Blue carbon in coastal ecosystems. Interview with Christine Dupuy
In Earth’s waters lies ‘blue carbon’, captured and stored in the sedimentary layers of coastal ecosystems. Similar to the Amazon rainforests, often dubbed ‘the lungs of the planet’, which are slowly disappearing year after year, these ecosystems are among the most threatened on the planet, with between 340,000 and 980,000 hectares being destroyed each year. Christine Dupuy, professor, researcher and assistant director of the Littoral, Environment and Societies research unit at La Rochelle Université, who specialises in coastal ecology, highlights the importance of preserving these ecosystems and, even more importantly, restoring them through ‘renaturation’.
Yên Bui
AA: How does preserving coastal ecosystems help mitigate climate change?
Christine Dupuy: The challenge for ecological research today is to promote the burial of organic matter rather than its decomposition so that the carbon it contains is not released back into the atmosphere. However, in a forest, an oxygen‐rich environment, organic matter is most often broken down by decomposers which release CO2. In contrast, in vegetated aquatic ecosystems, environments with low‐oxygen sediments – which is what makes them so interesting – these decomposers develop very slowly. They break down very little organic matter that can be covered by sediments. Therefore, coastal ecosystems are five to ten times more carbon‐dense compared to terrestrial ecosystems. […]
What solutions are being considered to preserve it?
In 2019, the city of La Rochelle launched a project to restore the Tasdon marsh, an 83‐hectare wetland on the outskirts of the city that was partially drained following the construction of the Villeneuve‐les‐Salines district in the 1970s, which filled in part of its basins and cut it off from the sea. One of the aims of the city was to make the marsh a resting place for birds and to bring wildlife back to the city. Renaturation involved the creation of a wetland, the rearrangement of sediments, and the redesign of the landscape [by landscape office Atelier Cépage (Nathalie Cadiou and Philippe Rossier) and the hydraulic engineering company Hydratec. Ed.]. It also included the removal of invasive vegetation and the planting of new species [63,000 aquatic plants have been replanted on the banks and islands of the marsh and the Moulinette, the coastal river that flows through the Tasdon marsh. Ed.], as well as the construction of footbridges. According to the atmospheric carbon level measurements before and after restoration, Tasdon marsh has been transformed from a carbon source to a promising carbon sink.
What are the main issues surrounding the restoration of coastal ecosystems today?
Although the city of La Rochelle and the region are very interested in restoring ecosystems to transform them into carbon sinks, this is still a relatively new issue in France. Certain types of wetlands, such as marshes and swamps, continue to have a bad reputation as they are perceived as unhealthy or as vectors of diseases such as malaria, also known as ‘marsh fever’ – which is no longer the case, of course. Furthermore, marsh restoration is a fairly brutal operation, as the sediment has to be completely exposed…
Read the whole interview in AA's lastest issue, « Water, Common Good », available on our online shop.
More about blue carbon on La Rochelle University's website.
