Preprints
https://doi.org/10.21203/rs.3.rs-3696866/v2
https://doi.org/10.21203/rs.3.rs-3696866/v2
25 Sep 2024
 | 25 Sep 2024
Status: this preprint is open for discussion.

A numerical model of microplastic erosion, transport, and deposition for fluvial systems

John J. Armitage and Sébastien Rohais

Abstract. Rivers are the primary pathway of microplastic pollution from source to the eventual sink in the marine environment. However, like sediments, microplastic will become trapped within the fluvial system as it makes its way from source-to-sink. There is therefore the potential that rivers are an important reservoir of microplastic pollution globally. To explore the transport of microplastic through the fluvial system we develop a reduced complexity model of microplastic erosion, transport, and deposition that builds on methods developed for the transport of sediment. We apply this model to the river Têt, France, where there has been punctual monitoring of the flux of microplastic at the outlet. We find that the reduced complexity model captures the observed quantity of microplastic under reasonable assumptions of the relationship between microplastic sources and population density. The model that best matches observed fluxes of microplastic at the outlet of the Têt river requires between 1 and 10 ppm volume concentration of microplastic per 200x200 m in the top half a meter of soil. The microplastic of grain size 300 μm then travels within the river network with a settling velocity of the order of 10-4 m/sec. The model results imply that a large proportion of microplastic will become entrained within the sediments along the fluvial system. This model is a first step in assessing where to sample for microplastic pollution within fluvial systems and points to regions susceptible to microplastic pollution.

John J. Armitage and Sébastien Rohais

Status: open (until 08 Nov 2024)

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John J. Armitage and Sébastien Rohais
John J. Armitage and Sébastien Rohais

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Short summary
Rivers transport microplastic pollution from its source to its eventual marine sink. Rivers are not simple conveyor belts of this pollution. Microplastic will become entrained within the sediments, becoming part of the river catchment environment. We develop a reduced complexity model to capture the transport and deposition of microplastic. By comparing our model to observations from the Têt River, France, we find that large quantities of microplastic must be stored within the river sediments.