###### Abstract  
Plastic debris is a growing threat in freshwater ecosystems and transport models predict that many plastics will sink to the benthos. Among the most common plastics found in the Laurentian Great Lakes sediments are polyethylene terephthalate (especially fibers; PET), polyvinylchloride (particles; PVC), and styrene-butadiene rubber resulting from tire wear (\"crumb rubber\"; SBR). These materials vary substantially in physical and chemical properties, and their impacts on benthic biogeochemistry and microbial community structure and function are largely unknown. We used a microcosm approach to evaluate the impact of these three plastics on benthic-pelagic coupling, sediment properties, and sediment microbial community structure and function using sediments from Iondequit Bay, a major employment of Lake Ontario in Rochester, New York, USA. Benthic metabolism and nitrogen and phosphorous cycling were all uniquely impacted by the different polymers. PET fibers and PVC particles demonstrated the most unique effects, with decreased ecosystem metabolism in sediments containing PET and greater nutrient uptake in sediments with PVC. Microbial diversity was reduced in all treatments containing plastic, but SBR had the most substantial impact on microbial community function, increasing the relative importance of metabolic pathways such as hydrocarbon degradation and sulfur metabolism. Our results suggest that individual polymers have unique impacts on the benthos, with divergent implications for ecosystem function. This provides deeper insight into the myriad ways plastic pollution may impact aquatic ecosystems and will help to inform risk assessment and policy interventions by highlighting which materials pose the greatest risk. micoplastic; nutrient cycling; freshwater lakes; sediment; microbial community structure and function +
Footnote †: journal: water especially for buoyant plastic debris. Modeling studies [10; 11; 12] and field observations suggest that plastic debris behaves differently in freshwater systems than oceans: rather than accumulating in a large floating \"patch\" [7], debris distribution in the Great Lakes is determined by source location and transport [8; 13; 14]. Plastic ultimately accumulates nearshore in the bentnos and on beaches, in concentrations that can be >10,000 particles kg\({}^{-1}\)[15; 16; 17; 18]. Further, plastic began accumulating in the bentnos of Lake Ontario, the terminal lake of the Laurentian Great Lakes system, between 20 and 40 years ago [16], with largely unknown impacts to the ecosystem. Freshwater benthic ecosystems are highly diverse and critical in regulating trophic dynamics and recycling and removing carbon and other nutrients [19]. These functions are largely driven by a diverse community of benthic microbes, but contamination to sediments may alter microbial community structure and function, with cascading effects [20; 21; 22; 23] and the potential to disrupt ecosystem services like water purification and climate regulation. In the environment, plastics are subject to conditions that may alter their physical and chemical properties (e.g., microorganisms, UV exposure, water-borne contaminants), influencing fate and subsequent impacts. Microplastics impact microbial diversity and function in soils [24; 25; 26], marine sediments [27; 28; 29; 30; 31; 32; 33; 34], and sewage sludge [35; 36; 37; 38]. The distinct microbial composition on plastic surfaces often differs from communities in the surrounding environment [28; 39], may accumulate toxins or pathogenic microbes [40; 41; 42; 43; 44; 45], and shift ecosystem processes in the water column and sediment. Potential impacts to key processes, like carbon and nitrogen cycling [36; 46; 47; 48; 49], require further investigation to fully understand how microplastics alter ecosystem function and microbial community structure in the bentnos of the Great Lakes.