GPS-Tracked Bottles in North American Rivers Show Marine Plastic Pollution Can Originate from Far Upstream

Rivers act as both major pathways for marine plastic pollution and as important features for the storage and burial of plastic pollution. To better understand plastic emissions from watersheds to the ocean, we measured retention and remobilization of floating plastic bottles in rivers using Global Positioning System (GPS) tracking across 30 river reaches in 7 coastal watersheds throughout the United States and southern Canada. Movement data revealed that mobilization events and travel distances were related to river discharge, reach geomorphology, and upstream land cover. Bottles moved an average of 6.1 km (min. 73 m, max. 53.5 km) over a mean deployment period of 87 days. Bottle mobilization events were related to specific stream power and the time a bottle remained lodged prior to a high-flow event. Mobilization distance increased with discharge, decreased with forest cover, and increased with urban cover (all with p < 0.001). A probabilistic model estimated that 50% of bottles that reach the ocean or the Great Lakes in any given year originated from more than 15.7( ± 0.8) km inland and up to 200 km. Our results suggest that cleanups and efforts to prevent plastic pollution from entering urban rivers in coastal watersheds are vital to help curb ever-increasing marine plastic pollution.