The Role of Management of Stream–Riparian Zones on Subsurface–Surface Flow Components

Round 1

Reviewer 1 Report

Overall information

The subject of the paper is interesting, corresponds with journal profile. The article was prepared neatly and the structure of the paper is proper. Also the methodology was tried to prepare neatly, so sometimes the descriptions e.g. “history” of piezometers seems to be complicated.  But I have one very serious doubt about methodology of stream discharge measurement and thus about results’ interpretation.

Detailed note about methodology

The authors wrote that the discharge measurement was carried out monthly. So it means that each result presented on the figure 5 are based on only one measurement event. These are indeed not monthly discharge but temporary discharge, measured in some single moment in time. And thus in my opinion disqualifies possibility of monthly analyses. Even the authors themselves noticed the mistakes which can be made in analyzes based on such a measurement procedure: “The significant decrease in discharge between  Q1 and Q2 (losing conditions, -0.22 m³s^-1) seen in August, is certainly because Q2 was measured last  and after a rainfall had stopped –  whereas Q1 and Q3 was measured during rainfall”. The discharge should be measured daily, than the basic statistics (maximum, minim, average or median discharge) should be calculated and analyzed. In this case average discharge can be connected with monthly sum of precipitation and maximum with highest daily precipitation, in some degree of accuracy of course. Even in the publication of Poulsen et al. [2015] quoted in the discussion (line 685) the discharge was measured daily (fig. 2 in Poulsen). So in my opinion this part of the paper should be rebuilt. And thus also estimating a water balance (subchapter 5.3) is also doubtful, and further conclusions can be based on uncertain facts. That’s in my opinion the main weakness of the paper.

Comments for author File: Comments.pdf

Author Response

Author response to reviewer #1 (R1). Reviewer evaluation in italic.

First of all, we would like to thank R1 for the review and comments made to our manuscript. We are pleased with the overall reception of our study and thank the reviewer for the positive comments made to the manuscript, i.e., “[t]he subject of the paper is interesting [and], corresponding with the journal profile”. We would also like to thank the reviewer for the positive statement that “[t]he article was prepared neatly and the structure of the paper is proper”.

R1 marks that the following ‘must be improved’; research design, description of methods, presentation of results, conclusions. However, R1 gives little guidance to exactly what he/she finds must be improved. We therefore assume that it all refers to the one major comment R1 has on stream discharge measurements. Please note that R2 finds that these issues are well described (‘yes’).

As correctly stated by R1, measurements of discharge were conducted once per month. It would certainly have been nice to have continuous stream flow data. However, our reasoning and methodology was the following. We had no possibility for measuring continuous flow from the springs. So, these were snapshot of flow every month. Likewise, we then found it reasonable to only measure stream flow once a month so that we could compute a snapshot of the gain in stream flow (DQ). So these measurements go in tandem. In this way, our water balance is the average of these monthly snapshots. We also have to remember that the flow through the streambed was only measured once; here we do not have monthly data. This is not critical, as the flow is very small.

In the revision, we have now included a better description of this approach.

In lines 194-198 and 228-231 (Methods) we have added text describing this approach. In lines 693-698 (discussion) we touch upon the uncertainty of not having continuous stream flow data. It should be noted, that despite the method used, the average stream gain is still based on two times twelve measurements, not just on one single pair of measurements made in one month only. Moreover, even if the absolute stream gain would be quite significantly erroneous by e.g. ±50%, still the springs flows would turn out as the major contributor to the stream gain. These considerations increase the robustness of our conclusion that the water balance shows that springs flows are the major contributor to stream flow gain, which we therefore maintain.

Regarding the minor issue of the complicated history of the piezometers, mentioned by the reviewer in the methodology section 3.2 ‘Hydrology’ we have addressed this by attempting to reformulating part of this section (on page 5: line number 174-186).

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper uses many different types of data and careful long-term observations to build out a water budget for a riparian zone in Denmark. Some implications of anthropogenic disturbances are mentioned but these are not really expanded sufficiently that any general conclusions can be drawn. Not sure how this study changes current conceptual models of riparian hydrology. In summary, I don't really understand what scientific advance this paper has made, but it does seem to comprise a useful guide to others who want to build headwater stream water budgets. I think the paper would serve much better as a "guide to determining a stream water budget" rather than a novel contribution to riparian hydrogeology or agricultural management. I don't see a significant advance in either of these topics despite the prolificity of datasets used.

Author Response

Author response to reviewer #2 (R2). Reviewer evaluation in italic.

We would like to thank reviewer #2 for the review and the positive reception of our manuscript. We are pleased that the reviewer finds our manuscript to provide the sufficient background and references. In addition, we are happy that he/she finds the research design, methods and results to be of a satisfying quality.

The two major comments by R2 refer to that the (1) anthropogenic disturbances are not really expanded and (2) the study does not per se advance conceptual models of riparian hydrology.

Regarding (1). We believe we fully describe that the wetland on the southern side of the stream is ‘disturbed’ in that it consists of a ditch, drainage well, artificial pond, and springs that maybe due to broken pipes (or natural). This results in a water balance where the major contributor to stream flow is from these springs/ditches etc. We have direct evidence that subsurface flow is captured by these instead of resulting in direct seepage through the stream bed. We have many other field sites along the same stream, where we for many years have measured direct seepage through the stream bed. At the current study site the seepage is a factor of 6 lower than what we typically measure in other places. This is because the drains etc. capture the subsurface flow. It is not often you see studies where it is possible to do such comparisons. If one developed a flow model with and without drains in the wetland it would give the same result, flow from the regional aquifer would mainly be captured by the drains. We see a managed/disturbed wetland and that has implications on the water balance.

While we find that it is difficult to expand more on this issue, we did include the following statement in the introduction, to perhaps point the reader more into that direction: “Riparian lowlands used for agricultural purposes are frequently drained, but whether such drainage increases of decreases nutrient retention is uncertain.” (Page 1 lines 39-40).

Regarding (2). We do not claim to have developed a new conceptual model of riparian hydrology. We compare our results with existing models and find that there are few studies that monitor the groundwater-fed surface flow and the stream bed seepage. We are pleased the reviewer finds our study a potential useful guide on “how to” create a water budget of a headwater stream. This is exactly what we state on the first few lines of the discussion, i.e., evaluate the relative importance of groundwater-fed surface flow and direct seepage to the stream. Likewise, this is also stated in the abstract.

We have not modified the manuscript.

Regarding the matter of ‘Moderate English changes required’.  We have been through the manuscript and revised wording and language. In addition, we have now changed our spelling and phrasing patterns from American to British English.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Short comment to the authors’ response and manuscript revision

Thank You for considering my opinion. I used to claim that no perfect articles exist, but it’s important to understand the potential weakness because it allows the readers to look at the article with a certain amount of criticism. I think the explanation in cover letter and changes and explanation made in revised version of manuscript seems to be sufficient and I can accept authors’ arguments. It’s also important that the authors gave the notification about uncertainty of not having continuous stream flow data. Such an information will be useful for further paper readers to interpret obtained results. In my opinion presented version of the article can be published.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer

Thank you for your positive reception of our manuscript. We are pleased that our first response and changes to the original manuscript was acceptable. 

In addition, we can mention we have now revised the manuscript according to the suggestions by the Academic Editor. We decided to re-write the conclusion (L739-L765) so it almost entirely focuses on the broader aspects of the implications of anthropogenic changes of the wetland.

Thank you for your time taken to review our manuscript.

Best regards and on behalf of all co-authors,

Mads Steiness

Author Response File: Author Response.pdf

Reviewer 2 Report

Authors chose not to carefully address the concerns raised in my review in the revised copy except for adding one sentence. If editor agrees that the original review did not merit making any significant changes to the paper, it can be published. My original review stands as "unaddressed" in the revised paper and I have the same concerns about the revised copy as I did the original since it has not really changed. Readers may have same concerns but unfortunately they are not going to get to see the author response letter, which was quite helpful. I advise another round of revision where authors incorporate their response into the paper. Then it should be good to go.

Author Response

Dear Reviewer

We have now revised the manuscript according to the suggestions by the Academic Editor and you.

In the end, we hope this new copy of our manuscript will now better answer the major comments raised by you in the first revision. We have decided to re-write the conclusion (L739-L765) so now it almost entirely focuses on the broader aspects of the implications of anthropogenic changes of the wetland. Furthermore, we have include a sentence saying that it is important to measure all flow components of water budget of riparian-stream systems.

We hope this will better address your original review of our first copy of the manuscript. We are thankful for the time you have taken to review our manuscript.

Changes made:

  - New conclusion L739-765.

  - To make this even clearer we also modified objective (3) (L 79-82).

Best regards and on behalf of all co-authors,

Mads Steiness

Author Response File: Author Response.pdf