Allocthonous detritus and algal productivity are key basal resources in freshwater ecosystems. These basal resources support primary consumers (i.e. algal grazers and leaf shredders) but also particle feeders (collector gatherers and filterers) that consume the fine particulate organic matter (FPOM) generated by primary consumers. Throughout these processes, microbial organisms form biofilms that increase the palatability of both leaf litter and FPOM. The biotic interactions underpinning these consumer chains may be threatened by global anthropogenic stressors, including climate-change-driven warming and microplastic (MP) contamination. Our study investigates the effects of temperature and MP exposure on the microbial communities, macroinvertebrates and ecosystem processes associated with FPOM production and consumption. Replicate aquarium mesocosms were subjected to one of three temperature (16, 19, 22 °C) and three microplastic exposure (0, 1000, 100000 particles/kgsediment of a polyethylene terephthalate MP fibre and fragment mixture) treatments in a fully factorial design. Each mesocosm contained leaf litter, and three tiles to support algal growth. At the start of the experiment, we added filtered stream water into the mesocosms, which were then left for 4 weeks for biofilm formation on the tiles and leaf litter. After this conditioning period, a representative grazer (Viviparus viviparus snails) and shredder (Asellus aquaticus isopods) were introduced to consume the leaf litter and algal resources, and produce FPOM. Finally, we add deposit-feeding Chironomus riparius midge larvae as a model collector-gatherer consumer of FPOM. We assessed effects of temperature and MP exposure on the survival, growth and development of our model grazer, shredder and collector-gatherer, as well as effects on microbial abundance, and on other processes including ecosystem respiration and decomposition.