Numerical Modelling of Plastic Debris Transport and Accumulation throughout Portuguese Coast

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 could adversely affect 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 living 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. Modeling predictions show that all MPs move to north following the local hydrodynamics. The higher density MPs with diameters of 5 mm tend to sink more than those of lower density with 10 mm diameters, which in turn tend to travel longer distances.. The main factors that influence the distribution and accumulation of MPs in the study area are the local hydrodynamic and geomorphology, and the MPs diameter. These results have a large number of applications, including detecting optimal removal locations, reducing the impact on the ecosystem, and understanding the flows of MPs pollution.