Amphibian decline and aquatic pollution: Effects of nitrogenous fertiliser on survival and development of larvae of the frog Rana temporaria

Abstract

Due to intensified agricultural practice, nitrate concentrations of surface waters have increased since the Second World War and are expected to continue to rise. Little is known about how these nitrate levels affect the early stages of amphibians in the field situation and if they contribute to the decline of amphibian populations. Exposure of Rana temporaria larvae to ammonium nitrate in a replicated pond experiment increased mortality, and mass at metamorphosis, but extended the larval period. In a second experiment exposure of both R. temporaria and Bufo bufo to elevated levels of nitrate but low levels of ammonium did not affect larval survival and larval period, but caused an increase in mass at metamorphosis for both species. When R. temporaria eggs were exposed to calcium nitrate in enclosures in a pond, survival at tailbud stage and at hatching did not differ from controls. The results suggest that ammonium nitrate can be detrimental to amphibian development but that increased nitrate levels have no direct adverse effects on tadpoles of R. temporaria and B. bufo and eggs of R. temporaria but indirectly enhance mass at metamorphosis.