Scandinavian amphibians: their aquatic habitat and tolerance to acidic water - a field study

To determine the impact that anthropogenic acidification has had on natural amphibian populations in Scandinavia and to trace the species' tolerance limits, in 1988-89 four poorly buffered areas in Norway were investigated; three were anthropogenically acidified and the fourth was not. The increasing acidification from the coastal to inland/highland region of Southern and Southeastern Norway (pH 7.2-4.1) was accompanied by a decreasing frequency of amphibian (Rana temporaria, Bufo bufo and Triturus vulgaris) localities. In the (anthropogenically) non-acidified Central Norway region (pH 6.8-4.6), R. temporaria was very common at all pH levels. The data strongly suggest that acidification explains the absence of amphibians locally in the acidified areas, and has caused their extinction in the inland/highland region of Southern Norway. A pH of 4.5-4.6 is the critical minimum for R. temporaria populations in small, poorly buffered, boggy, water-bodies as were investigated here. For B. bufo, the lowest pH recorded was 4.7, and for T. vulgaris 4.8. We did not find any signs of successful reproduction in Rana arvalis and Triturus cristatus below a pH of 5.2 and 5.3, respectively. Increased contents of Ca super(2+), Na super(+) (NaCl) or humus (NOM) had an ameliorating effect on the amphibians in acidic water. The presence of Al was of only minor importance for the amphibians in humic waters. In a strategy for the conservation of amphibians in acidified or acidifying areas, liming (CaCO sub(3)) and/or NaCl treatment of the localities may work well in order to establish a satisfying aquatic environment for the species. The study may act as a baseline for further surveys in the future when acidic precipitation hopefully has decreased, looking for improvements of the habitats and possible recoveries of amphibian sites.