Plastic hotspot areas in riverine habitats: Riparian vegetation diversity and structure entrap riverine plastics

Abstract

Plastics are a significant environmental problem, accumulating in ecosystems and causing harmful effects. While macroplastics in rivers have only recently gained attention, most studies focus on their transport to the sea, neglecting the fact that plastics often remain within fluvial systems. Previous research has primarily considered abiotic factors in this transport process. However, recent findings indicate that vegetation plays a crucial role in trapping plastics in urban and lowland watercourses. The role and structure of riparian vegetation in plastic entrapment are poorly understood. This study investigates the relationship between vegetation structure and plastic entrapment applying the 3D Vegetation Index (3DVI) to quantify vegetation complexity and its capacity to trap plastics. Field data on plastics and vegetation were collected from six rivers in central Italy across three riverine zones. Results show a significant correlation between macroplastics trapped in vegetation and vegetation structure, with denser and more diverse plant communities trapping more plastics. Particularly, a significant regression between 3DVI and plastics in vegetation was observed only in the lower river zone. The higher the 3DVI value, the more complex the vegetation, indicating greater plastic trapping efficiency. These findings suggest that biotic factors, particularly vegetation structure, are important variables for driving riverine plastic entrapment at local scales. This study is the first to apply a vegetation index to describe the complexity and diversity of plant communities related to plastic entrapment. Future research urgently needs to unveil this phenomenon at a global scale as well as to focus on the interactions and effects of macroplastics on plants. Understanding plant structures and 3DVI usage in retaining plastics can help identify plastic hotspot areas and inform mitigation and clean-up efforts to address plastic pollution effectively.