Reservoirs are not as carbon neutral as we thought, according to new studies from the Washington State University. Hydropower is an underestimated cause of greenhouse gasses, producing around one gigaton of carbon dioxide per year.

Hydropower is not as clean as it appears now. Though much attention has been paid to their effects on fisheries and the natural flow of rivers, little attention has been focused on their carbon footprint. According to new studies, the reservoirs are responsible for 1.3% of all GHG emissions worldwide. Now it is to calculate how it will affect the hydropower-depending nations, especially those who are developing ones, in the following years to meet the Paris Agreement guidelines and other international climate policies.

Tygart Lake and Dam on the Tygart River near the town of Grafton in Taylor County, West Virginia, USA. The U.S. Army Corps of Engineers constructed the dam on the Tygart River for flood control on the river. The view is upriver to the south. Image Credit: Margaret Luzier, U.S. Army Corps of Engineers

“While reservoirs are often thought of as ‘green’ or carbon neutral sources of energy, a growing body of work has documented their role as greenhouse gas sources,” Bridget Deemer, WSU research associate and lead author, and their colleagues write.

Hydropower isn’t as clean as we thought

Hydropower is a way to produce energy derived from falling water or fast running of water. Since ancient times, it has been used as a renewable source of energy. In 1879, the first commercial hydropower plant was opened at the Niagara Falls. It has even been considered by institutions such as the World Bank as a mean to economic development that didn’t add an important amount of carbon to the atmosphere.

However, the most common type of hydroelectric power plants require dams on a river to store water in a reservoir, and it has been proven now that they do have a significant negative impact on societies since they can destroy river ecosystems and displace millions of people. Also, new studies show that they are having big, though little known, impact on global warming.

Therefore, Hydropower is not as carbon neutral as we believed it to be. They produce 1.3% of Greenhouse gas emissions which is more than Canada’s net greenhouse gas production. The study – which will be published next week in “Bioscience” – established that the reservoirs represent an important source of methane, which is a GHG which is 34 times more damaging that carbon dioxide, trapping 86 times more heat than CO2 over 20 years.

The methane in reservoirs is produced by microbes living in the water consuming organic matter. The amount of methane gas produced in these places can even be compared to the amount produced by biomass burning or rice paddies according to the statistics of the Intergovernmental Panel on Climate Change. This international institution is discussing whether or not including reservoirs greenhouse gas emissions in the 2019 IPCC update about how states report their GHG emissions. It is important to be aware that hydropower-derived emissions are not yet considered in these inventories.

“We had a sense that methane might be pretty important but we were surprised that it was as important as it was,” said Bridget Deemer. “It’s contributing right around 80 percent of the total global warming impact of all those gases from reservoirs. It’s a pretty important piece of the budget” She added.

She acknowledged that reservoirs, though they have a negative side, they do have a positive one since they stand as providers of important services such as electrical power, navigation, water distribution and flood control.

Why are reservoirs a climate problem?

The study takes into consideration data from the year 2000, and it has proven that each square meter of the surface of reservoirs produces 25% more methane that it was thought by scientists. It all occurs because unlike other water bodies; reservoirs tend to flood large amounts of organic matter which produce gasses such as CO2, methane, and nitrous oxide as the organic matter discompose.

“There’s been a growing sense in the literature that methane bubbles are a really important component of the total emissions from lake and reservoir ecosystems,” said Deemer.

Bioscience published in 2000 one of the first papers highlighting the concerning release of gasses from reservoirs, and ever since several studies have been taken on the subject.  Scientists explain that the impact of reservoirs on global warming is best calculated by knowing how biologically productive it is since those with more algae and nutrients systems are also the most contaminating.

The Washington State University study is the first to look at the flow of the three major GHGs, carbon dioxide, nitrous oxide, and methane, in reservoirs. It is part of the WSU Grand Challenges which is aimed to tackle important societal issues, especially regarding the challenge posed by resources and their sustainable use to supply present and future generations.

Although the recent discovery is raising concern about the viability and sustainability of hydroelectric power, there are currently at least 3700 large reservoir projects under considerations and construction for the upcoming years mainly in emerging economies, according to research published by Aquatic Science in 2015.

Source: Phys Org