Effects of low pH, metals, and water hardness on larval amphibians

Abstract

The interactions between pH, metals, and water hardness in determining the suitability of vernal ponds for amphibian reproduction were investigated through a fully factorial laboratory microcosm experiment. Naturally-occurring metals (Al, Cu, Fe, Pb, Zn) at concentrations analogous to those observed in prior field studies had variable effects on acute (7 day) and chronic (28 day) exposure survival for both the Jefferson salamander, Ambystoma jeffersonianum, and the wood frog, Rana sylvatica. Acute exposure to Al and Cu significantly reduced wood frog survival; increased water hardness significantly increased acute exposure wood frog survival. Acute exposure mortality of the Jefferson salamander was significantly higher in the Al and Cu treatments; in toxic metal treatments (Al and Cu), survival was higher at the low pH level. Chronic exposure of wood frogs to Al and Cu, higher pH level, and lower hardness levels greatly reduced survival. Chronic exposure of Jefferson salamander larvae to Al and Cu significantly reduced survival. Chronic Jefferson salamander survival was significantly greater in the higher pH treatments in the presence of non-toxic metals, however, survival was significantly decreased in the higher pH treatments in the presence of Al and Cu. There were no statistically significant effects of metals, pH, or hardness on wet mass of the pre-metamorphic larvae.

The four conditions tested (pH, hardness, presence of metals, and amphibian species) are important determinants of toxicity observed in temporary pond amphibian breeding sites. Clearly, there is no single water chemistry parameter that can explain the toxicity of temporary ponds to the embryos and larvae of terrestrial amphibians that use the ponds for breeding.