Dataset for "Estuaries as filters for riverine microplastics: Simulations in a large, coastal-plain estuary"

Public awareness of microplastics and their widespread presence throughout most bodies of water are increasingly documented. The accumulation of microplastics in the ocean, however, appears to be far less than their riverine inputs, suggesting that there is a “missing sink” of plastics in the ocean. Estuaries have long been recognized as filters for riverine material in marine biogeochemical budgets. Here we test the hypothesis that estuaries are a potentially large filter, or “sink,” of riverine microplastics using a model of microplastic transport in the Chesapeake Bay, a large coastal-plain estuary in eastern North America. The one-year base-case simulation, which tracks an equal number of buoyant and sinking 5-mm particles, shows that 93% of riverine microplastics are beached, with only 3% exported from the Bay, and 4% remaining in the water column. We evaluate the robustness of this finding by conducting additional simulations in a tributary of the Bay for different years, particle densities, particle sizes, and shoreline characteristics. The resulting microplastic transport and distribution was sensitive to interannual variability over a decadal (2010–2019) analysis, with greater export out of the Bay during high streamflow years. Particle size was found to be unimportant while particle density—specifically if a particle was buoyant or not—was found to significantly influence overall distribution and mean duration in the water column. Positively buoyant microplastics are more mobile due to being in the seaward branch of the residual estuarine circulation while negatively buoyant microplastics are transported a lesser distance due to being in the landward branch, and therefore tend to deposit on coastlines close to their origin. By allowing particles to beach, specifically along a partially armored coastline, and be removed from the system, distribution patterns throughout the Bay are significantly altered, with over 90% now beaching, instead of all particles exiting the Bay. The majority of deposition happened close to riverine sources, although notable beaching of microplastics along the eastern shores of the Chesapeake Bay was also seen. Despite microplastic distributions being sensitive to some modeling choices (e.g., particle density and shoreline hardening), in all scenarios the overwhelming majority of riverine plastics do not make it to the ocean, suggesting that estuaries may serve as a filter for riverine microplastics.