Effects of acute and chronic acidification on three larval amphibians that breed in temporary ponds

This study explored the effects of acute (7 days) and chronic (4 months) exposure to pH 4.2 on three species of larval amphibians, Ambystoma jeffersonianum, Ambystoma maculatum, and Rana sylvatica. Acute tests were conducted in 24 impermeable enclosures in three temporary ponds. Total dissolved aluminum was higher in acidified enclosures in comparison with controls (pH 4.2, [Al] approximately 10-30 microM and pH greater than 4.7, [Al] approximately 5-15 microM, respectively). Greater mortality of A. jeffersonianum occurred at pH 4.2 than at pH greater than 4.7, whereas survival of A. maculatum and R. sylvatica were unaffected by pH. Mean wet masses of R. sylvatica were significantly lower at pH 4.2 than at pH greater than 4.7, but mean wet masses of surviving A. jeffersonianum and A. maculatum were not influenced by pH. There were no pH-related differences in body sodium concentration in larval R. sylvatica. Chronic acidification of mesocosms to pH 4.2 ([Al] approximately 16 microM) (controls = pH greater than 6, [Al] approximately 0.1 microM) resulted in total mortality of A. jeffersonianum. Survival of A. maculatum and R. sylvatica were not associated with pH, but survival of A. maculatum was low at both pH levels. Time to metamorphosis was longer for R. sylvatica maintained at pH 4.2, but not for A. maculatum. No differences in wet masses at metamorphosis were observed for R. sylvatica or A. maculatum. These results indicate that short and long term acidification of temporary wetlands could dramatically affect amphibians which rely upon them as breeding sites, either by causing mortality or by decreasing growth rates.