REVERSAL OF STREAM ACIDIFICATION AT THE BIRKENES CATCHMENT, SOUTHERN NORWAY - PREDICTIONS BASED ON POTENTIAL ANC CHANGES

As western European sulphur emissions continue to decline following peak levels in the 1970s, interest is now focusing on the reversibility of freshwater acidification. Here, streamwater and soilwater data from the Birkenes catchment in southern Norway are considered in an attempt to estimate the minimum reductions of sulphur deposition required to reintroduce brown trout to the stream. The results demonstrate that, for present soil conditions and atmospheric base cation inputs, a decrease of sulphate deposition of more than 85%, from 1985-1987 levels, is needed to allow successful restocking of brown trout. Since this is a minimum estimate, one can envisage several mechanisms implying that streamwater acidification would not be sufficiently reversible for fish survival even at a 100% reduction in sulphur deposition. © 1990.