Public Thesis Defense of Riana Randresihaja 

"Modelling storm surges in the Scheldt-North Sea continuum under present and future climate conditions" 

Summary

Estuaries are a key component of coastal systems, influencing hydrodynamics, ecosystem functioning and local socio-economic activities. 

At the interface between the Scheldt River and the North Sea, the Scheldt estuary forms a strongly convergent channel bordered by intertidal flats and marshes, with the port of Antwerp at its head. The estuary has been extensively modelled for its morphological evolution, dredging strategies and flood management, but storm surges have received less attention, and the estuary and the adjacent sea have rarely been resolved within a single domain. 

In this thesis, we use the 2D version of the multiscale hydrodynamic model SLIM to study how storm surges propagate and amplify along the Scheldt–North Sea continuum. 

We first build and validate a configuration that resolves the continuum on a single mesh, from the tidal channels of the upper estuary to the open shelf, over five continuous years. 

We then assess, for Storm Xaver (2013), how the resolution of the atmospheric forcing affects the simulated estuarine surge, and find that spatial resolution matters more than temporal resolution in this case. 

Finally, we simulate a panel of plausible future storms under a high-emission scenario up to the end of the 21st century. The panel shows no robust intensification of the meteorological surge over the century, and surge severity varies more with position along the continuum than with storm track, extreme flood levels increasing several-fold from the open sea to the head of the estuary. In this panel, positive and negative surges behave as distinct hazards: the rarest flood levels approach an upper limit, whereas the rarest low waters keep deepening, and Antwerp ranks among the most exposed gauges for both. 

This thesis provides a single-domain representation of the Scheldt–North Sea continuum and underlines the need to consider both signs of the surge when assessing estuarine hazard.

Jury members 

President    
Prof. Marnik VANCLOOSTER (UCLouvain)

Dr. Jonathan LAMBRECHTS, secretary (UCLouvain)
Dr. Olivier GOURGUE (Royal Belgian Institute of Natural Sciences)
Prof. Xavier FETTWEIS (ULiège)
Prof. Emil STANEV (Helmholtz-Zentrum Hereon)

Supervisors
Prof Emmanuel HANERT, promotor (UCLouvain)
Prof. Marilaure GRÉGOIRE, promotor (ULiège)

Mathieu Mahillon (UGent) will give this seminar, organized by the ELI-V department. 

Katharina Meurer (Swedish University of Agricultural Sciences) will give this seminar, organized by the ELI-E department. 

Abstract 

Extreme weather conditions, such as severe droughts, are expected to become more frequent in a future climate. Water availability controls crop growth, which in turn has a direct and indirect effects on flows of energy, water, carbon, and nutrients in the soil-plant system. Soil-crop models are potentially useful tools to support analyses of the effects of both climate and soil management practices on crop production and the environment. However, the effects of structure dynamics on different soil functions (e.g., hydrology, carbon cycling) at longer time scales are often not considered.

The aim of this presentation is to present  the USSF model that accounts for the interactions between soil structure dynamics, carbon cycling, soil physical and hydraulic properties, soil water balance and crop growth. The importance of soil structure dynamics is illustrated by long-term simulations of soil organic matter storage, soil water balance components and crop yields for a field site in central Sweden under climate change and contrasting management practices (organic amendments and crop varieties with an enhanced allocation of carbon to roots). 

Christophe Gandonou (Faculty of Science and Technology, University of Abomey-Calavi, Bénin) donnera ce séminaire, organisé par le pôle ELI-A. 

Résumé

La salinité constitue avec la sécheresse les principales contraintes de l’environnement qui limitent la production agricole dans toutes les régions du monde d’après la FAO. Au Bénin, depuis 2011, les acteurs du secteur agricole ont convenu que les défis climatiques actuels pourraient davantage accentuer les difficultés du secteur. 

Depuis 2012, l’équipe de recherche en Physiologie Végétale et Adaptation des Plantes aux Stress Abiotiques a initié des travaux de recherche sur l’adaptation des cultures maraîchères à la salinité et à la sécheresse. Un diagnostic salin effectué dans les principales zones de production maraîchère du pays a révélé que les eaux utilisées pour l’irrigation des cultures dans certaines zones présentent des salinités supérieures à la norme admise pour les cultures notamment en saison sèche, sans présence de stress salin dû exclusivement à la salinité du sol. 

Les études réalisées sur des légumes fruits (tomate, piment, gombo), légume bulbe (oignon), légumes racines (carotte) et légumes feuilles (amarante, chou, grande morelle, crincrin, tchiayo, etc.) ont montré que la salinité impactait négativement tous les stades de développement des plantes y compris la taille des fruits et les rendements avec une variabilité importante entre les cultivars de la même espèce. La qualité nutritionnelle des fruits et des feuilles est également affectée dans des proportions variables en fonction des espèces et des nutriments pris en compte. 

Les études plus approfondies réalisées conjointement par les équipes du Groupe de Recherche en Physiologie Végétale (GRPV, ELI-A, UCLouvain) et de l’Unité de Recherche en Physiologie Végétale et Adaptation des Plantes aux Stress Abiotiques (URPV-APSA, FAST, UAC) sur l’amarante ont permis dans un premier temps de sélectionner des lignées stables d’amarante grâce à l’induction de mutations dont certaines ont montré une production meilleure que les variétés traditionnelles et une bonne stabilité dans différentes zones agro-écologiques du pays. 

Les travaux de caractérisation de ces lignées et des cultivars existants ont montré que la vocation de la culture (production de feuilles ou de graines) influence fortement la réponse génotypique à la salinité et à la sécheresse et des génotypes plutôt sensibles à la salinité ou à la sécheresse pour la production de feuilles se sont révélés plutôt résistants pour la production de graines et vice-versa. De même, des génotypes plutôt sensibles à la salinité se sont révélés plutôt résistants à la sécheresse et vice-versa. 

La détermination des mécanismes physiologiques et biochimiques impliqués dans la résistance à la salinité et à la sécheresse est en cours et permettra de préciser, pour chaque génotype résistant et en fonction du stress considéré, les stratégies de résistance utilisées. L’utilisation des outils moléculaires permettra de déterminer les bases génétiques de la résistance observée notamment pour les lignées sélectionnées. 

L’exploration des stratégies d’atténuation des effets de ces stress sur les cultures en vue notamment grâce à l’utilisation des PGPR ou autres microorganismes promoteurs de croissance végétale ouvrira la voie à une intégration de ces pratiques en milieu producteur pour la gestion de ces stress. La récente homologation de certaines de ces lignées résistantes et leur inscription dans le Catalogue Béninois des Espèces et Variétés Végétales (CaBEV) comme nouvelles variétés à la disposition des producteurs ouvrent la perspective d’une valorisation efficace des résultats de ces travaux dans le système agricole béninois. 

Nathan Carlier will give this seminar, organized by the ELI-C department. 

Prof. Véronique Dehant will give this seminar, organized by the ELI-C department. 

Public Thesis Defense of Hugo Counoy 

"Improving the interpretation and applicability of epiphytic lichen biomonitoring for air quality assessment: 

Advances in bioindication, bioaccumulation, and citizen science" 

Summary 

Air pollution remains a major threat to human health and ecosystems, yet conventional monitoring networks are costly, too sparse to capture fine-scale variation in exposure, and restricted to a few pollutants. Biomonitoring with lichens offers a complementary approach, since these organisms respond to atmospheric conditions, integrate many contaminants over time and can be surveyed across large areas. 

However, inferring air quality from the composition of lichen communities (bioindication) remains hindered by identification difficulties and incomplete knowledge of how species respond to individual pollutants, while the contaminants accumulated in lichen tissues (bioaccumulation) are hard to trace back to their sources, notably because they reflect integrated and partly legacy inputs. 

This thesis aims to improve the interpretation and applicability of lichen bioindication and bioaccumulation. 

First, a European meta-analysis identifies species with consistent responses to NH3, NOx, SO2 and climate variables. 

These responses are then translated into operational indices which, tested in Wallonia (Belgium), partially discriminate NH3 from NOx. In the same region, trace elements accumulated in herbarium and contemporary samples of Xanthoria parietina reveal a marked, element-specific decline in enrichment since the 1960s and identify industry, non-exhaust traffic, and dust resuspension as the main current sources. Analyzing nitrogen content and δ15N indicates that isotopic signatures alone cannot discriminate sources in multi-source landscapes and vary with spatial scale. 

Finally, to open biomonitoring to non-specialists, the Lichens GO citizen science protocol is evaluated and adapted: targeted changes to sampling and identification procedures improve data quality without increasing sampling effort. 

Overall, this thesis supports a more pollutant-specific, source-informed and widely deployable use of lichens to complement conventional monitoring.

Jury members 

Supervisors
Prof. Yannick AGNAN (UCLouvain)
Dr. Laure TURCATI (Sorbonne Université)

Chairman
Prof. Emmanuel HANERT (UCLouvain)

Jury members    
Prof. Gabrielle MARTIN (Université de Toulouse)
Prof. Guillaume LOBET (UCLouvain)
Prof. Nadine MATTIELLI (ULB)
Prof. Nathalie SEJALON-DELMAS (Université de Toulouse)
Prof. Emmanuel HANERT (UCLouvain)

Théo Clotman will give this seminar, organized by the ELI-E department. 

Photo credit: © JBenoit, Wikipedia

Public Thesis Defense of Alexandre Winant 

"Atmospheric sensitivity of cosmic-ray-induced ionization and radiation dose: from quiet conditions to an extreme space-weather event" 

Summary 

Earth’s atmosphere is constantly struck by cosmic rays and, at times, by energetic particles from the Sun and from the radiation belts. These particles trigger cascades of secondary particles that ionize the air, deposit radiation dose, and can destroy ozone. Yet the computer models used to simulate this process usually assume one fixed, standard atmosphere, whatever the place or time.

This thesis asks how much that simplification matters, and how particle precipitation affects the upper atmosphere during an extreme space weather event.

Using a Monte Carlo simulation tool combined with empirical atmospheric models, three studies address these questions. 

The first characterizes every major secondary particle species, validates the simulations against an independent model and aircraft measurements, and shows that latitude and season change particle fluxes by up to 80 percent below 20 kilometres, even with high geomagnetic shielding. 

The second shows that ionization and radiation dose differ by up to 68 and 60 percent between equatorial and polar atmospheres, produces global maps that single-profile models cannot reproduce, and finds that this sensitivity reverses sign for solar proton spectra.

The third study examines the extreme geomagnetic storm of 11 May 2024 and the solar proton event of 8 June 2024. Satellite observations reveal ozone depletion of up to 60 percent in the polar upper atmosphere, lasting seven days in May and two days in June.

Overall, the state of the atmosphere is not a negligible input for simulating cosmic radiation, and its influence can grow under storm conditions. 

Jury members 

Prof. Hugues Goosse (UCLouvain) (Supervisor)
Prof. Viviane Pierrard (UCLouvain/BIRA-IASB) (Supervisor)
Prof. Qiuzhen Yin (UCLouvain) (Chairperson)
Prof. Michel Crucifix (Secretary)
Prof. Fabio Bacchini (KULeuven)
Prof. Konstantin Herbst (University of Oslo, UiO)
Prof. Véronique Dehant (UCLouvain)
Dr. Edith Botek (BIRA-IASB)