From sink to source: seagrass disturbance releases ancient carbon

Photo by Peter Macreadie

Photo by Peter Macreadie

In the 1960’s the Australian government bore massive holes into ancient seagrass beds in Jervis Bay, on the southeastern coast of Australia in the hope of identifying the most suitable location for a nuclear facility. The scheme was aborted by 1971, but the holes remained and have provided a group of researchers rare insight into the fate of the ancient carbon locked away in seagrass habitats when they are disturbed or destroyed. Known as blue carbon, these ancient seagrass soils are forty times more efficient at storing carbon than tropical forest soils and as such can play an important role in climate mitigation strategies. The team of researchers found that the disturbed seagrass soils had lost 70% of their carbon content, but those that had been re-colonized by seagrass were able to regain a large fraction of that loss in a few decades.

According to co-author Woods Hole Research Center scientist Jonathan Sanderman, “This study provides new evidence, that when seagrass ecosystems are disturbed, the organic 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.”

The results of the study, published in The Proceedings of the Royal Society, highlight the slow recovery rates for disturbed seagrass habitats, and provide promising evidence that restoring seagrass meadows can offset carbon emissions and help mitigate climate change impacts.

The lead author, marine ecologist Dr. Peter Macreadie, said that the study site at Jervis Bay, 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 soil organic carbon stocks from disturbed, partially disturbed and undisturbed seagrass habitat, he said. The disturbed areas of seagrass had 72% less organic carbon in the soil than the undisturbed controls which according to radiocarbon dating had taken hundreds to thousands of years to accumulate.”

Dr. Sanderman noted that it was encouraging to find that in the areas where seagrass had started to regrow the carbon levels had been restored by around 50% showing that natural revegetation of seagrass can lead to the recovery of carbon stocks. For him, “These results provide compelling evidence that protecting and restoring seagrass meadows can be an effective natural climate solution.”

Link to abstract: »

WHRC is an independent research institute where scientists investigate the causes and effects of climate change to identify and implement opportunities for conservation, restoration and economic development around the globe.