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Canadian accomplishments on Critical Load Mapping

Canadian accomplishments on Critical Load Mapping. 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. Forests Rock Ouimet, MRNFP, QC Paul A. Arp, UNB, N.B. Shaun Watmough, TU, ON

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Canadian accomplishments on Critical Load Mapping

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  1. Canadian accomplishments on Critical Load Mapping 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 Forests Rock Ouimet, MRNFP, QC Paul A. Arp, UNB, N.B. Shaun Watmough, TU, ON Julian Aherne, TU, ON Ian DeMerchant, NRCan, N.B.

  2. 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. History, definitions • 1983 Target load: 20 kg/ha/yr wet SO42- deposition • 1990 8 < S-CL > 20 kg/ha/yr NSS-wet SO42- deposition • 1997 Aquatic (6 < S-CL > 18 kg/ha/yr) Terrestrial (90 < S&N-CL < 2900 eq/ha/yr) • 1998 NEG/ECP initiative • 2005 EC 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. 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. 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) • Critical load • Terrestrial • Maintaining current soil base saturation of forest soils • Log(KGibb) = 9.0 BC/Al = 10 (M/M) • The Simple Mass-Balance Model (SMB)

  6. Critical loads and exceedances • Aquatic CL

  7. Critical loads and exceedances • Aquatic CL Exceedance

  8. Critical loads and exceedances • Terrestrial CL (no harvesting, no forest fire)

  9. Critical loads and exceedances • Terrestrial CL Exceedance

  10. Combined critical load

  11. Combined critical load exceedances

  12. 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 http://www.msc-smc.ec.gc.ca/saib/acid/acid_e.html

  13. Terrestrial critical loads

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