Macroplastic storage and remobilization in rivers

Processes of macroplastic (plastic particles > 5 mm) storage and remobilization in rivers have been overlooked so far, but are of crucial importance for the estimation of plastic accumulation and transport and associated risks. We present a conceptual model that defines phases of the macroplastic route through a fluvial system and systematizes their main controls. We divided macroplastic route into (1) input, (2) transport, (3) storage, (4) remobilization and (5) output phases. Phase 1 is mainly controlled by humans, phases 2–4 by fluvial processes, and phase 5 by both types of controls. We hypothesize that natural characteristics of fluvial systems and their modification by dam reservoirs and flood embankments construction are key controls on macroplastic storage and remobilization in rivers. The zone of macroplastic storage can be defined as a river floodplain inundated since the beginning of widespread disposal of plastic waste to the environment in the 1960s and the remobilization zone as a part of the storage zone currently influenced by floodwaters and bank erosion. The amount of macroplastic in both zones can be estimated using data on the abundance of surface- and subsurface-stored macroplastic, and the lateral and vertical extent of the zones. A demonstrated diversity of factors controlling the route of macroplastic through a fluvial system requires a broader, transdisciplinary perspective including humans who not only dispose plastic, but are also affected by it both physically and aesthetically, and who may remove it from rivers.