Dams like Muskrat Falls produce more greenhouse gas than expected: study

Some scientists are questioning whether energy produced by man-made dams is as green as previously believed.

• No thanks! Nunatsiavut rebuffs request to talk about mercury in Lake Melville

A study published recentlyin the monthly journalBioScience says carbon pollution from reservoirs like the one soon to be flooded at Muskrat Falls deserves more consideration.

Methane is biggest contributor

The research looked at a hundred pre-existing studies, that covered greenhouse emissions from different types of reservoirs.

"The rate of methane emission from these reservoirs was about 25% higher than what was previously thought," BridgetDeemer, the first author on the study, told CBC's Labrador Morning.

"That means acre-for-acre these systems are having a bigger impact on the global greenhouse gas budget than we previously thought."

The report found 79% of a dam's greenhouse effect was a result of methane. Carbon dioxide, at17 per cent, and nitrous oxide at 4 per centmake up remaining emissions.

Methane, which is formed primarily by rotting organic matter, has a short life in the atmosphere but has the stronger short-term warming effect of the three gasses.

'Working hypothesis' around clearing

While Muskrat Falls in particular wasn't studied, Deemer said she had a "working hypothesis" about how clearing vegetation prior to flooding would impact the amount of greenhouse gases emitted from the project.

We can't think of these systems as greenhouse neutral.- BridgetDeemer, study author

"I would think that [clearing] might reduce methane emissions," the aquatic biogeochemist and reservoir limnologist said.

"But it remains to be tested."

Emissions need to be calculated

Although hydroelectric projects generally have a better reputation than the oil and gas energy production industry, Deemer says emissions from all reservoirs should be calculated into the global carbon budget.

"We can't think of these systems as greenhouse neutral," she said.

"We need to be considering their emission when we're making management decisions either about building new reservoirs or how we're managing existing systems."