Permafrost Degradation Impact on Water Bodies in the Siberian Tundra (Samoylov and Kurungnakh Islands, Lena Delta) Using GIS Analysis of Remote Sensing Data and a Geochemical Approach

Round 1

Reviewer 1 Report

 

Reviewer’s comment / question	Authors answer	Reviewer: second round
The grouping of lakes is based on a-priory defined considerations/characteristics, not proven by statistical analysis. From Fig. 3 it seems there are gradients, but no clearly distinguishable groups. Groups have also not been used further on in the analysis. This leaves the questions whether the differentiation is indeed valid	The grouping of lakes was initially based on differences in the geomorphological characteristics of the lakes (the geological characteristics of the terrace on which the lake is located and the elevation). Figure 3 describes the relationship between the total content of elements, electrical conductivity, redox potential, pH value for all lakes of the Samoylov and Kurungnakh Islands, this figure does not reflect belonging to one or another group. The division into groups is used further when considering differences in the microelement composition of bottom sediments (illustrated in Figs. 6 and 7).	OK, grouping according to geomorphological characteristics is acceptable. Still, I wonder why no effort was made to substantiate the grouping by statistics – both concerning characteristics and chemical composition. In fact, I consider this a severe shortcoming of the study.
The sampling design (selection of sampling sites) should be explained in more detail. It should get clearer why the western parts of the islands have not been considered.	Water bodies were sampled in the eastern part of Samoylov Island. The western part of the island is located on the first river terrace, which is constantly flooded; there is no close lake basin on it.	OK
The characteristics of the different terraces might become clearer if summarized in a table? Also, I was still struggling with the term “Edoma”: is it a layer? In which terrace?	The references on characteristics of the various terraces that the authors mention have been added. The authors made a technical error when translating the term. It was meant «Yedoma» (an organic-rich Pleistocene-age permafrost with ice content of 50–90 % by volume). The «Edoma» was replaced by «Yedoma» in the text of the manuscript.	OK     OK, but if “Yedoma” is an established term, is it possible to add a reference? In Line 314 one “Edoma” was left – probably by mistake?
Also partly confusing is the use of the terms “lakes” and “reservoirs”. Latter term to many readers implies artificial water bodies with a dam. Better use one term consistently. Consider using a general term like “water body” since also “lake” might not be fully appropriate?	Many thanks to the reviewer for the valuable remark. The authors have replaced all terms with one "water body".	OK
Using lines in Figures 4-7 is not appropriate and misleading (explained in comment in PDF), please change to different type of Figure.	Yes, thank you. We removed Fig. 4. It is enough information in the Table 2 on the microelements concentrations in water. Also, we tried to change figures 5-7 (4, 5, 6 in new version) and add the information on chemical elements concentrations in waters.	OK, but re-numbering was not done properly: there is no figure 5.
No reference to Fig. 6 and 7 in the text (results). It is a must to explain main points from figures, otherwise skip them.	Yes, thank you. We tried to explain main points from these figures and reconfigurate them.	Still no reference to Fig. 6 (should be 5) in text!
Issue of mobility of elements is only mentioned but not clearly addressed – let alone analysed.	Yes, thank you. We tried to explain it in the text of the revised manuscript.	This issue is now addressed in a better way – but could still be improved, see comments in manuscript.
Formal issues: please use units consistently, English language needs editing.	Yes, thank you. We change the units according to the comments of the Reviewer in the pdf file. Authors tried to edit English language. We would be very grateful to the Editors for their cooperation in additional editing.	Units: partly OK, but still partly in the old style, e.g. mg/L; it seems sometimes instead of the degree symbol ° an upper-scale 0 was used. Also check all upperscale symbols such as L-1. Language was improved. Some additional editorial comments and changes were added in the manuscript, but there is still a need for a thorough final linguistic check.

 

see also comments in the Manuscript

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 1 Comments

 

Point 1: OK, grouping according to geomorphological characteristics is acceptable. Still, I wonder why no effort was made to substantiate the grouping by statistics – both concerning characteristics and chemical composition. In fact, I consider this a severe shortcoming of the study.

 

Response 1: We are very thankful to reviewer for this remark. We will take it into account and will try to substantiate the grouping by statistics after further studying larger quantity of water bodies.

 

Point 2: OK, but if “Yedoma” is an established term, is it possible to add a reference? In Line 314 one “Edoma” was left – probably by mistake?

 

Response 2: Yes, sorry, we have replaced “Edoma” to “Yedoma”. Also we have added a reference ([27]).

 

Point 3: OK, but re-numbering was not done properly: there is no figure 5.

 

Response 3: Yes, sorry, corrected.

 

Point 4: Still no reference to Fig. 6 (should be 5) in text!

 

Response 4: Yes, sorry, we addaed the reference.

 

Point 5: This issue is now addressed in a better way – but could still be improved, see comments in manuscript.

 

Response 5: Sorry, we couldn’t find the proper file with your comments in manuscript.

 

Point 6: Units: partly OK, but still partly in the old style, e.g. mg/L; it seems sometimes instead of the degree symbol ° an upper-scale 0 was used. Also check all upperscale symbols such as L^-1.

Language was improved. Some additional editorial comments and changes were added in the manuscript, but there is still a need for a thorough final linguistic check.

 

Response 6: Yes, corrected units again. Sorry, we didn’t find the proper file with your comments in manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

1. In Figure 1, are A and C UAV images?

2. If it is possible, there should be a processing flowchart to get the particular shapefile.  Moreover, an image example of UAV and Satellite of one location will show the importance of using UAV vs satellite images in this study as well.   What kind of satellite sensor image did you use and at what resolution.  Did the satellite image and UAS images collect in the same period of time? 

3. In Figure 2, Better have a cross-section height profile from the ArcticDEM you have used to show alongside in this Figure 2 as well.  Again, what satellite is it, and in what resolution?

4. What are the causes of permafrost degradation?

 

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 2 Comments

 

Point 1: In Figure 1, are A and C UAV images?

 

Response 1: We have corrected the name of the Figure 1. We have clarified that a and c are UAV images  and d is Landsat satellite image.

 

Point 2: If it is possible, there should be a processing flowchart to get the particular shapefile. Moreover, an image example of UAV and Satellite of one location will show the importance of using UAV vs satellite images in this study as well. What kind of satellite sensor image did you use and at what resolution. Did the satellite image and UAS images collect in the same period of time?

 

Response 2: Thank you for your remark. Unfortunately, the process of water bodies' areas and altitudes calculation is very simple two-step operation (1 — manual mapping, 2 — using “Zonal Statistics” tool in ArcGIS). This operation described in the text. We are afraid that a processing flowchart could complicate the manuscript. We believe that readers could understand the process of getting the shapefile and it's characteristics.

Likewise, we want to kindly clarify that we have not used any satellite images for analysis. ArcticDEM is digital elevation model which is the most accurate free use DEM with 2 meter pixel size. Also, we believe readers will are able to understand that manual mapping by UAV images with 0.05 m/px is more accurate than any free use satellite images with horizontal resolution of 10-15-20 m/px. Consequently, in view of the above, we suppose that image example of UAV and Satellite of one location is unnecessary for this manuscript.

 

Point 3: In Figure 2, Better have a cross-section height profile from the ArcticDEM you have used to show alongside in this Figure 2 as well. Again, what satellite is it, and in what resolution?

 

Response 3: Thank you for the remark. We have clarified that it is Sentinel 2 satellite image. We are extremely sorry, but a cross-section height profile is not informing in this case due to a slight elevation difference (from 60 to 10 meters) in some km distance. Moreover, we plan to create a detail scheme showing steps of permafrost degradation, as well as geomorphological and hydrochemical characteristics of water bodies. The creation of this scheme will be possible after further studying larger quantity of water bodies.

 

Point 4: What are the causes of permafrost degradation?

 

Response 4: Sorry, we would like to kindly inform you that causes and processes of permafrost degradation in the Arctic in general and in the Lena Delta in particular are detailed in many literary sources. We are afraid that description of usual thermokarst processes and their dynamic is unnecessary for this manuscript.

However, we are very thankful to a reviewer for this remark. We hope that we are able to reveal a prevalent influence of different thermal denudation processes during various steps of permafrost degradation in the Lena Delta landscapes. It will be possible after further investigations.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

It seems in the last round there was a problem with uploading the PDF with my comments, I apologize that it was missing. I checked and found that some had become obsolete since you addressed them during the revision. Others, however, in my view are still relevant, see attached.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer Comments

 

Point 1: Your hypothesis is still not very clear - it says that some marker elements (which - and would they be characteric for certain (groups of) elements?) will deplete in the water body, but accumulate in the sediments, right? You need to refer to your hypothesis in the conclusions.

 

Response 1: Yes, thank you. We tried to clarify it (lines 302-315 and lines 404-408) and added explanation in the “Discussion” section.

When considering the concentrations of chemical elements normalized to clark in different groups corresponding to different stages of permafrost degradation (for example, Kurungnakh Island), several obvious trends can be identified (Fig. 5). Firstly, the behavior of arsenic is interesting. In lakes of group I (on the surface of Yedoma) its concentration is the lowest, in groups II and III the concentration of As increases. It can be assumed that as the permafrost degrades (group I changes successively to group II and III), this element is removed from permafrost rocks into bottom sediments, and their enrichment occurs. Interestingly, for Zn, and Mo, we observe the opposite picture: the Clark-normalized concentrations of these elements are higher in the lakes of the first group located on the Yedoma, and as the permafrost (groups II and III) degrades, the concentrations of these elements in the bottom sediments decrease, which may indicate that the compounds of these elements come out from bottom sediments into solution in the course of geochemical processes accompanying the degradation of permafrost.

In addition, the bottom sediments in the waterbodies on the surface of Yedoma are enriched with La and depleted with Ce and Nd relative to the waterbodies on the first river terrace and the waterbodies of Samoylov Island, as well as in comparison with the clays of the Russian platform and North American Shale Composite (NASC)..

 

Point 2: could the high value be an outlier? At least discuss this...

 

Response 2: Yes, thank you. We tried to explain this value in the text (see lines 228-229). The highest EC (415 μSm∙cm^-1) is in the watercourse 1 (Fig. 1a), which is seasonally flooded by the river waters.

 

Point 3: not very clear what you mean

 

Response 3: Yes, thank you. We tried to rephrase this sentence.

We believe that the main sources of arsenic and beryllium entering the waters of the lakes are leaching from bottom sediments. Under oxidizing conditions in the range of Eh values of 150-200 mV and at sub-alkaline pH (7-9), soluble complexes of the type HAsO₄^2-, BeOH⁺ BeO(aq) are most likely formed in lake waters (Brookins, D. G. (2012). Eh-pH diagrams for geochemistry. Springer Science & Business Media.)

 

Point 4: meaning of circles should be explained

 

Response 4: Yes, thank you. We tried to explain the meaning of the circles and added it to the capture:

Сircles highlight elements whose concentrations are higher than Clark с.c. values.

 

Point 5: values are close. Is it justified to hightlight differences?

 

Response 5: Yes, indeed, the values are quite close. Therefore, we left in consideration only As Mo, and Zn.

 

Point 6: You should only use this term when it is substantiated by statistics.

Any indication why differences are particularly pronounced for Ce and Nd? Also the different "behaviour" of La asks for some explanation

 

Response 6: Yes, thank you. We deleted this word.

Ce and Nd are elements of variable valence, which can be in a two–, three- and four-valent state (Moeller T. The Chemistry of Lanthanides. Rheinhold Publ. Co., New York. 1963. 177 p.). Therefore, anomalies in the contents of these elements in the sediments of the studied waterbodies reflect, in our opinion, the features of the redox conditions of the formation of based rocks.

The measured Ce anomaly appears to represent an integrated signal related to the redox history of the based rocks (German, C. R., & Elderfield, H. (1990). Application of the Ce anomaly as a paleoredox indicator: the ground rules. Paleoceanography, 5(5), 823-833.). Negative Ce anomaly may reflect water chemistry at organic poor conditions (Seto, M., & Akagi, T. (2008). Chemical condition for the appearance of a negative Ce anomaly in stream waters and groundwaters. Geochemical journal, 42(4), 371-380.) 

As for La, indeed, we observe a significant enrichment of this element in the bottom sediments of lakes located on Yedoma relative to lakes located on degraded territory. Moreover, the ratio of waterbodies of Yedoma normalized to chondrite La/Yb is equal to 160-234, while for waterbodies of the first river terrace (group I) and lakes on the surface of the degraded part of Yedoma (subgroup II-6), this ratio is 0.99 and 0.75, respectively. Such a sharp contrast, according to the authors, can only be associated with differences in La content in the based rocks. Thus, it can be assumed that the Yedoma rocks are more enriched with light lanthanides (La) compared to heavy ones (Yb), and the rocks of the degraded territory are characterized by a decrease in light lanthanides.

 

Point 7: I recommend starting with a positive statement.

 

Response 7: Yeas, thank you. We rephrased this sentence.

 

Point 8: So, with regard to these elements, your hypothesis that elements will accumulate in the sediments has to be rejected? Please make this clear.

 

Response 8: Yes, thank you. We added our explanation in lines 366-388.

 

Point 9: is it indeed possible to use remote sensing for analysing chemical composition? maybe only indirectly via proxies?

 

Response 9: Yes, thank you. We tried to rephrase it.

 

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The issue of permafrost degradation is certainly of high relevance. However, this study is in my view not suitable in the current form for publication. It might be improved, but requires in parts complete re-analysis and rewriting. Besides, the English requires attention.

Main comments:

1. The grouping of lakes is based on a-priory defined considerations/characteristics, not proven by statistical analysis. From Fig. 3 it seems there are gradients, but no clearly distinguishable groups. Groups have also not been used furtheron in the analysis. This leaves the questions whether the differentiation is indeed valid.
2. The sampling design (selection of sampling sites) should be explained in more detail. It should get clearer why the western parts of the islands have not been considered. The characteristics of the different terraces might become clearer if summarized in a table? Also, I was still struggling with the term “Edoma”: is it a layer? In which terrace?
3. Also partly confusing is the use of the terms “lakes” and “reservoirs”. Latter term to many readers implies artificial water bodies with a dam. Better use one term consistently. Consider using a general term like “water body” since also “lake” might not be fully appropriate?
4. Using lines in Figures 4-7 is not appropriate and misleading (explained in comment in PDF), please change to different type of Figure.
5. No reference to Fig. 6 and 7 in the text (results). It is a must to explain main points from figures, otherwise skip them.
6. Issue of mobility of elements is only mentioned but not clearly addressed – let alone analysed.
7. Formal issues: please use units consistently, English language needs editing.

More comments directly in the PDF file

Comments for author File: Comments.pdf

Reviewer 2 Report

Dear Authors,

I have thoroughly revised your article titled „Permafrost Degradation Impact on lake waters in the Siberian tundra (Samoylov and Kurungnakh islands, Lena delta) using GIS Analysis of Remote Sensing data and Geochemical Approach” submitted for consideration for publication in Water, MDPI journal.

I regret to say, however, in my opinion, the presented manuscript does not have the character of a scientific article. The research niche has not been defined, the extensive literature research has not been carried out, it is not clear what exactly is the subject of the research and what are the implications of the presented results. The article is written using poor English and weak academic language. Additionally, the quality of graphics is unsatisfactory for a publication from the Philadelphia List (e.g. no precise map depicting the research area, simple graphs prepared using EXCEL).

In view of the above, I believe that the article should not be published in Water and I request that it be rejected.

Sincerely,

Reviewer