The Trash-Tracker: A Macroplastic Transport and Fate Model at River Basin Scale

Land-based plastic waste is assumed to be the major source for freshwater and marine plastic pollution. Yet, the transport pathways over land, in rivers and into the oceans remain highly uncertain. Here, we introduce a new modelling concept to predict plastic transport pathways on land: the Trash-Tracker; a numerical model that simulates the spatiotemporal distribution of macroplastic waste at the river basin scale. The plastic transporting agents are wind and surface runoff, while plastic transport is resisted by the friction of the terrain. The terrain resistance, a function of the terrain slope and type of land use, is translated to thresholds that define the critical wind and surface runoff conditions required to mobilise and transport macroplastic waste. When the wind and/or surface runoff conditions exceed their respective thresholds, the model simulates the transport of plastics, resulting in plastic accumulation hotspots maps and high probability transport route maps on the scale of river basins. The Trash-Tracker contributes to a better mechanistic understanding of plastic transport through terrestrial and freshwater systems, and upon future calibration and validation, can serve as a practical tool for stakeholders to optimise plastic waste prevention, mitigation, and reduction strategies.