Australian and US researchers have discovered that the “blue carbon” stored in coastal ecosystems by sea grasses, mangroves and salt marshes can make a comeback if environmental or human disruptions expose sediments to oxygen.
This activates long-dormant microbes, which release the carbon.
“We know blue carbon ecosystems are carbon sinks: that is, they store carbon. But we didn’t know what happened if the really old carbon was disturbed,” says lead researcher Peter Macreadie, from Australia’s Deakin University.
“We now have the data to demonstrate how unstable it really is.”
Macreadie and his team analysed blue carbon stores of around 5000 years old that had been retired from the carbon cycle and locked away by seagrass meadows.
“We exposed this carbon to oxygen, which is something that happens a lot in the coastal zone due to coastal development, such as through dredging or through the impact of climate change, including storms and rising temperatures,” he says.
“What happened really surprised us. We thought this ancient blue carbon would be indestructible, like eating rocks, but we discovered the oxygen woke up microbes that attacked the ancient carbon and turned it into the greenhouse gases that are responsible for climate change.
“This study tells us that although carbon sinks are a great asset for fighting climate change, they can also be a great liability.”
The findings, which are published in the journal Science of the Total Environment, have obvious implications for efforts to maximise the potential of blue carbon, including the international Blue Carbon Initiative.
“We now know the development of blue carbon ecosystems needs to factor in the risk of greenhouse gas emissions and the significant impact on the environment and look at ways to potentially off-set this through better environmental management,” says Macreadie.