New research from James Cook University shows mangroves are doing a lot of the heavy lifting in storing carbon and their importance may increase as climate change impacts increase.
Dr Nathan Waltham from JCU's Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER) was part of the study that used a machine learning approach to get a better idea of how much 'soil organic carbon' (SOC) is stored in coastal wetlands in the Great Barrier Reef catchments.
"We found the mangroves, seagrasses and tidal marshes in the region store 137 million tonnes of carbon in their soils, or about 9-13 per cent of Australia's total SOC stock while encompassing only 4–6 per cent of the total extent of Australian coastal wetlands.
"Mangroves are responsible for nearly 80 per cent of this," said Dr Waltham.
He said although losses have decreased in the past decade due to increased awareness of the importance of coastal wetlands, an estimated 63 per cent have been lost globally since 1900.
"In Australia alone, more than 57,000 square kilometres of coastal wetlands have been lost since European settlement, mainly due to coastal development," said Dr Waltham.
He said one silver lining of the widely predicted increase in sea levels would be the expansion of mangrove forests and tidal marshes inland.
"This landward migration may be a main driver for the resilience of coastal wetlands to sea level rise, but if it's prevented, an estimated 30% of current wetlands could be lost by the year 2100.
"Alternatively, if landward migration is considered, this provides opportunities to expand wetlands and may provide a tangible economic benefit to Australia," said Dr Waltham.
He said restoration opportunities are most likely on agricultural and grazing land that is non-productive because it is low-lying and frequently waterlogged, and where the market price for carbon outweighs farming profitability.
"These projects have the potential to decrease greenhouse gas emissions, while protecting and enhancing mangrove conditions and are likely to be eligible for carbon credits under the Australian Emissions Reduction Fund scheme in the near future," said Dr Waltham.
Dr Micheli Duarte from Deakin University's Blue Carbon Lab was also involved in the project. She said landward migration of wetlands due to projected sea level rise on the GBR coast has the potential to produce an increase in carbon capture of between 160 and 460 thousand tonnes.
"While the results here outline a case that sizable carbon stocks remain in coastal sediments, restoration actions that build on the total current and future area of coastal wetlands are necessary and present a potentially valuable investment to guard against future climate change," said Dr Duarte.
"Restoring coastal wetlands is fast becoming an important and necessary action in protecting and conserving these wonderful ecosystems. They hold so many values to us; we need to scale up efforts to meaningful levels to maximise the returns," said Dr Waltham.
