Events & Theses

Public thesis defense of Bryan ARBALESTRIE

"Role of exogenous organic matter in the transfer of trace elements in the soil-plant system: contribution of metal isotopes, rare earth elements, and organic matter characterization"

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Abstract

TBA

Jury Members

Prof. Yannick AGNAN (UCLouvain, Supervisor)

Prof. Mélanie DAVRANCHE (Université de Rennes)

Prof. Nadine MATTIELLI (ULB)

Prof. Sophie OPFERGELT (UCLouvain)

Prof. Katell QUENEA (Sorbonne Université)

Prof. Marnik VANCLOOSTER (UCLouvain, Chairman)

Public thesis defense of Timothée CLÉMENT

"Effectiveness of conservation cropping practices in mitigating runoff, soil erosion, and pesticide surface losses in Northwestern Europe"

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Abstract

Soils of the Western European loess belt are intensively cultivated and particularly prone to runoff and soil erosion. Besides threatening soil resources, overland flows cause muddy floods that damage infrastructure downstream and pollute water bodies by transferring nutrients and pesticides. Numerous conservation farming practices are known to mitigate surface flows, but the magnitude of their effectiveness remains uncertain in Northwestern Europe. Based on a systematic review and meta-analysis, we estimated the runoff and erosion mitigation effects of conservation (i.e., non-inversion) tillage, winter cover crops, and tied-ridging (i.e., micro-basin tillage in potato fields). These conservation practices decreased seasonal soil losses by 66%, 72%, and 92%, respectively, compared to conventional tillage. For conservation tillage, we further identified key factors explaining the variability of the flow mitigation effects, including the time since ploughing was stopped, the type of implemented conservation tillage scheme (e.g., number of operations), and the main crop type (winter or spring crop). Besides its use in potato crops, micro-basin tillage has also recently been developed in Belgium for maize crop, using an innovative agricultural roller designed to shape depressions in-between the maize rows. Based on past plot experiments, micro-basin tillage in maize was found to reduce runoff (-69%), soil erosion (-83%), and associated pesticide transfer (e.g., -65% for the active ingredient flufenacet). Lastly, two uncommon conservation practices in Northwestern Europe were investigated through original plot experiments in maize crops:  undersowing and strip-tillage. Undersowing (simultaneous sowing) red fescue or white clover in maize was very challenging in terms of weed control and resulted in no mitigation effect on surface flows compared to a conventionally tilled sole maize crop. Strip-tillage (i.e., tine-tilling the maize row only) significantly decreased runoff (-31%) and soil erosion (-60%). A hydrological process-based model was further calibrated based on the measured flow data in strip-tilled and conventionnaly-tilled maize plots. Subsequently, a scenario analysis was conducted to assess the conservation potential of the strip-tillage technique under extended climate, soil and slope conditions. Simulations reveal that strip-tillage cultivation would halve both the mean erosion rate as well as the flood risk (maximum daily runoff), as compared to conventional tillage. Unfortunately, available data did not allow to evaluate the impact of conservation practices on pesticide transfer in a conclusive way, neither from the quantitative review nor from our field trials. Meanwhile, the outcomes of this thesis can assist farmers, farm advisors or policy makers in (promoting) the implementation of effective conservation farming practices. 

Jury Members

Prof. Emmanuel HANERT (Chairman- UCLouvain)

Prof. Charles BIELDERS (Supervisor - UCLouvain)

Prof. Marnik VANCLOOSTER (secrétaire - UCLouvain)

Prof. Aurore DEGRE (ULiège Gembloux Agro-Bio Tech)

Prof. Wim CORNELIS (UGent)

Dr. Bruno HUYGHBAERT (CRA-W)

Public thesis defense of Nathan BEMELMANS

"Influence of pesticides on trace element transfer in the soil-solution-plant systems : a focus on glyphosate and tebuconazole"

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Abstract

TBA

Jury Members

Prof. Yannick AGNAN (UCLouvain, Supervisor)

Prof. Lionel ALLETTO (INRAE)

Dr Maryse CASTREC-ROUELLE (Sorbonne Université)

Prof. Stanley LUTTS (UCLouvain)

Dr Benoît PEREIRA (EREA)

Prof. Marnik VANCLOOSTER (UCLouvain, Chairman)

Public thesis defense of Sandratra Zonirina (Zo) RAMAHAIMANDIMBY

"Fonctionnement et altérations hydrologiques du bassin d’Ankavia (Madagascar) dans une perspective de gestion intégrée des ressources en eau."

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Abstract

Humid tropical environments, particularly the SAVA region in northeastern Madagascar, face important challenges in water resource management, exacerbated by land-use changes and climate modifications. Effective operationalization of Integrated Water Resources Management (IWRM) is imperative to develop sustainable approaches that reconcile current needs with resource preservation for future generations. However, its effective implementation is hindered by a lack of reliable hydrometeorological data and insufficient understanding of local hydrological processes. This study focuses on the Ankavia watershed, representative of the region, to elucidate its hydrological functioning and analyze its alterations in the face of environmental changes. A multiscale and interdisciplinary methodological approach was adopted, integrating analyses at different spatial and temporal scales, from micro-basin to large watershed, and covering periods ranging from isolated rainfall events to medium-term (2050) and long-term (2100) climate trends. The study identifies IMERG satellite data as a reliable alternative to ground rain gauges, while emphasizing the importance of continuing ground measurements. It reveals that land cover, particularly forest cover, as well as pedological and geological characteristics, strongly influence water flows. Future hydrological alterations are shown to be driven mostly by climate change rather than land uses changes. These results can serve as a solid foundation for IWRM adapted to the SAVA region and similar areas, addressing the growing challenges of environmental and climate changes.

Jury Members

Prof. Emmanuel HANERT (UCLouvain - Chairman)

Prof. Charles L. BIELDERS (UCLouvain - Supervisor)

Dr. Alain RANDRIAMAHERISOA (Université d’Antananarivo, Madagascar - Co-supervisor)

Prof. Marnik VANCLOOSTER (UCLouvain - Reader)

Prof. François JONARD (Université de Liège - Reader)

Prof. Sandra Soarez FRAZAO (UCLouvain  - Reader)

Dr. Quentin GOOR (Chargé de cours UCLouvain - Reader)

Public thesis defense of Louis DELVAL

"Quantifying soil-grapevine hydraulics from plant to field scale."

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Abstract

Grapevine (Vitis vinifera) is the world’s third most valuable horticultural crop. Today, climate change significantly threatens grape productivity, notably due to more frequent and extended drought periods. To address the critical issue of grapevine response to water stress, soil-plant hydraulic processes can be considered the cornerstone of the physiological mechanisms involved in grapevine tolerance to drought. Although recognized, the key role of belowground hydraulics on grapevine water status is rarely addressed because difficult to measure. This PhD thesis aims to understand how soil-grapevine hydraulics impacts the transpiration rate, water potential and root water uptake of in situ grapevine cv. Chardonnay. At the plant scale, we first revealed experimentally that the transpiration control of grapevine is soil texture specific and is triggered by a decrease of belowground hydraulic conductance, rather than xylem cavitation in the stem. We also highlighted the coordination of short-term hydraulic responses with longer-term growth strategies. Then, by using a biophysical model representing explicitly the series of hydraulic conductances between the bulk soil and the stem, we demonstrated that, during drought, root water uptake is mainly limited by the rhizosphere in coarse-textured soil, while it is the root system that controls root water uptake in fine-textured soil. Finally, a field scale experiment, in non-irrigated vineyards, provided evidence that the spatial distribution of grapevine leaf water potential is mainly governed by the within-vineyard soil hydraulic conductivity heterogeneity, especially during drought. By quantifying soil-grapevine water relations in different edaphic conditions during drought, this PhD thesis provides insights that could help winemakers to ensure better adaptation to climate change and enhance vineyard resilience.

Jury Members

Prof. Mathieu JAVAUX (promoteur - UCLouvain)

Prof. François JONARD (co-promoteur - UCLouvain)

Prof. Marnik VANCLOOSTER (président du jury - UCLouvain)

Prof. Xavier DRAYE (Secrétaire du jury - UCLouvain)

Prof. Bruno DELVAUX (UCLouvain)

Prof. Cornélis VAN LEEUWEN (Bordeaux Sciences Agro)

Prof. Jan VANDERBORGHT (Forschungszentrum Jülich et KULeuven)

Public thesis defense of Jean BOUCHAT

"Maize green area index retrieval from multistatic and multi-frequency SAR data"

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Abstract

Climate change and a rapidly growing world population are placing an ever-increasing pressure on the agricultural sector. In this context, green area index (GAI) monitoring plays an essential role in assessing the status and health of crops, making it a key source of information for farmers and decision-makers alike. Current operational methods for GAI monitoring rely mainly on optical imagery, and are therefore hampered by the recurring presence of clouds. Synthetic aperture radars (SARs) present a promising alternative for collecting data in almost all weather conditions. The main objective of this thesis is to improve the retrieval of the GAI in maize crops using SAR remote sensing, with a perspective towards near real-time, large scale crop monitoring. To this end, the potential of multistatic and multi-frequency SAR for crop monitoring is assessed using experimental data, and methods are developed for GAI retrieval from SAR data, both alone and in conjunction with optical imagery. The results of these investigations suggest that further efforts should be made to integrate SAR remote sensing, either as a complement or entirely on its own, into current crop monitoring systems to improve their temporal resolution, timeliness, and overall reliability, thereby contributing to food security.

Jury Members

Prof. Pierre DEFOURNY (UCLouvain, Belgium), supervisor

Prof. Marnik VANCLOOSTER (UCLouvain, Belgium), chairperson

Prof. Xavier DRAYE (UCLouvain, Belgium), secretary

Dr. Dominique DERAUW (Liège space centre, Belgium)

Prof. Leila GUERRIERO (Tor Vergata University of Rome, Italy)

Public thesis defense of Camille GUISSET

"Climate and drought response of four non-native tree species in their area of introduction in Wallonia."

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Abstract

TBA

Jury Members

Prof. Quentin PONETTE (supervisor) – UCLouvain

Prof. Caroline VINCKE (supervisor) – UCLouvain

Prof. Emmanuel HANERT (chairperson) – UCLouvain

Prof. Nathalie BREDA – INRAE (France)

Prof. Xavier DRAYE– UCLouvain

Prof. Mathieu LEVESQUE – ETH Zurich (Suisse)

Public thesis defense of Céline LAMARCHE

"Assessing 29 years of global land cover dynamics from satellite Earth Observation"

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Abstract:

Land use and land cover change contribute significantly to anthropogenic CO2 emissions and biodiversity loss. However, current inventory-based statistics miss year-to-year land changes, preventing a comprehensive global understanding.

Earth observation by satellite provides valuable information for mapping global annual changes at the pixel level. Yet, consistency is crucial to capture change signals among variability from natural surface fluctuations or evolving satellite mission capabilities. In this thesis, we co-develop and evaluate the very first global annual land cover change time series at 300 m from 1992 to 2020, maintaining consistency across space, time and satellite missions. This dataset, currently used for Intergovernmental Panel on Climate Change (IPCC) climate modeling and Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) analysis, enables us to quantify and analyze the global dynamics of land cover change over the last 30 years.

This research also contributes to enhancing the qualification of land cover datasets. While validation guidelines are well-established for individual product assessment, we introduced a stratified random sampling method for product benchmarking, tailored to areas prone to discrepancies between products, to highlight the satellite product strengths and weaknesses. To improve climate and land surface, we enabled the conversion of land cover categories to plant functional types (PFT) composition per pixel. This was made possible thanks to the development of a globally applicable framework to seamlessly integrate multiple high-resolution datasets that might otherwise not be compatible.

Finally, we investigate the impact of uncertainty in Earth observation surface reflectance measurement on the categorical land cover classification process. Building on a Monte Carlo simulation, we quantify errors and propose a classification ensemble approach to effectively mitigate them.

This work contributes to more informed land accounting in the context of rapid anthropogenic change and climate evolution, supporting the assessment of the Food and Agriculture Organization (FAO) and Organization for Economic Co-operation and Development (OECD) environmental-economic accounting systems.

Jury members:

Prof. Pierre DEFOURNY (Supervisor)

Prof. Patrick BOGAERT (Secretary)

Dr. Gregory DUVEILLER (Max Planck Institute for Biochemistry, Germany)

Dr. Martin Stefan BRANDT (University of Copenhagen, Denmark)

Prof. Emmanuel HANERT (President)