Increased Arctic NO₃⁻ Availability as a Hydrogeomorphic Consequence of Permafrost Degradation and Landscape Drying

Round 1

Reviewer 1 Report

The study by Arendt et al used the multiple geospatial methods to assess the impact of microtopography, soil moisture on NO3- availability in a polygonal permafrost landscape. The main finding is a mechanism about how permafrost thaw alters the NO3- availabilities that different moisture conditions of microtopography drive the differences of NO3- availabilities. This is an interesting and valuable topic and the contents and findings of the study are appropriate for the journal.

However, there are some questions necessary to be deeply thought out and modified.

Below are my general and specific comments that may help improve the quality of the paper before it is accepted for publication.

General comments:

1. Although the dataset of this study is not only with the original observational data but also with the synthesized data of previously published observations, the available NO3- and soil moisture data pairs are still limited to interpreting that moisture is the main driving factor to NO3- availabilities. Because there are many other factors among different sites of microtopography.
2. The author wanted to consider the impacts of microtopography, soil moisture, and plant functional types on NO3- availability in a polygonal permafrost landscape. However, the discussion about plant functional types is rare.
3. If drying can increase NO3- inventories, what is about it after refreezing? You can slightly discuss the changes before and after freeze-thaw with your and previous data from 2012 to 2017.

Specific comments:

1. Please add one or two sentences at the end of the ‘Abstract’ to conclude the significance of these results in this study.
2. The last sentence of ‘Result 3.1’ should be moved to the ‘Discussion’ part.
3. Why use two regressions (Figure 3-c and d) to show the relationships between NO3- and soil moisture at the same time? What is the logicality or mechanism?
4. ‘Conclusions’ is too long to highlight the main method and findings clearly. Try to move the explanation to the discussion part.
5. Figure 1: Please add the image to show the location of BEO in the USA on the left of this image.
6. Figure 3: Add the statistic to show the significant difference in the picture a) and b). The legend of picture d) is not right.

Author Response

Please see attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors put forward the new mechanism of increases nitrate availability under permafrost thaw, and investigated the potential changes in nitrate availability in response to possible hydrogeomorphic evolution scenarios of permafrost landscapes, by using multiple geospatial approaches. The topic of the study fits the scope of the journal, and the study has contributed some interesting new data points. The result are meaningful to clarify the response and feedback mechanism of nitrogen cycling in Arctic area under climate warming. The innovation and contributions of this manuscript paper is clear. The method is effective, and the manuscript is well organized. The interpretation of the results is appropriate.

Detail comments:

1. In the abstract section, [NO3-] should be revised as NO3-.
2. In the introduction section, nitrogen (N), the abbreviate should be given when it first appeared.
3. In the title of 3.1, “Soil moisture and NO3- distributions” should be revised as “Soil NO3- and soil moisture distributions”  
4. In the result section, the sentence “Our survey highlights that NO3- concentrations and soil moisture content of the BEO polygonal features have a strong inverse correlation between soil moisture content and NO3- concentration respective to polygon type”should be refined to make it clearer. 
5. The conclusion section should be refined to highlight the new mechanism of NO3- availabilityincreasing under permafrost degradation. 
6. Please remove the important information from appendix to the main body of paper, e.g. remove thesources of nitrate to the introduction section.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf