Capturing carbon
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In just the past decade, scientists have discovered that some of our underappreciated coastal habitats — called "blue carbon ecosystems" — play a huge role in tackling CO2 emissions.
But human activities such as burning fossil fuels and coastal development have already caused half of them to disappear.
"They're like the armpits of our coastline, but they are really important," said Deakin University marine ecologist Peter Macreadie.What is blue carbon?
This process is called carbon sequestration.
It was intense carbon sequestration by ancient forests and algae millions of years ago that helped create the very deposits of coal and oil we tap into for fossil fuels today.
Nearby on the ecology colour palette are the better-known green carbon systems of trees and forests. While important, they aren't nearly as efficient at storing carbon as their blue counterparts.
"We know that forests are pretty good at [carbon sequestration], but their carbon stores are bound to the lifetime of the trees, for only 100 or so years, and then it is released back into the atmosphere," Dr Macreadie said.
As well as being a temporary carbon store, trees can only soak up so much carbon before they become "saturated".
"These blue carbon ecosystems store carbon around 40 times faster than green carbon ecosystems," Dr Macreadie said."So you need a lot more green carbon habitat to do the same amount of carbon offsetting."
Conservation gets weird
Some ecologists are worried that these ecosystems don't receive the attention they deserve and are now being lost faster than we can conserve them.
Dr Macreadie estimated that about half of the world's blue carbon ecosystems have already disappeared, thanks to human activities.
Seagrass meadows have shrunk at a rate of 1 per cent every year since the start of the 20th century.
In 2016 there was extensive die-back of mangroves in the Gulf of Carpentaria, but it coincided with the mass coral bleaching on the Great Barrier Reef, which received more attention.
To spur people into action to protect these "ugly duckling" habitats, Dr Macreadie and his team are getting creative with tea bags.
Around the world, citizen scientists have been burying tea bags in the soil of blue carbon ecosystems to find out how well the area stores carbon.
Blue carbon researchers have had to come up with unexpected ways to entice citizen scientists to their cause. (Deakin University: Donna Squire)
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If, after a few months of being buried in mud, the tea leaves are still there, then that might be a good spot for locking away carbon.
But if you dig the tea bags back up and the tea leaves have gone, it means the carbon has decomposed — indicating that area's not capable of carbon storage.
The project is uncovering how carbon storage ability varies even within blue carbon ecosystems.
Ticking carbon bombs: sinks become sources
Coastal development is the major danger to blue carbon habitats, and is now raising the issue that stored carbon will be emitted as CO2 back into the atmosphere.
"The really big threat is that the damaged ecosystems will release their ancient carbon stores," Dr Macreadie said.
"That's where you get the really big numbers."An international team this week reported that a marine heatwave off Western Australia in 2010-11 that damaged seagrass meadows may have released of millions of tonnes of ancient carbon stores back into the atmosphere as CO2.
Oscar Serrano, a marine ecologist at Edith Cowan University involved in the research, said that the Shark Bay seagrass meadows accumulated around 144 million tonnes of carbon over the past 4,000 years.
It's a climate change double-whammy; losing carbon sequestration habitat while adding to our CO2 emissions at the same time.
However, scientists acknowledge that measuring CO2 emissions from blue carbon habitat loss is very challenging.
"We have to base our estimates on a number of assumptions, and the main uncertainty is the fate of the carbon stored in the system," Dr Serrano said.
"It's very hard to study mainly because of the time it takes for stored carbon to be converted back to CO2, and because it's such a complex system."
Dr Macreadie has been studying blue carbon ecosystems since the term was first coined around 9 years ago.
The field has grown exponentially since, but there's plenty more to discover about our coastal armpits, the benefits they provide and how to make sure they keep squirrelling away CO2.
"If we're going to keep burning fossil fuels, we need to find ways to pay for our carbon sins," he said.
"We need people to recognise the importance of these ecosystems and the weird things they do for us, and how they can form a sort of green infrastructure along our coasts."
Links
- Mangroves Protect Coastlines, Store Carbon – And Are Expanding With Climate Change
- 'They Died Of Thirst': Extreme Conditions Wipe Out Forest Over 1000 Kilometres
- 'Shocking images' reveal death of 10,000 hectares of mangroves across Northern Australia
- Can we manage coastal ecosystems to sequester more blue carbon?
- Shark Bay seagrass loss during ocean heatwave released up to 9m tonnes of CO2, scientists say
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