Application of the SAFE model to a Norway spruce stand at Ballyhooly, Ireland

Abstract

Acid rain results in qualitative and quantitative changes in terrestrial ecosystem boundary conditions. Typically these changes exceed the range of variation observed or inferred from past states. Methods of predicting future states are required, such as process-based models or experimental treatments that mimic future scenarios. The dynamic biogeochemical model SAFE was applied to Ballyhooly intensive forest monitoring plot located in southern Ireland. SAFE is a dynamic, process-oriented soil chemistry model developed with the objective of studying the effects of acid deposition on soils and groundwaters. It calculates the values of different chemical state variables as a function of time. The model requires input data on soil mineralogy, soil texture, CEC and base saturation, together with time-series data for atmospheric deposition, nutrient uptake and cycling, and hydrology. Model results indicate that the basic principles in the model are capable of describing the present soil-solution chemistry at Ballyhooly without extensive calibration. However, the gibbsite equilibrium model does not describe the observed concentrations of aluminium at Ballyhooly, and the assumption that sulphur adsorption is insignificant appears also to be incorrect. Inclusion of processes such as sulphur adsorption, aluminium complexation with organic matter, or a kinetic-based aluminium model may improve model results.