Title: Biofilms on Plastic Litter: Community Composition, Activity and Effects on Ecosystem Processes

https://luc.zoom.us/j/84841396469

Abstract

The rapid increase of plastic production and disposal has resulted in plastic pollution becoming a global problem. In aquatic ecosystems, plastic litter is a substrate for biofilms, but little research has simultaneously assessed its effects on biofilm activity, community composition, and ecosystem processes. Our objectives were to: (1) measure biofilm activity and community composition on plastic litter relative to a natural surface in an urban river and (2) assess the impact of microplastic pollution on the ecosystem processes of ecosystem metabolism and N₂ flux in an oligotrophic lake. For objective (1) we incubated three common plastics of distinct physical and chemical properties and wood at three size classes. Biofilm activity was similar among substrates, except respiration was greater on wood. Bacterial and algal richness and diversity were highest on foam and wood substrates compared to film and firm polyethylene. Bacterial biofilm community composition was distinct between wood and plastic substrates while the algal community was distinct on both foam and wood. Substrate size had no influence on either algal or bacterial community composition. Overall, results demonstrate polymer properties influence biofilm alpha and beta diversity, which may affect transport and distribution of plastic pollution and associated microbes, as well as biogeochemical processes in urban streams. For objective (2), we added microplastics at a range of concentrations to pelagic mesocosms. Ecosystem metabolism rates were low, as expected for an oligotrophic lake, and similar across microplastic treatments. N₂ was undersaturated in all treatments and showed no differences by microplastic concentration. Our results suggested minimal impact of microplastic

on ecosystem metabolism and N₂ flux in an oligotrophic lake. These data will be combined with results from collaborators on the larger project that assessed the role of microplastics at other levels of organization, including water chemistry, plankton, and fish. This study provides valuable insights into the effects of substrate on biofilm characteristics, the ecological impacts of plastic pollution in urban rivers, and is a novel addition to the literature as an assessment on the impacts of microplastic pollution on ecosystem-scale processes through in situ microplastic addition.