Chemical and biological recovery of Lake Saudlandsvatn, a formerly highly acidified lake in southernmost Norway, in response to decreased acid deposition

We studied acid-sensitive organisms in Lake Saudlandsvatn in southernmost Norway in relation to acidification: brown trout ( Salmo trutta), the caddisfly Hydropsyche siltalai and the zooplankter Daphnia longispina. The study lake was highly acidified with episodic pH depressions 20 μeq L − 1 and toxic inorganic aluminium of < 30 μg L − 1 . Projections made with the MAGIC model indicate that unless further reductions in deposition of S are made, the ANC will fluctuate around the ANC survival threshold for the biological elements described. Thus, full biological recovery will not occur in the near future. ► Sulphur (S) deposition was five times greater than the critical load in the study lake. ► Chemical recovery following reduced deposition of S became evident 10–15 years later. ► Any significant recovery in three organism groups, brown trout Salmo trutta, caddisfly Hydropsyche siltalai and the zooplankter Daphnia longispina coincided with an acid neutralizing capacity (ANC) of >20 μeq L − 1 . ► Projections made with the MAGIC model indicate that unless further reductions in deposition of S are made, the ANC will fluctuate around the ANC limit for the biological elements described.