Transport of Microplastics in a choked coastal lagoon in south Brazil

, Santos Ítele, Fernandes Elisa, Jalón-Rojas Isabel, Silva Pablo, Pinho Grasiela.

Microplastics in the marine environment are known to have impacts on marine life, ecosystems, and ultimately to human life. Therefore, it is important to understand how these materials behave, once in the aquatic environment, and the main physical forcings responsible for their transport. In this study, the transport of microplastics in Patos Lagoon was studied based on the coupling between the TELEMAC-3D hydrodynamic model results and the microplastic transport model TrackMPD, which takes into consideration specific physical properties of microplastic particles (as density and shape) and transport processes associated to them. Simulations were carried out for the 2013 year, which is considered an ENSO-neutral year. Hydrodynamic results showed that current velocities inside the lagoon present spatial variability, with weaker current velocities (max 0.35 m.s-1) in the inner Lagoon and stronger current velocities (3 m.s-1) at the Patos Lagoon mouth. Differences were also observed between the margins as a function of the Lagoon morphology and predominant wind direction, with current velocities around 0.35 m.s-1 on the west and 0.20 m.s-1 on the east margin. These spatial differences in current velocity inside the lagoon suggests the occurrence of areas of microplastic displacement and/or accumulation. The hydrodynamic response of the system to the main physical forcing (wind and freshwater discharge) promotes alternate in/out fluxes into the Lagoon and that is expected to affect the residence time of plastic debris inside the system. Simulations with the TrackMPD model are now being developed and processed and from the results we expect to understand the dynamics of microplastics and define the preferential areas of deposition inside Patos Lagoon. These results are the very first step towards the understanding of how microplastics are transported in coastal systems in South Brazil and will provide valuable information for the management of the plastic problem in the region.

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