Ozone in Great Smoky Mountains National Park: Dynamics and effects on plants

Ozone is the most widespread phytotoxic pollutant in the United States, and the National Park Service is concerned about its effects on plants and ecosystems in a number of parks. In Great Smoky Mountains National Park (GRSM), ozone and other meteorological parameters are monitored on a continuous basis throughout the year at two permanent high elevation sites (Look Rock and Cove Mountain), and at a lower third site during the growing season (Twin Creeks). Ozone is chronically elevated at higher elevations, with higher maxima and minima as compared to the lowest site, but diel (24 hr) fluctuations are more pronounced at the lowest site. Mean ozone concentrations average 90% and 47% at Look Rock and Twin Creeks, respectively, as compared to those at Cove Mountain, the highest site in the park. The number of episodes (periods where at least one hour is greater than 70 ppb) is greater at higher elevations. There have been no exceedences of the 120 ppb NAAQS in the last four years (1987-1990) at any site. A total of 95 species have been shown to exhibit foliar symptoms in the field consistent with putative ozone damage, and 39 species, 28 of them with field symptoms of ozone damage, have been fumigated at the Twin Creeks facility. Of the 28 that showed damage in the field, 25 have shown injury which tends to verify that the symptoms seen in the field was induced by exposure to ozone. Approximately 1/3 of the 39 species tested were classified as sensitive to foliar injury, another 1/3 were moderately sensitive, and the rest showed no symptoms at all. Sensitive species showed foliar loss, reduced diameter growth, and some reductions in biomass accumulation in the fumigation system in response to elevated ozone treatments. Other species showed little or no biomass responses to ozone, even after several seasons of fumigation. It appears that ambient levels of ozone may be having both overt and subtle effects on the vegetation and ecosystems contained within GRSM.