Fest of Birds kicks off with city rain garden planting
Once upon a time, stormwater runoff really wasn't a problem in northwestern Minnesota.
In sparsely populated areas, precipitation was naturally absorbed into the loose, un-compacted soil, which contained microbes and plant systems that filtered out pollutants before the water moved down into the water table below.
But as communities such as Detroit Lakes became increasingly urbanized, the amount of impervious (i.e., impenetrable to moisture) surfaces also increased dramatically.
As Urban Conservation Specialist Gregg Thompson explained Thursday at a Festival of Birds workshop in Detroit Lakes, the existing soil also became increasingly compacted by traffic, rendering it unable to absorb water as efficiently, if at all. Plants and grasses above the compacted soil also could not absorb water down below, because the roots could not penetrate the hard barrier, he added.
"With compacted soils (underneath), turf grass needs to be kept on 'life support' (i.e., irrigated) to survive," Thompson noted.
With fewer surface areas where water from rainstorms could be naturally absorbed into the soil, more and more water -- contaminated by oil, pesticides, sedimentation, etc. -- was running off these impervious surfaces and directly into storm drains, where it flowed, unfiltered, into local lakes, streams and rivers.
For instance, Thompson explained, "A 1,500 square foot house produces 925 gallons of runoff in a one-inch rain." And that's not even including the driveway and garage.
Besides rendering the water itself undrinkable, the unfiltered runoff also introduces contaminants such as phosphorus and other nitrates into area water bodies.
But nutrients are a good thing, right? Not always. Phosphorus, for instance, causes algae blooms that can overtake a lake's natural ecosystem.
"One pound of phosphorus equals 500 pounds of algae," Thompson said.
So how can stormwater runoff be contained and filtered before being released back into lakes and streams?
One increasingly popular method is by constructing rain gardens -- shallow depressions filled with loose soils and mulch, where native plants and prairie grasses are planted to act as a natural filtration system.
These rain gardens are placed at locations where they can capture the natural flow of stormwater runoff.
Much of this information was familiar to those who had attended a workshop given by Thompson early last year. But the 20 or so people who attended last Thursday's workshop were also given an additional, "hands-on" opportunity to experience planting a rain garden for themselves.
Working with Thompson and local master gardeners, the participants planted native grasses and plants inside the new Detroit Lakes City Park rain garden.
Taking advantage of one of the few warm spring days area residents have enjoyed this month, they worked throughout the afternoon.