Riverside CL meeting, Feb. 15-18, 2005

Canadian accomplishmentson 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

2Riverside CL meeting, Feb. 16-18, 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

3Riverside CL meeting, Feb. 16-18, 2005

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 assessmentFirst mapping of terrestrial CL for eastern CanadaUpdated mapping of aquatic CL for eastern and first

mapping of CL for western Canada

4Riverside CL meeting, Feb. 16-18, 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)

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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(KGibb) = 9.0 BC/Al = 10 (M/M) The Simple Mass-Balance Model (SMB)

Critical load

limitUptakeWeatheringDepositionAcidity ANCBCBCBCCL

6Riverside CL meeting, Feb. 16-18, 2005

Critical loads and exceedances Aquatic CL

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Critical loads and exceedances Aquatic CL Exceedance

8Riverside CL meeting, Feb. 16-18, 2005

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

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Critical loads and exceedances Terrestrial CL Exceedance

10Riverside CL meeting, Feb. 16-18, 2005

Combined critical load

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Combined critical load exceedances

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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

13Riverside CL meeting, Feb. 16-18, 2005

Terrestrial critical loads