Modelling chemical weathering in contrasted watersheds : new implementations and application at the global scale

The biogeochemical cycles will suffer impacts derived from global change hazards. Understanding and assessing the processes controlling the matter movement between reservoirs is critical to help on natural resource management. Rock weathering controls the amount of inorganic matter released to aquatic environments, which is eventually routed through rivers to oceans or lakes. However, the evaluation of these fluxes across spatial and temporal scales is challenging because of the number of factors involved. In this sense, the objective of this PhD thesis is to evaluate the role of chemical weathering on biogeochemical cycling at different spatial and temporal scales. Mainly, we have aimed at a) identifying the main drivers of chemical weathering at the global scale, b) developing a simple tool to estimate ionic fluxes derived from chemical weathering of rocks, c) evaluate downscaling capabilities of the model at the river basin scale, and d) estimate the impact of chemical weathering on the global carbon cycle. In the present PhD thesis, we have assessed the riverine exports of 1751 rivers to measure the role of hydrology, lithology, and soil on the different ionic fluxes released through chemical weathering of rocks. Such assessment allowed us to develop a simple model and apply it at the global scale to estimate a snapshot of the total amount (3374·106 Mg·y-1) of matter released by rocks, and characterise it among the major ion constituents, being 58% Ca2+, 24% Na+, 15% Mg2+, and 3% K+ of the total cation flux, and 74% alkalinity, 18% SO42-, and 8% Cl- for the total anion flux. Besides, an assessment of the geochemical processes governing the water major ion composition and dissolved loadings at a local case study (Deba river basin, Gipuzkoa, North Spain) has provided a framework to test the local performance of the model. The application of the model at the local scale has let the coupling of this simple equation to the SWAT model, which permitted the study of the capabilities and limitations of the model in estimating the daily geochemical loadings in a heterogeneous geological context affected by evaporitic springs. Once evaluated at the local scale, a dynamic application of the model at the global scale has allowed the assessment of the role of chemical weathering in the carbon sequestration under two climate change scenarios (RCP2.6 and RCP8.5). According to our simulations, the potential shifts in the global hydrological balance will increase C uptake by chemical weathering in an 8 to 13% by the 2069-2099 period, depending on the scenario studied. The results from this PhD thesis have allowed us to evaluate the role of chemical weathering on the carbon cycle at the global scale. Future research should be focused on the configuration of the model, by including physical weathering in its configuration and assessing the local effect of variables such as temperature and land-use change

Hydrological Alteration Index as an Indicator of the Calibration Complexity of Water Quantity and Quality Modeling in the Context of Global Change

Modeling is a useful way to understand human and climate change impacts on the water resources of agricultural watersheds. Calibration and validation methodologies are crucial in forecasting assessments. This study explores the best calibration methodology depending on the level of hydrological alteration due to human-derived stressors. The Soil and Water Assessment Tool (SWAT) model is used to evaluate hydrology in South-West Europe in a context of intensive agriculture and water scarcity. The Index of Hydrological Alteration (IHA) is calculated using discharge observation data. A comparison of two SWAT calibration methodologies are done; a conventional calibration (CC) based on recorded in-stream water quality and quantity and an additional calibration (AC) adding crop managements practices. Even if the water quality and quantity trends are similar between CC and AC, water balance, irrigation and crop yields are different. In the context of rainfall decrease, water yield decreases in both CC and AC, while crop productions present opposite trends (+33% in CC and -31% in AC). Hydrological performance between CC and AC is correlated to IHA: When the level of IHA is under 80%, AC methodology is necessary. The combination of both calibrations appears essential to better constrain the model and to forecast the impact of climate change or anthropogenic influences on water resources

Combining punctual and high frequency data for the spatiotemporal assessment of main geochemical processes and dissolved exports in an urban river catchment

The assessment of dissolved loadings and the sources of these elements in urban catchments' rivers is usually measured by punctual sampling or through high frequency sensors. Nevertheless, the combination of both methodologies has been less common even though the information they give is complementary. Major ion (Ca2+, Mg2+, Na+, K+, Cl−, SO42−, and alkalinity), organic matter (expressed as Dissolved Organic Carbon, DOC), and nutrients (NO3−, and PO43−) are punctually measured in the Deba river urban catchment (538 km2), in the northern part of the Iberian Peninsula (draining to the Bay of Biscay). Discharge, precipitation, and Electrical Conductivity (EC) are registered with a high frequency (10 min) in three gauging stations. The combination of both methodologies has allowed the assessment of major geochemical processes and the extent of impact of anthropogenic input on major composition of riverine water, as well as its spatial and temporal evolution. Three methodologies for loading estimation have been assessed and the error committed in the temporal aggregation is quantified. Results have shown that, even though carbonates dominate the draining area, the water major ion chemistry is governed by an evaporitic spring in the upper part of the catchment, while anthropogenic input is specially noted downstream of three wastewater treatment plants, in all nutrients and organic matter. The results of the present work illustrate how the combination of two monitoring methodologies allows for a better assessment of the spatial and temporal evolution on the major water quality in an urban catchment

A model for evaluating continental chemical weathering from riverine transports of dissolved major elements at a global scale

This study presents a process-based-empirical model for the assessment of ionic fluxes derived from chemical weathering of rocks (ICWR) at a global scale. The equations are designed and the parameters fitted using riverine transport of dissolved major ions Ca2+, Mg2+, K+, Na+, Cl−, SO42−, and alkalinity at a global scale by combining point sampling analysis with spatial descriptions of hydrology, climate, topography, lithology and soil variables such as mineral composition and regolith thickness. Different configurations of the model are considered and the results show that the previously reported “soil shielding” effect on chemical weathering (CW) of rocks presents different values for each of the ions considered. Overall, there is good agreement between median and ranges in observed and simulated data, but further analysis is required to downscale the model to catchment scale. Application to the global scale provides the first global ICWR map, resulting in an average cationic flux derived from chemical weathering of 734·106 Mg·y−1, where 58% is Ca2+, 15% is Mg2+, 24% is Na+ and 3% is K+, and an average anionic flux derived from chemical weathering of 2640·106 Mg·y−1, where 74% is alkalinity, 18% is SO42−, and 8% is Cl−. Hyperactive and hotspot areas are elucidated and compared between ions

Modelling chemical weathering in contrasted watersheds: new implementations and application at the global scale

xxx, 335 p.[EN]The biogeochemical cycles describe the matter and energy flux between ecosystems in the Earth System. However, climate change, human population growth and other global change hazards alter the natural balance of these cycles. Within this context, understanding which mechanisms control the mass transfer, and assessing their spatial and temporal evolution becomes necessary to balance a sustainable development with the environmental protection. In the biogeochemical cycles the relative importance of the different factors involved changes with the spatial and temporal scales used for their evaluation, creating the need of tools capable of integrating these factors for analysis. Commonly, these tools involve modelling.With regards to biogeochemical cycling research, focus has been pointed to the Critical Zone, a part of the environment comprising from the ground surface to the consolidated rock. Is within this zone where the geochemical cycle interacts with the biogeochemical cycles through the physical and chemical weathering processes. Weathering conditions the chemical composition of the aquatic environments through the liberation of products from the solid phase. In the continental zone, rivers act not only as reaction matrix in the Critical Zone, but also as a vector of transport for those products from the hydrographic basin to other environments, such as lakes or oceans. At the local level, this matter transfer is of interest for ecological analysis both at the river and wetland scale; while at the global scale, these processes impact on the oceanic and atmospheric composition in geological scales.The main objective of this work is to evaluate the role of chemical weathering in the biogeochemical cycles, paying special attention to the major ions derived from rocks through the modelling of this process at different spatial and temporal scales. In particular, a global-to-local and static-to-dynamic approach has been followed.At the beginning of this work, there existed several modelling tools capable of assessing the chemical weathering using a mechanistic approach, however, its application to large spatial and temporal scales is conditioned to the availability of input data and computing resources. As an alternative, there were other empirical models applicable at the global scale. Taking as starting point the most recent studies, and after the evaluation of 1751 river compositions, in this work we have been able to confirm that hydrology, lithology, and soil are the most relevant factors at the global scale regarding chemical weathering. Indeed, its implication on each major ion liberation has been proved, allowing the yield of the first global scale maps of specific fluxes derived from rocks, as well as the comparison of hotspots between ions. At the global scale, 3374·106 Mg·y-1 dissolved matter is yielded from rocks, where 58% is Ca2+, 24% is Na+, 15% is Mg2+, and 3% is K+ with respect to the cation flux, and a 74% is alkalinity, 18% is SO42-, and 8% is Cl- with regards to the anion flux.Besides, a more detailed analysis at a local scale case study (the Deba river basin, Gipuzkoa, Basque Country) has been accomplished, paying attention to the processes responsible of the chemical composition of the waters, as well as to the hydrological effect on the temporal evolution of the exports to the ocean. In this catchment, the effect of evaporitic springs and gypsum deposits in one of its headwaters has been shown to have a great impact on the stream water chemical composition down to the outlet. This study has also permitted to highlight the advantages of combining punctual sampling information with continuous registries to evaluate the temporal evolution of the system. Identifying the moments after the flood events as those with the greatest relative dissolved exports to the ocean within the year.Once the main processes governing the chemical composition of water in this study were identified, the application of the global model to the basin scale has been performed through the coupling of the model to the physically-based hydrological model (SWAT). Such assessment has allowed to evaluate the possibilities and limitations of the models in local scales, both under a static and a dynamic approach. The model allows to obtain results with a mean discrepancy of 13% with respect to reality, when the effects of point sources (such as the evaporitic springs and gypsum deposits) do not condition the ionic composition.Acknowledging the limitations at the local scale, the model has been again applied at the global scale, aiming to evaluate not only the spatial distribution of the chemical weathering derived fluxes, but the impact of this process on the global carbon cycle under a climate change context. The results from this simulation have allowed to see that the potential impacts derived from the climate change on the hydrological balance will increase between 8 to 13% the CO2 consumption rates derived from the chemical weathering of rocks, but its growth will not been nor spatially nor temporally homogeneous.The results from this PhD thesis have allowed to the assess the role of chemical weathering at the global scale, specially on the carbon cycle. Future research should focus on improving the model configuration and integrating the results from other studies following a local-to-global approach.[ES]Los ciclos biogeoquímicos describen el flujo de materia y energía entre los ecosistemas del Sistema Tierra. Sin embargo, el cambio climático, el aumento de la población y otras amenazas del cambio global alteran el equilibrio natural de estos ciclos. En este contexto se vuelve necesario tanto entender qué mecanismos controlan la transferencia de materia, como estimar su evolución espacial y temporal, para poder equilibrar un desarrollo sostenible con la protección del medioambiente. La relevancia de distintos factores involucrados en los distintos ciclos biogeoquímicos cambia con respecto a la escala temporal y espacial utilizada para su evaluación, creando la necesidad de herramientas capaces de integrar dichos factores para poder llevar a cabo su análisis. Generalmente, estas herramientas implican trabajo de modelización.Con relación a la investigación en los ciclos biogeoquímicos, la atención se ha centrado en la Zona Crítica, un espacio del ecosistema que comprende desde la superficie del suelo hasta la roca consolidada. Es en esta zona donde los ciclos geoquímicos interaccionan con los ciclos biogeoquímicos a través de la alteración física y química. La alteración condiciona la composición química de los entornos acuáticos tras la liberación de productos de la fase rocosa. En la zona continental, los ríos actúan no únicamente como matriz de reacción en la Zona Crítica, sino también como vector de transporte de esos productos desde la cuenca hidrográfica hacia otros entornos, como lagos u océanos. A nivel local, esta transferencia de materia resulta de interés para análisis ecológicos tanto a nivel de río como a nivel de estuario, mientras que a nivel global el impacto de estos procesos afecta a la composición de los océanos e incluso de la atmósfera en escalas geológicas.El objetivo principal de este trabajo es evaluar el papel de la erosión química en los ciclos biogeoquímicos, prestando especial atención a los iones mayoritarios derivados de las rocas, a través del modelado de este proceso a diferentes escalas espaciales y temporales. En particular, se ha seguido un enfoque espacial de global-a-local y temporal de estático-a-dinámico.Al inicio de este trabajo, existían varias herramientas de modelización capaces de evaluar la erosión química desde un punto de vista físico y termodinámico, sin embargo, su aplicación a grandes escalas espaciales y temporales se ve condicionada por disponibilidad de datos de entrada y de recursos de computación. Como alternativa, también constaban otros modelos de base empírica que permitían su aplicación a escala global. Tomando como referencia los estudios más actuales, y tras la evaluación de la composición de 1751 ríos en este trabajo, se ha podido confirmar que la hidrología, la litología y el suelo son los factores más relevantes a nivel global respecto a la erosión química. También se ha podido constatar que su implicación en la liberación de cada ion mayoritario de la roca es diferente, permitiendo obtener los primeros mapas a nivel global de flujos específicos derivados de la roca, así como la comparación de puntos calientes de cada ion. A nivel global, 3374·106 Mg·año-1 de material disuelto se libera de las rocas, siendo un 58% Ca2+, un 24% Na+, un 15% Mg2+, y un 3% K+ respecto al flujo de cationes, y un 74% alcalinidad, un 18% SO42-, y un 8% Cl- respecto al flujo de aniones.Paralelamente, se ha realizado un análisis más detallado de un caso local (la cuenca del río Deba, Gipuzkoa, País Vasco) prestando atención a los procesos condicionantes de la composición química de las aguas, así como al efecto de la hidrología sobre la evolución temporal de los flujos al océano. En esta cuenca destaca el importante efecto que ejercen las fuentes de evaporitas y los depósitos de yesos en una de las partes de cabecera, que condicionan fuertemente la química de las aguas hasta la desembocadura. Este estudio también ha permitido subrayar la ventaja de combinar muestreos puntuales con registros en continuo para evaluar la evolución temporal del sistema. Identificando los momentos después de las crecidas como los de mayores exportaciones disueltas relativas al océano a lo largo del año.Una vez identificados los procesos determinantes de la composición química del agua en este caso de estudio, se ha trasladado la aplicación del modelo global hasta la escala de cuenca mediante la integración de dicho modelo a un modelo hidrológico de base física (SWAT). Este estudio ha permitido evaluar las posibilidades y las limitaciones del modelo en escalas locales, tanto de forma estática como dinámica. El modelo permite obtener unos resultados con una discrepancia media respecto a la realidad del 13% siempre que los efectos puntuales (como las fuentes de evaporitas y los depósitos de yesos) no condicionen la presencia de iones mayoritarios.Conocidas las limitaciones que pueden existir a escalas locales, el modelo se ha aplicado a escala global nuevamente, tratando de evaluar no sólo la distribución espacial de los flujos derivados de la erosión química, sino el impacto que este proceso genera sobre el ciclo global del carbono bajo un contexto de cambio climático. Los resultados de la simulación nos han permitido ver que los potenciales impactos derivados del cambio climático en la hidrología aumentarán globalmente entre un 8 y un 13% las tasas de consumo de CO2 por la erosión de las rocas, pero su aumento no será uniforme ni espacial ni temporalmente.Los resultados de esta tesis doctoral permiten evaluar el papel de la erosión química a la escala global, especialmente en el ciclo del carbono. Investigación futura debería centrarse en mejorar la configuración del modelo e integrar los resultados de otros estudios con enfoques local-a-global.[FR]Les cycles biogéochimiques décrivent le flux de matière et d'énergie entre les environnements du système Terre. Cependant, le changement climatique, l'augmentation de la population et d'autres menaces du changement global altèrent l'équilibre naturel de ces cycles. Dans ce contexte, il devient nécessaire de comprendre quels mécanismes contrôlent le transfert de matière et estimer son évolution spatiale et temporelle, pour équilibrer le développement durable avec la protection de l'environnement. L¿importance relative des différents facteurs intervenant évoluant par rapport à l'échelle temporelle et spatiale utilisée pour leur évaluation, crée la nécessité des outils capables d'intégrer ces facteurs afin de réaliser les analyses. Normalement, ces outils utilisent la modélisation.Par rapport à la recherche des cycles biogéochimiques, une attention est dirigée sur la Zone Critique, une zone de l¿environnement allant de la surface du sol à la roche consolidée. C'est dans cette zone que les cycles géochimiques interagissent avec les cycles biogéochimiques par l¿altération physique et chimique. C¿est l¿altération qui conditionne la composition des milieux aquatiques après la libération des produits par la phase rocheuse. Dans la zone continentale, les rivières agissent non seulement comme matrice de réaction dans la zone critique, mais aussi comme vecteur de transport de ces produits du bassin hydrographique vers d'autres environnements, tels que les lacs ou les océans. Au niveau local, ce transfert de matière présente un intérêt pour les analyses écologiques à la fois au niveau des fleuves et des estuaires, tandis qu'au niveau global ces processus affectent la composition des océans et même l'atmosphère à l'échelle géologique.L'objectif principal de ce travail est d'évaluer le rôle de l'érosion chimique dans les cycles biogéochimiques, en accordant une attention particulière aux ions majoritaires dérivés des roches, à travers la modélisation de ce processus à différentes échelles spatiales et temporelles. En particulier, une approche spatiale globale-locale et temporelle statique-dynamique a été suivie.Au début de ce travail, il y avait plusieurs outils de modélisation capables d'évaluer l'érosion chimique d'un point de vue physique et thermodynamique, cependant, son application à de grandes échelles spatiales et temporelles est conditionnée par la disponibilité des données d'entrée et des ressources informatiques. Comme alternative, il y avait aussi d'autres modèles empiriques qui permettaient son application à l'échelle mondiale. En prenant comme référence les études les plus récentes et après l'évaluation de la composition chimique de 1751 rivières dans ce travail, il a été possible de confirmer que l'hydrologie, la lithologie et le sol sont les facteurs les plus pertinents à l'échelle mondiale en ce qui concerne l¿altération chimique. Il a également été vérifié que leur implication dans la libération de chaque ion majeur de la roche est différente, permettant d'obtenir les premières cartes globales d'écoulements spécifiques dérivés de la roche, ainsi que la comparaison des points chauds de chaque ion. À l'échelle mondiale, 3374·106 Mg·an-1 de matière dissoute sont libérés des roches, soit 58% de Ca2+, 24% de Na+, 15% de Mg2+ et 3% de K+ par rapport au flux de cations et 74% d'alcalinité, 18% SO42- et 8% Cl- en ce qui concerne le flux d'anions.Parallèlement, une étude plus détaillée a été réalisée dans un cas d¿étude local (le bassin versant de Deba, Gipuzkoa, Pays Basque), en prêtant attention aux processus de conditionnement de la composition chimique des eaux, ainsi qu'à l'effet de l'hydrologie sur l'évolution temporelle des écoulements vers l'océan. Dans ce bassin, se distingue l'effet important exercé par les sources d'évaporites et les dépôts de gypse dans l'une des parties de tête, qui conditionnent fortement la chimie jusqu'à l¿exutoire. Cette étude a également mis en évidence l'avantage de combiner des échantillonnages ponctuels avec des enregistrements continus pour évaluer l'évolution temporelle du système. En identifiant les moments après les crues comme ceux de plus grande exportation d¿éléments dissous relatifs vers l'océan tout au long de l'année.Une fois les processus déterminants identifiés issus de la composition chimique de l'eau dans cette étude de cas, l'application du modèle global a été transférée à l'échelle du bassin en intégrant ce modèle dans un modèle physique hydrologique (SWAT). Cette étude a permis d'évaluer les possibilités et les limites du modèle à l'échelle locale, à la fois statiquement et dynamiquement. Le modèle permet d'obtenir des résultats avec un écart moyen de 13% par rapport à la réalité, tant que les effets ponctuels (tels que les sources d'évaporites et les dépôts de gypse) ne conditionnent pas la présence d'ions majoritaires.Connaissant les limitations qui peuvent exister à l'échelle locale, le modèle a été appliqué à nouveau à l'échelle mondiale, essayant d'évaluer non seulement la distribution spatiale des flux issus de l'érosion chimique, mais l'impact que ce processus génère sur le cycle global de carbone dans un contexte de changement climatique. Les résultats de la simulation nous ont permis de voir que les impacts potentiels dérivés du changement climatique sur l'hydrologie augmenteraient globalement les taux de consommation de CO2 de 8 à 13% en raison de l'érosion des roches, mais leur augmentation ne serait pas uniforme ni spatiale ni temporairement.Les résultats de cette thèse de doctorat nous ont permis d'évaluer le rôle de l'érosion chimique à l'échelle mondiale, notamment dans le cycle du carbone. Les recherches futures devraient se concentrer sur l'amélioration de la configuration du modèle et l'intégration des résultats d'autres études aux approches locales à mondiales

Modélisation de l'érosion géochimique dans des bassins versant contrastés : nouvelles implémentations et application à l'échelle globale

Les cycles biogéochimiques subissent les impacts dérivés des menaces des changements globaux. Comprendre et évaluer les processus qui contrôlent le mouvement de la matière entre les réservoirs est essentiel pour aider à gérer les ressources naturelles. L'altération des roches contrôle la quantité de matière inorganique libérée dans les milieux aquatiques, qui finit par rejoindre les océans ou les lacs par les rivières. Cependant, l'évaluation de ces flux à travers les échelles spatiales et temporelles est difficile en raison du nombre de facteurs impliqués. En ce sens, l'objectif de cette thèse est d'évaluer le rôle de l'altération chimique dans les cycles biogéochimiques à différentes échelles spatiales et temporelles. Principalement, nous avons visé à a) identifier les variables clés de l’érosion chimique à l'échelle mondiale, b) développer un outil simple permettant d’estimer les flux ioniques dérivés de l'altération chimique des roches, c) évaluer les capacités d’extrapolation du modèle à l'échelle du bassin versant, et d) estimer l'impact de l'altération chimique sur le cycle mondial du carbone. Dans cette thèse de doctorat, nous avons évalué les exportations fluviales de 1751 rivières pour quantifier le rôle de l'hydrologie, de la lithologie et du sol dans les différents flux ioniques issus de l'altération chimique des roches. Une telle évaluation nous a permis de développer un modèle simple et de l'appliquer à l'échelle mondiale pour estimer un instantané de la quantité totale (3374·106 Mg·y-1) de matière libérée par les roches, et le caractériser parmi les principaux constituants ioniques, soit 58% de Ca2+, 24% de Na+, 15% de Mg2+ et 3% de K+ du flux cationique total et 74% d’alcalinité, 18% de SO42- et 8% de Cl- pour le flux anionique total. En outre, une évaluation des processus géochimiques qui régissent la composition en ions majeurs d’eau et les charges dissoutes dans une étude de cas local (le bassin versant de la rivière Deba, Gipuzkoa, nord de l'Espagne) a fourni un cadre pour tester les performances locales du modèle. L'application du modèle à cette échelle a permis le couplage de cette simple équation au modèle SWAT, ce qui a permis d'évaluer les capacités et les limites du modèle dans l'estimation des charges géochimiques au pas de temps journalier dans un contexte géologique hétérogène affecté par les sources évaporitiques. Une fois évaluée à l'échelle locale, une application dynamique du modèle à l'échelle mondiale a permis d’étudier le rôle de l'altération chimique dans la séquestration du carbone sous deux scénarios de changement climatique (RCP2.6 et RCP8.5). Selon nos simulations, les évolutions potentielles du bilan hydrologique global augmenteront la consommation de carbone par l'altération chimique de 8 à 13% d'ici 2069-2099, selon les scénarios étudiés. Les résultats de cette thèse nous ont permis d'évaluer le rôle de l'altération chimique sur le cycle du carbone à l'échelle mondiale. Les recherches futures dans ce domaine d’étude devraient être axées sur la configuration du modèle, en incluant l'altération physique dans sa configuration et en évaluant l'effet local de variables telles que la température et le changement des usages du sol.The biogeochemical cycles will suffer impacts derived from global change hazards. Understanding and assessing the processes controlling the matter movement between reservoirs is critical to help on natural resource management. Rock weathering controls the amount of inorganic matter released to aquatic environments, which is eventually routed through rivers to oceans or lakes. However, the evaluation of these fluxes across spatial and temporal scales is challenging because of the number of factors involved. In this sense, the objective of this PhD thesis is to evaluate the role of chemical weathering on biogeochemical cycling at different spatial and temporal scales. Mainly, we have aimed at a) identifying the main drivers of chemical weathering at the global scale, b) developing a simple tool to estimate ionic fluxes derived from chemical weathering of rocks, c) evaluate downscaling capabilities of the model at the river basin scale, and d) estimate the impact of chemical weathering on the global carbon cycle. In the present PhD thesis, we have assessed the riverine exports of 1751 rivers to measure the role of hydrology, lithology, and soil on the different ionic fluxes released through chemical weathering of rocks. Such assessment allowed us to develop a simple model and apply it at the global scale to estimate a snapshot of the total amount (3374·106 Mg·y-1) of matter released by rocks, and characterise it among the major ion constituents, being 58% Ca2+, 24% Na+, 15% Mg2+, and 3% K+ of the total cation flux, and 74% alkalinity, 18% SO42-, and 8% Cl- for the total anion flux. Besides, an assessment of the geochemical processes governing the water major ion composition and dissolved loadings at a local case study (Deba river basin, Gipuzkoa, North Spain) has provided a framework to test the local performance of the model. The application of the model at the local scale has let the coupling of this simple equation to the SWAT model, which permitted the study of the capabilities and limitations of the model in estimating the daily geochemical loadings in a heterogeneous geological context affected by evaporitic springs. Once evaluated at the local scale, a dynamic application of the model at the global scale has allowed the assessment of the role of chemical weathering in the carbon sequestration under two climate change scenarios (RCP2.6 and RCP8.5). According to our simulations, the potential shifts in the global hydrological balance will increase C uptake by chemical weathering in an 8 to 13% by the 2069-2099 period, depending on the scenario studied. The results from this PhD thesis have allowed us to evaluate the role of chemical weathering on the carbon cycle at the global scale. Future research should be focused on the configuration of the model, by including physical weathering in its configuration and assessing the local effect of variables such as temperature and land-use change

Global carbon sequestration through continental chemical weathering in a climatic change context

This study simulates carbon dioxide (CO2) sequestration in 300 major world river basins (about 70% of global surface area) through carbonates dissolution and silicate hydrolysis. For each river basin, the daily timescale impacts under the RCP 2.6 and RCP 8.5 climate scenarios were assessed relative to a historical baseline (1969–1999) using a cascade of models accounting for the hydrological evolution under climate change scenarios. Here we show that the global temporal evolution of the CO2 uptake presents a general increase in the annual amount of CO2 consumed from 0.247 ± 0.045 Pg C year−1 to 0.261 and 0.273 ± 0.054 Pg C year−1, respectively for RCP 2.6 and RCP 8.5. Despite showing a general increase in the global daily carbon sequestration, both climate scenarios show a decrease between June and August. Such projected changes have been mapped and evaluated against changes in hydrology, identifying hot spots and moments for the annual and seasonal periods

Global carbon sequestration through continental chemical weathering in a climatic change context

This study simulates carbon dioxide (CO2) sequestration in 300 major world river basins (about 70% of global surface area) through carbonates dissolution and silicate hydrolysis. For each river basin, the daily timescale impacts under the RCP 2.6 and RCP 8.5 climate scenarios were assessed relative to a historical baseline (1969–1999) using a cascade of models accounting for the hydrological evolution under climate change scenarios. Here we show that the global temporal evolution of the CO2 uptake presents a general increase in the annual amount of CO2 consumed from 0.247 ± 0.045 Pg C year−1 to 0.261 and 0.273 ± 0.054 Pg C year−1, respectively for RCP 2.6 and RCP 8.5. Despite showing a general increase in the global daily carbon sequestration, both climate scenarios show a decrease between June and August. Such projected changes have been mapped and evaluated against changes in hydrology, identifying hot spots and moments for the annual and seasonal periods

Global carbon sequestration through continental chemical weathering in a climatic change context

This study simulates carbon dioxide (CO2) sequestration in 300 major world river basins (about 70% of global surface area) through carbonates dissolution and silicate hydrolysis. For each river basin, the daily timescale impacts under the RCP 2.6 and RCP 8.5 climate scenarios were assessed relative to a historical baseline (1969–1999) using a cascade of models accounting for the hydrological evolution under climate change scenarios. Here we show that the global temporal evolution of the CO2 uptake presents a general increase in the annual amount of CO2 consumed from 0.247 ± 0.045 Pg C year−1 to 0.261 and 0.273 ± 0.054 Pg C year−1, respectively for RCP 2.6 and RCP 8.5. Despite showing a general increase in the global daily carbon sequestration, both climate scenarios show a decrease between June and August. Such projected changes have been mapped and evaluated against changes in hydrology, identifying hot spots and moments for the annual and seasonal periods

Global carbon sequestration through continental chemical weathering in a climatic change context

International audienceAbstract This study simulates carbon dioxide (CO 2 ) sequestration in 300 major world river basins (about 70% of global surface area) through carbonates dissolution and silicate hydrolysis. For each river basin, the daily timescale impacts under the RCP 2.6 and RCP 8.5 climate scenarios were assessed relative to a historical baseline (1969–1999) using a cascade of models accounting for the hydrological evolution under climate change scenarios. Here we show that the global temporal evolution of the CO 2 uptake presents a general increase in the annual amount of CO 2 consumed from 0.247 ± 0.045 Pg C year −1 to 0.261 and 0.273 ± 0.054 Pg C year −1 , respectively for RCP 2.6 and RCP 8.5. Despite showing a general increase in the global daily carbon sequestration, both climate scenarios show a decrease between June and August. Such projected changes have been mapped and evaluated against changes in hydrology, identifying hot spots and moments for the annual and seasonal periods