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Microplastic Deposition on St. Catherines Island, Georgia
Summary
Researchers collected sediment samples from beach, marsh, and washover fan environments on a Georgia barrier island and found microplastics at every location and depth tested, with fibers being the most common type, indicating that plastic contamination has penetrated deeply into even relatively undeveloped coastal ecosystems.
The discarded remains of plastics circumnavigating the globe via ocean currents and tides have been reported worldwide. Microplastics, pieces between 5.0 mm and 0.063 mm, are defined as fibers, pellets, and macroscopic pieces that are degraded into progressively smaller pieces. A growing global concern is the potential ecological and environmental impact of microplastics in the water column and in marine sediments. This study focuses on St. Catherines Island, Georgia, a barrier island located ~ 50 miles south of Savannah, Georgia. The Pleistocene island core is flanked by Holocene ridge and swale deposits and salt marsh. The island shoreline is eroding ~ 3 mm per year average except the northern end, where the island is prograding due to the presence of a large ebb tidal delta. Most microplastic studies have focused on sampling the surficial beach sediments and the water column. This study explores microplastic deposition in beach and marsh sediments of a barrier island. Samples from the salt marshes, washover fans, and middle shoreface were collected from the surface to a depth of ~25 cm in 5 cm increments. Additional samples were obtained from swales in the northern dunes. Density separation and visual inspection was used to capture and identify microplastics in the samples. Preliminary results have found microplastic in all samples. A total of 120 pieces of microplastics were found in four surficial samples, ~ 300 g of sediment each, taken from the washover fans. Microfibers have been the majority of microplastics recovered thus far and pellets the fewest. One sample contained ~ 50% microfibers compared to pellets and particles. The southern washover fans have had the highest percentage of recovered plastics at both the beach ridge and midpoint of the fan. The northern washover fans had the fewest particles at the midpoint but the beach ridge sample was comparable to the southern washover fans.