Microplastic distribution in a meandering river bed and its sedimentary predictors

<title>Abstract</title> The scale of microplastic pollution in river sediments is gradually being elucidated through an increasing number of large-scale studies. Despite these advancements, our knowledge about the microplastic distribution within a riverbed – a crucial aspect for quantification – remains poor. Here, we study the meandering River Lys, Belgium, to evaluate how microplastic concentration varies between different sedimentary environments within the riverbed. We find that microplastic abundance is an order of magnitude higher towards the riverbanks compared to the thalweg, corresponding with hydrodynamics. Moreover, apart from the erosional area near the outer banks, organic matter content and median grain size are robust predictors of microplastic concentrations. These results significantly increase our understanding of MP distribution at the small scale of the riverbed. They are a crucial element to guide for future sampling efforts across diverse river systems, paving the way for normalization and better quantification of amounts of microplastics trapped by river sediments.