Investigating microplastic behaviour in a well-mixed estuary

Rivers and estuaries act as conduits of microplastic transport, linking terrestrial and marine environments: however, it is unclear to what extent estuaries act as sources or sinks for marine plastic waste. In densely populated catchments, microplastic pollution could impact human populations and natural ecosystems including through industry, domestic activities or direct exposure. An investigation into the physical behaviour of microplastic within estuarine systems will allow for a greater understanding of plastic retention and exportation to coastal and offshore environments. A high resolution 3D model (Delft D-Flow FM) of the Conwy Estuary (UK) is under development, with current and future projections of microplastic concentrations used to determine local exposure levels, residence times and temporal variability.The Conwy Estuary (UK) is a well-mixed macro-tidal, embayment type system connecting the Conwy catchment to the North Wales coast and Irish Sea – where waters are used for leisure and aquaculture. Microplastics derived from the catchment population, industry and agriculture are thought to flow into the estuary primarily from the Conwy river network. Because of this, this study will incorporate in-situ samples of microplastic concentrations in river water to be able to predict microplastic levels in the estuary with greater accuracy. Plastic dispersal simulations through particle tracking and water quality monitoring will be undertaken using known concentrations and future projections of microplastic.The results of the model validation as well as application to plastic dispersal simulations will be presented.