Dynamic modelling of the response of UK forest soils to changes in acid deposition using the SAFE model.

Both observed and modelled data have been examined from the ten UN-ECE Level II forest intensive monitoring sites in the UK to determine the changes and potential impact on soil solution chemistry resulting from changes in acid deposition inputs. The sites represent a range of forest tree types, soil sensitivities and pollutant deposition inputs found in the UK. The dynamic biogeochemical SAFE model was used to explore temporal changes in soil and soil solution chemical parameters that have been used as indicators for potential forest ecosystem and tree damage in national and international assessments of critical loads. The observed data and model results show that there is significant inter-site variation. The model indicates that the historical pollutant inputs have resulted in significant soil acidification at most of the sites. Model predictions generally match current day observations. Recently declining pollutant inputs have reduced and in some cases reversed the trend of increasing soil acidification. A discussion of the results in terms of critical loads, recovery, their wider implications and uncertainty is presented.