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.
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Joséphine Hazera et al.
Status: closed
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CC1: 'Comment on bg-2023-66', Yakov Kuzyakov, 14 May 2023
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 -
AC3: 'Reply on CC1', Joséphine Hazera, 18 Jul 2023
The authors would like to thank Yakov Kuzyakov for taking the time to make a review of this manuscript and for his useful and constructive comments. We agree on all of them, and we will take them into account. We appreciate that you consider, like us, SOC/SIC quantification as an important issue and think that this issue is clearly explained in the Introduction.
Considering the three comments made on this article, we plan to make several new analyses and statistical tests and to complete and/or reorganize several parts of this article to improve the manuscript. This will obviously take some time. We plan to provide you a revised manuscript and a detailed answer to your comments at the end of August.
In waiting, please find below the description of the planed modifications according to your comments:
- We will carefully check the formatting of the texts, figures and data presented in this article
- We will describe more the two methods used in this article: the Rock-Eval thermal analysis (C pool assessed by the ramping temperature increase, choose of the temperature boundaries in the two phases: pyrolysis and oxidation, calibration, corrections, advantages, and disadvantages) and the Elemental Analysis (pretreatment conditions)
We did not understand your second comment on the Figures “Legend: … model of … scenarios. But not any scenarios are presented in Fig 1”. Please, could you explain what are you calling scenarios?
Citation: https://doi.org/10.5194/bg-2023-66-AC3 -
AC1: 'Reply on RC1', Joséphine Hazera, 18 Jul 2023
The authors would like to thank the Anonymous Referee #1 for his/her careful reading and his/her useful and precise comments. We agree on all of them, and we will take them into account.
Considering the three comments made on this article, we plan to make several new analyses and statistical tests and to complete and/or reorganize several parts of this article to improve the manuscript. This will obviously take some time. We plan to provide you a revised manuscript and a detailed answer to your comments at the end of August.
In waiting, please find below the description of the planed modifications according to your comments:
- We will add information (soil type, texture, pH) on the soil samples of the first panel
- We will carefully check the formatting of the texts, figures and data presented in this article
- We will describe more the two methods used in this article: the Rock-Eval thermal analysis (choose of the temperature boundaries in the two phases: pyrolysis and oxidation, calibration, corrections, advantages, and disadvantages) and the Elemental Analysis (pretreatment conditions)
Considering your summary of our article and your comment 9, we would like to precise that, we compared the Rock-Eval values with pretreated Elemental Analysis values i.e., obtained after heating at 550°C for SIC and after HCl fumigation for SOC. We did not calculate the SOC content as TC-SIC, with TC measured from Elemental Analysis, in this paper. Only the Figure 8 compares the SIC estimated after heating at 550°C and Elemental Analysis with the SIC estimated as TC-SOC. We will make this point clearer in the next version of the manuscript.
Moreover, we compared the Rock-Eval® analysis with the Elemental Analysis because these two methods are based on the measure of the gases emitted by the sample oxidation (Elemental Analysis) or pyrolysis + oxidation (Rock-Eval®). We did not use the LOI because this method is based on the measure of the mass loss during the sample oxidation, which is not the case of the Rock-Eval® analysis. However, we agree with you, this comparison could be interesting to perform. The extra work needed to perform that comparison will be suggested in the revised version of the discussion.
Citation: https://doi.org/10.5194/bg-2023-66-AC1 - AC4: 'Reply on CC1', Joséphine Hazera, 12 Sep 2023
- AC7: 'Reply on CC1', Joséphine Hazera, 18 Sep 2023
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RC1: 'Comment on bg-2023-66', Anonymous Referee #1, 06 Jun 2023
Review of the Manuscript:
Adjustments of the Rock-Eval® thermal analysis for soil organic and inorganic carbon quantification
This study presents a methodological protocol to determine soil organic content and soil inorganic content. Using Rock-Eval thermal analysis offers some benefits over Elemental analysis method, where the SOC is estimated by the difference between Total Soil Carbon and SIC. Rock Eval eliminates the chances of calculation error, and experimental error associated with the EA method.
Comments:
- In general, the formatting needs to be checked. Chemical formula should be written with proper subscript, and units should be given with proper superscript and subscript.
- Material-The soil type for the 24 samples should be mentioned. This will help to establish the effectiveness of using RE for different soil types.
- Sec 2.2.1: which acid was used for acid treatment?
- L105: The authors need to provide a justification on why no replicates were conducted.
- Figure 1: message from figure not adequate. What is S, S2. Why these temperature ranges were selected. The denotations for S-S3 appears later in the text, but it should be given at the first instance of their appearance.
- What is the purity of the nitrogen used?
- L125: The author must specify how these thermograms correlate to SIC and SOC (As mentioned later in Table1).As a reader it’s not directly given and needs to be inferred.
- L165: I appreciate that the author has taken the recalcitrant carbon into account.
- Figure 4: why EA was selected for comparison? Since SOC is estimated by the difference between TC and TIC, TOC is an estimate, as mentioned in the introduction. Shouldn’t LOI method come here? Please provide a solid justification for the use of EA. Rather TC from EA and TC from RE could have been co-related.
- p values should be denoted as p<0.001 for all numbers less than 0.001.
- Table 2: what is the p-value for these numbers? 12±20 seems statistically insignificant.
Citation: https://doi.org/10.5194/bg-2023-66-RC1 -
AC1: 'Reply on RC1', Joséphine Hazera, 18 Jul 2023
The authors would like to thank the Anonymous Referee #1 for his/her careful reading and his/her useful and precise comments. We agree on all of them, and we will take them into account.
Considering the three comments made on this article, we plan to make several new analyses and statistical tests and to complete and/or reorganize several parts of this article to improve the manuscript. This will obviously take some time. We plan to provide you a revised manuscript and a detailed answer to your comments at the end of August.
In waiting, please find below the description of the planed modifications according to your comments:
- We will add information (soil type, texture, pH) on the soil samples of the first panel
- We will carefully check the formatting of the texts, figures and data presented in this article
- We will describe more the two methods used in this article: the Rock-Eval thermal analysis (choose of the temperature boundaries in the two phases: pyrolysis and oxidation, calibration, corrections, advantages, and disadvantages) and the Elemental Analysis (pretreatment conditions)
Considering your summary of our article and your comment 9, we would like to precise that, we compared the Rock-Eval values with pretreated Elemental Analysis values i.e., obtained after heating at 550°C for SIC and after HCl fumigation for SOC. We did not calculate the SOC content as TC-SIC, with TC measured from Elemental Analysis, in this paper. Only the Figure 8 compares the SIC estimated after heating at 550°C and Elemental Analysis with the SIC estimated as TC-SOC. We will make this point clearer in the next version of the manuscript.
Moreover, we compared the Rock-Eval® analysis with the Elemental Analysis because these two methods are based on the measure of the gases emitted by the sample oxidation (Elemental Analysis) or pyrolysis + oxidation (Rock-Eval®). We did not use the LOI because this method is based on the measure of the mass loss during the sample oxidation, which is not the case of the Rock-Eval® analysis. However, we agree with you, this comparison could be interesting to perform. The extra work needed to perform that comparison will be suggested in the revised version of the discussion.
Citation: https://doi.org/10.5194/bg-2023-66-AC1 - AC5: 'Reply on RC1', Joséphine Hazera, 12 Sep 2023
- AC8: 'Reply on RC1', Joséphine Hazera, 18 Sep 2023
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RC2: 'Comment on bg-2023-66', Anonymous Referee #2, 27 Jun 2023
The study by Hazera et al. is a methodological manuscript dealing with the quantification of total carbon (TC), soil organic carbon (SOC), and soil inorganic carbon (SIC) in single analysis with the Rock-Eval6 method (RE). The proposed method is compared against the standard method using an elemental analyzer (EA) combined with acid fumigation or heating. The main conclusion by the authors is a necessary adjustment of the standard protocol to ensure complete combustion of SIC by increasing the last isotherm from 4 to 7 minutes.
The scientific significance itself is excellent, as RE offers the advantage to derive additional properties of SOC. Advancing the method, so that TC, SOC and some of its properties, as well as SIC could be measured in a single run would be an excellent methodological step forward.
However, as methodological work requires a very high standard, I have some reservations regarding the scientific quality of the description or application of the methods. As it is, I judge the scientific quality as “Fair”, but I hope the authors can amend their manuscript further. Please find some comments and questions in the paragraphs below.
Overall, I guess that addressing the major comments below would need additional work and analysis. This will take some time. If the authors and editors agree, I suggest the following major change to the manuscript: In my opinion, there are several topics which are addressed more in a “work-in-progress” way. The main conclusion, however, is the necessary prolongation of the last isotherm. By significantly cutting the word count it would be an alternative to focus on the topic of the last isotherm and change the “Research Article” into a “Technical Note”. This would mean to focus on the second panel of samples, for which I can see convincing results.
P.S.: After writing this review, I found the poster of Sebag et al. (2022, DOI: 10.13140/RG.2.2.27606.52800). Using the presented datasets or getting samples and re-analyzing them would render several of my comments unnecessary. Please justify why this large dataset was not used here.
General comments:
Number and range of samples
For a methodological study the number of samples (n = 24) is relatively low. Moreover, the samples are all (1) from agricultural soils, and (2) topsoil samples. Therefore, all results are strictly only valid for this limited sample set. This is discussed in the conclusion (see also “conversion factors” below), but should also be mentioned clearly in the Abstract and Discussion.
There is also no description of soil sample properties. At least, the range of TC (measured by EA) and a corresponding pH value should be given. It is also not clear if all soils contain carbonates. From Results & Discussion I suspect that all samples contained carbonate. It is highly preferable to mix some samples without carbonates into the set to show that these carbonate-free samples do not show any (or only the stated 9.2%) signal in the “MinC” range. It might even be a good idea to treat these carbonate-free samples exactly as the carbonaceous samples (muffle oven, acid pre-treatment) to show caveats of these methods.
There was only one sample of “natural calcite”. The description must be expanded. Was it taken from carbonaceous rock? If yes, which kind of rock? Calcite is also available as certified standard material and for methodological work, this should be preferred over a natural sample with unknown properties (e.g. purity, presence of other carbonates such as dolomite or magnesite, presence of traces of organic matter).
Precision and accuracy
In methodological studies two measures are essential, that is “precision” and “accuracy” (sometimes termed “bias”). EA, for example, is widely accepted as a standard method because it is both accurate (i.e. measures the true value) and precise (i.e. repeated measurements are very close to each other). The manuscript presents some indications for accuracy, but none for precision. A quantification of precision and accuracy often starts by using reproducible standard materials, which should be mixed together, and measured in replication. Bisutti et al. (2007) provide an excellent example for this. Vuong et al. (2013), for example, offer simple methods to compare precision and accuracy with well-known F- and t-tests.
Accuracy in the manuscript is quantified by linear regression. It is a very good start that not only R² is given, and there is more emphasis on the slope. However, I wonder (1) why no intercept is presented (I do hope the regression was not forced through zero, please confirm), and (2) why there is no measure of dispersion (e.g. standard error, confidence interval) for slope and intercept. The dispersion of the regression parameters is important to know. Moreover, the authors present the p-value for the regression, which is correctly interpreted as the probability that the slope differs from 0. In this case this is not of interest. We have to know if the slope is different from 1 to judge if methods correspond with each other. This is addressed in the text, but should also integrated into the figures. Furthermore, a large error of intercept or slope will indicate low precision. Do not only look on significances, but also on variability. With high variability, the difference to 0 or 1 will be insignificant, but the high error may render the method unsuitable for routine analysis.
Use of certified standard materials and device calibration
The use of reproducible standard material is highly encouraged. The readers also must be informed about the calibration of all involved devices; including calibration range, precision, and accuracy. There is some information about the assumed relative error, but the authors need to show this data.
Conversion factors
First of all, I wonder why the authors gave a constant conversion factor, whereas Disnar et al (2003) provided a regression function for correction [this information was taken from Saenger et al. 2013, as I have no access to the manuscript of Disnar et al. 2003, so please correct me if I am wrong].
It is especially important, that the conversion factor (SOTHIS) was stated to be valid for samples “enriched in poorly degraded organic compounds (…)”. In the used sample set the conversion factors seem to work well. However, to really establish the RE method it will be important to ensure that the method works well on a continuum of organic matter states. That is, from the litter, fermented, and humified forest floor layers down the profile of mineral soil. Conditions change through the profile from largely undecomposed to largely decomposed and mineral associated organic matter, often accompanied by a gradient of increasing carbonate content. It seems likely, the “standard” conversion factors will not work for all these conditions. And it is open to question at which depth the “additional 6.2%” shall be applied. Therefore, this will be important future work to address these conversion factors, or possibly change isotherm length or temperature settings.
SOTHIS as presented here seems to be a mixture between Disnar et al. (2003) and Sebag et al. (2022). The latter is a poster, a peer-reviewed source or the actual data would be preferable.
Use of two different devices and settings
LL 117 ff. The authors used devices from different labs, with slightly different settings. They state that “The minor differences between the standard cycles […] do not affect parameter calculations”. This may be so, but it has to be demonstrated with some samples. Overall, it would be essential to develop the method in one lab, using the same device with the same calibration, and after that set up a ring trial with different labs (inter-lab reproducibility).
Additional literature
I suggest to take a look on some additional work in the field of measuring SOC, SIC and TC in a single run (Bisutti et al., 2007; Vuong et al., 2016, 2013). Those references did not use RE, but offer some methodological examples. Bisutti et al. (2007) made excessive use of different material mixtures, which can be reproduced. Vuong et al. (2013) gave an example how to quantify precision and bias on a wider range of soil samples and calcite standard (though it would have been better to add an organic matter standard, and mix it with calcite). Vuong et al. (2016) advance the former work by using dolomite, not only calcite. Although on marine sediments, the work of Carrie et al. (2012) should be recognized, as they already divide RE peaks into OC and IC and discuss some methodological issues, which may be relevant for some special soil conditions (e.g. saline soils).
Additionally, Saenger et al. (2013) conclude that SOC (soil samples of different land use) can be quantified well with help of the correction provided by Disnard et al. (2003). Soucémarianadin et al. (2018 a; 2018 b) provide some insight on the potential for SOC fractionation – which gives reasoning why RE should be advanced in regards of SIC quantification.
Bisutti, I., Hilke, I., Schumacher, J., Raessler, M., 2007. A novel single-run dual temperature combustion (SRDTC) method for the determination of organic, in-organic and total carbon in soil samples. Talanta 71, 521–528. https://doi.org/10.1016/j.talanta.2006.04.022
Carrie, J., Sanei, H., Stern, G., 2012. Standardisation of Rock–Eval pyrolysis for the analysis of recent sediments and soils. Org. Geochem. 46, 38–53. https://doi.org/10.1016/j.orggeochem.2012.01.011
Saenger, A., Cécillon, L., Sebag, D., Brun, J.-J., 2013. Soil organic carbon quantity, chemistry and thermal stability in a mountainous landscape: A Rock–Eval pyrolysis survey. Org. Geochem. 54, 101–114. https://doi.org/10.1016/j.orggeochem.2012.10.008
Soucémarianadin, L., Cécillon, L., Chenu, C., Baudin, F., Nicolas, M., Girardin, C., Barré, P., 2018 a. Is Rock-Eval 6 thermal analysis a good indicator of soil organic carbon lability? – A method-comparison study in forest soils. Soil Biol. Biochem. 117, 108–116. https://doi.org/10.1016/j.soilbio.2017.10.025
Soucémarianadin, L.N., Cécillon, L., Guenet, B., Chenu, C., Baudin, F., Nicolas, M., Girardin, C., Barré, P., 2018 b. Environmental factors controlling soil organic carbon stability in French forest soils. Plant Soil 426, 267–286. https://doi.org/10.1007/s11104-018-3613-x
Vuong, T.X., Heitkamp, F., Jungkunst, H.F., Reimer, A., Gerold, G., 2013. Simultaneous measurement of soil organic and inorganic carbon: evaluation of a thermal gradient analysis. J. Soils Sediments 13, 1133–1140. https://doi.org/10.1007/s11368-013-0715-1
Vuong, T.X., Prietzel, J., Heitkamp, F., 2016. Measurement of organic and inorganic carbon in dolomite-containing samples. Soil Use Manag. 32, 53–59. https://doi.org/10.1111/sum.12233
Specific comments:
This is not exhaustive due to the suggestion to change the manuscript into a Technical Note. As a non-native speaker, I refrain from language editing.
Some of the figures need more precise explanations. As a guideline, figures should be interpretable without referring to the text.
Figures show very different dimensions. This could be streamlined. As a guideline, text should be approximately of the same size in all figures
Ll 96: At which temperature were the samples dried?
Ll 100 ff: Were samples corrected for residual moisture (105°C)? Overall, more methodological details are neede. Which acid was used? Molarity? General conditions, such vacuum etc. Even if Harris et al. (2001) was followed exactly, please provide some details. The same applies to heating.
L 143: The temperature was shifted to be consistent with the decarbonation treatment. However, decarbonation was likely performed in ambient air, pyrolysis without oxygen. Therefore conditions are not comparable. Please justify the shift from 400°C/local minimum to 550°C and estimate the consequences.
L199: As treated samples were used, I would prefer an indication, e.g. EAdecarb
L 247: “…are correlated (R² = 0.9935…” please use the term “related” as “correlated” is used for Spearmen or Pearson correlation coefficient
Figure 5 and text ll 263 ff: This is a good example, why reporting an intercept for the regression is useful. It also demonstrates the issue when correcting values with a fixed factor instead of of a regression (see “Conversion factors” above). Please discuss these consequences.
Table 2, column S3’CO2 MinC: 12+/-20 does not seem to be a reliable estimate. This should be addressed
Ll323 ff, Figure 8: This finding indicates, that including carbonate-free soil samples in the test may be a good idea.
Ll 340 ff: Would it be possible to prolongate the last phase even further? What does this finding mean for more thermostable carbonates?
Ll 351: If the SIC content is known, what is the advantage of the RE method?
Ll 356: Please indicate that further work on a wider range of samples and with different forms of carbonates is needed.
Citation: https://doi.org/10.5194/bg-2023-66-RC2 -
AC2: 'Reply on RC2', Joséphine Hazera, 18 Jul 2023
The authors would like to thank the Anonymous Referee #2 for his/her attentive reading and his/her numerous, useful, and constructive comments. We agree on most of them, and we will take them into account.
Considering the three comments made on this article, we plan to make several new analyses and statistical tests and to complete and/or reorganize several parts of this article to improve the manuscript. This will obviously take some time. We plan to provide you a revised manuscript and a detailed answer to your comments at the end of August.
In waiting, please find below the description of the planed modifications according to your comments:
- We will add several samples and 3 standard materials (two standards of soil: ERMCC690 from the European Commission – Joint Research Center and ISE850 from the Wepal International Soil-analytical Exchange Program and one well-known standard of rock: SR1 from the Norwegian Geochemical Standard) to the first panel.
- The precision of the Rock-Eval® method will be assessed by replicating 4 times the three standard materials. The precision of the Rock-Eval® method will be assessed by comparing these values with Elemental Analysis (4 replicates) estimating the SOC after HCl and estimating the SIC after heating at 550°C
- To avoid any confusion, the first panel will be analyzed with the Rock-Eval6 device of IFPEN with a constant amount of soil (70 mg).
- We will add information (soil type, texture, pH) on the soil samples of the first panel
- We will add more data on the calcite material (DRX result and thermograms in Supplementary Material and contributions of each curve integration to the TOC and MinC parameters in the Table 2)
- We will highlight and add more data on the 4 carbonate-free samples of the first panel (thermograms in Material & Methods and contributions of each curve integration to the TOC and MinC parameters in the Table 2)
- We will carefully check the formatting of the texts, figures and data presented in this article
- We will describe more the two methods used in this article: the Rock-Eval thermal analysis (choose of the temperature boundaries in the two phases: pyrolysis and oxidation, calibration, corrections, advantages, and disadvantages) and the Elemental Analysis (pretreatment conditions)
- We will put more efforts on the statistic. Thank you very much for your advice. We will present the regressions with intercept, add the variability of the regression slopes and intercepts and compare the slopes to 1
- We will study the bibliography you give us and, possibly integrate them in the bibliography of the article
Considering the number of elements we plan to add, we think that shortening the manuscript to few pages to transform it into a technical note might curtail the understanding by future readers. We would like to keep the Research Article format if you agree.
Citation: https://doi.org/10.5194/bg-2023-66-AC2 - AC6: 'Reply on RC2', Joséphine Hazera, 12 Sep 2023
- AC9: 'Reply on RC2', Joséphine Hazera, 18 Sep 2023
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AC2: 'Reply on RC2', Joséphine Hazera, 18 Jul 2023
Status: closed
-
CC1: 'Comment on bg-2023-66', Yakov Kuzyakov, 14 May 2023
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 -
AC3: 'Reply on CC1', Joséphine Hazera, 18 Jul 2023
The authors would like to thank Yakov Kuzyakov for taking the time to make a review of this manuscript and for his useful and constructive comments. We agree on all of them, and we will take them into account. We appreciate that you consider, like us, SOC/SIC quantification as an important issue and think that this issue is clearly explained in the Introduction.
Considering the three comments made on this article, we plan to make several new analyses and statistical tests and to complete and/or reorganize several parts of this article to improve the manuscript. This will obviously take some time. We plan to provide you a revised manuscript and a detailed answer to your comments at the end of August.
In waiting, please find below the description of the planed modifications according to your comments:
- We will carefully check the formatting of the texts, figures and data presented in this article
- We will describe more the two methods used in this article: the Rock-Eval thermal analysis (C pool assessed by the ramping temperature increase, choose of the temperature boundaries in the two phases: pyrolysis and oxidation, calibration, corrections, advantages, and disadvantages) and the Elemental Analysis (pretreatment conditions)
We did not understand your second comment on the Figures “Legend: … model of … scenarios. But not any scenarios are presented in Fig 1”. Please, could you explain what are you calling scenarios?
Citation: https://doi.org/10.5194/bg-2023-66-AC3 -
AC1: 'Reply on RC1', Joséphine Hazera, 18 Jul 2023
The authors would like to thank the Anonymous Referee #1 for his/her careful reading and his/her useful and precise comments. We agree on all of them, and we will take them into account.
Considering the three comments made on this article, we plan to make several new analyses and statistical tests and to complete and/or reorganize several parts of this article to improve the manuscript. This will obviously take some time. We plan to provide you a revised manuscript and a detailed answer to your comments at the end of August.
In waiting, please find below the description of the planed modifications according to your comments:
- We will add information (soil type, texture, pH) on the soil samples of the first panel
- We will carefully check the formatting of the texts, figures and data presented in this article
- We will describe more the two methods used in this article: the Rock-Eval thermal analysis (choose of the temperature boundaries in the two phases: pyrolysis and oxidation, calibration, corrections, advantages, and disadvantages) and the Elemental Analysis (pretreatment conditions)
Considering your summary of our article and your comment 9, we would like to precise that, we compared the Rock-Eval values with pretreated Elemental Analysis values i.e., obtained after heating at 550°C for SIC and after HCl fumigation for SOC. We did not calculate the SOC content as TC-SIC, with TC measured from Elemental Analysis, in this paper. Only the Figure 8 compares the SIC estimated after heating at 550°C and Elemental Analysis with the SIC estimated as TC-SOC. We will make this point clearer in the next version of the manuscript.
Moreover, we compared the Rock-Eval® analysis with the Elemental Analysis because these two methods are based on the measure of the gases emitted by the sample oxidation (Elemental Analysis) or pyrolysis + oxidation (Rock-Eval®). We did not use the LOI because this method is based on the measure of the mass loss during the sample oxidation, which is not the case of the Rock-Eval® analysis. However, we agree with you, this comparison could be interesting to perform. The extra work needed to perform that comparison will be suggested in the revised version of the discussion.
Citation: https://doi.org/10.5194/bg-2023-66-AC1 - AC4: 'Reply on CC1', Joséphine Hazera, 12 Sep 2023
- AC7: 'Reply on CC1', Joséphine Hazera, 18 Sep 2023
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RC1: 'Comment on bg-2023-66', Anonymous Referee #1, 06 Jun 2023
Review of the Manuscript:
Adjustments of the Rock-Eval® thermal analysis for soil organic and inorganic carbon quantification
This study presents a methodological protocol to determine soil organic content and soil inorganic content. Using Rock-Eval thermal analysis offers some benefits over Elemental analysis method, where the SOC is estimated by the difference between Total Soil Carbon and SIC. Rock Eval eliminates the chances of calculation error, and experimental error associated with the EA method.
Comments:
- In general, the formatting needs to be checked. Chemical formula should be written with proper subscript, and units should be given with proper superscript and subscript.
- Material-The soil type for the 24 samples should be mentioned. This will help to establish the effectiveness of using RE for different soil types.
- Sec 2.2.1: which acid was used for acid treatment?
- L105: The authors need to provide a justification on why no replicates were conducted.
- Figure 1: message from figure not adequate. What is S, S2. Why these temperature ranges were selected. The denotations for S-S3 appears later in the text, but it should be given at the first instance of their appearance.
- What is the purity of the nitrogen used?
- L125: The author must specify how these thermograms correlate to SIC and SOC (As mentioned later in Table1).As a reader it’s not directly given and needs to be inferred.
- L165: I appreciate that the author has taken the recalcitrant carbon into account.
- Figure 4: why EA was selected for comparison? Since SOC is estimated by the difference between TC and TIC, TOC is an estimate, as mentioned in the introduction. Shouldn’t LOI method come here? Please provide a solid justification for the use of EA. Rather TC from EA and TC from RE could have been co-related.
- p values should be denoted as p<0.001 for all numbers less than 0.001.
- Table 2: what is the p-value for these numbers? 12±20 seems statistically insignificant.
Citation: https://doi.org/10.5194/bg-2023-66-RC1 -
AC1: 'Reply on RC1', Joséphine Hazera, 18 Jul 2023
The authors would like to thank the Anonymous Referee #1 for his/her careful reading and his/her useful and precise comments. We agree on all of them, and we will take them into account.
Considering the three comments made on this article, we plan to make several new analyses and statistical tests and to complete and/or reorganize several parts of this article to improve the manuscript. This will obviously take some time. We plan to provide you a revised manuscript and a detailed answer to your comments at the end of August.
In waiting, please find below the description of the planed modifications according to your comments:
- We will add information (soil type, texture, pH) on the soil samples of the first panel
- We will carefully check the formatting of the texts, figures and data presented in this article
- We will describe more the two methods used in this article: the Rock-Eval thermal analysis (choose of the temperature boundaries in the two phases: pyrolysis and oxidation, calibration, corrections, advantages, and disadvantages) and the Elemental Analysis (pretreatment conditions)
Considering your summary of our article and your comment 9, we would like to precise that, we compared the Rock-Eval values with pretreated Elemental Analysis values i.e., obtained after heating at 550°C for SIC and after HCl fumigation for SOC. We did not calculate the SOC content as TC-SIC, with TC measured from Elemental Analysis, in this paper. Only the Figure 8 compares the SIC estimated after heating at 550°C and Elemental Analysis with the SIC estimated as TC-SOC. We will make this point clearer in the next version of the manuscript.
Moreover, we compared the Rock-Eval® analysis with the Elemental Analysis because these two methods are based on the measure of the gases emitted by the sample oxidation (Elemental Analysis) or pyrolysis + oxidation (Rock-Eval®). We did not use the LOI because this method is based on the measure of the mass loss during the sample oxidation, which is not the case of the Rock-Eval® analysis. However, we agree with you, this comparison could be interesting to perform. The extra work needed to perform that comparison will be suggested in the revised version of the discussion.
Citation: https://doi.org/10.5194/bg-2023-66-AC1 - AC5: 'Reply on RC1', Joséphine Hazera, 12 Sep 2023
- AC8: 'Reply on RC1', Joséphine Hazera, 18 Sep 2023
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RC2: 'Comment on bg-2023-66', Anonymous Referee #2, 27 Jun 2023
The study by Hazera et al. is a methodological manuscript dealing with the quantification of total carbon (TC), soil organic carbon (SOC), and soil inorganic carbon (SIC) in single analysis with the Rock-Eval6 method (RE). The proposed method is compared against the standard method using an elemental analyzer (EA) combined with acid fumigation or heating. The main conclusion by the authors is a necessary adjustment of the standard protocol to ensure complete combustion of SIC by increasing the last isotherm from 4 to 7 minutes.
The scientific significance itself is excellent, as RE offers the advantage to derive additional properties of SOC. Advancing the method, so that TC, SOC and some of its properties, as well as SIC could be measured in a single run would be an excellent methodological step forward.
However, as methodological work requires a very high standard, I have some reservations regarding the scientific quality of the description or application of the methods. As it is, I judge the scientific quality as “Fair”, but I hope the authors can amend their manuscript further. Please find some comments and questions in the paragraphs below.
Overall, I guess that addressing the major comments below would need additional work and analysis. This will take some time. If the authors and editors agree, I suggest the following major change to the manuscript: In my opinion, there are several topics which are addressed more in a “work-in-progress” way. The main conclusion, however, is the necessary prolongation of the last isotherm. By significantly cutting the word count it would be an alternative to focus on the topic of the last isotherm and change the “Research Article” into a “Technical Note”. This would mean to focus on the second panel of samples, for which I can see convincing results.
P.S.: After writing this review, I found the poster of Sebag et al. (2022, DOI: 10.13140/RG.2.2.27606.52800). Using the presented datasets or getting samples and re-analyzing them would render several of my comments unnecessary. Please justify why this large dataset was not used here.
General comments:
Number and range of samples
For a methodological study the number of samples (n = 24) is relatively low. Moreover, the samples are all (1) from agricultural soils, and (2) topsoil samples. Therefore, all results are strictly only valid for this limited sample set. This is discussed in the conclusion (see also “conversion factors” below), but should also be mentioned clearly in the Abstract and Discussion.
There is also no description of soil sample properties. At least, the range of TC (measured by EA) and a corresponding pH value should be given. It is also not clear if all soils contain carbonates. From Results & Discussion I suspect that all samples contained carbonate. It is highly preferable to mix some samples without carbonates into the set to show that these carbonate-free samples do not show any (or only the stated 9.2%) signal in the “MinC” range. It might even be a good idea to treat these carbonate-free samples exactly as the carbonaceous samples (muffle oven, acid pre-treatment) to show caveats of these methods.
There was only one sample of “natural calcite”. The description must be expanded. Was it taken from carbonaceous rock? If yes, which kind of rock? Calcite is also available as certified standard material and for methodological work, this should be preferred over a natural sample with unknown properties (e.g. purity, presence of other carbonates such as dolomite or magnesite, presence of traces of organic matter).
Precision and accuracy
In methodological studies two measures are essential, that is “precision” and “accuracy” (sometimes termed “bias”). EA, for example, is widely accepted as a standard method because it is both accurate (i.e. measures the true value) and precise (i.e. repeated measurements are very close to each other). The manuscript presents some indications for accuracy, but none for precision. A quantification of precision and accuracy often starts by using reproducible standard materials, which should be mixed together, and measured in replication. Bisutti et al. (2007) provide an excellent example for this. Vuong et al. (2013), for example, offer simple methods to compare precision and accuracy with well-known F- and t-tests.
Accuracy in the manuscript is quantified by linear regression. It is a very good start that not only R² is given, and there is more emphasis on the slope. However, I wonder (1) why no intercept is presented (I do hope the regression was not forced through zero, please confirm), and (2) why there is no measure of dispersion (e.g. standard error, confidence interval) for slope and intercept. The dispersion of the regression parameters is important to know. Moreover, the authors present the p-value for the regression, which is correctly interpreted as the probability that the slope differs from 0. In this case this is not of interest. We have to know if the slope is different from 1 to judge if methods correspond with each other. This is addressed in the text, but should also integrated into the figures. Furthermore, a large error of intercept or slope will indicate low precision. Do not only look on significances, but also on variability. With high variability, the difference to 0 or 1 will be insignificant, but the high error may render the method unsuitable for routine analysis.
Use of certified standard materials and device calibration
The use of reproducible standard material is highly encouraged. The readers also must be informed about the calibration of all involved devices; including calibration range, precision, and accuracy. There is some information about the assumed relative error, but the authors need to show this data.
Conversion factors
First of all, I wonder why the authors gave a constant conversion factor, whereas Disnar et al (2003) provided a regression function for correction [this information was taken from Saenger et al. 2013, as I have no access to the manuscript of Disnar et al. 2003, so please correct me if I am wrong].
It is especially important, that the conversion factor (SOTHIS) was stated to be valid for samples “enriched in poorly degraded organic compounds (…)”. In the used sample set the conversion factors seem to work well. However, to really establish the RE method it will be important to ensure that the method works well on a continuum of organic matter states. That is, from the litter, fermented, and humified forest floor layers down the profile of mineral soil. Conditions change through the profile from largely undecomposed to largely decomposed and mineral associated organic matter, often accompanied by a gradient of increasing carbonate content. It seems likely, the “standard” conversion factors will not work for all these conditions. And it is open to question at which depth the “additional 6.2%” shall be applied. Therefore, this will be important future work to address these conversion factors, or possibly change isotherm length or temperature settings.
SOTHIS as presented here seems to be a mixture between Disnar et al. (2003) and Sebag et al. (2022). The latter is a poster, a peer-reviewed source or the actual data would be preferable.
Use of two different devices and settings
LL 117 ff. The authors used devices from different labs, with slightly different settings. They state that “The minor differences between the standard cycles […] do not affect parameter calculations”. This may be so, but it has to be demonstrated with some samples. Overall, it would be essential to develop the method in one lab, using the same device with the same calibration, and after that set up a ring trial with different labs (inter-lab reproducibility).
Additional literature
I suggest to take a look on some additional work in the field of measuring SOC, SIC and TC in a single run (Bisutti et al., 2007; Vuong et al., 2016, 2013). Those references did not use RE, but offer some methodological examples. Bisutti et al. (2007) made excessive use of different material mixtures, which can be reproduced. Vuong et al. (2013) gave an example how to quantify precision and bias on a wider range of soil samples and calcite standard (though it would have been better to add an organic matter standard, and mix it with calcite). Vuong et al. (2016) advance the former work by using dolomite, not only calcite. Although on marine sediments, the work of Carrie et al. (2012) should be recognized, as they already divide RE peaks into OC and IC and discuss some methodological issues, which may be relevant for some special soil conditions (e.g. saline soils).
Additionally, Saenger et al. (2013) conclude that SOC (soil samples of different land use) can be quantified well with help of the correction provided by Disnard et al. (2003). Soucémarianadin et al. (2018 a; 2018 b) provide some insight on the potential for SOC fractionation – which gives reasoning why RE should be advanced in regards of SIC quantification.
Bisutti, I., Hilke, I., Schumacher, J., Raessler, M., 2007. A novel single-run dual temperature combustion (SRDTC) method for the determination of organic, in-organic and total carbon in soil samples. Talanta 71, 521–528. https://doi.org/10.1016/j.talanta.2006.04.022
Carrie, J., Sanei, H., Stern, G., 2012. Standardisation of Rock–Eval pyrolysis for the analysis of recent sediments and soils. Org. Geochem. 46, 38–53. https://doi.org/10.1016/j.orggeochem.2012.01.011
Saenger, A., Cécillon, L., Sebag, D., Brun, J.-J., 2013. Soil organic carbon quantity, chemistry and thermal stability in a mountainous landscape: A Rock–Eval pyrolysis survey. Org. Geochem. 54, 101–114. https://doi.org/10.1016/j.orggeochem.2012.10.008
Soucémarianadin, L., Cécillon, L., Chenu, C., Baudin, F., Nicolas, M., Girardin, C., Barré, P., 2018 a. Is Rock-Eval 6 thermal analysis a good indicator of soil organic carbon lability? – A method-comparison study in forest soils. Soil Biol. Biochem. 117, 108–116. https://doi.org/10.1016/j.soilbio.2017.10.025
Soucémarianadin, L.N., Cécillon, L., Guenet, B., Chenu, C., Baudin, F., Nicolas, M., Girardin, C., Barré, P., 2018 b. Environmental factors controlling soil organic carbon stability in French forest soils. Plant Soil 426, 267–286. https://doi.org/10.1007/s11104-018-3613-x
Vuong, T.X., Heitkamp, F., Jungkunst, H.F., Reimer, A., Gerold, G., 2013. Simultaneous measurement of soil organic and inorganic carbon: evaluation of a thermal gradient analysis. J. Soils Sediments 13, 1133–1140. https://doi.org/10.1007/s11368-013-0715-1
Vuong, T.X., Prietzel, J., Heitkamp, F., 2016. Measurement of organic and inorganic carbon in dolomite-containing samples. Soil Use Manag. 32, 53–59. https://doi.org/10.1111/sum.12233
Specific comments:
This is not exhaustive due to the suggestion to change the manuscript into a Technical Note. As a non-native speaker, I refrain from language editing.
Some of the figures need more precise explanations. As a guideline, figures should be interpretable without referring to the text.
Figures show very different dimensions. This could be streamlined. As a guideline, text should be approximately of the same size in all figures
Ll 96: At which temperature were the samples dried?
Ll 100 ff: Were samples corrected for residual moisture (105°C)? Overall, more methodological details are neede. Which acid was used? Molarity? General conditions, such vacuum etc. Even if Harris et al. (2001) was followed exactly, please provide some details. The same applies to heating.
L 143: The temperature was shifted to be consistent with the decarbonation treatment. However, decarbonation was likely performed in ambient air, pyrolysis without oxygen. Therefore conditions are not comparable. Please justify the shift from 400°C/local minimum to 550°C and estimate the consequences.
L199: As treated samples were used, I would prefer an indication, e.g. EAdecarb
L 247: “…are correlated (R² = 0.9935…” please use the term “related” as “correlated” is used for Spearmen or Pearson correlation coefficient
Figure 5 and text ll 263 ff: This is a good example, why reporting an intercept for the regression is useful. It also demonstrates the issue when correcting values with a fixed factor instead of of a regression (see “Conversion factors” above). Please discuss these consequences.
Table 2, column S3’CO2 MinC: 12+/-20 does not seem to be a reliable estimate. This should be addressed
Ll323 ff, Figure 8: This finding indicates, that including carbonate-free soil samples in the test may be a good idea.
Ll 340 ff: Would it be possible to prolongate the last phase even further? What does this finding mean for more thermostable carbonates?
Ll 351: If the SIC content is known, what is the advantage of the RE method?
Ll 356: Please indicate that further work on a wider range of samples and with different forms of carbonates is needed.
Citation: https://doi.org/10.5194/bg-2023-66-RC2 -
AC2: 'Reply on RC2', Joséphine Hazera, 18 Jul 2023
The authors would like to thank the Anonymous Referee #2 for his/her attentive reading and his/her numerous, useful, and constructive comments. We agree on most of them, and we will take them into account.
Considering the three comments made on this article, we plan to make several new analyses and statistical tests and to complete and/or reorganize several parts of this article to improve the manuscript. This will obviously take some time. We plan to provide you a revised manuscript and a detailed answer to your comments at the end of August.
In waiting, please find below the description of the planed modifications according to your comments:
- We will add several samples and 3 standard materials (two standards of soil: ERMCC690 from the European Commission – Joint Research Center and ISE850 from the Wepal International Soil-analytical Exchange Program and one well-known standard of rock: SR1 from the Norwegian Geochemical Standard) to the first panel.
- The precision of the Rock-Eval® method will be assessed by replicating 4 times the three standard materials. The precision of the Rock-Eval® method will be assessed by comparing these values with Elemental Analysis (4 replicates) estimating the SOC after HCl and estimating the SIC after heating at 550°C
- To avoid any confusion, the first panel will be analyzed with the Rock-Eval6 device of IFPEN with a constant amount of soil (70 mg).
- We will add information (soil type, texture, pH) on the soil samples of the first panel
- We will add more data on the calcite material (DRX result and thermograms in Supplementary Material and contributions of each curve integration to the TOC and MinC parameters in the Table 2)
- We will highlight and add more data on the 4 carbonate-free samples of the first panel (thermograms in Material & Methods and contributions of each curve integration to the TOC and MinC parameters in the Table 2)
- We will carefully check the formatting of the texts, figures and data presented in this article
- We will describe more the two methods used in this article: the Rock-Eval thermal analysis (choose of the temperature boundaries in the two phases: pyrolysis and oxidation, calibration, corrections, advantages, and disadvantages) and the Elemental Analysis (pretreatment conditions)
- We will put more efforts on the statistic. Thank you very much for your advice. We will present the regressions with intercept, add the variability of the regression slopes and intercepts and compare the slopes to 1
- We will study the bibliography you give us and, possibly integrate them in the bibliography of the article
Considering the number of elements we plan to add, we think that shortening the manuscript to few pages to transform it into a technical note might curtail the understanding by future readers. We would like to keep the Research Article format if you agree.
Citation: https://doi.org/10.5194/bg-2023-66-AC2 - AC6: 'Reply on RC2', Joséphine Hazera, 12 Sep 2023
- AC9: 'Reply on RC2', Joséphine Hazera, 18 Sep 2023
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AC2: 'Reply on RC2', Joséphine Hazera, 18 Jul 2023
Joséphine Hazera et al.
Joséphine Hazera et al.
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