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.
One way you could add to the bioremediation capabilities of such a garden would be to innoculate it with oyster mushroom spores. Apparently they are excellent at breaking down hydrocarbons into harmless substances and promoting the regeneration of habitat. I came across this info in the newsletter of a mycological society I used to belong to. If anyone is interested in the article, just drop me an E-mail and I'll send a copy.
For more info on "mycoremediation" online check out Paul Stamet's work at:
I would imagine, given a lively microbial community, a number of compunds could get broken down. For more info on that look for John Todd's Living Machines. Heavy metals would need to be accumulated and removed or transformed into a non-bioavailable form.
So the question is, how much of the removal is actually conversion into simpler compunds and how much is "filtering" and accumulation.
Good to see either way.
I would love to read the article. Your email link is not currently working. Can you either update the link or send the article to my address? Thanks!
I apologize, I see mine did not link either. My address is randy (at) citizenscholar (dot) com. Thank you!
The link seems to be working fine, Randy. Perhaps you might try again?
Interesting to note where this inspiring study (by Michael Dietz and John Clausen of the University of Connecticut) was published:
Feb. 15 issue of the American Chemical Society journal, Environmental Science and Technology
Science Daily has a bit more info than the BBC article:
including a link on how to design and construct your own rain garden:
If everyone reading this shared the link with a local gardener or landscape architect, that would be WorldChanging indeed!
And could we again go a little deeper in understanding the soil foodweb? The best ways to get the soil anywhere to come alive again is to add beneficial microbs and beneficial fungi carefully to the swales and the city gardens. The highest quality actively aerobic compost and compost teas are defined and directly read here:
Nose around in that area for awhile and see the scope of this work. A fine way to blop about....