P***** Cakita, j'ai fini ! Bon je sais qu'en tapant ces mots il me reste une dernière(s ?) relect... more P***** Cakita, j'ai fini ! Bon je sais qu'en tapant ces mots il me reste une dernière(s ?) relecture avant quand même. La thèse ? Un projet qui t'obsède. Un marathon intellectuel et physique. J'ai mis plus de 3 ans à répondre à une question, et encore que partiellement. Mais j'ai eu l'impression de me construire mon meilleur cours, celui qui m'a le plus intéressé ! La mise en application de tes connaissances pour répondre à une question... Une aventure faite de rencontres, d'épreuves et de supers moments. Une véritable étape ! Alors merci un immense merci à toi ma Cakita, pour ton indéfectible soutien et tes petits plats qui ont le pouvoir de garder motivé. L'aventure ne fait que commencer. Encore désolé pour toutes ces nuits de travail où Tortilla m'a veillé. Au passage, merci à cette boule de poils, même si ça n'est pas évident d'écrire au clavier avec un chat dessus. A mes parents pour tout ce qu'ils ont fait pour moi, leur éducation et leur foi en moi. A mes frères Lucas et Yann, partager vos vies est un grand honneur ! Et à tous mes ami.e.s qui m'ont soutenu.e.s à base de soirées, pour s'assurer de ma survie, et de « toujours pas fini ? ». C'est bon maintenant. BIG UP au 225 éternel, au BGSL et au P5 ! Un merci spécial à Florian, qui comprend le sens profond d'abnégation et de patience nécessaire au modélisateur. A l'aventurière éternelle du 93 et à Michou ! Un grand merci à mes directeurs de thèse Marie-Elodie Perga et Damien Bouffard pour leur accompagnement dans cette expérience passionnante. Les contraintes géo-professionnelle n'ont pas rendu la tâche facile et j'apprécie d'autant plus leur investissement. Merci ! Merci au CIH-EDF, et plus particulièrement Vincent Chanudet, Agnès Bariller et Stéphane Descloux pour leurs soutiens scientifiques, amical et leurs confiances, et Segula Engineering (Sébastien Bréteche, Pierre Gervais, Florence Russo et Lionel Verrière) pour leurs soutiens dans le montage de ce projet. Merci à Julien Hacquard et à tout le GU du Cheylas, ainsi que HDF, pour leurs disponibilités et leurs sympathies. Toujours dispo pour un vol en hélico ou pour aller voir ce qu'il se passe là-haut ! Début Juillet, au lever de soleil, c'est le must! A ces heures à porter du matos en claies de portage, parfois en plein orage, à ce temps où tu te retrouves en kayak à 2000m en Août sous la neige, à cette Mike Giver académie qu'est une thèse terrain -Pensée spéciale au Projet survie du bateau du lac Blanc et à l'optimisation de la filtration in situ (merci aux inventeur.e.s du scotch orange), au projet centrifugation in-situ de sédiment (merci Ce projet de thèse a commencé il y a maintenant 5 ans. Déjà en poste au sein de Segula Engineering, j'ai voulu initier une progression de mon travail, autant sur les outils que sur les compétences générales. L'idée de reprendre mes études en parallèle de mon travail m'est alors apparu comme un bon axe pratique (malgré des avertissements contraire d'ami.e.s docteur.e.s, que je saisi bien mieux aujourd'hui). Une discussion s'est donc mis en place sur cette possibilité avec Segula et EDF qui m'ont soutenu et laisser de grande libertés dans la définition de mon sujet. J'ai par la suite monté le projet de thèse (coût, financement, planning et objectifs initiaux) avant de finaliser le tout avec mes directeurs de thèse rencontrés en cours de réflexion. La qualité de l'encadrement scientifique m'a permis de venir à bout de ce projet, malgré des difficultés inhérentes à un éloignement géographique et une activité professionnelle continue (30% du temps). Enfin, ce travail de thèse s'est révélé fructueux dans la progression de mes compétences scientifiques et techniques et m'a ainsi permis de faire évoluer mes missions professionnelles, au travers de nombreuses collaborations scientifiques hors-thèse et liées à ma thèse, tel qu'espéré lors de la mise en place de ce projet. Contributions en co-auteur aux trois articles suivants:
Through the artificial manipulation of hydrological residence time, hydropower operations on alpi... more Through the artificial manipulation of hydrological residence time, hydropower operations on alpine lakes should not only alter their hydro-biogeochemical characteristics but also modulate the degree of sensitivity of the lake to atmospheric forcing. These hypotheses were addressed by means of in situ observations that were combined with a three-dimensional lake model of a high-altitude pump-storage reservoir, i.e., Lake Corne, during the ice-free period. The fitted model (Pumping scenario) was used to simulate the hydrodynamics and oxygen concentrations of the lake under natural conditions (without pump-storage). Thereafter, the lake response to direct or catchment-mediated meteorological conditions (e.g., changes in inflows during storms) was investigated with a sensitivity analysis of the forcing parameters under both the pumping and natural hydrological scenarios. The pumping operation resulted in significant changes in water temperature, heat content and water mass stability during summer, as compared to a natural scenario. The lake hydrodynamics during the ice-free season were highly responsive to changes in the summer weather conditions, and more sensitive to realistic changes in cloudiness and water transparency than changes in air temperatures for both the pumped and natural scenarios. The spatial and temporal evolution of dissolved oxygen was comparatively less responsive to summer weather conditions, in both scenarios. The pump-storage operation from Lake Corne had a comparatively smaller effect on the lake functioning than the natural meteorological variability in summer. However, the pump-storage operation decreased the sensitivity of the lake hydrodynamics to changes in water transparency and limited water mass stability during summer.
Knowledge and Management of Aquatic Ecosystems, 2019
This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake eco... more This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake ecological status according to the European water framework directive (WFD). A method, based on threedimensional coupled hydrodynamic and ecological modeling, is presented to assess the variability of lake ecological status, and to locate the most representative sampling station of Lake Geneva (France/ Switzerland). Five variables used in the lake ecological status evaluation were simulated by using the free software Delft3D. The numerical simulation results showed that the simulated ecological status based on chlorophyll a and total phosphorus concentrations measured at the regulatory monitoring station depend on the choice of the sampling date. Results also indicated a strong spatial heterogeneity in ecological status that varies from "poor" to "good" along an East-West gradient. Finally, the numerical simulation results showed that the most representative point of a mean theoretical ecological quality for Lake Geneva would be located in the center of the upper basin, close to the historical sampling station.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 24, 2015
International audienceContext : In 2000, the European Parliament set out a framework (European Wa... more International audienceContext : In 2000, the European Parliament set out a framework (European Water Framework Directive) for managing and protecting water bodies in Europe. Classification of water bodies into «ecological status» is a key issue for the implementation of that framework. For lakes, the assessment of this status is based on biological (e.g . fish, phytoplankton and macrophyte), physical-chemical and hydro-morphological indicators. The physical-chemical and phytoplankton indicators are based on 4 observations given by integrated samples over the growing season during one year for a 6 years management plan. The sampling occur in the euphotic zone over the deepest point of the lake. However, in large lakes, ecological parameters, used for water quality assessment (e.g . chlorophyll-a concentration and Secchi depth), exhibit strong spatial-temporal heterogeneities. Consequently, the representativeness of those data versus the whole lake might be questionable and needs to be verified (Kiefer et al., 2015). The objective is to evaluate how spatial and temporal heterogeneities in chlorophyll-a may impact the assessment of Lake Geneva ecological status; we propose to combine remote sensing data and 3D modellin
Lake biological parameters show important spatio-temporal heterogeneities. This is why explaining... more Lake biological parameters show important spatio-temporal heterogeneities. This is why explaining the spatial patchiness of phytoplankton abundance has been a recurrent ecological issue and is an essential prerequisite for objectively assessing, protecting and restoring freshwater ecosystems. The drivers of these heterogeneities can be identified by modeling their dynamics. This approach is useful for theoretical and applied limnology. In this study, a 3D hydrodynamic model of Lake Geneva (France/Switzerland) was created. It is based on the Delft3D suite software and includes the main tributary (Rhône River) and two-dimensional high-resolution meteorological forcing. It provides 3D maps of water temperature and current velocities with a 1 h time step on a 1 km horizontal grid size and with a vertical resolution of 1 m near the surface to 7 m at the bottom of the lake. The dynamics and the drivers of phytoplankton heterogeneities were assessed by combining the outputs of the model and chlorophyll-a concentration (Chl-a) data from MERIS satellite images between 2008 and 2012. Results highlight physical mechanisms responsible for the occurrence of seasonal hot-spots in phytoplankton abundance in the lake. At the beginning of spring, Chl-a heterogeneities are usually caused by an earlier onset of phytoplankton growth in the shallowest and more sheltered areas; spatial differences in the timing of phytoplankton growth can be explained by spatial variability in thermal stratification dynamics. In summer, transient and locally higher phytoplankton abundances are observed in relation to the impact of basin-scale upwelling.
Extreme weather events may be just as important as gradual trends for the long-term trajectories ... more Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e., warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season through reduced light penetration. The long-lasting effects of turbid storms were related to the inputs and in-lake persistence of very-light glacial suspensoids from the watershed. The occurrence of the observed turbid storms was not related to the wind or rain intensities during the events. Instead, the turbid storms occurred after dry and atypically warm spells, i.e., meteorological conditions expected to be more frequent in this alpine region in the upcoming decades. Consequently, storm events, notwithstanding their intensity, are expected to strongly imprint the future ecological status of alpine lakes under climate warming.
International audienceContext : In 2000, the European Parliament set out a framework (European Wa... more International audienceContext : In 2000, the European Parliament set out a framework (European Water Framework Directive) for managing and protecting water bodies in Europe. Classification of water bodies into «ecological status» is a key issue for the implementation of that framework. For lakes, the assessment of this status is based on biological (e.g . fish, phytoplankton and macrophyte), physical-chemical and hydro-morphological indicators. The physical-chemical and phytoplankton indicators are based on 4 observations given by integrated samples over the growing season during one year for a 6 years management plan. The sampling occur in the euphotic zone over the deepest point of the lake. However, in large lakes, ecological parameters, used for water quality assessment (e.g . chlorophyll-a concentration and Secchi depth), exhibit strong spatial-temporal heterogeneities. Consequently, the representativeness of those data versus the whole lake might be questionable and needs to b...
International audienceLake biological parameters show important spatio-temporal heterogeneities. ... more International audienceLake biological parameters show important spatio-temporal heterogeneities. This is why explaining the spatial patchiness of phytoplankton abundance has been a recurrent ecological issue and is an essential prerequisite for objectively assessing, protecting and restoring freshwater ecosystems. The drivers of these heterogeneities can be identified by modelling their dynamics. This approach is useful for theoretical and applied limnology. In this study, a 3D hydrodynamic model of LakeGeneva (France/Switzerland) was created. It is based on the Delft3D suite software and includes the main tributary (Rhône River) and two-dimensional high-resolution meteorological forcing. It provides 3D maps of water temperature and current velocities with a 1 h time step on a 1 km horizontal grid size and with a vertical resolution of 1 m near the surface to 7 m at the bottom of the lake. The dynamics and the drivers of phytoplankton heterogeneities were assessed by combining the o...
Ce sujet de these s'inscrit dans la continuite du programme de recherche Lacs sentinelles, vi... more Ce sujet de these s'inscrit dans la continuite du programme de recherche Lacs sentinelles, visant a une meilleure comprehension de ces biotopes extremement sensibles que sont les milieux lacustres de hautes montagnes. L'etude cherchera a specifier le role de l'hydrologie sur le cycle du carbone dans les milieux alpins de haute altitude par rapport aux processus metaboliques internes. Pour repondre a cette problematique, l'etude se definira par une approche scientifique combinant analyse de donnees et modelisation. L'acquisition des donnees necessaires reposera sur la mise en place d'un suivi des parametres climatologiques et bio-physicochimiques du milieu sur un ensemble de trois lacs alpins (Cos et Corne pour les lacs equipes et Blanc pour le temoin naturel) situe sur le site des Sept-Laux (2060-2260m, massif de Belledonne). Ces donnees permettront le parametrage d'un modele hydro-biogeochimique qui servira d'outil integrateur de donnees recoltees afin de pouvoir tester differents scenarios et affiner les bilans biogeochimiques. Les donnees acquises au cours du programme scientifique, consolidees par les resultats de modelisation, devraient permettre de discriminer et quantifier les forcages saisonniers principaux du fonctionnement biogeochimique lacustre de lacs alpins de haute altitude et de determiner le bilan du role des lacs dans le cycle du carbone.
Extreme weather events may be just as important as gradual trends for the long-term trajectories ... more Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e., warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season through reduced light penetration. The long-lasting effects of turbid storms were related to the inputs and in-lake persistence of very-light glacial suspensoids from the watershed. The occurrence of the observed turbid storms was not related to the wind or rain intensities during the events. Instead, the turbid storms occurred after dry and atypically warm spells, i.e., meteorological conditions expected to be more frequent in this alpine region in the upcoming decades. Consequently, storm events, notwithstanding their intensity, are expected to strongly imprint the future ecological status of alpine lakes under climate warming.
This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake eco... more This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake ecological status according to the European water framework directive (WFD). A method, based on three-dimensional coupled hydrodynamic and ecological modeling, is presented to assess the variability of lake ecological status, and to locate the most representative sampling station of Lake Geneva (France/Switzerland). Five variables used in the lake ecological status evaluation were simulated by using the free software Delft3D. The numerical simulation results showed that the simulated ecological status based on chlorophyll a and total phosphorus concentrations measured at the regulatory monitoring station depend on the choice of the sampling date. Results also indicated a strong spatial heterogeneity in ecological status that varies from “poor” to “good” along an East-West gradient. Finally, the numerical simulation results showed that the most representative point of a mean theoretical ecol...
Using 3D modeling and remote sensing capabilities for a better understanding of spatiotemporal he... more Using 3D modeling and remote sensing capabilities for a better understanding of spatiotemporal heterogeneities of phytoplankton abundance in large lakes. Journal of Great Lakes Research, 44(4), 756-764. https://doi.Bastiaan W Ibelings +41 22 379 3013 [email protected] Dominique Trevisan +33 4 50 26 78 30 +33 4 50 26 07 60 [email protected] Rob Uittenbogaard +31 88 335 8181 [email protected] Orlane Anneville +33 4 50 26 78 04 +33 4 50 26 07 60 [email protected] Abstract 26
Extreme weather events may be just as important as gradual trends for the long-term trajectories ... more Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e., warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season throug...
P***** Cakita, j'ai fini ! Bon je sais qu'en tapant ces mots il me reste une dernière(s ?) relect... more P***** Cakita, j'ai fini ! Bon je sais qu'en tapant ces mots il me reste une dernière(s ?) relecture avant quand même. La thèse ? Un projet qui t'obsède. Un marathon intellectuel et physique. J'ai mis plus de 3 ans à répondre à une question, et encore que partiellement. Mais j'ai eu l'impression de me construire mon meilleur cours, celui qui m'a le plus intéressé ! La mise en application de tes connaissances pour répondre à une question... Une aventure faite de rencontres, d'épreuves et de supers moments. Une véritable étape ! Alors merci un immense merci à toi ma Cakita, pour ton indéfectible soutien et tes petits plats qui ont le pouvoir de garder motivé. L'aventure ne fait que commencer. Encore désolé pour toutes ces nuits de travail où Tortilla m'a veillé. Au passage, merci à cette boule de poils, même si ça n'est pas évident d'écrire au clavier avec un chat dessus. A mes parents pour tout ce qu'ils ont fait pour moi, leur éducation et leur foi en moi. A mes frères Lucas et Yann, partager vos vies est un grand honneur ! Et à tous mes ami.e.s qui m'ont soutenu.e.s à base de soirées, pour s'assurer de ma survie, et de « toujours pas fini ? ». C'est bon maintenant. BIG UP au 225 éternel, au BGSL et au P5 ! Un merci spécial à Florian, qui comprend le sens profond d'abnégation et de patience nécessaire au modélisateur. A l'aventurière éternelle du 93 et à Michou ! Un grand merci à mes directeurs de thèse Marie-Elodie Perga et Damien Bouffard pour leur accompagnement dans cette expérience passionnante. Les contraintes géo-professionnelle n'ont pas rendu la tâche facile et j'apprécie d'autant plus leur investissement. Merci ! Merci au CIH-EDF, et plus particulièrement Vincent Chanudet, Agnès Bariller et Stéphane Descloux pour leurs soutiens scientifiques, amical et leurs confiances, et Segula Engineering (Sébastien Bréteche, Pierre Gervais, Florence Russo et Lionel Verrière) pour leurs soutiens dans le montage de ce projet. Merci à Julien Hacquard et à tout le GU du Cheylas, ainsi que HDF, pour leurs disponibilités et leurs sympathies. Toujours dispo pour un vol en hélico ou pour aller voir ce qu'il se passe là-haut ! Début Juillet, au lever de soleil, c'est le must! A ces heures à porter du matos en claies de portage, parfois en plein orage, à ce temps où tu te retrouves en kayak à 2000m en Août sous la neige, à cette Mike Giver académie qu'est une thèse terrain -Pensée spéciale au Projet survie du bateau du lac Blanc et à l'optimisation de la filtration in situ (merci aux inventeur.e.s du scotch orange), au projet centrifugation in-situ de sédiment (merci Ce projet de thèse a commencé il y a maintenant 5 ans. Déjà en poste au sein de Segula Engineering, j'ai voulu initier une progression de mon travail, autant sur les outils que sur les compétences générales. L'idée de reprendre mes études en parallèle de mon travail m'est alors apparu comme un bon axe pratique (malgré des avertissements contraire d'ami.e.s docteur.e.s, que je saisi bien mieux aujourd'hui). Une discussion s'est donc mis en place sur cette possibilité avec Segula et EDF qui m'ont soutenu et laisser de grande libertés dans la définition de mon sujet. J'ai par la suite monté le projet de thèse (coût, financement, planning et objectifs initiaux) avant de finaliser le tout avec mes directeurs de thèse rencontrés en cours de réflexion. La qualité de l'encadrement scientifique m'a permis de venir à bout de ce projet, malgré des difficultés inhérentes à un éloignement géographique et une activité professionnelle continue (30% du temps). Enfin, ce travail de thèse s'est révélé fructueux dans la progression de mes compétences scientifiques et techniques et m'a ainsi permis de faire évoluer mes missions professionnelles, au travers de nombreuses collaborations scientifiques hors-thèse et liées à ma thèse, tel qu'espéré lors de la mise en place de ce projet. Contributions en co-auteur aux trois articles suivants:
Through the artificial manipulation of hydrological residence time, hydropower operations on alpi... more Through the artificial manipulation of hydrological residence time, hydropower operations on alpine lakes should not only alter their hydro-biogeochemical characteristics but also modulate the degree of sensitivity of the lake to atmospheric forcing. These hypotheses were addressed by means of in situ observations that were combined with a three-dimensional lake model of a high-altitude pump-storage reservoir, i.e., Lake Corne, during the ice-free period. The fitted model (Pumping scenario) was used to simulate the hydrodynamics and oxygen concentrations of the lake under natural conditions (without pump-storage). Thereafter, the lake response to direct or catchment-mediated meteorological conditions (e.g., changes in inflows during storms) was investigated with a sensitivity analysis of the forcing parameters under both the pumping and natural hydrological scenarios. The pumping operation resulted in significant changes in water temperature, heat content and water mass stability during summer, as compared to a natural scenario. The lake hydrodynamics during the ice-free season were highly responsive to changes in the summer weather conditions, and more sensitive to realistic changes in cloudiness and water transparency than changes in air temperatures for both the pumped and natural scenarios. The spatial and temporal evolution of dissolved oxygen was comparatively less responsive to summer weather conditions, in both scenarios. The pump-storage operation from Lake Corne had a comparatively smaller effect on the lake functioning than the natural meteorological variability in summer. However, the pump-storage operation decreased the sensitivity of the lake hydrodynamics to changes in water transparency and limited water mass stability during summer.
Knowledge and Management of Aquatic Ecosystems, 2019
This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake eco... more This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake ecological status according to the European water framework directive (WFD). A method, based on threedimensional coupled hydrodynamic and ecological modeling, is presented to assess the variability of lake ecological status, and to locate the most representative sampling station of Lake Geneva (France/ Switzerland). Five variables used in the lake ecological status evaluation were simulated by using the free software Delft3D. The numerical simulation results showed that the simulated ecological status based on chlorophyll a and total phosphorus concentrations measured at the regulatory monitoring station depend on the choice of the sampling date. Results also indicated a strong spatial heterogeneity in ecological status that varies from "poor" to "good" along an East-West gradient. Finally, the numerical simulation results showed that the most representative point of a mean theoretical ecological quality for Lake Geneva would be located in the center of the upper basin, close to the historical sampling station.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 24, 2015
International audienceContext : In 2000, the European Parliament set out a framework (European Wa... more International audienceContext : In 2000, the European Parliament set out a framework (European Water Framework Directive) for managing and protecting water bodies in Europe. Classification of water bodies into «ecological status» is a key issue for the implementation of that framework. For lakes, the assessment of this status is based on biological (e.g . fish, phytoplankton and macrophyte), physical-chemical and hydro-morphological indicators. The physical-chemical and phytoplankton indicators are based on 4 observations given by integrated samples over the growing season during one year for a 6 years management plan. The sampling occur in the euphotic zone over the deepest point of the lake. However, in large lakes, ecological parameters, used for water quality assessment (e.g . chlorophyll-a concentration and Secchi depth), exhibit strong spatial-temporal heterogeneities. Consequently, the representativeness of those data versus the whole lake might be questionable and needs to be verified (Kiefer et al., 2015). The objective is to evaluate how spatial and temporal heterogeneities in chlorophyll-a may impact the assessment of Lake Geneva ecological status; we propose to combine remote sensing data and 3D modellin
Lake biological parameters show important spatio-temporal heterogeneities. This is why explaining... more Lake biological parameters show important spatio-temporal heterogeneities. This is why explaining the spatial patchiness of phytoplankton abundance has been a recurrent ecological issue and is an essential prerequisite for objectively assessing, protecting and restoring freshwater ecosystems. The drivers of these heterogeneities can be identified by modeling their dynamics. This approach is useful for theoretical and applied limnology. In this study, a 3D hydrodynamic model of Lake Geneva (France/Switzerland) was created. It is based on the Delft3D suite software and includes the main tributary (Rhône River) and two-dimensional high-resolution meteorological forcing. It provides 3D maps of water temperature and current velocities with a 1 h time step on a 1 km horizontal grid size and with a vertical resolution of 1 m near the surface to 7 m at the bottom of the lake. The dynamics and the drivers of phytoplankton heterogeneities were assessed by combining the outputs of the model and chlorophyll-a concentration (Chl-a) data from MERIS satellite images between 2008 and 2012. Results highlight physical mechanisms responsible for the occurrence of seasonal hot-spots in phytoplankton abundance in the lake. At the beginning of spring, Chl-a heterogeneities are usually caused by an earlier onset of phytoplankton growth in the shallowest and more sheltered areas; spatial differences in the timing of phytoplankton growth can be explained by spatial variability in thermal stratification dynamics. In summer, transient and locally higher phytoplankton abundances are observed in relation to the impact of basin-scale upwelling.
Extreme weather events may be just as important as gradual trends for the long-term trajectories ... more Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e., warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season through reduced light penetration. The long-lasting effects of turbid storms were related to the inputs and in-lake persistence of very-light glacial suspensoids from the watershed. The occurrence of the observed turbid storms was not related to the wind or rain intensities during the events. Instead, the turbid storms occurred after dry and atypically warm spells, i.e., meteorological conditions expected to be more frequent in this alpine region in the upcoming decades. Consequently, storm events, notwithstanding their intensity, are expected to strongly imprint the future ecological status of alpine lakes under climate warming.
International audienceContext : In 2000, the European Parliament set out a framework (European Wa... more International audienceContext : In 2000, the European Parliament set out a framework (European Water Framework Directive) for managing and protecting water bodies in Europe. Classification of water bodies into «ecological status» is a key issue for the implementation of that framework. For lakes, the assessment of this status is based on biological (e.g . fish, phytoplankton and macrophyte), physical-chemical and hydro-morphological indicators. The physical-chemical and phytoplankton indicators are based on 4 observations given by integrated samples over the growing season during one year for a 6 years management plan. The sampling occur in the euphotic zone over the deepest point of the lake. However, in large lakes, ecological parameters, used for water quality assessment (e.g . chlorophyll-a concentration and Secchi depth), exhibit strong spatial-temporal heterogeneities. Consequently, the representativeness of those data versus the whole lake might be questionable and needs to b...
International audienceLake biological parameters show important spatio-temporal heterogeneities. ... more International audienceLake biological parameters show important spatio-temporal heterogeneities. This is why explaining the spatial patchiness of phytoplankton abundance has been a recurrent ecological issue and is an essential prerequisite for objectively assessing, protecting and restoring freshwater ecosystems. The drivers of these heterogeneities can be identified by modelling their dynamics. This approach is useful for theoretical and applied limnology. In this study, a 3D hydrodynamic model of LakeGeneva (France/Switzerland) was created. It is based on the Delft3D suite software and includes the main tributary (Rhône River) and two-dimensional high-resolution meteorological forcing. It provides 3D maps of water temperature and current velocities with a 1 h time step on a 1 km horizontal grid size and with a vertical resolution of 1 m near the surface to 7 m at the bottom of the lake. The dynamics and the drivers of phytoplankton heterogeneities were assessed by combining the o...
Ce sujet de these s'inscrit dans la continuite du programme de recherche Lacs sentinelles, vi... more Ce sujet de these s'inscrit dans la continuite du programme de recherche Lacs sentinelles, visant a une meilleure comprehension de ces biotopes extremement sensibles que sont les milieux lacustres de hautes montagnes. L'etude cherchera a specifier le role de l'hydrologie sur le cycle du carbone dans les milieux alpins de haute altitude par rapport aux processus metaboliques internes. Pour repondre a cette problematique, l'etude se definira par une approche scientifique combinant analyse de donnees et modelisation. L'acquisition des donnees necessaires reposera sur la mise en place d'un suivi des parametres climatologiques et bio-physicochimiques du milieu sur un ensemble de trois lacs alpins (Cos et Corne pour les lacs equipes et Blanc pour le temoin naturel) situe sur le site des Sept-Laux (2060-2260m, massif de Belledonne). Ces donnees permettront le parametrage d'un modele hydro-biogeochimique qui servira d'outil integrateur de donnees recoltees afin de pouvoir tester differents scenarios et affiner les bilans biogeochimiques. Les donnees acquises au cours du programme scientifique, consolidees par les resultats de modelisation, devraient permettre de discriminer et quantifier les forcages saisonniers principaux du fonctionnement biogeochimique lacustre de lacs alpins de haute altitude et de determiner le bilan du role des lacs dans le cycle du carbone.
Extreme weather events may be just as important as gradual trends for the long-term trajectories ... more Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e., warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season through reduced light penetration. The long-lasting effects of turbid storms were related to the inputs and in-lake persistence of very-light glacial suspensoids from the watershed. The occurrence of the observed turbid storms was not related to the wind or rain intensities during the events. Instead, the turbid storms occurred after dry and atypically warm spells, i.e., meteorological conditions expected to be more frequent in this alpine region in the upcoming decades. Consequently, storm events, notwithstanding their intensity, are expected to strongly imprint the future ecological status of alpine lakes under climate warming.
This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake eco... more This study deals with the impact of spatio-temporal heterogeneities on the assessment of lake ecological status according to the European water framework directive (WFD). A method, based on three-dimensional coupled hydrodynamic and ecological modeling, is presented to assess the variability of lake ecological status, and to locate the most representative sampling station of Lake Geneva (France/Switzerland). Five variables used in the lake ecological status evaluation were simulated by using the free software Delft3D. The numerical simulation results showed that the simulated ecological status based on chlorophyll a and total phosphorus concentrations measured at the regulatory monitoring station depend on the choice of the sampling date. Results also indicated a strong spatial heterogeneity in ecological status that varies from “poor” to “good” along an East-West gradient. Finally, the numerical simulation results showed that the most representative point of a mean theoretical ecol...
Using 3D modeling and remote sensing capabilities for a better understanding of spatiotemporal he... more Using 3D modeling and remote sensing capabilities for a better understanding of spatiotemporal heterogeneities of phytoplankton abundance in large lakes. Journal of Great Lakes Research, 44(4), 756-764. https://doi.Bastiaan W Ibelings +41 22 379 3013 [email protected] Dominique Trevisan +33 4 50 26 78 30 +33 4 50 26 07 60 [email protected] Rob Uittenbogaard +31 88 335 8181 [email protected] Orlane Anneville +33 4 50 26 78 04 +33 4 50 26 07 60 [email protected] Abstract 26
Extreme weather events may be just as important as gradual trends for the long-term trajectories ... more Extreme weather events may be just as important as gradual trends for the long-term trajectories of ecosystems. For alpine lakes, which are exposed to both exacerbated atmospheric warming and intense episodic weather events, future conditions might not be appropriately forecast by only climate change trends, i.e., warming, if extreme events have the potential to deflect their thermal and metabolic states from their seasonal ranges. We used high-frequency monitoring data over three open-water seasons with a one-dimensional hydrodynamic model of the high-altitude Lake Muzelle (France) to show that rainstorms or windstorms, notwithstanding their intensity, did not trigger long-lasting consequences to the lake characteristics when light penetration into the lake was not modified. In contrast, storms associated with high turbidity input from the watershed ("turbid storms") strongly modified the lacustrine hydrodynamics and metabolism for the rest of the open-water season throug...
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