Wetlands are an essential part of healthy urban ecosystems. Whether they are present year-round or flood and dry up seasonally, all wetlands help to prevent flooding and keep pollution out of rivers and lakes, all while providing essential habitat for wildlife.
Protecting and restoring wetlands promotes healthy communities and thriving nature, two of the focus areas of the Humber Arboretum's 2019-2024 Strategic Plan.
Wetlands play a unique and essential role in Ontario's ecosystem, and are increasingly rare in urban areas. What do wetlands do?
There are many microorganisms and plants which can't survive in drier forest, meadow, or park habitats but will thrive in the saturated soils of a wetland. This includes fully aquatic plants, semi-aquatic plants, and those which grow beside the wetlands. Having a wider variety of plants in an area means food and shelter for a wider variety of insects, birds, fishes, and other animals. A wide variety of life is key to ecological health, because all organisms have their own role to play.
In a natural water cycle, most of the rain that falls on land is absorbed by the soil and used by the plants, with only the excess slowly making its way to streams, rivers, and lakes. But in urban areas where most of the natural ground has been covered over by buildings and pavement, the rainwater can't be absorbed. Constructed drainage systems often funnel rainwater directly into streams, rivers, and lakes but that rainwater will carry with it all kinds of loose dirt and contaminants picked up from the urban environment, and will enter waterways untreated and with a heavy flow.
Wetlands act like sponges, absorbing large amounts of rainwater and meltwater. Loose soil and dirt picked up by the rain has a chance to settle to the bottom of the wetlands, while the plants soak up the available nutrients. The natural water treatment provided by wetlands helps keeps other waterways healthy.
By soaking up rainfall and meltwater, wetlands can also reduce the impact of these events on the surrounding land. The wetlands help prevent other areas from flooding and can prevent erosion by slowing down moving water.
When there is a lot of water in the environment, wetlands soak up and retain that water. But on hotter drier days, some of that water will slowly be released through evaporation from the water surface and transpiration from the leaves of the dense vegetation. Adding this moisture back into the air helps reduce the heat island effect of urban areas.
There are wetlands of various sizes and types spread around the Arboretum:
The oxbow is a natural, seasonal wetland found in the Arboretum forest. It is a u-shaped depression that used to be a meander of the West Humber River. The river slowly cut a new, more direct path for itself, and new banks were built up that cut the oxbow off from the river.
You can see the oxbow from the main forest trail, just off the wooden boardwalk that connects the forest and meadow. But what the oxbow looks like will depend on the time of year and the weather. During a hot summer the oxbow will look dry, but it will be lush and green with plants that are still able to draw moisture out of the soil. During transitional times of year, you may only see a centimeter or two of water, while during the spring there can be nearly a meter of water at the oxbow's deepest point.
From spring 2019 through fall 2020, the Humber Arboretum and its founding tri-partners worked together to restore a large pond beside Hwy 27, on the north side of the West Humber River. As part of that project, a new constructed wetland was also created beside the pond to help catch and treat more water runoff from the campus. With the support of Humber College and the City of Toronto, the Toronto and Region Conservation Authority led the construction and initial plantings and the partners will work together to continue to monitor and improve the wetland in the coming years.
Along with helping to protect water quality in the West Humber River, the new wetland also contributes to the health of both human and animal communities by creating new habitat for wildlife and new spaces for people to relax, recharge, and connect with nature.
Found on the south side of the West Humber River off the West Humber Trail, this large year-round restored wetland also helps protect the water quality of the river. It can absorb and help purify runoff coming from residential areas and parking lots near Woodbine Mall, and creates an extra buffer between the river and a portion of nearby Rexdale Blvd. The largest of the Humber Arboretum’s wetlands, it also provides a more secluded area for wildlife. It was the first wetland re-constructed at the Arboretum by the TRCA, and efforts by Humber Arboretum staff to control invasive plants in the area continue.
There are several wetlands spread throughout the Arboretum's shrubland-meadows. This includes two small seasonal wetlands near the bottom of the switchback trail behind the Centre for Urban Ecology, and larger wetlands near the sports fields and the Humberwood Community Centre.
Most of these are restored wetlands. The Toronto Region Conservation Authority used old maps and aerial photographs to identify areas of the Arboretum which were likely wetlands before being filled in so the area could be used as farmland. Over the years they have worked with Arboretum staff to restore those wetlands to their natural state. While the wetlands are back, restoration plantings and other activities continue, sometimes with the help of visiting school groups and the local community.