Urban Water Systems: An Urban Metabolism Approach
Over 6 million people live in the Greater Toronto Area. Toronto is Canada’s largest city and its population is expected to double in the next 50 years. This rapid urban growth will reshape social, economic, and environmental aspects of our cities. One of these environmental impacts is changing nutrient cycles.
Humans have disrupted the Earth’s nutrient cycles by mining nutrients and then mismanaging them. These systems will continue to be under pressure as human populations rise. To manage nutrients more efficiently, we need to move towards a circular economy of recycling nutrients within local areas.
To do this, we need to know how our cities use nutrients. Where do a cities’ nutrients come from, and where do they go? This is called ‘the urban metabolism’ and it can help us find opportunities to reduce nutrient inefficiencies in our growing cities and their surrounding areas.
We have started tackling this issue by investigating the urban metabolism in the Greater Toronto Area (GTA).
Humans have disrupted the Earth’s nutrient cycles by mining nutrients and then mismanaging them. These systems will continue to be under pressure as human populations rise. To manage nutrients more efficiently, we need to move towards a circular economy of recycling nutrients within local areas.
To do this, we need to know how our cities use nutrients. Where do a cities’ nutrients come from, and where do they go? This is called ‘the urban metabolism’ and it can help us find opportunities to reduce nutrient inefficiencies in our growing cities and their surrounding areas.
We have started tackling this issue by investigating the urban metabolism in the Greater Toronto Area (GTA).
What we asked:
- Can we quantify the urban metabolism of the GTA? How are nitrogen (N) and phosphorus (P) processed in the urban, suburban, and rural parts of the GTA?
- What is the GTA‘s footprint on soil, streams and lakes, and the external landscape surrounding it?
- What are the opportunities for creating a more circular nutrient economy and reducing fluxes of nutrients to lakes and landfills in the GTA?
What we found:
- Humans require nutrients. Urban areas have a nutrient input 5 to 6 times higher than suburban areas, and double inputs in rural areas, when compared on a per hectare basis.
- Urban areas have distinctly different nutrient flows compared to surrounding rural areas. Sewer overflows, pet waste, and lawn fertilizers are significant components of the urban nutrient environment. We cannot ignore these unique nutrient inputs in urban areas.
- Wastewater treatment plants are essential to manage nutrient outflows in cities, even though their nutrient concentrations disposals can be high. We may see larger and more frequent bypasses of wastewater treatment plants in the future due to climate change. We need to use strategies like low impact development and composting to effectively regulate the flow of nutrients in urban areas.
- Change in a city’s metabolism is driven by people and their choices. Human behaviours, and how to change them, must be considered as we aim to move towards a circular nutrient economy.
- In the GTA, there is little interaction between urban and suburban areas and the surrounding rural areas in terms of nutrients. The GTA relies on fertilizer and food imports. Our research showed there are opportunities for optimizing nutrient use between rural and urban areas in Southern Ontario. If the Greater Toronto Area implemented composting, manure application, and biosolid reuse, we could eliminate the need for imported fertilizer.
Relevant Work
Melani-Ivy Samson (2019). The Urban Metabolism of the Greater Toronto Area: A Study of Nitrogen and Phosphorus Fluxes across the Urban, Suburban, and Rural Continuum. UWSpace. http://hdl.handle.net/10012/14658
Melani-Ivy Samson (2019). The Urban Metabolism of the Greater Toronto Area: A Study of Nitrogen and Phosphorus Fluxes across the Urban, Suburban, and Rural Continuum. UWSpace. http://hdl.handle.net/10012/14658