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Canal Housing Releases Carbon Stored in Estuaries

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. “Natural estuarine floodplains are areas of intense carbon sequestration. They lock up significant amounts of carbon in soils,” said Paul Macklin, who was lead author of a paper published in the journal Marine Chemistry.

The team measured carbon dioxide concentrations along more than 300 km of canal estates, natural estuarine and riverine areas on the Gold Coast, which has the largest estuarine residential canal system in the world. Co-author Dr Damien Maher said that the results provided convincing evidence that the construction of canals has led to the loss of “blue carbon”sequestered by coastal vegetation like mangroves.

“Although canals make up around 30% of the waterways area, they contributed to around 50% 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,” Maher said.

Co-author A/Prof Isaac Santos 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,” Santos said.

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,” he said. “Canals allowing for tidal flushing had lower emissions.”