What do the Crest Horticulture Program, the Ellis Pond neighborhood and the Mercer Island Right of Way and Storm Water manager have in common? They are all working to create a demonstration bioswale on Mercer Island.
But take note: a bioswale is not a large marine mammal.
Kahley Blankenship, a Mercer Island High School senior, who is enrolled in the Crest Horticulture Program, explains that “a bioswale is a natural system allowing water to flow so that impurities and chemicals are removed before the water flows into the lake.”
Rather than having a V-shaped ditch that allows water laden with pollutants to move quickly into the lake, ditches are re-shaped to have a wider bottom and are planted with native plants that filter the water into the soil. The water-soluble pesticides and road run-off, which contains motor oil and asbestos from brake linings, can easily flow into our watershed if they are not stopped. A bioswale provides a stopping place for this water, and plants’ roots direct this water to the bacteria in the soil, where carbon-based pollutants like motor oil can be broken down. Bioswales also reduce the amount of storm water that goes into the sanitary sewer system, thus reducing or preventing sanitary sewer discharge directly into bodies of water.
