Hydrologic controls on aperiodic spatial organization of the ridge&ndash;slough patterned landscape

Casey, Stephen T.; Cohen, Matthew J.; Acharya, Subodh; Kaplan, David A.; Jawitz, James W.

doi:https://doi.org/10.5194/hess-20-4457-2016

Articles | Volume 20, issue 11

https://doi.org/10.5194/hess-20-4457-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-20-4457-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 20, issue 11

Research article

|

04 Nov 2016

Research article |

| 04 Nov 2016

Hydrologic controls on aperiodic spatial organization of the ridge–slough patterned landscape

Stephen T. Casey, Matthew J. Cohen, Subodh Acharya, David A. Kaplan, and James W. Jawitz

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Final revised paper (published on 04 Nov 2016)
Supplement to the final revised paper
Preprint (discussion started on 16 Mar 2015)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC C1577: 'Referee Comment', Anonymous Referee #1, 18 May 2015
RC C4712: 'Review', Anonymous Referee #2, 06 Nov 2015
AC C5422: 'Reply to reviewers', Matt Cohen, 04 Dec 2015

Peer-review completion

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

ED: Reconsider after major revisions (14 Dec 2015) by Roger Moussa

Dear Authors,

Thank you for submitting your paper to HESS.

First, I would like to apologize for the delay in reviewing this paper and I would like to thank both reviewers. When the paper was submitted, three reviewers had accepted to review the paper. One reviewer sent his comments on time. The two remaining reviewers didn't send any comment. I contacted personally five times both remaining reviewers and sent reminders, but I haven't received any response. After I had contacted an important number of reviewers, and I had difficulties to find an additional reviewer.

Both reviewers stated that the paper is original, especially the observation of a robust scale-free patterning. But both reviewers made valuable comments about the paper structure, the need to clarify some specific terms, the justification and extension of conclusions.

An additional lecturer have also looked at the last part on scaling of the patch dynamics, and suggests that it would benefit by putting 95% confidence limits on the parameters themselves (in the supplementary material) as there is a large discussion about scaling and power-laws, and will allow the reader to better understand the differences between these from region to region (within the context of uncertainties based on fit of data and number of data). The lecturer also suggests the need to clean things up in various places (e.g., sometimes numbers done with multiple sig figs, sometimes not; sometimes with scientific notation, sometimes not; units missing e.g. for area in Table S1).

The paper will be reconsidered after major revisions. In the revised version, authors are invited to respond point by point to each comment of each reviewer, and giving convincing proofs to all problems raised by reviewers. Please highlight clearly what you changed in the revised manuscript, so the reviewers are able to assess your changes.

Kind regards,

Roger Moussa

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AR by Matt Cohen on behalf of the Authors (07 Feb 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Feb 2016) by Roger Moussa

RR by Laurel Larsen (20 Mar 2016)

RR by Anonymous Referee #4 (09 May 2016)

Suggestions for revision or reasons for rejection

The paper addressed an interesting question, which is can we identity whether the
pattern is self-organized (scale-dependent feedbacks) using spatial statistics. It used
different spatial statistical technics and applied them to the everglades ridge-slough
patterns, which are often assumed to self-organized regular patterning. Their results are
also intriguing. Firstly, the authors identified the water depth as the major control of the
patterns, and secondly, they found that the pattern is not regular, since the patch size
distribution is scale free and the pattern is aperiodic. I think the work is significant, but I
have several concerns:

1. The landscape has a water gradient from northeast to southwest already introduced by
human activities. And the ridge densities and shapes are shown to be significantly
correlated to the water gradient. However, the statistical significant relationship
between water depth and ridge density does not necessarily imply that hydrology
causes the formation of ridge-slough pattern. This may be subtle: the mechanism that
causes certain ecological pattern could be entirely different from variables that could
influences the already formed pattern –it is likely that many variables could
influences the pattern once it is formed.

2. Line 314-318: (1) the mention of percolation threshold is not relevant, because it
depends on the size of the site chosen. The decision of 6km by 6km is arbitral, and if
the size of 10km by10km were chosen, the number would be below ~0.59. The
mention of percolation threshold here is only misleading for the readers. (2) The logic
flow from the “0.59” to the statement “the failure of Monte Carlo tests within this
group may be density driven, rather than a result of an underlying patterning
mechanism” is shaky. I do see that the failure of the Monte Carlo significance tests is
density driven, but that could indicate an underlying mechanism operating.

3. I am no expert on the wavelet analysis, and only know the basic knowledge of it. I
looked up the literature they cited on this analysis and some other literature on this
method, and I have some questions:
a. Line 330- 346: the purpose of the spectral analysis was to identify peaks, and
it is a little confusing to me why the authors tried to do the correlation
between the r spectra and wave numbers on log-log scale. Maybe I am
missing something?
b. Line 332: Why the authors excluded the smallest wavenumber? Some
explanation would be needed.
c. Do you need to use null models to get the confidence interval to determine
whether the result is statistically robust?
d. Line 336-337: authors found that r spectra monotonically decrease with
wavenumber, and conclude that “maximum spatial variation at the largest
scale, and decreasing consistently at smaller scales”. Meanwhile, in Figure 2
(b), wavenumber is “cycle/km”, meaning that spatial scales decrease along xaxis,
which would a complete opposite conclusion as arrived by the authors?
Just a little confusing to me.

4. Just a comment. Line 453-459: If the author’s hypothesis is valid, it means that the
ridges have grown since drainage (the dry part) to compensate for the decline in water
level, and ridges in the wet areas should have kept the same, if not shrinking. The
pattern they observed agreed with this hypothesis. The current landscape shows a
gradient of degradation from north to southeast. This is interesting.

Referee Report: PDF

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ED: Reconsider after major revisions (09 May 2016) by Roger Moussa

AR by Matt Cohen on behalf of the Authors (12 Jul 2016)

ED: Referee Nomination & Report Request started (19 Jul 2016) by Roger Moussa

RR by Laurel Larsen (17 Aug 2016)

Suggestions for revision or reasons for rejection

The authors’ revisions have been commendably thorough, and I think it is time this paper moves along to publication. I really like the new figure 3 and am appreciative of the new analyses in the supplementary section. I have a few further minor suggestions, and at the risk of being somewhat annoying, there are a few points I’m going to push back on.

First, I’m a little confused by the discussion about shouldering. Figure 3 does show a clear slope break, which, as the authors point out, could very well arise from undersampling large ridges within the finite-size domains. But some of the lateral spectra do show a little hump (for sites 11, 5, 2, and 25) around the vicinity of these slope breaks. For the longitudinal spectra, sites 5 and 2 appear to exhibit a small hump. I was unclear about whether “shouldering” referred to the general slope break or the small hump in the spectra. (See also my comments further down about monotonicity.)

I do think it is worth discussing that the sites without one of these humps are the two wettest sites along the gradient—I think there may be something to this. Seeing the new Figure 3 made me wonder whether the other sites analyzed also follow this pattern, with the wettest sites not exhibiting a hump in the spectrum. It might be nice to show all of the spectra in an appendix, arranged along a wetness gradient. It was interesting to me that the driest site (which looks to the eye as though it has lost all patterning) still shows a hump, but the overall spectral density was greatly diminished, indicating a general “flattening” of features. This decrease in spectral density might also be worth mentioning in the interpretation, particularly if it emerges as a pattern across all of the driest sites.

Secondly, in the discussion of the new ridge center analysis presented in the supplementary material, the authors equate the similar modes for the longitudinal and lateral directions with a lack of anisotropy. This is not necessarily true. The similar modes indicate a general regularity in the centers of these features, but if features are longer than they are wide, the landscape would still be considered anisotropic.

Minor comments:

Lines 80-82: Cheng et al.’s model included evapotranspiration contrasts between ridge and slough as well as a hydrologic conductivity contrast. Flow-parallel ridges required a high evapotranspiration contrast but did not require a difference in hydraulic conductivity, so I would consider this to be more of an evapotranspiration focusing/nutrient accumulation mechanism rather than a water ponding mechanism.

Lines 89-90: I would disagree with listing Ross or Cheng here. Ross et al. was really focused on tree island processes (although they did provide measurements of limited nutrient accumulation on ridges) while Cheng’s model only produced flow-parallel ridges under conditions far from those in the Everglades (i.e., gradients of 2.5% and much higher ET on ridges than in sloughs, which subsequent measurements have shown is not the case.

Line 142: Probably best not to include the Larsen et al. citation here, as I cited that wavelength from other sources (probably SCT 2003).

Line 161: How did these features “allow” this resolution?

Line 256: Add “in elongation” at the end of this sentence.

Line 230: Note the misspelling of the word “perpendicular”

Line 284-285: Significant Spearman’s rho correlations are not verification of monotonicity. Do a search on “tests of monotonicity”. I am not experienced in these tests, but I think you would want it to be able to distinguish a part of the generally decreasing function that appears to be going up from noise. One approach might be to take the derivative of the power-law function used to fit the data at each point and subtract it from the discrete derivative of the data. Identify points that lie in the tail of the distribution. If they cluster together (e.g., around the “hump”), that would be an indication of a part of the spectrum that is not monotonic.

Line 319: “perimeter values”: Should this be “perimeter to area values” or “perimeter per patch area”?

Line 361-362: I don’t think I buy that r-spectra or power-law scaling would necessarily be robust to hydrologic modification. If small losses in the connectivity of sloughs caused the merging of ridges (which appears to have happened in hydrologically modified areas), this would seemingly have a big effect on power-law scaling.

Lines 368-369: Bernhardt and Willard did show that patches expanded during climatically drier periods (e.g., Medieval Warm Period), which would have been associated with an increase in the areal coverage (density) of ridges and certain metrics of their configuration (e.g., elongation, perimeter/area relationships). I’d suggest modifying this sentence.

Line 373: Do you mean “power-law scaling in patch areas over a range of densities along environmental gradients” here, rather than “smooth variation in ridge densities along environmental gradients”?

Lines 405-409: The water level-ridge density feedback occurs throughout landscape development in RASCAL, not just at early phases, and is the main reason why velocities at ridge edges eventually increase enough to achieve a balance in sediment redistribution. I would suggest modifying these sentences to “Indeed, the RASCAL model of ridge-slough development (Larsen and Harvey 2011) represents this feedback, though in that model, velocity-field feedbacks alone could not impose elongation and regular patterning…”

Line 409: important → importance

Line 411: Add “expansion is” after “This.”

Caption of figure 3: May need to modify this based on previous comments about monotonicity vs a small hump

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ED: Publish subject to minor revisions (Editor review) (17 Aug 2016) by Roger Moussa

AR by Matt Cohen on behalf of the Authors (07 Sep 2016) Author's response Manuscript

ED: Publish as is (21 Sep 2016) by Roger Moussa

AR by Matt Cohen on behalf of the Authors (27 Sep 2016) Manuscript

Short summary

The ridge–slough landscape is a major part of the Everglades, a critically imperiled wetland in south Florida (USA). The landscape consists of two wetland types, shallow water ridges and deep water sloughs, interspersed in a complex pattern. Human changes to hydrology have changed this pattern, impacting water flow, fish movement, and bird habitat. Restoring pattern requires understanding its origins. We describe the pattern in detail, gaining insights relevant for management on its origins.