Elemental chemistry of four lichen species from the Apostle Islands, Wisconsin, 1987, 1995 and 2001

Four lichen species sampled three times over a 15-year time span at four of the Apostle Islands, Wisconsin were analyzed for 16 chemical elements in order to determine time trends and spatial patterns. Factor analyses of the data revealed that elements associated with soils (Al, Cr, Fe, Na, Ni and S) have increased over the study period, while nutrient and pollutant elements (Cu, K, P, Pb and Zn) have decreased. Four other elements (Ca, Cd, Mg and Mn) were unchanged over time. Cladina rangiferina, a terricolous species, contained the lowest concentrations of all elements, while the corticolous species Evernia mesomorpha was highest in soil elements, Hypogymnia physodes was highest in Ca, Cd, Mg and Mn, and Parmelia sulcata was highest in the nutritional elements. Lichens on islands within 3–4 km of the mainland were highest in soil elements, which decreased with distance from the mainland. Elements that were 18–43% greater on the nearest islands were significantly different between near and far islands. Eight elements (Al, Ca, Cd, K, Mg, Mn, P and S) exceeded enrichment levels for Hypogymnia physodes, suggesting possible contamination problems for this species. Although Pb has decreased significantly over the time period, other elements have increased in the lichens while decreasing in the atmosphere, suggesting that accumulation in the environment is continuing.