Effects of Urban Hydrology on Plastic Transport in a Subtropical River

Abstract

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.

Rivers as Plastic Reservoirs

“…Various hydrometeorological variables have been correlated to the mobilization, transport, dispersion, and accumulation of plastics in rivers. Examples include wind (Bruge et al, 2018;Roebroek et al, 2021a), river flow velocity and discharge (Haberstroh et al, 2021), and precipitation-induced runoff (Treilles et al, 2021). Hydrology is not only important for mobilization and transport processes, but also determines when and where plastics accumulate in river systems (Liro et al, 2020).…”

Microplastic in Water and Sediments at the Confluence of the Elbe and Mulde Rivers in Germany

“…Due to their low density, small fibres tend to occur rather close to the surface, which is reflected especially in our cascade samples. Numerous potential sources can contribute microplastics to the river, e.g., urban and industrial areas within the catchment in general and waste water treatment plants as typical effluents for fibres in particular (Kay et al, 2018;Haberstroh et al, 2021).…”

“…A comparison with rivers on a global scale remains challenging as well. Besides the complexity of fluvial dynamics, different climatic and geomorphological conditions, the occurrence and distribution of microplastics may vary strongly (Kay et al, 2018;Haberstroh et al, 2021). Nevertheless, several studies showed that rivers draining large, densely populated and industrialized catchments carry considerable loads of microplastics (Lebreton et al, 2017;Gerolin et al, 2020;Napper et al, 2021) and discharge an amount of approximately 1.15-2.41 million tonnes of (micro and macro) plastic per year into the world oceans (Lebreton et al, 2017).…”

“…Indeed, microplastics can be transported by surface run-off from agricultural areas, aerial emission from industries or application of sewage sludge, and be released from discharge of waste water treatment plants (WWTP) (Horton and Dixon, 2018;Wagner and Lambert, 2018;Sun et al, 2019;Brandes et al, 2021). Although WWTPs filter more than 90% of microplastics, they still contribute a certain share of microplastic particles to fluvial systems (Murphy et al, 2016;Horton et al, 2017;Kay et al, 2018;Schmidt et al, 2020;Haberstroh et al, 2021;Schell et al, 2021).…”

“…Consequently, the occurrence and distribution of microplastics in fluvial systems is rather complex and depends on the distribution of sources and pollutants (Kay et al, 2018;Haberstroh et al, 2021) as well as on fluvial dynamics, such as seasonality (Mani and Burkhardt-Holm, 2020) and flood events . In this context, recent studies suggest that smaller and medium-sized rivers are of crucial importance for the microplastic distribution in the whole catchment.…”