Magazine article Science News

Legacy of Fire: The Soil Strikes Back

Magazine article Science News

Legacy of Fire: The Soil Strikes Back

Article excerpt

Legacy of fire: The soil strikes back

Slash-and-burn agriculture has been taking much heat from scientists concerned with the loss of tropical rain forests and with the accumulation of carbon dioxide in the atmosphere. But new studies of experimental forest fires in California are suggesting that widespread burning of vegetation may be even more dangerous to the environment than scientists had expected.

Researchers have long known that fire is a factory for chemicals. As biological material burns, the combustion process produces carbon dioxide, methane, nitric oxide, nitrous oxide and other chemicals that play important roles in the atmosphere. Now, evidence indicates that months after the flames are gone, the burned soil continues to emit high levels of nitric oxide (NO) and nitrous oxide (N2O).

"Nitrous oxide and nitric oxide are two of the most environmentally important gases in the atmosphere," says Joel S. Levine, an atmospheric chemist at NASA Langley in Hampton, Va. Nitrous oxide is a "greenhouse" gas that traps infraed radiation from the earth, leading to a global temperature increase. In the stratosphere, this gas also converts to a form that helps destroy ozone. Nitric oxide, on the other hand, contributes to acid precipitation.

According to Levine, microbes living in the burned soil produce these two gases. The soil is enriched in ammonium, created when heat breaks down protein in the burning vegetation. The bacteria convert the ammonium's nitrogen into N2O and NO.

These findings, which will appear in the April 20 JOURNAL OF GEOPHYSICAL RESEARCH, are based on studies of a 1986 chaparral fire in California (SN: 10/4/86, p. …

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