Possible Effects of Acidic Deposition on a Rocky Mountain Population of the Tiger Salamander Ambystoma tigrinum

To investigate possible biological effects of acidic deposition in the western United States, we performed population censuses and dose-response experiments at a subalpine watershed in the Rocky Mountains of Colorado. An adult tiger salamander (Ambystoma tigrinum nebulosum) population decline by 65% over seven years, while larval recruitment declined over all but the last year of this period. A. tigrinum eggs had an LD-50 pH of 5.6, which is within the range encountered by eggs at this site during snow melt. Although the decline of A. tigrinum at this watershed could be a natural fluctuation, the available evidence is consistent with the hypothesis that acidic deposition is its cause. Thus, the decline of A. tigrinum at the watershed may be the first indication of biological damage from acidic deposition in the western United States.