March of the mangroves good news for blue carbon storage

December 15, 2015
Credit: Jeffrey Kelleway

The carbon capture and storage capacity of wetland vegetation, known as blue carbon, makes coastal habitats some of the most carbon rich ecosystems on the planet. A new study, published in Global Change Biology by Australian environmental scientists investigating the impact of shifts in coastal vegetation over a 70 year period, provides unique insight into how blue carbon stocks change in these dynamic and vulnerable environments.

The study supports Australia's aim to become one of the first countries to include blue carbon in its national emissions inventory.

Using historical aerial photos, together with field surveys and sediment core analyses, the research team tracked the continuous encroachment of mangrove forest into two NSW saltmarshes over a 70 year period. The researchers estimated that over the past 70 years, the expansion of mangroves into salt marsh habitat may have increased blue carbon storage by as much as half a million tonnes in NSW alone. This represents an important natural feedback against climate change and quantifies for the first time changes in carbon storage associated with widespread environmental change in these habitats.

"We now know that seagrass, mangroves and salt marsh habitats are more efficient at locking away carbon than rainforests.  This 'blue carbon' resource is finally gaining recognition in carbon accounting efforts so it's very important to be able to quantify the changes that are taking place in a changing climate," says Jeffrey Kelleway, lead author of the study and a PhD candidate in the UTS Plant Functional Biology and Climate Change Cluster (C3).

Kelleway explained that the migration of mangrove forests into treeless saltmarsh ecosystems is a worldwide phenomenon that is expected to continue as sea levels and global temperatures rise.

"Our study tested whether this mangrove expansion into salt marsh habitat altered the long-term capacity of coastal ecosystems. Attempts to quantify this type of change have been inconclusive so far because studies have only taken place in parts of the world where mangrove expansion has only become apparent in the past 30 years or so," Kelleway says. "Here in Australia we have a record in the aerial photos which shows mangroves have been expanding into salt marshes for at least the past 70 years."

Kelleway  says the findings will offer insights relevant for other regions because changing climate is likely to shift mangrove encroachment from 'short-term pulses' towards longer term ecosystem change.

"In the southern states of the US for example, there are vast areas of salt marsh where mangroves are now expanding because of changes in winter climate. Historically cold winter snaps have kept the mangroves in check, but they now haven't seen decent frosts in those areas since the 1980s, which is allowing the mangroves to survive and compete with salt marshes."

In NSW, sea-level rise is considered a key factor in the migration of mangroves upslope into the higher elevation salt marshes. The researchers also found evidence to suggest that mangroves may be able to "build" the elevation of the wetland surface.

"Through the growth of their dense root networks, which itself is rich in carbon, mangroves expanding into may also be able to survive rising sea levels and continue to capture carbon into the future," Kelleway says.

Future directions for ongoing research include the characterisation of the extra carbon being stored as mangroves expand.

"We want to know how much of it is carbon captured by the themselves through photosynthesis and how much of it is washed in from the catchments and trapped by the mangrove roots."

Explore further: Rising seas will drown mangrove forests

More information: Seventy years of continuous encroachment substantially increases "blue carbon" capacity as mangroves replace intertidal salt marshes. Global Change Biology (2015), DOI: 10.1111/gcb.13158

Related Stories

Rising seas will drown mangrove forests

October 14, 2015

Mangrove forests around the Indo-Pacific region could be submerged by 2070, international research published today says.Even with relatively low sea-level rises, many mangrove forests had a poor outlook said Professor Catherine ...

Protected areas save mangroves, reduce carbon emissions

September 14, 2015

Protected areas not only keep significant swaths of Indonesia's shrinking mangrove habitats intact, but also prevent emissions of carbon dioxide that would have been released had these mangroves been cleared, according to ...

Mangroves help protect against sea level rise

July 23, 2015

Mangrove forests could play a crucial role in protecting coastal areas from sea level rise caused by climate change, according to new research involving the University of Southampton.

Human activity pulling the plug on a vital carbon sink

November 16, 2011

( -- Under better conditions coastal ecosystems might be the ace in the hole to mitigate climate change, but human activity is significantly weakening their ability to naturally dampen the impacts of rising CO2 ...

Salt marsh carbon may play role in slowing climate warming

September 26, 2012

A warming climate and rising seas will enable salt marshes to more rapidly capture and remove carbon dioxide from the atmosphere, possibly playing a role in slowing the rate of climate change, according to a new study led ...

Recommended for you

Cool roofs have water saving benefits too

October 20, 2017

The energy and climate benefits of cool roofs have been well established: By reflecting rather than absorbing the sun's energy, light-colored roofs keep buildings, cities, and even the entire planet cooler. Now a new study ...

Carbon coating gives biochar its garden-greening power

October 20, 2017

For more than 100 years, biochar, a carbon-rich, charcoal-like substance made from oxygen-deprived plant or other organic matter, has both delighted and puzzled scientists. As a soil additive, biochar can store carbon and ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.