Lichens as bioindicators of geothermal air pollution in central Italy

The suitability of lichens as bioindicators of geothermal air pollution was evaluated in central Italy. Fifty-one sites were sampled in the Travale-Radicondoli geothermalfield, an area of about 15 km2. Lichens on 1-5 trees per station were sampled, using 30 x 50 cm grids on tree boles, where lichens were most dense. Index of Atmospheric Purity (IAP) was calculated as the sum of the frequencies of all lichen species present at the station. Using automatic mapping programs, the area was divided into four air quality zones and the lowest IAP values were found within about 500 m of geothermal power plants. No direct measurements of air pollution are available for the whole study area, however, other studies show that air pollution levels (mercury, boron) fall with distance from a geothermal source. Also no substrate parameter (height, circumference, bark pH, and buffer capacity of the trees) discriminates between IAP zones. This suggests that air pollution arising from geothermal emissions is responsible for the zonation shown, with values for species richness and IAP rising with distance from geothermal installations. It is concluded that lichens are reliable bioindicators of geothermal air pollution.