More Kudzu Blues: Now the Invasive Vine Is Increasing Air Pollution

By Andrew Moseman | May 18, 2010 9:48 am

KudzuKudzu: It’s worse than you thought. The invasive plant now covers more than 7 million acres in the United States, mostly in the Southeast but not limited to there. Besides overrunning trees as it spreads like wildfire, the vine also brings another danger: In a study in the Proceedings of the National Academy of Sciences, Jonathan Hickman sounds the alarm that kudzu could cause a spike in ozone, polluting the air.

Ozone, of course, is a good thing when it’s high in our atmosphere, blocking some of the sun’s harmful radiation. But down on the surface of the planet, ozone isn’t such a good thing. It can cause respiratory problems in people and harm plants’ ability to absorb carbon dioxide; it also is a major constituent of smog.

Kudzu’s contribution to ozone levels works like this: Like other members of the pea family, or legumes, Kudzu grabs nitrogen from the air and puts it into the soil. There microbes convert nitrogen into nitrous nitric oxide, one of the pollutants that also comes from automobile exhaust. That gas escapes from the soil and into the air, and undergoes reactions that lead to the creation of ozone [Discovery News].

When this reaction happens on a small scale it’s not a big problem. However, there’s getting to be so much kudzu in the U.S. that Hickman decided to measure what its ozone contribution might be. So his team studied the soil of Madison County, Georgia, picking some areas where kuzdu had invaded and some where it had not. In the kudzu-ed areas, he says, nitric oxide emissions were double that of the kudzu-free areas.

To drive home the point, Hickman and his colleagues ran a simulation in which kudzu spread over the entirety of its region except for soils in the city or those used in agriculture. Crunching those numbers, the team estimated a dramatic increase—35 percent—in the number of days that would register an atmospheric ozone level in excess of the safe limit set by the Environmental Protection Agency.

That’s a pretty extreme scenario; kudzu alone isn’t going to drive up ozone pollution by a third. Even with kudzu stretching out ever further, its present contribution to ozone is most likely a minor one, Hickman says, but the ozone potential is one more reason to loathe the vine.

He acknowledged that any soil used to grow nitrogen-fixing plants or were fertilised for agricultural reasons would result in an increase in gases involved in the formation of ozone. “But in those cases, we are doing these things for necessary reasons — namely food production,” he observed. “In the case of Kudzu, it is an undesirable plant that is spreading over a large area in the south-east US” [BBC News].

It’s also an undesirable plant that people brought to America on purpose, making it not just a poster child for invasive species, but also for importing a foreign organism to try to fix some other problem in an ecosystem.

Kudzu (Pueraria montana) is a rapidly growing vine native to Asia that was introduced to the United States in 1876 at the Centennial Exposition in Philadelphia as an ornamental plant and later promoted to farmers in the Southeast as a means of controlling soil erosion by the U.S. Soil Conservation Service during the 1930s [LiveScience].

Related Content:
DISCOVER: The Truth About Invasive Species
DISCOVER: Humans vs. Animals: Our Fiercest Battles With Invasive Species (photo gallery)
80beats: Should Humans Relocate Animals Threatened by Global Warming?
80beats: Globalized Pollution: Asian Smog Floats to American Skies
80beats: Today’s Biggest Threat to the Ozone Layer: Laughing Gas

Image: flickr / SoftCore Studios

CATEGORIZED UNDER: Environment, Living World
  • Flange

    It also adds nitrogen back to the soil.
    We might have been grateful for that, under other circumstances.
    Now, time to go grab a big balloon and a circus tent… Oooohohohohoho Yeeeeahahhahahah

  • Ian

    At least we’ve stopped soil erosion…

  • Marc

    This post (and the Discovery News item that it cites) contains a very significant technical error: it mistakenly substitutes NITROUS oxide (N2O) for NITRIC oxide (NO). The abstract in the PNAS article clearly states that the gas in question is nitric oxide: “Its spread has the potential to raise ozone levels in the region by increasing nitric oxide (NO) emissions from soils as a consequence of increasing nitrogen (N) inputs and cycling in soils. ” and “Nitric oxide emissions from invaded soils were more than 100% higher…”

    Some nitrous oxide is emitted from soil after nitrogen is added to the soil, either naturally via fixation or artificially via fertilizer. But the issue in question here is emission of nitric oxide, which is precursor of urban smog and health hazards in its own right. In the lower atmosphere, nitric oxide goes through a complex set of reactions with sunlight and other pollutants to form ozone and the other harmful gases that are normally called “urban smog”.

    Nitrous oxide (N2O) is relatively harmless to humans and has little smog forming potential. However, despite its locally benign nature, nitrous oxide is several hundred times more effective than carbon dioxide at keeping heat within the atmosphere, and is thus a greenhouse gas of concern.

    Unfortunately, this mix-up is fairly common. I have seen it in the New York Times, the New Yorker (twice in the last few years), and many other newspapers and magazines.

  • http://blogs.discovermagazine.com/80beats/ Eliza Strickland

    Thanks for bringing your expertise to the table, Marc. I’ll correct the error.

    — Eliza, DISCOVER online news editor

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    thanks for pointing that out marc. that should teach people not to believe everything thats on the internet.

  • http://www.preferreddoorservice.com Amarr Houston

    Thanks for bringing your expertise to the table, Marc.

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