Postdoctoral Fellowship: OCE-PRF: Influence of Environmentally-Induced Changes on the Transport and Fate of Microplastics at a Regional Scale

Plastic in the ocean breaks down into small pieces known as microplastics due to weathering by environmental conditions. Microplastics are increasingly pervasive and harm the ecological health of coastal areas, so it is important to understand where they are and how they are transported by coastal flows. As microplastics are exposed to varying environmental conditions (e.g., light, oxygen, and sediment abrasion), they fragment into smaller pieces and facilitate the growth of organic matter. These transformations affect how easily microplastics remain suspended in the water column. Yet, it is not known how these transformations impact microplastic transport at regional scales. This project will investigate when, where, and how much microplastics are exposed to conditions that lead to changes in their density, size, and shape. Additionally, this project will quantify how exposures to varying environmental conditions impact the dispersion and fate of microplastics at a regional scale. The increased understanding of microplastic transport that will result from this project will be useful for informing policy decisions and cleanup efforts. Over the course of the project, the PI will also engage in outreach to local schools and mentoring of university students. The objective of this project is to better understand how microplastic transformations impact their transport on regional scales. First, the PI will use Lagrangian tracers representing microplastics and existing model output to quantify the exposure of microplastics to conditions that cause weathering or biofouling. Specifically, use of output from an existing hydrodynamic-sediment transport-biogeochemical model for the northern Gulf of Mexico will be used to estimate microplastic exposure to light, sediment abrasion, and other environmental conditions. Second, microplastics will be added to the numerical model described above as a sediment class, and new model runs will be used to analyze how environmentally produced changes in microplastic properties impact their dispersal and fate. To represent microplastic transport, their settling velocities and critical shear stresses for erosion will be parameterized as a function of their exposure to different environmental conditions. For both parts of the project, sensitivity tests will be performed to evaluate the uncertainty of model results. Overall, this approach will allow us to better understand how microplastic transport on regional scales is influenced by particle transformations due to environmental conditions, which is important for future microplastic management efforts and therefore for preserving coastal ecosystems that provide food, recreation, and tourism for society. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.