What plant, other than trees, can mitigate climate change by feeding on atmospheric CO2? The seaweeds !
At the Acfas congress in mid-May in Ottawa, researchers took stock of the potential of “blue carbon” to mitigate climate change.
“Marine ecosystems can help store carbon,” explains Fanny Noisette, biologist at the University of Quebec at Rimouski and specialist in the ecophysiology of algae in the estuary and Gulf of St. Lawrence. “Large algae capture CO2 from the water. As they can reach several meters, they accumulate carbon quickly. »
The drop in CO2 levels in the sea, due to algae growth, results in atmospheric CO2 being dissolved in the sea as a replacement, because the CO2 levels in the atmosphere and the sea are in balance constant. CO2 is the main greenhouse gas responsible for global warming.
Are increasing temperatures and decreasing oxygen levels in the Gulf a problem? “Deoxygenation occurs in the deeper layers, while algae is found where there is light, in the top 40 meters. Warming episodes, on the other hand, can affect their growth. »
Reducing ice cover in winter is a more immediate problem. When there is less ice, coasts are more exposed to winter storms, which can strip away algae, Noisette said.
In the latter scenario, the algae could decompose and release the carbon accumulated when they absorbed CO2 from the water.
Marcel Velasquez, a biologist at Université Laval who works on Arctic algae, is working on a Canadian inventory of marine organisms capable of storing carbon. “There is a large quantity and diversity of kelp forests in the Arctic that are not studied.” These kelp forests are composed of large algae.
Mr. Velasquez wants to develop a model to predict the reaction of Arctic kelp forests to climate change, particularly in terms of their growth and therefore carbon storage.
To complicate the analysis, melting ice in the Arctic will release sediments, a source of nutrients for algae.
Before becoming interested in the Arctic, the Chilean-born biologist worked on Antarctic algae as a “scientific diver”.
Is it possible to encourage the growth of coastal algae so that they absorb more CO2 from seawater? In the oceans, there have been attempts to “fertilize” with iron, among other minerals, to encourage the growth of algae.
“In the Gulf, there are no factors limiting growth, there is no lack of nutrients,” says Ms. Noisette. But we can encourage their growth with artificial reefs. There have been attempts of this type for a long time. » These artificial reefs, particularly in Gaspésie and Sept-Îles, have been used to study lobster or were built to compensate for coastal disturbances linked to construction.
According to the Ramsar convention, which has monitored wetlands since 1971, blue carbon is particularly stable, being able to be stored in marine sediments for thousands of years. “Seagrass beds,” kelp forests like those Ms. Noisette and Mr. Velasquez study, can store 512 tons of carbon per hectare, a figure similar to terrestrial forests.
Blue carbon, which includes mangrove forests, is responsible for half of marine sediment carbon storage, even though it is only present in 2% of ocean surface area. According to the Ramsar Convention, the degradation of blue carbon ecosystems is responsible for one billion tonnes of CO2 each year, or 20% of emissions linked to terrestrial deforestation. Seagrass losses are particularly significant, having increased from 1% to 7% per year between 1940 and 2020.
For this reason, a recent RBC report estimated last year at 130 million CAN per year the potential in carbon credits from the restoration of Canadian seagrass beds, which have lost 90% of their surface area over the past century.
“In no case does the storage of carbon by marine ecosystems constitute the solution to the overproduction of CO2 in the atmosphere”, however, wishes to clarify Ms. Noisette.
