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Little bay in Denmark stored record amount of carbon

Staff Writer |
Forests are potent carbon sinks, but also the oceans' seagrasses can store enormous amounts of carbon. A little bay in Denmark stores a record amount of carbon.

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Seagrass plays a bigger role in Earth's carbon cycle than most of us think.

The underwater meadows of seagrass are capable of storing large amounts of carbon - a talent that draws attention in a time, where decision makers and scientists are searching for ways to bring down the release of CO2 to the atmosphere.

Efficient meadows of carbon storing seagrass are found in coastal areas in many parts of the world. But according to biologists one particular meadow in Denmark is by far the most efficient.

The meadow is situated in the bay Thurøbund on the island Thurø in the South Funen Archipelago, Denmark.

"Many seagrass meadows in the world have been investigated. Recently I was part of investigating and measuring carbon storing capabilities of 10 seagrass meadows in the Baltic Sea. No place comes even close to Thurøbund," says Professor Marianne Holmer, University of Southern Denmark (SDU).

Professor Holmer is head of SDU's Department of Biology and she is an expert in seagrass ecology and biogeochemistry. The explanation is found in the special conditions in Thurøbund.

It is a very protected bay and also very productive. So the seagrass thrives and when the plants die they stay in the meadow. They are buried in the sediment and in this process their content of carbon gets stored with them.

In Finland the seagrass grows in open coast areas, which means that the dead plants much more often are washed off to sea, taking the carbon with them. Once the carbon has been taken out to the sea it is unsure what happens to it, says Professor Holmer.

Thurøbund stores ca. 27,000 grams of carbon (gC) pr. square meter. This figure has never been measured to be more than 10,000-11,000 gC pr. m2 in other parts of the world.

According to the new study Danish seagrass meadows store 3-4 times more carbon than Finnish meadows.

The study's lead author is PhD student Emilia Röhr, University of Southern Denmark and Åbo Akademi University in Finland. Co-authors are Marianne Holmer and Christoffer Boström from Åbo Akademi University.

"The Finnish meadows in our study are more exposed than the Danish and they grow in harsher environments where the dead plants do not sink to the bottom, so their carbon content does not get stored in the sediment," explains Emilia Röhr.

It is unknown where the dead seagrass plants go and what happens to them, when they get washed out to the open sea. Maybe their carbon gets stored elsewhere, maybe it ends up as CO2 in the atmosphere.

Due to the carbon storing efficiency of seagrass meadows, a system has been designed to calculate the economic value of their stored carbon.

"The value in Denmark is 1809 Euro pr. hectar while in Finland it is 281 Euro," says Emilia Röhr.

Other scientists have calculated that the global loss of seagrass equals $1.9 - $13.7 billion in lost carbon storing.

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