Modeling the transport and accumulation of microplastics in the Gulf of Finland

In this study, we conduct numerical simulations to investigate the transport and accumulation of microplastics (MPs) in the Gulf of Finland (eastern Baltic Sea). The transport of MPs is simulated using a Lagrangian particle tracking model, developed by the authors, which accounts for the physical transport and transformational processes specific to MPs, such as diffusion, beaching, resuspension, and biofouling.

Positively and negatively buoyant particles were included to represent different types of MPs. High-resolution (250 m) 3D hydrodynamic and biogeochemical model data are used as input to the MPs model. Major rivers and wastewater treatment plants around the Gulf of Finland are the sources of MPs in the model.

The main objectives of the study are 1) to perform a sensitivity analysis of four processes (beaching, mixing, resuspension, and biofouling) to investigate the importance of each process on the distribution of MPs in the Gulf of Finland; and 2) to execute a multi-year simulation using realistic MPs input to locate the main accumulation areas in sediments and beaches around the Gulf of Finland.

Results of the initial sensitivity analysis indicate that the changes in the parametrization of beaching have a stronger effect on the horizontal distribution of MPs in off-shore sediments than the changes in the parametrization of resuspension. The maximum MPs concentration is observed near the sea surface; however, MPs have also spread into the water column.