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Residential canal estates enhance greenhouse gas emissions from estuaries


Sharlene King
14 October 2014
The construction of residential canal estates within estuarine floodplains can dramatically increase emission of carbon dioxide to the atmosphere, scientists from Southern Cross University have found.

Estuarine canal estate waters: Hotspots for CO2 outgassing driven by enhanced groundwater discharge?, recently published in the journal Marine Chemistry, was co-authored by Mr Paul Macklin, Dr Damien Maher and Associate Professor Isaac Santos.

“Natural estuarine floodplains are areas of intense carbon sequestration. They lock up significant amounts of carbon in soils,” said Paul Macklin, an Honours graduate from the School of Environment, Science and Engineering.

The team measured carbon dioxide concentrations along more than 300km of canal estates, natural estuarine and riverine areas on the Gold Coast. The Gold Coast has the largest estuarine residential canal system in the world.

Dr Damien Maher from the University’s Centre for Coastal Biogeochemistry Research said that the results provided convincing evidence that the construction of canals has led to the loss of some ‘blue carbon’ (that is, carbon locked out by coastal vegetation like mangroves, seagrasses and salt marshes).

“We found that canals were areas of intense carbon dioxide flux to the atmosphere. Although canals make up around 30 percent of the waterways area, they contributed to around 50 per cent of the carbon dioxide emissions to the atmosphere.

“This carbon dioxide is likely coming from the breakdown of carbon that has been buried and locked up in the soils over thousands of years, in what were previously extensive mangrove, saltmarsh, and floodplain wetlands,” Dr Maher said.

Associate Professor Isaac Santos, also from the Centre for Coastal Biogeochemistry Research, said that changes in hydrology seem to control the enhanced carbon dioxide emissions.

“Canals create a connection between groundwater and the atmosphere. This groundwater has extremely high carbon dioxide concentrations. Once it seeps into the rivers, estuaries and canals, the carbon dioxide moves from the water to the atmosphere.

“The carbon dioxide hotspots coincided with sites of higher groundwater seepage into the canals. This process essentially turns ‘blue carbon’ into atmospheric carbon dioxide,” said Professor Santos.

Mr Macklin said the results of the study revealed management options to minimise carbon release from canals.

“Not all canals behaved the same in terms of carbon dioxide emissions. Canals allowing for tidal flushing had lower emissions. This research not only identifies an overlooked environmental issue but should help inform management authorities on how to best manage canals to reduce emissions of carbon dioxide to the atmosphere.”

The research was funded by the Australian Academy of Science, through a WH Gladstones Fund grant and the Australian Research Council.

Photo: Paul Macklin and Dr Damien Maher measuring carbon dioxide emissions on the Gold Coast canals at Broadbeach.