Round 1

Reviewer 1 Report

Geochemical behaviors of heavy metals in soil ferromanganese nodules in typical karst areas in Southwest China

Wenbing Ji, Zhixiang Luo, Jianyu Huang, Xu Liu, Haiyun He, Yang Gong, Chen Meng, Yubo Wen and Rongrong Ying

This work describes the elemental composition of soil ferromanganese nodules, and analyses the correlations between the elements. Results are interpreted in terms of three main components, one related to trapped particles, the other related to Mn oxides, and the third related to Fe oxy(hydroxi)des. The main contribution is to add more data to the literature on ferromanganese nodules.

The experiments seem to have been well-done, and all of my concerns are related to the writing and organization.

Major concerns:

(i)               In some cases, interpretation of results is too much speculative – for instance, the discussion on the presence of specific minerals without results on the minerals present.

(ii)              Some values in the text are slightly different from those presented in tables.

(iii)            In several cases, the cited references do not contain the data the text said they had. Some mistakes are annotated directly in the text (see the attached file). And I did not check every reference. Please check all references.

(iv)            In the text, Table 4 appears before Table 3. Please correct it.

(v)              There is no description of how the control of selective extractions was done in the Methods section.

Comments for author File: Comments.pdf

Although there is a certificate of language checking by a native speaker, there are several truncated sentences and repeated words - it seems that it was checked electronically, and not by a person.

Author Response

Response to Reviewer 1 Comments

Point 1: In some cases, interpretation of results is too much speculative – for instance, the discussion on the presence of specific minerals without results on the minerals present. 

Response 1: We have published an article Mineral Composition and Environmental Importance of Fe–Mn Nodules in Soils in Karst Areas of Guangxi, China (https://doi.org/10.3390/su141912457). The minerals we discuss are those that have been publicly reported by other researchers.

Point 2: Some values in the text are slightly different from those presented in tables.

Response 2: We have checked the values in the text and in tables. And we have checked the annotations in the attached file.

Point 3: In several cases, the cited references do not contain the data the text said they had. Some mistakes are annotated directly in the text (see the attached file). And I did not check every reference. Please check all references.

Response 3:Thank you for your valuable advice. We have checked the mistakes in the attached file. We have corrected the mistakes and check all references in the manuscript.

Point 4: In the text, Table 4 appears before Table 3. Please correct it.

Response 4: We have correctted the Table order in the manuscript.

Point 5: There is no description of how the control of selective extractions was done in the Methods section.

Response 5: The data quality control was assessed by comparing the measured contents in standard substances (SS2001, SS3001, and SS4001) with those revealed in the FMN powder sample. The ratio of the actual results to the results of the standard substances ranged from 80 to 120%, indicating the reliable quality of the results.

Point 6: Although there is a certificate of language checking by a native speaker, there are several truncated sentences and repeated words - it seems that it was checked electronically, and not by a person.

Response 6: Moderate English have been changed in the new manuscript.

Author Response File: Author Response.doc

Reviewer 2 Report

I really enjoyed reading the manuscript that is presenting a geochemical study on Fe-Mn nodules in karst areas of China. Although the mineralogical analysis of nodules that is important to justify the binding capacity of iron and manganese oxides is refered to another paper of the authors, it is my pleasure to accept the manuscript for publication after minor changes.

I suggest to authors to include in M&M, the size of the studied nodules for comparison terms.

Please also clarify the data of table 2 adding the appropriate locations of cited papers.

Minor languange editing is required

Author Response

Point 1: I really enjoyed reading the manuscript that is presenting a geochemical study on Fe-Mn nodules in karst areas of China. Although the mineralogical analysis of nodules that is important to justify the binding capacity of iron and manganese oxides is refered to another paper of the authors, it is my pleasure to accept the manuscript for publication after minor changes.

Response 1: Thank you for your approval of our manuscript, which will be revised point by point in response to your suggestions.

Point 2: I suggest to authors to include in M&M, the size of the studied nodules for comparison terms.

Response 2: We have published an article Geochemical characteristics of Fe-Mn nodules with different sizes in soils of high geological background areas (in Chinese) in 2021 in Journal of Ecology. Our focus is not the size of the studied nodules, it will make the main idea of the article unclear if added the size.

Point 3: Please also clarify the data of table 2 adding the appropriate locations of cited papers.

Response 3: We have added the locations of cited papers of table 2.

Point 4: Moderate English changes required.

Response 4: Moderate English have been changed in the new manuscript.

Author Response File: Author Response.doc

Round 2

Reviewer 1 Report

I still have some comments on minor issues, as follows:

In lines 26-27, the order does not comply with the use of the signal ">".

Lines 268-269: I could not find the exception (Cu and Pb) in Table 2.

Line 270 (Caption of Table 2): Data in Table 2 are from FMNs, soils and the AUCC.

Lines 318-320: Fe is not the most abundant element in the Earth's crust. Please correct the text.

The text in lines 41-43 is hard to understand, and you have already reviewed it. I suggest "Migration and enrichment of metal(loid)s in soils subject to seasonal changes in the redox potential (Eh) and pH may lead to the formation of ferromanganese nodules (FMNs) consisting largely of Fe and Mn (oxyhydr)oxides." 

Lines 232-234: I suggest to change to: "The interconversion of the Fe and Mn oxidation states is influenced mainly by pH, redox potential (Eh), ..." 

Lines 277-278: The sentence beginning with "Gasparatos" means the same as the previous one and should be deleted.

Author Response

Response to expert2 comments（Round2）

Point1：In lines 26-27, the order does not comply with the use of the signal ">".

Response1：We deleted the the signal ">" in the new manuscript.

Point2：Lines 268-269: I could not find the exception (Cu and Pb) in Table 2.

Response2：We have revised the original sentence. However, the average heavy metal(loid)s contents in the soil FMNs of karst areas were higher than those in non-karst regions except Cu and Pb(Table 2). In Table 2, karst areas included Guangxi, while non-karst regions included Namibia, Italy, Quaternary red earth of Eastern China.

Point3：Line 270 (Caption of Table 2): Data in Table 2 are from FMNs, soils and the AUCC.

Response3：We have revised the title of Table 2.

Point4：Lines 318-320: Fe is not the most abundant element in the Earth's crust. Please correct the text.

Response4：In the original article, I did not mean that Fe is the most abundant element in the Earth's crust. The majority of Fe(oxyhydr)oxides in FMNs are in the mineral form. I want to express that Fe are in the mineral form in the FMNs.

Point5：The text in lines 41-43 is hard to understand, and you have already reviewed it. I suggest "Migration and enrichment of metal(loid)s in soils subject to seasonal changes in the redox potential (Eh) and pH may lead to the formation of ferromanganese nodules (FMNs) consisting largely of Fe and Mn (oxyhydr)oxides."

Response5：We have revised the sentences.

Point6：Lines 232-234: I suggest to change to: "The interconversion of the Fe and Mn oxidation states is influenced mainly by pH, redox potential (Eh), ..."

Response6：We have revised the sentences.

Point7：The sentence beginning with "Gasparatos" means the same as the previous one and should be deleted.

Response7：We have deleted the sentences beginning with "Gasparatos".

Author Response File: Author Response.doc