Are maps of nitrate reduction in groundwater  altered by climate and land use changes?

Seidenfaden, Ida Karlsson; Sonnenborg, Torben Obel; Refsgaard, Jens Christian; Børgesen, Christen Duus; Olesen, Jørgen Eivind; Trolle, Dennis

doi:https://doi.org/10.5194/hess-26-955-2022

Articles | Volume 26, issue 4

https://doi.org/10.5194/hess-26-955-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-26-955-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 26, issue 4

Research article

|

21 Feb 2022

Research article |

| 21 Feb 2022

Are maps of nitrate reduction in groundwater altered by climate and land use changes?

Ida Karlsson Seidenfaden, Torben Obel Sonnenborg, Jens Christian Refsgaard, Christen Duus Børgesen, Jørgen Eivind Olesen, and Dennis Trolle

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Final revised paper (published on 21 Feb 2022)
Supplement to the final revised paper
Preprint (discussion started on 21 Dec 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 “Are maps of nitrate reduction in groundwater altered by climate and land use changes?” for HESSD', Anonymous Referee #1, 18 Jan 2021
- AC1: 'Reply on RC1', Ida Seidenfaden, 06 May 2021
  - AC4: 'Reply on AC1', Ida Seidenfaden, 07 May 2021
RC2: 'Review of Karlsson Seidenfaden et al.', Fanny Sarrazin, 25 Jan 2021
- AC2: 'Reply on RC2', Ida Seidenfaden, 06 May 2021
- AC5: 'Reply on RC2', Ida Seidenfaden, 07 May 2021
RC3: 'Review of Karlsson Seidenfaden et al.', Pia Ebeling, 26 Jan 2021
- AC3: 'Reply on RC3', Ida Seidenfaden, 06 May 2021
- AC6: 'Reply on RC3', Ida Seidenfaden, 07 May 2021

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (18 May 2021) by Rohini Kumar

Dear authors,

Thank you for taking part in the interactive discussion round.
Your manuscript was seen by the three referees, and they have rated your work from poor to good. While they find some positive things in your work, the referees have also raised some critical points and provided detail comments (on both methodological and overall presentation of the work) as well as suggested ways to improve the manuscript. I appreciate your responses to the referee comments in the interactive discussion; and your plan to revise the manuscript. Besides this, based on my reading of your responses to the reviewer’s comments, I strongly recommend to put more emphasis on:

1. Demonstrating sufficiently the model skills for both water quantity (streamflows) and water quality (in-stream or groundwater nitrate concentrations). Put more emphasis on showing how the model simulates the observed reality across different settings of landscapes (varying degree of landcovers) and hydroclimate variability (e.g., over space and time). It can follow e.g., spilt-sample testing approach (Klemes 1986; Andréassian 2009).

Klemes, V.: Operational testing of hydrological simulation models, Hydrolog. Sci. J., 31, 13–24, 1986.

Andréassian, V., Perrin, C., Berthet, L., Le Moine, N., Lerat, J., Loumagne, C., Oudin, L., Mathevet, T., Ramos, M.-H., and Valéry, A.: HESS Opinions "Crash tests for a standardized evaluation of hydrological models", Hydrol. Earth Syst. Sci., 13, 1757–1764, https://doi.org/10.5194/hess-13-1757-2009, 2009.

2. Analysis on the parametric uncertainty and how this would affect the modelling results. All reviewers have raised this point of parameters and in general more elaboration on the model settings (uncertainties); and I also consider this as a very legitimate point to look into this issue with greater details.

Given that the nature of revision being major, I will seek further advices from the referees after receiving your revisions. Please consider whether such a revision is feasible in the available time framework. I look forward receiving your revised manuscript.

Best regards,
Rohini Kumar

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AR by Ida Seidenfaden on behalf of the Authors (02 Jun 2021) Author's response Author's tracked changes Manuscript

ED: Reconsider after major revisions (further review by editor and referees) (02 Jun 2021) by Rohini Kumar

AR by Ida Seidenfaden on behalf of the Authors (28 Jun 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (30 Jun 2021) by Rohini Kumar

RR by Fanny Sarrazin (24 Jul 2021)

Suggestions for revision or reasons for rejection

In the revised version of the manuscript, the authors clarified the methods used in Section 3 and added a discussion about other sources of uncertainty beyond climate and land use in Section 5.2. The analyses performed and the results remain unchanged. I think that the manuscript has significantly improved in terms of clarity. However, I still have a number of comments, in particular regarding the nitrogen and climatic input data and the derivation of the value of 10% for the uncertainty in the reduction map. In addition, although the authors did not assess the uncertainty coming from the model parameters, the manuscript highlights other sources of uncertainty (bug in Mike She code or model error in validation) that are of the same order of magnitude as the uncertainty due to climatic/land use conditions (10%). I think that this should be better discussed.

Importantly, I would like to make a clarification with respect to the authors’ reply to my second comment that ‘A global search engine (Shuffled Evolution Complex) was used. Thus, limiting the risk of equifinality’. I would like to highlight that this statement is not correct. Equifinality results from a lack of information/data to constrain the parameters of a given model, and does not depend on the method used to estimate the parameters. Optimization method such as the Shuffled Evolution Complex algorithm may not reveal equifinality because they identify only one parameter set that ‘best’ fit the data, while there is likely to be other parameter sets with similar performance that have very different parameter values. I refer e.g. to Beven et al. (2006) for a discussion on the issue of equifinality.

I report below detailed comments.

p9 L203: Could the authors briefly explain what the crop recommended nitrogen rate is and where the value come from (reference)?

p9 L210: Could the authors add the source of the nitrogen atmospheric deposition dataset.

p12 L279: The calculation of potential evapotranspiration is still unclear. What is ‘water vapour’ and ‘water pressure’? I guess that the authors mean vapour pressure/relative humidity and atmospheric pressure, which are the variables used in the Penman Monteith equation. In addition, more details are required on the radiation term. Net radiation is necessary to compute Penman Monteith equation, while typically climate models provide the downward radiation terms only.

p18 Table 4: I guess that the mean and standard deviation refer to the spatial distribution of the nitrate distribution potential? Please clarify.

p21 L421: Figure 4 does not report results on reduction potential. Please refer to the appropriate figure/table for this.

p28 L573-579: What about nitrate reduction in soils?

p28 L594: Where does the value of 10% comes from? It is not clear from the results presented in Section 4 (Figure 6).

p29 L602-603: I think that this uncertainty of up to 10% should be also discussed with respect to other modelling uncertainties that are reported in the manuscript and that are of the same order of magnitude, i.e. the uncertainty due to the bug in the Mike-SHE code (that is up to 9% p12 L267), and the model error in the validation period (that is up to 10% for Mike She p15 L328 and up to 23% for Daisy model p15 L333)

p29 L612: There is something wrong is this sentence. Please clarify.

P30 L628 ‘Thus, the uncertainty of the reduction maps is dependent on both model setup and assumptions’: to which model setup and assumptions do the authors refer? The uncertainty to model setup and assumptions is not analysed in the study, but only discussed as potential uncertainty that may arise. This second conclusion should be amended to reflect this.

Minor edits
p3 L57 ‘have been applied’: what is the subject of ‘have’? Is it ‘a nitrate reduction map’? In this case it should be replaced by ‘has’.
p4 L93: replace ‘constitute’ by ‘constitutes’
p4 L94 ‘fellow’: Do the authors mean ‘fallow’?
p4 L97: replace ‘as a results’ by ‘as a result’
p5 L112: replace ‘in 100 meter’ by ‘at 100 meter’
p6 L131: ‘inverse’ should be replace by ‘inversely’, but I would actually remove this term.
p7 L147: replace ‘need’ by ‘needed’.
p10 L224‘accumulated’: do the authors mean ‘cumulative’?
p11 L239: replace ‘representable’ by ‘representative’.
p11 L261: add ‘it’ after (‘the data from which’)
p14-15 Table 2: I suggest to refer to ‘observational period’ and ‘reference period’ rather than ‘control period’
p16 Table 3 caption: replace ‘for the crop type’ by ‘for the crop types’
p20 L404-405: the verb is missing is this sentence.
p22 L437: remove the ‘s’ at the end of ‘results’ (in ‘these changes results’).
‘p.p.’ is used multiple times in the manuscript: what does it stand for?
p25 L520: replace ‘figure 9’ by ‘figure 6’.
p30 L624-625: replace ‘the main finding of the study was by ‘the main findings of the study were’

References

Beven, K. (2006). A manifesto for the equifinality thesis. Journal of Hydrology, 320(1–2), 18–36. https://doi.org/10.1016/j.jhydrol.2005.07.007

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RR by Pia Ebeling (05 Aug 2021)

Suggestions for revision or reasons for rejection

The authors have addressed the previous comments and have greatly improved their manuscript and its clarity. I have a few more, but minor comments that should be addressed before publication of this manuscript.
General (minor) comments:
- I appreciate the much clearer Method Sections that you greatly improved. Just, sometimes I feel it is not completely which methods were set up previously in other studies and simply reused for this manuscript or which ones you extended from previous studies. One example is the part on redox depth estimation paragraph L236-242. Maybe in some cases it would be helpful to start with the reference instead of at the end of the description. “Following …, we did…” or “We extended on the method … presented by ….”. Please revise those sections to be clear. This is not easy as your work makes use of many previous approaches from the study region and in general, but I think it would further improve the readability and the connection to the references.
- Check consistency of spelling: 1.) NO3-N should all be NO3-N or “nitrate-N” ; 2.) lower and upper case usage for each of the models MIKE SHE and DAISY; 3.) When going through the manuscript I found mostly 2080-2099 for the future period, but in some instances 2088-2099, please revise to ensure these are correct.
Detailed comments:
L 10: I still think this formulation is overly complicated. I suggest formulating the goal of your study in a positive way, something like investigating the “potential improvement of using transient nitrate reduction maps compared to …”.
L 36: This sentence should be more precise in my opinion. Denitrification is one of the removal processes not just a synonym of the term, e.g. what about N uptake? Especially when you talk about processes in the unsaturated zone as you simulated with Daisy and in surface waters as you mention here, I think the terms should be introduced more carefully. It merits this attention for the aim of your study. I think the next paragraph would also fit to include “denitrification” term.
L 40: remove “(nitrate reduction)”
L 42 and 45: inconsistent spelling lower and upper case “quaternary”
L 55: An approach is singular, please revise
L 102: “the load is approximately …” What kind of load? Is this input as N surplus or the export in the stream? This should be more specific, and depending on your answer possibly also include how it is estimated, e.g. mean discharge times mean concentration?
L 106: To start a sentence with a number is not a nice style. Plase revise
L125: Danish
L 155: I am curious: why did you select these periods for calibration and validation? Why do you use more years for validation (in total) than for calibration? From my knowledge this is rather uncommon, therefore I am curious about this decision.
L231-235: Can these graphs be shown in the supplements? I think this could be good additional information. Also add reference to SI here.
L 270: 16 models, but L 306 20 simulations. Is this correct?
L 597: New inserts “N reduction” are not consistent with “nitrate reduction” in the rest of the text, recheck please
L 615: “To account for this, a full solute” comma missing
Table 4: response to your response: “Table 4: Do you have an idea why the standard deviations of all models are that similar (Table 4, 0.36‐0.39)? Can you comment on that, please?” – “This could be related to the fact that most changes in the reduction map are happening for values close or
around the mean. Areas with 0% og 100% reduction are perhaps less likely to change reduction potential, as they are either very close to surface water (0% reduction) or located at areas with a deep groundwater level (long deep flow paths and limited drain flow) (100% reduction).” Maybe, that is what you meant. Actually, now with your response, I think that it is because all models cover the range of 0-100% with relatively high amount of cells in the extremes, stretching the standard deviation to similar values independent of the mean. I am not sure, the standard deviation is telling considering this perspective and the not normal distributed values. Figure 2b for example clearly shows that <10% and >90% prevail.

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RR by Anonymous Referee #1 (22 Sep 2021)

ED: Reconsider after major revisions (further review by editor and referees) (24 Sep 2021) by Rohini Kumar

AR by Ida Seidenfaden on behalf of the Authors (19 Nov 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (19 Nov 2021) by Rohini Kumar

RR by Fanny Sarrazin (22 Nov 2021)

ED: Publish subject to technical corrections (03 Jan 2022) by Rohini Kumar

AR by Ida Seidenfaden on behalf of the Authors (10 Jan 2022) Author's response Manuscript

Short summary

This study investigates how the spatial nitrate reduction in the subsurface may shift under changing climate and land use conditions. This change is investigated by comparing maps showing the spatial nitrate reduction in an agricultural catchment for current conditions, with maps generated for future projected climate and land use conditions. Results show that future climate flow paths may shift the catchment reduction noticeably, while implications of land use changes were less substantial.