Impacts of Stormwater and Land Cover on the Abundance, Transport, and Composition of Anthropogenic Litter in Urban Watersheds

Anthropogenic litter (AL; trash) is defined as any manufactured item that ends up in the environment. AL consists of many different materials including glass, metal, and plastic, the latter of which typically represents a dominant constituent and has been a major focus of research. Plastic litter and other AL types are pervasive to all types of ecosystems, are persistent in the environment, and are increasing. Rivers are a major conduit transporting AL to oceans. However, rivers also retain and transform AL. More research is needed to understand AL dynamics within rivers, which will improve global models of AL movement and distribution. This work examined AL and plastic transport dynamics in rivers spanning a gradient of watershed positions and land cover types. In the first study we used cameras to quantify macroplastic movement in rivers before, during, and after floods (N=18 individual flood events at 10 locations in 3 different watersheds). Across all sites, macroplastic count during floods was positively related to both flood speed and magnitude. In our second study, we quantified the relationship between watershed land cover and watershed position on AL abundance and assemblage. We examined these relationships for both mass and number of particles. We found that the best predictors of AL by count were impervious surface and urban area. The relationships with AL mass were less clear. AL in the floating and overhanging zones was significantly different than AL found in the benthic and riparian zones. This is likely due to a difference in transport dynamics between low-density AL and high-density AL. These results will contribute to predictive models of macroplastic transport, which will help inform management and policies aiming to reduce freshwater macroplastic pollution.