"Organo-mineral interactions in permafrost environments affected by physical degradation"
 

Registration form

Teams link

Abstract:

Permafrost soils are found at high latitudes and altitudes, and contain three times more carbon than in the atmosphere. As permafrost thaws, a portion of this carbon - still largely uncertain - is released in the form of greenhouse gases (GHG), resulting in a permafrost carbon-climate-feedback. This feedback still awaits to be integrated in global models of GHG emissions used by the IPCC, but is estimated as equivalent to the emissions from one additional large industrialized country. The uncertainties are partly attributable to the unknown contribution of the thawing of ice-rich permafrost, which manifests by physical degradation, named thermokarst terrains. Another source of uncertainty relates to the proportion of organic carbon (OC) that is linked to mineral surfaces or mineral elements, as mineral-interacting OC. These stabilization mechanisms are presumed to render the corresponding OC fraction less accessible to decomposition and emissions as GHGs. This thesis investigates the abundance, nature and control of mineral-OC interactions in permafrost soils and sediments affected by thermokarst disturbances. Chemical stabilization mechanisms have been shown to stabilize on average 31 ± 12% of total OC, and this pool of mineral-interacting OC is preserved in materials exported by the thermo-erosion process. We also show that historical permafrost thaw dynamics have a decisive influence on the concentration and proportion of mineral-interacting OC in permafrost environments. Finally, we have shown that the formation of lowland thermokarst landscapes has progressed locally five times faster in recent years than in the last few decades, with an expected release of mineral-bound OC. Such findings demonstrate the urgent need to integrate OC-mineral interactions into global ecosystem carbon balance models. This requires establishing links between concentrations and proportions of mineral-interacting OC and GHG emissions.
 

Jury members:

Supervisor: 
Prof. Sophie OPFERGELT – UCLouvain

President of the jury: 
Prof. Emmanuel HANERT – UCLouvain

Other jury members: 
Prof. Veerle VANACKER | UCLouvain
Prof. Sandra ARNDT - Université Libre de Bruxelles
Prof. Julien FOUCHÉ - Institut Agro Montpellier, France
Prof. François JONARD - ULiège

Public Thesis Defense of Louis de WERGIFOSSE

UCLouvain | ELI | Environmental Sciences

21 JUNE 2021 - 14:00-17:00

Le Carnoy - Place Croix du Sud - Louvain-la-Neuve & Online Teams Presentation 

SUPERVISORS

Prof. Mathieu JONARD, UCLouvain
Prof. Hugues GOOSSE, UCLouvain

PRESIDENT OF THE JURY

Prof. Emmanuel HANERT, UCLouvain

OTHER JURY MEMBERS

Dr. Nicolas DELPIERRE, Université Paris Saclay, France
Prof. Thierry FICHEFET, UCLouvain
Prof. Quentin PONETTE, UCLouvain
Dr. Christopher REYER, Potsdam-Institut für Klimafolgenforschung, Germany

Public Thesis Defense of Géraud de STREEL

UCLouvain | ELI | Environmental Sciences

28 MAY 2021 - 10:00-13:00

Le Carnoy - Place Croix du Sud - Louvain-la-Neuve & Online Teams Presentation 

SUPERVISORS

Prof. Quentin PONETTE, UCLouvain
Prof. Catherine COLLET, INRAE

PRESIDENT OF THE JURY

Prof. Emmanuel HANERT, UCLouvain

OTHER JURY MEMBERS

Prof. Kris VERHEYEN, UGent
Prof. Damien BONAL, INRAE
Prof. Andres BRAVO-OVIEDO, National Museum of Natural Sciences, Madrid
Prof. Xavier DRAYE, UCLouvain

ENGE Seminar by Afshin FARHADI 

15 June 2021

13:00 - 14:00

Online Event - Teams Link

Public Thesis Defense of Léolo GONAY

UCLouvain | ELI | Environmental Sciences

28 JUNE 2021 - 17:00

Auditoire SUD 08 – Place Croix du Sud  
& 
Online Teams Presentation 

SUPERVISORS

Prof. Emmanuel HANERT, UCLouvain

Prof. Christophe PIERREUX, UCLouvain

PRESIDENT OF THE JURY

Prof. Marnik VANCLOOSTER, UCLouvain

OTHER JURY MEMBERS

Prof. René REZOHAZY, UCLouvain, secretary

Prof. Xavier DRAYE, UCLouvain

Prof. Frédéric LEMAIGRE, UCLouvain

Dr. Paul VAN LIEDEKERKE, INRIA, Paris, France

Dr. Alexander FLETCHER, University of Sheffield, UK

ENGE Seminar by Nicolas DEFFENSE

22 June 2021

13:00 - 14:00

Online Event - Teams Link

Simon de CANNIERE

Online Seminar

“Behaviour of SIF emission under water limited conditions.”

Pour l’obtention du grade de Docteur en sciences de l’ingénieur et technologie

Coral populations have declined dramatically worldwide under the combined effects of climate change and local anthropogenic stressors. In addition to ocean warming and acidification, threats to coral reefs in the Caribbean include frequent and virulent disease outbreaks, and intensifying hurricanes. In particular, Florida's Coral Reef (FCR) is currently facing a multi-year outbreak of the stony coral tissue loss disease (SCTLD). First observed in 2014 during the monitoring of the PortMiami Deep Dredge Project (PMDDP), the disease has now spread through the entire FCR and has been reported in numerous territories of the Caribbean. However, the propagation of the disease through FCR seemed to slow down when it reached its southwestern end, between the Marquesas and the Dry Tortugas (DRTO). Although the causative agent of the disease remains unknown, studies showed that its transmission was likely waterborne and that sediments could act as SCTLD vectors. The hydrodynamics should therefore be highly explanatory of its spread. Furthermore, Florida is a prime landfall target for hurricanes during the reproduction period of corals. In addition to causing wholesale destruction of the reefs, hurricanes might thus also impact larval dispersal through wind-wave-induced currents. Here, we use the high resolution coastal ocean model SLIM to capture transport processes in the FCR, and study the impact of SCTLD and hurricanes to coral reefs. First, a coupled epidemio-hydrodynamic model is developed to reproduce and understand the observed spread of SCTLD in Florida. A sediment transport model is then used to evaluate the impact of the PMDDP on the observed onset of the disease in 2014. Finally, a coupled wave-current model is implemented to study the impact of Hurricane Irma (2017) on transport processes over reefs in the Florida Keys. Assuming the dispersal of disease agents within neutrally buoyant material, our model successfully reproduced the observed spread of SCTLD through the FCR and linked its apparent stalling before reaching the DRTO to eddy activity in the Loop Current/Florida Current system. Furthermore, the results of our sediment transport model suggest that the PMDDP might have triggered the onset of the disease. Finally, our coupled wave-current model showed the important impact of wave-induced currents on transport processes over reefs during hurricanes. This thesis highlights the potential of models informed by and confronted against field knowledge as powerful tools to inform the management of complex marine ecosystems such as Florida's Coral Reef.

Jury members :

• Prof. Emmanuel Hanert (UCLouvain), supervisor
• Prof. Marnik Vanclooster (UCLouvain), chairperson
• Prof. Eric Deleersnijder (UCLouvain), secretary
• Dr. Jonathan Lambrechts (UCLouvain)
• Dr. Christopher Thomas (Risk Management Solutions London, UK)
• Prof. Claire Paris-Limousy (Univ. Miami, USA)

Pay attention :

The public defense of Thomas Dobbelaere scheduled for Monday 25 April at 3:00 p.m will also take place in the form of a video conference

Pour l’obtention du grade de Docteur en sciences agronomiques et ingénierie biologique

Arctic warming and permafrost loss modify northern ecosystems through soil subsidence, changes in soil hydrology, nutrient availability and vegetation succession. In particular, warming and soil moisture conditions influence Arctic tundra vegetation production and distribution: wetter soil conditions favor sedge expansion and drier soil conditions drive woody shrub expansion. While these shifts in vegetation may alter permafrost integrity by modifying the surface energy transfers, they may also be responsible for further changes in the tundra vegetation production and distribution by influencing plant nutrient cycling. Specifically, this PhD thesis investigates the influence of permafrost degradation on mineral nutrient distribution in soils and the influence of tundra vegetation shift on mineral nutrient cycling. Along a permafrost thaw gradient in Interior Alaska, our results demonstrate that permafrost is an important frozen reservoir of nutrients for plants, with stocks of total and exchangeable base cations in the permafrost soil layers more than twice as high as in the seasonally thawed active layer. Moreover, we observe that foliar elemental stocks and annual fluxes from leaf to soil litter change with vegetation shift; sedge expansion promotes Si, P and Fe foliar cycling and shrubification promotes Ca and Mn foliar cycling. Lastly, we highlight that shrub and sedge species both take up nutrients from deeper soil horizons upon permafrost thaw, with the deeply rooted sedge benefitting first from the release of nutrients at depth. These findings provide insights to improve the integration of changes in mineral nutrient cycling into models predicting Arctic ecosystem evolution and feedbacks on climate.

Jury members :

• Prof. Sophie Opfergelt (UCLouvain), supervisor
• Prof. Emmanuel Hanert (UCLouvain), chairperson
• Dr. Valentin Couvreur (UCLouvain), secretary
• Prof. Yannick Agnan (UCLouvain)
• Prof. Julien Fouche (SupAGRO, Montpellier, France)
• Dr. Arsène Druel (INRAE, France)

Pay attention :

The public defense of Elisabeth Mauclet scheduled for Tuesday 17 May at 4:00 p.m will also take place in the form of a video conference

Pour l’obtention du grade de Docteur en sciences agronomiques et ingénierie biologique

The Kapuas River delta (KRD) is a low-lying marshy delta on the western coast of Borneo Island, Indonesia. In the last decades, palm oil cultivation and forest fires have encroached on the Kapuas water catchment areas, changing the Kapuas hydrological regime and triggering more intense flooding in the KRD. Meanwhile, climate change has also rendered flooding events in the delta less natural and more disastrous. As population density rises, flooding risks attributed to riverine and coastal surges must be properly assessed. The importance of this assessment for urban planning and coastal protection development cannot be overstated. However, as in most developing countries, local water managers in the KRD lack data and tools to assess flooding risks properly. Consequently, the mechanisms that drive the flooding events in the KRD remain poorly known. Creating robust forecasting to predict flooding events is challenging with the lack of observational data, even more so with limited computational resources.

The first objective of this thesis is to investigate the impact of the interaction between tides, storm surges, and river discharges in the KRD, particularly in the densely-populated city of Pontianak, which lies on the delta. The interactions between the driving forces and the effects on compound flooding are simulated using a hydrodynamic model (SLIM). Then, based on the maximum water-level profile, compound flooding hazard zones along the Kapuas River are delineated. In the second phase, this thesis combines the process-based and data-based modeling approaches to tackle the issue caused by limited computational resources and observational data. The process starts with building a hydrodynamic model to run flood scenarios in the KRD. The next step is to create machine learning (ML) models and train them using the outputs of the hydrodynamic model to predict water levels and future floods. Several ML algorithms are evaluated to ensure that the ML model is robust. Random forest (RF) performs best, highly accurate for the application in the study area. The last phase is to assess future compound flooding risks in the KRD using limited observation data under climate change in the three emission scenarios: low (RCP2.6), medium (RCP4.5), and high (RCP8.5). The assessment is conducted using integrated ML and GIS-based bathtub models, resulting in current and future flood maps of the potentially inundated areas under a 100-year flood (1% annual exceedance probability) scenario. The results suggest that in 2100, more buildings will be exposed (increased by about 6.4% - 11.9%), and more roads will be impacted (increased by approximately 6.8% - 12.7%) depending on the emission scenarios. These assessment outputs are essential for the local water managers in the KRD to mitigate the impacts and create adaptation strategies.

Jury members :

• Prof. Emmanuel Hanert (UCLouvain), supervisor
• Prof. Jacques Mahillon (UCLouvain), chairperson
• Prof. Charles Bielders (UCLouvain), secretary
• Prof. Sandra Soares Frazao (UCLouvain)
• Dr. Olivier Gourgue (Universiteit Antwerpen)
• Dr. Agus Atmadipoera (IPB University)

Pay attention :

The public defense of Joko Sampurno scheduled for Friday 19 August at 04:00 p.m. will also take place in the form of a video conference

On September 7th, 2022

Auditoire sud 1
&
Online on MS Teams 

"Bridging the gap between small and large spatial scales in marine dispersal modelling - Applications to coral ecosystems in the Great Barrier Reef"

Jury members:

Prof. Emmanuel Hanert (Supervisor) - UCLouvain, Belgium

Prof. Eric Deleersnijder (Supervisor) - UCLouvain, Belgium

Dr. Alana Grech - James Cook University, Australia

Dr. Geneviève Lacroix - Royal Belgian Institute of Natural Sciences, Belgium UCLouvain, Belgium

Dr. Jonathan Lambrechts (Secretary) - UCLouvain, Belgium

Prof. Marnik Vanclooster (President) - UCLouvain, Belgium

"Organo-mineral interactions in permafrost environments affected by physical degradation"
 

Registration form

Teams link

Abstract:

Permafrost soils are found at high latitudes and altitudes, and contain three times more carbon than in the atmosphere. As permafrost thaws, a portion of this carbon - still largely uncertain - is released in the form of greenhouse gases (GHG), resulting in a permafrost carbon-climate-feedback. This feedback still awaits to be integrated in global models of GHG emissions used by the IPCC, but is estimated as equivalent to the emissions from one additional large industrialized country. The uncertainties are partly attributable to the unknown contribution of the thawing of ice-rich permafrost, which manifests by physical degradation, named thermokarst terrains. Another source of uncertainty relates to the proportion of organic carbon (OC) that is linked to mineral surfaces or mineral elements, as mineral-interacting OC. These stabilization mechanisms are presumed to render the corresponding OC fraction less accessible to decomposition and emissions as GHGs. This thesis investigates the abundance, nature and control of mineral-OC interactions in permafrost soils and sediments affected by thermokarst disturbances. Chemical stabilization mechanisms have been shown to stabilize on average 31 ± 12% of total OC, and this pool of mineral-interacting OC is preserved in materials exported by the thermo-erosion process. We also show that historical permafrost thaw dynamics have a decisive influence on the concentration and proportion of mineral-interacting OC in permafrost environments. Finally, we have shown that the formation of lowland thermokarst landscapes has progressed locally five times faster in recent years than in the last few decades, with an expected release of mineral-bound OC. Such findings demonstrate the urgent need to integrate OC-mineral interactions into global ecosystem carbon balance models. This requires establishing links between concentrations and proportions of mineral-interacting OC and GHG emissions.
 

Jury members:

Supervisor: 
Prof. Sophie OPFERGELT – UCLouvain

President of the jury: 
Prof. Emmanuel HANERT – UCLouvain

Other jury members: 
Prof. Veerle VANACKER | UCLouvain
Prof. Sandra ARNDT - Université Libre de Bruxelles
Prof. Julien FOUCHÉ - Institut Agro Montpellier, France
Prof. François JONARD - ULiège

Public thesis defense of Aubry VANDEUREN

"Occurrence and mobility of arsenic and other trace elements in high background concentration soils: A case study in Wallonia (Belgium)"
 

Registration form

Teams link

Abstract:

Elevated arsenic (As) contents in topsoils with high background levels of potentially toxic elements (PTEs) poses human, environmental and regulatory challenges, as total PTE contents may exceed soil quality values. Understanding As distribution and mobility in these soils is important, as total content measurements alone are insufficient for reliably estimating potential exposure risks. This PhD thesis investigates the presence, origin and mobility of As and other PTEs in soils with high background contents in Liège’s industrial basin and Belgian Lorraine. In Liège, As originates from historical industrial activities, whereas in Belgian Lorraine, it is linked to Fe-rich sedimentary formations (Aubange and Grandcourt). To assess variability at three spatial scales and along the soil profile (0–85 cm depth), total As content was measured in 495 soil samples from Lorraine. Topsoil As mobility was estimated through phytoavailability using plant-based biotests, selective extractions and human bioaccessibility analysis. The solid-phase As was also characterized. The results indicate that As phytoavailability correlates positively with total As content in the Liège soils but not in Belgian Lorraine. The bioaccessible fraction ranges from 19 to 27% in Liège soils and from 8 to 11% in Lorraine soils, decreasing to 4% in the eastern part of the Aubange Formation. This reflects the increasing incorporation of As (and other PTEs) into Fe oxyhydroxides formed during a paleoweathering episode. Pedogenesis occurred in a heterogeneous context, with exogenous processes further redistributing As across the landscape. Together, the Liège basin and Belgian Lorraine encompass over 100 km² of soils where total As contents likely exceed soil quality values. However, our results indicate that the potentially mobilizable As fraction does not exceed 30% of the total content. The PhD research will contribute to informed decision-making for the sustainable management of soils.
 

Jury members:

Supervisors: 
Prof. Pierre DELMELLE - UCLouvain
Prof. Patrick BOGAERT – UCLouvain

President of the jury: 
Prof. Marnik VANCLOOSTER - UCLouvain

Other jury members: 
Prof. Valérie CAPPUYNS - KU LEUVEN - SIM²
Prof. Sophie OPFERGELT | UCLouvain
Prof. Aurélie PELFRÊNE | JUNIA

"Différenciation spatiale du potentiel de transfert modal vers le vélo : méthode d’analyse prospective sur base de facteurs territoriaux 
et comportementaux"
 

Registration form

Teams link

Abstract:

Dans le contexte actuel d’urgence climatique, de congestion urbaine généralisée et de manque d’activité physique, promouvoir l'usage du vélo pour remplacer une partie des trajets réalisés en voiture devient un impératif reconnu à plusieurs niveaux politiques. Les avantages du vélo sont bien documentés : il nécessite peu d’espace, est silencieux, présente un faible impact environnemental et encourage une activité physique modérée. Sur le plan socioéconomique, investir dans le vélo offre un retour sur investissement estimé à près de trois fois la valeur des investissements réalisés. En Wallonie, l’objectif de multiplier par cinq l’usage du vélo d'ici à 2030 appelle une évaluation de la faisabilité de cette ambition, ainsi qu’une réflexion sur les actions et les territoires à prioriser pour engager un véritable transfert modal.
Cette thèse propose une grille d’analyse prospective du potentiel cyclable, structurée autour de quatre composantes clés : l’accessibilité, le domaine vital, la motilité et la perception. Cette méthodologie, en adoptant une approche multifactorielle de la cyclabilité, se distingue de la littérature existante, souvent limitée à l’analyse des infrastructures et de l’aménagement de l’espace urbain.
Des méthodes de modélisation spatialement explicite ont permis d'appliquer cette grille d'analyse de manière détaillée. Elle a été validée à partir d'une enquête de mobilité impliquant 1 600 employés d'une université, d’une part, et à partir des enquêtes de mobilité menées auprès de plus de 2 600 entreprises réparties sur l'ensemble du territoire wallon, d’autre part. Le comportement des cyclistes quant à leur choix d'itinéraire a été reproduit en paramétrant les algorithmes d'analyse réseau des systèmes d'information géographique, sur la base des interviews d'une cinquantaine de cyclistes quotidiens. Deux échelles d'analyse prospective ont été mobilisées sur l'ensemble du territoire wallon : celle de l'ancienne commune et celle de l'entreprise.
Mieux comprendre les choix de mobilité est un enjeu majeur, et cette thèse apporte une perspective novatrice en combinant facteurs sociaux et territoriaux dans une analyse prospective spatialement explicite. Cette approche permet à la fois un ciblage territorial et une priorisation des interventions pour atteindre des objectifs de transfert modal déclinés selon chaque commune. L’approche proposée est applicable à diverses échelles spatiales, facilitant ainsi la comparaison entre territoires et le suivi de l’évolution du potentiel du vélo. Elle permet également d’identifier les facteurs à améliorer pour optimiser l’usage du vélo comme moyen de transport, ainsi que d’évaluer la concrétisation de ce potentiel dans le temps.

 

Jury members:

Co-supervisors: 
Prof. Pierre DEFOURNY - UCLouvain
Prof. Yves HANIN – UCLouvain

President of the jury: 
Prof. Emmanuel HANERT - UCLouvain

Other jury members: 
Dr. Julien RADOUX - UCLouvain
Prof. Patrick RÉRAT - UNIL, Switzerland 
Dr. Tanguy ISAAC - SNCB
Prof. Sebastiaan de GEUS - UCLouvain

"From geophysical subsurface imaging to hydrological and geochemical monitoring in peatlands"

26/02 – 16:30-19:30

SUD03 + Teams

Abstract:

Peatlands are globally important ecosystems, essential for carbon storage, water regulation, and biodiversity. However, they are increasingly threatened by multiple direct human pressures and by climate change. They are highly sensitive and exhibit pronounced spatial and temporal heterogeneity in their physical and chemical properties, making them challenging to study. 

This thesis primarily aims to improve our capacity to characterize and understand peatland spatial variability in terms of subsurface composition and spatial moisture patterns. A second objective focuses on monitoring temporal variability in moisture and porewater solute content, and understanding their drivers. Two study sites were investigated: one in the Belgian Hautes Fagnes, representing a peatland degraded by forestry, and another in the Alaskan permafrost region, representing ongoing degradation by climate change.

First, regarding spatial variability, ground-coupled ground-penetrating radar (GPR) proved effective for subsurface imaging, enabling the determination of peat thickness variability and the delineation of taliks (zones of unfrozen ground year-round within permafrost areas). Drone-borne GPR was successfully used to map spatial moisture patterns, revealing marked heterogeneity associated with topography, peat thickness, and vegetation. Soil moisture variations further induced hotspots in porewater solute concentration. Second, regarding temporal variability, drone-borne GPR and on-ground sensors captured moisture seasonal dynamics, showing that most variations occurred during summer. Porewater solute concentrations also varied seasonally, strongly influenced by moisture fluctuations. 

Overall, this thesis demonstrates the potential of geophysical methods to advance peatland research by revealing detailed subsurface and moisture variability. At the Belgian Hautes Fagnes site, results revealed high heterogeneity in subsurface composition, moisture, and porewater chemistry. By integrating mapping and monitoring approaches, this thesis provides an improved understanding of peatland ecosystem functioning and key properties, offering guidance for their conservation.

Jury members:

Prof. Marnik VANCLOOSTER (President), UCLouvain

Prof. Sébastien Lambot (Supervisor), UCLouvain

Prof. Kristof VAN OOST (Supervisor), UCLouvain

Prof. Veerle VANACKER (secretaire), UCLouvain et Wageningen University

Prof. Sophie OPFERGELT, UCLouvain 

Dr. Michel BECHTOLD, KU Leuven

Dr. Craig WARREN (Northumbria University)

REGISTRATION >

TEAMS LINK >

MORE INFORMATION >

"Three tools for the reduction of pesticide impacts: A case study in the Province of Luxembourg." 
 

October 10 - 4 to 7 PM
Océan room - de Serres building
 

Teams link

Oral presentation will be given in French. 
La présentation orale sera donnée en français. 

Jury members:

Supervisors:
Prof. Philippe V. BARET : UCLouvain
Prof. Yannick AGNAN : UCLouvain

Other jury members:
Prof. Frédéric GASPART : UCLouvain ; Chairperson
Prof. Pierre BERTIN : UCLouvain ; secretary
Prof. Per KUDSK : Aarhus University (Danemark)
Dr. Lionel ALLETTO : INRAE Toulouse (France)

Abstract:
This dissertation develops three practical tools to reduce the health and environmental impacts of pesticide use, supporting diagnosis, design and decision-making from field to territorial scales. Combining regulatory, agronomic and environmental perspectives, the deliberately pluralistic approach aims to guide more sustainable agricultural practices, with applications in the Province of Luxembourg and beyond.

First, the Pesticide Load Indicator is adapted to support taxation, policy evaluation and farm-level decisions at EU-wide scale, by promoting lower-risk pesticide use. Building on Danish and British versions of the indicator, the proposed modifications incorporate updated toxicological and environmental hazard data as well as improved normalization and weighting procedures.

Second, crop sequence diversity and agronomic optimisation are addressed as core strategies of integrated pest management. Using detailed 2015–2020 field-level IACS data, two existing crop sequence indicators were refined to better capture organic and mixed crop-livestock systems by including temporary grasslands and fodder crops. The results show a strong link between organic certification, temporary grasslands and more diverse, resilient rotations, with implications for both territorial assessments and on-farm preventive strategies.

Third, the agri-environmental role of cover crops is investigated in a greenhouse experiment involving 18 pesticides ingredients across three treatments: bare soil, thin cover crop and thick cover crop. Results show thin cover crops retain residues in topsoil and reduce leaching, while thick cover crops promote degradation in the rhizosphere, especially for compounds with low to high water solubility (s⩽1400mg/L) and low to moderate soil mobility (Koc⩾160mL/g). These findings highlight the multifunctionality of cover crops in enhancing soil resilience and protecting water quality.

Together, these tools offer actionable insights to reduce pesticide dependency and negative impacts. While no single measure can transform high-input agriculture alone, their combined use (integrated into a systemic, stakeholder-driven policy mix) can support a transition toward more sustainable and ecologically sound farming systems.

Résumé :
Cette thèse développe trois outils complémentaires visant à réduire les impacts sanitaires et environnementaux des pesticides, en appui au diagnostic, à la conception et à la prise de décision, de la ferme au territoire. Adoptant une approche volontairement pluraliste croisant les dimensions réglementaires, agronomiques et environnementales, elle contribue à orienter les pratiques agricoles vers plus de durabilité, de la province de Luxembourg à des échelles plus larges.

Le premier outil consiste en une adaptation de l’Indicateur de Charge en Pesticides, conçue pour soutenir la taxation des pesticides, le suivi des politiques régionales et européennes et les décisions d’usage au niveau des exploitations. Inspirée des versions danoise et britannique, cette version actualisée intègre des données récentes de toxicologie et écotoxicité, ainsi que des méthodes affinées de normalisation et de pondération dans un cadre transparent et transférable à l’échelle internationale.

Le deuxième outil explore la diversité des successions culturales et leur optimisation agronomique comme leviers de lutte intégrée. À partir de données détaillées du SIGeC (2015–2020), deux indicateurs existants ont été adaptés pour mieux prendre en compte l’agriculture biologique et mixte (cultures-élevage), incluant prairies et cultures fourragères temporaires. Les résultats révèlent une forte corrélation entre certification biologique, prairies temporaires et rotations plus diversifiées et résilientes.

Le troisième outil analyse le rôle des cultures intermédiaires dans la réduction de la persistance et du transfert des pesticides vers les eaux souterraines. Une expérimentation en serre avec 18 substances actives montre que les couverts légers retiennent les résidus en surface, tandis que les couverts denses favorisent leur dégradation dans la rhizosphère. Ces effets différenciés confirment leur rôle multifonctionnel pour la résilience des sols et la protection de l’eau.

En synergie, ces outils offrent des leviers concrets pour réduire l’usage et l’impact négatif des pesticides. Leur efficacité dépend d’une intégration cohérente dans les politiques pour accompagner la transition vers une agriculture productive, résiliente et respectueuse de l’environnement.

"Optimisation de la gestion de l’eau dans les bas-fonds des zones soudaniennes du Bénin "
 

August 26 - 4 to 7 PM
Océan room - de Serres building 

Teams link

Abstract:

TBA

 

Jury members:

Supervisors: 
Prof. Marnik VANCLOOSTER
Prof. Pierre AKPONIKPE (Univ. Parakou, Bénin)

Other jury members:
Prof. Frédéric GASPART, Chairperson
Prof. Charles BIELDERS, Secretary
Dr. Pierre TOVIHOUDJI (Univ. Parakou, Bénin)
Dr. Basile HECTOR (UGA Grenoble/IRD, France)
Ir. Philippe DIERICKX (SPW, Région wallonne, Belg.)

"Multiscale hydrodynamic modelling of the Danube Delta"
 

December 10 - 4:45 to 7:45 PM
 

•    Defense place: B7b A142 (Campus du Sart Tilman - Quartier AGORA, allée du 6-Août 17, 4000 Liège)
•    Deliberation place: B7b A3 (Campus du Sart Tilman - Quartier AGORA, allée du 6-Août 17, 4000 Liège)
•    Cocktail place: B7b Galerie des Arts (Campus du Sart Tilman - Quartier AGORA, allée du 6-Août 17, 4000 Liège)

Teams link

Abstract:

Floodplains are a key component of deltaic systems, influencing hydrodynamics, ecosystem functioning, and local socio-economic activities. Situated at the interface between the Danube River and the Black Sea, the Danube Delta forms a complex mosaic of channels, lakes, and floodplains. Despite its key role as a transition region—that filters nutrients, buffers floods, supports biodiversity, and sustains local livelihoods and economic activities—the Danube Delta remains understudied. In this thesis, we use the 2D version of the multiscale hydrodynamic model SLIM to evaluate the influence of floodplains on the hydrodynamics of the Danube Delta. We first examine the role of mesh configuration in such braided river–floodplain environments and propose hybrid curvilinear–unstructured meshes as the best compromise between accuracy and computational efficiency. We then present a first comprehensive, high-resolution, easily accessible bathymetric dataset for the three main branches of the Danube Delta, filling a key gap in available data for hydrodynamic modeling in the region. Finally, we demonstrate that including floodplains in deltaic hydrodynamic models improves hydrodynamic representation and offers alternative pathways for water flows. In the Danube Delta, we estimate that the proportion of the upstream discharge reaching the sea through routes other than the six main river mouths ranges from 10.0±4.1% (2024) to 10.8±4.8% (2021). This thesis highlights the essential role of floodplains in deltaic environments and represents an important step toward a more realistic representation of the Danube–Black Sea continuum.

Jury members:

Prof. Marilaure Grégoire (Supervisor), ULiège
Prof. Emmanuel Hanert (Supervisor), UCLouvain
Dr. Luc Vandenbulcke, ULiège
Dr. Olivier Gourgue, Royal Belgian Institute of Natural Sciences
Dr. Christian Ferrarin, Institute of Marine Sciences of the National Research Concil of Italy
Dr. Jonathan Lambrechts (Secretary), UCLouvain
Prof. Xavier Fettweis (President), ULiège
 

"Agronomic and environmental determinants of coffee yield, quality and cyclicity across Burundi"

26/02 – 16:30-19:30

Teams link >>>

Promoteurs :

Prof. BIELDERS Charles : Université catholique de Louvain, Belgium

Dr. VANLAUWE Bernard: International institute of tropical agriculture, Kenya

Président du jury:

Prof. VANCLOOSTER Marnik : Université catholique de Louvain, Belgium

Membres du jury

Prof. DELVAUX Bruno: Université catholique de Louvain, Belgium

Dr NIBASUMBA Anaclet : Université du Burundi, Burundi

Dr. LOBET Guillaume : Université catholique de Louvain, Belgium

Dr. TAYE Kufa-Obso: Ethiopian institute of agriculture research, Ethiopia

Abstract
Coffee is Burundi’s main export crop and a cornerstone of rural livelihoods, yet Arabica coffee production faces persistent challenges, including declining yields, strong year-to-year production variability, and inconsistent quality. Despite favorable agroecological conditions, the agronomic, environmental, and nutritional factors influencing coffee performance have rarely been analyzed together in an integrated framework.
This thesis investigates the determinants of Arabica coffee performance in Burundi by simultaneously examining three key dimensions: yield and yield variability, production cyclicality, and physical and sensory quality. The study combines field surveys, soil and leaf analyses, sensory evaluations, and multivariate statistical approaches across 155 farms located in the country’s main coffee-growing regions.
Results reveal that agronomic management and soil fertility are the primary drivers of coffee performance, outweighing environmental factors such as climate and altitude. Significant yield gaps were observed, with average production about 59% below potential. Soil organic carbon, mulching practices, and soil magnesium emerged as key variables influencing yield, while soil acidity, nutrient deficiencies, aging plantations, and inadequate field management limit productivity. Production stability can be improved through better soil fertility management, particularly by optimizing nitrogen and phosphorus levels and balancing soil cations. Coffee quality, meanwhile, depends largely on soil nutrient balance rather than altitude alone, while diseases and pests remain major constraints.
By integrating yield, stability, and quality into a single analytical framework, this thesis highlights the central role of manageable agronomic factors in improving coffee production. It demonstrates that substantial improvements in productivity, quality, and income stability are possible without expanding cultivated areas, offering practical insights for agricultural advisory services and policies aimed at strengthening the resilience and sustainability of Burundi’s coffee sector.

Résumé
Le café constitue la principale culture d’exportation du Burundi et une source essentielle de revenus pour des centaines de milliers de ménages ruraux. Pourtant, malgré des conditions agroécologiques favorables, la caféiculture burundaise est confrontée à plusieurs défis majeurs : une baisse marquée de la production, des rendements faibles et très variables d’une année à l’autre, ainsi qu’une qualité insuffisamment compétitive sur le marché international.
Cette thèse analyse les facteurs déterminant la performance du café arabica au Burundi en intégrant simultanément trois dimensions essentielles : le rendement et ses variations, la cyclicité de la production et la qualité physique et sensorielle des grains. L’étude repose sur des enquêtes de terrain, des analyses de sols et de feuilles, des évaluations sensorielles standardisées et des analyses statistiques multivariées réalisées sur 155 exploitations réparties dans les principales zones caféicoles du pays.
Les résultats montrent que les facteurs agronomiques et la fertilité des sols jouent un rôle déterminant dans la performance des caféiers, bien plus que les facteurs environnementaux tels que l’altitude ou le climat. D’importants écarts de rendement ont été observés, les productions moyennes restant nettement inférieures au potentiel. La gestion de la fertilité des sols, notamment la teneur en carbone organique, le paillage et l’équilibre nutritionnel, apparaît comme un levier majeur pour améliorer la productivité et réduire la cyclicité de la production. La qualité du café dépend quant à elle principalement de l’équilibre des éléments nutritifs du sol, en particulier du calcium, tandis que les maladies et ravageurs constituent des contraintes importantes.
En proposant une approche intégrée combinant rendement, stabilité et qualité, cette recherche met en évidence le rôle central des pratiques agronomiques dans l’amélioration durable de la caféiculture burundaise. Elle souligne également l’existence d’importantes marges de progression permettant d’améliorer simultanément la productivité, la qualité et la stabilité des revenus des producteurs sans extension des surfaces cultivées. Les résultats fournissent ainsi des bases scientifiques solides pour l’élaboration de recommandations agronomiques et de politiques agricoles visant à renforcer la durabilité et la résilience du secteur caféier au Burundi.

Résumé

La production rizicole en Afrique de l’Ouest, en particulier dans les écosystèmes de bas-fonds du sud du Bénin, est confrontée à d’importants défis liés à une gestion inefficace de l’eau et à la variabilité climatique. 

Cette thèse a pour objectif de consolider les bases scientifiques nécessaires à la conception de stratégies innovantes de gestion de l’eau et des nutriments, fondées sur des principes agroécologiques afin d’améliorer la productivité et la durabilité de la riziculture. 

Plusieurs approches de recherche ont été combinées, incluant une revue quantitative de la littérature, des expérimentations en station, en milieu paysan et la modélisation. 

Une méta-analyse portant sur 573 observations issues de 56 études a montré que les pratiques agroécologiques notamment l’Irrigation Intermittente Modérée (IIM) et la saturation du sol (SS) combinées à une fertilisation organique ou mixte, améliorent significativement le rendement du riz (+5 à 15 %) et la productivité de l’eau (+20 à 46 %) par rapport à l’inondation continue. 

Des expérimentations menées sur deux sites contrastés, Matékpo (saison humide) et Sèwahoué (saison sèche), selon un dispositif en parcelles subdivisées à trois répétitions dont les traitements comprenaient quatre régimes d’irrigation : inondation continue (IC), saturation du sol (SS), Irrigation Intermittente modérée (-15 kPa, IIM) et sévère (-30 kPa, IIS), ainsi que huit modalités de fertilisation : témoin (C), minéral recommandé (M), microdosage minéral (MM), compost (CO), paille de riz (PR), biochar + compost (BCO), paille de riz + compost (PRCO) et biomasse de mucuna (BM). 

Les résultats issus des expérimentations conduites en station et en milieu paysan durant deux campagnes agricoles ont confirmé que l’IIM combinée à des amendements organiques (BCO, CO et PRCO) accroît le rendement en grain (jusqu’à +18 %) tout en réduisant les besoins en irrigation de 20 à 25 %. 

Les évaluations socio-économiques ont révélé que ces pratiques améliorent la rentabilité des exploitants en réduisant les coûts de production et en renforçant leur résilience face aux risques climatiques. 

De plus, les simulations numériques effectuées avec le modèle DSSAT CERES-Rice ont validé les résultats expérimentaux et projeté la durabilité à long terme de ces pratiques dans le contexte de la variabilité climatique historique (1986–2015), montrant que les systèmes II et SS peuvent maintenir des rendements supérieurs à 4 t ha⁻¹ tout en réduisant la demande en eau d’irrigation d’environ un tiers. 

Dans l’ensemble, cette thèse fournit des preuves quantitatives solides que l’intégration de stratégies agroécologiques d’économie d’eau et de gestion des nutriments améliore la productivité rizicole, l’efficacité de l’utilisation des ressources et la viabilité économique des producteurs, tout en renforçant la résilience climatique des systèmes rizicoles de bas-fonds en Afrique de l’Ouest. 

Ainsi, cette recherche souligne que l’intégration d’innovations agroécologiques dans les systèmes rizicoles de bas-fonds constitue une approche prometteuse pour atteindre une intensification durable, améliorer la sécurité alimentaire et accroître la résilience climatique de l’agriculture ouest-africaine.

Membres du jury

Présidente : Dr. Christine A. I. OUINSAVI, Professeure Titulaire, Université de Parakou, Bénin
Co-directeur 1 : Dr. P. B. Irénikatché AKPONIKPE, Professeur Titulaire, Université de Parakou, Bénin
Co-directeur 2 : Dr. Marnik VANCLOOSTER, Professeur, Université catholique de Louvain, Belgique
Examinateur 1 : Dr. Luc O. SINTONDJI, Professeur Titulaire, Université d’Abomey-Calavi, Bénin
Examinateur 2 : Dr Lawani Adjadi MOUNIROU, Maître de Conférences, Institut International d’ingénierie de l’Eau et de l’Environnement (2iE), Burkina Faso
Examinateur 3 : Dr. Rodrigue Vivien Cao DIOGO, Professeur Titulaire, Université de Parakou, Bénin

"Disentangling drivers of leaf litter decomposition using a synthetic community approach"

21/08 – 16:00-19:00

Teams link >>>

Supervisors :
Prof. Quentin PONETTE - UCLouvain
Prof. Bart MUYS – KU Leuven

Chair:
Prof. Frédéric GASPART - UCLouvain

Jury: 
Prof. Yannick AGNAN - UCLouvain
Prof. Bart MUYS – KU Leuven - 
Prof. Karen VANCAMPENHOUT – KU Leuven
Prof. Olivier HONNAY – KU Leuven 
Prof. Laurent AUGUSTO – INRAE 

Abstract:
Tree species as ecosystem engineers: shaping decomposition and carbon stocks in forest soils.
Forest soils store vast amounts of carbon, but the pathways leading to this storage are strongly influenced by the trees growing above them. In this PhD, I explored how tree species and forest composition affect leaf litter decomposition, above-belowground interactions and topsoil carbon stocks.
By studying mature forest communities from around the world growing under the same climate and soil conditions in the Arboretum of Tervuren, I showed that tree species create distinct decomposition environments through their litter, canopy structure and effects on the local environment. These differences influence how nutrients are recycled and where carbon is stored in the soil.
The results highlight that tree species identity and functional traits are key drivers of forest ecosystem functioning and should be considered in climate-smart forestry and future forest design.
 

"Informing tropical seagrass recovery in the Great Barrier Reef using a biophysical modelling approach"

03/09/2026 - 12:00

Teams link >>>

Jury members: 

Prof. Emmanuel HANERT (UCLouvain), Supervisor
Prof. Alana GRECH (James Cook University, Australia), Supervisor
Prof. Marnik VANCLOOSTER (UCLouvain), Chairperson
Dr. Jonathan LAMBRECHTS (UCLouvain), Secretary
Dr. Severine CHOUKROUN (James Cook University, Australia)
Prof. Tom VAN DER STOCKEN (VUB, Belgium)
Dr. Eric TREML (Australian Institute of Marine Sciences, Australia)
Dr. Michael RASHEED (James Cook University, Australia)

Abstract: 
Seagrasses provide essential services for human well-being, including fisheries habitat, water filtration, coastal protection and carbon sequestration. Globally, these coastal ecosystems have been declining due to the cumulative and interactive effects of coastal development, pollution and climate change. Coastal and catchment management and restoration projects have been implemented to mitigate the impact of these threatening processes. However, the success rate of management interventions is highly variable. A comprehensive understanding of seagrass dynamics, particularly tropical seagrasses, is critical to protect and preserve these ecosystems. For example, dispersal and connectivity of seagrasses supports the replenishment and natural recovery of seagrasses. These processes can be assessed using biophysical models, combining ocean circulation simulations with biological traits. Yet, only few of them account for the interspecific and interannual variability inherent in tropical seagrass ecosystems, suggesting opportunities to improve the predicted dispersal patterns. These dispersal processes have not been assessed comprehensively in one of the world’s largest tropical seagrass ecosystems - the Great Barrier Reef World Heritage Area (GBRWHA) of Queensland, Australia. By using a biophysical modelling approach, this thesis assessed dispersal and connectivity processes of GBRWHA seagrasses to inform their management. Overall, this thesis underscores the importance of modelling parametrization and its impacts on seagrass dispersal predictions. It highlights the value of using robust biophysical models, built on well-considered assumptions including forcing choices, that integrate species-specific traits to accurately capture connectivity. This thesis highlights the drivers of seagrass dispersal in the GBRWHA, that include strong seasonal variations, complex coastal topography influencing wind patterns, and large dispersal variability between species. Broadly, this thesis advances the capacity to model and interpret connectivity in dynamic coastal ecosystems, providing a transferable framework to improve ecological forecasting and guide management strategies.