Effects on water chemistry, benthic invertebrates and brown trout following forest fertilization in Central Sweden

Two coniferous forest drainage areas in central Sweden were partially fertilized with ammonium nitrate and calcium ammonium nitrate respectively, both at a dose of 150 kg N ha‐1. During the following years observations were made on stream water chemistry, invertebrates and brown trout (Salmo trutta L.). Upstream stations were used as controls. Very high concentrations of inorganic N (up to 45 mg l‐1) were recorded immediately after the fertilization. Thereafter, concentration decreased rapidly but remained elevated during the whole study period. Acidity conditions (pH, alkalinity, aluminium) were unaffected by both treatments. The only registered effect on the benthic fauna was a three‐ to five‐fold increase of drifting invertebrates during the first four‐five days after the treatment. However, this did not reduce the population density at the treated stations. No effects on population of trout were recorded.