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Influence of plastic-clastic bed composition on the threshold conditions for the plastic fraction
Summary
Researchers conducted flume experiments to investigate how mixed plastic-clastic bed composition affects the threshold conditions required to mobilize negatively buoyant plastic grains, distinguishing the influence of bed layer characteristics from those of individual grain properties. Their findings provide insight into the sedimentary behavior of dense plastic particles in river systems, improving understanding of plastic transport dynamics along fluvial pathways.
With substantial evidence of the spread of plastic pollution, understanding the transport dynamics along fluvial pathways becomes imperative. This experimental study tackles the sedimentary behavior of negatively buoyant plastic grains with the aim of distinguishing the effects of bed layer characteristics on the remobilisation of compact microplastics from a flat bed. Experiments with two different types of ellipsoidal plastic particles were performed, on three types of bed (i.e. homogeneous plastic bed and two types of natural bed), and the conditions for onset of transport of the plastic particles were measured. Plastic particles’ motion was triggered by imposing steady flow in the flume, and was observed via the use of a camera, while shear velocity was calculated from Ultrasonic Velocity Profiler measurements. The mobilization threshold we observed depended not only on the bed substrate (and its roughness) but also on the availability of mobile particles.