Scientists Find New Climate ‘Feedback Loop’ in Lakes

Reeds in a lake near Sudbury, Ontario, in the Canadian Boreal Shield.

Reeds in a lake near Sudbury, Ontario, in the Canadian Boreal Shield. Andrew Tanentzap

Warming global temperatures have helped boost the growth of freshwater plants like cattails in the world’s lakes in recent decades. Now, scientists have found that this surge in aquatic plant growth could double the methane being emitted from lakes — already significant sources of methane — over the next 50 years.

The research, published in the journal Nature Communications, reveals a previously unknown climate feedback loop, where warming triggers the release of greenhouse gases, which in turn triggers more warming — similar to what is happening with Arctic’s melting permafrost. Freshwater lakes currently contribute as much as 16 percent of the world’s methane emissions, compared with just 1 percent from oceans.

Lakes produce methane when plant debris is buried in sediment and consumed by microbes. The scientists studied differences in methane production from biomass that originated in lakeside forests and from dead aquatic plants growing in the water. They found that forest-derived biomass helped to actually trap carbon in the lake sediment, reducing methane emissions. But aquatic plant biomass actually fueled methane production. Lake sediment full of decaying cattails produced over 400 times the amount of methane as sediment with plant debris from coniferous trees, and almost 2,800 times the methane from deciduous tree-filled sediment.

“The organic matter that runs into lakes from the forest trees acts as a latch that suppresses the production of methane within lake sediment,” Erik Emilson, an ecologist at Natural Resources Canada and lead author of the study, said in a statement. “Forests have long surrounded the millions of lakes in the northern hemisphere, but [they] are now under threat. At the same time, changing climates are providing favorable conditions for the growth and spread of aquatic plants such as cattails, and the organic matter from these plants promotes the release of even more methane from the freshwater ecosystems of the global north.”

Using models of the Boreal Shield, a lake-filled ecosystem that stretches across central and eastern Canada, Emilson and his colleagues calculated that the number of lakes colonized by just the common cattail (Typha latifolia) could double in the next 50 years — resulting in a 73 percent increase in lake-produced methane in that part of the world alone.