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Abstract Plastic litter is a globally pervasive pollutant. Storms are likely key drivers of plastic transport to oceans, but plastic transport during rising and falling limbs of storm hydrographs is rarely measured. Measurements of plastic movement throughout individual storms will improve watershed models of plastic dynamics. We used cameras to quantify macroplastic movement (i.e., particles > 5 mm) in rivers before, during, and after individual storms (N = 18) at 10 sites within three North American watersheds. Most storms showed no difference in macroplastic transport between rising and falling hydrograph limbs or evidence of hysteresis (transport rate range = 0–236 items/30 min). Total macroplastic exported during storm events was positively related to storm magnitude and was greatest at more urban sites. Thus, macroplastic transport during storms was driven by storm size and land use. The quantitative relationships between macroplastic movement and hydrology will improve discharge‐weighted calculations of macroplastic transport which can benefit modeling, monitoring, and mitigation efforts. Practitioner PointsMacroplastic particles (i.e, > 5 mm) are both retained in urban streams (e.g., in debris dams), and move downstream during baseflow and stormflow conditionsStorm flows are key periods of macroplastic transport: transport rates are higher on both rising and falling limbs of storm hydrographs relative to baseflow.The amount of macroplastics moving during storm flows is positively related to storm intensity.The predictive relationships generated between storm flow and macroplastic transport will improve estimates of annual export, and policies for macroplastic pollution reduction. 

Microplastics are widespread in the environment, including in the bodies of freshwater fish, with their concentrations influenced by factors such as proximity to point sources, such as wastewater treatment plants (WWTPs), and trophic level. However, few studies have simultaneously assessed the combined effects of these factors on microplastic abundance in urban stream fish. To do so, we measured microplastics and assessed trophic level via N stable isotope (δ15N) content in 6 species of small-bodied fishes (species = Lepomis macrochirus Rafinesque, 1819, Neogobius melanostomus [Pallas, 1814], Fundulus notatus [Rafinesque, 1820], Pimephales notatus [Rafinesque, 1820], Notemigonus crysoleucas [Mitchill, 1814], and Dorosoma cepedianum [Lesueur, 1818]) collected upstream, at, and downstream of a large WWTP in Chicago, Illinois, USA. Additionally, we analyzed stomach contents for 2 of these species (L. macrochirus and N. melanostomus). Four of the six species exhibited δ15N enrichment at and downstream of the WWTP, indicating prolonged residence times at the study sites (i.e., several weeks). Stomach contents of the 2 species measured supported this pattern, showing high chironomid consumption at the WWTP and variable stomach contents elsewhere. For microplastics, 1 species had higher concentrations near the WWTP, but microplastic concentrations did not differ among locations in the other 5 species. We found no evidence of a relationship between δ15N enrichment and microplastic concentration. Overall, the stable isotope and stomach content results suggest a strong relationship of WWTP effluent with fish diet but not with microplastic concentrations in fish. The results suggest that microplastic concentrations in fish is are shaped by interacting, species-specific factors including behavior (i.e., movement and foraging) and physiology (i.e., egestion rates and feeding mechanisms), in addition to proximity to point sources. Our study highlights the complexity of microplastic infiltration into food webs and underscores the need for further research to disentangle the drivers of microplastic accumulation in aquatic organisms.