Sediment trapped behind dams makes them 'hot spots' for greenhouse gas emissions

Jul 31, 2013
Sediment trapped behind dams makes them 'hot spots' for greenhouse gas emissions

With the "green" reputation of large hydroelectric dams already in question, scientists are reporting that millions of smaller dams on rivers around the world make an important contribution to the greenhouse gases linked to global climate change. Their study, showing that more methane than previously believed bubbles out of the water behind small dams, appears in ACS' journal Environmental Science & Technology.

Andreas Maeck and colleagues point out that the large reservoirs of water behind the world's 50,000 large dams are a known source of methane. Like carbon dioxide, methane is one of the , which trap heat near Earth's surface and contribute to global warming. Methane, however, has a warming effect 25 times more powerful than carbon dioxide. The methane comes from organic matter in the sediments that accumulate behind dams. That knowledge led to questions about hydroelectric power's image as a green and nonpolluting energy source. Maeck's team decided to take a look at methane releases from the water impoundments behind smaller dams that store water less than 50 feet deep.

They describe analysis of methane release from water impounded behind six small dams on a European river. "Our results suggest that sedimentation-driven methane emissions from dammed river hot spot sites can potentially increase global freshwater emissions by up to 7 percent," said the report. It noted that such emissions are likely to increase due to a boom in dam construction fostered by the quest for new energy sources and water shortages.

Explore further: Climate rhetoric faces devil in the detail at Lima talks

More information: Sediment Trapping by Dams Creates Methane Emission Hot Spots, Environ. Sci. Technol., Article ASAP. DOI: 10.1021/es4003907

Abstract
Inland waters transport and transform substantial amounts of carbon and account for 18% of global methane emissions. Large reservoirs with higher areal methane release rates than natural waters contribute significantly to freshwater emissions. However, there are millions of small dams worldwide that receive and trap high loads of organic carbon and can therefore potentially emit significant amounts of methane to the atmosphere. We evaluated the effect of damming on methane emissions in a central European impounded river. Direct comparison of riverine and reservoir reaches, where sedimentation in the latter is increased due to trapping by dams, revealed that the reservoir reaches are the major source of methane emissions (0.23 mmol CH4 m–2 d–1 vs 19.7 mmol CH4 m–2 d–1, respectively) and that areal emission rates far exceed previous estimates for temperate reservoirs or rivers. We show that sediment accumulation correlates with methane production and subsequent ebullitive release rates and may therefore be an excellent proxy for estimating methane emissions from small reservoirs. Our results suggest that sedimentation-driven methane emissions from dammed river hot spot sites can potentially increase global freshwater emissions by up to 7%.

add to favorites email to friend print save as pdf

Related Stories

A new global warming culprit: Dam drawdowns

Aug 08, 2012

Washington State University researchers have documented an underappreciated suite of players in global warming: dams, the water reservoirs behind them, and surges of greenhouse gases as water levels go up and down.

Explainer: What is hydroelectricity?

Apr 18, 2013

Hydroelectricity is an established power-generation technology with over 100 years of commercial operation. Hydroelectricity is produced when moving water rotates a turbine shaft; this movement is converte ...

Geoscientist finds beavers play a role in climate change

Jul 18, 2013

Ellen Wohl, a geology professor at Colorado State University, has published a paper in the journal Geophysical Research Letters, describing the role beavers play in climate change. In a field study she un ...

New link could battle greenhouse gas emissions

Jul 30, 2013

The discovery of a new form of microbial life that can consume the potent greenhouse gas methane has earned University of Queensland (UQ) researchers a place in the prestigious journal Nature.

Breaking down the impact of greenhouse gases

Oct 23, 2012

It's called the global warming potential or GWP for short and it bundles together the importance of carbon dioxide, methane, and other greenhouse gases on future climate change.  Researchers from DOE's Pacific ...

Recommended for you

Gold rush an ecological disaster for Peruvian Amazon

20 hours ago

A lush expanse of Amazon rainforest known as the "Mother of God" is steadily being destroyed in Peru, with the jungle giving way to mercury-filled tailing ponds used to extract the gold hidden underground.

Australia out of step with new climate momentum

22 hours ago

Australian Prime Minister Tony Abbott, who rose to power in large part by opposing a tax on greenhouse gas emissions, is finding his country isolated like never before on climate change as the U.S., China ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Humpty
1 / 5 (6) Sep 16, 2013
Yeah yeah yeah - pissing into the wind.

What next? My smelly socks are a source of radio isotopes.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.