Effects of aluminium and low pH on growth and development in Rana temporaria tadpoles.

Rana temporaria tadpoles were raised to metamorphosis at 6 levels of pH (pH 3.6-6.5) and 2 levels of aluminium (800 and 1,600 μg l-1) at pH 4.4. Treatments involved both chronic and acute exposure to depressed pH. Decreasing pH reduced maximum body size and delayed metamorphosis. Growth was depressed and metamorphosis delayed by 800 μg l-1 Al, and several tadpoles died at foreleg emergence. At 1,600 μg l-1 Al, small tadpoles suffered arrested growth and development and eventually died, while larger tadpoles metamorphosed without delay, though at a very small size. There was no mortality among controls. The levels of pH and inorganic monomeric aluminium measured in the experiments were similar to field levels at a site in Scotland, and it is concluded that individual tadpoles will, in certain types of water body, be adversely affected by both acidity and aluminium. The impact of these factors on populations remains to be determined.