The Impact of Permafrost Change on Soil Organic Carbon Stocks in Northeast China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Reviewers Comments

Title: The Impact of Permafrost Change on Soil Organic Carbon Stocks in Northeast China

 

Major revisions:

·         Line 84-85: Give a brief of why there is a significant change.

·         Line 302 and 315: An explanation for this observation needs to be added to the discussion.

Minor revisions:

·         Line 32: Keywords should be arranged according to alphabetical order.

·         Line 50 and 51: Leave a space before the degree sign. Please check this throughout the manuscript.

·         Line 54: CO2, here 2 has to be subscript. Please check this throughout the manuscript for all the super and subscript letters.

·         Line 67: It seems that the sentence needs to be rearranged to give the correct meaning.

·         Line 88: GST, give full form at first mention.

·         Figure 1: In the figure caption, mention the full form of DEM.

·         Line 134: Space after cm.

·         Line 139: Add the reference to this model. Mentioning the reference in the introduction alone is not sufficient.

·         Equation 7: The parameter T is not defined in the description.

·         Equation 8: The parameter wi is not defined.

·     Figure 2: include the abbreviations in the figure caption rather than a special note.

·         Figure 4(b): space between parameter and unit.

 

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

 The article exhibits a proficient command of the English language.

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper, title “The Impact of Permafrost Change on Soil Organic Carbon Stocks in Northeast China” discusses a study on the impact of climate warming on permafrost and soil organic carbon (SOC) stocks in Northeast China. The study uses regression and top temperature of permafrost (TTOP) models to assess changes in permafrost extent and analyses the relationship between land use and land cover (LULC), SOC stocks, and permafrost changes. Key findings include: 1-Permafrost Shrinkage, from the 1980s to the 2010s, the permafrost area in Northeast China significantly reduced from 37.43×10^4 km² to 16.48×10^4 km². 2-Changes in SOC Stocks, there was a decrease of 24.18 Tg C in SOC from the 1980s to the 1990s, followed by a rapid increase of 102.84 Tg C in the 2000s. 3- Impact of Permafrost Degradation on LULC, permafrost degradation has accelerated the succession of LULC, affecting approximately 90% of the SOC in these regions. 4- Relationship Between Permafrost Changes and SOC, the study finds that permafrost degradation initially reduces SOC stocks but increases them over the long term. LULC significantly influences this relationship. And, 5- Study Goals and Implications, the study aims to understand the status of permafrost and the dynamics of SOC. It also seeks to provide scientific references for policy-making on sustainable land use and management. This is important for promoting ecological balance and sustainable development in the region. In summary, the study highlights the complex interactions between permafrost degradation, SOC dynamics, and land use changes, underlining their significance in the context of global carbon cycles and climate change.

The research is indeed very interesting and relevant. It addresses critical topics such as climate change, permafrost degradation, and sustainable resource management, which are key for both environmental science and sustainable development policies. The study provides valuable insights into how changes in permafrost affect soil organic carbon (SOC) stocks, a crucial component in understanding the global carbon cycle and its implications for climate change. Furthermore, the study highlights the relationship between land use and cover and permafrost changes, which is crucial for land-use planning and ecosystem conservation. The findings can assist in formulating more effective policies for land management and sustainable development, especially in regions impacted by climate change. Thus, the work is not only interesting from an academic perspective but also highly relevant for decision-making in policy and environmental management.

However, I see some issues in this work that imply it cannot be published in its current form.

Main concerns

1: Although it is true that if permafrost thaws and temperature increases, vegetation grows exuberantly and this sustained change over time causes an increase in SOC, we do not know which fraction of SOC increases (oxidizable, dissolved, particulate, etc.). The authors are working with TOC. As a first approximation, this may be sufficient, but to truly understand the real consequences of the disappearance of permanent permafrost on the SOC pool, it is necessary to study the main forms of carbon. It is very possible that what increases with the melting of permafrost is the oxidizable carbon. This does not invalidate the work, but the authors should include this reflection in their discussion and conclusions.

2: In addition, the citations chosen by the authors not always are the most appropriate for a work of the international importance and relevance of this topic. For example:

 

Linea 65:   the work cited here ( nº 27) is not the most suitable.  Changes in permafrost have been described since the 19th century. A pioneering scientific study in the field of permafrost research related to changes due to rising atmospheric temperatures is the research work conducted by Vladimir Romanovsky and his colleagues. Romanovsky,  is a prominent scientist in the field of permafrost research and has made significant contributions to our understanding of how permafrost responds to global warming. One citation suitable to include in this asseveration could be the (nº 35). Also, one of the pioneering international works in the study of changes in Earth's permafrost with the rise in atmospheric temperature is the Special Report on Climate Change and Land Use from the Intergovernmental Panel on Climate Change (IPCC). The special report on permafrost, published in 2019, examines in detail how permafrost, which is permanently frozen soil, is undergoing significant changes due to global warming. The document reviews available scientific literature and presents projections on the future impacts of climate change on permafrost.  Some of the key findings of this report include that permafrost is thawing in many regions, which can release large amounts of greenhouse gases such as carbon dioxide and methane into the atmosphere. Authors should review the cited literature in more depth. Especially when they refer to topics that relate the evolution of permafrost to climate changes or the effects of increasing the thickness of the active permafrost layer.

 

3: Other main concerns is related to the data used to train the TTOP models.  Using data with known errors to train models can be problematic and is not a suitable practice in most cases. If the temperature (GST) data before 2003 had systematic errors, using them as a basis for training and validating a model could lead the model to learn and perpetuate those errors. This could result in incorrect predictions and analyses. In data science and modeling, it's essential to work with high-quality data and correct any known systematic errors before using them to train models. Instead of using inaccurate data, it's preferable to make corrections to the data or seek more reliable data sources if available. Using flawed data as a basis for a model can lead to erroneous and biased conclusions. The authors rectified errors in data before using them for model training, but it is not clear what soil surface temperature data were well taken. In CALM permafrost plots, TTOPS data are taken with I-buttons placed on the soil surface and protected from the influence of ambient temperature. It is important for the authors to better explain how the data have been taken in the first part of the time series (up to 2003) since these data were used to train the models.

 

4: Some important conclusions are not supported by the results, for example:

Line 367: “1.23°C and the Mean absolute error (MAE) was 0.94°C. This indicates that the map of the distribution of perennial permafrost in Northeast China 368 developed through this study has a high degree of confidence”. I disagree with this assessment. The difference between perennial permafrost and not is values of GST above and below zero degrees. The values of table 5 are close to zero degrees, adding or subtracting the RMSE (+-1.23 ºC) or MAE (+- 0.94ºC) to the values in the table can mean that perennial permafrost locations become non-existent. In this context, contrarily of authors I believe that the error of the models is very significant.

 

5: At least the SOC: The link they provide is a geoportal for data download, but this is not sufficient. They need to explain what the SOC data consists of, how it was obtained, and with what techniques. The authors must to explain the SOC data used.

Line 134-135: “The global 1 km surface (0-30cm) SOC pool product for the years 1981 to 2019 obtained from the National Earth System Science Data Center”. Authors must explain in detail what SOC data they have used.

Lines 412-414: “…..In the later period, both the carbon sequestration capacity and the carbon content of vegetation and soil began to increase, indicating that Northeast China was continuously adding carbon to SOC 4 during this period.” Perhaps this is true, but it is very important to know how the SOC coverages weremade? With samples or using remote sensing? It is very important to clarify the section “2.2.4 Soil Organic Carbon (SOC)”. Perhaps in the geoportal of National Earth System Science Data Center, this term is explained, but for the international science community (that not know Chinese language) this connexion it not enough information.

 

Figures

Fig.1 Are the heights really below sea level? The minimum elevation appears as negative -135m. Putting some points with its elevation (the highest peak or the lowest point) would make it easier to read the DEM.

Fig.2 The symbology is very complex and difficult to read, perhaps this figure needs to simplify the legend and clarify the terms using a table?

Fig.3 Maps need homogeneous legends in order to be read properly. When classifying the model according to its values, the same value is always seen when in the legend (a)-3.86_10.64 ºC; (b) -5.3 _9.78; etc, authors should adjust the values in the legends so that the color patterns in the maps vary according to homogeneous class boundaries. Another issue is the scale and the North that is repeated in the composition four times, I think the authors should use a single scale bar and a single north.

Line 378: Fig.7 are the same boreholes? if they are different boreholes the comparation between graphics it is not relevant…..the authors could sustitute the graphic by statistical parameters of the both populations…..

 

Minor concers

Line 49: Repeat the quote from line 47, put it only once?

Line 62: Explain which remote sensing techniques have been an advance in the study of permafrost and why?

Líne 83: Mentions the remote sensing techniques again but doesn't say which ones

Lines 142:145…separar para entender bine los símbolos del modelo de Riseborough 1996. Poner en orden las ecuaciones y su descripción. La formulación de DDT debería antes que DDF

Line 157: Again remote sensing but doesn't say how to use it...infrared? In this case...explain a little more than remote sensing techniques have been used to measure GST.

Lineas 162-164: It is not very clear which data were taken with errors, because they were taken directly on the surface of the ground, I understand that with remote sensing, why have they been used to train the TTOP models? TTOP data should not be taken from sensors that are touching the ground, or within the active permafrost layer....  What data are the wrong ones, before or after 2003???

Line 178: what result TTOP? Data or model estimations?

Line 194: Apart from the name, put longitude and latitude and altitude of the stations....this informs the type of data expected from each station and if they are homogeneously distributed.

Line 254-256 : cite Table 3

Line 322: It is very important compare similar things. The amount of SOC at soil surface and at 30 cm of depth in the soil profile are complete different things.  30 cm is too much depth in soil profile and is possible that the accretion of the SOC due to the melting of permafrost or the increase of the active layer during a decade not has any influence at this depth….the author have to sure that they are compared similar things to obtain valid conclusions.

Line 339 - 346: It is very confusing and difficult to understand. The authors have to decide if this is an important ítem. If dedice that this is important try to simplified. In my point of view this paragraph it is not relevant and can be to be removed

Line 349: Model evaluation subsection. This subsection is primarily results, not discussion. This analysis is not in the margin of results. Also in Table 5, line 362, the data are shown..... The authors may prefer to organize the article by including a results and discussion section. But, in the current structure of the article, authors have to separate what the results are and discuss about the results of other authors compared to their results.

Line 381: only one citation???? “51: Wang, J.; Liu, D., Vegetation green-up date is more sensitive to permafrost degradation than climate change in spring across the northern permafrost region. Global Change Biology 2022, 28, (4), 1569-1582.” “Under the influence of global climate change, the degradation of permafrost in the northern hemisphere is an undeniable fact”…This lapidary sentence need more  than one citations…or IPCC compilation report….but only one paper it is not suitable.

Line 429: “4.4 Response of SOC to changes in perennial permafrost”. In this apart, the authors discuss mainly the relations between the distribution of soil uses ( LULC) and SOC evolution ( lines 430_452). This discussion is not contemplate in the title of the section. Perhaps a more suitable title could be: SOC in different LULC and response to changes in perennial permafrost..

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

As you know, climate change is currently underway, which leads to disruption of the natural processes of "freezing-thawing" of glaciers, the formation of permafrost territories. Changes that occur in the biosphere have an impact on the cycle of climate-forming elements, become a trigger for violation of soil properties, their degradation. Due to the fact that this process is currently irreversible and covers the entire globe, in this regard, the study of the HPE on this topic in a particular region (China) is very relevant. The article provides a comprehensive analysis of the spatial and temporal changes in the properties of soils formed on the territory of China. A very good and detailed material about the carbon content in soils is given in the article. These data are very informative, as they allow the world community to understand the contribution of the territory (soils) to carbon gas emissions. The data is also very interesting, as it can be compared with other territories of the Eurasian continent. There are a lot of drawings in the article, which are very clear, understandable, informative. The tabular material is presented in great detail, well designed, which allows other researchers to make comparisons and draw certain conclusions. The article will make a very good impression. I especially liked the link to the materials National Meteorological Information Center 113 (https://data.cma.cn), which allow us to clarify the features of the studied territory of China. I think that this article will be very interesting for scientists of related specialties, since it affects not only the problem of carbon balance, but also the influence of plants on the processes of carbon cycling in the soil. The latter, as is known, determines their fertility, which is one of the world's key areas for studying agroecosystem soils. There are comments in the work, which are presented below.

3- the plants are not indicated in the name, I think we need to refine a little, very narrowly

28 - the goal should be forward,

15-18 - indicate at the beginning where the study was conducted...in general, it is not clearly written

31 - why only in China, we can say for other areas

18 is already the more important part, you can start with it

32 - ... model...is it possible to write

75- where is the purpose of the work, where are the tasks? the most important thing is what is your hypothesis? please write where you can use the data obtained in the new carbon agenda?

152 - make the name of the table more informative

210 - it is necessary to make a table in which to specify the maximum, minimum, average temperature data for this period...something is very not clearly visible from the graph

 

235 - very valuable data, informative, but poorly readable...it is necessary to divide into 2 drawings, make them clearer!!!

251 - why did they put everything in a "pile"...it is also necessary to make everything clearer in the explanation

253 - the table is "floating", very huge...I recommend changing it...give a clearer name

294 - specify where (place)?

310 - I recommend to recalculate (*103), then the numbers will be smaller!the table will "stand up" on the sheet

312-347 - why there are no paragraphs. Everything is clearly written here, very well

346 - can not write conclusions...this is already in the discussion

364 - CW13 124.31 50.70 1.90 0.12

CW14 124.21 50.47 3.00 0.17 - why the data is positive, it should be noted in the text

376 - how do you blow why a straight line on the graph... or maybe a hyperbole or another line?such graphs are always in doubt, nature is unpredictable!

404 -...I propose to separate the graphs, make 2 drawings

411 - decomposition..I suggest another term

Comments on the Quality of English Language

everything is clear, the terms are used correctly

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I have completed my review of the article assigned to me. After a thorough and detailed examination, the article in its current state is ready for publication. I have done a very thorough review because I think the article has a lot of interest and will have many readers around the world.  Thank you for requesting me as a reviewer