Sustainable cities, we're increasingly realizing, are cities alive with greenery. Designers are increasingly using artificial habitats with living plants to cool our roofs, reduce our energy consumption, make us more mindful of our water use, control erosion and help wildlife move through built-up areas. Now, it turns out, they can also cleanse the water running off our streets and parking lots.
A new study shows that rain gardens -- shallow swales and holes which catch run off and let it trickle slowly through soil and roots -- can filter most of the pollutants from stormwater:
"Most of the rain that falls on cities lands on impervious surfaces, such as roads, where it absorbs pollutants before it finally drains away.
[The study shows that] a shallow depression in a garden containing bark mulch and shrubs can remove up to 99% of toxins. ...
"The concept of rain gardens has been around for 10 or 15 years but there has not been a lot of research. A lot of places are hesitant to use something that has not been verified, so we felt it was an important step to bridge that gap..."
Of course, the question remains: what do we do with the pollution once we've filtered it. Adding to the rain gardens plants capable of bioremediation -- plants capable of sucking toxics from the soil and locking it in their stems and leaves (or even of breaking it down into less toxic substances -- might provide one solution. But even without further innovation, rain gardens make sense, as it's a heck of a lot easier to clean up pollution concentrated in one place than dispersed through rivers, lakes and seas.
via: spinneyhead
