Acid precipitation has been implicated as causing the loss of Sphagnum species, and thus of Sphagnum peatlands from the southern Pennines in Great Britain. Thus, the effects of pH, SO42-, NO,-, and NH4+, at levels feasible for acid precipitation in eastern North America, on the growth and chlorophyll contents of Sphagnum fallax, S. henryense and S. pulchrum were evaluated in 40-50 day laboratory studies. Growth responses were species-specific, and also differed between two populations of S. pulchrum collected from different locations. In general, growth was not correlated with chlorophyll concentrations. If the acidity in precipitation lowers wetland pH values to 3 or less, growth of Sphagnum species in general will be inhibited. Otherwise, our results do not suggest that elevated concentrations of H+, SO42-, NO,-, and NH4+ in acid precipitation will have severe negative short-term effects on Sphagnum growth, at least for these 3 species. One of the earliest suggestions that acid precipi- tation may negatively impact Sphagnum-dominat- ed peatland ecosystems was that of Tallis (1964), who commented that the disappearance of Sphag- num species from the southern Pennines in Great Britain may have been the result of atmospheric pollution dating from the Industrial Revolution. Only 5 Sphagnum species were present in 1964 as compared to 18 species in 1913 (Ferguson & Lee 1983). Ombrotrophic Sphagnum bogs may be es- pecially susceptible to the chemistry of precipita- tion, since these bogs rely exclusively on atmo- spheric deposition as a source of both water and nutrients (Kilham 1982; Gorham et al. 1983). In the absence of acid precipitation, bogs are nat- urally acidic, with surface water pH values of about 4.0 (Clymo 1984); however, in the presence of acid precipitation, a significant pH depression can result (Hemond 1980; Clymo 1984). Since pH is an im- portant environmental variable affecting the success of individual species of Sphagnum in the field (see review by Andrus 1986), increasing acidity of sur- face bog waters resulting from acid precipitation may affect Sphagnum species and thereby the struc- ture of Sphagnum communities. Atmospheric sul- fur compounds associated with acid precipitation (SO2, HS03-, SO42-) have inhibitory effects on the growth, photosynthesis, and survival of Sphagnum