http://cfs.nrcan.gc.ca/authors/read/20245?lang=en_CA Publications by J. Aherne en-ca 2007-05-23 00:00:00 MST 2007-05-23 00:00:00 MST webmaster@nofc.cfs.nrcan.gc.ca http://cfs.nrcan.gc.ca/publications?id=27006 Critical loads are a broad-scale modelling approach designed to assess the potential risk of pollutants to ecosystems. A description of the methodology for estimating critical loads (sulphur and nitrogen) for acid deposition (CL(A)) for upland forests in eastern Canada is presented, using a case study in central Ontario. In eastern Canada, CL(A) have been calculated for upland forests, with the objective of maintaining the molar ratio of base cations to aluminium in soil solution above 10. In the current approach, nitrogen (N) dynamics including N fixation, N immobilisation and denitrification have been set to zero. Further, critical load estimates presented in this study do not include nutrient removals through harvesting, and dry deposition input is estimated to be 20 percent of wet (1994 to 1998) deposition. Critical loads were calculated separately for Ontario, Québec and the Maritime Provinces (New Brunswick, Nova Scotia and Newfoundland) using the same methods, but using different soil and forest databases. Mean area-weighted critical loads among provinces are similar, ranging between 273 eq ha--1 yr--1 (Newfoundland) and 512 eq ha--1 yr--1 (Ontario). Preliminary estimates indicate that more than 50 percent of the upland forest area in Ontario and Québec and between 10 (Newfoundland) and 33 percent (Nova Scotia) of upland forest in the Maritimes receive acid deposition in excess of the critical load. Current efforts are being directed toward improving the accuracy of critical load estimates and current exceedances using better estimates of dry deposition and harvesting removals, and investigating the linkage between exceedance of the critical load and adverse biological effects. Wed, 23 May 2007 http://cfs.nrcan.gc.ca/publications?id=27006 http://cfs.nrcan.gc.ca/publications?id=26190 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-1y-1 (Prince Edward Island), with a median critical load value for eastern Canada of 559 eq ha-1y-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. Fri, 28 Apr 2006 http://cfs.nrcan.gc.ca/publications?id=26190