| The study evaluates methods using lichens as air pollution bioindicators in southern Wisconsin. The study area is a 375 km northwest-trending transect originating in the southeast corner of Wisconsin (upper Midwest, USA). Of the total 15 sites, 10 were sampled for heavy metals, sulfur, and nitrogen deposition (21 elements) using mesh bags containing Sphagnum russowii . Statistically significant trends of decreasing deposition to the northwest occurred in: Al, B, Ca, Cd, Co, Cu, Cr, Fe, Mg, Mn, Ni, S and Zn. Calcium, Mg, and S results are consistent with national network deposition patterns.; A biological impact index was developed using non-metric multidimensional scaling (NMS) models of epiphyte community data. At 15 sites, thirty species of lichens and mosses were sampled on limbs of large bur oak trees ( Quercus macrocarpa) in a savanna-like setting. To minimize habitat variability, strict criteria were used to select sites, trees and branches. The final model represents 90% of the community data variability: 76% in an axis strongly related to pollution (r = .92; p < 0.01), and 14% in an axis related to light levels (r = .56; p < 0.05) and branch height (r = .46; p < 0.10). Minimizing microhabitat variability contributed to the strength of the relationship between community composition and pollution. Communities at two sites near a coal-burning power facility (downwind and crosswind) that differ three-fold in annual average SO2 levels were compared and results support the interpretation of community differences along the transect as pollution mediated.; The use of a bioindicator index (index of atmospheric purity, IAP) was compared to the use of NMS models. IAP formulations included: number of companion species (Q), species cover, and species frequency. The resulting IAP values are strongly correlated with the community data (averaging above 0.9), and the index based on frequency is recommended. Results using a reduced species set (tolerant species removed) are consistently stronger than those using the full set. Strengths and weaknesses of indices versus models to evaluate pollution impacts are discussed. These methods are used to examine impacts, hence the term “Index of Atmospheric Impacts” (IAI) is recommended to replace IAP. |
