Lakes with low oxygen levels release large amounts of methane

As temperatures rise, the bottom waters of lakes and reservoirs are becoming increasingly deprived of oxygen. Now, in a new study from Virginia Tech, experts have discovered that low oxygen levels lead to the production and emission of massive amounts of methane, which could accelerate global warming in a reinforcing feedback loop.

“We found that low oxygen levels increased methane concentrations by 15 to 800 times at the whole-ecosystem scale,” said study co-author Alexandria Hounshell. “Our work shows that low oxygen levels in the bottom waters of lakes and reservoirs will likely increase the global warming potential of these ecosystems by about an order of magnitude.”

To investigate the relationship between oxygen and methane concentrations, researchers conducted a three-year field experiment in two reservoirs outside of Roanoke. In collaboration with the Western Virginia Water Authority, the team operated an oxygenation system in Falling Creek Reservoir, which pumps oxygen into the bottom waters.

“Methane levels were much higher when there was no oxygen in the bottom waters of these reservoirs; whereas the carbon dioxide levels were the same, regardless of oxygen levels,” said study co-author Professor Cayelan Carey. “With low oxygen levels, our work shows that you’ll get higher production of methane, which leads to more global warming in the future.”

“We were able to do a substitution of space for time because we have these two reservoirs that we can manipulate and contrast with one another to see what the future may look like, as lower bottom water oxygen levels become more common. We can say with high certainty that we are going to see these lakes become bigger methane emitters as oxygen levels decrease.”

According to Hounshell, the strength of their results lie in the study’s expanse over multiple years. The researchers confirmed that low oxygen conditions lead to higher methane concentrations every year, regardless of the air temperature.

Previous studies have shown that carbon cycling is changing in terrestrial and marine ecosystems worldwide. However, the current study is one of just a few to address this phenomenon in lakes and reservoirs.

The research is published in the journal Limnology and Oceanography Letters.

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By Chrissy Sexton, Earth.com Staff Writer