Large hydroelectric dam reservoirs release large volumes of greenhouse gases due to organic matter, contributing to 1% global greenhouse gas emissions. An aerial view of the Hoover Dam, one of the largest in North America (image via Wikimedia Commons, free media repository)
I’ve been a critic of “green energy” in the past, since a lot of us don’t know all the downsides. For example, wind turbines depleting the earth of its natural energy or how have many other issues come alone with them – especially in urban areas. Now info on Hydroelectric dams impact comes to light.
It’s been suggested before that the reservoirs in large dams are a source of greenhouse gases and have some kind of environmental impact on Earth’s atmosphere. But until a team of collaborating scientists released their findings, how much of an impact was just conjecture.
Looking at data from 250 dams around the world, the scientists looked at surface area and greenhouse gas emissions from each site.
Turns out the news is not good. According to the team headed by Bridget Deemer, from the School of Environment in Vancouver, Washington, dams release 25% more methane and carbon dioxide than previously imagined. In total, the study concluded that hydroelectric dams around the world contribute a total of 1 billion tons of greenhouse gases annually, or 1.3% of all anthropogenic greenhouse gas emissions globally.
Why is that? Well, the large, deep lakes in reservoirs store a lot of organic material, like dead trees and leaves, carried to the dam by river. It sinks to the bottom of the reservoir and is decomposed by bacteria there, emitting gases in the process.
This isn’t the first study to talk about dams contributing to emissions. Other studies have looked at the location and size of the dam as producing the most gas. But the key finding of Deemer’s team is that the biggest predictor of how gas a dam will produce is how much chlorophyll is present in the water-i.e., how much plant matter was carried downstream. This means that dams full of sludge are highly polluting dams.
That the numbers are so much higher may come as a shock to renewable energy enthusiasts, who laud dams as being a relatively low-impact way to get electricity. But these findings likely won’t surprise environmental scientists who have studied the long term impacts of dams on ecosystems. Dams dramatically alter the ecology of freshwater systems, often making rivers uninhabitable to fish, salmon being one famous example.
If not the nail on the coffin lid of hydroelectric power, this study may at least inspire scientists to keep looking for alternatives.
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