Soil carbon and nitrogen erosion in forested catchments: implications for erosion-induced terrestrial  carbon sequestration

Stacy, E. M.; Hart, S. C.; Hunsaker, C. T.; Johnson, D. W.; Berhe, A. A.

doi:https://doi.org/10.5194/bg-12-4861-2015

Articles | Volume 12, issue 16

https://doi.org/10.5194/bg-12-4861-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-12-4861-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 16

Research article

|

17 Aug 2015

Research article |

| 17 Aug 2015

Soil carbon and nitrogen erosion in forested catchments: implications for erosion-induced terrestrial carbon sequestration

E. M. Stacy, S. C. Hart, C. T. Hunsaker, D. W. Johnson, and A. A. Berhe

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Final revised paper (published on 17 Aug 2015)
Preprint (discussion started on 04 Feb 2015)

Interactive discussion

Status: closed

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

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RC C165: 'Soil carbon and nitrogen erosion in forested catchments: implications for erosion-induced terrestrial carbon sequestration', Anonymous Referee #3, 12 Feb 2015
- AC C2171: 'Response to reviewer # 1', Asmeret Asefaw Berhe, 15 May 2015
RC C505: 'Review Stacy et al. Soil carbon and nitrogen erosion...', Bert VandenBygaart, 04 Mar 2015
- AC C2172: 'Response to reviewer # 2', Asmeret Asefaw Berhe, 15 May 2015

Peer-review completion

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

AR by Asmeret Asefaw Berhe on behalf of the Authors (27 May 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Jun 2015) by Daniel Obrist

RR by Anonymous Referee #3 (29 Jun 2015)

Suggestions for revision or reasons for rejection

General
The authors provided a detailed response following the previous review, and made various important changes. Comparison between the two versions is complicated since no document was provided indicating where changes were made exactly. Some text in the revised manuscript was highlighted, but many more changes were made that were not highlighted.

Despite the positive changes, I consider the paper requires some further revisions and clarification of several inconsistencies before publication.
Most importantly, the authors have added hypothesis to the introduction section, which could be a good idea, but in its present form seems artificial and poorly worked out. The hypotheses do not link to the research questions and at various points in the manuscript (especially discussion) reference is made to hypotheses that are not in the introduction. The paper could benefit from a much better explanation of its main objectives and a structured and systematic elaboration of these objectives and/or hypothesis in the discussion and conclusions.

Specific comments:
L 283: (Depositional hillslope positions…) is this not in contradiction with previous sentence that no significant differences were found?
L302: previous sentence says that higher elevation soils are more acidic, not lower elevation soils. Please correct or clarify.
L333: The number 15.6 kg ha refers to bioturbation?
L334-337: I don’t understand the point you are trying to make here. First of all, sediment export rates are strongly dependent o the size of the catchment (see for example Walling 1983; Journal of Hydrology 65, the Sediment Delivery Problem), making comparison between catchments of different size meaningless. Second, why would the fact that you find agreement with other catchments mean that ‘there are still erosive forces that mobilize sediment in non-flood years’?
L341: to which hypothesis of the introduction does this relate?
L355: you mean chemical composition of sediments?
L354-355: What exactly does this mean and how does it support (or not) your hypothesis regarding the relation btw sediment composition and rainfall/discharge versus catchment characteristics?
L359: It seems likely that spatial variability in catchment characteristics is so limited that it is to be expected that this will not affect your sediment composition, as you also state later on? Besides, what about the significant correlation with source catchment mentioned in L265?
L363: so what does this say about the importance of lateral C fluxes for the C budget?
L368: they = there
L395: and low ER for wet years, possibly pointing at erosion of deeper soil layers, or loss from the sediment basins?
L440: on which of your results is this statement based? On the fact that erosion rates are low and therefore not likely to form an important sink? Please clarify.
L441: climate change is likely to affect temperature and annual rainfall volume, so most likely also discharge, but probably vegetation cover and so protection against soil erosion will also be affected by climate change.
L449: what about results in Figure 4 showing a significant negative correlation between discharge and C concentration? This conclusion seems to contradict your discussion section stating that discharge is important for sediment composition?
L452: eroding sediments, eroded sediments, or simply sediments?
L452-453: sediment mobilization = erosion?
L457: your study did not test differences in timing; only inter annual precipitation differences but not timing within the year, right? Your results do show that not form of precipitation but total volume is important.

Figure 4: The legend in these figures shows negative R^2 values. These should probably be r values not R^2?

Figure 6: please add legend with hillslope positions (that was present in previous version of the graph).

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ED: Publish subject to minor revisions (Editor review) (29 Jun 2015) by Daniel Obrist

AR by Anna Wenzel on behalf of the Authors (15 Jul 2015) Author's response Manuscript

ED: Publish as is (22 Jul 2015) by Daniel Obrist

Short summary

In the southern parts of the Sierra Nevada in California, we investigated erosion of carbon and nitrogen from low-order catchments. We found that eroded sediments were OM rich, with a potential for significant gaseous and dissolved loss of OM during transport or after depositional in downslope or downstream depositional landform positions.