Storm Response of Fluvial Sedimentary Microplastics

Abstract

Up to 80% of the plastics in the oceans are believed to have been transferred from river networks. Microplastic contamination of river sediments has been found to be pervasive at the global scale and responsive to periods of flooding. However, the physical controls governing the storage, remobilization and pathways of transfer in fluvial sediments are unknown. This means it is not currently possible to determine the risks posed by microplastics retained within the world's river systems. This problem will be further exacerbated in the future given projected changes to global flood risk and an increased likelihood of fluvial flooding. Using controlled flume experiments we show that the evolution of the sediment bed surface and the flood wave characteristics controls the transition from rivers being 'sinks' to 'sources' of microplastics under flood conditions. By linking bed surface evolution with microplastic transport characteristics we show that similarities exist between granular transport phenomena and the behavior, and hence predictability, of microplastic entrainment during floods. Our findings are significant as they suggest that microplastic release from sediment beds can be managed by altering the timing and magnitude of releases in flow managed systems. As such it may be possible to remediate or remove legacy microplastics in future.

Macroplastic Storage and Remobilization in Rivers

“…The processes of transport, deposition and remobilization of mineral and organic sediments are controlled by their physical properties (e.g., density, size) and their relation to river size and hydrodynamics [42][43][44][45]. Recent insights into interactions of macroplastic debris with fluvial processes documented by laboratory experiments [46,47] and the monitoring of floating [24,26,27] and deposited macroplastic debris [48] suggest that transport, storage and remobilization of macroplastic debris are also partly related to fluvial processes. The main similarities between macroplastic and larger particles of organic debris (e.g., seeds, vegetation propagules, large wood pieces) encompass their relatively low density and large surface area determining their transport by water in flotation (see [45]).…”

Macroplastic Storage and Remobilization in Rivers

“…The processes of transport, deposition and remobilization of mineral and organic sediments are controlled by their physical properties (e.g., density, size) and their relation to river size and hydrodynamics [42][43][44][45]. Recent insights into interactions of macroplastic debris with fluvial processes documented by laboratory experiments [46][47] and monitoring of floating [24,26,27] and deposited macroplastic debris [48] suggest that transport, storage and remobilization of macroplastic debris are also partly related to fluvial processes. The main similarities between macroplastic and larger particles of organic debris (e.g., seeds, vegetation propagules, large wood pieces) encompass their relatively low density and large surface area determining their transport by water in flotation [see 45].…”

A Geomorphic Framework for the Analysis of Microplastics in Riverine Sediments

“…Armoring of the channel bed can significantly influence the frequency with which sediments are mobilized. A recent flume study by Oakelford et al [34] showed that microplastic mobilization and storage was also linked to the dynamics of the active layer, which in turn was influenced in a complex way to the nature of the flood's hydrograph. Their data, then, suggest that the active layer may also control the accumulation and transport of MPs in rivers, and should be examined in more detail for natural systems.…”