Concentration and vertical distribution of plastic pieces in the Meuse

A major transport route of plastic towards the ocean is though rivers, but the data on plastic transport below the water surface in rivers are scarce. This research therefore focuses on the concentration and vertical distributions of meso- and macroplastics in the Dutch part of the Meuse, to build a database on plastic transport in the Meuse. This is necessary to create substantiated policy goals. Samples were collected using trawl nets at three different depths (surface middle bottom), in Eijsden, Ohé en Laak and Sambeek, downstream of the weir.
For every sample the pieces were categorized using the OSPAR protocol, and the concentration and surface area concentration were determined. The samples were compared locally, within the same year, and temporarily, at the same location.
Both the concentration and the surface area concentration decreased going downstream from Eijsden to Sambeek. This indicates that not many plastic pieces are added to the Meuse anymore in the Netherlands and that the fragmentation increases going downstream. The vertical distribution of plastic pieces becomes homogenous at all locations when the discharge is high. In Eijsden hysteresis could affect the transport of plastic in the surface of the water column, resulting in a counter-clockwise hysteresis pattern.
The transport of plastic particles does not increase with discharge as much as the Rhine, meaning that the smaller catchment area of the Meuse becomes more easily exhausted. Moreover, discharge does not affect the degree of fragmentation.
These finding contribute to understanding of plastic transport in rivers, and it can serve as an improvement on the current protocol for future monitoring campaigns.