A Continuous Approach to Macrolitter Monitoring in Large River Systems: Identifying Sources, Drivers, and Quantities

Anthropogenic macrolitter (ML) in rivers affects ecosystems and human health. A custom-built, interception-based litter trap (LT) passively collected ML in the Rhine River, one of Europe’s largest river watersheds, continuously, over a one year-long sampling period. The LT, anchored in Cologne, captures floating ML >4.24 cm without disturbing shipping traffic. This location covers 90% of the rivers total length, including the rivers tributaries. By systematically covering the discharge range of an entire year that did not included extreme floods, the dataset, with information on ML composition and sources, was correlated with five environmental factors. Plastics made up the largest share of ML among all 10 monitored material types, which may affect water quality. The detailed monitoring revealed 145 EU Marine Strategy Framework Directive ML list (MSFD list) categories in the Rhine. Untraceable items account for 36.0% of the total ML, with fragments making up 30.6%. The sources of 64.0% of ML were identified, with private consumers responsible for the largest share (56.0%) of land-based ML. Single-use items contribute 40.4%. Based on the continuous data, discharge and precipitation affect riverine ML numbers. A linear extrapolation scenario estimates that around 53,000 ML items are transported in the Rhine at Cologne every day.