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800 Million Tons of Blue Carbon Lie Buried in U.S. Tidal Wetlands

22 Jun 2018

Prof Benjamin Horton   Dr Tim Shaw

Wetlands are one of humanity’s best defences against climate change. Besides shielding cities from extreme weather like hurricanes, wetlands can also store massive amounts of carbon—up to 10 times faster than upland forests, according to some estimates. This carbon, known as “blue carbon,” has become a buzzword among those looking to protect the coasts from the more devastating effects of climate change, and those looking to sell credits as part of a “blue carbon market”.

A new study from a team of over 30 scientists, including Professor Benjamin Horton and Dr Tim Shaw from the Asian School of the Environment, show that that tidal wetlands in the contiguous U.S. can store roughly 800 million tons of carbon in their soils. This latest estimate was published June 21 in Nature Scientific Reports

Nailing down a precise figure for carbon in U.S. tidal wetlands was a challenge. For much of the nation’s history, wetlands were routinely dismissed as unprofitable, so there is not much data on the books. The U.S. Department of Agriculture has a century’s worth of carbon data from soil surveys in a dataset called SSURGO (Soil Survey Geographic Database), but most of it comes from other soil types, such as land that could be used for agriculture. To fill in the gaps, Professor Horton, Dr Shaw and the other researchers pooled their own data and scoured the literature for any additional data on wetland soils. In total, they were able to gather data from 1,959 wetland soil cores, found in peer-reviewed literature, government reports and some data still awaiting publication.

Armed with their newly merged datasets, the researchers did the simplest estimate first: the average. The team took the average of the carbon density in all 1900-plus soil cores, and then extrapolated it across all U.S. tidal wetlands to get an overall estimate of 793 million U.S. tons of carbon. But the team suspected not all wetlands would store carbon in the same way, so they also searched for a way to get more nuanced figures, using mapping techniques and models.

Accurate and precise soil carbon mapping strategies are needed in order to both evaluate existing carbon stocks, and estimate carbon losses from degrading wetlands.

Read the full paper here .

Read more about sea level research at ASE and EOS here.