Riverside CL meeting, Feb , 2005 Canadian accomplishments on Critical Load Mapping Forests Rock Ouimet, MRNFP, QC Paul A. Arp, UNB, N.B. Shaun Watmough, TU, ON Julian Aherne, TU, ON Ian DeMerchant, NRCan, N.B. Surface waters Dean Jeffries, EC, ON Jacques Dupont, MENV, QC Jill Franklyn, EC, ON David Lam, EC, ON Fred Norouzian, EC, ON Isaac Wong, EC, ON

2 Riverside CL meeting, Feb , 2005 Canadian Accomplishments on Critical Loads  History  Definitions  Chemical thresholds and methods Aquatic Terrestrial  Critical loads and exceedances Aquatic Terrestrial  Combined critical loads and exceedances  Uncertainties

3 Riverside CL meeting, Feb , 2005 History, definitions  1983Target load: 20 kg/ha/yr wet SO 4 2- deposition  kg/ha/yr NSS-wet SO 4 2- deposition  1997Aquatic (6 18 kg/ha/yr) Terrestrial (90 < S&N-CL < 2900 eq/ha/yr)  1998NEG/ECP initiative  2005EC report on acid deposition science assessment First mapping of terrestrial CL for eastern Canada Updated mapping of aquatic CL for eastern and first mapping of CL for western Canada

4 Riverside CL meeting, Feb , 2005 Definitions  Critical load « The highest deposition of acidifying compounds that will not cause chemical changes leading to long-term harmful effects on ecosystem structure and functions » Nilsson and Grennfelt (1988) « A quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified elements do not occur according to present knowledge » UN ECE (1994) « A quantitative estimate of an exposure to one or more pollutants below which the probability of long-term unacceptable effects on specified elements is acceptable according to present knowledge and policy » Barkman (1998)

5 Riverside CL meeting, Feb , 2005 Chemical thresholds and methods : the steady-state approach  Aquatic Biotic toxicity of the lower aquatic food web Acid neutralizing Capacity (ANC) = 40 µeq/L (~pH = 6.0) Model : Expert (Lam et al. 1994) SSWC (Henriksen & Posch 2001)  Terrestrial Maintaining current soil base saturation of forest soils Log(K Gibb ) = 9.0BC/Al = 10 (M/M) The Simple Mass-Balance Model (SMB)  Critical load

6 Riverside CL meeting, Feb , 2005 Critical loads and exceedances  Aquatic CL

7 Riverside CL meeting, Feb , 2005 Critical loads and exceedances  Aquatic CL Exceedance

8 Riverside CL meeting, Feb , 2005 Critical loads and exceedances  Terrestrial CL (no harvesting, no forest fire)

9 Riverside CL meeting, Feb , 2005 Critical loads and exceedances  Terrestrial CL Exceedance

10 Riverside CL meeting, Feb , 2005 Combined critical load

11 Riverside CL meeting, Feb , 2005 Combined critical load exceedances

12 Riverside CL meeting, Feb , 2005 Uncertainties  Assumptions Steady state  Methodological, technical, epistemological  There is a potential for reducing uncertainties  Critical loads : an environmental risk assessment for international and domestic policy development The complete report of the Canadian Acid Deposition Science Assessment is available next week at

13 Riverside CL meeting, Feb , 2005  Terrestrial critical loads