Lichens and Air Quality in Big Bend National Park, Texas

Abstract

This study was undertaken because of reports of decreased visibility due to haze and the possibility of increased air pollution in the park. Numerous localities where lichens had been collected 10 years ago were revisited in 1980 to look for any changes in the lichen flora. Photographs were taken from scenic vistas where photographs had been taken earlier. Permanent photographic points for lichens were established for long term monitoring. It is argued that fruticose li- chens are just as useful for monitoring air quality in arid areas as in wetter areas. There has been no loss of lichen species at any locality over the past 10 years and haze conditions have not changed much. It is concluded that no significant increase in air pollution has occurred within the park over the past 10 years. In 1966, 1969 and 1970, complete lichen collections were made at 38 localities in Big Bend National Park. Label data for all collections are stored in a computer data base at the University of Minnesota (Wetmore 1979) and a report on the macrolichens (foliose and fruticose lichens) from these localities has been published (Wetmore 1976). Even though the general climate in the park is quite dry, several species of fruticose lichens were found at numerous localities in the mountains. At the time these collections were made, color photographs were taken from various scenic vistas throughout the park. Recent observations by various people have reported the visibility in the park has been degraded due to increased haze conditions. There has also been concern that the haze might be associated with air pollutants that could damage the vegetation of the park. Possible sources of the air pollution are Carlsbad, New Mexico, and El Paso, Texas, These cities are about 400 km northwest of the park and wind patterns are such that air masses from these cities could blow into the park. Lichens are slow growing and remain alive for many years, and therefore can be used as long-term indicators of air quality. They are also known to be very sensitive to many atmospheric pollutants. Some lichens are damaged or killed by low levels of sulfur dioxide (0.5 ppm, Nash 1973), nitrogen oxides (2-4 ppm, Nash 1976) and other strongly oxidizing compounds (Nash 1972, 1975; Ferry et al. 1973). The algae of the thallus seem to be the