###### Abstract
While the impacts of plastic pollution on freshwater systems remain understudied compared to marine environments, recent evidence suggests that microplastics induce similar disruptions to microbial community structure and function by shifting microbial diversity [50; 51; 52; 53; 54; 55]. For example, in riverine systems, increased relative abundance of nitrifying bacteria in plastic-associated bacteria [56] may increase nitrification in sediments and wastewater effluents [35], creating nitrification hotspots in affected streams and sediments. Alterations in nitrogen cycling from shifts in sediment microbial communities may cascade to impact primary production, trophic structure, and water quality, underscoring the importance of the bentnos in whole-ecosystem dynamics. Further, because different plastics have unique impacts on nitrification and denitrification activity [57], it is critical to investigate multiple polymers rather than treating \"plastic\" as a single pollutant [58]. Plastics vary substantially in their chemical composition and physical properties, both of which influence fate and environmental impacts. While many types of plastics have been identified in freshwater bentnos, polymers are not equally distributed and may therefore have different impacts on ecosystem function. Polymers with a higher material density, like synthetic microfibers, (e.g., polyester, nylon), polyvinyl chloride (PVC), and tire wear particles comprised of butylated rubber are among the most commonly reported materials in nearshore sediments [59; 60; 61]. Fibers have been found in quantities as high as 34,000 fibers kg-sediment dry weight\({}^{-1}\) (kg-dw\({}^{-1}\)) [62] in the Great Lakes basin. Despite being one of the most commonly reported polymers and with a substantial recent investigation into microfiber transport pathways [5; 63; 64; 61], little is known about ecosystem impacts in freshwater environments. PVC is another plastic of concern due to its high material density and frequent use in construction materials that may release significant microplastic particles over time [65]. PVC may negatively affect bioturbating organisms [66] and reduce denitrification [57] in marine ecosystems, and shift both denitrification and nitrogen fixation rates in freshwater systems [36; 67]. Tire wear particles have been found at densities up to 5500 particles kg-dw\({}^{-1}\)[60]. Despite rising concern about toxicity and ecosystem impacts [68; 69; 70; 71], the full effects of butylated rubber particles on aquatic environments remain unclear. By evaluating how the ecological impacts of different plastics vary within the same system, we can better understand risks and generate a more targeted policy. In this study, we use a microcosm approach to evaluate the impacts of three commonly identified consumer microplastics--polyethylene terephthalate microfibers from clothing (PET); styrene-butadiene rubber (SBR) \"crumb rubber\" from tires and athletic turf fields; and PVC particles from construction material--on carbon, nitrogen, and phosphorus cycling, community metabolism, benthic microalgal abundance, and microbial community structure and function. This work adds to our growing holistic understanding of microplastic pollution in freshwater systems.