Nitrex project - Gårdsjöen, Status report for 1990-91

Abstract

At the NITREX site at Gårdsjön, Sweden, ambient nitrogen deposition of 90 meg m² yr 1 will be experimentally increased by 286 meg m² yr 1 to an entire forested catchment G2 to study the potential for nitrogen saturation. Investigations include mearsurements of catchment inputs and outputs, as well as studies of vegetation, soil, mycorrhiza, fine roots and fish response. Results from the pre-treatment period 1990-91 show acidic runoff and soil solution with high concentrations of inorganic aluminium. Concentrations of nitrate and ammonium are very low, indicating no nitrogen satuation. The trees are slightly-to-moderately defoliated, and the needles are discolored. The nutrient contents of needles indicate that no elements are in the deficiency or the toxin range. The mycorrhiza of the root mat at the forest floor are generally 100 % alive and healthy. At catchment G2 nitrogen addition began April 1991.