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Transport and accumulation of plastic particles on the varying sediment bed cover: Open-channel flow experiment
Summary
Researchers conducted open-channel flow experiments to study how various plastic particles of differing shape, size, density, and flexibility are transported and retained across sediment beds of varying grain size, finding that friction-driven retention zones consistently form at boundaries between finer and coarser sediments, offering a mechanism to explain the patchy distribution of microplastics in seafloor sediments.
Contamination of sea bottom sediments by microplastics is widely confirmed, but the reasons for its patchiness remain poorly understood. Laboratory experiments are reported where combined sets of various plastic particles, different by shape, size, density, and flexibility, were transported by the step-wise increasing open-channel flow over the bottom covered with natural sediment of increasing grain size. For every particular flow velocity, observations revealed the recurrent formation of relatively narrow retention areas, where plastic particles lingered for some time in their motion. These areas follow the line of change of the sediment type from finer to coarser grains. It is shown that contact friction drives the retention of a particle at finer sediments, while particle/sediment-grain interaction becomes of importance when particles and sediment grains are of similar sizes. The presence of this effect can be expected for a relatively wide range of natural conditions.