Articles | Volume 19, issue 7
© Author(s) 2022. This work is distributed underthe Creative Commons Attribution 4.0 License.
Low biodegradability of particulate organic carbon mobilized from thaw slumps on the Peel Plateau, NT, and possible chemosynthesis and sorption effects
- Final revised paper (published on 04 Apr 2022)
- Supplement to the final revised paper
- Preprint (discussion started on 02 Jul 2021)
- Supplement to the preprint
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor |
: Report abuse
RC1: 'Comment on bg-2021-150', Anonymous Referee #1, 08 Sep 2021
- AC1: 'Reply on RC1', Sarah Shakil, 03 Dec 2021
RC2: 'Comment on bg-2021-150', Anonymous Referee #2, 01 Oct 2021
- AC2: 'Reply on RC2', Sarah Shakil, 03 Dec 2021
Peer review completion
AR: Author's response | RR: Referee report | ED: Editor decision
ED: Publish subject to minor revisions (review by editor) (11 Dec 2021) by Nicolas Brüggemann
AR by Sarah Shakil on behalf of the Authors (06 Jan 2022)  Author's response Author's tracked changes Manuscript
ED: Publish as is (28 Jan 2022) by Nicolas Brüggemann
AR by Sarah Shakil on behalf of the Authors (04 Feb 2022)  Author's response Manuscript
This paper advanced knowledge regarding mobilized POC biodegradability as a result of Arctic thaw slumps. The identification of the rate of biodegradability of slump-mobilized POC answers an important piece of the lateral carbon flux puzzle in this region, making this paper very worthy of publication. Ultimately, this paper also answers the separate question by proxy, that there is a trend for slump-mobilized DOC to decrease during incubation despite the low biodegradability of POC and TOC. The knowledge gap is clearly stated, and the introduction does a comprehensive job of outlining the main question. The paper also detailed comprehensive experimentation over the course of many years in order to answer a series of related, nested questions. There are a few modifications and clarifications that I have outlined below that I believe would help to heighten the considerable impact of this paper’s findings. I have broken up my main points into four bullets below. Line edits and more detailed questions follow in the Specific Comments and Technical Comments sections.
L11: Mineralization as CO2 and sedimentation are two POC fates, but this sentence does not address re-sequestration of stream C by aquatic plants or transportation downstream (though transportation is not an ultimate, chemical fate). I believe 1) it would be useful if the abstract jumped right into POC as this is the primary focus of the paper’s research OR 2) for the abstract to include mention of transportation as the mechanism allowing for soil organic carbon to become transported POC, mineralized CO2, or re-sequestered sediment within stream systems.
Suggestion 1: “Upon thaw, permafrost particulate organic carbon (POC) may be mineralized into CO2…”
Suggestion 2: “Upon thaw, permafrost carbon entering and transported within streams may be…”
L30-35: Transport is covered in this section, I believe it should be mentioned in the abstract, briefly as is presented in Specific Comment #1 above. The dichotomy of fates as it relates to the transport trajectory (transport vs deposition according to size and density fractions) is ultimately relevant to the study findings.
L32: It is probably worth mentioning that anoxia reduces overall mineralization rates but also shifts carbon loss towards methane (Schaedel et al. 2017 Nature Climate Change)
L40: Might be helpful to discuss different sources of POC in slump affected- and non-affected streams so reader can understand why lability might go up/down.
L127: circumneutral-pH, in my experience, pH of many Arctic water tracts is closer to pH5 than pH7.
L190: for clarity, identifying SE particles as slump SE would be useful and parallel HA slump particles later in the sentence. However, see point #3 in the general comments.
L184: most organic matter is partially oxidized because it has oxygen molecules. For example, glucose has a lot of oxygen molecules. Would this line be expected to be a 1:2 line instead of a 1:1 line? Most organic matter has oxygen as a part of it, does this change the heterotopic respiration line of 1:1?
L250-255: Some DOC may be decreasing as it is converted to CO2 alongside consumption of O2 as shown in Figure 3F and mentioned in L215. I would propose DOC declines as a possible reason for O2 consumption mentioned in L250-255.
Figure 4: Please note, MQ water has been found to carry a baseline amount of DOC, typically below the standard detection limits of a TICTOC but enough to impact radiocarbon measurements (0.5 ppm) if MQ water is used to generated standards.
Page 3: Do you suspect that the varying incubation timing (7, 11, 8, and 27 days) has any impact on the resulting POC degradation?
Unresolved general question: How did you store your samples prior to analysis? How many days were they stored once collected, were they refrigerated, frozen, or acidified? Were they stored in the dark? These questions impact the ultimate degradation of the C within the samples.
Table 1: In my copy of the manuscript, Table 1 text is too large for the cells, with overhanging letters in the first four columns.
L56: 1) removing the slump site identifiers entirely from the text regarding the 2016 and 2019 experiments or 2) Identifying which three slump sites were used (HA, HB, HD) in 2015 would be useful for the reader and would mirror the identification of slumps SE and FM3 in the 2016 and 2019 experiments in line 61 and 62, respectively (see comment on L59, below). However, see point #3 in the general comments.
L59: Site HD-UP is introduced in the text before the reader is oriented to what site “HD” represents; supplemental Figure S5 does not portray HD-UP, I believe this should be updated to Figure S4 and HD could be introduced in Line 56 as mentioned above. However, see point #3 in the general comments.
Figure 1: It would be beneficial to the reader to identify slump SE on the larger map as well as in the map inset (slumps HB, HA, FM3, and HD are all identified on the larger map, but SE is missing). Indicating that SE, HB, HA, FM3, and HD are slumps on the map key would be useful. Within the inset, SE-IN is identified. Should UP, DN-1, and DN-2 also be described with the SE- prefix in the inset? I would suggest labeling the entire inset as the slump SE transect and omitting the label SE- from the IN location. However, see point #3 in the general comments.
L81-83: The settling component of the 2015 experiment is distinct from the 2015 incubation experiment. I believe this would be best organized in a subsection, rather than grouping the incubation and settling together by year in one paragraph, as variation over year is not a factor of interest in the overall paper.
L85: Slump SE is referred to in this section however the 2015 sites were not mentioned by name in the previous section (2.2.1). I’d recommend consistency between the sections. However, see point #3 in the general comments.