Microplastics in an aerial insectivore and aquatic emergent insects: observational and experimental field studies

marine megafauna, however knowledge on plastic litter in terrestrial and aquatic systems is less understood. The focus of plastic pollution has shifted from macroplastics (> 5 mm in diameter) to microplastics (MPs; plastic particles < 5 mm). MPs come in various morphological forms such as fibres, fragments, spheres and foams and can be either primary (manufactured MPs) or secondary (larger plastics broken down into smaller ones). MPs can be transported throughout and across ecosystems, reaching nearly every corner of the planet. With millions of tons of microplastics released into the environment annually, it is critical to understand their fate and effects they can impose on biota. Moreover, MPs can move within and among habitats, potentially providing additional pathways of effects on fauna. Microplastics are ingested by benthic invertebrates, such as aquatic emergent insects. Emergent insects in their larval stages live and feed in the sediment of freshwater systems before emerging into flying adults, where they become prey for terrestrial predators, such as the tree swallow (Tachycineta bicolor). Consequently, aquatic emergent insects provide a link between aquatic and terrestrial ecosystems and could thus be biotransporting microplastics from water to land. I investigated two key components of potential MP bio-transport: a) MP ingestion by aquatic emergent insects subjected to MPs in a mesocosm experiment; and b) the presence of microplastics in fecal sacs collected from tree swallow chicks. Insects were collected at the International Institute of Sustainable Development Experimental Lakes Area, in northwestern Ontario, Canada, where my research was part of a large, whole-lake MP dosing experiment to investigate the fate and effects of MPs on aquatic biota. Twelve open-bottom mesocosms were dosed with a known concentration of MPs, and emergent insects were collected at the surface water for 8 weeks. Insects from the groups Chironomidae and Ephemeroptera ingested microplastics (0.021 ± 0.10 and 6.25 ± 5.91 MP/insect, respectively), and chironomids ingested more MPs when exposed to higher concentrations. My findings show that emergent insects exposed to MPs in their larval stages in a natural setting have the potential to carry those MPs to the terrestrial ecosystem after emergence. In the second chapter of my thesis, I studied MP ingestion by tree swallows in two habitat types in Nova Scotia and New Brunswick, Canada; birds foraging over an agricultural site and birds foraging over salt marsh. Fecal sacs collected from both sites contained suspected microplastics (SMPs) (1.02 ± 1.15 and 1.40 ± 1.46 SMP/fecal sac at the agricultural site and saltmarsh, respectively), though no differences were detected between the two sites. Only microfibers were found in the fecal sacs from both sites. While I conclude that tree swallow chicks are ingesting SMPs from the environment, likely from their prey, my findings do not strongly suggest that tree swallow fecal sacs are optimal for biomonitoring MP pollution in their habitat. Through my two chapters, I show plastic ingestion occurs in key components of different trophic members in a food chain, highlighting the complexity of the movement of MPs, and warranting further research into the interface between two linked ecosystems.