Water reservoirs are favorite venues for tourism, but a new review reveals the dark side of these dams. According to the paper to be published in BioScience next week, water reservoirs actually produce a large amount of greenhouse gases.
Popular Science reports that man-made reservoirs are responsible for releasing one gigaton of greenhouse gas, particularly methane, per year. To put this into perspective, one gigaton of greenhouse gas is more or less equal to one-sixth of the total greenhouse gas emissions in the U.S. Also, the said amount is just below Brazil, the 7th biggest greenhouse gas emitter in the world.
To add to the problem, methane emitted from water reservoirs are in the form has a short yet big impact to the environment because the said gas has a short lifespan but strong warming effect.
The researchers came up to this conclusion by analyzing more than 200 studies regarding the effects and relationships of man-made reservoirs to greenhouse gas emissions.
Washington Post notes that there have been a significant decrease in carbon dioxide emissions, methane emissions is still causing a problem. Methane, which could be emitted from a variety of sources, accounts for 79 percent of emissions from reservoirs.
"Natural systems do produce methane, but studies have consistently found that reservoirs produce methane more rapidly than other systems do for a number of reasons," John Harrison, a co-author of the paper, told Popular Science.
Harrison further explained that the soil in reservoirs contain organic matter, which in turn, can be converted into methane and carbon dioxide. Also, because water reservoirs are designed to be connected to a water source such as a river, these manmade dams receive high amounts of organic matter and sediment; thus, the continuing production of methane.
One sign of methane production, according to Harrison, are the bubbles forming on the suface of water reservoirs. These bubbles form because methane is less soluble than other greenhouse gases.
"We synthesized all known estimates from reservoirs globally, for hydropower and other functions, like flood control and irrigation," said Bridget Deemer, the study’s first author and a researcher with Washington State University. “And we found that the estimates of methane emissions per area of reservoir are about 25 percent higher than previously thought, which we think is significant given the global boom in dam construction, which is currently underway."
The researchers says that methane emissions from reservoirs are expected to be on the rise with the current global boom in reservoir construction.
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