Sources and Deposition of Polycyclic Aromatic Hydrocarbons to Western US National Parks

Seasonal snowpack, lichens, and lake sediment cores were collected from fourteen lake catchments in eight western U.S. National Parks and analyzed for sixteen polycyclic aromatic hydrocarbons (PAHs) to determine their current and historical deposition, as well as to identify their potential sources. Seasonal snowpack was measured to determine the current wintertime atmospheric PAH deposition; lichens were measured to determine the long-term, year around deposition; and the temporal PAH deposition trends were reconstructed using lake sediment cores dated using Pb-210 and Cs-137. The fourteen remote lake catchments ranged from low-latitude catchments (36.6 degrees N) at high elevation (2900 mast) in Sequoia National Park, CA to high-latitude catchments (68.4 degrees N) at low elevation (427 mast) in the Alaskan Arctic. Over 75% of the catchments demonstrated statistically significant temporal trends in Sigma PAH sediment flux, depending on catchment proximity to source regions and topographic barriers. The Sigma PAH concentrations and fluxes in seasonal snowpack, lichens, and surficial sediment were 3.6 to 60,000 times greater in the Snyder Lake catchment of Glacier National Park than the other 13 lake catchments. The PAH ratios measured in snow, lichen, and sediment were used to identify a local aluminum smelter as a major source of PAHs to the Snyder Lake catchment. These results suggest that topographic barriers influence the atmospheric transport and deposition of PAHs in high-elevation ecosystems and that PAH sources to these national park ecosystems range from local point sources to diffuse regional and global sources.