Southern Ontario’s wetlands are disappearing fast. 

About three-quarters of the wetlands once present in the region are now gone, either drained or filled in. Which is bad news because swamps and bogs are incredibly important: they naturally sequester carbon, mitigate floods, filter water and provide habitat for species at risk.

Now, a study done by researchers at the University of Waterloo has found that small wetlands — those under two hectares, or about the size of two sports fields —  are disappearing from the landscape at a disproportionate rate, and may be most likely to be lost on land used for urban development and resource extraction. 

These wee wetlands aren’t usually considered for Ontario’s “provincially significant” status, which would protect them from being developed, though they have an outsize benefit for the environment. Developers and governments often try to replace wetlands with stormwater management ponds but human-made substitutions don’t have the same benefit for ecosystems. 

“There’s quite a bit of literature that says small wetlands matter,” said the study’s lead author, Waverley Sunday Birch, who worked on it as a graduate student at Waterloo’s faculty of environment.

“But that’s perhaps not made it as far into policy systems yet.”

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The paper by Birch and her co-authors, Michael Drescher, Jeremy Pittman and Rebecca Rooney, was published in May in the Journal of Environmental Management. It zoomed in on seven Southern Ontario municipalities: Cambridge, Kitchener, London, Markham, Vaughan, Waterloo and Whitby. 

Using geospatial data from the province and municipalities, the researchers looked at both the loss of wetlands and the creation of stormwater management ƒhisponds from 2002 to 2010, the most recent year for which data was available. Birch and the team also used that data to project what wetland losses in Southern Ontario might look like up to 2026. They found that wetland loss is likely to continue and stormwater management ponds — artificial pits often lined with synthetic material, sometimes incorporating natural features like aquatic plants — are unlikely to perform the same functions for the environment.

The study recommends that policy protections be strengthened for wetlands of all sizes, especially for small ones. In Ontario, that might be tricky: the current government quietly abandoned a provincial wetland conservation strategy, took powers away from the watershed management agencies that often oversee wetlands and hasn’t shied away from approving projects that involve filling them in. 

The Narwhal caught up with Birch to talk about how stormwater ponds stack up to natural wetlands, and why small wetlands need extra protection in an era of climate crisis. 

How does Southern Ontario’s rate of wetland loss compare to other places?

The global average that we referenced was 54 to 57 per cent of wetlands lost. And for Ontario, the wetland extent has declined by more than 72 per cent since European settlement … so yeah, it’s greater than the global average that we referenced.

In many places in Southern Ontario, natural wetlands have been replaced with stormwater management ponds. What can wetlands do that stormwater ponds can’t, especially in an era of climate change?

So stormwater management ponds, they’re designed to control urban runoff, quantity and quality, but they’re not necessarily designed to provide habitat. They will sometimes have more naturalized features. But you’re not looking at a natural wetland habitat.

In our study region, where you’re expecting there to be more precipitation due to climate change, one can look at flooding. In somewhere like Southern Ontario, wetlands are going to serve a huge role with flooding mitigation. They’re going to protect human communities where there might be a storm event … there’s somewhere for that water to go versus, you know, ending up in your basement. 

An aerial view of a creek flowing into a pond, then draining into Lake Ontario in an area surrounded by houses.
An aerial view of Carruthers Creek as it enters Lake Ontario in Ajax, Ont. Urbanization along the creek has put Ajax at increased risk of flooding. Photo: Toronto and Region Conservation Authority

Somewhere like the prairies, you’re looking at wetlands actually helping with drought mitigation. In a drought year, wetlands are going to hold on to water that can become part of river base flow.

In southern Ontario, there are communities that are very reliant on groundwater. As we create more impervious surfaces, like paved roads and sidewalks and all that kind of stuff that water doesn’t infiltrate into as easily, wetlands are increasingly important in helping to maintain the [quantity of] water that’s going into the ground and into those aquifers that communities are drawing the water that drink, cook with, shower with. 

Another ecosystem service that we can look at is greenhouse gas storage. So wetlands can sequester and store greenhouse gasses like carbon, whereas stormwater ponds don’t really do that in the same way. 

We really need to look to connect with those ecosystems that we’re ultimately part of. We really aren’t able to recreate the ecosystem services that wetlands give us, the really clear example being the greenhouse gas storage piece. And those are ultimately a huge part of those nature-based climate solutions that help us with both mitigation and adaptation.

An aerial view of a river winding past Ontario wetlands and farmland
Wetlands along the Holland River east of Bradford West Gwillimbury, Ont. Natural wetlands can sequester and store carbon in a way that constructed stormwater ponds can’t. Photo: Christopher Katsarov Luna / The Narwhal

Your research looked at the rate of wetland loss in these seven communities, and the rate that stormwater management ponds were built to replace them. What did you find?

We saw that in that time period from 2002 to 2010, there was 95.5 hectares of wetland loss and 111.6 hectares of stormwater pond creation. We saw more stormwater pond creation than there was wetland loss. But [individual] stormwater ponds themselves were on average smaller in size than the average lost wetland. Which could show that we’re seeing somewhat of a reorganization of the landscape into aquatic features that are smaller and dispersed in a different way.

One of the major things that we found was that the majority of lost wetlands were smaller than two hectares. Those are typically not evaluated for provincial significance under the Ontario wetland evaluation system. Our work really shows that we have a problem there.

We know that development in southern Ontario isn’t slowing down. How should decision-makers be applying your findings to new projects?

Future development needs to avoid wetland impacts to the greatest degree possible, since the cumulative impacts of various forms of development on wetlands in southern Ontario has already been so great. 

Housing development outside of Milton, Ont.
A housing development outside of Milton, Ont., in Halton Region. In Southern Ontario, nearly three-quarters of the wetlands that once existed have been filled in or drained for urban development, agriculture and quarries. Photo: Christopher Katsarov Luna / The Narwhal

I think it’s fair to say also that beyond just avoiding loss, it will be really interesting to see the planning process move towards restoration that could help to tackle the biodiversity and climate pieces of this.

What would meaningful policy change look like?

Having greater, more consistent protections for small [wetland] features would be really important. In Ontario, a lot of that management goes to conservation authorities which have their own policies. Some of those policies work well, some may not. 

Since doing this research, I’ve continued working with wetlands as an ecologist and environmental planner. And I’ve been really lucky to do work directly for Indigenous nations, who have rights and relationships that have and continue to be impacted by the cumulative effects of various policies and development within Southern Ontario and elsewhere. And I’d really love to see us work towards co-created wetland policies that exemplify things that go beyond western values.

This interview has been edited for length and clarity. 

Like a kid in a candy store
When those boxes of heavily redacted documents start to pile in, reporters at The Narwhal waste no time in looking for kernels of news that matter the most. Just ask our Prairies reporter Drew Anderson, who gleefully scanned through freedom of information files like a kid in a candy store, leading to pretty damning revelations in Alberta. Long story short: the government wasn’t being forthright when it claimed its pause on new renewable energy projects wasn’t political. Just like that, our small team was again leading the charge on a pretty big story

In an oil-rich province like Alberta, that kind of reporting is crucial. But look at our investigative work on TC Energy’s Coastal GasLink pipeline to the west, or our Greenbelt reporting out in Ontario. They all highlight one thing: those with power over our shared natural world don’t want you to know how — or why — they call the shots. And we try to disrupt that.

Our journalism is powered by people just like you. We never take corporate ad dollars, or put this public-interest information behind a paywall. Will you join the pod of Narwhals that make a difference by helping us uncover some of the most important stories of our time?
Like a kid in a candy store
When those boxes of heavily redacted documents start to pile in, reporters at The Narwhal waste no time in looking for kernels of news that matter the most. Just ask our Prairies reporter Drew Anderson, who gleefully scanned through freedom of information files like a kid in a candy store, leading to pretty damning revelations in Alberta. Long story short: the government wasn’t being forthright when it claimed its pause on new renewable energy projects wasn’t political. Just like that, our small team was again leading the charge on a pretty big story

In an oil-rich province like Alberta, that kind of reporting is crucial. But look at our investigative work on TC Energy’s Coastal GasLink pipeline to the west, or our Greenbelt reporting out in Ontario. They all highlight one thing: those with power over our shared natural world don’t want you to know how — or why — they call the shots. And we try to disrupt that.

Our journalism is powered by people just like you. We never take corporate ad dollars, or put this public-interest information behind a paywall. Will you join the pod of Narwhals that make a difference by helping us uncover some of the most important stories of our time?

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