the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Apr 2024
Complexity of nutrient enrichment on subarctic peatland soil CO2 and CH4 production under increasing wildfire and permafrost thaw
Abstract. The adverse impacts of excessive soil nutrients on water quality and carbon sequestration have been recognized in tropical and temperate regions, with already widespread industrial farming and urbanization, but rarely in subarctic regions. However, recent studies have shown significant increases in porewater nitrogen (N) and phosphorus (P) concentrations in burned subarctic peatlands and downstream waters, which is a growing concern as climate change leads to increasing wildfires, permafrost thaws, and waterlogged peatlands. In this study, we present the results of a short-term incubation experiment conducted on soils from subarctic bogs and fens, aimed at evaluating the effects of high levels of nutrients on carbon gas production rates. We divided aliquots of the peatland soil samples into separate containers and added artificial porewater to each, enriching them with dissolved inorganic nitrogen (N), phosphorus (P), both, or none for controls. Overall, the fen samples showed higher carbon dioxide (CO2) and methane (CH4) production rates at 1, 5, 15, and 25 °C compared to the bog samples, which we attributed to differences in soil properties and initial microbial biomass. The bog sample with added N produced more CO2 compared to its control, while the fen sample with added P produced more CO2 compared to its control. It was unexpected that the addition of both N and P reduced CO2 but increased CH4 production in both soils compared to their controls. After a month, the pore water C, N, and P stochiometric ratios approached the initial soil microbial biomass ratios, suggesting microbial nutrient recycling in an inherently nutrient-poor soil environment. These preliminary results imply a complex response of carbon turnover in peatland soils to nutrient enrichment.
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RC1: 'Comment on egusphere-2024-1047', Anonymous Referee #1, 19 Jul 2024
The authors investigate the effects of nutrient enrichment that comes with wildfires and permafrost thaw in subarctic peat lands on soil CO2 and CH4 production. While they name "subarctic peat lands" in the title, they investigate basically samples from two sites in the same region of Canada. That means the title promises more than is presented in the manuscript. The choice and combination of methods is valid, however, the core concern regarding this manuscript is the fact that the authors used only four samples. I doubt that the informative value of this set-up is sufficient. While the experiment itself is interesting and promising, I stongly recommend to add more samples to the experiment and do/repeat the experiment at least in duplicates, better in triplicates (of every single sample) to check if the obtained data is valid. In the given form I can not recommend the manuscript for publication as I am not convinced that the extent of the experiment is sufficient to support the authors' conclusions. However, it might be an option to address this clearly and adjust the discussion accordingly.
The quality of the language is good and causes at no point problems regarding the comprehensibility. However, the manuscript needs some polishing it should be taken care that a more scientific language is used. The introduction needs to be restructured and rephrased in some parts. Very often, single sentences or parts of the introduction are not connected to each other and therefore the authors' reasoning is not clear. The authors also use very general terms frequently without explaining their meaning in the given context. With the Methods section, it is the same - some parts are more evocative of a staccato than of a coherent text.Please find my detailed comments below:
Title
Having read your manuscript, it is clear what you want to express using this title. However, I suggest to change it slightly to arouse interest in more readers, for instance, "complexity" is a very broad term. In addition, just mentioning "subarctic peatland" suggest that you investigated samples from several subarctic areas - you should clarify this.Abstract
l. 15-17 Why is an increasing N and P concentration a growing concern in this context? This should be made clear.
l. 18 I suggest to add "which" here: "...from subarctic bogs and fens, which aimed at..."
l. 23-25 Please rephrase this sentence to make it clearer ("It was unexpected..."). Do you mean N and P were added together or both treatments?
l. 20-26 It is not really clear how you treated the samples. You had three treatments + control (N, P, N+P, none), but what about the different temperatures you name in line 21? And how long did your experiment last? In line 25 you mention "after a month" - was this the end of the experiment or just the point where you observed that C, N, and P ratios approached initial soil microbial biomass ratios? This needs to be more precise.
l. 26 What do you mean by "nutrient recycling" here and how do the approaching ratios suggest this? Please explain.Introduction
l. 30-32 In line 30 you name "subarctic regions", in line 31 you refer to "the region". In line 32 you name additionally western Canada, Siberia, and Alaska. #
Which region is meant here? Do western Canada, Siberia, Alaska not belong to (or contain) subarctic regions? Please check these sentences and clarify your
statements.
l. 36-40 Again, please explain why increasing nutrient inputs are a rising concern here. Above, you only mentioned the increase in POC and DOC, you do not give a reason for the enrichment in N and P.
l. 40-44 I suggest to seperate the two parts of this sentence and emphasize the effects of permafrost thaw you name here. And still, you do not mention why all of this is a problem. What is the effect of dissolved nutrients? What is the effect of an increased hydrological and geochemical connectivity?
l. 52 Where does "generally most poor in soil nutrients" refer to? To the N-fixing microbes? And what do you mean by "most poor"?
l. 53-56 Here it could help to add one sentence that describes the impacts in temperate and tropical peatland soils.
l. 60-63 The connection between the first part ("Recent observations...") and the second one ("but the effects...") is not clear.
l. 64 To me it is still not clear what you mean by "nutrient recycling".Methods
Figure 1 Please check the caption. It could also help to mark your sampling area in the small map in the upper left corner.
l. 93-96 Please split this sentence in at least two sentences. And please clarify its second part: it should be made clear that the named steps belong to the MgNO3 digestion method.
l. 96-97 I do not understand the last sentence here. Do you mean you did not attempt to compare the pools prior to the treatment with the pools after the treatment?
l. 101-104 Please rephrase this part.
l. 105-106 Why did you measure microbial biomass C, N, and P after the pre-incubation?
l. 102-103/108-111 You repeated the measurement of moisture content after pre-incubation to decide how much porewater solution should be added, but then you use data from adjacent meterorological stations to obtain this information? Please explain what you did clearly and in comprehensible steps.
l. 165-166 "The subsamples were treated either with chloroform for 24 hours to fumigate in a vacuum desiccator, or with no fumigation."? Please explain why,
this way it sounds like you just randomly fumigated some samples and some not.Results and Discussion
l. 190 It should be "resulted in" (whole section, not only this line).
l. 192-194 "...are consistent with its higher microbial biomass than the bog initially."? Please check again thoroughly your manuscript if references within sentences are correct.
l. 196-203 It would massively enhance the comprehensibility if you would focus on one treatment after the other.
l. 216 Why do you refer to Table 2 here?
Table 2 Given are the Q10 values - why don't you mention this in the caption? Why are there no values for bog CH4?
l. 222 Here, it is 3.89 - in the table it is 3.90. In gnereal: Is your method sufficiently precise to give two decimals?
Figure 3 Your caption should make clear which differences are given: "Relative differences (%) between x and y in the..."
l. 263-270 These are very general statements and should be better connected to your data.
l. 273-275 Please rephrase this sentence.
Figure 4 "The shades ara indicates where the initial porewater ratios are marked"?Citation: https://doi.org/10.5194/egusphere-2024-1047-RC1 -
AC1: 'Reply on RC1', Eunji Byun, 14 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1047/egusphere-2024-1047-AC1-supplement.pdf
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AC5: 'Correct attachment', Eunji Byun, 14 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1047/
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AC1: 'Reply on RC1', Eunji Byun, 14 Oct 2024
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CC1: 'Comment on egusphere-2024-1047', Nasrollah Sepehrnia, 27 Jul 2024
This study investigates the impact of nutrient enrichment on carbon gas production in subarctic peatlands. Authors have examined addition of nitrogen and phosphorus to soil samples from bogs and fens, and observed varied effects on CO2 and CH4 production, indicating complex interactions between nutrient levels and carbon cycling in these regions. The results have illustrated the importance of nutrient enrichment on microbial activity and carbon turnover in nutrient-poor subarctic soils. I think this lab experiment can provide strong evidence for conducting large-scale studies. I recommend the manuscript for publication after consideration of the following comments (minor revisions).
1- Introduction
Authors may provide readers with clear hypotheses (in one or two sentences) and objectives afterward “ …..but the effects of sudden nutrient inputs to the peatland soils remain poorly understood…..”
-Authors may rephrase lines 60-70 to highlight the following hypotheses accordingly.
-Why nutrient addition in subarctic peatland soils?
-Microbial Responses in the short-term and the impacts?
-Nutrient enrichment and GHG emission in subarctic peatland soils?
2- Materials and methods
This part is organized very well.
3- Results and discussion
The results are described very well using the illustrated figures and tables. Authors may compare their results with other relevant studies (e.g., from the cited Refs) in the following parts.
“3.1 Transient changes in the soil CO2 and CH4 production and,
3.2 Variations in the temperature sensitivity of CO2 and CH4 productions”
Citation: https://doi.org/10.5194/egusphere-2024-1047-CC1 -
AC2: 'Reply on CC1', Eunji Byun, 14 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1047/egusphere-2024-1047-AC2-supplement.pdf
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AC2: 'Reply on CC1', Eunji Byun, 14 Oct 2024
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CC2: 'Comment on egusphere-2024-1047', Nasrollah Sepehrnia, 27 Jul 2024
This study investigates the impact of nutrient enrichment on carbon gas production in subarctic peatlands. Authors have examined addition of nitrogen and phosphorus to soil samples from bogs and fens, and observed varied effects on CO2 and CH4 production, indicating complex interactions between nutrient levels and carbon cycling in these regions. The results have illustrated the importance of nutrient enrichment on microbial activity and carbon turnover in nutrient-poor subarctic soils. I think this lab experiment can provide strong evidence for conducting large-scale studies. I recommend the manuscript for publication after consideration of the following comments (minor revisions).
1- Introduction
Authors may provide readers with clear hypotheses (in one or two sentences) and objectives afterward “ …..but the effects of sudden nutrient inputs to the peatland soils remain poorly understood…..”
-Authors may rephrase lines 60-70 to highlight the following hypotheses accordingly.
-Why nutrient addition in subarctic peatland soils?
-Microbial Responses in the short-term and the impacts?
-Nutrient enrichment and GHG emission in subarctic peatland soils?
2- Materials and methods
This part is organized very well.
3- Results and discussion
The results are described very well using the illustrated figures and tables. Authors may compare their results with other relevant studies (e.g., from the cited Refs) in the following parts.
“3.1 Transient changes in the soil CO2 and CH4 production and,
3.2 Variations in the temperature sensitivity of CO2 and CH4 productions”
Citation: https://doi.org/10.5194/egusphere-2024-1047-CC2 -
AC3: 'Reply on CC2', Eunji Byun, 14 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1047/egusphere-2024-1047-AC3-supplement.pdf
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AC3: 'Reply on CC2', Eunji Byun, 14 Oct 2024
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RC2: 'Comment on egusphere-2024-1047', Anonymous Referee #2, 24 Sep 2024
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AC4: 'Reply on RC2', Eunji Byun, 14 Oct 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1047/egusphere-2024-1047-AC4-supplement.pdf
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AC4: 'Reply on RC2', Eunji Byun, 14 Oct 2024
Data sets
Dataset for Examining the Effects of Nutrient Pulses on Biogeochemical Cycling in Subarctic Peatlands in the Context of Permafrost Thaw and Wildfires Eunji Byun, Fereidoun Rezanezhad, Stephanie Slowinski, Christina Lam, Saraswati Saraswati, Stephanie Wright, William L. Quinton, Kara L. Webster, and Philippe Van Cappellen https://doi.org/10.20383/102.0712
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