Combined water table and temperature dynamics control CO<sub>2</sub> emission estimates from drained peatlands under rewetting and climate change scenarios

Denager, Tanja; Christiansen, Jesper Riis; Schneider, Raphael Johannes Maria; Langen, Peter L.; Quistgaard, Thea; Stisen, Simon

doi:10.5194/egusphere-2025-2503

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https://doi.org/10.5194/egusphere-2025-2503

Preprints

25 Jun 2025

| 25 Jun 2025

Combined water table and temperature dynamics control CO₂ emission estimates from drained peatlands under rewetting and climate change scenarios

Tanja Denager, Jesper Riis Christiansen, Raphael Johannes Maria Schneider, Peter L. Langen, Thea Quistgaard, and Simon Stisen

Abstract. This study integrates process-based hydrological modeling and empirical CO₂ flux modeling at a daily temporal resolution to evaluate how peatland hydrology influence CO₂ emissions under scenarios of rewetting and climate change.

Following the calibration of a three-dimensional transient groundwater flow model for a peat-dominated catchment, daily groundwater table dynamics were simulated to represent hydrological conditions in drained peat soils. These simulations were coupled with an empirical CO₂ flux model, developed from a comprehensive daily dataset of groundwater table depth, temperature, and soil CO₂ flux measurements. The empirical CO₂ flux model captures a clear temperature-dependent response of soil CO₂ emissions to variations in groundwater table depth.

By applying this coupled modeling framework, we quantified CO₂ emissions at daily timescales. The results demonstrate that incorporating both temperature sensitivity and high-resolution temporal variability in water level significantly influences projections of CO₂ fluxes. Especially the co-occurrence of elevated air temperature and low groundwater table significantly influence CO₂ emissions under scenarios of rewetting and climate change. These insights highlight the importance of including changing climate conditions in future peatland management strategies for emission inventories.

The study illustrates the value of combining detailed hydrological simulations with emission models. It also emphasizes the need for detailed monitoring of greenhouse gas emissions across multiple sites and the development of robust empirical models that can be generalized and spatially upscaled.

Received: 28 May 2025 – Discussion started: 25 Jun 2025

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15 Jan 2026

Combined water table and temperature dynamics control CO₂ emission estimates from drained peatlands under rewetting and climate change scenarios

Tanja Denager, Jesper Riis Christiansen, Raphael Johannes Maria Schneider, Peter Langen, Thea Quistgaard, and Simon Stisen

Biogeosciences, 23, 441–462, https://doi.org/10.5194/bg-23-441-2026,https://doi.org/10.5194/bg-23-441-2026, 2026

Short summary

Tanja Denager, Jesper Riis Christiansen, Raphael Johannes Maria Schneider, Peter L. Langen, Thea Quistgaard, and Simon Stisen

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2503', Anonymous Referee #1, 10 Sep 2025
The manuscript presents a well-structured and scientifically sound study with valuable findings on the prediction of CO₂ emissions from peatlands under warming climate and rewetting scenarios. The modeling approach and discussion are generally well executed. I recommend the authors consider the following minor revisions to improve clarity and consistency:
Lines 63–66: The sentence is difficult to follow due to the use of both WTD and groundwater level, which change in opposite directions. Please consider reformulating the sentence using only WTD.

Lines 70–71: Correct the double negative in “not … neither ... nor.”

Table S3: Please define the variables Alpha, N, L, and Kint.

Line 201: The term KGE_WTD is not defined—please add a definition.

Line 203: To maintain consistency with other objective functions, consider using subscripts for q_head_amp.

Lines 215–217: It is unclear how the objective functions are combined, given their differing ranges and optimal values. Please clarify the methodology.

Tables S3 and S4: Both tables present water retention parameters for peat, but with differing values. Could you explain the reason for this discrepancy?

Line 287: Remove the unnecessary line break.

Line 433: The temperature sensitivity of soil fCO₂ is commonly reported as non-linear. While the selected model and alternatives are well addressed in the discussion, I’m curious—did you explore temperature sensitivity within WTD bins? The model appears to miss many of the observed high fCO₂ values; perhaps a non-linear temperature dependence could improve performance?

Lines 479–487: While I understand the need to limit fCO₂, the rationale behind the chosen thresholds (WTD 62.5 cm and Tair 25°C) is unclear. I expect hese values to strongly influence the comparison of modeled fluxes for extreme years (Lines 516–517). Please elaborate.

Lines 488–491: The statement that “both CO₂ flux models exclusively account for the CO₂ emissions from the peat soil” is misleading. The Annual model includes NEBC, and thus GPP, as discussed earlier in the manuscript. GPP is also used as a reason for downscaling the daily model for fCO₂. Please revise this statement for accuracy.

Figure 6: Consider combining panels c and d, as they contain overlapping information.

Discussion: The section is generally well structured. However, it would benefit from additional citations, e.g., regarding the advantages of hydrological models and process-based emission models.
Citation: https://doi.org/10.5194/egusphere-2025-2503-RC1
- AC1: 'Reply on RC1', Tanja Denager, 14 Nov 2025
  
  Thank you for reviewing the manuscript. Our responses to your comments are provided in the attachment.
  Best regards
  Tanja Denager and co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2025-2503-AC1
RC2:
'Comment on egusphere-2025-2503', Anonymous Referee #2, 31 Oct 2025

The authors have done hydrological modelling of peatland WTD and its impacts on CO₂fluxes in current and future climates under different rewetting scenarios. Overall the study is well conducted and clearly represented. The study is highly topical considering the importance of peatland ecosystems in GHG budgets and the open questions still surrounding them. I only have a few minor comments on the manuscript.
1. Concerning the rewetting scenarios: Are there actual management practices, that can focus the rewetting seasonally? I am only aware of the more nature-based methods, such as ditch-blocking. I appreciate that discussing actual, real-life management practices is not the point of this manuscript but it would perhaps be helpful to somewhere explain how these scenarios used here relate to real life, as your findings rather strongly suggest that considering the seasonal variation in rewetting is important.
2. Choosing one RCP is understandable considering the amount of variables that are already present in the study. I do not suggest that you introduce a milder climate scenario here but I think it would be good to acknowledge in the discussion that this is the scenario leading to strongest impacts of climate change. This is particularly relevant for your manuscript, as you assess the cascading impacts of two climate-related variables. It would be highly interesting to know (perhaps in a future paper) if this relationship of WTD and T_acancelling each other out is visible in other climate change scenarios, or would the influence of one overpower the other.
3. Throughout the paper, you refer to the ground surface as "terrain", i.e. on L63 and L129. Is there a particular reason why you don't just say "surface"? I'm not sure I've ever heard this use of the term terrain, and at least for me, this was somewhat confusing.
4. I would advise on renaming the two future time periods as "mid-century" (or something like that" and "end of century". Distant future, to me at least, seems to be something further in the future than within my own lifespan, and since your simulation covers this century, it seems like a much clearer choice to refer to that.
Fig.3: Could you make the lines within the legend a little thicker, so that it is clear which line (blue or black) is referring to modelled and measured values?
Finally, while the language is generally very good, I would advise a thorough read-through of the manuscript, or employing the help of a proof-reader. I have listed below some parts that need refining, but I did not conduct a thorough language check.
L70. Do not account for neither: double negative.
L85: Sentence starting with "For example through..." is not a full sentence.
L91: field-scale, not field scale
L113: Should this be "continuous", not "contiguous"?
L126: This probably should be "automatically", not "automatic"
L306: There is no need to say "such as rewetting", since this is the only management practice discussed in this paper.
L311-313: This is a confusing sentence.
L657: "In 2023, CO₂ emissions from drained organic soils in croplands and grasslands was estimated to

accounted for 6.7% of Denmark's total emissions" --> "was estimated to have accounted for"
L687: "Such nature-based solutions are not likely to reduce..."

Citation: https://doi.org/10.5194/egusphere-2025-2503-RC2
- AC2: 'Reply on RC2', Tanja Denager, 14 Nov 2025
  
  Thank you for reviewing the manuscript. Our responses to your comments are provided in the attachment.
  Best regards
  Tanja Denager and co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2025-2503-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-2503', Anonymous Referee #1, 10 Sep 2025
The manuscript presents a well-structured and scientifically sound study with valuable findings on the prediction of CO₂ emissions from peatlands under warming climate and rewetting scenarios. The modeling approach and discussion are generally well executed. I recommend the authors consider the following minor revisions to improve clarity and consistency:
Lines 63–66: The sentence is difficult to follow due to the use of both WTD and groundwater level, which change in opposite directions. Please consider reformulating the sentence using only WTD.

Lines 70–71: Correct the double negative in “not … neither ... nor.”

Table S3: Please define the variables Alpha, N, L, and Kint.

Line 201: The term KGE_WTD is not defined—please add a definition.

Line 203: To maintain consistency with other objective functions, consider using subscripts for q_head_amp.

Lines 215–217: It is unclear how the objective functions are combined, given their differing ranges and optimal values. Please clarify the methodology.

Tables S3 and S4: Both tables present water retention parameters for peat, but with differing values. Could you explain the reason for this discrepancy?

Line 287: Remove the unnecessary line break.

Line 433: The temperature sensitivity of soil fCO₂ is commonly reported as non-linear. While the selected model and alternatives are well addressed in the discussion, I’m curious—did you explore temperature sensitivity within WTD bins? The model appears to miss many of the observed high fCO₂ values; perhaps a non-linear temperature dependence could improve performance?

Lines 479–487: While I understand the need to limit fCO₂, the rationale behind the chosen thresholds (WTD 62.5 cm and Tair 25°C) is unclear. I expect hese values to strongly influence the comparison of modeled fluxes for extreme years (Lines 516–517). Please elaborate.

Lines 488–491: The statement that “both CO₂ flux models exclusively account for the CO₂ emissions from the peat soil” is misleading. The Annual model includes NEBC, and thus GPP, as discussed earlier in the manuscript. GPP is also used as a reason for downscaling the daily model for fCO₂. Please revise this statement for accuracy.

Figure 6: Consider combining panels c and d, as they contain overlapping information.

Discussion: The section is generally well structured. However, it would benefit from additional citations, e.g., regarding the advantages of hydrological models and process-based emission models.
Citation: https://doi.org/10.5194/egusphere-2025-2503-RC1
- AC1: 'Reply on RC1', Tanja Denager, 14 Nov 2025
  
  Thank you for reviewing the manuscript. Our responses to your comments are provided in the attachment.
  Best regards
  Tanja Denager and co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2025-2503-AC1
RC2:
'Comment on egusphere-2025-2503', Anonymous Referee #2, 31 Oct 2025

The authors have done hydrological modelling of peatland WTD and its impacts on CO₂fluxes in current and future climates under different rewetting scenarios. Overall the study is well conducted and clearly represented. The study is highly topical considering the importance of peatland ecosystems in GHG budgets and the open questions still surrounding them. I only have a few minor comments on the manuscript.
1. Concerning the rewetting scenarios: Are there actual management practices, that can focus the rewetting seasonally? I am only aware of the more nature-based methods, such as ditch-blocking. I appreciate that discussing actual, real-life management practices is not the point of this manuscript but it would perhaps be helpful to somewhere explain how these scenarios used here relate to real life, as your findings rather strongly suggest that considering the seasonal variation in rewetting is important.
2. Choosing one RCP is understandable considering the amount of variables that are already present in the study. I do not suggest that you introduce a milder climate scenario here but I think it would be good to acknowledge in the discussion that this is the scenario leading to strongest impacts of climate change. This is particularly relevant for your manuscript, as you assess the cascading impacts of two climate-related variables. It would be highly interesting to know (perhaps in a future paper) if this relationship of WTD and T_acancelling each other out is visible in other climate change scenarios, or would the influence of one overpower the other.
3. Throughout the paper, you refer to the ground surface as "terrain", i.e. on L63 and L129. Is there a particular reason why you don't just say "surface"? I'm not sure I've ever heard this use of the term terrain, and at least for me, this was somewhat confusing.
4. I would advise on renaming the two future time periods as "mid-century" (or something like that" and "end of century". Distant future, to me at least, seems to be something further in the future than within my own lifespan, and since your simulation covers this century, it seems like a much clearer choice to refer to that.
Fig.3: Could you make the lines within the legend a little thicker, so that it is clear which line (blue or black) is referring to modelled and measured values?
Finally, while the language is generally very good, I would advise a thorough read-through of the manuscript, or employing the help of a proof-reader. I have listed below some parts that need refining, but I did not conduct a thorough language check.
L70. Do not account for neither: double negative.
L85: Sentence starting with "For example through..." is not a full sentence.
L91: field-scale, not field scale
L113: Should this be "continuous", not "contiguous"?
L126: This probably should be "automatically", not "automatic"
L306: There is no need to say "such as rewetting", since this is the only management practice discussed in this paper.
L311-313: This is a confusing sentence.
L657: "In 2023, CO₂ emissions from drained organic soils in croplands and grasslands was estimated to

accounted for 6.7% of Denmark's total emissions" --> "was estimated to have accounted for"
L687: "Such nature-based solutions are not likely to reduce..."

Citation: https://doi.org/10.5194/egusphere-2025-2503-RC2
- AC2: 'Reply on RC2', Tanja Denager, 14 Nov 2025
  
  Thank you for reviewing the manuscript. Our responses to your comments are provided in the attachment.
  Best regards
  Tanja Denager and co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2025-2503-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Publish subject to minor revisions (review by editor) (15 Nov 2025) by Mirco Migliavacca

AR by Tanja Denager on behalf of the Authors (24 Nov 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (01 Dec 2025) by Mirco Migliavacca

Dear authors,
The manuscript improved after the review, still there are many issues with language, abbreviation, and inconsistencies in units.
Please carefully revise the manuscript.

In response to reviewer 1 about the real-world application of the authors added the following sentence (lines 676-683):

“Nature-based approaches represent the most common real-world rewetting strategies, aiming to restore peatlands towards their natural hydrological regime. At a minimum, such rewetting requires terminating tillage activities and eliminating artificial drainage for instance by blocking of drainpipes and ditches. The rewetting scenarios implemented in this study, represented as simple modifications to WTD, are not reflective of practical management interventions - except perhaps in a few rare and costly restoration projects that involve installing artificial impermeable membranes along peatlands edges (Naturstyrelsen, 2022). However, the outcome of this study can serve as a reference for discussions on realistic expectations on CO2 emission reductions from rewetted peatlands.”
Although the sentence clarifies some aspects, such as the fact that the tested rewetting solution is only partly applicable in the real world due to the high costs, I think the authors should explain more clearly how the study can serve as a reference. How can the study serve as a benchmark? How can other solutions be implemented, and what would the expected results be compared to the benchmark? Is the selected strategy the one that can achieve the greatest emission reduction potential? Can you compare it with other studies and provide more context on this aspect?
On line 57, there is something wrong with the parentheses.
Line 88: 'most LSM's' should be 'most LSMs'.
On line 170, 'LAI' please define LAI.
I have noticed that units are sometimes reported as kg/m³ or kg m⁻³. Please use only the second throughout the manuscript.
Define KGE before line 202.
Between lines 202 and 230, the description is a mixture of equations and undefined terms. Please rewrite it, making sure that all the symbols and acronyms are defined, and that this part of the text is written as an equation (for example, the beta equation at line 207).
Figure S1: Clarify what Kristensen and Jensen mean.
The units are missing from Figure S3. Please ensure that you add them to the axes.
Line 263: Please clarify what MgCO2-C refers to. I believe it is cumulative, but it should be defined.
Line 324: I suggest changing the title to 'Uncertainty of future climate CO₂ emissions'.
Line 451: This is the third time that the NECB has been introduced.
Figure 5: Please add the uncertainty of the fitting to the figure.
Line 709: RCP has already been defined above.

Hide

AR by Tanja Denager on behalf of the Authors (12 Dec 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (23 Dec 2025) by Mirco Migliavacca

AR by Tanja Denager on behalf of the Authors (29 Dec 2025) Manuscript

Journal article(s) based on this preprint

15 Jan 2026

Combined water table and temperature dynamics control CO₂ emission estimates from drained peatlands under rewetting and climate change scenarios

Tanja Denager, Jesper Riis Christiansen, Raphael Johannes Maria Schneider, Peter Langen, Thea Quistgaard, and Simon Stisen

Biogeosciences, 23, 441–462, https://doi.org/10.5194/bg-23-441-2026,https://doi.org/10.5194/bg-23-441-2026, 2026

Short summary

Tanja Denager, Jesper Riis Christiansen, Raphael Johannes Maria Schneider, Peter L. Langen, Thea Quistgaard, and Simon Stisen

Supplement

https://doi.org/10.5194/egusphere-2025-2503-supplement

Tanja Denager, Jesper Riis Christiansen, Raphael Johannes Maria Schneider, Peter L. Langen, Thea Quistgaard, and Simon Stisen

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Short summary

This study demonstrates that incorporating both temperature and temporal variability in water level in emission models significantly influences CO₂ emission from peat soil. Especially the co-occurrence of elevated air temperature and low groundwater table significantly influence CO₂ emissions under scenarios of rewetting and climate change.


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Combined water table and temperature dynamics control CO2 emission estimates from drained peatlands under rewetting and climate change scenarios

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Combined water table and temperature dynamics control CO₂ emission estimates from drained peatlands under rewetting and climate change scenarios