Monitoring organic matter dynamics in soil profiles by ‘Rock‐Eval pyrolysis’: bulk characterization and quantification of degradation

Abstract

SummaryRock-Eval pyrolysis was designed for petroleum exploration to determine the type and quality of organic matter in rock samples. Nevertheless, this technique can be used for bulk characterization of the immature organic matter in soil samples and recent sediments. We studied 76 samples from seven soil classes and showed that their pyrograms can be described by a combination of four elementary Gaussian components: F1, F2, F3 and F4. These four components are related to major classes of organic constituents differing in origin and their resistance to pyrolysis: labile biological constituents (F1), resistant biological constituents (F2), immature non-biotic constituents (F3) and a mature refractory fraction (F4). We discriminated the relative contributions of these components and used them to derive two indices: (i) to quantify the relative contributions of labile and resistant biological constituents and (ii) to quantify the degradation stage of the soil organic matter. The practical applications are illustrated via the influence of vegetal cover on soil organic matter dynamics and peat development in a Holocene sedimentary sequence, but we suggest that the approach is of much wider application.

Three-dimensional soil organic matter distribution, accessibility and microbial respiration in macroaggregates using osmium staining and synchrotron X-ray computed tomography

“…This may have been a dominant control on SHR, and we cannot account for it when we compare our measurements of SHR with the accessibility of OM in each aggregate. If similar studies are undertaken in future, it may be preferable to make more frequent measurements of headspace CO 2 concentrations over a more prolonged period and to establish the quantities of more labile organic matter in each aggregate using advanced analytical approaches (Sebag et al, 2006).…”

Tracking Holocene glacial and high-altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments (Lake Blanc Huez, Western French Alps)

“…Soils ( figure 5A) are defined by a lower degree of thermal maturity (Tmax<400°C). Superficial soil layers are described by HI superior to 300 mgHC.g -1 TOC, typical of non-alterated terrestrial debris (Sebag et al, 2005) and high organic content (TOC>10%), while deeper soil layers are defined both by lower HI values (around 200 mgHC.g -1 TOC), typical of the terrestrial pole (Simonneau et al, 2013b) and a lower TOC (7>TOC>2% figure 5A) and a variable TOC ranging between 8 and 0.4%.…”

Quantitative palynofacies analysis as a new tool to study transfers of fossil organic matter in recent terrestrial environments

“…Previously developed for petroleum purposes and the analysis of sedimentary rocks, the method has been now been successfully tested for recent material (Di-Giovanni et al, 1998;Disnar et al, 2003;Copard et al, 2006;Sebag et al, 2006c).…”