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Silt from Suburbs Threatens Cootes Paradise

October 25, 2007

Eric McGuinness
The Hamilton Spectator
(Oct 25, 2007)

Cootes Paradise will be filled in within 90 years, unless steps are taken to stop silt washing downstream from rapidly urbanizing areas of the west Mountain, Ancaster, Dundas and Waterdown.

That’s the forecast in a new Royal Botanical Gardens (RBG) report that says the marsh is filling at the rate of 17,000 tonnes a year.

Jennifer Bowman, restoration ecologist for the RBG, says the wetland, which serves as a fish nursery for the western end of Lake Ontario, will be filled in 90 years at the present rate of sedimentation. Her report on sediment accumulation from 1998 to 2005 shows the rate is down slightly from past years, but still high enough to threaten sensitive fish and wildlife habitat the RBG’s Project Paradise is trying to improve.

Bowman says the low lake level has been good for Cootes in recent months, because it’s allowed cattails and other aquatic plants to spread onto exposed mud flats that will flood in spring, when fish migrate in from the lake to spawn. But she worries about the continued infilling, saying, “The marsh supplies vital habitat for fish and wildlife of Lake Ontario and its loss would be devastating.”

Despite the filling, her study found some areas had deepened slightly, which she attributes to bottom sediment compacting now that a fishway at the outlet excludes carp that used to dig up the mud in their hunt for food. Peat beneath the sediment is also decomposing and shrinking.

But Bowman says people living upstream in the Spencer, Chedoke, Ancaster, Spring and Borer’s creek watersheds have to do more to combat erosion and runoff that carries sediment into Cootes.

“A lot of people don’t realize putting up new homes and other activities are impacting the marsh, but water from 14 creeks drains into Cootes Paradise. We’ve cleaned up our act a little bit, but there’s still a lot more sediment in the streams than is natural.”

The report says provincial guidelines for aquatic life call for no more than 25 milligrams of suspended sediment per litre of water, but Ancaster creek last year had a mean value of 135.31 mg/L and Spencer Creek, below the junction with Ancaster Creek, had a value of 84.85 mg/L.

emcguinness@thespec.com

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