Exponential increase of plastic burial in mangrove sediments as a major plastic sink

Abstract

Sequestration of plastics in sediments is considered the ultimate sink of marine plastic pollution that would justify unexpectedly low loads found in surface waters. Here, we demonstrate that mangroves, generally supporting high sediment accretion rates, efficiently sequester plastics in their sediments. To this end, we extracted microplastics from dated sediment cores of the Red Sea and Arabian Gulf mangrove (Avicennia marina) forests along the Saudi Arabian coast. We found that microplastics <0.5 mm dominated in mangrove sediments, helping explain their scarcity, in surface waters. We estimate that 50 ± 30 and 110 ± 80 metric tons of plastic may have been buried since the 1930s in mangrove sediments across the Red Sea and the Arabian Gulf, respectively. We observed an exponential increase in the plastic burial rate (8.5 ± 1.2% year−1) since the 1950s in line with the global plastic production increase, confirming mangrove sediments as long-term sinks for plastics.

Plastic Plants: The Role of Water Hyacinths in Plastic Transport in Tropical Rivers

“…However, it is possible that in certain configurations-for instance large floating patches close to the riverbanks, with low flow velocity-the hyacinths act more as a barrier than a means of transport. Recent studies prove the role of mangrove forests in trapping anthropogenic litter in estuarine (Ivar do Sul et al, 2014) and coastal environments (Martin et al, 2019;Martin et al, 2020). Focus on the residence time, and spatial interactions between hyacinths and plastic and degradation rates could be beneficial in that sense.…”

“…Other drivers, such as sediment loads have also been recently examined in Australia (He et al, 2020), China (Liu et al, 2021) and Amazonian rivers (Gerolin et al, 2020) in relation to microplastic transport. Mangrove forests and coastal vegetation habitats can also be an important sink of plastic debris (Ivar do Sul et al, 2014;Cozzolino et al, 2020;Martin et al, 2020). In the Saigon river, Vietnam, macroplastic (>5 mm) transport was correlated to the abundance of floating vegetation material found (mainly drifting water hyacinths), rather than hydrological variables (van Emmerik et al, 2019a).…”

Investing in Blue Natural Capital to Secure a Future for the Red Sea Ecosystems

“…Mangrove vegetation also provides ecosystem services, such as sediment trapping and erosion protection, flood protection, and nutrient cycling (Duarte et al, 2013;Saderne et al, 2018). Additionally, mangrove forests are capable of trapping and sequestering pollutants, such as heavy metals, hydrocarbons, and plastic particles, from the water column (Ashok et al, 2019;Martin et al, 2019Martin et al, , 2020Rabaoui et al, 2020). Mangroves' capacity to improve water quality is particularly beneficial for aquaculture practices.…”

Presence of nanoplastics in rural and remote surface waters

“…Intriguingly, PET was entirely absent from the chain of sampled lakes (Figure 1, sites 3, 4, 5, 9) despite PET being detected in three streams that enter the lake chain (sites 2, 6, 7). This could point towards burial of PET during lake sediment deposition, which can be an e cient sink process in aquatic sediments 30 . Alternatively, removal could be via in-lake photodegradation which is capable of fully or partially photochemically oxidising PS (and therefore potentially other polymers) to carbon dioxide or dissolved organic carbon 31 .…”