川震餘波蕩漾 溫室氣體大量釋出影響長久 - 地球科學討論

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China quake leaves CO2 legacy

March 2nd, 2009
Posted by: Peter Henderson
http://blogs.reuters.com/environment/2009/03/02/china-quake-leaves-co2-legacy/

Last year’s horrendous China earthquake may have big, lingering effects on
the atmosphere. Mudslides after the deadly May 12 quake in Sichuan province
are likely to trigger a release of carbon dioxide equal to 2 percent of the
world’s current carbon emissions from fossil fuel combustion, geophysicists
say.

“Mudslides wipe away plants and topsoil, depleting terrain of nutrients for
plant regrowth and burying swaths of vegetation. Buried vegetable matter
decomposes and releases carbon dioxide and other gases to the atmosphere,”
according to a statement ahead of a report in American Geophysical Union
journal Geophysical Research Letters.

The gases, along with nitrous oxide, another major greenhouse gas, should
spew into the atmosphere over a number of decades, according to the report
due out on March 4.


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Wenchuan earthquake mudslides emit greenhouse gas
http://www.agu.org/sci_soc/prrl/2009-07.html

AGU Release No. 09-07
2 March 2009

Mudslides that followed the 12 May 2008 Wenchuan, China earthquake, ranked by
the US Geological Survey as the 11th deadliest earthquake ever recorded, may
cause a carbon-dioxide release in upcoming decades equivalent to two percent
of current annual global carbon emissions from fossil fuel combustion, a new
study shows.

Mudslides wipe away plants and topsoil, depleting terrain of nutrients for
plant regrowth and burying swaths of vegetation. Buried vegetable matter
decomposes and releases carbon dioxide and other gases to the atmosphere.

The expected carbon dioxide release from the mudslides following the Wenchuan
earthquake is similar to that caused by Hurricane Katrina's plant damage,
report Diandong Ren, of the University of Texas at Austin, and his
colleagues, who used a computer model to predict the ecosystem impacts of the
mudslides.

What's more, the vegetation destruction will lead to a loss of nitrogen from
the quake-devastated region's ecosystem twice as large as the loss of that
nutrient from California ecosystems because of the October 2007 wildfires
there, Ren says. And, as the biomass buried by the China quake rots, 14
percent of the nitrogen will be spewed into the atmosphere as nitrous oxide,
a pollutant typically released from agricultural operations, automobiles, and
other sources.

The team will publish its findings on 4 March 2009 in Geophysical Research
Letters, a journal of the American Geophysical Union (AGU).

Although landscapes devastated by the Chinese earthquake may re-green soon,
the recovery will be cosmetic, says Ren. "From above, the area will look
green in a few years, because grass grows back quickly, but the soil
nutrients recover very slowly, and other kinds of plants won't grow," he says.

The magnitude-7.9 Wenchuan quake was followed by many aftershocks in the
Sichuan Basin, an area that, because of its geological features — deep
valleys enclosed by high mountains with steep slopes — is already prone to
landslides. May is also the rainy season in Sichuan, and the combination of
aftershocks and major precipitation events in the days following the
earthquake caused severe mudslides. The avalanches killed thousands,
destroyed roads and blocked rivers and access to relief, and shredded water
and power stations, among other facilities. To predict ecosystem impacts of
the mudslides, Ren and his collaborators applied a comprehensive computer
model of landslides that incorporates several physical parameters, such as
soil mechanics, root mechanical reinforcement (the root's grip of the dirt,
which mitigates erosion), and precipitation.

Ren's model also shows that the primary mudslides following the earthquake
removed large areas of nutrient-rich topsoil, leaving behind deep scars in
the land that will take decades to recover, preventing the re-growth of
vegetation.

The researchers write in their paper that, although being able to predict the
location and timing of a mudslide is essential to mitigate its impacts,
current mudslide models are not accurate enough.

"Previous approaches, which are mainly based on statistical approaches and
empirical measures, have no predictive ability of where mudslides are going
to happen," Ren says. His model, he claims, could be applied to forecast
under what circumstances a landslide would occur at a specific location. He
points out this would be particularly useful for places such as Southern
California, where global warming predictions call for an increase in the
frequency of these events.


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