Numerical modelling framework for micro and macro plastic transport dynamics in surface waters

Plastic pollution in surface waters spans a wide range of particle sizes, yet the transport dynamics of both micro‑ and macro‑plastics remain insufficiently quantified at the catchment scale. Addressing this challenge requires modelling approaches capable of linking realistic hydrological variability with particle‑specific transport behaviour. In this work, we develop a numerical framework that couples large‑scale hydrological simulations with a process‑based transport model for plastics of different size classes. 

We begin by reusing and re‑calibrating the mesoscale Hydrological Model (mHM) using benchmark datasets and hypothetical test cases to generate space–time fields representing flow dynamics across river basins. These hydrological outputs are exported as NetCDF files, providing a consistent and high‑resolution description of discharge and flow conditions in surface waters. To simulate plastic transport, we extend the DRUtES modelling platform by implementing a module that reads the mHM‑generated NetCDF files and solves an ADER‑based advection–dispersion–reaction equation designed to represent the transport dynamics of both micro‑ and macro‑plastic particles under realistic hydrological forcing. This coupled framework enables the simulation of plastic transport across size classes and supports scalable assessments of plastic transport dynamics in river systems.