Microplastic and macroplastic dynamics along a barrier island: Matagorda Peninsula, TX

Each year, around 400 million tons of plastic waste is produced, and 15% of that is mismanaged, ending up in the environment. As plastics are sourced on land and are transported via runoff and the atmosphere, they must move through coastal environments in order to reach the ocean (theorized as the ultimate sink for plastics). Coastal sediment dynamics and final microplastic transport mechanisms to the ocean are critical to unravel the land-to-ocean plastic flux. Studies suggest that marine plastics concentrate near the coastline at years- to decade-long time scales. Matagorda Peninsula, located at the Texas coast, is a 74 km (46 mi) long barrier island. The western Matagorda Peninsula has little anthropogenic influence and it is ideal to understand coastal micro- and macroplastics dynamics. Data from 20 sediment samples across 5 beach transects, and drone images from 4, 15, and 30 m altitude, were analyzed to understand the distribution of plastic debris along a dissipative beach setting. We hypothesize that microplastics (<5 mm) will be most abundant at the landward extent of the swash zone, as they will be deposited as the wave energy dissipates/infiltrates the sand. For macroplastics, we hypothesize that they will accumulate near organic flotsam, getting trapped in the vegetation. Preliminary results show that macroplastic debris indeed associates with flotsam and is more prevalent in the storm berm to front of the vegetated dune area. The microplastics show a weaker trend across beach profiles, possibly because they are easily remobilized by swash processes and aeolian transport. These results suggest that substantial plastic debris can accumulate even in coastal environments with minimal direct human influence. This highlights the importance of coastlines as dynamic, intermediate reservoirs of plastic debris between terrestrial sources and their ultimate sink in the ocean.