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Numerical modelling of microplastics transport and accumulation throughout Portuguese coast
Summary
Researchers used computer modeling to simulate how microplastics move and accumulate along Portugal's coastline. The modeling approach helps identify areas of highest plastic concentration and informs strategies to reduce microplastic pollution in marine environments.
Microplastic (MP) accumulation and dispersal is a growing problem at a global marine scale. The accumulation of MPs in aquatic systems is increasing due to their high perseverance and inadequate management, affecting all marine environments and adversely impacting ecosystem services and even human health. The study of these contaminants, namely their concentration and spatial distribution, as well as their physical characteristics, is fundamental to mitigate and reduce the associated risks. Due to the high population density on the Portuguese coast, this area is a zone of high contamination by MPs, being the rivers their main transport mode to coastal waters. In order to understand the distributions of MPs and the way they evolve in space and time, is essential to develop studies in this area. Thus, the purpose of this study is to simulate the transport and accumulation of MPs along the Portuguese coast and adjacent waters. The methodology followed comprised the development and implementation of a three-dimensional model using the Delft3D suite, coupling the Flow and particle-tracking (D-WAQ PART) models. Three scenarios were created: scenario 1 aims to comprehend the trajectory of the MPs of different diameters and types; scenario 2 was developed to understand the distribution and accumulation zones of MPs released per river; and scenario 3 aims to assess the effect of wind on the MPs fate. The simulations show that all MPs move to north in winter and tend to stay close to the release point in summer, following the local hydrodynamics. The higher density and larger MPs tend to sink more than those of lower density and smaller dimension, which in turn tend to travel longer distances. The effect of wind on the distribution of MPs, regardless of direction and season, favors the sinking of particles and dispersion off the platform. The main factors that influence the distribution and accumulation of MPs in the study area are the local hydrodynamic and geomorphology, followed by the diameter of the MPs. This study contributes to improve the understanding about the fate and transport of MPs along the Portuguese coast and to detect critical accumulation zones.