High macroplastic pollution in a subtropical urban lake affects macroinvertebrate community structure

Abstract Plastic pollution in freshwaters is globally ubiquitous, yet compared with marine ecosystems, little research has explored the ecological impacts of macroplastic debris in freshwater, particularly in tropical and subtropical waterbodies. We aimed to examine the effects of macroplastics on benthic invertebrates, since these taxa are often sensitive to environmental change, and can both indicate and cause broader ecological responses. We hypothesised that macroplastics would have significant structuring effects on benthic invertebrate communities, particularly through the addition of hard substrate, resulting in community compositions on plastics distinct from those in sediments. To test this, we sampled macroinvertebrate communities from both plastics and lake sediment in Dhanmondi Lake, a heavily polluted urban lake in central Dhaka, Bangladesh. We found significant differences between the macroinvertebrate communities in plastic and underlying sediment. Sediment samples contained more scrapers, particularly snails, whilst plastic samples contained more collectors, including Naididae and Chironomidae. Although different taxa dominated communities in plastics versus sediments, there was no difference in overall taxonomic richness between the two substrates. These effects on macroinvertebrate communities could alter ecosystem functioning, and highlight the pervasive impacts of plastics on aquatic ecosystems. We emphasise the need for better waste management to minimise further habitat degradation.