What a load of rubbish: The impact of anthropogenic litter on urban freshwater diversity

The abundance of anthropogenic litter (AL) in aquatic environments is an increasing global problem. Most research on the effects of AL has focussed on marine environments, with research examining the ecological effects of AL in freshwater ecosystems largely missing. Our study examines the impacts of AL on macroinvertebrate diversity in two urban freshwater systems in West Yorkshire, in the United Kingdom. Two urban river and two canal reaches were surveyed for macroinvertebrates from the bed sediments of riffles (in a river), open water and macrophyte habitats (in a canal), and AL items (from both freshwaters). We found higher local taxonomic richness and differences in community composition in 1) the bed sediments of riffles compared to AL items within urban rivers, and 2) open water and emergent vegetation than AL items within our canal reaches. Taxonomic richness was higher on metals and plastics in urban rivers than canal reaches, and macroinvertebrate community composition was distinct between AL types (e.g., fabrics and metals, plastics and polystyrenes), possibly due to differences in structure, shape and texture. AL items in both urban freshwaters supported unique taxa, indicating that AL items may provide a habitat for macroinvertebrates where physical habitat complexity is poor. The restoration of natural physical habitat and removal of AL should be a key priority for freshwater conservation. However, rinsing AL items prior to removal during litter clean-ups is essential to minimise any potential macroinvertebrate loss. In urban freshwaters, physical habitat could be increased by gravel augmentation, installing large wood or boulders.