Spatial Patterns of Mercury and Geochemical Baseline Values in Arctic Soils
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsGeneral comment:
The evolution of soil mercury in the background area is a key indicator factor for feedback on human activities. This paper aimed to investigate Hg content and its distribution patterns in various types of tundra soils in the European North-East of Russia. This is somewhat helpful for understanding the deposition and distribution of mercury in the cryosphere. I suggest making an appropriate improvement.
Special comments:
L19-20 What is this “complex influence”?
L70-72 It is suggested that the research on tundra mercury be introduced. I don't think taking crop enrichment as an example is suitable for tundra.
L217-219 How did such a large spatial disparity come about?
L303-304 The decomposition of organic matter how affects its binding capacity for Hg.
L313 In Section 2.1, the authors have presented a considerable amount of temporal and spatial variations in climatic conditions. Whether this has led to a corresponding response in soil mercury spatial heterogeneity is a topic that merits further discussion.
L337-338 Is the direct deposition of atmospheric Hg and their interception by organic matter another reason?
L447-457 This seems to be a contradictory statement? Low pH levels facilitate the release of mercury from the soil, but a negative correlation between pH and mercury was observed, suggesting that acidic conditions are conducive to mercury retention?
Author Response
Dear reviewer,
I would like to express my sincere gratitude for your thorough work on the manuscript, and for the suggestions and recommendations you have provided to improve the text. I have revised the manuscript in accordance with your recommendations.
All changes in the text we marked yellow.
Comment 1: L19-20 What is this “complex influence”?
Response 1: “Complex influence” refers to the combined and synergistic effects of several physicochemical soil factors rather than the individual effects of each factor. More specifically, it refers to the accumulation and migration of Hg in conjunction with organic matter content and quality, particle size distribution, soil acidity and hydrological conditions. These parameters influence Hg sorption, complexation and mobility simultaneously, creating spatial and profile heterogeneity in its distribution.
Comment 2: L70-72 It is suggested that the research on tundra mercury be introduced. I don't think taking crop enrichment as an example is suitable for tundra.
Response 2: This text has been corrected.
Comment 3: L217-219 How did such a large spatial disparity come about?
Response 3: The content of organic carbon always varies greatly depending on the genesis of the soil horizon.
Comment 4: L303-304 The decomposition of organic matter how affects its binding capacity for Hg.
Response 4: The proposal was poorly drafted. The text has been corrected.
Comment 5: L313 In Section 2.1, the authors have presented a considerable amount of temporal and spatial variations in climatic conditions. Whether this has led to a corresponding response in soil mercury spatial heterogeneity is a topic that merits further discussion.
Response 5: Yes, the wide variety of natural soil formation conditions in the region under study resulted in spatial heterogeneity in Hg distribution in soils. I took this into account when discussing the obtained results.
Comment 6: L337-338 Is the direct deposition of atmospheric Hg and their interception by organic matter another reason?
Response 6: Yes, of course. The accumulation of Hg compounds in the upper (organic) horizons is partly due to their atmospheric input via the sorption of organic matter. The relevant text has now been added.
Comment 7: L447-457 This seems to be a contradictory statement? Low pH levels facilitate the release of mercury from the soil, but a negative correlation between pH and mercury was observed, suggesting that acidic conditions are conducive to mercury retention?
Response 7: In this case, there is no contradiction. Indeed, under acidic conditions (at a pH of less than 4), the mobility of mercury ions increases. This is noted in line 262. However, within the observed pH range (3.9–6.2), the solubility of mercury compounds does not increase as the pH decreases, and sorption processes prevail. For clarity, a small clarification has been added to the text.
With Kind Regards,
Author
Reviewer 2 Report
Comments and Suggestions for AuthorsAbstract
Lines 8 to 12: I think that this part can be moved in the introduction (aim of the work);
The Conclusions section may be overly long; therefore, I suggest making it more concise and checking for redundancies.
I also suggest introducing Hg speciation in soils (chemical or pyrolysis-based) as a potential avenue for further investigation in the Conclusions section, given that Hg mobility may change under climate change conditions. In this context, I suggest the following references:
Bloom, N.S.; Preus, E.; Katon, J. Selective extractions to assess the biogeochemically relevant fractionations of inorganic mercury
in sediments and soils. Anal. Chim. Acta 2003, 479, 233–248.
Mashyanov, N.R., Matsuyama, A., Akagi, H., Pogarev, S., Ryzhov, V., 2004. Mercury
thermos-speciation in contaminated soils and sediments. RMZ Mater. Geoenviron,
part III 51, 1980–1983.
Mashyanov, N.R., Pogarev, S.E., Panova, E.G., Panichev, N., Ryzhov, V., 2017.
Determination of mercury thermospecies in coal. Fuel 203, 973–980.
Author Response
Dear reviewer,
I would like to express my sincere gratitude for your thorough work on the manuscript, and for the suggestions and recommendations you have provided to improve the text. I have revised the manuscript in accordance with your recommendations.
All changes in the text we marked yellow.
Comment 1: Lines 8 to 12: I think that this part can be moved in the introduction (aim of the work);
Response 1: Similar information is contained in the Introduction, to varying degrees. In my opinion, the abstract should also explain the purpose and relevance of the study.
Comment 2: The Conclusions section may be overly long; therefore, I suggest making it more concise and checking for redundancies.
Response 2: Several duplicate sentences have been removed from the Conclusions section.
Comment 3: I also suggest introducing Hg speciation in soils (chemical or pyrolysis-based) as a potential avenue for further investigation in the Conclusions section, given that Hg mobility may change under climate change conditions. In this context, I suggest the following references: Bloom, N.S.; Preus, E.; Katon, J. Selective extractions to assess the biogeochemically relevant fractionations of inorganic mercury in sediments and soils. Anal. Chim. Acta 2003, 479, 233–248. Mashyanov, N.R., Matsuyama, A., Akagi, H., Pogarev, S., Ryzhov, V., 2004. Mercury thermos-speciation in contaminated soils and sediments. RMZ Mater. Geoenviron, part III 51, 1980–1983. Mashyanov, N.R., Pogarev, S.E., Panova, E.G., Panichev, N., Ryzhov, V., 2017. Determination of mercury thermospecies in coal. Fuel 203, 973–980.
Response 3: Two relevant sentences have been added.
With Kind Regards,
Author
Reviewer 3 Report
Comments and Suggestions for AuthorsThe text entitled Spatial Patterns and Threshold Concentration of Mercury in Arctic Background Soils is very interesting. However, there are some shortcomings: 1) the introduction and the text in general lack a section explaining what the author means by natural or anthropogenic background values and the difference between the two
2) the discussions lack references
3) some things are repeated, as indicated below
4) The methods could be implemented (see below).
Lines 78-84 This part appears to be a repetition; try to rephrase it.
Chapter Materials and Method: It is unclear whether there are two types of samples: one representing the organic horizon and the second representing the mineral horizon. Please explain how many samples are from the first and second group.
Line 156: What is the thickness of the soil samples? Please add it
Line 163 Please report the soil location in Fig. 1 and also the presence of the industry.
lines 171-174 This part is not necessary because it is written yet
Line 177 dot
Line 217: What is the range?
lines 220-230 This part is Ok for discussion, not for results.
Line 233 : The methods do not mention particle size analysis. How was it carried out? Were further particle size analyses carried out in addition to those on clays? If only clays were analysed, it would be better to refer to clay content analysis. In this case, however, how was it carried out? Report everything in the methods; if only clays were analysed, it would be better not to refer to particle size composition.
How was the pH of the soils analysed? Add to methods.
Lines 366-367 Regarding this part, I would recommend reading the recent article https://doi.org/10.1016/j.scitotenv.2025.181169, which determines and distinguishes the geochemical background value from the anthropogenic background value or anomalies related to Hg mineralisation using a new robust method.
lines 371-382 There is no bibliography to support this statement. Furthermore, it is highly unlikely that Hg follows a normal distribution, especially in soils and with high variability. It is therefore not certain that 95% offers an excellent distinction between natural and anthropogenic background values.
linee 383-389: Was the underlying value calculated using the data as a single dataset, or were the soils divided according to different soil types?
In general, the discussion section lacks bibliographies to support the statements made. Please add them.
Author Response
Dear reviewer,
I would like to express my sincere gratitude for your thorough work on the manuscript, and for the suggestions and recommendations you have provided to improve the text. I have revised the manuscript in accordance with your recommendations.
All changes in the text we marked yellow.
Comment 1: Lines 78-84 This part appears to be a repetition; try to rephrase it.
Response 1: The text has been corrected.
Comment 2: Chapter Materials and Method: It is unclear whether there are two types of samples: one representing the organic horizon and the second representing the mineral horizon. Please explain how many samples are from the first and second group.
Response 2: Soil samples were sampled from organic and mineral horizons. Table 2 shows how many samples of each type that were sampled and analysed.
Comment 3: Line 156: What is the thickness of the soil samples? Please add it
Response 3: Table 1 shows the average thickness of each of the studied horizons.
Comment 4: Line 163 Please report the soil location in Fig. 1 and also the presence of the industry.
Response 4: Soil sampling points have been added to Figure 1. So have settlements. And industrial sites. And roads. And railways.
Comment 5: lines 171-174 This part is not necessary because it is written yet
Response 5: The paragraph was kept because it describes the total number of samples analysed.
Comment 6: Line 177 dot
Response 6: The comma was replaced by a dot.
Comment 7: Line 217: What is the range?
Response 7: The range has been added. A link to Table 1 has also been added.
Comment 8: lines 220-230 This part is Ok for discussion, not for results.
Response 8: This part of the text has been moved to the Discussion section.
Comment 9: Line 233 : The methods do not mention particle size analysis. How was it carried out? Were further particle size analyses carried out in addition to those on clays? If only clays were analysed, it would be better to refer to clay content analysis. In this case, however, how was it carried out? Report everything in the methods; if only clays were analysed, it would be better not to refer to particle size composition.
Response 9: The study included a comprehensive analysis of soil particle size distribution. However, the article only included data on clay content, as this fraction determines Hg sorption. A description of the particle size distribution analysis has been added to the Methods section.
Comment 10: How was the pH of the soils analysed? Add to methods.
Response 10: The Methods section has been updated with a description of pH analysis.
Comment 11: Lines 366-367 Regarding this part, I would recommend reading the recent article https://doi.org/10.1016/j.scitotenv.2025.181169, which determines and distinguishes the geochemical background value from the anthropogenic background value or anomalies related to Hg mineralisation using a new robust method.
Response 11: Thank you very much for this article. The relevant text has been added to the Introduction section.
Comment 12: lines 371-382 There is no bibliography to support this statement. Furthermore, it is highly unlikely that Hg follows a normal distribution, especially in soils and with high variability. It is therefore not certain that 95% offers an excellent distinction between natural and anthropogenic background values.
Response 12: Thank you very much for this valuable comment. Mercury levels indeed do not follow a normal distribution. The Shapiro–Wilk test showed that they follow a lognormal distribution. Consequently, the method for calculating upper confidence limits of Hg concentrations has been modified. The relevant text, Table 2 and Figure 2 have been amended. The Methods section has also been updated.
Comment 13: linee 383-389: Was the underlying value calculated using the data as a single dataset, or were the soils divided according to different soil types?
Response 13: The values were calculated separately for each soil type.
Comment 14: In general, the discussion section lacks bibliographies to support the statements made. Please add them.
Response 14: The Discussion section has been edited. The necessary bibliography has been added.
With Kind Regards,
Author
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Author,
I think your work is excellent. More studies like yours, dealing with Hg in Arctic areas, are needed.
With that said, I believe your article is ready for publication.
Author Response
Dear reviewer,
Good afternoon!
Thank you very much for your positive evaluation of my manuscript and for your helpful comments.
Best regards,
Evgeny Lodygin
