Riparian vegetation entraps macroplastics along the entire river course: implications for eco-safety activities

Abstract

Macrolitter, with a focus on plastics, causes detrimental effects on freshwater biota affecting human health. Although rivers are of particular interest as they carry macroplastics from the land to the seas, most plastics remain stuck into the fluvial ecosystem, accumulated in infrastructure, river sediment, aquatic plants, and riverbank vegetated areas. However, those studies focused mainly on the river’s lower zone near the sea, neglecting the role of vegetation in entrapping macrolitter on riverbanks. Thus, for the first time, we aimed at quantifying the entrapment of plastics by riparian vegetation along the entire river rod. To do so, we sampled riparian areas along six rivers in the three riverine zones (i.e., upper, middle, and lower course) in central Italy. Overall, we found 1,548 macrolitter items on ~300 m² of sampled riparian areas, with riparian vegetation entrapping 93.9% of total litter. Riverbank and riparian vegetation plastics were correlated. We emphasized the trapping efficiency at the species level highlighting that vegetation entrapped plastics along the up, middle, and lower river zones. The best plastic trapper species were trees and shrubs (Populus spp., Salix spp., Rubus ulmifolius, Phragmites australis, and Ficus carica), blocking 85.4% of the total macrolitter entrapped by plants. All the species mostly blocked: (i) plastic pieces, (ii) plastic bags, (iii) plastic bandages, (iv) sanitary and hygienic towels, and (v) plastic packaging. Among river zones, plants in the river’s lower course entrapped more macrolitter than in upper and middle zones. Moreover, well-vegetated and higher diversity of small and medium-sized rivers contribute to blocking plastics. Thus, as the role of riparian vegetation in entrapping macrolitter shows high potential as an ecosystem service, further studies should investigate riparian vegetation characteristics and community structures involved in the plastic entrapment process. These advances might be key for conservation and mitigation strategies aimed at the ecological integrity of riverine ecosystems.