Estuaries surrounded by tall grasses and wildflowers, which are home to birds, crabs, small fish and other wildlife, are more effective than young coastal forests in capturing and storing carbon dioxide, the study said.
The Kouichan estuary on Vancouver Island captures and stores about twice as much carbon as an actively growing 20-year-old Pacific Northwest Forest in the same area, according to a recent study in the journal Frontiers in Marine Science.
Tristan Douglas, a graduate of the University of Victoria and lead author, said the so-called blue carbon or greenhouse gas stored in marine and coastal ecosystems is different from that stored on land.
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He said the saltwater estuaries, where fresh water meets the ocean, contain as much carbon as forests, although they make up only a small part of the area.
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“Plants and algae that grow on the surface of the seabed and in water are very effective in absorbing carbon dioxide and converting it into organic molecules,” he said.
Trees capture greenhouse gases but have limited life, die, decompose and turn back into carbon dioxide, he said.
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In the estuary, Douglas said, carbon quickly turns into plant material, buries itself in the sediment and becomes oxygen-free just a few millimeters below the surface.
“So it is very likely that the deposited organic matter will not be returned to the atmosphere as carbon dioxide.”
The study says estuaries have a much greater potential to mitigate climate change than forests, especially because of the threat of forest fires that send carbon jets back into the atmosphere.
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“If the carbon stored in the estuaries is not broken, it does not have the same risk of being suddenly converted back into massive amounts of carbon dioxide,” Douglas said.
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Wetlands with plants such as salt marsh grasses, sedges, mangroves and seagrass are particularly effective natural carbon sinks, the study said.
“They capture and store up to 70% of the organic carbon that resides in marine systems, although they occupy only 0.2% of the ocean’s surface.
Douglas said the world had lost about 70 percent of its mangrove forests and about 30 to 40 percent of all swamps and seagrass over the past 100 years and would lose another 40 percent if it was a “business as usual” approach in the next century.
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The study suggests that human activity has reduced the carbon capture and storage capacity of the Kouichan-Koksila estuary from 466 hectares by about 30 percent, equivalent to the return of 53 gasoline-powered vehicles.
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Eel grass on about 129 hectares of the tidal zone was disrupted by the processing and storage of logs, while about 100 hectares of salt marshes were dried for agriculture and livestock pastures after being settled by colonists, the report said.
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Douglas said it was up to politicians to protect these areas by adopting more sustainable land use and development practices.
The Kouichan estuary is traditionally used by coastal salis people and is an important area for mussels, salmon and seaweed, among other things. But since the mid-1800s, the land has been used mainly for agriculture and sawmills, he said.
“Many historical accounts of eel grass describe that it covers almost the entire lower tidal zone, but now it has indeed been displaced to less than a third of where it grew historically.”
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These estuaries act as a buffer, mitigating tides and mitigating storms, he said.
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Many of these areas have been destroyed to protect coastal communities, he said, leaving no room for them to adapt to rising sea levels.
“It has been pushed beyond its level of natural resilience,” Douglas said.
“They can withstand many gradual changes, but things have changed so quickly and they are under so much stress that they cannot cope with these current land use practices.”
© 2022 The Canadian Press
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