Radboud University ecologists carrying out a long-term freshwater experiment have discovered that a shift in the types of bacteria living in the water may be the reason that warmer lakes produce more greenhouse gas emissions. Lakes and rivers are the world’s largest natural source of methane emissions. Lakes are known to produce more emissions when they warm up and when levels of nutrients such as phosphorus and nitrogen increase, for example due to leaching from manure (called eutrophication). Scientists already suspected that the higher emissions are due to bacteria living in the waters, but until now little research has investigated the precise mechanisms behind this. Twenty years ago, Aarhus University in Denmark installed large water tanks on their campus to mimic the natural ecosystems of lakes. The researchers from Radboud University used these tanks to study the effect of warming and eutrophication on the methane-consuming and methane-producing bacteria in the tanks. Photo by Stefan Weideveld “We noticed a particularly interesting effect when the water warmed up: you would expect the entire bacterial population – both methane producers and consumers – to become more active,” says ecologist Tom Nijman. “But instead we saw that a different type of methane consumer prevailed in warmer tanks. This type grows more slowly and therefore also breaks down methane more slowly, which may explain the increased methane emissions.” The researchers can use this new insight to further improve ecosystem models of lakes, which will help to better predict how climate change will affect methane emissions from our waters. Photo: Linpaul Rodney via Unsplash.