Amphibian decline and fertilizers used on agricultural land in south-eastern Australia

Evidence is provided that fertilizer use increased markedly from the 1960s in New South Wales (NSW), south-eastern Australia. The agrochemicals probably accumulated on agricultural land until 1974, when they were washed or leached after heavy rains into waterbodies that may have been occupied by the endangered green and golden bell frog (Litoria aurea). The numbers of annual sightings suggest that the range of this species contracted in 1975, following the suspected pulse of fertilizers into aquatic habitats. There was no such decline for the common eastern froglet (Crinia signifera) and the striped marsh frog (Limnodynastes peronii), which commonly occur in many agricultural waterbodies. A laboratory study showed that L. aurea, C. signifera, and L. peronii tadpoles exposed to ammonium nitrate and calcium phosphate fertilizers over 150, 21, and 91 days differed in survivorship. Significantly few L. aurea tadpoles survived to metamorphosis in 10 and 15 mg/l ammonium nitrate, and 15 mg/l calcium phosphate, which had no effect on the survivorship of C. signifera and L. peronii tadpoles. Historical and experimental evidence suggests that the elevated nitrate and phosphate concentrations in waterbodies in 1974–1975 contributed to the decline of L. aurea in its former range.