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Hydroelectric dam still a greenhouse gas source after 10 years

Hydroelectric power is often promoted as green energy, yet dams, especially in the tropics, can be significant sources of greenhouse gas emissions. When built, reservoirs trap vegetation, which, as it rots, emits both methane and carbon into the atmosphere. A new study in Science of the Total Environment found that a dam in Lao PDR remained a significant source of greenhouse gas emission even a decade after construction. According to the study, the Nam Leuk Reservoir emits between 1.2 and 3.2 gigagrams of carbon annually, an amount comparable to other dam reservoirs in the tropics.

Looking at another reservoir in Lao PDR, however, the study found that distance from construction likely makes a difference in greenhouse gas emissions. Built in 1971—four decades old, instead of onev—the Nam Ngum Reservoir is no longer a source of carbon in the atmosphere, but carbon a sink.

The study further notes that clearing vegetation prior to impounding a reservoir may make little difference in resulting carbon emissions, since vegetation around Nam Leuk was partially cleared and burned, yet the dam still emits significant greenhouse gases.

Currently there is a rush of dam building both in Southeast Asia and South America.

CITATION: Vincent Chanudet, Stéphane Descloux, Atle Harby, Håkon Sundt, Bjørn Henrik Hansen, Odd Brakstad, Dominique Serça, Frédéric Guerin. Gross CO2 and CH4 emissions from the Nam Ngum and Nam Leuk sub-tropical reservoirs in Lao PDR. Science of The Total Environment. Volume 409, Issue 24, 15 November 2011, Pages 5382-5391.

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