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From sink to source: seagrass disturbance releases ancient carbon

Posted October 22, 2015

An unusual event that took place in Australia 50 years ago has given UTS scientists, and their collaborators from CSIRO and ANSTO, rare insight into the fate of ancient carbon locked away in seagrass habitats when they are disturbed or destroyed.

The study provides new evidence that when seagrass ecosystems are disturbed the “blue carbon” that has been locked away in their sediments for thousands years disappears and may be released into the atmosphere with potential major global warming consequences.

Photo credit: Dr Peter Macreadie

Photo credit: Dr Peter Macreadie

Lead author, marine ecologist Dr Peter Macreadie from The Plant Functional Biology and Climate Change Cluster, said that the study site at Jervis Bay in NSW contained one of the oldest documented records of seagrass disturbance.

“The legacy of seismic testing for a proposed nuclear facility is 11 large circular holes that remain to this day as bare sand. There has been some recovery of seagrass from the surrounding meadow and this has given us a rare opportunity to compare the SOC stocks [soil organic carbon] from disturbed, partially disturbed and undisturbed seagrass habitat,” he says.

“The disturbed areas of seagrass had 72 per cent less organic carbon in the soil than the undisturbed controls which according to radiocarbon dating had taken hundreds to thousands of years to accumulate.”

While the results of the study, published in The Proceedings of the Royal Society B, highlight the slow recovery rates for disturbed seagrass habitats, they also provide promising evidence that restoring seagrass meadows can offset carbon emissions and help mitigate climate change impacts. The study also reveals significant differences in the microbial community associated with disturbed and undisturbed habitats.

Dr Macreadie noted that it was encouraging to show that in the areas where seagrass had started to regrow the carbon levels had been restored by around 50 per cent, showing that natural revegetation of seagrass can lead to the recovery of SOC stocks.

“However, we estimate that these circular bare patches will still be visible on google maps for some time. The process of recovery is slow and will go on well into this century.”

“We know that these blue carbon habitats are highly efficient at locking up carbon, 40 times more effective than terrestrial ecosystems such as rainforests. These results provide compelling evidence that if we want seagrass habitats to remain as carbon sinks, and not become carbon sources, then we need to protect them and help restore them if possible.”

Source: UTS

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