EXPERIMENTAL ACIDIFICATION OF ALPINE CATCHMENTS AT SOGNDAL, NORWAY - RESULTS AFTER 8 YEARS

Manipulations with whole catchments were initiated in Norway in 1983 ( RAIN project Reversing Acidification In Norway) to obtain direct exper imental evidence relating to the reversibility of soil and water acidi fication, rate of change, and the relative roles of sulfur and nitroge n. We present here results for soil and runoff chemistry during 8 year s of acid addition at Sogndal, a pristine acid-sensitive site in centr al Norway characterized by gneissic bedrock, thin and patchy soils, an d alpine vegetation. Catchment SOG2 receives 100 meg m(-2) yr(-1) H2SO 4, catchment SOG4 receives a 1:1 mixture of H2SO4 and HNO3, while catc hments SOG1 and SOG3 serve as untreated controls. Acid is applied to t he snowpack in April and in 5 portions of 11 mm of pH 3.2 acidified la kewater during the snowfree period. The 8-years of acid addition have caused major changes in runoff chemistry. Concentrations of sulfate an d base cations have increased while acid neutralizing capacity (ANC) h as decreased. Henriksen's F-factor (change in concentration of non-mar ine Ca + Mg divided by change in concentration of nonmarine SO4) is ab out 0.35, but is expected to decrease as soil acidification proceeds. Runoff is acidic, aluminum-rich, and toxic to fish and other aquatic o rganisms. Repeated soil sampling indicates no dramatic trends related to treatment. Year-to-year variations are large, and mask changes expe cted. The input-output budgets indicate that over the 8-yr period Ca h as been depleted by about 5% of the total soil pool of exchangeable Ca . The observed trends are consistent with response predicted by MAGIC, a process-oriented model of soil and water acidification. The gradual increase in nitrate flux from catchment SOG4 may be the first indicat ion of 'nitrogen saturation' induced simply by increasing nitrogen dep osition.