Macroplastic accumulation across different surface covers, a case study of two South African rivers

Abstract

Plastic pollution in freshwater ecosystems is an escalating global concern, yet riverine macroplastic pollution and dynamics remain poorly understood in Southern Africa. This study investigated macroplastic accumulation across different surface covers in two rivers with contrasting anthropogenic inputs. We hypothesised that wood jams in the current study would contribute to high macroplastic loads across Bloukrans and Palmiet rivers and that the polymer composition of plastics would be diverse across all four surface covers. A total of 452 macroplastic items were collected, with significantly higher loads recorded in the Bloukrans River (3.5 items/m2; 93.3 g/m2) compared to the Palmiet River (0.8 items/m2; 10.1 g/m2). Multilayer plastics and soft polyolefins dominated across both rivers, particularly in herbaceous vegetation and wood jams. Significant differences were observed in macroplastic loads between rivers and among surface covers for Palmiet River. The increased macroplastic loads in the Bloukrans River were associated with untreated municipal effluent, stormwater runoff, and informal waste dumping, while in Palmiet River, macroplastic pollution was mainly linked to recreational littering and runoff. Wood jams emerged as an effective hotspot for macroplastic debris. These findings highlight the critical role of surface cover in enabling macroplastic accumulation and distribution thus the study further calls for targeted waste management, cleanup operations, and riparian protection strategies to safeguard river health and resilience in Southern Africa.