The sub-lethal effects of ammonium nitrate fertiliser on the common frog 'Rana temporaria'
Increased use of fertilisers and pesticides has raised levels of agricultural pollution in surface and ground waters. Organism using these water sources are at risk of exposure to ammonium nitrate fertiliser. The effects of ammonium nitrate on spawn, larva and adult common frogs was investigated using ammonium nitrate fertiliser in solution and granular form at various stages of frog development. The concentrations used, up to 100mgIL NO-3-N used reflect nitrate concentrations on agricultural land in the United Kingdom in water bodies located within and adjacent to agricultural land at times when common frogs are actively breeding or developing. Nitrate concentrations in frog breeding ponds were high (> 1OOmgIL NO-3-N) during the frog breeding season, especially when water entered from field drains, but significantly lower (<25 mglL) for the remainder of the year. Frogs did not show a selective preference for ponds with low nitrate concentrations. Frog spawn swelled when exposed to ammonium nitrate and its viability was reduced (87% survival in controls; 63% at 80 mgIL NH\NO-3). The 96 hour LCso for frog larvae was 781 mglL (95% confidence intervals of 587 to 942) and the 48 hour ECso was 399 mgIL (95% Cl = 234 to 546). Long term exposure to 100 mgIL NW4NO-3 in a flow through system reduced larval survival from 85% (controls) to 53% after 96 days, with most mortality occurring during the three weeks prior to metamorphosis. Larval growth was affected marginally but with some evidence of enhanced mass in the treated larvae, especially at the lowest nitrate concentration of 25 mWL NH\NO-3. Metamorphosis in this group was earlier than in the other groups; by day 80, 48% of the metamorphs had emerged, by comparison with 38, 34 and 24% for the controls and those exposed to 50 and 100 mgIL NW4NO'3 respectively. Furthermore, the mass of emergent metamorphs in the 25 mgIL treatment group was significantly higher than that of the controls.