Public thesis defense of Maud HENRION

"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)

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