Biophysical controls of marsh soil shear strength  along an estuarine salinity gradient

Gillen, Megan N.; Messerschmidt, Tyler C.; Kirwan, Matthew L.

doi:https://doi.org/10.5194/esurf-9-413-2021

Articles | Volume 9, issue 3

https://doi.org/10.5194/esurf-9-413-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/esurf-9-413-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 9, issue 3

Research article

|

25 May 2021

Research article |

| 25 May 2021

Biophysical controls of marsh soil shear strength along an estuarine salinity gradient

Megan N. Gillen, Tyler C. Messerschmidt, and Matthew L. Kirwan

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Final revised paper (published on 25 May 2021)
Preprint (discussion started on 09 Jul 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'review of esurf-2020-58', Anonymous Referee #1, 29 Sep 2020
RC2: 'Review of Gillen et al - Biophysical controls of marsh soil shear strength', Anonymous Referee #2, 23 Nov 2020
AC1: 'Comment on esurf-2020-58', Megan Gillen, 31 Jan 2021

Peer-review completion

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

AR by Megan Gillen on behalf of the Authors (08 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (10 Feb 2021) by Orencio Duran Vinent

RR by Anonymous Referee #1 (16 Feb 2021)

RR by Anonymous Referee #2 (20 Mar 2021)

Suggestions for revision or reasons for rejection

The authors have done a laudable job in responding to my review-comments of the first draft. However, I suggest additional improvements of the manuscript as follows:

1. Line 144: “Interior sites yielded higher values of shear strength than edge sites in the brackish and the salt marshes (Fig. 4).”
Reviewer Comment: Does the following statement signify a significant interaction between marsh type and marsh zone? It would appear so, but it should be specifically stated.

2. Lines 144-146: “While shear strength values appear nearly equal between the edge and interior sites for freshwater marshes (Fig. 4), the ANOVA test showed significant differences in shear strength between marsh edge and interior across all marsh types (p = 5.62e-20).”
Reviewer Comment: This sentence appears to state that the main effect of marsh zone (edge versus interior) is significant. However, because there is a significant interaction between the main effects of marsh type and zone (as shown in the ANOVA tables provided as responses to the first review), the main effects are little value, i.e., the effect of marsh zone on shear strength varies with marsh type. Hence, there is a need to discuss the results with respect to the significant interactions. Statements of main effects are misleading because they give a picture that all marshes are responding similarly. Where ANOVAs have been conducted, explicit statements regarding statistically significant interactions, or the lack thereof, are necessary to better interpret the study’s inferences.

3. Lines 147-148: “The most substantial difference between edge and interior shear strength values occurred at the salt marsh sites, with an increase from 5.1 kPa at the edge to 18.5 kPa in the interior (Fig. 4).”
Reviewer Comment: The difference presented is not likely statistically significant. If this is so, why state it. If fact, it looks to me that the absolute difference between edge and interior for the brackish marsh is of the same magnitude as that for the salt marsh.

4. Lines 150-151: “Belowground biomass had the most significant influence on shear strength in the marsh interior (R2 = 0.58, p = 1.09e-5) (Fig. 5).”
Reviewer Comment: Figure 5b shows clearly that this statement is indeed true for salt and brackish marshes, but not for freshwater marshes. This should be clearly stated in the results. The slopes of the three lines in Figure 5b could be statistically compared to confirm that the fresh marshes differ from the salt and brackish marshes, which do not differ.

5. Lines 151-152: Insert “(data not shown)” after biomass in line 151.

6. Lines 188-189: “Nevertheless, our findings indicate that belowground biomass drives soil shear strength variability in the marsh interior (Fig. 5), and soil properties influence marsh edge shear strength (Fig. 6).”
Reviewer Comment: In addition to the soil properties controlling the edge shear strength, isn’t low root biomass, especially low root mass per unit volume of soil), found at virtually all edge sites another important factor (Figure 5a). In fact, it may equally important as soil water content. This point needs mention in the Discussion both here and again in lines 211-212. .

7. Line 231: Delete “along the York River”

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ED: Publish subject to minor revisions (review by editor) (20 Mar 2021) by Orencio Duran Vinent

AR by Megan Gillen on behalf of the Authors (30 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (20 Apr 2021) by Orencio Duran Vinent

ED: Publish subject to technical corrections (26 Apr 2021) by Tom Coulthard (Editor)

AR by Megan Gillen on behalf of the Authors (28 Apr 2021) Manuscript

Short summary

We measured the shear strength of marsh soils along an estuarine salinity gradient to determine salinity's influence on marsh erodibility. Our work is one of the first studies to directly examine the relationship between salinity and marsh erodibility. We find that an increase in salinity correlates with higher soil shear strength values, indicating that salt marshes may be more resistant to erosion. We also show that both belowground biomass and soil properties drive shear strength differences.