Mr Pierre Gatel1, Dr Katell Quenea1, Mrs Sylvie Derenne1, Mr Manuel Nicolas2, Mrs violaine Lamoureux Var3, Mrs Isabelle Kowalewski3
1Sorbonne University, Paris, France, 2ONF, Fontainebleau, France, 3IFPEN, Rueil malmaison, France
Rock-Eval pyrolysis is a powerful technique developed for the rapid characterization of sedimentary organic matter (OM), based on its thermal reactivity. Originally designed for the study of petroleum rocks, Rock-Eval is increasingly used for soil OM characterization and more recently to assess its stability. The thermal reactivity of OM evaluated by Rock-Eval analysis could be influenced by its chemical composition, but also by interaction with minerals. It is thus necessary to take into account the soil characteristics to establish the potential of the Rock-Eval analysis to diagnose the thermal stability of soil OM in relation to their level of biodegradability and therefore their biological sensitivity. To this end, we have selected surface soil samples from the French national network for the long term monitoring of forest ecosystems. The selection comprises on the one hand, soil samples with similar amount of organic carbon content but with contrasting texture (sandy vs clayey), and on the other hand, samples exhibiting similar texture but differing in TOC content. Due to the higher level of chemical functions in soil OM with respect to sedimentary OM, the Rock-Eval parameters must be optimized. The effect of different heating rates and starting temperatures in Rock-Eval analysis on the commonly measured parameters (total organic carbon, hydrogen index and oxygen index) was first evaluated. Taken together, these analyses aimed at evaluating the influence of i) OM content, ii) texture and iii) forest litter chemical composition on Rock-Eval measured parameters and at providing a reliable protocol for soil OM analysis. Finally, in parallel to Rock-Eval pyrolysis, the released effluents have been directly characterized by GC /MS in an attempt to relate the Rock-Eval parameters to the molecular composition of the pyrolysed soil OM.
Quenea is assistant professor in geochemistry in Sorbonne University. She is a specialist in chemical characterisation of soil organic matter. She focused her research on the processes implied in organic matter stabilisation, and on the role of macrofauna on this stabilisation.