New research shows that mangrove forests that died along the coast of the Gulf of Carpentaria have been emitting methane eight times the normal level.
Scientists from Southern Cross University conducted the research amid the swathes of mangrove forests than died along a 1000 kilometre stretch of coastline north of Normanton.
The massive dieback was noted by James Cook Uni researchers in 2016 but had stabilised in 2017
The new SCU results published in a leading international journal New Phytologist, revealed that while living mangroves emit some methane, dead mangroves emit about eight times more of the potent greenhouse gas.
It is the first time methane emissions from mangrove tree-stems have been quantified and lead author and PhD candidate Luke Jeffrey said the findings were a surprise.
"Currently very little is known about the role of tree-stem methane emissions globally and quantifying these from mangrove tree-stems has never been attempted," Mr Jeffrey said.
"Due to the unique nature of the dieback event, we were able to compare methane tree-stem emissions from living and dead mangrove forests. This allowed us to understand what happens when climatic-change stressors result in forest mortality.
"What was concerning was that the dead mangrove forest emitted about eight times more methane than the living forest."
The findings have implications for scientific understanding of how mangrove systems sequester 'blue carbon', which is carbon dioxide absorbed from the atmosphere and locked up in coastal wetlands such as mangroves.
Mr Jeffrey said that as the climate changes into the future, we may see events like the catastrophic Gulf mangrove dieback becoming the norm.
"This has significant implications for greenhouse gas emissions from these valuable coastal habitats," he said.
Mr Jeffrey's PhD thesis with Southern Cross University is entitled "The drivers and dynamics of methane and carbon dioxide in disturbed coastal wetlands" and was funded by the Australian Research Council.
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