the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Adjustments of the Rock-Eval® thermal analysis for soil organic and inorganic carbon quantification
Joséphine Hazera
David Sebag
Isabelle Kowalewski
Eric Verrecchia
Herman Ravelojaona
Tiphaine Chevallier
Abstract. Quantifying both soil organic and inorganic carbon (SOC & SIC) is essential to understand carbon (C) dynamics and to assess the atmospheric C sequestration potential in calcareous soils. The procedures usually used to quantify SOC and SIC involve pretreatments (decarbonation, decarbonatation) and calculation of the difference between C contents estimated by elemental analysis on raw and pretreated aliquots. These procedures lead to analytical bias associated to pretreatments, measurement deviations associated to the sample heterogeneity, and cumulative errors associated to calculations. The Rock-Eval® thermal analysis, used in soil sciences since the 2000s, provides two parameters estimating the organic (TOC) and inorganic (MinC) C contents of a non-pretreated aliquot with a single analysis. Nevertheless, the Rock-Eval® protocol has been standardized in the 70s by IFP Energies Nouvelles for studying oil bearing rocks and is, thus, not perfectly suited for soil study. Previous studies suggested statistical corrections of the standard parameters to improve their estimations of C contents assessed by elemental analysis but only few of them focused on the estimation of inorganic C content using the MinC parameter. Moreover, none of them suggested adjustments of the standard Rock-Eval® protocol. This study proposes to adapt this protocol to optimize SOC and SIC quantifications in soil samples. Comparisons between SOC and SIC quantifications by elemental analysis and by Rock-Eval®, with and without statistical corrections of the standard TOC and MinC parameters, were carried out on a soil panel with a wide range of SOC and SIC contents. The results show that the standard Rock-Eval® protocol properly estimates SOC contents once the TOC parameter is corrected. However, it cannot achieve a complete thermal breakdown of SIC amounts > 4 mg leading to an underestimation of high SIC contents by the MinC parameter, even after correcting it. Thus, the final oxidation isotherm is extended to 7 min to complete the thermal breakdown of SIC before the end of the analysis.
Joséphine Hazera et al.
Status: open (extended)
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CC1: 'Comment on bg-2023-66', Yakov Kuzyakov, 14 May 2023
reply
Review of the Manuscript:
Adjustments of the Rock-Eval® thermal analysis for soil organic and inorganic carbon quantification
submitted by Joséphine Hazera, David Sebag, Isabelle Kowalewski, Eric Verrecchia, Herman
Ravelojaona, Tiphaine Chevallier
for Biogeosciences
https://bg.copernicus.org/preprints/bg-2023-66/
Analysis of soil organic carbon (SOC) and soil inorganic carbon (SIC) from one sample without pretreatments is an urgent necessary and crucial procedure, about which many soil scientists, especially working in arid and semiarid environments are dreaming. Previously, the analysis of SOC and SIC was always after pretreatment with acid to remove SIC, and the SIC was calculated by the difference between total C and SOC. Various other approached to analyze SOC and SIC are mentioned in the Introduction, but all methods are based on a separate and subsequent analyses of SOC and SIC. These shortcomings are clearly mentioned in the Introduction. Beside the problems with assessment of any properties by difference, the pretreatment with acid may modify also the SOC leading to many uncertainties.
In the submitted paper, the authors adjusted the Rock-Eval® approach known from geology and petrology of the oil containing rocks to analyze SOC and SIC simultaneously. 24 soils covering broad range of SOC and SIC contents were used to test the Rock-Eval® approach. This methodical study is urgent necessary, and can be accepted after Minor improvements and some addition of the background information to the Rock-Eval® approach.
General comments
- The Introduction in the Abstract can be shortened, but instead more space can be used for the details of the new approach.
- Introduction provide a good overview about the methods for SOC and SIC analyses in calcareous soils.
- Figures are well prepared, but more details need to be explained in the legends of some Figs.
- The most Figures and Tables need more explanations.
- As the Rock-Eval® approach is/was not frequently used in soil science, the authors should provide a short background on the measurement principle, and which obstacles can be in soils compared to the initial applications in geology. It is also not clear / not known (at least for me) what are the shortcomings and potential problems of the Rock-Eval® approach?
- Temperature ranges: in various parts of the paper, different temperature ranges are used / presented to differentiate between SOC and SIC are used: 550, 650, 850, 1000 °C. This needs clarification and unification.
- The Rock-Eval® approach is a new method in soil science. I guess most soil scientists are not experienced with it (in contrast to EA, and other SOC & SIC analyses). Also the equipment necessary for the Rock-Eval® approach needs to be mentioned and in the final section the its applicability in soil science should be assessed, considering the equipment costs as well as the necessary standardization etc. Are the other soil properties, which can be well analyzed by Rock-Eval® in soils?
Specific remarks
L113-123 Please add explanations which C pools will be assessed by this ramping temperature increase
L250 the p value presented here is: 1.192 10-7, but in the Fig 4 it is 2.2 10-16. Please check. Actually, if the points for the Uncorrected TOC regression on Fig 4 are just multiplied with a fixed constant, the regressions for Corrected and Uncorrected TOC should be exactly the same.
Actually, all p values below 0.001 are the same. It is no matter is the p value 10-7 or 10-16.
L346 if the Rock-Eval® obtained results should be corrected by EA analyses, what is the actual advantage of Rock-Eval®?
Figures
Fig 1 Explanation of all abbreviations on the Figs is necessary.
Legend: … model of … scenarios. But not any scenarios are presented in Fig 1
Fig 5 the side figure-insets need more explanations
Figs 4, 6, 8: the presented measurement error – is this the 95% confidence interval, or the analytical measurement error of the equipment? If equipment – then for EA or for Rock-Eval®?
The individual points presented on Figs 4, 6, 8: are these means of some replications or individual measurements without replications? The regressions should be based on individual replications.
14.5.23
Citation: https://doi.org/10.5194/bg-2023-66-CC1
Joséphine Hazera et al.
Joséphine Hazera et al.
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