Acidification and Atlantic salmon critical limits for Norwegian rivers

Abstract

An analysis of water chemistry and salmon population status based on data for 1993-94 shows that of 73 salmon rivers in Norway, 23 have extinct populations and an additional 22 have affected populations. Acidification is one of several causes of damage to salmon populations. The extinct rivers have ANC below about 0 µeq L-1, whereas the unaffected rivers have ANC above about 25 µeq L-1. Salmon catch statistics from the late 1800's to the present indicate declining populations in many rivers, especially those on the south coast. Historical ANC reconstructed by application of the MAGIC model in 6 rivers indicates declining ANC (acidification) to levels potentially damaging to salmon. Of the rivers tested, only in Tovdal river do the salmon catch statistics and reconstructed ANC give a consistent clear-cut picture. The data indicate that the critical limit for salmon in Norway is about 30 µeq L-1. This limit is compatible with data from laboratory and field experiments with salmon. Setting this as a limit does not necessitate revision of the critical load maps for Norway, which are based on critical limit for brown trout.