment of overburden as a growing medium. The main objective of this study was to investigate and quantify the effects of inorganic and organic amendments and weathering on nutrient availability and plant growth in topsoil and overburden material obtained from the OceanaGold Globe Progress mine at Reefton, New Zealand. A series of glasshouse experiments were carried out on topsoil, fresh overburden and mullock (old waste rock) amended with biosolids, green manure, sawdust, lime and mineral fertiliser nutrients (nitrogen (N) and phosphorus (P)). R esults demonstrated that 300 kg N ha⁻¹ was sufficient to overcome N deficiency in topsoil, while 100 kg P ha⁻¹ was required to overcome P deficiency. Addition of biosolids to topsoil and overburden increased plant biomass production, without increasing heavy metal concentrations. Amendment of overburden significantly affected weathering rates by accelerating the formation of secondary minerals. In particular, lupin green manure accelerated the formation of organic iron (Fe) and aluminium (Al) organic complexes, resulting from the decomposition of the green manure and release of Fe from primary minerals. Results revealed that wineberry and red beech required 200 kg N ha⁻¹ for optimum growth. Overall, the findings of this research identified key parameters for effective utilisation of overburden as a restoration substrate. A sustainable restoration method for managing the topsoil and/or any overburden or waste rock material remaining at mine sites can be achieved by careful selection of organic amendments and allowing an initial weathering period.

L’île de La Réunion a été couverte par une vaste campagne de géophysique héliportée en 2014. Le dispositif SkyTEM a permis de cartographier l’anomalie du champ magnétique et la résistivité électrique du sous-sol jusqu’à 300 m de profondeur, et ce, sur l’ensemble de l’île. L’acquisition de ce jeu de données met en évidence la problématique de l’interprétation des données électromagnétiques héliportées à l’échelle régionale. L’interprétation d’un modèle 3D de résistivité d’une superficie 2 500 km2 nécessite la mise en place de méthodologies innovantes pour le confronter aux données géologiques, climatiques et hydrogéologiques. L’objectif de la thèse est de valoriser ce jeu de données géophysique à l’échelle régionale en intégrant l’analyse hydrogéologique à différentes échelles spatiales. Pour répondre à ces problématiques, cette thèse s’organise autour d’une méthodologie hydrogéophysique multi-échelle qui permet d’étudier la répartition et le fonctionnement des aquifères à des échelles inédites jusqu’alors. Pour interpréter les 350 000 sondages électromagnétiques de la campagne, une approche statistique a été développée pour synthétiser une information sur les contrastes 3D en 2D. Les résultats, cohérents avec les connaissances géologiques et hydrogéologiques de l’île, ont permis d’analyser l’impact des paramètres géologiques et climatiques régionaux sur la répartition des aquifères et les processus d’altération. Sur le littoral, les données de résistivité sont confrontées à des logs de conductivité électrique de l’eau souterraine afin de valider l’interprétation de la géophysique. Le modèle de résistivité permet ainsi de cartographier et d’analyser les paramètres de contrôle du phénomène d’intrusion saline à l’échelle de l’île. En altitude, l’utilisation conjointe des données électromagnétiques et magnétiques héliportées permet de caractériser la géométrie des structures géologiques et d’imager les profils et paléo-profils d’altération météorique. / In 2014, Reunion Island was covered by a vast airborne geophysics campaign. The SkyTEM device mapped magnetic anomalies and bulk resistivity at an extra 300 m depth throughout the island. The resulting dataset revealed the issue of interpreting airborne electromagnetic data at the regional scale. The interpretation of a 3D resistivity model wrapping 2 500 km2 requires the implementation of innovative methodologies to compare it with geological, climatic and hydrogeological data. The aim of the thesis is to enhance this geophysical dataset at the regional scale by integrating hydrogeological analysis at different spatial scales. To answer these issues, this thesis revolves around a multi-scale hydrogeophysical methodology, which allows to analyze how aquifers are distributed and their behaviors on unprecedented scales. A statistical approach has been developed to synthesize 3D geo-electrical contrasts in 2D to interpret the 350 000 soundings. All outcomes are consistent with the geological and hydrogeological knowledge of the island, enabling us to study how regional geological and climatic parameters impact the distribution of aquifers and weathering processes. In the coastal zone, resistivity data are compared with groundwater electrical conductivity logs to validate the interpretation of geophysics. Thus, the resistivity model helped mapping saltwater intrusion and analyzing its control parameters at the island scale. Inland, the combined use of airborne electromagnetic and magnetic data made it possible to characterize the geometry of geological structures and to image weathering profiles and paleo-profiles. Combining results gathered on various scales allows the analysis of weathering impact on aquifers of shield volcanoes. On the coastal zone, un-weathered and highly permeable lithological units (up to 10-1 m/s) are subject to saltwater intrusion, even with recharge rates up to 6 to 8 m per year. With decreasing transmissivity, aquifers become less exposed to saltwater intrusion. According to geophysics outcomes, the contacts between different eruptive phase products at high altitude are characterized by specific weathering paleo-profiles which create permeability contrasts conducive to perched aquifers establishment. Examining the geophysical response in different areas of the island made it possible to analyze the dynamics of weathering processes, initially controlled by the age of the formations and secondly, by the rainfall rates and the temperature. These results showed that weathering and structure of basaltic volcanoes depend on their age and on windward/leeward slopes. Thus, our research helped improve the accuracy of the conceptual hydrogeological model including geological structuring and time evolution of basaltic volcanic aquifers in an insular environment.

[pt] Um perfil de alteração de granito-gnaisse é estudado objetivando um melhor conhecimento das propriedades mecânicas e hidráulicas de solos residuais. A feição estudada encontra-se no município de Campo Magro, região Metropolitana de Curitiba. A região situa-se na borda da Bacia de Curitiba, acima de 900 metros, fortemente sujeita aos fenômenos tectônicos que deram origem à calha da Bacia. As investigações geotécnicas contemplam a caracterização física, química e mineralógica dos materiais. O comportamento dos solos no estado compactado e indeformado é analisado. Curvas características de sucção e de resistividade fornecem dados que auxiliam no entendimento das propriedades hidráulicas. A influência do intemperismo e da sucção são avaliados na resistência à tração e na resistência à compressão não confinada. Parâmetros de resistência em cinco diferentes níveis de intemperismo são apresentados. Ensaios de adensamento fornecem parâmetros de quebra da estrutura (yelding) dos solos. O comportamento tensão- deformação do solo mais intemperizado, no estado não saturado, é analisado através de ensaios triaxiais com medida de deformação local, em compressão axial com tensão controlada e deformação controlada. As conclusões da pesquisa permitem identificar a variabilidade de comportamento de resistência e compressibilidade, efeito do material de origem e intemperismo a que os solos foram submetidos. / [en] A granite-gneiss weathering profile is studied with the aim of achieving a better understanding of mechanical and hydraulic properties of residual soils. The site in focus is located at the city of Campo Magro, in Curitiba Metropolitan Area. The region under research lies at the border of Curitiba Basin, above 900 m of elevation, and it was heavily influenced by tectonic events that originated the basin. The geotechnical investigation comprised physical, chemical and mineralogical characterization. The soil behavior was assessed in both natural and compacted conditions. Suction and resistivity characteristic curves provide useful information for assessing the hydraulic properties. The weathering degree and suction levels influence are assessed in respect to unconfined compressive and tensile strength. The resistance properties are analyzed according five distinct weathering degrees. Consolidation tests are used for identifying yielding stress levels. Unsaturated triaxial tests with local strain measurements in both stress and strain control conditions are used to study the deformation behavior of the most weathered soil. The conclusions provide an overall assessment of the soil strength and compressibility variability, origin material influence and weathering evolution effects.

Cette thèse se propose de définir les temps caractéristiques des processus d’altération à l'échelle de profil d'altération (bassin versant de Rio Icacos à Porto Rico) et de transfert sédimentaire subséquent dans les plaines alluviales (bassins du Gange et du Brahmapoutre). Cette problématique est abordée par l’analyse des nucléides des séries de désintégration radioactives de l’uranium-238. L’étude du système d’altération sphéroïdale développée sur le site de Porto Rico a permis de développer une méthode numérique de type quasi-Newton afin de résoudre le système d'équations qui rend compte du comportement des nucléides et du taux de formation de la saprolite et des couronnes d’altération.Pour les bassins du Gange et du Brahmapoutre, les sédiments ont été collectés sur différents affluents et à son exutoire. La variation des déséquilibres 238U-234U-230Th dans les sédiments, différente pour les sédiments en suspension et les sédiments à grains grossiers d’amont en aval, semble être une caractéristique générale des rivières himalayennes coulant dans la plaine Indo-gangétique. Par ce travail de thèse, nous avons montré l’utilité d’inclure l’analyse du 226Ra à l’analyse des autres nucléides de la chaîne de décroissance radioactive de l’238U (l’238U -234U-230Th 230Th) pour déterminer un taux d’altération dans un système bien défini. Néanmoins, l’étude du système du Brahmapoutre montre que la méthode proposée demande à être affinée car le transfert sédimentaire est un processus plus complexe dû à la variabilité minéralogique, granulométrique et à la dynamique sédimentaire (locale) des échantillons récoltés. / This thesis proposes to define the time-scales of weathering processes on a spheroidal weathering profile, (Rio Icacos watershed, Puerto Rico ) and the transfer time of sediments within alluvial plains (Ganges and Brahmaputra basins). This issue is addressed through the analysis of the nuclides of the 238U decay chain. The study of a spheroidal weathering system developed on the site of Puerto Rico permit to develop a limited memory quasi-Newton algorithm in order to solve the system of equations that reflects the behavior of nuclides and the rate of formation of the saprolite and the rindlet zone. For the Ganges and Brahmaputra basins, sediments were collected from different tributaries and their outlets. The variation of 238U - 234U - 230Th disequilibria in the sediments, with different variation trends for suspended and coarse-grained sediments, is probably a general feature of all Himalayan rivers flowing across the Indo-Gangetic plain. For this work, we have shown the usefulness of including the analysis of 226Ra analysis of other nuclides in the chain of radioactive decay of 238U (238U - 234U - 230Th) to determine the weathering rate in a well-defined system. Nevertheless, the study of the Brahmaputra system shows that proposed method needs to be refined as the sediment transfer is a complex process due to the mineralogical variability, size and (local) dynamics of sediments samples collected.