PlAsTic effecTs on the Exchanges of nutRients and biological informatioN in aquatic ecosystems

Plastic pollution is a global environmental issue. Freshwaters are particularly exposed to the accumulation of plastic waste and microplastics. In these environments the continuous increase of plastic amount makes it an abundant and new component of the water ecosystem. As such, plastic may play a role in altering the natural ecosystem fluxes of nutrients and organisms. Plastic can in fact be a substrate for the colonization by several microorganisms, including bacteria and algae. These organisms compose a biofilm which may play an important role in altering the natural fluxes in the ecosystem. Biofilms can extract the chemicals contained in plastics, compete for nutrients with the natural algal community and exchange part of the organisms with natural sediments and water. These processes can cause the alteration of natural nutrient cycles and the natural composition of the algal community in water. In PATTERN, we will assess how the biofilms growing on plastics can compete for nutrient with natural communities and whether plastic can favor the dispersal of the organisms present in the biofilms in laboratory experiments. We will first assess these effects in simulated freshwater conditions and then we will integrate natural sediments to increase complexity. We will investigate the responses of the community regarding taxonomy and measurements of functional and physiological responses. This project may open new research questions to understand how the ecosystems will function in plastic polluted environments.

Plastic is ubiquitous in the environment with freshwater ecosystems acting as major accumulators. Here plastic can be seen as a new substantial component of benthic and pelagic habitats. As such, plastic can potentially affect sediment physical-chemical properties and energy balance, altering the natural exchange of nutrients and organisms with the water column. Biofilms surrounding environmental plastics may mobilize chemicals contained in plastics (including metals), compete for nutrients and exchange biological information with sediments and water. I hypothesize that these processes can impair natural nutrient cycles and the assembling of natural microbial communities in polluted environments. First, I will assess whether biofilms growing on plastics can utilize nutrients present in the ageing polymer matrix and whether they can affect the development of the natural pelagic microbial community through competition and exchange of organisms. Next, using germination experiments, I will study how dispersal of organisms from and to the plastic biofilm can affect the pelagic microbial community. For this, I will translocate plastics naturally or artificially coated with biofilms into microcosms containing pristine sediments and hosting a pelagic community spontaneously germinated from them. I will do this while factoring out for the effects of plastic type, ageing and biofilm origin. Changes in physical-chemical properties of sediments, alterations of fluxes of nutrients between benthic and pelagic phases, and responses in community structures and functions will be monitored. Community level responses will be analyzed through both taxonomy, trait distribution analysis and measurements of functional and physiological responses. PATTERN will possibly unfold a new avenue for addressing ecosystem-level responses to plastics, enabling to rate the influence of driving factors and to scale evidences for their actual environmental relevance.