PARENT SESSION
Wednesday, August 9, 8:00-11:30 am
COS 55 - Forest ecology III: historical and enviornmental changes
L-11, Lobby Level, Cook Convention Center
Presiders: W Currie

The Fernow Watershed Acidification Study: results from the first 15 years.

Peterjohn, William^*,1, Adams, Mary Beth², ¹ West Virginia University, Morgantown, WV² USDA Forest Service, Parsons, WV

ABSTRACT- To assess the long-term effects of acid deposition, results from a 15-year, whole-watershed fertilization (NH₄SO₄) experiment are used to examine the consequences of accelerated acidification on a deciduous forest ecosystem in central Appalachia. Changes in the chemistry of soils, soil solution, and stream water are consistent with conceptual models of ecosystem acidification. Temporal changes in soil chemistry are uncertain due to a small sample size and high spatial variability. However, a limited amount of early soil data suggest that during the first 5 years of the experiment, the exchangeable concentrations of Ca⁺⁺ and Mg⁺⁺ in surface soils declined while acidity increased. A rapid change in surface soil chemistry is supported by temporal changes in soil solution chemistry. In the first 3-4 years the concentrations of Ca⁺⁺, Mg⁺⁺, and acidity increased in solutions collected beneath the A & B horizons. In the next 3-4 years, the levels of Ca⁺⁺ & Mg⁺⁺ in these solutions declined while those in water leaching from the C horizon increased. In the last 7 years, levels of Ca⁺⁺ and Mg⁺⁺ in water leaching from the C horizon decreased. Since fertilization began, baseflow pH in stream water has declined from 6 to 5.5, and the concentrations of NO₃^-, SO₄^--, Ca⁺⁺, and Mg⁺⁺ increased. In recent years, the increase of NO₃^-, Ca⁺⁺, and Mg⁺⁺ in stream water appears to have stopped, and may be declining. Long-term monitoring and tree ring analyses suggest that fertilization initially increased forest growth but it now appears that growth is no longer stimulated and may be declining for several important tree species including red maple (Acer rubrum), black cherry (Prunus serotina), and yellow poplar (Liriodendron tulipifera). If acidification due to atmospheric deposition mimics these results, significant changes in forest structure and function could occur.

Key words: watershed, acidification, forests