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Simulated Responses of Red Spruce Forest Soils to Reduced Sulfur and Nitrogen Deposition

Desert Res. Inst., P.O. Box 60220, Reno, NV 89506 and Environmental and Resource Sciences, University of Nevada, Reno 89512;

P. F. Brewer

Tennessee Valley Authority, Chattanooga, TN 37402.

^* Corresponding author (dioj{at}maxey.dri.edu).

ABSTRACT

Implications of reducing S and N deposition on red spruce forests of the southern Appalachians are explored using the Nutrient Cycling Model (NuCM). We hypothesized that reducing deposition would cause (i) large reductions in soil solution NO^–₃, SO^2–₄, Al and Ca/Al ratios, but (ii) small changes in exchangeable base cation reserves. Hypothesis (i) was supported in part: simulated reductions in atmospheric deposition had substantial and nearly immediate effects upon soil solution mineral acid anions, Ca²⁺, and Al³⁺ concentrations. Ca/Al molar ratios were much less sensitive to changes in deposition and soil solution ionic strength than either Ca²⁺ or Al³⁺ separately. Hypothesis (ii) was not supported: although the increases in base saturation and exchangeable cation pools were small relative to cation exchange, they were large relative to initial exchangeable base cation pools. These changes in base cation pools and base saturation were of sufficient magnitude to affect simulated soil solution composition during a very short time.