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© 2019. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.

Abstract

Leaching of nitrate (NO3-) from animal waste or fertilisers 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 isotopic enrichment of the stable isotope values ofNO3- to quantify the amount of denitrification in groundwater at two confined feeding operations overlying glacial sediments in Alberta, Canada. Uncertainty in δ15NNO3 andδ18ONO3 values of the NO3- source and denitrification enrichment factors are accounted for using a Monte Carlo approach. When denitrification could be quantified, we used these values to constrain a mixing model based on NO3- and Cl- concentrations. Using this novel approach we were able to reconstruct the initial NO3-N concentration and NO3-N/Cl- ratio at the point of entry to the groundwater system. Manure filtrate had total nitrogen (TN) of up to 1820 mg L-1, which was predominantly organic N and NH3. Groundwater had up to 85 mg L-1 TN, which was predominantly NO3-. The addition of NO3- to the local groundwater system from temporary manure piles and pens equalled or exceeded NO3- additions from earthen manure storages at these sites. On-farm management of manure waste should therefore increasingly focus on limiting manure piles in direct contact with the soil and encourage storage in lined lagoons. Nitrate attenuation at both sites is attributed to a spatially variable combination of mixing and denitrification, but is dominated by denitrification. Where identified, denitrification reduced agriculturally derived NO3- concentrations by at least half and, in some wells, completely. 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, especially if local groundwater is not used for potable water supply.

Details

Title
Sources and fate of nitrate in groundwater at agricultural operations overlying glacial sediments
Author
Bourke, Sarah A 1 ; Iwanyshyn, Mike 2 ; Kohn, Jacqueline 3 ; Hendry, M Jim 4 

 Department of Geological Sciences, University of Saskatchewan, Saskatchewan, SK, S7N 5C9, Canada; School of Earth Sciences, University of Western Australia, Crawley, WA, 6009, Australia 
 Natural Resources Conservation Board, Calgary, AB, T2P 0R4, Canada 
 Alberta Agriculture and Forestry, Irrigation and Farm Water Branch, Edmonton, AB, T6H 5T6, Canada 
 Department of Geological Sciences, University of Saskatchewan, Saskatchewan, SK, S7N 5C9, Canada 
Pages
1355-1373
Publication year
2019
Publication date
2019
Publisher
Copernicus GmbH
ISSN
10275606
e-ISSN
16077938
Source type
Scholarly Journal
Language of publication
English
ProQuest document ID
2189482748
Copyright
© 2019. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.