144-8 Analyzing Microplastic Distributions in Fluvial Flood Sediments from Hurricane Helene, Upper French Broad Subbasin, North Carolina

Session: Microplastics in the Environment (Posters)

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Abstract:

Microplastics are of particular concern because of their pervasiveness in natural systems and unknown transport and deposition patterns during extreme storm events. Their small size allows for ease of movement through major disturbances, including heavy floods and hurricanes. However, it is unclear how deposition of these particles differs between normal conditions and storm conditions. This project aims to characterize microplastic distributions in flood sediments deposited by Hurricane Helene around Asheville, North Carolina in the Upper French Broad River Subbasin. The hurricane's extreme rainfall, estimated to have ranged from 20-30 inches across Western North Carolina, resulted in nearly 2,000 reported landslides and displaced large amounts of sediment in the French Broad and Swannanoa rivers and their tributaries. Sediment samples were collected from 4 of these tributaries in Asheville, all of which were creeks that experienced extreme flooding during the storm. Microplastics were isolated from sediment through density separation in a sodium chloride solution and vacuum microfiltration. Several fibers found in the samples underwent a hot needle test (350°C) using a soldering iron and a Leica S9D dissecting microscope and were determined to likely be plastic in origin. 3 of the 4 sites had significant white, and to a lesser degree black, fibers that were often matted together. Few fragments were found across all four samples compared to the number of fibers. Although microplastics are known to be mobilized significantly during heavy floods as suspended particles, their release and resettlement into fluvial sediments depends strongly on the mechanics and degree of riverbed disturbance. We hypothesize that the higher prevalence of microplastic fibers in these post-hurricane sediments is caused by the ability of synthetic fibers to embed themselves more securely in coarser riverbed sediments, making them less likely to mobilize to the extent of microplastic fragments. In future work, chemical composition of microplastics will be determined using laser direct infrared imaging (LDIR) to further assess implications of microplastic pollution. Findings from this study will inform patterns of distribution and deposition caused by major storms like Hurricane Helene.    

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9650

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