CHARACTERIZING MICROPLASTIC POLLUTION IN MAMMOTH CAVE NATIONAL PARK

Lint contamination from visitors’ clothing is a well-known issue in tourist caves. Mammoth Cave National Park hosts 2 million visitors each year and has taken important steps to mitigate cave lint including installing path barriers, periodic vacuuming, and hosting annual “lint camps” to remove lint. Nevertheless, the potential for this lint to be transported into cave streams and the degree to which it contributes to microplastic pollution in cave ecosystems has not been extensively studied. To examine the effects of ecotourism and microplastic (MP) contamination within this delicate karst ecosystem, we attempted to quantify MP pollution in Mammoth Cave National Park.

Using a peristaltic pump, we filtered water from two streams within the cave through sequential filters of 1 mm, 332 μm, and 102 μm pore sizes. Sampling sites were chosen based on proximity to touristed routes and to control for reverse flow events from the Green River, in which surface stream water flows into cave springs after heavy precipitation. Echo River is more isolated from the park tourist operation, and not affected by reverse flow, while the River Styx flows close to several tour routes and receives water from the Green River during reverse flow conditions. The Green River was sampled upstream and downstream of the spring where cave water flows out of the cave into the river. Sediment from River Hall, a touristed path, was also taken. MPs counted were categorized by morphotype as films, fragments, or fibers. The predominance of fibers (between 54-79%) may indicate textiles from cave lint as a primary source of MPs into the cave. However, the Green River samples yielded the most MPs/L (2.24 MP/L), compared to counts from cave streams, which varied between 0.66 MPs/L to 1.08 MPs/L. The MP concentration of the sediment sample (1.9 MPs/g) indicates accumulation of MPs in a location frequented by tour groups. The slight increase of MPs into the cave after reverse flow may indicate the Green River as a source of MPs in addition to tourists. Overall, the Green River and tourists appear to contribute MPs to the cave. Understanding transport mechanisms is essential to effectively controlling these ubiquitous contaminants.