Hydroelectricity is the only renewable that produces any meaningful amounts of energy on a global scale (about 16% of all electricity, compared to the paltry cumulative total from all other renewables of less than 3.5%). Oh the dilemma, hydropower turns out to release more methane than people realized. New research suggests dams are the main source of methane from rivers, and they could potentially lift global freshwater emissions by 7%.
There are 50,000 large dams around the world, but many, many more smaller ones.
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.
From the paper:
Sediment Trapping by Dams Creates Methane Emission Hot Spots
…
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%.
Life is so complicated if you are trying to save the planet. Still, someone’s got to do it.
The Bureaucrat’s burden… (like “The White Mans burden” all over again).
h/t Science Daily
REFERENCE
Andreas Maeck, Tonya DelSontro, Daniel F. McGinnis, Helmut Fischer, Sabine Flury, Mark Schmidt, Peer Fietzek, Andreas Lorke. Sediment Trapping by Dams Creates Methane Emission Hot Spots. Environmental Science & Technology, 2013; : 130715152553007 DOI: 10.1021/es4003907 [Abstract]