High-frequency NO3− isotope (δ15N, δ18O) patterns in groundwater recharge reveal that short-term changes in land use and precipitation influence nitrate contamination trends

Suchy, Martin; Wassenaar, Leonard I.; Graham, Gwyn; Zebarth, Bernie

doi:https://doi.org/10.5194/hess-22-4267-2018

Articles | Volume 22, issue 8

https://doi.org/10.5194/hess-22-4267-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-22-4267-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 22, issue 8

Research article

|

13 Aug 2018

Research article |

| 13 Aug 2018

High-frequency NO₃⁻ isotope (δ¹⁵N, δ¹⁸O) patterns in groundwater recharge reveal that short-term changes in land use and precipitation influence nitrate contamination trends

Martin Suchy, Leonard I. Wassenaar, Gwyn Graham, and Bernie Zebarth

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Final revised paper (published on 13 Aug 2018)
Supplement to the final revised paper
Preprint (discussion started on 07 Feb 2018)
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: 'Referee hess-2018-35', Anonymous Referee #1, 18 Mar 2018
- AC1: 'Reply to Reviewer #1', Leonard Wassenaar, 22 May 2018
RC2: 'HESS-2018-35', Anonymous Referee #2, 20 Apr 2018
- AC2: 'Response to Reviewer #2', Leonard Wassenaar, 22 May 2018

Peer-review completion

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

ED: Publish subject to revisions (further review by editor and referees) (25 May 2018) by Christine Stumpp

AR by Leonard Wassenaar on behalf of the Authors (25 May 2018) Author's response

ED: Referee Nomination & Report Request started (11 Jun 2018) by Christine Stumpp

RR by Anonymous Referee #1 (12 Jul 2018)

RR by Anonymous Referee #2 (17 Jul 2018)

Suggestions for revision or reasons for rejection

Nitrate contamination in groundwater is a widespread problem often associated with industrial agriculture. Many attempts to address excessive nitrate concentrations in groundwater by landuse management changes have yielded only sluggish or negligible success, indicating that our knowledge about sources and processes affecting nitrate in groundwater and the associated transit times are still rather incomplete. The manuscript by Suchy et al. makes a highly valuable contribution to close this knowledge gap by providing excellent new insights into sources and processes affecting nitrate concentrations in young groundwater in the transboundary Abbotsford-Sumas aquifer. The determination of 700 nitrate isotope compositions for age-controlled groundwater (< 5 years old) collected between summer 2008 and spring 2013 yielded novel insights about sources of groundwater nitrate in a study area where the predominant nitrogen inputs have recently shifted somewhat from manure towards synthetic fertilizers. In addition, the authors were able to determine the effects of local crop rotations and disturbances due to their spatially and temporally intensive sampling strategy.
The originally submitted manuscript had some moderate and several minor deficiencies. In my review of the revised manuscript, and of the detailed explanations provided by the authors, I found that most of these deficiencies have been addressed in an excellent and comprehensive fashion. In some case, the authors did not agree with the reviewers but provided solid and defendable arguments why they stuck to their original interpretation. In summary, I am highly satisfied with the revised version of this manuscript and the modifications that have been made, and recommend the revised version of this paper for publication as is. Since nitrate contamination in this aquifer has previously been reported by Wassenaar (1995) and Wassenaar et al. (2006), the authors were able to report on subtle shifts of nitrate sources on decadal time scales. These new findings make a highly valuable contribution to enhancing the understanding of sources, processes, and timelines of nitrate contamination of groundwater and hence will be of high interest to the readership of Hydrology and Earth System Sciences.

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ED: Publish subject to technical corrections (17 Jul 2018) by Christine Stumpp

AR by Martin Suchy on behalf of the Authors (26 Jul 2018) Manuscript

Short summary

Groundwater contamination by nitrate is a global problem. Understanding sources and transformations of nitrate in aquifers is key to inform remediation, and isotopes of nitrate (¹⁵N, ¹⁸O) are used for this. Most isotopic investigations are synoptic studies. Here we show that high-frequency nitrate isotope sampling of aquifer recharge better reveals the impact of short-term changes in land use practice or climatic conditions that need to be taken into account when considering long-term trends.