Yael Lewis, MSc Candidate, Orihel Lab The effects of microplastics on zooplankton and emerging insect communities in a littoral limnocorral experiment Although microplastics research has rapidly accelerated in the last few years, our understanding of their effects on freshwater invertebrates, particularly under environmentally relevant conditions, remains limited. Using in-situ limnocorrals at the International Institute for Sustainable Development – Experimental Lakes Area (IISD-ELA), we investigated the effects of a microplastic mixture on zooplankton and emerging insect communities. We installed 12 open-bottom limnocorrals in the littoral zone of a boreal lake in June of 2022 and added an environmentally relevant range of microplastic concentrations in a regression-based design. Our microplastic mixture consisted of distinctively coloured polystyrene, polyethylene, and polyethylene terephthalate fragments in equal parts by count, manufactured with common plastic additives. I sampled the zooplankton and emerging insect communities pre-addition and every week thereafter for the 8-week duration of the experiment. To evaluate possible longer-term effects, I sampled the emerging insect community again in May of 2023 over the partially enclosed bases of the limnocorrals. I assessed the relationship between nominal microplastic concentration and the abundance and community composition of zooplankton and insects. Microplastic concentration was negatively related to total zooplankton abundance at weeks 1 and 5 post-addition and drove changes in community composition at week one. Evidence for microplastic effects on the emerging insect community was more limited – microplastic concentration was negatively related to insect emergence only at week 2, and the total seasonal emergence exhibited only a weak relationship with microplastic concentration. There were no effects of microplastic on insect community composition. I anticipate my results will inform policy regarding ecological risk thresholds for microplastics in freshwater ecosystems.
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