2018 - Mangrove methane needs to be accounted for in global carbon budgets

Words: Sharlene King
Published: 14 June 2018

Mangroves are highly valued for their efficiency in storing the greenhouse gas carbon dioxide. But those calculations need to be adjusted to account for the methane emitted during the carbon burial process, according to new research from Southern Cross University.

Organic material within the mangrove system releases methane as it breaks down. However scientists from the University’s Centre for Coastal Biogeochemistry Research have found the methane being released is offsetting on average 20 per cent of the carbon dioxide removed from the atmosphere and buried as blue carbon.

The paper Methane emissions partially offset ‘blue carbon’ burial in mangroves, published today in the highly prestigious journal Science Advances, provides the first estimate of the global magnitude of this offset.

“Our results show that high water and sediment methane emissions have the potential to partially offset ‘blue carbon’ burial rates in mangrove sediments on average by 20 per cent,” said lead researcher Dr Judith Rosentreter.

“The offsets may be as high as 60 per cent around the boundary between the tropics and subtropics, driven by lower mangrove carbon burial rates and higher methane emissions.

“Although there are some uncertainties associated with global emission estimates of methane - mainly due to the lack of data from countries with large mangrove areas such as Indonesia or Brazil - the overall conclusion that there are some offsets remains the same.”

Professor Bradley Eyre, Director of the Centre for Coastal Biogeochemistry Research at Southern Cross, is one of the co-authors.

“Methane emissions from mangroves need to be accounted for when assessing their importance in in future ‘blue carbon’ assessments and climate change mitigation,” said Professor Eyre.

As well as offering valuable ecosystem services to the coastal zone and its inhabitants, coastal vegetated ecosystems have been highlighted as efficient natural carbon stores. The term ‘blue carbon’ was coined to describe the carbon sequestered in sediments of mangroves, seagrasses and salt marshes and considered as a long-term storage of atmospheric carbon dioxide.

Yet mangrove and other coastal wetlands are threatened ecosystems needing protection and conservation.

Climate change is driven primarily by increased carbon dioxide concentrations in the atmosphere (due to burning of fossil fuel). Climate change mitigation strategies include emission reduction and preserving and enhancing natural carbon stores.

Science Advances journal

‘CH4 emissions partially offset ‘blue carbon’ burial in mangroves’ by Rosentreter, J. A., D. T. Maher, D. V. Erler, R. Murray, and B. D. Eyre. https://www.science.org/doi/10.1126/sciadv.aao4985