AN EMPIRICAL MAP OF CRITICAL LOADS OF ACIDITY FOR SOILS IN GREAT-BRITAIN

The method used to produce a critical load map of acidity for soils in Great Britain is described. Critical loads were assigned to the dominant soil in each I km grid square of the UK national grid. Mineral soils were assigned a critical load based on mineralogy and chemistry, using approaches appropriate to UK conditions. Critical loads for peat soils are based primarily on a maximum acceptable reduction of peat pH, and results from laboratory equilibration studies. The map shows that soils with small critical loads (< 0.5 kmol(c) ha(-1) year(-1)) i.e. highly sensitive to acidic deposition, dominate in the north and west of Britain, the south and east are dominated by soils with large critical loads, with small areas of more sensitive soils associated with sandy soil-forming materials. A modified critical load map illustrates the potential impact of agricultural liming on soil critical loads.