Dissolved organic carbon mobilized from organic horizons of mature and harvested black spruce plots in a mesic boreal region

Bowering, Keri L.; Edwards, Kate A.; Prestegaard, Karen; Zhu, Xinbiao; Ziegler, Susan E.

doi:https://doi.org/10.5194/bg-17-581-2020

Articles | Volume 17, issue 3

https://doi.org/10.5194/bg-17-581-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-17-581-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 3

Research article

|

05 Feb 2020

Research article |

| 05 Feb 2020

Dissolved organic carbon mobilized from organic horizons of mature and harvested black spruce plots in a mesic boreal region

Keri L. Bowering, Kate A. Edwards, Karen Prestegaard, Xinbiao Zhu, and Susan E. Ziegler

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Final revised paper (published on 05 Feb 2020)
Supplement to the final revised paper
Preprint (discussion started on 10 Jan 2019)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Review of bg-2018-516', L. Thieme, 11 Mar 2019
- AC3: 'Response to Reviewer 1', Keri Bowering, 24 May 2019
RC2: 'Review BG2018-516 Bowering et al.: Dissolved organic carbon mobilized from organic horizons....', Anonymous Referee #2, 06 Apr 2019
- AC1: 'Response to Reviewer 2', Keri Bowering, 24 May 2019
RC3: 'Bowering et al. review', Anonymous Referee #3, 30 Apr 2019
- AC2: 'Response to Reviewer 3', Keri Bowering, 24 May 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (12 Jun 2019) by Frank Hagedorn

AR by Keri L. Bowering on behalf of the Authors (28 Oct 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Nov 2019) by Frank Hagedorn

RR by Anonymous Referee #2 (15 Nov 2019)

Suggestions for revision or reasons for rejection

The authors have nicely revised their manuscript and have better clarified their sampling scheme. The results clearly shows that forest harvesting has a long-term impact on DOC fluxes and that this influence primarily occurs through changes in hydrology. Overall, this is a solid work and provides important knowledge, but the presentation and discussion of water and DOC fluxes is still too uncritical.
The main critiques are as follows:
1. Water-DOC fluxes. While the authors convincingly discuss the importance of macropore and/or lateral flow by stating that water fluxes in the O horizon exceeded precipitation, it has to be clearly stated that this quantitative relationship applies only for their lysimeters used. At the landscape scale, water fluxes in the O horizon cannot exceed those of precipitation. Consequently, the authors have either clarify that precipitation data used might be an underestimate as they have been measured 50 km away (which is reasonable) or clearly state that the fluxes measured here only applies for the water collected by the lysimeters used and represent an overestimate at the landscape scale. Instead writing that leaching exceeds precipitation one may also describe this as the ratio between leaching and precipitation.
In the reply to the first review the authors have written: “The 1305 total annual precipitation recorded could be an underestimate of this input at the plots especially because snowfall was not measured at the plot level but was used from a meteorological station 50km away from the site in Deer Lake, NL.”
I do not see that this statement has been implemented in the manuscript and find the reporting of fluxes in its current form incorrect.
Moreover, the reporting of precipitation is confusing.
p. 3. L. 25 The region receives approximately 1095 mm of precipitation
on P. 9 L. 4 The regional mean annual air temperature over the July 2013 to July 2014 study period was + 3.4 °C (daily mean range: - 21.0 °C to + 22.7°C), and 1305 mm of total precipitation fell, including 483 mm water equivalents as snowfall.
I guess that the first values represents the long-term mean, while the second one represents the actual year – in the responses, I learnt that these measurements were taken 50 km away – this information has to be added.
The collection of lateral flow has implications for the estimation of DOC fluxes. As the water fluxes in the O horizon exceed precipitation inputs, the area where DOC is coming from must exceed a m2. As other scientist may take the 38 and 54 g C/m2 (and the authors compare is with other studies and with net ecosystem C balances), I find that a critical discussion of this value is required.
p.12 L. 20 ff the concept of DOC transport in boreal landscapes should be more strongly discussed by considering similar concepts that have been developed in other boreal regions, e.g. Sweden.
p. 12 L.25 The statement ‘These models may be particularly inappropriate for use in highly porous surface organic soils and hillslopes with high precipitation rates as demonstrated here.’ is principally correct. However, there are several hydrological models that include a macropore component (with their own uncertainty) and I find it impertinent to write such a statement and present the own data lysimeter based data rather uncritical and writing bluntly that water fluxes in O horizons exceed precipitation.

2. Litterfall inputs (mass and C) is inconsistent/wrong. The C input by litter hardly differs from the mass input (Table 1), but it should be approx.. 50% of it as C-concentration in litter are approx. 50%. The C input by litter is also reported at page 8, L. 11. I suppose that the mass provided in Table 1 is wrong but this has to be clarified.

3. Digits are reported incorrectly. The reporting of digits is related to the accuracy of the measurement and estimation. In this manuscript, this is not applied, for instance:
Table 1 only 1 digit is given for soil moisture, which seems to coarse
Table 2: 3 decimals for statistical significance are sufficient
Figure 4: 4 decimals in the equations are too much
P. 8, L. 23. CO2 flux, reported with 4 digits

4. Minor comments
- Statistical analyses: provide fixed and random effects in your lme-analysis to clarify that experimental design was captured.
- p. 9 , L. 30 a ‘and’ is missing in the sentence
- p.10, L. 19 I suggest to write ‘measured water fluxes’
- p.10, L. 21 replace ‘corresponded’
- Superscripts seem all written as subscripts

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ED: Reconsider after major revisions (15 Nov 2019) by Frank Hagedorn

AR by Keri L. Bowering on behalf of the Authors (20 Dec 2019) Author's response Manuscript

ED: Publish as is (10 Jan 2020) by Frank Hagedorn

AR by Keri L. Bowering on behalf of the Authors (12 Jan 2020) Manuscript

Short summary

We examined the effects of season and tree harvesting on the flow of water and the organic carbon (OC) it carries from boreal forest soils. We found that more OC was lost from the harvested forest because more precipitation reached the soil surface but that during periods of flushing in autumn and snowmelt a limit on the amount of water-extractable OC is reached. These results contribute to an increased understanding of carbon loss from boreal forest soils.