Developing hydrogeophysics for critical zone studies, importance of heterogeneities and processes at the mesoscopic scale
Creators: name: Damien, Jougnot
Publisher: name: Zenodo
Year: 2020
Subjects: Critical zone
Hydrogeophysics
Heterogeneous media
Petrophysics
Up-scaling

description: The critical zone is the thin outer layer supporting life on earth. It is a compartment in which many complex and coupled bio-chemico physical processes take place. Characterizing and monitoring these processes is of utmost importance to understand and protect the critical zone. Geophysical methods are very appropriate tools to study them in situ and non-intrusively thanks to the sensitivity of measurable physical parameters to properties of interest. However, the critical zone is also a very heterogeneous medium at different scales and the quantitative use of geophysics rely on our capability to take them into account effectively. In this manuscript I present the various works that I conducted during the last ten years to better use hydrogeophysical methods by taking heterogeneities into account: from theoretical petrophysical model developments to laboratory experiments and in situ monitoring in critical zone observatories. After presenting the geophysical methods I have been using, I define the concept of mesoscopic scale heterogeneities, that is: larger than the pore scale but smaller than the resolution of the considered geophysical method. The first heterogeneities that I present are related to the pore size distribution and its impact on the water saturation, flow and solute transport properties. The second heterogeneities that I study are the presence of fractures and fracture networks in porous media. The final kind of heterogeneities that I am considering are induced by local biogeochemical reactions and their impact on geophysical signals. These new advances and on-going research projects pave the way to a more quantitative and more integrated use of geophysics to study the critical zone in its true complexity.
description: This document is a dissertation to obtain the HDR (Habilitation à Diriger la Recherche), a french diploma for research and student supervision. I defended this degree on January 17 2020, at Sorbonne University, in Paris, in front of a Jury composed of Colette Siriex, Jean-François Girard, Frédéric Nguyen, Linda Luquot, and Valérie Plagne (president). The present manuscript synthesizes the research that I have been conducting during the last ten years (i.e., since the my PhD defense): during 5 years at University of Lausanne as a post-doc in the group of Niklas Linde and during 5 years at UMR 7619 METIS, Sorbonne Université, as a CNRS researcher. These investigations are the result of a collective work in close interaction with PhD students, postdocs, and researchers in my labs but also abroad. Indeed, in addition to my host institutions, I had the chance build up a network of fruitful national and international collaborations (Argentina, Belgium, Denmark, France, Germany, United States, Spain, Switzerland). More information about my research and links to my publications can be found on my website: https://sites.google.com/site/damienjougnot/