the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Years of extraction determines CO2 and CH4 emissions from an actively extracted peatland in eastern Québec, Canada
- 1Department of Geography, McGill University, Montreal, H3A 0B9, Canada
- 2Department of Natural Resource Sciences, McGill University, Ste Anne de Bellevue, H9X 2V8, Canada
- 3Department of Geography and Environmental Management, University of Waterloo, Waterloo, N2L 3G1, Canada
- 4Ecohydrology & Biogeochemistry Group, Institute of Landscape Ecology, University of Münster, Heisenbergstr. 2, 48149 Münster, Germany
- 1Department of Geography, McGill University, Montreal, H3A 0B9, Canada
- 2Department of Natural Resource Sciences, McGill University, Ste Anne de Bellevue, H9X 2V8, Canada
- 3Department of Geography and Environmental Management, University of Waterloo, Waterloo, N2L 3G1, Canada
- 4Ecohydrology & Biogeochemistry Group, Institute of Landscape Ecology, University of Münster, Heisenbergstr. 2, 48149 Münster, Germany
Abstract. Draining and extracting peat alters a peatland’s control of CO2 and CH4 emissions. Carbon (C) emissions from peatlands undergoing extraction are not well constrained due to a lack of measurements. We determine the effect that production duration (years of extraction) has on the CO2 and CH4 emissions from an actively extracted peatland over three years of measurements (2018–2020). We studied five sectors identified by the year when extraction began (1987, 2007, 2010, 2013, 2016). Higher average CO2 and CH4 emissions were measured from the drainage ditches (CO2: 2.05 ± 0.12 g C m-2 d-1; CH4: 72.0 ± 18.0 mg C m-2 d-1) compared to the field surface (CO2: 0.9 ± 0.06 g C m-2 d-1; CH4: 9.2 ± 4.0 mg C m-2 d-1 regardless of sector. For peat fields, CO2 fluxes were highest in the youngest sector, which opened in 2016 (1.5 ± 0.2 g C m-2 d-1). The four older sectors all had similar mean CO2 fluxes (~0.65 g C m-2 d-1) that were statistically different from the mean 2016 CO2 flux. A spatial effect on CO2 fluxes was observed solely within the 2016 sector, where CO2 emissions were highest from the centre of the peat field and declined towards the drainage ditches. These observations occur due to operators' surface contouring to facilitate drainage. The domed shape and subsequent peat removal resulted in a difference in surface peat age hence different humification and lability. 14C dating confirmed that the remaining peat contained within the 2016 sector was younger than peat within the 2007 sector and that peat age is younger toward the centre of the field in both sectors. Humification indices derived from mid-infrared spectrometry (MIRS) (1630/1090 cm-1) indicated that peat humification increases with increasing years of extraction. Laboratory incubation experiments showed that CO2 production potentials of surface peat samples from the 2016 sector increased toward the centre of the field and were higher than for samples taken from the 1987 and 2007 sectors. Our results indicate that peatlands under extraction are a net source of C where emissions are high in the first few years after opening a field for extraction and then decline to about half the initial value and remain at this level for several decades, and the ditches remain a 2 to 3 times greater source than the fields, but represent < 7 % of the total area of a field.
Laura M. Clark et al.
Status: final response (author comments only)
-
RC1: 'Comment on bg-2022-156', Anna-Helena Purre, 21 Aug 2022
The manuscript „Years of extraction determines CO2 and CH4 emissions from an actively extracted peatland in eastern Québec, Canada“ approaches the significant topic for the scientific community and also practicioners working with peatland management issues. The manuscript is well prepared and written, generally easy to understand. The methodology and presentation of results is on sound basis. I especially like that the manuscript has not been over-complicated statistically, and the figures are also nice and supporting the undestanding of the methodology and the results. So the manuscript is in my opinion well worth reaching the wider audience of readers after some more specific comments have been approached.
Specific comments
Introduction
-lines 47-50 please give an explanation what do you mean under the peat quality? Some economic value or quality for microorganisms or something else?
Section 1.2- for giving the audience the hunch of the significance of the topic, please also bring out the area of peat production sites (e.g. globally) or percent of peat production sites from global peatland area.
-lines 81-83- GHGs on active milled peatlands was also measured by Salm et al. (2012) (some of the sites in his study), please also consider his work in the introduction and also in the discussion.
Methods
- Section 2.1: I would prefer to have more background data about the sectors of the site, like peat layer thickness, and some general parameters such as pH, peat decomposition
- Section 2.1: Also I would like to have the information if the similar peat production works were done on all sectors in similar amount. Also, if similar amount of peat per hectare (or production field) was removed in all sections. In peat production, they tend to remove different amounts depending on the peat decomposition (e.g. white, brown or black peat)
- Section 2.2: how often the chamber measurements were made? Maybe you could also give the number of measurements per sector.
- Line 150-151: was peat temperature profile measured during each flux measurement campaign?
Results
- I would like to have the short analysis of all measured variables (peat temperatures at different depth, peat volumetric water content), e.g. average values with standard deviations or some table, per sections. The the rest of the results sectors can be easier to discuss;
- In different parts 3.1.2, 3.2.2, 3.4.1 sentences with long lists of nummerical results are given (marked in yellow in uploaded pdf), although the results are also presented in easier to understand figure. I would prefer the numerical results as a table (maybe in annexes), to make understanding these values easier.
Discussion
- Lines 360-364: discuss also the results of Salm et al. 2012
- Lines 378-379: it is said that there is almost no influence of surface temperatures on measured CO2 flux, but you also measured temperatures in deeper peat layers, what about those?
Please also control the citations and reference, there were some missing references and some redundant references in the list. I marked those I noticed as yellow in the uploaded document.
Technical comments are given in the uploaded pdf.
Reference
Salm, J. O., Maddison, M., Tammik, S., Soosaar, K., Truu, J., & Mander, Ü. (2012). Emissions of CO2, CH4 and N2O from undisturbed, drained and mined peatlands in Estonia. Hydrobiologia, 692(1), 41-55.
-
AC1: 'Reply on RC1', Ian Strachan, 04 Oct 2022
We thank the Reviewer for the detailed comments on our manuscript.
Introduction
-lines 47-50 please give an explanation what do you mean under the peat quality? Some economic value or quality for microorganisms or something else?
RESPONSE: we have reworded as “Carbon dioxide production rates indicate the biogeochemical quality (e.g. nutrients, humification etc.) because…”
Section 1.2- for giving the audience the hunch of the significance of the topic, please alsobring out the area of peat production sites (e.g. globally) or percent of peat productionsites from global peatland area.
RESPONSE: we will add global numbers for greater context.
-lines 81-83- GHGs on active milled peatlands was also measured by Salm et al. (2012) (some of the sites in his study), please also consider his work in the introduction and also in the discussion.
RESPONSE: added as per reviewerMethods
Section 2.1: I would prefer to have more background data about the sectors of the site, like peat layer thickness, and some general parameters such as pH, peat decomposition
Section 2.1: Also I would like to have the information if the similar peat production works were done on all sectors in similar amount. Also, if similar amount of peat per hectare (or production field) was removed in all sections. In peat production, they tend to remove different amounts depending on the peat decomposition (e.g. white, brown or black peat)RESPONSE: we have the above information from student theses, we will add the information as per above.
Section 2.2: how often the chamber measurements were made? Maybe you could also give the number of measurements per sector.
RESPONSE: could be added in summary table
Line 150-151: was peat temperature profile measured during each flux measurement campaign?
RESPONSE: yes it was. Line in text modified “For each measurement, peat temperature was taken…”Results
I would like to have the short analysis of all measured variables (peat temperatures at different depth, peat volumetric water content), e.g. average values with standard deviations or some table, per sections. The the rest of the results sectors can be easier to discuss; In different parts 3.1.2, 3.2.2, 3.4.1 sentences with long lists of nummerical results are given (marked in yellow in uploaded pdf), although the results are also presented in easier to understand figure. I would prefer the numerical results as a table (maybe in annexes), to make understanding these values easier.
RESPONSE: agree that the text can get a bit cumbersome. We will condense these into summary tables and reword to highlight main findings. Editor, please advise if these are best in the text or in supplementary information.
Discussion
Lines 360-364: discuss also the results of Salm et al. 2012
RESPONSE: added sentence to discussion reporting the mined results in Estonia.
Lines 378-379: it is said that there is almost no influence of surface temperatures on measured CO2 flux, but you also measured temperatures in deeper peat layers, what about those?
RESPONSE: there was no correlation with deeper soil temps but no attempt at correlating with time-lag temperature was made
REVIEWER 1 COMMENTS IN THE M/S (supplement)
GENERAL RESPONSE: All issues related to citations (missing or not in reference section) have been addressed. All minor editorial suggestions and changes have been accepted.
2.1 The site coordinates were indeed incorrect and these have been corrected.
Around Line 380, the citation to be added is a Pers. Comm. with an industry scientist.
- AC3: 'Reply on RC1', Ian Strachan, 04 Oct 2022
-
RC2: 'Comment on bg-2022-156', Anonymous Referee #2, 22 Aug 2022
General comments.
The manuscript by Clark et al. reports carbon dioxide (CO2) and methane (CH4) fluxes (over three summers), and CO2 production potential, in active peat extraction fields in Canada. The authors report that flux rates were greatest at the youngest site, which they suggest is related to the age of the peat (14C dating), and declined thereafter. Emissions from drainage ditches were found to be much greater than from the peat field. While data from extraction sites are already available, most have been collected from post-extraction sites (bare peat) – data from active extraction sites remains scarce given the difficulties in measuring while machinery passes over the study site. As such, this study provides important information for land managers and GHG inventory reporting.
The manuscript is competently written and I believe that the subject matter/methodology would be of interest to the readers of Biogeosciences. In my opinion, the manuscript requires only minor revisions before it could be considered for publication (see specific comments below).
Specific comments.
L1 “Year of extraction....”?
L14 “..a peatlands control of CO2/CH4” strikes me as odd phraseology. Consider re-phrasing.
L18 “Higher” is used throughout the manuscript to describe some of the results. This can be confusing when the study also involves a vertical aspect, e.g. tree height, peat depth. Consider using “greater”.
L36 Soil C stores.
L40 Carbon dioxide is released.
L50 “Decomposition rates are greatest...”
L63 Vacuum harvesters are not used everywhere peat is extracted – perhaps state “in Canada”?
L64 also, peat structure/porosity after years of drainage?
L67-68 Abdalla et al, 2016 is a review paper – they do not directly measure CH4 or the oxic layer of the peat.
L73 Add “...in North-American undisturbed peatlands” as you do not cite studies from other geographical areas.
L74-75 Too many references cited here, especially as you use e.g.
L76-77 If I were new to peatland research, I would get the distinct impression from reading this introduction that C studies have only been carried out in Canada. Would suggest that you either explicitly state “in Canada” or add references from other parts of the world to support the generalized statements here.
L88 There is no real sense of the composition of the study site. Please add peat depths, bulk density, nutrient composition, C content etc. presence of vegetation in the ditches.
L100-101 Please state the reason(s) for these times? How often were the sites measured within these dates?
L110 Extraction not production
L116 Previous measurements by others or preliminary measurements in this study? If the former, please state by whom.
L124 Change to “As the first C flux measurements began....”
Fig. 2 I’m struggling to understand this figure. What does the horizontal dashed line represent? A caption should be stand-alone information, so please provide some of the information from L111-114 here.
L131 Collars have not been measured before now. Please add details of size.
L131 prior to measurement? Please state the length of time until the first measurement. Do you think that collar insertion may have influenced subsequent flux values?
L138 Was the chamber equipped with an internal thermometer? In the absence of a cooling system, temperature increases well beyond the ambient air temperature must be a feature, even with opaque chambers. How did you minimise/account for chamber heating?
L158-159 Air temperatures from within the chamber?
L162 Why such a high rejection rate in 2018?
L171-175 Delete “spanning...site”.
Fig. 3 Do we assume from the diagram that peat depth at the site is around 85-90cm?
L204 Why were two GCs used?
L270 I don’t think you state the number of flux measurements used. Rejection rates (L162) seem very high so perhaps the number of fluxes left for modelling and discerning a relationship with soil temperature was too small?
L297 I don’t think you state the number of flux measurements used. Rejection rates (L162) seem very high so perhaps the number of fluxes left for modelling and discerning a relationship with soil temperature was too small?
L316-317 And yet they appear in Fig. 8?
Fig. 8 What does the horizontal dashed line represent?
L323-337 It is very hard to read the data in this section – would it be possible to condense the numbers and direct the reader to the relevant figure/table?
L380 I don’t think you state the number of flux measurements used. Rejection rates (L162) seem very high so perhaps the number of fluxes left for modelling and discerning a relationship with soil temperature was too small?
L386 subscript 2 in CO2.
L456 Not surprising if your dataset is too small or you haven’t covered all possible temporal variation.
L469 Please add details of absence/presence of vegetation in drain ditches in Methods section.
L476-477 ...and at other times of the year, especially outside the active extraction period.
L481-482 Is this relevant for how emission factors are derived for this land use category?
Reference list I have only glance through the list but please check the formatting (espec. Subscript of CO2 etc.)
-
AC2: 'Reply on RC2', Ian Strachan, 04 Oct 2022
We thank the Reviewer for their comments on our Manuscript.
L1 “Year of extraction....”?
RESPONSE: Changed to “Duration of extraction…”L14 “..a peatlands control of CO2/CH4” strikes me as odd phraseology. Consider rephrasing.
RESPONSE: changed to “…alters the controls on CO2 …”
L18 “Higher” is used throughout the manuscript to describe some of the results. This can be confusing when the study also involves a vertical aspect, e.g. tree height, peat depth. Consider using “greater”.
RESPONSE: changed as suggested throughout
L36 Soil C stores.
RESPONSE: changed
L40 Carbon dioxide is released.
RESPONSE: changed
L50 “Decomposition rates are greatest...”
RESPONSE: changed
L63 Vacuum harvesters are not used everywhere peat is extracted – perhaps state “in Canada”?
RESPONSE: changedL64 also, peat structure/porosity after years of drainage?
RESPONSE: Not sure what reviewer is referring to.
L67-68 Abdalla et al, 2016 is a review paper – they do not directly measure CH4 or the oxic layer of the peat.
RESPONSE: removed this citation
L73 Add “...in North-American undisturbed peatlands” as you do not cite studies from other geographical areas.
RESPONSE: sentence was unclear. We are referring to ditches and not geographical area. Reworded as “…labile C normally found in the ditches…”
L74-75 Too many references cited here, especially as you use e.g.
RESPONSE: these references are representative of relevant previous work
L76-77 If I were new to peatland research, I would get the distinct impression from reading this introduction that C studies have only been carried out in Canada. Would suggest that you either explicitly state “in Canada” or add references from other parts of the world to support the generalized statements here.
RESPONSE: Not all are reporting research in Canada, Updegraff et al. conducted their research in Minnesota, USA. Can add others.
L88 There is no real sense of the composition of the study site. Please add peat depths, bulk density, nutrient composition, C content etc. presence of vegetation in the ditches.
RESPONSE: similar to Reviewer 1. We have this info from student theses and will include.L100-101 Please state the reason(s) for these times? How often were the sites measured within these dates?
RESPONSE: harvesting starting dates are determined by spring snow thaw – when the fields are dry enough such that harvesting equipment can get on the fields; Measurements were taken to attempt to cover the summer and shoulder seasons but we had COVID restrictions on travel that restricted our coverage towards the later end of the study.L110 Extraction not production
RESPONSE: change made
L116 Previous measurements by others or preliminary measurements in this study? If the former, please state by whom.
RESPONSE: added ‘our’ “…because our previous measurements…”L124 Change to “As the first C flux measurements began....”
RESPONSE: change madeFig. 2 I’m struggling to understand this figure. What does the horizontal dashed line represent? A caption should be stand-alone information, so please provide some of the information from L111-114 here.
RESPONSE: Sentence added to figure caption “The field contouring results in about 50 cm difference in surface peat elevation between the centre of the field and the edge of the field.
L131 Collars have not been measured before now. Please add details of size.
RESPONSE: in the next line the size of the chambers is given. The chambers fit into the collars as is standard in this technique. No change made.L131 prior to measurement? Please state the length of time until the first measurement. Do you think that collar insertion may have influenced subsequent flux values?
RESPONSE: In this actively harvested site, we did not have the ability to keep collars in the fields as they would have been destroyed by machinery during harvest operations. Collars were inserted and measurements were taken within minutes. This would be a potential issue in a saturated environment especially for methane. However, the surface layer is dry such that harvesting can be done. We don’t believe that this had any adverse affect on the results.
L138 Was the chamber equipped with an internal thermometer? In the absence of a cooling system, temperature increases well beyond the ambient air temperature must be a feature, even with opaque chambers. How did you minimise/account for chamber heating?
L158-159 Air temperatures from within the chamber?
RESPONSE: We use cooling systems when working in vegetated systems to avoid any chance of a temperature increase inhibiting stomatal response. All of our chambers have fans to stir the air; while this does not cool the air, it does prevent gradients building from the surface. However, this is an actively harvested site without vegetation and with machinery on the fields. The practicality of moving over the peat to efficiently measure from a variety of locations for the times that we had access dictated a more compact system. Yes, the Ta is inside the chamber. We can discuss any effects that may have occurred in the revision stage but we would surmise that any increase in temperature would cause an overestimation of the CO2 emissions thus making our numbers an upper range.
L162 Why such a high rejection rate in 2018?
RESPONSE: Our protocol is designed to be conservative in rejecting data and likely removes more than is required. But remaining data is robust. Note 2018 was a preliminary campaign and short in duration so no adverse affect on larger data set.
L171-175 Delete “spanning...site”.
RESPONSE: we feel that this would change the intent of the passage. It is intended to indicate that the fields chosen represent the widest possible range of the continuously extracted fields at this location. From less than 3 years to greater than 30 years.
Fig. 3 Do we assume from the diagram that peat depth at the site is around 85-90cm?
RESPONSE: no. This is the ditch surface. The peat depth is much greater. This will be clear when peat descriptive information is added earlier in the paper as per R1 and R2 requests.L204 Why were two GCs used?
RESPONSE: simple logistics. Very busy lab.L270 I don’t think you state the number of flux measurements used. Rejection rates (L162) seem very high so perhaps the number of fluxes left for modelling and discerning a relationship with soil temperature was too small?
L380 I don’t think you state the number of flux measurements used. Rejection rates (L162) seem very high so perhaps the number of fluxes left for modelling and discerning a relationship with soil temperature was too small?
RESPONSE: Number of samples is given in the F stat as per standard reporting notation where the second number is N-1. For example, F8,942 means that there were 943 observations.
L316-317 And yet they appear in Fig. 8?
RESPONSE: modified. “The 50 and 80 cm samples…in the profile, however they were included in the C14 dating.”Fig. 8 What does the horizontal dashed line represent?
RESPONSE: sentence added to caption. “The horizontal line is drawn to show that these elevations are approximately equal”L323-337 It is very hard to read the data in this section – would it be possible to condense the numbers and direct the reader to the relevant figure/table?
RESPONSE: similar to R1 comments. We will reformat into a Table. Editor: Please guide us on whether this should be in m/s or in supplementary info.L386 subscript 2 in CO2.
RESPONSE: changed.
L456 Not surprising if your dataset is too small or you haven’t covered all possible temporal variation.
RESPONSE: methane is complicated by production and oxidation. Tight relationships occur in wet, saturated sites which is not our case. Sentence was removed.L469 Please add details of absence/presence of vegetation in drain ditches in Methods section.
RESPONSE: added.
L476-477 ...and at other times of the year, especially outside the active extraction period.
RESPONSE: Sentence was deleted. Please note that the ditches are frozen 5-6 months of the year in this location.
L481-482 Is this relevant for how emission factors are derived for this land use category?
RESPONSE: sentence changed for clarity. “The newly opened sectors are a greater source of CO2 to the atmosphere for the first few years but then the emissions become independent of the duration of harvesting. This suggests that two different emission factors, one for newly opened and then for older sectors may be appropriate.”
-
AC2: 'Reply on RC2', Ian Strachan, 04 Oct 2022
Laura M. Clark et al.
Laura M. Clark et al.
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 261 | 70 | 20 | 351 | 1 | 4 |
- HTML: 261
- PDF: 70
- XML: 20
- Total: 351
- BibTeX: 1
- EndNote: 4
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1