1. Acid-Base Properties of Aluminum in a Hardwood Forest Soil
(or: Acid Rain is Dead…)
Chris E. Johnson & Sheila M. Palmer
Syracuse University

2. Acid Rain Effects Elevated SO42- in drainage waters.
Decreased pH, ANC.
Elevated Alm.
Decreased base saturation in soil.

3. Recovery Should Result in:
Decreased SO42- in drainage waters.
Increased pH, ANC.
Decreased Alm concentrations.
Increased base saturation in soils.

4. Base Saturation and Soil pH
Brady (1974)

5. Base Saturation-pH Relationships in NE USA
Johnson (2002)

6. Organic Matter is the Principal Sorbent for Cation Binding
Johnson (2002)

7. Competition for Binding Sites: Al/H
Reaction:
Al-X + 3H+ ↔ Al3+ + H3-X KAl/H
Linear Relationship:
(log[Al3+] + 3pH) vs. log(NAl/NH)
NAl = fraction of sites occupied by Al
(CuCl2 extraction)
NH = fraction of sites occupied by H (Total Acidity – AlCuCl2)
Skyllberg (1999)

8. Swedish Spodosols
Skyllberg (1999)

9. Hubbard Brook, NH Soils This Study: n = 2.53 KAl/H = 9.87
Skyllberg (1999):
n = 2.47
KAl/H = 8.13

10. “Non-Acidic” Behavior of Aluminum
Johnson (2002)

11. Modeling Cation Binding with WHAM
Windermere Humic Aqueous Model – Tipping (1994) and updates.
Model V for cation binding by soil organic matter.
Multiple sites with varying binding properties.
Donnan-type double-layer model.

12. Hubbard Brook Soils – Titration Experiments
Brown: No model fitting – measured soil properties.
Blue: Concentration of humic substances optimized.

13. Effects of Changing Soil Al Pools

14. Field Evidence of “Excess” Al-binding Capacity

15. So, What Does It All Mean?
Al-H interactions – not Al-Ca – appear to govern Al levels in acid forest soils.
Aluminum exhibits “non-acidic” behavior in a range of forest soils of the NE USA.
“Recovery” from acidification may contain some surprises!
Increased soil Al?
Limited replenishment of soil Ca?
Acid rain is dead…
Long Live Acid Rain!