Veronica Nava

Plastics are now pervasive across all environments. Although numerous studies have investigated their chemical and toxicological effects, their role in ecological processes remains poorly understood. This contribution explores key mechanisms and presents results illustrating how plastics can influence the functioning of freshwater environments. A central mechanism is mediated by the “plastisphere”, defined as the community of autotrophic and heterotrophic microorganisms colonizing plastic surfaces and forming localized hotspots of biological activity capable of influencing ecosystem metabolism. Large-scale experiments conducted across broad geographical gradients show that the plastisphere enhances substrate availability for bacteria and microalgae, effectively acting as a novel “floating-benthic” habitat. Plastisphere biodiversity appears primarily driven by local environmental conditions, suggesting opportunistic colonization processes. Effects on ecosystem metabolism vary among sites: in more eutrophic systems, positive values of net ecosystem production have been observed, indicating a shift towards autotrophy. These findings suggest a potential role of plastics in modulating carbon cycling and broader biogeochemical processes in lake ecosystems. Despite being carbon-based materials, plastics are not yet incorporated into conceptual or numerical models of lakes as dynamic systems of carbon transformation, degradation, and emission (“active pipes”). Their inclusion may be critical depending on system characteristics and sensitivity to carbon inputs. Through plastisphere-associated processes and the release of labile carbon, plastics can alter nutrient cycling, influence food-webs, and contribute to greenhouse gas emissions. Here, we provide a conceptual framework for explicitly integrating plastics into freshwater carbon cycling, highlighting their potential role as active components of biogeochemical pathways in aquatic ecosystems.