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Researchers have created a model that tracks the fate and pathways of plastic debris in the Mediterranean Sea from land-based sources. They found that plastic debris can be seen across the Mediterranean from beaches to surface waters to the seafloors. The researchers also estimate that there are approximately 3,760 metric tonnes of plastics currently floating in the Mediterranean.
Since the 1950s, global plastic production has increased each year. In 2019, 368m tonnes of plastic was produced. Plastic waste is a large part of the oceans. Estimates suggest that there are more than 250,000 tonnes of plastic debris floating around in the oceans.
A shocking amount of microplastic and macroplastic debris are currently floating in the Mediterranean Sea, according to a new Frontiers in Marine Science study.
Plastic pollution is a major problem in the Mediterranean Sea. It is due to its densely populated coastlines and tourism. There is also a small amount of water that flows to the Atlantic. The Mediterranean is also rich in biodiversity making it a concern for conservation of marine ecosystems.
Plastic pollution has an impact on all levels of marine biodiversity. It can be found on the sea surface, beaches and seafloor as well as within the bodies and organs of large and small marine animals. Plastic can also be ingested by humans through seafood consumption.
Modelling plastic pollution
Researchers from Greece's Hellenic Centre for Marine Research created a new model that tracked the fate and pathways of plastic debris in Mediterranean Sea. The simulation covered the period 2010-2017 and tracked plastics coming from rivers and coastal cities. It also considered important dispersion processes like sinking, vertical/horizontal mix, wind, and currents. The model also identified possible accumulation patterns of micro-and macroplastics in the water column, surface layer, seafloor, as well as on beaches.
The total plastics annual load into the Mediterranean was approximately 17,600 tonnes. 3,760 tons of this are currently floating in its waters. 84% of the total end up on beaches, while 16% end up in the ocean floor or water column.
"Simulations on plastic distribution in marine environments have a high degree of uncertainty at the moment. Dr. Kostas Tiaras, the lead author, said that there is not much experimental data available on plastics' fates such as sinking, ingestion, and fragmentation by marine organisms.
"Our model was able to reproduce the observed distributions and plastics in the marine environment with reasonable skill. It can therefore be used to assess current plastic pollution levels in the Mediterranean and determine the potential impact of future cleaning and management actions."
Biofouling was also mentioned in the model as a possible mechanism to remove microplastics from seawater surface. Biofouling is when microorganisms like algae build up on submerged or floating objects, such as plastic debris.
The oceans are being overtaken by plastics
Microplastics are less common in the sea surface because they sink faster from attachments of heavier marine organisms (biofouling). They also accumulate deeper in the ocean floor and water column. Tsiaras said that macroplastics like plastic bags and Styrofoam can float for longer periods of time and travel far from their source.
Microplastics were found in areas near major cities, as well as heavily populated areas on the Spanish, French and Italian coasts. Microplastics of larger size were often found in areas that have high levels of untreated wastewater such as the coastlines off Greece or Turkey.
Macroplastics were plentiful in areas that had significant riverine input, such as the Algerian, Turkish, and Albanian coasts. They also found themselves close to major cities and high-populated coasts (Spain and France, Italy).
Recommendations for policy
The model outputs can be used for ecological (bird and cetacean habitats), or commercially (aquaculture, fisheries), identifications of areas potentially endangered by plastic pollution. This information is essential for the development of ecosystem-based management plans.
Implementing a common policy to manage the marine ecosystem is difficult due to the cultural, political and social diversity of the inhabited countries that lie along the coast of the Mediterranean. However, models like the one in the study can help to mitigate this problem.
"The identification of successful management plans requires the use of predictive models such as the one shown here.
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Further information: Kostas Tiaras et. al. Modeling the Pathways and Accumulation patterns of Micro- and Macro-Plastics in The Mediterranean, Frontiers in Marine Science (2021). Journal information: Frontiers in Marine Science Kostas Tsiaras et al, Modeling the Pathways and Accumulation Patterns of Micro- and Macro-Plastics in the Mediterranean,(2021). DOI: 10.3389/fmars.2021.743117