Invertebrate Responses to Restoration across Benthic and Hyporheic Stream Compartments

Round 1

Reviewer 1 Report

Dear Authors,

Overall, the article is well structured, the text reads fluently and figures and tables are mostly clear. I read the paper with great interest. It nicely demonstrates the differences between benthos and hyporheos pre and post-restoration river compartments and I think studies like this are necessary to raise the biological model community’s awareness for the role of river restoration in a catchment. However, while reading I came across several major issues that concerned me several times throughout the text. These three major concerns and several minor issues should be addressed and clarified before publication:

1) The first issue is related to the methodology, more precisely with the depth of sampling in the hyporeic zone. The depth of only 30 cm is referring to the shallow hyporheic assemblage!!! In fact, it belongs more properly to the bentic communities than hyporheos, which is visible from the results with almost the same assemblage composition in both zones. I understand that you wanted to select target groups for easier comparison, but this is not an indication of the restoration of a complete hyporeic zone community.  This suggests that the study was focused mainly on the aspect of the benthic community revitalization in surface and transitional zone rather than a comparison of benthos and hyporheos. 

2) In addition, the amount of only 5 liters of filtered water, using a Bou Rouch pump, is not sufficient to obtain a complete picture of the density and diversity of fauna in the hyporeic zone.

3) The third main issue concerns the community analysis. Neither in the results nor in the discussion you do not refer deeply to the structure of the communities, especially EPT community, which is a key indicator of the state and success of community renewal. In fact, I suggest using the EPT index, since representatives of all groups in both study zones are present. This would give greater value to the work, both qualitatively and quantitatively.

Minor comments:
4) I suggest to change the title to: Invertebrate Responses to Restoration Across Benthic and Hyporheic Stream Compartments

5) all other comments were added directly in the pdf document of the manuscript.

Technical corrections:

6) all technical corrections and comments were added directly in the pdf document of the manuscript (figure captions, text corrections,...)

There are no corrections in the supplementary materials.

After explanations, corrections, and additions, I warmly recommend the manuscript for publication in the journal Water as the paper is of utmost importance for research and monitoring of river post-restoration.

All the very best,

Reviewer

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

General comments:

The evaluation of river restoration programs that include hyporheic compartment are still rare and field data are really needed on this topic. The present study compares the answers of the benthos and the hyporheos of a river following a weir removal. This article may be of interest for both scientists and river managers.

The authors used a very efficient sampling strategy (i.e. BACI) over a rather long period, from one year before the removal to four years after. Even if the results of the weir removal are not spectacular, this type of well-designed study has its place in an international journal like Water.

Finally, the manuscript is very well written, figures are of good quality, methods and results are very well presented and the discussion (with some modifications) is convincing.

Specific comments:

Firstly, the manuscript must include some physical parameters that allow the reader to compare the control and impacted reaches, before and after weir removal. Did the authors measured (or roughly estimated) the mean water velocity, the mean depth and the dominant grain size class in both reaches, before and after the restoration? These data are important to understand the effect of weir removal and the potential consequences (or lack of consequences) on the fauna. This can constitute a table (in the text or in the supplementary material).

Secondly, I have a big concern with the difference in the mesh-net size used for hyporheos (63 µm) and the benthos (250 µm). The analyses of the two compartments separately are perfectly correct, but the calculation of a B-diversity index between benthic and hyporheic communities may be widely impacted by the smallest organisms (e.g. the occurrence of Ostracoda in the hyporheic samples that lack in the benthos). This problem of mesh-net size may be included in the discussion.

Finally, I was surprised by the very low differences observed in the communities sampled in the control and impacted reaches in 2013 (for S and H’, for the species traits and for the major taxonomic groups). Are there differences at the species level for Trichoptera and Ephemeroptera?  If the weir had such a low effect on invertebrate composition and community structures, it is logic that its removal has poor consequences on fauna. This point may be rapidly included in the discussion.

A last detail: at page 9 the authors wrote “diversity decline immediately after restoration” while samples were performed in 2015, this is really not immediate.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

The manuscript has been corrected according to the instructions, and the recommendations have been accepted following the suggestions in the text of the manuscript. 

I warmly recommend the manuscript for publication in the journal Water.

All the very best,

Reviewer