A long-term plan to create wetland habitat on the Leslie Street Spit, also known as Tommy Thompson Park, hits a milestone this month, as contaminated materials on the site are capped by clean material that will provide a foundation for the plants and vegetation that provide home for a range of fish, birds and wildlife.
In 2007, a seven-hectare area called Cell 1 was completed and currently provides a habitat for marsh birds, including nesting common terns, turtles, amphibians, small mammals and native fish in areas that were used as confined disposal. Work on the area known as Cell 2, which is about nine hectares, started late last year. A layer of soil and clay is being created with about 21,500 truckloads of excavated material to make sure the underlying contaminated material is biologically unavailable. Rock and wood will also shape the landscape.
One of the project’s challenges is making sure the layers of soil have the right elevation relative to the water levels of Lake Ontario. “The vegetation that is within the wetlands is driven by water,” says Karen McDonald, project manager with Restoration and Infrastructure Services at
Toronto and Region Conservation Autority (TRCA). “Water levels within the Great Lakes are managed, and the management doesn’t necessarily facilitate the development of coastal wetlands. The lakes are managed for ships, not necessarily for habitat.”
While there is a detailed plan for how the wetlands should look, materials and site conditions will drive the work. Right now, dump trucks and bulldozers are the main tools for shaping the wetlands, with excavation continuing until things are frozen hard over the winter. In the spring, the living components of the wetlands will be added to the landscape.
“It’s basically gardening in water,” says McDonald. “We’ll be installing aquatic vegetation like potted plant material, native cattails, bulrushes and bur-reed into the completed area and then letting nature do the rest.”
One big surprise came in July when
workers discovered Asian grass carp, an invasive species that’s not particularly welcome in the wetlands, in one of the contained ponds.
The Leslie spit’s job as a disposal site isn’t yet over. The final cell, called Cell 3, continues to be used for dredged materials, with approximately 30 to 40 years of capacity remaining.
Writer: Paul Gallant
Source: Karen McDonald