The warming climates that promote the growth of aquatic plants have the potential to trigger a damaging feedback loop in natural ecosystems
- Andrew Tanentzap
A new study of chemical reactions that occur when organic matter decomposes in freshwater lakes has revealed that the debris from trees suppresses production of methane – while debris from plants found in reed beds actually promotes this harmful greenhouse gas.
As vegetation in and around bodies of water continues to change, with forest cover being lost while global warming causes wetland plants to thrive, the many lakes of the northern hemisphere – already a major source of methane – could almost double their emissions in the next fifty years.
The researchers say that the findings suggest the discovery of yet another “feedback loop” in which environmental disruption and climate change trigger the release of ever more greenhouse gas that further warms the planet, similar to the concerns over the methane released by fast-melting arctic permafrost.
“Methane is a greenhouse gas at least twenty-five times more potent than carbon dioxide. Freshwater ecosystems already contribute as much as 16% of the Earth’s natural methane emissions, compared to just 1% from all the world’s oceans,” said study senior author Dr Andrew Tanentzap, from the University of Cambridge’s Department of Plant Sciences.
“We believe we have discovered a new mechanism that has the potential to cause increasingly more greenhouse gases to be produced by freshwater lakes. The warming climates that promote the growth of aquatic plants have the potential to trigger a damaging feedback loop in natural ecosystems.”
The researchers point out that the current methane emissions of freshwater ecosystems alone offsets around a quarter of all the carbon soaked up by land plants and soil: the natural ‘carbon sink’ that drains and stores CO2 from the atmosphere.
Up to 77% of the methane emissions from an individual lake are the result of the organic matter shed primarily by plants that grow in or near the water. This matter gets buried in the sediment found toward the edge of lakes, where it is consumed by communities of microbes. Methane gets generated as a byproduct, which then bubbles up to the surface.
Working with colleagues from Canada and Germany, Tanentzap’s group found that the levels of methane produced in lakes varies enormously depending on the type of plants contributing their organic matter to the lake sediment. The study, funded by the UK’s Natural Environment Research Council, is published in the journal Nature Communications.
Image: Lake near Sudbury, Ontario, in the Canadian Boreal Shield, with aquatic plants in the foreground providing fuel for methane production.
Credit: Andrew Tanentzap
Reproduced courtesy of the University of Cambridge