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

Plastic pollution in terrestrial and aquatic ecosystems is of growing global concern due to its negative impact on environmental health and human livelihood. Most plastic research to date focused on observing and modelling plastic in the oceans, revealing that the highest plastic concentrations are found in the five ocean gyres (“the garbage patches”). Plastic waste originating from land has been identified as the main source of marine plastic debris. Yet it remains highly uncertain which processes control the mobilisation and transport of plastic waste over land to rivers and eventually to the ocean. Here, we introduce the Trash Tracker, a numerical model to forecast the pathways and fate of plastic waste in terrestrial and freshwater systems. In this model, the plastic transporting agents, wind and surface runoff, are resisted by the friction of the terrain. The terrain resistance, a function of the surface slope and the type of land use, is translated to thresholds that define the critical wind and surface runoff conditions required to mobilise and transport macroplastics. By repeatedly checking whether the wind and/or surface runoff conditions are strong enough to overcome their respective thresholds, the Trash Tracker simulates the transport of plastics and allows us to identify accumulation hotspots and high probability transport routes of plastic waste within river basins. This makes the Trash Tracker a practical tool for preventing, mitigating and reducing plastic pollution in the natural environment.