Hydropower is usually touted as clean energy, but a new study has found man-made reservoirs are producing far more greenhouse gases than previously believed, with most of those emissions in the form of methane, a potent climate-warming gas.
“We weren’t super-surprised at the magnitude of the emissions, but one thing we were surprised to see is the per area rate of methane emissions. They are 25 per cent higher than previously thought,” Washington State University researcher Bridget Deemer, lead author of the study, published Wednesday in the journal BioScience, told DeSmog Canada.
“(Methane emissions) contribute about 80 per cent of the total global warming impact of the gases from reservoirs.” The remaining emissions are carbon dioxide and nitrous oxide.
Methane is 34 times more potent than carbon dioxide and emissions have previously been difficult to measure, but new research is using tools such as bubble-tracking sonar to measure methane bubbles.
Researchers from the Washington State University along with colleagues from around the world looked at the results of more than 100 studies of emissions from 250 reservoirs around the world.
The startling results are leading to calls for reservoir emissions to be included in calculations made by countries and organizations such as the Intergovernmental Panel on Climate Change when gauging greenhouse gas emissions.
The emissions from reservoir water surfaces are comparable to those from rice paddies or biomass burning, both of which are incorporated in carbon budgeting, the study says.
The new information also points to the need for countries to look carefully at where they build dams.
The emissions, including carbon dioxide and nitrous oxide, come from decomposing plant material under the water and methane is produced by microbes devouring rotting material, such as algae, in sediment that builds up behind dams. The emissions are then boosted by nutrients that come from human activities such as agriculture or septic systems.
Natural lakes produce less greenhouse gases as there is not so much rotting material beneath the water and because reservoirs have more fluctuations in water levels than natural lakes — something which enhances methane production.
Ideally, to reduce emissions, dams should be built in areas with minimal vegetation and human activity as biologically productive reservoirs, with more algae and nutrient-rich systems, produce more methane, Deemer said.
More than one-million dams exist around the world and thousands of hydroelectric dams are in the planning or building stages, including the controversial Site C dam in B.C.’s Peace River Valley, which will create an 83-kilometre long reservoir in an agriculturally rich region of the province.
Deemer said Site C was not part of the study and she could not immediately estimate the emissions from a reservoir of that size.
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The study did not look at how emissions from reservoirs compared to power generated by natural gas or coal, but a 2013 study by Edgar G. Hertwich of the Norwegian University of Science and Technology found that carbon dioxide emissions from hydropower, per unit of electricity delivered, were 10 per cent higher than emissions from natural gas-fired plants.
One of the B.C. government’s major arguments in favour of construction of the $9-billion Site C dam is that it would provide clean energy to British Columbians for more than a century, but this latest study brings into question whether hydropower from reservoirs can be described as green.
The project will flood 5,500 hectares of prime agricultural land and, as former farmland and forests disappear beneath the water, the reservoir will meet all criteria, pinpointed in the research paper for producing large quantities of methane and other greenhouse gases.
Site C critic Ken Boon, who is being forced off his third-generation family farm by BC Hydro to allow for highway re-alignment away from the Site C flood zone, said the study provides some interesting revelations.
“Going through the environmental assessment process, BC Hydro really diminished the greenhouse gases that would result from Site C, so it really wasn’t a big issue going through the review hearings,” he said. A June 2016 report released by the University of British Columbia found the greenhouse gas impacts of the Site C dam eliminate any possibility of the project's advantage over alternative forms of power production like wind and solar.
“Now, again, the landscape changes and it’s one more strike against building large hydroelectric dams,” he said.
Boon hopes that Premier Christy Clark will take notice of the new information, but he is not optimistic.
“She seems to have a whole hypocritical, twisted view of climate change,” Boon said.
Helen Knott, a member of the Prophet River First Nation and active Site C opponent, pointed out that the provincial government’s reason in 2010 for exempting Site C from a B.C. Utilities Commission review was that it was a green project.
“Actually it is not a green project and this is just one more reason why it should not be built,” said Knott, pointing to myriad other problems with Site C such as questionable economics, opposition by First Nations and loss of agricultural land and food security.
“And now there is this. It’s just a project that doesn’t make sense,” Knott said.
BC Hydro and Environment Ministry spokespeople did not respond to questions about the study by time of publication.
Image: W.A.C. Bennett Dam. Photo: Carol Linnitt/DeSmog Canada