Lichen response to changes in atmospheric sulphur: isotopic evidence.

In June of 1997, several thalli of the lichen species Alectoria sarmentosa were transplanted from a remote area (Bonavista) to an urban area (St John's) on the island of Newfoundland, Canada. The purpose was to assess the response of these epiphytic lichens to a change in the level of atmospheric sulphur pollution as measured by sulphur concentration and isotopic composition. The dominant source of atmospheric sulphur in the Bonavista area is sea spray, therefore, lichens growing there have relatively high sulphur isotopic compositions and low concentrations (approximately + 15 per/thousand, 250 ppm). Atmospheric sulphur in the St John's area is dominated by anthropogenic sources, primarily oil burning. Lichens in this area have lower isotopic compositions and higher concentrations (approximately + 6 per thousand, 500 ppm). The transplanted lichens were monitored monthly for a period of 1 year. In all experiments the sulphur isotopic composition decreased and the sulphur concentration increased linearly. It is estimated that, within 18 months, transplanted A. sarmentosa would be indistinguishable from the same species naturally growing in the transplant site, both in terms of sulphur concentration and isotopic composition.