A field simulation of the effect of acidic rain on ion balance in a woodland salamander

Abstract

The natural density of red-backed salamanders, Plethodon cinereus, is 4–5 times greater at the New York study site in hardwood than in hemlock forests. The hypothesis that physico-chemical differences between forest types differentially affect the physiology of P. cinereus was tested. Salamanders were confined in individual enclosures in either a beech or a hemlock forest for 22 d. At the end of the enclosure period, they were analyzed for total body content of sodium, potassium, calcium, and magnesium, and for wet mass, dry mass, and body water concentration. Salamanders from the two forest types did not differ in any body parameter after the 22 d enclosure period. Also, the hypothesis that artificially acidified “rain” would inhibit the ability of salamanders to maintain ion balance was tested. Salamanders were confined for 34 d in individual enclosures in the two forests and exposed periodically to artificial rain of either pH 3 or pH 5. Soil pHs in the enclosures changed during the enclosure period, and artificial rain of both pHs caused soil pHs in the hemlock forest to increase even though pHs outside enclosures decreased. Enclosures that received artificial rain of pH 3 had lower soil pHs than enclosures that received artificial rain of pH 5. Salamanders in enclosures at pH 3 had reduced body sodium levels and tended to have lower body water concentration than salamanders in enclosures at pH 5 or controls. Thus, these terrestrial salamanders in a field setting demonstrated a physiological response to simulated acidic deposition consistent with the effects of exposure to acidic substrate previously observed in the laboratory. Since P. cinereus is frequently an abundant member of forest floor communities, and since it is sensitive to altered chemical inputs, it may be a useful indicator for assessing anthropogenic changes in ecosystems.