PhD position at IFP Energies nouvelles (IFPEN) and Sorbonne University (METIS): « Assessment of the stable soil organic carbon by Rock-Eval analysis »

So as to reduce the greenhouse gas emissions, new environmental measures would rapidly be taken. These future legal constraints led the scientists to consider the soil/atmosphere relationships and the ability of soil to durably store organic carbon. The organic carbon stock in soil results from the balance between the incoming flows, especially plant residues and organic amendment, and the outgoing flows associated with the soil microbial mineralization. As a result, the evolution of the carbon contents in soil will strongly depend on environmental conditions and on the mechanisms protecting the organic matter (OM) against this microbial degradation. In France, 3 to 4 billion tons of carbon are stored in the first 30 centimeters of soil.

Several kinetic compartments are commonly distinguished in soil OM based on their residence time, which ranges from year to decades and even millennia for the most stable fraction. This reflects differences in the efficiency of the microbial mineralization related to their interaction with minerals, leading either to mineralization (release of carbon) or stabilization (carbon storage).

In this context, assessing the stability of soil organic carbon (SOC) is a key challenge. To this end, a first step is the development of a standardized method to analyze the SOC stability. The Rock-Eval pyrolysis, a well-established technique in oil exploration, is now more and more used to characterize SOC and its biogeochemical stability. Recent studies show that this method is well suited to follow the amount and quality of SOC.

So far, Rock-Eval in soil science has been used through the adaptation of the analytical protocols used in oil industry without questioning some fundamental hypotheses. Soil OM being characterized by a large content of heteroelements (O and N), contrary to the sediment samples, their pyrolysis products are expected to be more thermally sensitive and it will be crucial to check their evolution as a function of temperature. In addition, it is well-known that minerals influence the thermal cracking of the sediment OM. The potential impact of the mineral matrix on the thermal cracking of the soil OM and thus on the Rock-Eval signal must therefore be quantified.

The aim of this PhD work is to validate a reference method based on Rock-Eval dedicated to soil, optimized to quantify the stable fraction of SOC. To this end, samples from soil representative of a large diversity of pedoclimatic conditions, mineralogical composition and organic content will be studied. This method should also precisely assess the quality and quantity of the organic carbon present in the soil OM fractions differing by their thermal stability as defined by Rock-Eval. To get a better insight in the soil OM, the molecular composition of the pyrolysis effluents will be determined. This characterization step is crucial to relate the thermal reactivity of the soil OM to its biological stability. Incubation experiments under controlled conditions measuring the potential of mineralization of the soil OM will be set up to substantiate our hypotheses on the stable SOC as a function of its thermal stability, molecular features and biodegradability. This experimental part should also allow relating the kinetics of mineralization to the Rock-Eval parameters. Finally, Rock-Eval criteria diagnostic for stable SOC should be proposed.

Keywords: Soil, Rock-Eval, Mineralisation activity, Organic matter, Persistent organic carbon, Biodegradation, climate challenge, Pyrolysis, Mineral Carbon, carbon storage, biogeochemical stability, incubation experiments

Academic supervisor Directeur de Recherche CNRS, Sylvie DERENNE, co-supervised with Katell Quénea, Assistant Professor at Paris-Sorbonne University. UMR CNRS 7619 METIS, Biogeochemistry Department,
Doctoral School 398 – Ecole Doctorale Geosciences et Ressources Naturelles, http://ed398.sorbonne-universite.fr/
IFPEN supervisor PhD. Kowalewski Isabelle, Georesssources Department, isabelle.kowalewski@ifpen.fr
PhD location IFP Energies nouvelles, Rueil-Malmaison and Université Paris Sorbonne, Paris (France).
Duration and start date 3 years, starting preferably on October 1, 2019
Employer IFP Energies nouvelles, Rueil-Malmaison, France
Academic requirements University Master degree in Geochemistry and inclination to laboratory in relevant disciplines
Language requirements Fluency in French or English, willingness to learn French
Other requirements analytical and microbiology skills and inclination to signal processing methods

For information or to submit an application, contact Sylvie.derenne@upmc.fr and isabelle.kowalewski@ifpen.fr

About IFP Energies nouvelles

IFP Energies nouvelles is a French public-sector research, innovation and training center. Its mission is to develop efficient, economical, clean and sustainable technologies in the fields of energy, transport and the environment. For more information, see www.ifpen.fr.

IFPEN offers a stimulating research environment, with access to first in class laboratory infrastructures and computing facilities. IFPEN offers competitive salary and benefits packages. All PhD students have access to dedicated seminars and training sessions.

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