Mangrove forests help mitigate climate change, by sequestering carbon in their sediments, which gained them the name of Blue Carbon habitats. The mesh created by their aerial roots slows down water currents and allow particles suspended in the water, like carbon, to sink and ultimately being stored in sediments for millennia.
Waters do hold also microplastics, a recent threat in the marine environment resulting from fragmentation of large plastic items. This is the consequence of improper waste management practices that haven’t been able to cope with the plastic mass production started in the post-war and exponentially increased until nowadays.
Similarly to carbon storages, are microplastic particles long-term sequestered in mangrove sediments? To answer this question, we, an international research team led by the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, have collected sediment cores from mangrove forests in the Red Sea and the Gulf. These were dated by means of isotopes (210-Pb) that allowed to determine when the sediment layers piling up in the cores, and the plastic particles extracted from them, have been deposited.
This approach showed that plastics have been buried in the mangrove sediments for decades and their burial has exponentially increased at the same pace as the global plastic production. Moreover, stocks of plastics in the mangrove sediments were found to be 100,000 times larger than in the surface waters of the Red Sea and the Gulf.
The surface waters of the two basins, similarly to global findings, were found to hold extremely low concentrations of plastics than those expected considering the inputs received annually. With this new research, mangroves are revealed as important and permanent reservoirs of that plastic missing from the surface waters, which they have been locking up since the start of the plastic mass production in the 1950s.
“Our research brings light to the mystery of missing marine plastic to reveal that mangroves, Blue Carbon habitats, are hugely efficient at trapping plastics and burying them in their soils where they cannot harm vulnerable marine life or their human consumers” said Carlos Duarte, KAUST professor of marine science who supervised the research.
Despite the recent diffuse awareness around the marine plastic issue, the global plastic production curve is getting steeper every year and no deceleration of the process is foreseen in the next future. This research shows the importance of mangrove forests in mitigating the plastic threats and offers an additional reason to cherish the Blue Carbon habitats.
Mangroves wipes up our mistakes, from carbon to plastics, and conserving them is a key strategy for the future of our planet.
To learn more about this research read the full paper.
King Abdullah University of Science and Technology
Cecilia recently obtained her PhD in Marine Science studying the fate of marine plastic pollution in the Red Sea.