Mangroves could be playing a vital role in climate change mitigation by soaking up greenhouse gases from the atmosphere, according to Australian scientists.
Researchers from Southern Cross University measured the concentrations of nitrous oxide in the creeks of six mangrove systems from around the country and found that mangroves were soaking up the potent greenhouse gas and effectively curbing its effects on climate change. The study was published today in Scientific Reports.
“We went in with a hypothesis that these things would probably be releasing nitrous oxide into the atmosphere and contributing to that pool,” lead author and coastal biogeochemistry expert Dr Damien Maher told SBS Science.
“What we found was the opposite .. Most of the mangroves and creeks were soaking up the nitrous oxide from the atmosphere, which was quite an unexpected finding.”
Comparing the levels
Nitrous oxide (N2O) is naturally found in the atmosphere and regulates ozone levels, but human activity such as fertiliser run-off into waterways from farming and fossil fuel combustion has resulted in rise in its atmospheric concentrations.
Although N2O levels are lower than carbon dioxide, as a greenhouse gas it is around 300 times more potent and its increased presence contributes to depletion of the ozone layer.
Maher and his team set up monitoring equipment in creeks in Darwin, Hinchinbrook Island, Newcastle, Melbourne, and Seventeen Seventy and Moreton Bay in Queensland.
The data collected allowed the researchers to compare the concentration of N2O in the water to that in the atmosphere and determine what effect, if any, the mangroves had on it. The exact mexchanism that turns them into N2O sinks is yet yo be uncovered, though.
“We’re kind of unsure whether the microbes or possibly some chemical evolutionary defence mechanism in mangroves conserve the nitrogen, or a combination of the two,” says Maher.
Mangroves need protection
According to Dr Robert Haworth, an expert in the geography of mangrove ecosystems from the University of New England, the finding is significant because it challenges the assumption that mangroves pump out nitrous oxide like other water systems do.
“While it is generally accepted that freshwater wetlands, especially rice paddies, et cetera, pump out much dangerous greenhouse gas such as methane and nitrous oxide, it was assumed that saline wetlands did so also, but to a much lesser extent,” says Haworth.
“Their work suggests that under the right pristine conditions, mangroves can actually be sinks for these gases.”
Other natural systems, such as seagrass meadows, also play a crucial role in fighting climate change by storing carbon dioxide from the atmosphere as well as providing food and habitat for marine life.
Maher thinks the next step in the research will be to investigate the mechanisms responsible. He also stresses the importance of maintaining the health of these systems.
“[Mangroves] offer protections from storm surges, they’re very important nursery habitats and they also lock up massive amounts of carbon,” he says. “They’re very critical in the global carbon and oxygen budget.”