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Key components and contrasts in the nitrogen budget across a US-Canadian transboundary watershed
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  • Jiajia Lin,
  • Jana Compton,
  • Chris Clark,
  • Shabtai Bittman,
  • Donna Schwede,
  • Peter S. Homann,
  • Peter M. Kiffney,
  • David Hooper,
  • Gary Bahr,
  • Jill Baron
Jiajia Lin
The Oak Ridge Institute for Science and Education

Corresponding Author:jlin42@outlook.com

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Jana Compton
US EPA Corvallis
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Chris Clark
Whatcom Conservation District
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Shabtai Bittman
Agriculture and Agri-Food Canada
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Donna Schwede
U.S. Environmental Protection Agency
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Peter S. Homann
Western Washington Univ, Huxley Coll Environm, Bellingham, WA 98225 USA
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Peter M. Kiffney
NOAA Fisheries Service, Northwest Fisheries Science Center
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David Hooper
Western Washington University
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Gary Bahr
Washington State Department of Agriculture
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Jill Baron
United States Geological Survey
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Watershed nitrogen (N) budgets provide insights into drivers and solutions for groundwater and surface water N contamination. We constructed a comprehensive N budget for the transboundary Nooksack River Watershed (BC, Canada and WA, US) using locally-derived data, national statistics and standard parameters. Feed imports for dairy (mainly in the US) and poultry (mainly in Canada) accounted for 30 and 29% of the total N input to the watershed, respectively. Synthetic fertilizer was the next largest source contributing 21% of inputs. Food imports for humans and pets together accounted for 9% of total inputs, slightly lower than atmospheric deposition (10%). Returning salmon represented <0.06% of total N input but was an important ecological flux by importing marine-derived nutrients. Quantified N export was 80% of total N input, driven by ammonia emission (32% of exports). Animal product export was the second largest output of N (31%) as milk and cattle in the US and poultry products in Canada. Riverine export of N was estimated 28% of total N export. The commonly used crop nitrogen use efficiency (crop NUE) alone did not provide sufficient information on farming activities and should be combined with other criteria such as farm-gate NUE to understand management efficiency. Agriculture was the primary driver of N inputs to the environment despite widespread adoption of conservation practices, illustrating a need to optimize management to minimize hydrologic and volatilization losses. The N budget provides key information for stakeholders across sectors and borders to create environmentally and economically viable and effective solutions.