Environmental and socioeconomic factors impacting floating litter accumulation in streams

Freshwater litter is an increasing environmental and economic concern, yet it remains less studied than marine debris despite its role as a pathway to ocean systems. This study quantified floating litter accumulation and evaluated the influence of watershed characteristics across 30 in-stream litter collection devices distributed throughout the southeastern United States. Seven watershed variables (catchment size, annual rainfall, land cover, population size, population density, median household income, and median population age) were assessed in relation to litter accumulation rates collected throughout 2022. A total of 5149.81 kg of litter and 24,106 individual items were recorded, with plastic and styrofoam comprising the majority of debris by count. Among all variables examined, land cover classification was the strongest predictor of litter accumulation, with developed land positively associated with increased litter and agricultural and open land negatively associated. Median household income was also a significant predictor, with lower-income watersheds exhibiting higher litter accumulation rates. In contrast, precipitation and population density were not significant predictors of litter inputs across sites. These findings highlight the importance of watershed land use and socioeconomic context in driving freshwater litter accumulation. Results from this study can inform the strategic placement of in-stream litter capture devices and improve watershed-scale litter prevention and management strategies.