『Abstract
　Critical loads of acidity were estimated for upland forests in eastern Canada using the steady-state Simple Mass Balance (SMB) Model. A consistent methodology was applied to the entire region, although critical loads were estimated separately for the Atlantic provinces (New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland), Quebec and Ontario using different data sources. In this project, critical load estimates and steady-state exceedance values did not include the effect of forest fire and forest harvesting, which could have a considerable impact on critical loads in Eastern Canada. The observed soil pH - base saturation relationship for forest soils indicated that the constants used into the calculation of alkalinity leaching should be set to 10 (M/M) for the molar Bc/Al ratio in soil leachate and 10⁹ (mol L^-1)² for the gibbsite dissolution constant. The area-weighted median critical load for each province varied between 519 (Quebec) and 2063 eq ha^-1 y^-1 (Prince Edward Island), with a median critical load value for Eastern Canada of 559 eq ha^-1 y^-1. It is estimated that approximately 52％ of the mapped area is exceeded in terms of acidity according to the 1994-1998 average total (wet + dry) atmospheric deposition. Greatest exceedances occurred in Ontario and Quebec and in the south of Nova Scotia, due to low critical loads and high loads of acid deposition.

Keywords: acid deposition; Bc/Al ratio; critical loads; Eastern Canada; ecological mapping; forest soils』

1. Introduction
2. Calculation and mapping of critical loads and exceedances
　2.1. The SMB model
　2.2. Determining the appropriate values for Bc/Alcrit and KGibb using the soil pH - base saturation relationship
　2.3. Data sources
3. Results and discussion
　3.1. Critical values that relate soil pH to base saturation
　3.2. Critical loads and exceedances
4. Conclusion
Acknowledgements
References

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