TOWARDS A NEW METHOD OF SETTING A CRITICAL LOAD OF ACIDITY FOR OMBROTROPHIC PEAT

Critical loads of acidity for mineral soils can be set according to th e capacity of the underlying bedrock to replenish the base cations lea ched by acid deposition. Unfortunately, this relatively simple approac h cannot be applied to pest, one of the most widely occurring soil typ es in the wetter, western areas of Europe. These organic soils depend on atmospheric deposition for their supply of base cations rather than mineral weathering. We aim to develop a critical load methodology for ombrotrophic pest, using a combination of field observations and labo ratory experiments. Simulated rain has been applied to intact cores of pest to determine the key chemical processes governing the response o f these soils to both increases and decreases in acid deposition. It i s evident that pest does not behave as a simple ion exchanger; the com plex reactions of decomposition, sulphate reduction, nitrate uptake an d organic acid production also control the response to acid inputs. Th is paper looks at some of the results from these experiments and consi ders the implications for setting critical loads.