Spatiotemporal patterns of plastic entrapment by the invasive water hyacinth (Pontederia crassipes Mart.) in temperate South European Rivers

The water hyacinth Pontederia crassipes Mart., native to Brazilian watercourses, has become among the most widespread and risky alien species globally. Introduced in Europe and Italy as an ornamental species, it has many detrimental effects on native biota and ecosystem functioning. However, it can filter water from contaminants, organic pollution and plastics. In central Italy, P. crassipes was first recorded in the Lazio region's Pontine plains in 1983. Given the neglect of the dispersal path, we (1) investigated the distribution along rivers in central Italy and (2) assessed plastic entrapment in small temperate rivers. Specifically, we compared recent field observations with historical records to evaluate trends in both species presence and associated macrolitter accumulation. Our findings reveal that P. crassipes spread in the Amaseno, Sisto, and Ufente rivers in agricultural land use, with historical invasions of P. crassipes in the Pontine area covering up to 20,000 m2. Recent surveys identified two new records totaling 67.2 m2 in small canal. Plastic entrapment ranged between 0.0 items/m2 and 2.2 items/m2. Precisely, the maximum plastic entrapment was found in “The small canal” (max: 2.2 items/m2) and in a canal in the Ufente river (max: 1.7 items/m2). Among polymers, PET was the dominant polymer (55.1 %), followed by EPS/PS and PO soft items (21.3 % and 16.9 %, respectively). Over the years, macrolitter density was highest in 2005 and 2024 (i.e., 1.7 and 2.2 items/m2, respectively). These results might be pivotal to understanding future actions on species eradication as well as on clean-up activities using this alien species.