How coastland development 'blue carbon' contributes to climate change

This article appeared in The Age Newspaper on Sunday 28 June 2015 

Scientist Peter Macreadie says wetlands bury carbon faster than trees and keep it from escaping for much longer.Photo Simon O'Dwyer

John Elder 
Published: June 28, 2015 - 12:15AM

Coastal developers should be paying to offset air pollution – not from their bulldozers and or dredging barges, but from the tonnes of ancient carbon released into the atmosphere when wetlands are drained and dug up. 

This is the view of Dr Peter Macreadie, award-winning marine ecologist and Australian Research Council Fellow, who has just completed the first major survey of "blue carbon" stocks along 2000 kilometres of Victorian coastline.

Blue carbon is stored many metres deep in the sediment of vegetated coastal ecosystems such as mangrove forests, seagrass beds, and salt marshes. 

Dr Macreadie, who holds senior lecturing positions at Deakin University and Sydney's University of Technology cites the proposed $4 billion marina in Geelong and the vast dredging required to expand Hastings as a container port as projects where developers will not be held to account for large-scale carbon pollution.

"These developers stand to make a lot of money ... and yet they won't have to pay for the carbon released as invisible gas from the sediments being disturbed," he says. "Before those projects proceed, there needs to be a weighing up of the cost ... an understanding of what's being lost."

Unless governments act, by either preserving wetlands or re-establishing a carbon price, Victoria's environment will suffer "a death by a thousand cuts," he says. But the legislation designed to protect coastal ecosystems is vague. He says it does not take into account the recent discovery of the amount of carbon captured in wetlands.

When reminded that the political environment may not be friendly or responsive to his predictions, Dr Macreadie tells the story of the Sacramento delta, where a billion tonnes of carbon was released during a century of dredging, draining a development. "It was the equivalent to chopping down half the trees in California," he says.

That billion tonnes was accumulated over 5000 years. "And once it's released it's hard to get it back into the ground," he says. Independent reports suggest the drained soils of the delta continue to emit up to two million tonnes of carbon dioxide a year. 

Macreadie, who has researched the blue carbon question in Australia and abroad, says wetlands are able to bury carbon more than 40 times faster than trees, and keep the carbon from escaping for much longer. "Wetlands are able to sequester carbon for thousands of years, where a tree will breakdown and release its carbon after a couple of hundred years at most," he says. 

In the unruly climate change debate, the role of blue carbon as potential saviour and destroyer, is a relatively new phenomenon. Peter Macreadie, just one more scientist beating his head against the wall, reflects: "Offsetting the world's carbon emissions can sometimes feel like bailing water out of the sinking Titanic with a teacup, but when I look at the keeling curve [the graph that shows the rapid increase of emissions] and see it oscillating up and down due to photosynthesis – the earth 'breathing' – I realise that this whole biosequestration is so important.

"Indeed, it is the only known way of reducing concentrations of already-released carbon dioxide, and is now seen by the world as a necessary mechanism for keeping global warming under two degrees celsius as the world transitions to a low-carbon economy."

The next stage of Macreadie's research will look at how fast carbon is accumulating in our wetlands. The research, completed as part of scientist Carolyn Ewers' PhD project within Deakin's School of Life and Environmental Sciences, will be released as part of next week's Australian Marine Sciences Association Conference, hosted by Deakin at its Waterfront Geelong campus, beginning July 5.

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