Critical Loads Meeting at Mission Inn, Riverside CA February Jack Cosby University of Virginia Scientific Justification for Using the Critical Loads Approach Geochemical Processes Patterns of Response Dynamics of Response

Critical Loads Meeting at Mission Inn, Riverside CA February Jack Cosby University of Virginia Scientific Justification for Using the Critical Loads Approach Geochemical Processes Patterns of Response Dynamics of Response

Atmosphere Soil and Soil Water Stream Water Al-X BC-X CO 2 Al(OH) 3 HCO 3 BC + H+H+ Al 3+ HCO 3 ANC > 0.0

Atmosphere Soil and Soil Water Stream Water Al-X Al(OH) 3 HCO 3 H+H+ Al 3+ CO 2 Al(OH) 3 CO 2 Al 3+ HCO 3 H + OH - ANC = 0.0

Atmosphere Soil and Soil Water Stream Water Al-X BC-X CO 2 Al(OH) 3 HCO 3 BC + H+H+ Al 3+ HCO 3 Primary Mineral BC+ Weathering Long-term Steady- state Condition Weathering rate = ANC production rate ANC SS > 0.0

Atmosphere Soil and Soil Water Stream Water Effects of Acidic Deposition on Soils and Drainage Waters H 2 SO 4 Al-X BC-X CO 2 Al(OH) 3 HCO 3 BC + H+H+ Al 3+ HCO 3 BC+ Weathering ANC SS > 0.0

Atmosphere Soil and Soil Water Stream Water Al-X BC-X CO 2 Al(OH) 3 HCO 3 BC + H+H+ Al 3+ HCO 3 BC+ Weathering H + OH - H 2 SO 4 SO SO 4 -X Initial Response to Acidic Deposition - without mobile anion - Buffering by adsorption of sulphate anion ANC > 0.0

Atmosphere Soil and Soil Water Stream Water Al-X BC-X CO 2 Al(OH) 3 HCO 3 BC + H+H+ Al 3+ HCO 3 BC+ Weathering H+H+ H 2 SO 4 SO SO 4 -X SO Initial Response to Acidic Deposition - with mobile anion - Buffering by cation exchange ANC > 0.0 ( neutral salt of sulphate )

Atmosphere Soil and Soil Water Stream Water Long-term Response to Acidic Deposition depletion of soil base saturation Al-X CO 2 Al(OH) 3 BC + H+H+ Al 3+ HCO 3 Al 3+ BC+ Weathering Al(OH) 3 CO 2 Al 3+ HCO 3 H + OH - H+H+ H 2 SO 4 SO SO 4 -X SO ??? Final ANC depends on relative magnitudes of BC and SO 4

Atmosphere Soil and Soil Water Stream Water Long-term Response to Acidic Deposition depletion of soil base saturation Al-X CO 2 Al(OH) 3 BC + H+H+ Al 3+ HCO 3 Al 3+ BC+ Weathering Al(OH) 3 CO 2 Al 3+ HCO 3 H + OH - H+H+ H 2 SO 4 SO SO 4 -X SO HCO 3 If BC > SO 4 ANC > 0.0 ( but < ANC SS )

Atmosphere Soil and Soil Water Stream Water Long-term Response to Acidic Deposition depletion of soil base saturation Al-X CO 2 Al(OH) 3 BC + H+H+ Al 3+ HCO 3 Al 3+ BC+ Weathering Al(OH) 3 CO 2 Al 3+ HCO 3 H + OH - H+H+ H 2 SO 4 SO SO 4 -X SO H + Al 3+ If SO 4 > BC ANC < 0.0

Atmosphere Soil and Soil Water Stream Water Initial Recovery from Acidic Deposition replenishment of soil base saturation Al-X CO 2 Al(OH) 3 BC + H+H+ Al 3+ HCO 3 Al 3+ BC+ Weathering Al(OH) 3 CO 2 Al 3+ HCO 3 H + OH - ANC ~ 0.0 ( ANC < ANC SS )

Atmosphere Soil and Soil Water Stream Water Final Recovery from Acidic Deposition soil base saturation restored Al-X BC-X CO 2 Al(OH) 3 HCO 3 BC + H+H+ Al 3+ HCO 3 BC+ Weathering ANC = ANC SS

Critical Loads Meeting at Mission Inn, Riverside CA February Jack Cosby University of Virginia Scientific Justification for Using the Critical Loads Approach Geochemical Processes Patterns of Response Dynamics of Response

Use Dynamic Model for Quantitative Understanding of Changes in Soil Properties Responsible for Time Scales of Acidification and Recovery

Use Dynamic Model for Quantitative Understanding of Changes in Soil Acid-Base Properties During Acidification and Recovery

Critical Loads Meeting at Mission Inn, Riverside CA February Jack Cosby University of Virginia Scientific Justification for Using the Critical Loads Approach Geochemical Processes Patterns of Response Dynamics of Response

Recovery delay time From the UN ECE ICP mapping and modeling (Max Posch) DDT: Damage delay time RDT: Recovery delay time Stage 1Stage 2Stage 3Stage 4Stage 5 Critical load Critical response Chemical target (ANC) Biological response Acid deposition Chemical response t1t1 t2t2 t3t3 t4t4 t5t5 t6t6 RDT DDT