Impacts of plastic type and surface properties on periphyton biovolume and composition under contrasting nutrient and temperature scenarios in shallow lake mesocosms.

Plastics have become pervasive pollutants in aquatic ecosystems, acting not only as contaminants but also as novel substrates for organism colonization. Periphyton communities are highly sensitive to environmental disturbance such as eutrophication and climate warming, which may interact with plastic surfaces to alter ecosystem structure and function. In this study, we examined the combined effects of temperature (ambient, +3 °C, +4.5 °C), nutrient levels (low, high), polymer type, and surface roughness on periphyton development using outdoor mesocosms, running since 2003. Warming and nutrient enrichment exerted strong and interactive effects on periphyton biovolume and community composition. Biovolume increased under both stressors, plateauing at the higher temperature level. Substrate roughness promoted biovolume accrual, particularly on highly roughened surfaces (R2), whereas polymer type had no significant effect. Community composition was primarily driven by temperature and nutrient levels, with Oedogonium, Closterium, and Fragilaria accounting for up to 70% of the compositional dissimilarity between treatments. Warming favored thermotolerant taxa such as Achnanthidium, Fragilaria, and Gongrosira, whereas Closterium and Gomphonema dominated under ambient temperature conditions. Under high nutrient conditions, generalist taxa such as Gongrosira and Cocconeis were predominant. Overall, our results demonstrate that warming and eutrophication jointly enhance periphyton biovolume on plastics, suggesting that the persistence of plastics in natural waters may reinforce periphyton colonization and alter aquatic ecosystem dynamics under global change.