Plastic accumulation on riverbanks after the July 2021 Meuse flood

The majority of mismanaged plastic waste does not reach the oceans, and rather accumulates in terrestrial and freshwater environments. Since 2017, riverbanks along the Dutch part of the river Meuse have been monitored by volunteers in spring and fall. At each monitored riverbank macroplastic and other litter items were collected along a 100 m section and classified in over 100 specific item categories. In July 2021, the Meuse was hit by a severe flood event with an estimated return period between 100 - > 1000 years, similar to other rivers in Germany, France, Belgium, and the Netherlands. Flood conditions can highly increase plastic (re)mobilization and transport within river systems, and plastic discharge into the oceans. However, the impact of a severe flood event on plastic litter accumulation on riverbanks, to the authors knowledge, was never measured before. Within three weeks after the flood event we counted and classified macroplastic and other litter items on 25 riverbanks along the Meuse, from the Dutch-Belgian border to the river mouth. The additional sampling allows us to, for the first time, assess the impact of such a flood event on plastic accumulation on riverbanks. In this presentation we compare plastic accumulation on riverbanks after this flood event to plastic accumulation during normal conditions. We compare the amounts and types of litter, and possible litter sources. This study aims to contribute to better understand mobilization, transport, and accumulation dynamics of plastics in river systems, and the role and impact of extreme events on plastic accumulation on riverbanks.