Arctic charr (Salvelinus alpinus) re-established in a formerly acidified and highly dilute mountain lake under declining acidic deposition

Abstract

Arctic charr in Rondvatn, a formerly highly acidified mountain lake in southern Norway, was re-established through stocking. The population became extinct during the early 1980s when the lake had an annual mean pH of 5.2-5.4, with occasional declines to 4.3-4.7. From the mid to late 1990s, the pH and acid-neutralizing capacity (ANC) rose to 5.8-5.9 and 13-15 μeq L-1, respectively. The lake is poor in ions with a mean conductivity and calcium concentration of 7.7 μS cm-1 and 0.35 mg L-1, respectively. The lake was stocked with 250 young Arctic charr from four small neighbouring lakes between 1998 and 2000. This introduction was successful. Test-fishing in 2004, 2008 and 2012 revealed a relatively dense population of Arctic charr, and the presence of several new age-groups. pH and ANC has remained stable since the late 1990s, or has slightly improved.