Trash, especially plastic, is a significant global pollutant affecting both populated and remote areas, including oceans and rivers. Plastic waste constitutes 60%-80% of litter in freshwater and marine environments, with increasing macrotrash emissions anticipated. The study focused on Southern California, a region with high trash prevalence due to urbanization and a Mediterranean climate, which exacerbates trash accumulation during the dry season.
The study aimed to assess the extent and types of trash in local rivers and streams, using a probabilistic design to quantify trash presence across various land uses. Findings showed that 77% of Southern California’s wadeable streams contained trash, with urban areas being most affected. An estimated 7 million pieces of trash were identified, with plastic representing 70% of the total. Key findings highlighted the correlation between trash prevalence and proximity to urban infrastructure, such as roads and parking lots, as well as human disturbance metrics.
While the overall trash extent remained similar between 2011-2013 and 2018-2019 surveys, there was a significant reduction in plastic bags, likely due to regulations implemented in 2016. This study underscores the effectiveness of management strategies in reducing specific types of trash and suggests a need for continued monitoring and targeted actions to mitigate pollution in watersheds. Future studies should also focus on trash mass for a better correlation with coastal pollution loadings.
