Floods play a role in releasing greenhouse gases from acid sulphate soil wetlands

Flood events dramatically increase the release of greenhouse gases from coastal floodplains into the atmosphere where the landscape’s hydrology has been modified by human activity, Southern Cross University scientists have found.

The study was the first research looking at the impact of flooding on carbon dioxide and methane in acid sulphate soil wetlands, which are widespread along the Australia coastline.

‘Carbon dioxide and methane emissions from an artificially drained coastal wetland during a flood: Implications for wetland global warming potential’, recently published in Journal of Geophysical Research, was co-authored by PhD student Jackie Gatland, Associate Professor Isaac Santos, Dr Damien Maher, Tahlia Duncan and Dr Dirk Erler.

“Natural wetlands store large amounts of carbon. However artificial drainage of wetlands modifies the carbon balance,” said Ms Gatland in the School of Environment, Science and Engineering.

“A flood event in February 2013 in Rocky Mouth Creek at Woodburn (south of Ballina on the NSW Far North Coast) stimulated huge losses of carbon from the wetland. Most of this carbon was lost in the form of carbon dioxide and, more importantly, methane, an extremely potent greenhouse gas.

“Drains, which are widespread throughout the catchment, accelerated water loss from the wetland into the creek which resulted in an overflow of decomposing vegetation and some of the highest carbon dioxide and methane levels ever observed in waterways.”

Dr Damien Maher from the University’s Centre for Coastal Biogeochemistry Research (CCBR), said the study had widespread implications on how much carbon wetlands could sequester.

“The intensity and frequency of floods is predicted to increase due to climate change, and our study shows that more floods will likely provide a positive feedback to global warming.

“The production of methane, a greenhouse gas much more powerful than carbon dioxide, makes wetlands punch above their weight in terms of greenhouse gas emissions.”

Associate Professor Isaac Santos, also from the CCBR, said modifying the hydrology of wetlands seemed to decrease their ability to retain carbon in the soil.

“Our study shows that restoring hydrological function of drained wetlands may be important not only from a water quality, but also from greenhouse gas and carbon accounting perspectives.”

Photo: Jackie Gatland taking water quality samples in the wetlands near Woodburn, NSW.