Nitrogen processes are now included in a new version of MAGIC (version 7), a process-orientated catchment scale model for simulating runoff chemistry. Net retention of nitrogen (N) is assumed to be controlled by plant uptake and the carbon/nitrogen (C/N) ratio of the soil organic matter, the latter is evidence by empirical data from forest stands in Europe. The ability of this version of MAGIC to simulate and predict inorganic N concentrations in runoff is evaluated by means of data from whole ecosystem manipulation experiments at Aber, Wales, UK, (nitrogen addition as part of the NITREX project) and Risdalshiea, Norway (exclusion of acid deposition as part of the RAIN project and climate change as part of the CLIMEX project). MAGIC 7 simulated the changes in N leaching satifactorily as well as changes in base cations and acid neutralising capacity observed at these two sites. MAGIC 7 offers a potential tool for regional assessments and scenario studies of the combined effects of acid deposition, land use and climate change.
Figure 1 Measured bulk (top panel) and estimated total (bottom panel) deposition of SO4, NO3, and NH4 at Aber over the period 1950-1995. Total deposition for the years 19941-1995 includes the N addition at the AN35 plots.
Figure 2 Net uptake of base cations and nitrogen in the vegetation at Aber over the period 1950-1995. The large uptake since 1975 reflects the accumulation of elements in biomass of the growing forest.
