Effects of Urban Hydrology on Plastic Transport in a Subtropical River

Temporal and spatial variability are thought to drive river plastic transport, but most field data collections are limited to sporadic sampling at one location, constraining our ability to predict plastic pollution accurately. In this study, we assessed the impact of seasonal and longitudinal variability on river plastic loads collected during 18 months in Florida (USA). We used multipoint cross-sectional sampling, coupling a 500 μm Neuston net with an Acoustic Doppler Currency Profiler at three sites along the river, followed by laboratory measurements and Raman spectroscopy characterization. Annual plastic loads were highly variable, with median values of 1.67 × 109 particles (coefficient of variation CoV 89%) or 1.01 tons (CoV 203%) at the river mouth. The impact of urban pollution was evident and persistent in urban sections of the river, where plastic loads were found to be concentration-limited. Drivers of plastic pollution varied along the river; rainfall seasonality dictated transport in the least urbanized sub-watershed, but anthropogenic factors played a greater role in the urban sites. This study is one of the first to shed light on interconnections between plastics, river flow components, and rainfall. Understanding these mechanisms driving plastic pollution provides a tool to manage and reduce plastic in rivers.