COUNTERACTIONS AGAINST ACIDIFICATION IN FORESTS ECOSYSTEMS, EFFECTS ON STREAM WATER-QUALITY AFTER DOLOMITE APPLICATION TO FOREST SOIL IN GJERSTAD, NORWAY

The deposition of strong acids is one of many threats to forest ecosys tems and viable forestry. Several counteractions against acidification have been launched, e.g. changes in forestry management and the intro duction of chemicals. The inter-institutional programme ''Counteractio ns Against Acidification in Forest Ecosystems'' was established in 199 3 to evaluate existing knowledge and run experimental and full-scale f ield experiments. A total of 240 metric tons of coarse dolomite powder was spread by helicopter in September 1994 on 84 ha forest catchment dominated by pine (Pinus sylvestris) and Norway spruce (Picea abies). potential desirable and undesirable effects after this carbonate appli cation may be less pronounced than recorded at other sites due to the relatively moderate dose (3 tons ha(-1)). Pre-liming stream water qual ity (mean values for May 1993-September 1994) was as follows: pH 4.8; Ca 1.13 mg L(-1); reactive Al (RA1) 248 mu g L(-1); inorganic monomeri c Al (A1(i)) 72 mu g L(-1). The reference station was slightly higher in Ca and slightly lower in both RA1 and Al-i. Dolomite application re sulted in a significant increase in pH to 5.7 as mean value for the po st-liming period (September 1994-April 1995). Both Ca and Mg increased significantly after liming, and both RAI and Al, declined significant ly. The rapid detoxification of stream-water may be explained by disso lution of dolomite particles in both streams and catchment, a resultin g pH increase and change in Al species composition. Retention of Al in the catchment probably explains the reduction in RA1. No increase in NO3, total N, total P or TOC was recorded the first seven months.