the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Carbon balance and emissions of methane and nitrous oxide during four years of moderate rewetting of a cultivated peat soil site
Abstract. We experimented a gradual water table rise at a highly degraded agricultural peat soil site with plots of willow, forage and mixed vegetation (set-aside) in southern Finland. We measured the emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) for four years. The mean annual ground water table depth was about 80, 40, 40 and 30 cm in 2019–2022, respectively. The results indicated that a 10 cm raise in the water table depth was able to slow down annual CO2 emissions from soil respiration by 0.87 Mg CO2-C ha-1. CH4 fluxes changed from uptake to emissions with a raise in the water table depth, and the maximum mean annual emission rate was 11 kg CH4-C. Nitrous oxide emissions ranged from 2 to 33 kg N2O-N ha-1 year; they were high from bare soil in the beginning of the experiment but decreased towards the end of the experiment. Short rotation cropping of willow reached net sequestration of carbon before harvest, but all treatments and years showed net loss of carbon based on the net ecosystem carbon balance. Overall, the short rotation coppice of willow had the most favourable carbon and greenhouse gas balance over the years (10 Mg CO2 eq. on the average over four years). The total greenhouse gas balance of the forage and set-aside treatments did not go under 27 Mg CO2 eq. ha-1 year-1 highlighting the challenge in curbing peat decomposition in highly degraded cultivated peatlands.
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Status: open (until 15 Jun 2024)
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RC1: 'Comment on egusphere-2024-934', Anonymous Referee #1, 21 May 2024
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General comments:
Kristiina Lång and co-authors present data from four years of measuring greenhouse gas emissions (CO2, N2O, CH4) of a (moderately) rewetted former agricultural field site in southern Finland. Three treatments were established (willow, forage, set-aside (bilberry was planted but didn’t grow)). The presented dataset comprises greenhouse gas flux data for four years. In addition, a full C balance including photosynthesis, ecosystem respiration, net ecosystem exchange, carbon in the plant biomass, and net ecosystem carbon balance was calculated. Overall, it is a very detailed dataset which will certainly be of interest for biogeochemical modeling of greenhouse gas emissions from rewetted peatlands. The paper is well written and easy to read. My main remarks are:
- A knowledge gap / description of the relevance of the study is missing.
- Methodology is not always clear (see specific comments).
- The authors did a lot of modeling on measured fluxes, but it remains unclear why and what the additional knowledge gain is.
Specific comments:
The introduction nicely summarizes the current knowledge about greenhouse gas emissions from peat soils and the effects of rewetting and changing water table depths. The introduction is followed by three hypotheses but misses a description of the research gap. After reading the introduction, it remains unclear why this study was necessary and what knowledge the authors attempt to gain. Similarly, results are mostly discussed separately in relation to other studies. There’s only little comparison between treatments and the overall significance of the (new?) findings remains unclear. The end of the abstract hints towards the general challenge, but also misses the description of a research gap/challenge.
The description of the greenhouse gas measurements in the methods section is not easy to follow. It would help to get an overview of the different measured parameter first and then a description of the sampling techniques and different chambers applied. It could also help to include a figure summarizing how GP, ER, NEE, and NECB relate to each other. This could also help to explain why some fluxes have negative signs. Which is not consistently used throughout the manuscript: sometimes GP fluxes/values are described as positive values, sometimes as negative values (compare Fig. 1, Tab. 3, and L294ff).
It is unclear why some parameters were not assessed for willow (see Tab. 3). This is not described in the methodology.
A lot of outlier removal was done. It is well described and mostly justified. However, if you have 9 high values in one plot (L236), there might be an explanation to that and it feels strange that you simply decided to exclude these values.
In addition to flux measurements, a lot of modeling was done. However, it’s neither part of the introduction, nor of the hypotheses. Also, the importance/relevance of the modeling approaches in addition to measuring is unclear as it is not described.
The description of the vegetation in the set-aside plots is not clear. It is written that ‘The number of species in the set-aside plots was determined once in the summer 2021’ (L80). While in L276ff there is a species number for summer 2022. It’s also unclear how there can be 19 different vascular plants in 18 different plant species.
Technical corrections:
Graphical abstract: shouldn’t that be < 30 in the figure?
L13 11kg CH4 à what area?
L43 not clear that paludiculture is always on peat soils
L46 regarding
L51 what is an oxidized layer? Please add an example
L114 reference for Canopeo app
L127 please add information why these different chambers were used
L148 what is the Vaisala GMP-343 probe measuring?
L151 why is this done? (the shading)
L178 equation 2 does not match description
L186 what about willow?
L235 leading to
L318 why are results not shown? Could be in the supplementary
L369 why are results not shown? Could be in the supplementary
L371ff headline numberings not consistent, headings in discussion are meaningless
L375 what crop was grown in the nearby field?
L421 comparable number
Tabe 2: please explain STD
Figure 1: panel letters missing, description of panels doesn’t match y-axes, please check if colors are color-blind-safe?
Figure 2: panel letters are huge in comparison to the font in the figure. Where do the fitted values come from? What’s their level of significance? Not clear from the description.
Figure 3: unclear is it important to show the variation in CH4 fluxes in the first two years (first panel a) but not in the remaining time (second panel a) or N2O? Broken y-axes might be a solution
Citation: https://doi.org/10.5194/egusphere-2024-934-RC1
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