We especially think of trees to capture, store and sequester the carbon emitted by human activities. We often forget that aquatic plants like algae also do this very effectively. For several years, the Intergovernmental Panel on Climate Change (IPCC) has even considered algae cultivation as a possible strategy to mitigate climate change.
During a conference entitled Blue carbon and climate change presented Tuesday at the Acfas congress, which takes place at the University of Ottawa, the professor of biological oceanography at the University of Quebec at Rimouski, Fanny Noisette, presented the great potential of macroalgae to store and sequester carbon in our regions.
“In coastal areas of temperate to polar regions, brown macroalgae—kelps—form highly productive communities. These macroalgae generate detritus, some of which washes up on beaches, and some of which disappears into the depths of the ocean which are often covered with sediments devoid of oxygen which sequester carbon,” she explained.
Macroalgae have several qualities that make them interesting for capturing, storing and sequestering carbon, she emphasized. First, there are suitable habitats for brown algae in almost every coastal area around the world, representing enormous “carbon storage potential”.
According to measurements published in 2022, algae assimilate – that is to say, capture through photosynthesis, and therefore store – on average between 0.2 and one kilogram of carbon per square meter per year, depending on whether it is green algae, mid-coastal algae (where tides occur), brown algae (i.e. large kelps which are constantly underwater), algae from coral reefs or red algae from deep environments .
“In cold regions, like here for example, there is storage of around one kilogram of carbon per square meter, while in slightly warmer regions, only a third of this value is stored. product. We therefore have ecosystems that store a lot of carbon,” noted the researcher at the Rimouski Institute of Marine Sciences.
“However, of this kilogram of algae per square meter, there are more than 50% which return to the environment in the form of detritus and dissolved carbon. We therefore have ecosystems which are capable of storing a lot, but which release a lot into the environment, which is a problem for sequestration,” she added.
To find out where the carbon stored by these algae was sequestered, scientists took water samples from different depths and analyzed the DNA it contained. They were thus able to detect traces of several families of algae up to 4000 meters, a depth particularly favorable to sequestration.
Blue carbon
“It was from the mid-2000s that we began to develop and test the first technologies using macroalgae to store carbon. And it was in 2008 that the concept of “blue carbon” was introduced,” recalled Mr.me Hazelnut.
This mariculture sector emits very little carbon compared to fish farming and the cultivation of bivalves (mussels, oysters, etc.), underlined the researcher. The main advantage of seaweed farming is the very rapid storage of carbon in the tissues. The algae that are harvested can then be used for human food or livestock, as well as in pharmaceuticals or nutraceuticals.
A second advantage is that carbon sequestration can take place under or near these algae farms, because the carbon that the algae loses when it breaks falls to the bottom of the water and will bury in sediments. Macroalgae can be grown on lines that can be towed by boat and sunk to the bottom of the sea. There are also circular lines equipped with large knives that regularly cut the algae so that debris falls to the surface. bottom of the water. There are also biodegradable platforms on which we would grow algae and float in the middle of the oceans. After a while, these platforms would sink to the bottom of the water by themselves, she gives as an example.
A third advantage is the ability of aquaculture companies to achieve carbon neutrality. “Since seaweed stores a lot of carbon, there are therefore advantages for mariculturists in growing seaweed with other seafood,” says the professor.
“The quantity of carbon that is captured and assimilated by algae is very often greater than that of terrestrial agricultural production. And it is sometimes even much superior to the cultivation of sugar cane, which is one of the crops that captures the most carbon in terms of growth and speed. Algae aquaculture therefore has real storage potential,” underlines M.me Hazelnut.
“However, we cannot rely solely on blue carbon to save the climate change crisis. It is not by cultivating more algae that we are going to save the planet. The main solution remains reducing our emissions. The protection and maintenance of these environments are also extremely important, because if we lose them, all the carbon stored inside will be re-emitted,” she warns.