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Annual Elemental Input/Output Estimates for Two Forested Watersheds in Eastern Tennessee

Tennessee Valley Authority, Coop. Forest Studies Program, Building 1505, ORNL, P.O. Box X, Oak Ridge, TN 37831-6038.

^* Corresponding author.

ABSTRACT

Atmospheric inputs of SO^2–₄, NO^–₃, PO^3–₄, NH⁺₄, Ca²⁺, Mg²⁺, Na⁺, and H⁺ via wet and dry deposition were compared to stream water outputs at two study sites, Camp Branch and Cross Creek, during the period 1978 to 1983. The Cross Creek site is located 19 km from a major coal-fired point source and has been subjected to approximately 30 yr of elevated atmospheric input while Camp Branch is located in an area removed from the possible local influences of a major point source. Hydrologic comparison of mean streamflow output to incoming precipitation indicates a greater loss of water (64%) to streamflow at Cross Creek than Camp Branch (56%). No site differences (p = 0.05) could be detected in mean annual wet input for any element. The dryfall comparison indicated only a higher level of Mg²⁺ input at Cross Creek. The relative contributions of anions and cations in both wetfall and dryfall was similar at both sites with SO^2–₄ > NO^–₃ > PO^3–₄ for the anions and H⁺ > Ca²⁺ > NH⁺₄ > Na⁺ > Mg²⁺ > K⁺ for the cations. Export of anions in streamflow had the same relative relationship as observed for wetfall and dryfall. The SO^2–₄ ion accounted for 86% of the measured anion export at Camp Branch and 91% at Cross Creek. Although SO^2–₄ export varies between sites as a function of flow, concentration values remain relatively constant from year to year. Cation export was dominated by Mg²⁺ at Camp Branch, followed by Ca²⁺ > Na⁺ > K⁺ > NH⁺₄ > H⁺. At Cross Creek, the order of cation export was Mg²⁺ > Ca²⁺ > Na⁺ > K⁺ > H⁺ > NH⁺₄. Comparing base cation inputs to outputs, there is a mean efflux of 203 mol_c ha^–1 yr^–1 at Cross Creek. Although SO^2–₄ retention rates are 78% of input, it is still the dominant measured companion anion, although there is circumstantial evidence for a substantial HCO^–₃ contribution. The H⁺ ion input is also almost completely retained within the system. Base cation loss at Cross Creek was 31% higher than that at Camp Branch. However, it is difficult to demonstrate any significant impact of the elevated historical S input because nutrient export was highly correlated with streamflow and streamflow volume was 29% higher at Cross Creek.

This article has been cited by other articles:

				J. M. Kelly and P. A. Mays SOIL CARBON CHANGES AFTER 26 YEARS IN A CUMBERLAND PLATEAU HARDWOOD FOREST Soil Sci. Soc. Am. J., April 11, 2005; 69(3): 691 - 694. [Abstract] [Full Text] [PDF]