Mud and organic content are strongly correlated with microplastic contamination in a meandering riverbed

Abstract

The scale of microplastic pollution in river sediments is gradually being elucidated through an increasing number of large-scale studies. Nevertheless, microplastic distribution within a riverbed – a crucial aspect for quantification – remains poorly understood. Here we evaluate in the meandering River Lys, Belgium, how microplastic concentration varies between different sedimentary environments within the riverbed. We find that microplastic abundance is about an order of magnitude higher towards the riverbanks compared to the thalweg, corresponding with river hydrodynamics. Moreover, organic-matter and mud content are robust predictors of microplastic concentrations, apart from the outer bends, where erosion into organic-rich, muddy floodplain sediments inhibits microplastic deposition. These results increase our understanding of microplastic distribution at the small riverbed scale. They are a crucial element to guide for future sampling efforts across diverse river systems, paving the way for normalization and better quantification of microplastics trapped by river sediments and in other aquatic environments. (Figure presented.)