From: Alex Michael Bonnici (albonnici_at_vol.net.mt)
Date: Wed Sep 07 2005 - 20:10:45 UTC
Hello Gang,
This Just came in from one of the other mailing lists I belong
to.
Alex
http://www.nature.com/news/2005/050905/full/050905-8.html
Earthy bacteria faced with climate rap
Carbon loss from soil may speed global warming.
Jennifer Wild
Soil in Britain has lost an alarming amount of carbon over
the past 25 years: more than enough to cancel out the
country's reductions in carbon dioxide emissions.
The UK researchers who measured the loss claim its ultimate
cause is climate change, which could be increasing the
metabolism of soil bacteria so that they spit more carbon
into the air. If true, this could feed more greenhouse gas
into the atmosphere, causing more warming.
But others say the carbon change is due to changes in land
use and precipitation patterns, which may not be linked to
climate change.
Guy Kirk and colleagues at Cranfield University in
Bedfordshire measured soil samples from almost 6,000 sites
throughout England and Wales covering all types of land:
grassland, peat land, uplands, woodlands, croplands and
scrub. They measured the amount of organic carbon per gram
of soil from each site twice between 1978 and 2003.
The net loss of carbon across the country was 13 million
tonnes a year. That is roughly the amount by which Britain
has reduced its carbon emissions from the base level that
was set in 1990. It is only a small fraction of the 2,500
million tonnes of carbon thought to exist in the top 30
centimetres of British soil. But it is still a staggering
amount.
"This is alarming," says earth-systems analyst Tim Lenton
of the University of East Anglia in Norwich.
Ear to the ground
Losses occurred everywhere, irrespective of land use. This,
say the authors, points to climate change as the likely
culprit.
But the destination of the carbon is unclear. It may be
leaching into water systems and deeper soils as bicarbonate
and organic materials, or into the atmosphere as carbon
dioxide, say the researchers. Their study did not use any
tracers to determine where the carbon went.
It is crucial to understand the reason for the carbon loss,
says Annette Freibauer at CarboEurope, an umbrella research
group aiming to quantify carbon exchange between land and
air. Until we know why soil is losing carbon it is
difficult to know what conservation measures to implement.
Others argue that the study made certain assumptions that
might not hold water. The team measured only the top 15
centimetres of the soil, where the majority of carbon
changes occur, notes Lenton. But their extrapolation to the
top 30 centimetres may make the results misleading, he
says.
And the study did not keep a detailed history of land use
in each site, with data on the amount of fertilization or
whether animals grazed the land, for example.
Sexing up dirtxhe team says its next step will be to look
in detail at sites where land use has not changed, to pin
down whether climate change is to blame for the carbon loss
or not.
In the meantime, the researchers encourage policy-makers to
think about conversion of some areas of farmland to forest
as a means of stemming carbon loss from soils.
In the global warming debate, soil hasn't received enough
attention, says Kirk. Most of the attention has focused on
reducing fossil-fuel emissions, or studying whether the
oceans and forests have the capacity to suck up extra
carbon dioxide.
"People don't think soil is very sexy. They think it's
boring old dirt," says Kirk. The researchers hope their
study will change that focus.
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