Mangroves mopping up greenhouse gases

Nitrous oxide is around 300 times more potent than the widely studied greenhouse gas, carbon dioxide.

The paper ‘Pristine mangroves are a sink of nitrous oxide’, published today in the Nature publication Scientific Reports, was authored by Southern Cross University researchers Dr Damien Maher, James Sippo, Dr Douglas Tait, Ceylena Holloway and Professor Isaac Santos.

“Most natural systems produce nitrous oxide, so the finding that mangroves might be consuming atmospheric nitrous oxide is intriguing,” said lead author Dr Damien Maher from the School of Environment, Science and Engineering.

“The greenhouse sink capacity of natural systems is a cheap and effective option for curbing climate change. Unfortunately we are losing critical mangrove habitats at an alarming rate, which means that the benefits they provide might not be with us for much longer.”

Postdoctoral researcher Dr Douglas Tait said the findings warranted further investigation.

“There may be unique microbial or plant chemical defences in mangroves systems that prevent the production and release of nitrous oxide,” said Dr Tait.

“Considering that nitrous oxide release from agriculture is a significant global problem, if we can understand why mangroves soak up nitrous oxide from the atmosphere we may be able to apply that to reduce the impact of agriculture on climate change.”

Professor Isaac Santos, based at the University’s National Marine Science Centre in Coffs Harbour, said the value of coastal communities extended far beyond acting as nurseries for juvenile marine life.

“Coastal communities like seagrasses, salt marshes and mangroves have been receiving a lot of attention lately because they store massive amounts of carbon,” said Professor Santos.

“We are starting to realise that mangroves also play a big role in other global cycles, including soaking up atmospheric nitrous oxide.

“The study adds to other recent studies published in the international journal Geophysical Research Letters that found that mangroves play a big role in coastal hydrology.”

The scientific team travelled the country – Darwin (NT), Hinchinbrook Island, Seventeen Seventy and Moreton Bay in Queensland, Newcastle (NSW) and Melbourne (Vic) - taking measurements.

“We used high-tech instrumentation to measure nitrous oxide concentration in the creeks of six mangrove systems in Australia, from the tropics in Darwin to the mangroves in the temperate zone around Melbourne,” said Ms Holloway, a recent Bachelor of Science (Honours) graduate.

“Initially we thought we would find that the mangroves would be producing nitrous oxide but we soon realised we were seeing something unusual,” said doctoral candidate James Sippo.

“We still have large gaps in our knowledge of how nitrous oxide is produced and consumed by natural systems.”

The study was funded by the Australian Research Council: DECRA (Discovery Early Career Researcher Award) DE150100581 (Maher); DECRA DE140101773 (Santos); and LIEF (Linkage Infrastructure, Equipment and Facilities) 14010083 (Santos and Maher).

The SCU researchers are also studying mangrove systems in Indonesia, India, Brazil and USA.

Photo: Sampling nitrous oxide in Moreton Bay, near Brisbane (credit: Damien Maher).