Review Reports - Acidification Assessment after Peat Bog Drainage in the Catalan Pyrenees (NE Iberia)

Round 1

Reviewer 1 Report

I have now finished reviewing the manuscript. The title is of high interest, and I hoped to get some information of acidififaction risk of drained peatbog in relation to the management of the site.

However, the manuscript is just based on two samples from area and some chemical analyses. I do not find any results regarding the management of the site as was mentioned in the introduction.

The study is a comprehensive one to look at mainly chemical analyses of the site. the figure is very primitive without any standard error of the mean.

In my view, it is the required study of the site, but it is not providing a story. The title and introduction needs to be rewritten to be less misleading.

Author Response

Thank you for your comments. The manuscript tries to find an explanation to the low pH of some preliminary analyses, and not to fully characterize the variability of chemical properties of the peat bog. We studied two profiles in depth and made some additional augerings to determine the extent of the organic layers, but it was not our purpose to make any geostatistical study of the site. We think that for the limited extent of the peat bog (between 2-3 ha) the exhaustive characterization of these two profiles can give already a plausible explanation of what happened.

We agree with the comment on the apparent lack of relationship between the title introduction and the results regarding the management of the site. We corrected them according to your suggestions: we changed the title removing the word “risk”, and modified several parts of the introduction, to better reflect the content of the research.

Reviewer 2 Report

This is a nice study on an exciting and environmentally relevant topic; It is interesting and relevant to see that acid sulfate soils can also occur in the Pyrenees. The soils were analyzed and identified by well-known methods. However, some topics that hardly contribute to the description of the acid sulfate soils (such as the humus chapters) are very detailed and should be shortened. In addition, the manuscript could be structured more clearly: In general, the manuscript would be more readable and understandable if the numerous method descriptions (some repetitions) would be removed from the results section. Then the results and interpretations would be more condensed, and the conclusions regarding the classification as acid sulfate soils would be more stringent. In addition, there are some further questions and remarks, see comments below.

Abstract

Line 19: „… was the responsible for… “ – the sentence lacks a noun?

Keywords

It is not necessary to repeat terms that are already mentioned in the title.

Introduction

Line 48: “… which lowers the pH to below 3.0…” – given that the buffering capacity is too low to neutralize the sulfuric acid formed.

Line 80: “… of a partly drained peat bog’s soils…” – check syntax (suggest to delete “a”)

Materials and Methods

Line 86: “… The study area is in located the Catalan Pyrenees…” – check syntax (suggest: “is located in”)

Results and discussion

Chapter 3.2: This chapter describes in great detail humus analysis methods, humus contents, and horizon designations. This should be shortened as it does not contribute significantly to the topic of the manuscript. Similarly, Table 3 contains a lot of descriptions of organic residues, but how far does this information necessary to explain the “Acidification Risk after Peat Bog Drainage in the Catalan Pyrenees” – explain or shorten/remove this information.

Why do analyses of micromorphology exclusively focus on H2 horizons?

Line 219-223: This section belongs to the Materials and Methods chapter.

Line 232-233: “… The precipitation of gypsum did not buffer all the potential acidity, probably due to the depletion of Ca²⁺ source (low Ca²⁺ availability) … “ – to the best of my knowledge, the precipitation of gypsum does not buffer acidity at all, because the reaction does not remove protons:

Ca²⁺ + SO₄²⁻ + 2H₂O ↔ CaSO₄ ∙ 2H₂O

Line 235-237: “… no pyrite framboids have been observed in none of the horizons, which supports the hypothesis of the pyrite contained in the Cambro-Ordovician parent material being the cause of the existence of sulfidic materials…” – confusing and contradicting information.

Chapter 3.5: Here, also a lot of methodological explanations distract from the results and their interpretation and make the text long. Restructuring would make the text more focused and would delete repetitions between the Results and the Methods chapter. For example, a sentence like this: “The pH(ox) is the determination of pH after treatment with 30% hydrogen peroxide solution.” (line 278) clearly belongs to the Methods.

Line 304: “… The results of the application of this set of analyses are found in Tables 3 and 4…” – I think it is only Table 4, not Table 3.

Line 332: “… Acid Base Account equation is calculated using the results of Table 3… “ – again, the table reference is wrong.

Line 335-342: Calculations should be explained in the Methods chapter.

Line 359-361: Confusing explanation – please explain the implications of the results in more detail.

Author Response

Thank you for your comments. We restructured parts of the manuscript according to them, shortening the methods section and condensing the humus description. Nevertheless, we think that this information is relevant since it gives the context for the description of the processes occurring in these soils, and also indicates the presence/absence of some key minerals as gypsum, pyrite and jarosite.

Abstract

Line 19: „… was the responsible for… “ – the sentence lacks a noun?

We think not, the subject of the sentence is “The oxidation of pyrite”, at the beginning of it (line 18-19).

Keywords

It is not necessary to repeat terms that are already mentioned in the title.

Thank you for the remark. We changed “peat bog” and “acidification risk” by “gypsum” and “pyrite”.

Introduction

Line 48: “… which lowers the pH to below 3.0…” – given that the buffering capacity is too low to neutralize the sulfuric acid formed.

We completed the sentence with your suggestion.

Line 80: “… of a partly drained peat bog’s soils…” – check syntax (suggest to delete “a”)

Thank you. We prefer to rephrase it as “the characterization of a partly drained peat bog soil”, since we only studied this one.

Materials and Methods

Line 86: “… The study area is in located the Catalan Pyrenees…” – check syntax (suggest: “is located in”)

Corrected, thanks.

Results and discussion

Text shortened, only the information relevant for the conclusions of the research have been kept. Nevertheless, we think that these methodological issues are important for the characterization of the peat bog and for the interpretation of its genesis.

Why do analyses of micromorphology exclusively focus on H2 horizons?

Because they were the only samples taken, since the formation and oxidation of pyrite are more likely to occur associated to the decomposition of organic materials.

Line 219-223: This section belongs to the Materials and Methods chapter.

Yes, part of the paragraph has been moved to that section.

Ca²⁺ + SO₄²⁻ + 2H₂O ↔ CaSO₄ ∙ 2H₂O

You are right, according to this reaction it does not remove protons, but taking into account the global reaction of pyrite oxidation, and knowing that sulfuric acid is a strong acid we have:

4FeS₂(solid) + 15O₂ + 14H₂O → 4Fe(OH)₃ (solid) + 8SO₄^2- + 16H⁺

In this situation, if calcite is present it reacts with the dissociated sulfuric acid giving:

2H⁺ + SO₄^2- + CaCO₃ + H₂O → CaSO₄·2H₂O + CO₂

And therefore removing protons.

Yes, you are right. We rephrased the text like that:

“… no pyrite framboids have been observed in none of the horizons, although possible pseudomorphs after pyrite were detected associated to organic rests (Fig. 2d). Therefore, we think that the oxidation of fine primary pyrite contained in the Cambro-Ordovician parent material, not observable in thin sections, could be the main cause of the existence of sulfidic materials.”

We shortened the section according to your suggestions.

Line 304: “… The results of the application of this set of analyses are found in Tables 3 and 4…” – I think it is only Table 4, not Table 3.

Corrected.

Line 332: “… Acid Base Account equation is calculated using the results of Table 3… “ – again, the table reference is wrong.

Corrected.

Line 335-342: Calculations should be explained in the Methods chapter.

We removed those calculations since they can be found in the references in more detail.

Line 359-361: Confusing explanation – please explain the implications of the results in more detail.

We tried to clarify the explanation:

In Profile 1, the content of actual acidity is between 67.3 mol H⁺/t to 903.9 mol H⁺/t, this is directly related to the low pH values and the higher actual acidity values. In Profile 2, the values of actual acidity are lower (272.5 and 572.5 mol H⁺/t). On the other hand, the content of potential acidity is between 34.9 to 489.6 mol of H⁺/t in Profile 1 and lower (192.7 and 102.9 mol of H⁺/t) in the H horizons of Profile 2. These differences between profiles and horizons can be due to:

· The initial content of pyrite in the horizons. The successive accumulation of detrital materials from upslope combined with periods of peat formation could be the cause of varying pyrite contents along the profile, and therefore of variable potential acidity.

· Part of the pyrite content has already been oxidized due to the drainage works. Again, the degree of oxidation has varied depending on local profile conditions and also on the position and characteristics of the horizons.

Reviewer 3 Report

Not sure Quaternary is best journal for this--the acidification is in response to modern day change in drainage, an Anthropocene problem. A lot of literature on ASS has appeared in soil/environmental science journals such as Geoderma, e.g. Fanning D, Rabenhorst M, Fitzpatrick R (2017) Historical developments in the understanding of acid sulfate soils. Geoderma 308: 191-206. doi:10.1016/j.geoderma.2017.07.006 ,

and Science of the Total Environment

Hall KC, Baldwin DS, Rees GN, Richardson AJ (2006) Distribution of inland wetlands with sulfidic sediments in the Murray–Darling Basin, Australia. Sci Tot Env 370: 235-244. doi:10.1016/j.scitotenv.2006.07.019

A more thorough literature search may be worth doing to improve the general context in the Introduction: although ASS are often a coastal problem, there are many instances of them in inland settings such as the one described in Catalonia. For example,

Fitzpatrick RW, Fritsch E, Self PG (1996) Interpretation of soil features produced by ancient and modern processes in degraded landscapes: V. Development of saline sulfidic features in non-tidal seepage areas. Geoderma 69: 1-29. doi:10.1016/0016-7061(95)00046-1

But the paper is generally sound and so is publishable with minor changes.

There are a few odd phrasings:

l. 18, 'newformed', should be 'newly formed'

l. 21, it is not clear to me how the results of this study could used to 'locate' other PASS but they are useful to evaluate the risk of other peats in the Pyrenees becoming ASS if drained.

l. 65, ...'plant rests, ...vegetable coals' is not idiomatic, maybe 'plant remains'...'lignite' or 'bituminous coal'

l. 76, should be '... can be responsible for freshwater acidification...'

l. 77, should be 'aquatic and soil ecosystems'

l. 83, what is ICGC? spell out and elaborate.

l. 100, should be, '...Ordovician and the overlying Holocene deposits'...

l. 227, define 'phlobaphenized' for those who aren't familiar with soil micromorphology jargon

l. 373 and Conclusion, It would be nice to know how extensive peat deposits are? The area you studied was only 2.8 ha. How much other land would be affected by acid drainage? What aquatic ecosystems are downstream? How far downstream does acidity persist?

Are there enough data points to make a map predicting extent of ASS in Pyrenees, see

Bui, E. N. (2018). High-resolution mapping of acid sulfate soils in Northern Australia through predictive models. Environmental chemistry letters, 16(4), 1449-1455.

Author Response

Thank you for your comments. We are aware of inland ASS in other parts of the world, and we introduced the suggested references in the introduction, in order to stress the similarities with our findings, and to highlight the importance of the first record of an inland ASS in the Mediterranean side of the Pyrenees.

There are a few odd phrasings:

l. 18, 'newformed', should be 'newly formed'

Done.

l. 21, it is not clear to me how the results of this study could used to 'locate' other PASS but they are useful to evaluate the risk of other peats in the Pyrenees becoming ASS if drained.

Thank you for your suggestion, we changed this last sentence.

l. 65, ...'plant rests, ...vegetable coals' is not idiomatic, maybe 'plant remains'...'lignite' or 'bituminous coal'

Changed.

l. 76, should be '... can be responsible for freshwater acidification...'

Corrected.

l. 77, should be 'aquatic and soil ecosystems'

Corrected.

l. 83, what is ICGC? spell out and elaborate.

We spelled it out in the previous paragraphs where it appears for the first time.

l. 100, should be, '...Ordovician and the overlying Holocene deposits'...

Done.

l. 227, define 'phlobaphenized' for those who aren't familiar with soil micromorphology jargon

Explanation added: containing reddish compounds from the oxidation of tannins.

Are there enough data points to make a map predicting extent of ASS in Pyrenees, see

Bui, E. N. (2018). High-resolution mapping of acid sulfate soils in Northern Australia through predictive models. Environmental chemistry letters, 16(4), 1449-1455.

Thank you for the suggestion. There are not yet enough data to make a detailed map predicting the extent of PASS in the Pyrenees, but it could be elaborated in the near future from the surveys of peat bog sites and from the parent material (more or less pyrite-containing). It is indeed the next step of this research. In spite of the lack of systematic surveys of peatlands in the Pyrenees, we added a short paragraph with a proposal of the way to proceed when mapping and assessing the extent of potential environmental problems associated to their management.

Round 2

Reviewer 1 Report

I agree with the other reviewers' comments. And I would like the coauthors for the clarification. The manuscript can be considered based on the comments from the other two reviewers.

Author Response

As required by the referee, the manuscript has been thoroughly revised regarding English language and style by a English-speaking, earth sciences specialist.

Author Response File: Author Response.docx