Anthropogenic litter is abundant, diverse, and mobile in urban rivers: Insights from cross-ecosystem analyses using ecosystem and community ecology tools

Anthropogenic litter (AL; trash) in the environment is increasing and persistent. Rivers are considered a major source of AL to oceans, but AL ecology within rivers is rarely examined. Also, the rapidly developing field of AL research will benefit from fundamental approaches in community and ecosystem ecology. We adapted methods for communities of organisms and movement of organic matter to measure density, mass, assemblages, sources, and flux of AL in riparian and benthic zones at 15 sites in five rivers. We compared riverine AL density, mass, and assemblages to marine habitats worldwide. Benthic zones had greater AL mass and a different assemblage than riparian zones. Reach-scale metrics of human activity (e.g., parking spaces) explained more variation in AL assemblages than total urban land use. AL export was driven by material type and hydrology, and turnover time was ≤ 1 yr. Riparian AL density was similar to beaches, but benthic AL density was higher than marine benthic habitats. Finally, AL assemblages in river benthic and riparian zones were similar to assemblages at beaches rather than marine benthic habitats. AL is abundant and mobile in rivers, which show dynamic periods of AL retention and export. Rivers are likely sites of AL breakdown and burial, with significant biotic interactions which have not yet been studied. Comprehensive assessments of AL across ecosystems require continued adaptation of fundamental ecosystem and community ecology tools. Results will integrate riverine AL dynamics with the growing field of marine AL ecology, and inform management of global AL accumulations.