Saturday, January 23, 2010

Urban green ain't so green

That little patch of grass in an urban Honolulu or Wailuku or Hilo setting, breathing out a little oxygen, it's a good thing, right?

Sure, for any number of reasons, but not because it helps improve air quality.

Actually the opposite is true.

It may cool the area, may be nice to sit on, and might even make you feel better, but a new piece of research suggests that it ain't doing anything for the atmosphere.

Indeed, it's a big negative—largely because of the amount of effort trimming and mowing with gas-powered appliances that pump greenhouse gas into the air, plus the use of fertilizer, which also releases greenhouse gases.

“Lawns look great — they're nice and green and healthy, and they're photosynthesizing a lot of organic carbon. But the carbon-storing benefits of lawns are counteracted by fuel consumption,” said Amy Townsend-Small, Earth system science postdoctoral researcher at University of California, Irvine.

She and co-researcher Claudia Czimczik conducted a study on the issue, which has been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union (AGU).

The scientists studied both ornamental picnic areas and actively managed athletic fields. They evaluated soil samples over time to determine how much carbon was being sequestered. They sampled the air above the grassy areas to determine emissions of nitrous oxide from fertilizer. And they calculated the carbon dioxide cost of these lawns from the groundskeeping procedures, from irrigation to mowing.

In general, all that active management releases four times more greenhouse gas than the lawns are capable of sequestering, they found.

“It's impossible for these lawns to be net greenhouse gas sinks because too much fuel is used to maintain them,” Townsend-Small said.

© Jan TenBruggencate 2010

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