CHEMICAL-ELEMENT CONCENTRATIONS IN 4 LICHENS ON A TRANSECT ENTERING VOYAGEURS-NATIONAL PARK

A three factor transect study was conducted to test the hypothesis tha t chemical elements from air emissions in the vicinity of Internationa l Falls, Minnesota could not be detected in lichens along a 24 km tran sect reaching into Voyageurs National Park. It was hypothesized that e lement concentrations in lichens would decline exponentially downwind and would reach background values at a distance before the park bounda ry. Four species (Cladina rangiferina, Evernia mesomorpha, Hypogymnia physodes, and Parmelia sulcata) were sampled at ten sites for 3 years and 17 chemical elements were measured. The most notable result was a curvilinear geographic trend for many elements, which decreased from I nternational Falls and then increased towards the park. This trend was significant for many anthropogenic elements, including S, Hg, Cd, and Cr, and for all four species. This type of distribution pattern has b een observed in Hypogymnia physodes in other studies downwind of a ste el mill and an oil refinery. Cladina, a ground-dwelling lichen, genera lly had lower tissue concentrations of the elements than the three epi phytic species. Tissue concentrations over the 3 years of sampling dec lined an average of 12%. Sufficient evidence exists to conclude that l ichen tissue element concentrations in the vicinity of International F alls may be related to local air emissions, and that an exponential de cline of element concentrations downwind of the sources does not apply to this situation. (C) 1997 Elsevier Science B.V.