Monday, November 13, 2006 - 2:15 PM
109-5

Continuing Acidification of Organic Horizons in Forest Soils of the Northeastern USA.

Chris E. Johnson, Richard A. F. Warby, and Charles T. Driscoll. Syracuse Univ, Dept of Civil and Environmental Engineering, 151 Link Hall, Syracuse, NY 13244

Legislation-driven reductions in sulfur emissions have resulted in decreases in acid inputs to forest ecosystems of the northeastern United States in the last 10-15 years.  While there is some evidence that surface waters are beginning to respond to lower acid inputs, the rate of surface-water recovery is much less than expected.  We examined changes in the chemistry of Oa soil horizons throughout the northeastern USA, comparing samples collected in 2001-02 with samples collected in 1984 as part of the EPA's Direct/Delayed Response Program.  Oa horizons throughout the region exhibited reduced base saturation and increased exchangeable acidity between 1984 and 2001-02.  Normalized to soil carbon, the sum of exchangeable base cations (Ca, Mg, K, Na) declined from a median value of 39.2 cmolc kg-1 in 1984 to 18.9 cmolc kg-1 in 2001-02.  Median exchangeable acidity increased from 15.0 cmolc kg-1 to 24.3 cmolc kg-1 in the same period.  Acidification was most pronounced in the eastern part of the region (NH and Maine).  The continuing acidification of soils that we observed helps to explain the lower-than-expected recovery of surface waters in the region.