Simulating pathways and beaching effects of plastic originating from the Dutch coast

Abstract

In this thesis, we look at the pathways of plastic originating from the Dutch shore and are interested in where this plastic ends up. We use global buoy trajectory observations and model data to construct transition matrices to model the ocean at the surface layer. With these transition matrices, we simulate a plastic tracer distribution over time by means of a Markov model. We also construct a model to simulate beaching effects based on the proximity of tracer to a coast and investigate its effects. It was found that most plastic released from the Dutch coast moves northwards towards the Barents Sea and remains circulating in the gyre formed there, while a considerable portion of plastic moves towards and remains in circulation east of Denmark. When beaching is taken into account, we see that the highest concentration of plastic washed ashore accumulates on the (east) Danish shore, while considerable amounts end up on the Norwegian and Dutch coasts as well. Remarkably, very little plastic washes up on the UK coast.

Since there is little empirical data on the scale of beaching, we vary the intensity of our beaching model to explore how this affects the results. To grasp these variations will allow for easier retroactive calibration of our model as more data on beaching becomes available. It was found that increasing the scaling factor in our model increased the total amount of beaching and showed a slight proportional beaching increase for areas closer to the point of origin of the plastic.