Hydraulic shortcuts increase the connectivity  of arable land areas to surface waters

Schönenberger, Urs; Stamm, Christian

doi:https://doi.org/10.5194/hess-25-1727-2021

Articles | Volume 25, issue 4

https://doi.org/10.5194/hess-25-1727-2021

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

https://doi.org/10.5194/hess-25-1727-2021

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

Articles | Volume 25, issue 4

Research article

|

06 Apr 2021

Research article |

| 06 Apr 2021

Hydraulic shortcuts increase the connectivity of arable land areas to surface waters

Urs Schönenberger and Christian Stamm

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Final revised paper (published on 06 Apr 2021)
Supplement to the final revised paper
Preprint (discussion started on 07 Sep 2020)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of hess-2020-391', Anonymous Referee #1, 01 Nov 2020
- AC1: 'Reply to Anonymous Referee #1', Urs Schönenberger, 12 Nov 2020
  - AC3: 'Correction to Comment concerning L116-117', Urs Schönenberger, 07 Dec 2020
RC2: 'Review: Hydraulic Shortcuts Increase the Connectivity of Arable Land Areas to Surface Waters', Anonymous Referee #2, 17 Nov 2020
- AC2: 'Reply to Anonymous Referee #2', Urs Schönenberger, 23 Nov 2020

Peer-review completion

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

ED: Publish subject to revisions (further review by editor and referees) (07 Dec 2020) by Insa Neuweiler

AR by Urs Schönenberger on behalf of the Authors (26 Dec 2020) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (07 Jan 2021) by Insa Neuweiler

RR by Anonymous Referee #1 (28 Jan 2021)

Suggestions for revision or reasons for rejection

The authors did a great job responding to my comments, thank you for that. I also appreciated the discussion with reviewer #2.
In all honesty, I still don’t see much value in the up-scaled map. Moreover, I was somewhat troubled by the discussion raised by the authors about the role of scientific models in matters of public interest. From my perspective, models are mostly useful to create understanding about phenomena and to make predictions and simulations about them. Sometimes these predictions are useful to society. Now, your upscaling accomplishes very little in terms of creating understanding. It is predicting the output of a model, using the outputs of another model (with similar parameters), based on a fitted linear…model. Apparently the final national maps are different, but who is to say that is not just the residuals from the regression? The bootstrapping approach for quantifying the uncertainty from catchment choice does not represent the regression uncertainty (see my suggestion in the first review round). Regardless, the usefulness of the final model predictions to society, which seems to be of great concern to the authors, is impossible to assess without testing. Hence, I would be very careful about recommending untested models for decision-making in matters of public interest (e.g. L769-775).
That being said, the authors state the limitations of their approach quite clearly, and make a serious effort to address the uncertainty in their models. Moreover, I really enjoyed the first part of the manuscript, which focuses on mapping drainage locations and simulating how they increase runoff connectivity in several small catchments.
In the end, the more I read this manuscript, the more I think the up-scaling would be better suited to a technical report, as it does not contribute to advance the science. But I would be interested to hear what the editor and the other reviewer have to say about this. Hence, I am recommending another minor review.

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RR by Anonymous Referee #2 (05 Feb 2021)

Suggestions for revision or reasons for rejection

I perceive, the authors have acknowledged and addressed most of my reservations. I agree with the adaptations made, or explanations given in the authors response and find the paper improved. I suggest two further adjustments:
In my previous comment 19, I argued that the 2nd research question could not be fully answered. I don’t want to split hairs over this, but it seems central to the papers aim. The question was stated as follows:
What is [the] relevance [of hydraulic shortcuts] for surface runoff connectivity and for surface-runoff related pesticide transport?
The paper shows the occurrence and prevalence of hydraulic shortcuts among Swiss catchments (and answers therefore research question 1 and the first part of question 2. The authors argue that they don’t find or expect systematic differences in other boundary conditions of pesticide transport. Hence, they conclude that surface runoff related pesticide transport is proportional to connected area (L 536 – 539 / 748 – 751 ACT). This is likely true, if the other conditions remain unchanged, e.g. for varying connectivity in the same catchment. But it does not account for the effect size of hydraulic shortcuts as compared to other conditions e.g. pesticide application timing and intensity or soil hydraulic properties may have a dominant effect on overall surface-runoff related pesticide transport. This is acknowledged in the discussion section (L 751-752 ATC).
I suggest to adapt question 2) as follows:
What is the contribution of hydraulic shortcuts to surface runoff connectivity and what are implications for surface-runoff related pesticide transport?
And to extend L 536 – 539 ACT as follows:
Analogously, if other boundary conditions of pesticide transport remain unchanged, directly and indirectly transported pesticide loads are expected to be proportional to directly and indirectly connected crop areas.
As a general remark: If available, a revision of phrasing, esp. of the M&M section, could make the text easier to read. Some needlessly complicated sentence constructions are:
L 212 – 214 We created a surface runoff connectivity model to estimate which fraction of potentially pesticide loaded surface runoff originating on agricultural land is reaching surface waters via hydraulic shortcuts in comparison to direct transport.
L 236 – 239 The extent of agricultural areas was defined by subtracting all nonagricultural areas (forests, water bodies, urban areas, traffic areas, and other non-agricultural areas) as defined by the national topographical landscape model SwissTLM3D (Swisstopo, 2010) from the total area of each study area.
L 328 - 330 In order to assess the relevance of shortcuts for the whole country and to evaluate how the empirical data affect the predictions on the national scale, we developed a model for extrapolating the results from our study areas (local surface runoff connectivity model, LSCM) to the national scale.
L 362 – 365 Since there are no high-resolution datasets of crop areas yet available in Switzerland, we considered the total extent of agricultural areas for building the local surface runoff connectivity model and extrapolation to the national scale. These areas include areas with rare pesticide application, such as meadows and pastures.

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ED: Publish subject to minor revisions (review by editor) (17 Feb 2021) by Insa Neuweiler

AR by Urs Schönenberger on behalf of the Authors (22 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (01 Mar 2021) by Insa Neuweiler

Short summary

Pesticides are a major pollutant of surface waters. In this study, we assessed how so-called hydraulic shortcuts (e.g. inlet and maintenance shafts of road or field storm drainage systems) influence surface runoff and pesticide transport to Swiss surface waters. The study suggests that transport via hydraulic shortcuts is an important pesticide transport pathway and that current regulations may fall short in addressing this pathway.