What is it about?

Tidal wetlands are global hotspots of carbon storage but errors exist with current estimates on their carbon density due to the use of factors estimated from other habitats for converting loss-on-ignition (LOI) to organic carbon (OC); and the omission of certain significant carbon pools. Here we show that the widely used conversion factor (LOI/OC = 1.724) is significantly lower than our measurements for saltmarsh sediments (1.92 ± 0.01) and oversimplifies the polynomial relationship between sediment OC and LOI for mangrove forests. Global man- grove OC stock in the top-meter sediment reaches 1.93 Pg when corrected for this bias, and is 20% lower than the previous estimates. Ecosystem carbon stock (living and dead biomass, sediment OC and inorganic carbon) is estimated at 3.7–6.2 Pg. Mangrove deforestation leads to carbon emission rates at 23.5–38.7 Tg yr−1 after 2000. Mangrove sediment OC stock has previously been over-estimated while ecosystem carbon stock underestimated.

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Why is it important?

The article offered new estimates on carbon pools in “Blue Carbon”, with ecosystem carbon stock 23% higher in global mangrove forests than previous estimates. This revises the contribution of mangroves to counter carbon emission.

Perspectives

This article have combined data from past studies on sediment organic carbon and loss-on-ignition and new field measurements of sediments in tidal wetlands. Through comparison and analyse, the team can better constrain the relationship between sediment organic carbon and loss-on-ignition for different types of tidal wetlands (i.e. mangroves and saltmarshes). This relationship is then used to improve the estimate on sediment organic carbon stock in global mangroves. As a result, they have unravelled that carbon stocks in mangrove forests reach 3.7-6.3 Pg (one Pg = 1015 g or one billion metric tonnes), which were previously underestimated by 23%. These values suggest mangrove deforestation has resulted in carbon emission rates at 23.5 – 38.7 Tg yr−1 after 2000 (one Tg = 1012 g or one million metric tonnes).

PhD Xiaoguang Ouyang
Chinese University of Hong Kong

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This page is a summary of: Improved estimates on global carbon stock and carbon pools in tidal wetlands, Nature Communications, January 2020, Springer Science + Business Media, DOI: 10.1038/s41467-019-14120-2.
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