Macroplastic deposition and flushing in the Meuse river following the July 2021 European floods

Rivers play an important role in the macroplastics transport and retention dynamics in the environment. Therefore, gaining an understanding of these processes is vital in order to help determine the fate of macroplastic in the environment. During flood events the transport of floating macroplastic is known to increase. We compared plastic accumulation and flushing on sixteen riverbanks along the Dutch Meuse river during the period that includes the July 2021 extreme flood to plastic accumulation on the same riverbanks as during normal discharge conditions between 2018 and 2021. Here we show that following the flood small macroplastic categories ( <2.5 cm) were flushed from the riverbanks, while larger soft plastic fragments (2.5-50 cm) and wet tissues were deposited. We found that for all plastic categories and for all riverbanks averaged, the plastic accumulation rate during the July 2021 flood was higher than that which would be expected for that time of year. However, the average accumulation rate for all locations during the period that included the flood was lower than the average accumulation rate over the Dutch winter (Oct/Nov-Feb/Mar). Our results show that litter category composition following the July 2021 flood differed from normal conditions. This indicates that plastic deposition and remobilization processes on riverbanks differ between extreme flood and annually average conditions. These observations contribute to a better understanding of the fate of macroplastic in the environment in terms of the drivers of both its transport and deposition.

Automated summary

Rivers play a crucial role in the transport and retention of macroplastics in the environment. Understanding these processes is essential for determining the fate of macroplastic in the environment. A study conducted during a flood event found that smaller macroplastics were flushed away from riverbanks, while larger soft plastic fragments and wet tissues were deposited. These findings suggest that plastic deposition and remobilization processes differ between extreme flood and normal conditions, contributing to a better understanding of macroplastic fate.