Hydroelectricity: large dams produce lots of greenhouse gases

Hydroelectricity: large dams produce a lot of greenhouse gases


Hydroelectric dams produce about 6% of greenhouse gases on the planet and continue to pollute more than 20 years after their construction, concludes a team of Quebec researchers.

“Methane is a devastating type of greenhouse gas. We expected to measure a certain amount of it emitted by the reservoirs [of the hydroelectric dams], but we were surprised by the importance of these emissions ”, confides to the Journal the biologist Yves Prairie, of the 'UQAM, which published this week in Nature Geosciences the result of a study that measures for the first time the methane emitted by large dams.  

The publication of the study is consistent with the announcement on Tuesday by the Premier of Quebec and leader of the Coalition Avenir Quebec, François Legault, who said he wanted to “build new dams in Quebec to have additional clean energy” if he were re-elected.

Hydropower is not flawless for the environment. In addition to the carbon footprint left by the construction of dikes, dams and roads, we have to deal with greenhouse gas emissions from flooded areas, says Professor Prairie, who has been studying greenhouse gases for 15 years. greenhouse emanating from dams.

Decomposing matter 

It is the decomposing organic matter in the soil which, under the action of bacteria , emits gases into the atmosphere when the reservoirs are filled and flood a vast territory to turn the turbines. 

The first 20 years are the most productive, therefore devastating; afterwards, the decomposition is slower and the emissions decrease.

Fortunately, the bacteria at the bottom of the water do not like the cold.

“In northern regions like ours, the effects are less powerful. It is that the action of the bacteria is reduced, as if we kept them in the refrigerator, ”explains Professor Prairie.

The researchers' data came from studies conducted since 1900 across the world. They studied 9,000 dams on five continents and developed a model for measuring methane. According to their conclusions, the peak of emissions of this gas from dams was reached in 1987. 

“The worst is behind us, but in recent years we have witnessed a new boom in projects, especially in Asia and South America. »

Wind power is greener 

The president of the Rivières Foundation, Alain Saladzius, was surprised by the Prime Minister's announcement Legault to revive dam projects. 

“We are opposed to the development of hydroelectricity, especially for large dams,” he says. 

To in his opinion, the additional energy needs of 10 terawatt hours can be met by wind power with less impact on the environment.

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