Presenting a global riverine microplastic transport model based on mechanical principles

Abstract

Recently, there has been more and more research on the abundance of MPs (MPs) in oceans, seas, and rivers. A lot is still uncertain about the distribution of MPs, and whether they are mainly deposited in seas & oceans, or river sediments. As global models on MP transport through rivers have only used statistical methods, we present a global riverine MP transport model based on mechanical principles. The model incorporates particle advection, settling, entrainment, and input emissions from wastewater treatment plants. The model was run for a period of 5 years, on 8 MP mixes of 15 MPs each, with the same 24 uncertainty scenarios for each MP mix (totalling 192 runs). Exported (to seas and oceans) and sedimented MPs showed a linear increase over time, while MPs suspended in the river reached steady state, but showed heavy seasonal fluctuations. Under the modelled uncertainties, after 5 years of simulation time, 76% of MPs are exported to seas and oceans and 19 % of MPs are deposited in river sediment. 5% of MPs were suspended in the water column. Major contributing areas to global MP emissions are area’s with large population densities, like Europe, North America, China & South East Asia, and India. Our work contributes to the understanding of MP flows through rivers, and could be used as a starting point for a MP material flow analysis, or as the basis for MP impact assessments. Future iterations of the model should implement man-made barriers and reservoirs, which
were not considered in the current version of the model.