Peat bogs harbour carbon time bomb
Peat bogs harbour carbon time bomb
(published by: NewScientist,07 July 2004)
The worlds peat bogsare haemorrhaging carbon dioxide into the atmosphere, accelerating globalwarming, warns a UK researcher.
And worse still, theprocess appears to be feeding off itself, as rising atmospheric levels of carbondioxide are triggering further releases from the bogs.
Billions of tonnes ofcarbon could pour into the air from peat bogs in the coming decades, says ChrisFreeman of the University of Wales at Bangor, UK. The worlds peatlandstores of carbon are emptying at an alarming rate, he says. Its avicious circle. The problem gets worse and worse, faster and faster.
Peat bogs are a vastnatural reservoir of organic carbon. By one estimate, the bogs of Europe,Siberia and North America hold the equivalent of 70 years of global industrialemissions. But concern is growing that such bogs are releasing ever more oftheir carbon into rivers in the form of dissolved organic carbon (DOC).
There seems to be anincrease of DOC in rivers of about 6 per cent a year at present, says FredWorrall of the University of Durham in the UK, who collates global data on DOClevels in rivers. Worrall suspects the rise in DOC began about 40 years ago.
Summer droughts
Bacteria in the riversrapidly convert DOC into carbon dioxide that bubbles into the atmosphere. Butspeculation has been rife about why the peat bogs are giving up their carbon inthe first place. In 2001, Freeman proposed that global warming was the cause (NewScientist print edition, 25 August 2001). But that hypothesis failed tostand up in field trials. A second suggestion, that increased river flows wereflushing more carbon out of the bogs, also failed.
So Freeman tested a thirdidea – that summer droughts cause more vegetable matter in bogs to decompose,freeing up more carbon that is released into the rivers. But that too failedwhen Freeman simulated drought conditions in a bog in central Wales, and foundthat this reduced the DOC in rivers, rather than increasing it.
The trials indicate thatthere may be another culprit altogether: the direct effects of carbon dioxide inthe atmosphere. Freeman grew plants on soil from peat bogs in igloo-like glassstructures, some containing normal air and others with a CO2-rich atmosphere.
He found that plants inthe CO2-rich atmosphere began to assimilate much larger amounts of CO2, which inturn was released into the soil moisture. There it can feed bacteria in thewater that break down the peaty soil itself, releasing stored carbon from thebog into the rivers.
Rate of acceleration
After three years, theproportion of DOC in the CO2-rich soil was 10 times that within the normal soil.And there was no sign of the increase tailing off. This shows that evenwithout global warming, rising CO2 can damage our environment, says Freeman.The peat bogs are going into solution.
Recent data from theCentre for Ecology and Hydrology in Lancaster, UK shows a 90 per cent increasein DOC levels in Welsh mountain rivers since 1988.
The rate ofacceleration suggests that we have disturbed something critical that controlsthe stability of the carbon cycle in our planet, Freeman says. On thesetrends, by the middle of the century, DOC emissions from peat bogs and riverscould be as big a source of CO2 to the atmosphere as burning fossil fuels.
Journal reference: Nature (vol 430 , p 195)