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Discussion papers | Copyright
https://doi.org/10.5194/hess-2018-31
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Feb 2018

Research article | 13 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).

Sources and fate of nitrate in groundwater at agricultural operations overlying glacial sediments

Sarah A. Bourke1,2, Mike Iwanyshyn3, Jacqueline Kohn4, and M. Jim Hendry1 Sarah A. Bourke et al.
  • 1Department of Geological Sciences, University of Saskatchewan, SK, S7N 5C9, Canada
  • 2School of Earth Sciences, University of Western Australia, Crawley, WA, 6009, Australia
  • 3Natural Resources Conservation Board, Calgary, AB, T2P 0R4, Canada
  • 4Alberta Agriculture and Forestry, Irrigation and Farm Water Branch, Edmonton, AB, T6H 5T6, Canada

Abstract. Leaching of nitrate (NO3) from animal waste or fertilizers at agricultural operations can result in NO3 contamination of groundwater, lakes, and streams. Understanding the sources and fate of nitrate in groundwater systems in glacial sediments, which underlie many agricultural operations, is critical for managing impacts of human food production on the environment. Elevated NO3 concentrations in groundwater can be naturally attenuated through mixing or denitrification. Here we use snapshots of the stable isotope values of NO3 to quantify denitrification in groundwater at two confined feeding operations overlying glacial sediments in Alberta, Canada. Uncertainty in δ15NNO3 and δ18ONO3 values of the NO3 source and denitrification enrichment factors are accounted for using a Monte Carlo approach. When denitrification could be quantified, we reconstructed the initial NO3-N concentration and NO3-N/Cl ratio at the point of entry to the groundwater system. The addition of NO3 to the local groundwater system from temporary manure piles and pens equalled or exceeded NO3 additions due to leaching from earthen manure storages at these sites. Nitrate attenuation at both sites is attributed to a spatially variable combination of mixing and denitrification, but is dominated by denitrification. On-site denitrification reduced agriculturally derived NO3 concentrations by at least half and, in some wells, completely. These results indicate that infiltration to groundwater systems in glacial sediments where NO3 can be naturally attenuated is likely preferable to off farm export via runoff or drainage networks. The application of isotopes of nitrate to constrain a mixing model based on concentrations of Cl and NO3, which can be routinely monitored in groundwater, provides a relatively simple method to assess the sources and fate of agriculturally derived NO3 in these settings.

Sarah A. Bourke et al.
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Sarah A. Bourke et al.
Sarah A. Bourke et al.
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Short summary
Agricultural operations can result in nitrate contamination of groundwater, lakes and streams. At two confined feeding operations in Alberta Canada, nitrate in groundwater from temporary manure piles and pens exceeded nitrate from earthen manure storages. Denitrification reduced agriculturally derived nitrate concentrations in groundwater by at least half. Infiltration to groundwater systems where nitrate can be naturally attenuated is likely preferable to off farm export via runoff or drainage.
Agricultural operations can result in nitrate contamination of groundwater, lakes and streams....
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