Effects of a "Clean" Coal-Fired Power Generating Station on Four Common Wisconsin Lichen Species

Abstract

Algal plasmolysis percentages and other morphological character- istics of Parmelia bolliana Miill. Arg., P. caperata (L.) Ach., P. rudecta Ach., and Physcia millegrana Degel. were compared for specimens growing near to and far from a rural coal-fired generating station in south central Wisconsin. SO, levels were 389 g/Im3, maximum 1 hr level, and 5-9 Ag/mm3, annual averages. Parmelia bolliana and P. caperata showed evidence of morphological alterations near the station; P. rudecta and Physcia millegrana did not. Studies of lichen communities in the vicinity of a relatively clean rural Wisconsin coal-fired power generating station in 1974 and 1978 showed that some small changes that oc- curred in lichen communities were probably caused by air pollution from the station (Will- Wolf 1980). In an attempt to further document the subtle impact of the generating station upon lichens in the area, I investigated selected morphological characteristics of four common corticolous lichen species in the vicinity of the generating station during 1979. In the community study, two of the species, Parmelia bolliana Miill. Arg. and P. caperata (L.) Ach., exhibited some distributional changes near the generating station; the other two species, P. rudecta Ach. and Physcia millegrana Degel., appeared to be unaffected. Many species of lichens are adversely affected by SO2 air pollution (Ferry et al. 1973, Le Blanc & Rao 1975). SO2 causes plasmolysis of lichen algal cells near SO2 sources (Le Blanc & Rao 1966, 1973), and increased percentages of plasmolyzed algal cells have been found in lichens exposed in the field to controlled releases of SO2 (Eversman 1978). Other morphological alterations such as yellowing or bleaching of lichens also result from SO2 exposure (Gilbert 1973, Showman 1975, Eversman 1978). Eversman (1978) reported that as SO2 levels increased, large numbers of bacteria were found attached to lichen fungal hyphae, making the hyphae appear rough rather than smooth under a microscope. The above phenomena have been observed in field or laboratory investigations of lichens ex- posed to a wide range of SO2 concentrations, the lowest being 17 pphm for several hours (Tiirk et al. 1974) or an average of 1.8 pphm for three months (Eversman 1978). The incidence of two morphological estimates of SO, injury, the percent of algal cells plasmolyzed and the percent area of fungal hyphae with bacteria attached, was surveyed for the four lichen species mentioned. In addition, the presence of an unusual character- istic, white pruinose lobe tips, was recorded for Parmelia bolliana. White pruinose lobe tips were noted on some P. bolliana specimens collected in the higher-SO2 impact area during the community study (Tibbitts et al., in press), so the phenomenon was investigated further. White pruinose deposits are common on many species of lichens, but they are not characteristic of P. bolliana. Therefore, I suspected that they may be an SO2 response in this species. The occurrence of pruina is known to be environmentally determined in many species (Weber 1962, Poelt 1973), and unusual pruina or other surface deposits have been noted in some lichen species exposed to SO2 (Le Blanc & Rao 1966, 1973).