Monitoring Lichens as Indicators of Pollution

Abstract

Erasmus Darwin observed how lichens failed to grow near Copper Smelters at Parys Mountain in Wales over 200 years ago. But it was not until sulphur dioxide, a product of fuel combustion, was identified as a major factor influencing lichen growth, distribution and health in the 1960’s that the exponential growth world-wide in lichen biomonitoring studies occurred with now well over 1500 papers published on this subject, including several books (see [3]) and an on-going literature series published in the Lichenologist. Today it is recognised that a wide range of other substances including ammonia, fluorine, eutrophication, alkaline dust, metals and radionuclides, chlorinated hydrocarbons and ‘acid rain’ may all be detected and monitored using lichens. Many countries, particularly France, Germany, Italy, Switzerland, The Netherlands and US, are currently using lichens to monitor the effects of gaseous and metal pollution using lichens at both local and national levels, a trend set to continue. There are several reasons why lichens have enjoyed such an extraordinary success in this field:

• Lichens are ubiquitous and are currently increasing in many urban areas as a direct consequence of decreased SO₂ levels (see chapters 1–3, this volume).

• They lack a protective outer cuticle and absorb both nutrients and pollutants over much of their outer surface from predominantly aerial sources.

• Their symbiotic nature. The fungus is obligate; if either partner is damaged by pollution this will result in a breakdown of the symbiosis, and ultimately to the death of the lichen.

• They are perennial organisms available for monitoring throughout the year.

• Many lichen species accumulate high metal contents without exhibiting damage, thereby permitting monitoring over wide areas.

• Different methods exist providing opportunities for all ages and abilities.

• Instruments are vulnerable to theft and vandalism.