Modeling the Influence of Turbulent Vertical Mixing and Polymer Density on Microplastic Distribution and Deposition in Lake Erie

Mass estimates of plastic pollution in the world’s oceans and the Great Lakes based on surface samples differ by several orders of magnitude from what is predicted by production and input rates. Here we present the first three-dimensional modeling effort in the Great Lakes to incorporate turbulent vertical mixing and non-neutrally buoyant particles representing different polymer types. A Lagrangian particle transport model is driven using output from the National Oceanic and Atmospheric Administration’s operational forecast model of Lake Erie and plastic input is released from the shoreline taking into account nearshore population. We investigate the relative contributions of advection, vertical mixing, and rise/sink velocity in this model and how these processes influence the transport and predicted 3D distributions of the different polymers. Idealized deposition is included to provide a first pass sediment deposition rate in addition to 3D mass estimates. The inclusion of vertical mixing allows buoyant particles to move below the surface and keeps some dense particles in the water column for longer periods of time before they are deposited on the lake bed. The results indicate the importance of accounting for vertical mechanisms driving movement from the surface for improved estimates of distribution and eventually exposure of organisms in the water column and in the sediment.