Study aims to reduce methane emissions from lakes

Methane is considered the second most important greenhouse gas, after carbon dioxide. Freshwater systems account for 49 percent of all methane emissions. As a result of global warming and eutrophication, methane emissions are increasing. 

Eutrophication is a buildup of nutrients in a body of water, often from runoff. The process leads to an overabundance of organic material and a lack of animal life due to oxygen depletion. Researchers at Radboud University wanted to know if reducing eutrophication in lakes could reduce overall methane emission. 

The experts tested 16 ponds. Some of the ponds were simply dredged, meaning that organic material was removed from the bottom of the lake. Others were treated with Phoslock (a phosphate-binding clay particle), and some were subjected to both methods. 

“Dredging sediment from the ponds’ bottom reduced methane emissions by approximately 52 percent,” said study co-author Tom Nijman. “In the ponds where we used Phoslock, emissions were even reduced by 74 percent.”

“Phoslock leads to less phosphate in water, which in turn reduces the number of floating plants. Invasive plant species such as Azolla (also known as water fern) grow less fast with Phoslock, resulting in less methane being produced in the water.”

“Dredging also allows us to remove organic material from the bottom, i.e. the carbon that produces methane. Our study shows that both methods reduce eutrophication in a lake, thereby also reducing emissions.”

Although this finding is encouraging, the researchers are cautiously optimistic. “These experiments first have to be repeated on a large scale. The first results are promising, but we want to measure the effect in more locations and over a longer period of time to see whether the positive effects lasts.”

Moreover, these techniques are costly and will not always be feasible. “An approach based on the use of Phoslock can easily be six to ten times more expensive than an approach that focuses on the environment surrounding the lake. This is not always possible in the Netherlands, think of lakes that are surrounded by trees or agricultural land, in some cases with little to no water flowing through,” explained Nijman.

“In such places you cannot simply overhaul the entire environment, in which case it might be useful to use dredging or Phoslock. But in places where the environment can be adjusted, the latter is always preferable. Prevention is still better than a cure.”

This study is published in Science of The Total Environment. 

—

By Erin Moody , Earth.com Staff Writer