13 January 2021
Mangrove forests act as sinks for plastic waste
Published online 2 November 2020
The Red Sea and Arabian Gulf mangrove forests have been sequestering plastic waste for decades.
The Red Sea and Arabian Gulf surface waters hold smaller volumes of plastic litter than what originally entered them. In a new study, international researchers, including from Saudi Arabia, have found the reason for this discrepancy: mangrove forests have been sequestering substantial loads of plastic since its mass production began in the 1950s.
“Conserving mangrove forests is key to avoiding the resuspension of buried plastic into the water column where they could affect marine organisms,” says the study’s lead author, Cecilia Martin, a marine scientist from King Abdullah University of Science and Technology, Saudi Arabia.
Mangrove plant aerial roots and branches trap plastic items brought in by ocean currents, where they fragment into less buoyant, smaller particles. Microorganisms colonising the particles make them heavier, rapidly sinking them, where they eventually deposit in the sediment.
The scientists had analysed plastic pieces extracted from dated mangrove sediments and found small fragments and films that probably came from bottles, food wraps and ropes. They also found that plastic concentration decreased from the surface to the deeper layers of the sediments.
They conclude that plastic burial rates in marine sediment have risen exponentially since the 1950s, at a rate of 8.5 per cent each year, in line with the rise in global plastic production. The researchers predict burial rates will rise to 7 to 20 times higher than the present rates by 2050.
Martin, C. et al. Exponential increase of plastic burial in mangrove sediments as a major plastic sink. Sci. Adv. 6, eaaz5593 (2020).