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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2018-35
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
07 Feb 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).
High-frequency NO3 isotope (δ15N, δ18O) patterns in groundwater recharge reveal that short-term land use and climatic changes influence nitrate contamination trends
Martin Suchy1, Leonard I. Wassenaar2, Gwyn Graham1, and Bernie Zebarth3 1Environment and Climate Change Canada, 201-401 Burrard St., Vancouver, BC, Canada
2Present address: International Atomic Energy Agency, Vienna International Centre, 1400, Vienna, Austria
3Fredericton Research and Development Center, Agriculture and Agri-Food Canada, 850 Lincoln Rd., PO Box 20280 Fredericton, NB, Canada E3B 4Z7
Abstract. Poultry manure is the primary source of nitrate (NO3) exceedances in the transboundary Abbotsford-Sumas aquifer (Canada-USA) based on synoptic surveys two decades apart, but serious questions remained about seasonal and spatial aspects of agricultural nitrate fluxes to the aquifer to help better focus remediation efforts. We conducted over 700 monthly δ15N and δ18O of nitrate assays, focusing on newly recharged groundwater (< 5 yr.-old) over a five-year period to gain new insight on spatiotemporal sources and controls of groundwater nitrate contamination. NO3 concentrations in recharge ranged from 1.3 to 99 mg N L−1 (n = 1041) with a mean of 16.2 ± 0.4 mg N L−1. These high-frequency isotope data allowed us to identify 3 distinctive nitrate flux patterns, i) nitrate in recharge influenced by synthetic fertilizer inputs ii) nitrate in recharge impacted by short-term climatic and local agricultural crop rotations and iii) long-term widespread manure and synthetic fertilizer inputs. A key finding was that the source(s) of nitrate in recharge could be quickly influenced by short-term near-field management practices and stochastic climatic factors, which linger and ultimately impact long-term nitrate contamination trends. Overall, the isotope data affirmed a subtle decadal-scale shift in agricultural practices from manure towards fertilizer nitrate sources, nevertheless poultry-derived N remains a predominant source of nitrate contamination. Because the aquifer does not support denitrification, remediation of the Abbotsford-Sumas aquifer is possible only if agricultural N sources are seriously curtailed, a difficult proposition due to longstanding high-value intensive poultry and berry operations over the aquifer.

Citation: Suchy, M., Wassenaar, L. I., Graham, G., and Zebarth, B.: High-frequency NO3 isotope (δ15N, δ18O) patterns in groundwater recharge reveal that short-term land use and climatic changes influence nitrate contamination trends, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2018-35, in review, 2018.
Martin Suchy et al.
Martin Suchy et al.
Martin Suchy et al.

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Short summary
Groundwater contamination by nitrate is a global problem. Understanding sources and transformations of nitrate in aquifers are key to inform remediation, and isotopes of nitrate (δ15N, δ18O) 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.
Groundwater contamination by nitrate is a global problem. Understanding sources and...
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