After the seminal works by Freeze and Harlan (1969), the scientific community realized that groundwater and vadose zone equation were breaking up. Hydrologists split into three communities following the motto “you are my boundary condition”: groundwater people, vadose zone scientists and surface water hydrologists. This compartmentalization of the scientific community fostered a deepening of knowledge in single branches, allowing to break things down into simple parts. However, this division represented an obstacle to the comprehension of the complexity that characterises the interactions between them. Eventually, this separation of the communities continued into software code. As a matter of fact, the boundary conditions were hard-wired, but they offered a poor representation of the physics in the interaction between different domains. Recently, there has been a renewed interest in studying the big picture, the interactions between different domains. This it is evident in the development of a new research field named the Earth’s Critical Zone (CZ). It is defined as the “ heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air, and living organism regulate the natural habitat and determine the availability of life-sustaining resources” (National Research Council, 2001). Further interest in the studying the CZ is given by the ever-increasing pressure due to the growth in human population, wealth, and climatic changes. This thesis focuses on the CZ while recognising the central role of having a solid set of tools for modeling the water movements in all conditions. Recently, Prentice et al. (2015) identified Reliable, Robust, and Realistic, the three R’s, as the three characteristics that numerical models should have. Soil moisture is one of the key components to simulate the processes in the critical zone. The governing equation to describe the water flow in a porous material is know as the Richards equation and it dates back to 1931.The numerical solution of the Richards equation is far from trivial because of its mildly nonlinearity and it is often discarded in favour of more empirical models. After the pioneering work by Celia et al. (1990), a lot of work has been done in this direction and several model, for instance Hydrus, GEOtop, Cathy, Parflow adopted variants of the Newton algorithm to allows global convergence. Since Casulli and Zanolli (2010), anticipated by Brugnano and Casulli (2008), a new method called nested Newton has been found to guarantee convergence in any situation, even under the use of large time steps and grid sizes. The research presented in this thesis used this integration algorithm. Besides the numerical aspect, another issue was the correct definition of the boundary condition at the soil surface. As a matter of fact, the definition of the surface boundary condition is necessary to capture the generation of surface run-off. In the literature several approaches were proposed to couple surface and subsurface flow, and in this work the approach presented by Gugole (2016) has been used. The novelty regarded the discretization of the shallow water equation and the Richards equation in an unique algebraic system that was solved in a conservative manner. Richards equation was criticized from many points of view, but it is difficult to criticize its core mass conservation. The definition of the hydraulic properties of the soil, including both the soil water retention function (SWRC) and the hydraulic conductivity models, often uses simplified representation of the pore system describing it as bundle of cylindrical capillaries where the largest ones drain first and are filled last. As pointed out by Bachmann et al. (2002), “physical effects, like surface water film adsorption, capillary condensation and surface flow in liquid films, as well as volumetric changes of the pore space are often ignored”. Thus, the capillary bundle concept is a rough, even if still useful approximation of soil reality. From these observations, during the research the code has been designed to offer the opportunity to easily implement new soil water hydraulic models that might be proposed in the future. The Richards’ equation alone is not anymore sufficient to model the water flow in soils. In fact, soil temperature affects the water flow in soils. This is evident in cold regions where soil water is subject to freezing and thawing processes, but also in unfrozen soil, where temperature modifies water properties such as viscosity, the surface tension, and the contact angle. These microscopic variations of the water physical properties have significant impacts in the mass and energy budget within the CZ. For instance, it has been observed that the infiltration rates between the stream and the vadose zone show a clear diurnal pattern: infiltration rates are highest in late afternoon, when stream temperature is greatest, and they are lowest in early morning when stream temperature is least. In cold regions the run-off production is strongly affected by the presence of ice with the soil. Nonetheless, soil moisture modifies the thermal properties of the soil: water is characterised by a high thermal inertia and the thermal conductivity of ice is almost four times larger than that of liquid water, and water flow carries a significant amount of sensible heat. These aspects come under one the R of realistic. Hence, the Richards’ equation has been coupled with the energy equation for the unfrozen case. Moreover, the research developed a model to study the heat transfer considering the phase change of water. In both cases robust numerical schemes have been used. There are few models that already coupled the equations. One of these models is GEOtop that was conceived and built in the research group where this work was carried out. Such models have some limitations. One of the main limitations regards their implementations. In fact, these models were built as a monolithic code and this turns in difficulties in maintaining and developing existing codes. In this work the codes have been developed by using Design Patterns. As a result, the codes are easy to maintain, to extend, and to reuse. Considering the CZ, these aspects are of crucial importance. Researchers should have a model that can be extended to include more processes, i.e. increase its complexity and avoiding the code to become too complicated. The models were integrated in the Object Modelling System v3 (OMS3) framework. The system provides various components for precipitation treatment, radiation estimation in complex terrain, evaporation and transpiration that can be connected to each other’s for generating inputs and outputs. Due to the modularity of the system, whilst the components were developed and can be enhanced independently, they can be seamlessly used at run time by connecting them with the OMS3 DSL language based on Groovy. OMS3 provides the basic services and, among them, tools for calibration and implicit parallelization of component runs. In sum, the thesis analyses the relevant literature to date. It presents a detailed description of the physical processes related to the water flow and the energy budget within the soil. Then, it describes the numerical method used to solve and coupled the equations. It also provides the informatics behind WHETGEO 1D (Water HEat Tracers in GEOframe). Finally, the work focuses on the WHETGEO extension for the bidimensional case by showing how the code can be designed to store grid information.

La Zone Critique de la Terre désigne la fine pellicule recouvrant sa surface, à l’interface du cycle de l’eau, de lithosphère et de la biosphère. Cette couche est produite à sa base par altération chimique et détruite à son sommet par érosion mécanique. Parce que le lithium et ses isotopes ont la particularité de se partager entre la phase dissoute et la phase solide au cours des réactions d’interactions eaux-roches, nous explorons, dans cette thèse, le potentiel des isotopes du lithium dissous dans les rivières comme traceurs des processus d’altération chimique des continents. Nous nous sommes focalisés, dans un premier temps, sur le Bassin Congolais. Cette étude met en évidence le caractère équivoque de la réponse de la composition isotopique du Li (δ7Li) dissous des rivières aux topographies plates (et aux intensités d’altération élevées). Deux valeurs extrêmes de δ7Li dissous sont, en effet, produites dans le bassin du Congo, qui tracent deux styles d’altération continentale distincts, dans lesquels les processus d’altération chimique sont différents. D’autre part, nous proposons une nouvelle estimation du flux moyen de Li et de sa composition isotopique moyenne exportés à l’océan par les rivières aujourd’hui (5,5×1010 g.an−1 et 19±2‰, respectivement). Nous montrons que le δ7Li dissous dans les grands fleuves est contrôlé, au premier ordre, par la réincorporation du Li dans les minéraux secondaires (dans les sols et les plaines d’inondation) et, d’une manière équivoque, de l’intensité d’altération. En outre, l’étude des δ7Li dissous dans les rivières drainant les îles volcaniques (Islande, Java, Martinique, Sao Miguel et Réunion) montre que l’hydrothermalisme continental, générant des eaux très concentrées en Li avec une valeur basse de δ7Li (car très peu fractionnée par rapport à la roche mère basaltique), influence le δ7Li dissous des rivières des îles volcaniques et peut avoir un impact significatif sur le flux de Li (et son δ7Li) transféré(s) à l’océan à l’échelle globale. Enfin, nous proposons une interprétation de l’augmentation de l’ordre de 9‰ qu’a connue la signature isotopique du Li de l’eau de mer au cours du Cénozoïque à l’aide d’un modèle de boîtes simple de l’océan et au regard de nos résultats. Il émane de ce travail de thèse que les isotopes du Li dissous dans les rivières prouvent là encore leur capacité à être de bons traceurs des régimes d’altération des roches silicatées continentales (et ce, même en contexte anthropisé, comme le montre notre étude du bassin de l’Orgeval, en Seine-et-Marne). Le Li et ses isotopes constituent donc des traceurs prometteurs de la Zone Critique de la Terre et des paléo-processus d’altération chimique ainsi que de l’évolution géodynamique des continents voire des grands mouvements verticaux affectant la lithosphère continentale / The Critical Zone of the Earth is the layer covering its surface, at the interface between the water cycle, the lithosphere and the biosphere. This layer is produced at its base by chemical weathering and destroyed at its top by mechanical erosion. We explore the potential of lithium isotopes dissolved in rivers as tracers of continental chemical weathering processes as lithium and its isotopes are highly fractionated between the dissolved and solid phases during water-rock interaction processes. First, we are focused on the Congo Bassin. This study demonstrates the equivocal response of the isotopic composition of the riverine dissolved Li isotope compositions (δ7Li) to flat topography (and high weathering intensities). Two extreme values of dissolved δ7Li are produced in the Congo Basin, which trace two distinct continental weathering styles in which chemical weathering processes are different. On the other hand, we refined the mean flux of Li and its average isotopic signature exported to the ocean by rivers today (5.5×1010 g. an-1 et 19±2‰, respectively). We show that dissolved δ7Li in large rivers is controlled, at first-order, by the re-incorporation of Li into secondary weathering minerals (in soils and floodplains) and in, an equivocal way, of the weathering intensity. Moreover, the study of dissolved δ7Li in rivers draining volcanic islands (Iceland, Java, Martinique, Sao Miguel and Reunion) shows that continental hydrothermal activity, producing waters with high Li concentration with low value of δ7Li (as low fractionated towards the basaltic bedrock), influences the dissolved δ7Li in rivers of volcanic islands and can have an impact on the Li flux (and its δ7Li) transferred to the ocean on a global scale. Finally, by using a simple box model of the ocean and our results, we suggest an interpretation of the 9‰ increase of seawater δ7Li during the Cenozoic. This thesis highlights that riverine dissolved Li isotopes confirm once again their capacity to be powerful tracers of the weathering regimes of continental silicate rocks (even in anthropized context, as showed by our study of the Orgeval catchment, in Seine-et-Marne). Li and its isotopes are thus promising tracers of the Critical Zone of the Earth and the chemical weathering paleo-processes as well as the long-term geodynamic evolution of the continents or even the large vertical movements affecting the continental lithosphere

Cette thèse constitue une étude de référence sur la qualité des ressources hydriques du bassin versant du fleuve Ibrahim au Liban, notamment avant la construction d’un grand barrage (Jannah). Pour ce faire, 7 stations (NI7 à NI1) ont été sélectionnées de l’amont vers l’aval sur l’Ibrahim et ses sources karstiques. L’ensemble des sept sous bassins a été caractérisé d’un point de vue hydroclimatologie et états de surface (sols, végétation, cultures, géologie, relief). Les débits mesurés à l’amont (2 stations) et à l’aval (1 station) nous ont permis de reconstituer les débits des autres stations intermédiaires grâce à des relations débits-surfaces spécifiques. À partir de prélèvements et d’analyses chimiques de la composition des eaux tout au long d’un cycle hydrologique et avec une fréquence mensuelle, les flux de matières exportées en solution par l’Ibrahim ont été estimés à 122 372 t/an. 80% de ce tonnage est exporté durant la période des hautes eaux. À partir de ce tonnage, on a pu estimer que l’altération chimique des roches carbonatées sur l’ensemble du bassin s’effectue à la vitesse de 81 cm/10000 ans. Cette altération consomme un flux élevé de CO2 typique des régions carbonatées soumises à un drainage intense (1500 mm/an), soit 2,23 x106 moles/km2/an de CO2. L’analyse de la concentration en éléments traces dans les sédiments de fond des cours d’eau, intégrateurs des transports solides, en hautes eaux et en basses eaux, montre des concentrations élevées pour le Sc, V, Cr, Co, Ni, Ga et Cu en passant de NI5 jusqu’à NI2. L’évaluation du degré de cette contamination et de sa variation spatio-temporelle a été effectuée grâce au facteur d’enrichissement en normalisant par rapport à l’aluminium et en prenant les sédiments de la station amont NI7 (source karstique) considérés comme peu ou pas contaminés en ET, comme fond géochimique naturel. Des teneurs élevées en Zn, Pb, Cu et d’autres éléments traces montrent que dans cette région où les activités industrielles, agricoles, et urbaines sont développées, il existe un apport anthropique non négligeable en éléments métalliques. Mais cette contamination reste modérée / Throughout the study framework conducted on the quality of the water resources in the Ibrahim River watershed in Lebanon (notably before the construction of a large dam, Jannah), 7 stations (NI7 to NI1) were selected, from upstream to downstream, including its karst springs. Hydroclimatological and specific catchment characteristics (such as land cover use, geology, hydrology, soil and topography) where characterized for the whole seven sub-basins respectively. Discharge data from the sources (2 stations) and the basin outlet (1 station) enhanced our study to determine and further calculate the discharge of other stations. Sampling and analyzing the chemical composition of water collected monthly during one hydrological cycle allowed us to determine the amount of dissolved material carried by the Ibrahim River. The river flux of dissolved material was estimated at 122 372 tons / year of which 80% of is exported during high flow season. Therefore this flux allowed us to estimate the rate of chemical weathering of carbonate rocks across the basin at 81 cm / 10000 years. This alteration consumes a high flux of CO2 (around 2,23x106 moles/km2/year of CO2) typical for carbonate regions subject to intense drainage (1500 mm). The analysis for the concentration of trace elements in fluvial sediments for the Ibrahim River for the low and high flow periods shows high concentrations of Sc, V, Cr, Co, Ni, Cu and Ga in the from NI5 station up to NI2. The assessment of the extent of the contamination and its spatio-temporal variation was conducted using the enrichment factor by normalizing to aluminium concentration and using the element concentrations in the sediments of station NI7 (karstic sspring) considered as the natural geochemical background for this catchment. High levels of Zn, Pb, Cu and other traces of noticeable elements show that in this region where industrial, agricultural and urban activities are developed, there is a significant anthropogenic contribution for some metallic elements; thus the trace element contamination remains moderate.

No description available.

Depuis plus d’un siècle, les changements globaux sont à l’origine de profondes modifications de nos sociétés, nos modes de vie et il en va bien sûr de même pour notre environnement. Cette trajectoire empruntée, bon gré mal gré, par l’ensemble de l’humanité n’est pas sans conséquences pour les systèmes naturels et semble déjà mener les générations futures au-devant de grands défis. Afin de ne pas compromettre notre capacité à relever ces épreuves futures et, devant l’urgence du besoin d’action, une partie de la communauté scientifique a choisi de concentrer ses efforts sur la couche superficielle de notre planète qui soutient la vie terrestre : la Zone Critique. L’émergence de ce concept souligne la nécessité de développer des approches scientifiques pluridisciplinaires intégrant une large variété d’échelles de temps et d’espace. En tant que lien entre les différents compartiments de la Zone Critique (Atmosphère, Biosphère, Hydrosphère, Lithosphère et Pédosphère), l’eau est une molécule essentielle aux échanges d’énergie et de matière dont la dynamique requiert une attention particulière. Compte tenu de la diversité et de la variabilité spatiotemporelle des transferts d’eau et de matière dissoute dans les milieux aquatiques, de nouvelles méthodes d'investigations sont nécessaires. L'objectif général de cette thèse est de décrire l’intérêt et le potentiel qui résident dans l’utilisation des gaz dissous, en particulier lorsqu’ils sont mesurés à haute fréquence sur le terrain, afin de caractériser la dynamique hydrobiogéochimique des eaux naturelles de la Zone Critique à différentes échelles spatiales et temporelles. Pour parfaire cette ambition, ce travail s’est tout d’abord attaché au développement d'une instrumentation innovante puis, à la mise en place de nouveaux traceurs intégrés dans des dispositifs expérimentaux originaux et enfin, à l'acquisition, au traitement et à l'analyse de différents jeux de données de gaz dissous en se focalisant sur les eaux souterraines. / For more than a century, global change has led to a profound modification of our societies, our lifestyles and, of course, our environment. This trajectory followed willy-nilly by all mankind has consequences for natural systems and already seems to lead the future generations ahead of serious challenges. In order not to compromise our ability to meet these future ordeals, and because of the urgent need for action, part of the scientific community has chosen to concentrate on the near-surface environment that supports terrestrial life: the Critical Zone. The emergence of this concept underlines the need to develop multidisciplinary scientific approaches integrating a wide variety of temporal and spatial scales. As the link between the different compartments of the Critical Zone (Atmosphere, Biosphere, Hydrosphere, Lithosphere and Pedosphere), water is an essential molecule controlling the exchanges of energy and matter whose dynamics require special attention. In view of the diversity and spatiotemporal variability of water and matter transfers arising in aquatic environments, new methods of investigation are needed. The general objective of this thesis is to describe the interest and the potential lying in the use of dissolved gases, especially when they are measured at high frequency in the field, in order to characterise the hydrobiogeochemical dynamics of the natural waters of the Critical Zone at different spatial and temporal scales. To perfect this ambition, this work focused first on the development of an innovative instrumentation, then, on the implementation of novel tracers integrated into original experimental setups and finally, on the acquisition, processing and analysis of different dissolved gas datasets focusing on groundwater.