CAS-MNP: Evaluating Patterns and Controls on Microplastic Accumulation in Floodplains

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Plastic accumulation in the environment is a pervasive global problem with severe consequences for organisms, ecosystems, and human health. Plastics behave like natural materials in the environment in that they are degraded to form smaller particles including microplastics (fragments 5 mm in length). These plastic particles are transported by conventional geomorphic processes including wind and water. The degradation and transport of plastics has led to its accumulation across a range of environments, providing the basis for a global plastic-carbon cycle. However, a key component of the plastic-carbon cycle — namely the transport and storage of microplastics through rivers and floodplains — remains poorly constrained. Understanding where and why plastics accumulate along rivers and floodplains is critical for mitigating and managing plastic pollution because rivers connect plastics production and use upstream to coasts and the open ocean. This project will analyze soil samples to quantify the amount and types microplastics found in different floodplain environments, and relate patterns of plastic accumulation to environmental parameters. The team will co-develop and deliver bilingual educational materials on plastic transport through watersheds for high school students as part of the Beach Sisters program in Lynn, Massachusetts, an environmental justice community. The project will provide mentored research opportunities for an undergraduate and graduate student and support an early career researcher.Floodplains serve as critical sinks for sediments, carbon, and pollutants, but their role in the global plastic-carbon cycle is poorly understood owing to the unique material properties of plastics, and the complex and dynamic processes that mediate floodplain sedimentation. The same geomorphic processes that control floodplain sedimentation should mediate microplastic accumulation in these environments, although the relatively low density of common plastics (~0.05 to 1.5 g/cm3) relative to natural sediments (~1.4 to 2.9 g/cm3) imply that patterns of plastic erosion and deposition across a floodplain will be unique. This project integrates field-based surveys and sampling with geochemical analyses and hydraulic modeling to test a series of hypotheses describing the interaction of flood inundation, flow velocity, geomorphic setting, and the physical and chemical properties of plastics on their accumulation in floodplains. The study will allow the investigators to build a comprehensive model of where and how plastics accumulate across the geomorphic units of a floodplain, providing a basis to quantify microplastic storage along other river-floodplain corridors. More broadly, the project will allow them to test the suitability of settling velocity models developed for natural sediments on plastic particles with different material properties in an observational setting.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.