(October 14, 2009) The operators of the Three Gorges dam may soon have to answer to criticisms over its environmental credentials, as a recent study in the Journal of Geophysical Research says the marshlands created during the draining of the dam’s reservoir may be major a emitter of greenhouse gas emissions.
Researchers found that during the summer months, when the dam is partially drained, much of vegetation that turns to marshland emits methane. The research comes after a pilot study performed by the scientists, where they studied an area of 37 square kilometres near the Pengxi River—a branch of the Yangtze River that turns to marshland when the reservoir is lowered. As part of their research they covered an area of the wetland with a plastic chamber in order to trap gas emissions.
Their results show that different species of plants emit a varying degree of methane. Plants in deep water emit more greenhouse gas emissions that those that live in shallow water. The researchers also found that plants emitting high levels of methane grow in soil with high levels of dissolved organic carbon.
According to the study, the researchers calculated that, on average, the marshland created from the Three Gorges reservoir along the Pengxi River emitted 6.7 milligrams of methane per square metre per hour. This figure is higher than the amount of methane emissions from dam reservoirs in the tropics such as Petit Saut reservoir in French Guiana or the Balbina and Samuel reservoirs in Brazil. Research from International Rivers says dams in tropical areas are believed to produce the highest level of methane emissions.
“Little attention has been paid to the drawdown regions, probably because they usually constitute a small part of the reservoir surface area,” said Huai Chen, an ecologist at Chongqing University in China, who was first author of the study.
The Three Gorges reservoir, however, has a particularly large drawdown area of 350 square kilometers—accounting for around one-third of the total flooded reservoir area when the dam is in full operation.
Huai says the amount of total methane released from the surface of Three Gorges reservoir has not been accurately measured. But, based on the assumption that methane emissions from the surface of Three Gorges are similar to those of tropical reservoirs, the marshlands could be contributing as much as a fifth of the amount of methane coming from the reservoir’s surface.
“This is an important study because it is the first careful look at greenhouse-gas emissions from a major Chinese dam,” says David Victor, an energy-policy expert at Stanford University in California who was quoted in Nature News.
Chen and his team of researchers are continuing their research to determine the total amount of methane emissions from the Three Gorges dam. They will also be looking into additional marshes at low-water levels and the amount of surface emissions.
But their research will not be complete as they have been denied access to the hydro station to study the amount of methane emissions from dam’s turbines, which some scientists believe could be the biggest emitter of them all.
For critics of the dam, the study adds one more reason to the long list of reasons the dam shouldn’t have been built in the first place.
“We applaud the research being done on the methane emissions from the raising and lowering of Three Gorges dam. It’s important to calculate the true costs and benefits of the Three Gorges dam and not just rely on fictional claims that the dam is a boon to China,”says Patricia Adams, Executive Director at Probe International. “The Chinese people deserve no less.”
The study is particularly important, as both the Chinese government and multilateral institutions, such as the World Bank, are praising hydro electric dams as a renewable, carbon-free source of energy. The World Bank recently released a report, saying it is actively pursuing hydro electric projects in developing nations around the world. And China has received more than 3-million carbon credits—worth over €36-million—for construction of over 50 dams—in order to reduce CO2 emissions. This new research throws that rationale, and one that will be front and center in the upcoming UN climate change conference in Copenhagen, into dispute.
Brady Yauch, Probe International, October 14, 2009
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