Reactive nitrogen emissions contribute to greenhouse gases, as well as air and water pollution. For the first time, researchers at McGill University have calculated Canada’s nitrogen footprint (similar to a carbon footprint) – nationally and provincially. They looked at the three main sectors that contribute to the supply of nitrogen to the environment to calculate the annual average nitrogen footprint: food production and consumption, wastewater treatment, and fossil fuel use. There were a few surprises when analyzing their results.
“Past studies of nitrogen footprints in other countries have generally focused on the food system as the main source of nitrogen released to the environment,” says Graham MacDonald, associate professor in the Department of Geography at McGill and main author of the article published recently in Environmental research letters. âAlthough food production and consumption are important sources of nitrogen in Canada, our research shows that most of the variation between provinces in a relative sense is related to fossil fuels. This surprised some of our colleagues.
Regional variations in the magnitude and drivers of nitrogen footprints
The researchers used a new top-down approach, which took national and provincial data on 2018 agricultural, energy, and other nitrogen emissions to estimate total provincial nitrogen footprints and divided them by provincial populations. Typically, nitrogen footprint ratings are estimated using a bottom-up approach based on information on personal consumption patterns (e.g. household electricity use, distances traveled or traveled, beef consumption , etc.). Using this new hybrid approach, the researchers calculate that Canada’s total annual reactive nitrogen footprint is approximately 996 gigagrams (or 996 billion kilograms) per year. This translates into an average nitrogen footprint of approximately 27 kilograms of nitrogen emitted per person per year in Canada. But this figure hides many regional variations, both in terms of magnitude and of the factors responsible for these emissions.
“Ontario and Quebec contribute the most to the national nitrogen footprint simply because more than two-thirds of the Canadian population live in these provinces,” says Sibeal McCourt, doctoral student in McGill’s geography department and first author of study. âBut Saskatchewan’s nitrogen footprint, per capita, is the largest in the country, almost double that of Ontario. This is because the province has a strong mining sector and depends on coal and natural gas for its energy.
Towards a more efficient use of nitrogen
âBefore we can reduce our overall national nitrogen footprint, it is essential to understand which areas of each province contribute the most to nitrogen pollution so that the problem can be addressed at a more local level,â adds McCourt. âThis research will help us better understand where / who / how to take action to reduce nitrogen emissions, assign responsibility to different actors (including our own consumption patterns, such as our personal food) and ultimately , use nitrogen more efficiently in Canada. â
Given the relative contribution of meat consumption and fossil fuel-related emissions to provincial nitrogen footprints, the researchers suggest that the shift towards more plant-based diets, the promotion of electric vehicle use, and the pursuit of the transition to renewable energy sources for electricity are among the policy options that would be most relevant in much of the country. Steps can also be taken to make the food system as a whole less “permeable” in terms of nitrogen.
âMuch research attention is paid to improving the efficiency of nitrogen use in agriculture, which can go a long way in reducing Canada’s nitrogen footprint,â said MacDonald. “What’s particularly interesting about a footprint-based approach is that it allows us to compare the potential of these different individual and collective efforts towards sustainability.”
Some details on variations in provincial nitrogen footprints
The researchers analyzed the three main sectors that contribute to provincial nitrogen footprints: 1) food production and consumption, 2) wastewater treatment, 3) fossil fuels
Food production and consumption
- In all provinces, 35 to 40% of nitrogen footprints come from the consumption of beef.
- In Ontario, New Brunswick and Quebec, beef consumption is the primary overall factor in the provincial nitrogen footprint and the 2sd the largest driver in all other provinces except Alberta and Saskatchewan.
- Apart from Ontario and Quebec, in all other provinces, less than 50% of the nitrogen footprint comes from food production.
- Differences in the types of crops grown and farm management techniques affect the share of provincial nitrogen footprints related to agriculture.
- Wastewater treatment is the 3rd the most important factor in national and provincial footprints, given that there are relatively low levels of nitrogen removal from wastewater treatment across the country.
- Only about 30% of the Canadian population is connected to municipal sewer systems that receive treatment focused on nitrogen removal.
- Coastal provinces (British Columbia, Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador) with relatively low population densities and which discharge mainly into coastal waters, generally have lower effluent (and nitrogen removal) standards than the interior provinces (Ontario, Manitoba, Saskatchewan and Alberta).
- Alberta is the province with the largest proportion of its population covered by wastewater treatment, which also explicitly focuses on nitrogen removal.
- In British Columbia, only 10% of the population is covered by this type of wastewater treatment and it is also the province with the largest nitrogen footprint of wastewater.
- Fossil fuel combustion accounts for 40% of the average nitrogen footprint in Canada, but the nitrogen footprint associated with fossil fuels varies considerably from province to province.
- Nitrogen emissions from transportation account for the majority of the nitrogen footprint of fossil fuels.
- Heavy-duty diesel vehicles, typically associated with trucking, mining, and other resource extraction activities, contribute significantly to transportation emissions.
- In Nova Scotia, Saskatchewan and Alberta, relatively high proportions of energy networks are powered by the combustion of coal. The 3 provinces have a combined average nitrogen energy footprint of almost 7 kg of nitrogen per person.
- In other provinces that rely on renewables and nuclear power, the average energy-related nitrogen footprint is around 1.5 kg per person.
(The three northern territories were excluded from the study due to limited data.)
About the study
“Provincial nitrogen footprints highlight variability in reactive nitrogen emission factors in Canada,” by Sibeal McCourt and Graham MacDonald, Environmental research letters.
The research was funded by McGill University’s Trottier Institute for Science and Public Policy (TISPP) and the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants Program.
About McGill University
Founded in Montreal, Quebec, in 1821, McGill University is the best medical doctoral university in Canada. McGill is consistently ranked among the top universities, both nationally and internationally. It is a world-renowned higher education institution with research activities spanning three campuses, 11 faculties, 13 vocational schools, 300 study programs and over 40,000 students, including over 10,200 graduate students. McGill attracts students from over 150 countries around the world, with its 12,800 international students representing 31% of the student body. More than half of McGill students report having a mother tongue other than English, including around 19% of our students who say French is their mother tongue.