Modeling river and urban related microplastic pollution off the southern United States

The enclosed basin surrounding the Southern United States (the Gulf hereafter) faces increasing threats from microplastic (MP) pollution especially in its northern region. A Lagrangian particle-tracking model coupled with a high-resolution circulation model is used to investigate the short-term (30 days) transport of MPs in the northern Gulf over three years. The particle-tracking accounts for MP size and density and incorporates the influence of Stokes drift on floating MPs. Particle density is key in determining the distribution of settled MPs, with limited effects on non-settled MPs. The impact of Stokes drift on floating MP is negligible. River-sourced MPs emerge as dominant contributors to pollution. The simulated MP dispersal patterns are then linked to habitats and marine protected areas. A prominent accumulation zone is found west of the Mississippi River Delta, which overlaps with ecologically and economically important marine habitats, including Kemp’s ridley sea turtles, red snapper and bottlenose dolphins.