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Effects of Acidic and Neutral Sulfate Salt Solutions on Forest Floor Arthropods¹

ABSTRACT

Acidic and neutral SO₄^2– solutions were applied to a mixed oak (Quercus spp.) forest floor on Walker Branch Watershed in eastern Tennessee to study effects of increased acid deposition on decomposer arthropods and arthropod regulation of P cycling. Treatments consisted of ambient (no applications), 2 x (low), and 10 x (high) annual atmospheric inputs of SO₄^2– (as K₂SO₄) and H⁺ plus SO₄^2– (as KHSO₄). Arthropods were sampled monthly in litter and mineral soil. Soils were analyzed for Bray no. 2 P and for salt pH, NH₄Cl exchangeable Al³⁺ and K⁺, and water-extractable SO₄^2–.

Over a 14-month period, the number of forest floor macroarthropods averaged 19% lower in the high SO₄^2– salt treatment compared with the control. Macroarthropod fungivores also were adversely affected by the high SO₄^2– salt treatment and by the high and the low KHSO₄ treatments. The effects of the high SO₄^2– treatment on macroarthropods may have resulted from a salt effect caused by the concentrated K₂SO₄ applications (112 mmol K⁺ m^–2 per application). Microarthropod numbers increased significantly in response to the low K₂SO₄ additions and to the high and low KHSO₄ treatments. Microarthropod fungivores, predators, and detritivores responded similarly. Comparison of microarthropod densities and soil K⁺ concentrations suggested that the response resulted from a direct fertilizer effect of K⁺ on arthropods or indirectly from an effect on microorganisms.

Mineral soil pH, exchangeable Al³⁺, and Bray P were unaffected by the treatments. Soil pH (0–15 cm) was unaffected by the KHSO₄ applications because most of the H⁺ addition was neutralized by the forest floor. Analysis of litter leachate during a single treatment interval (5 weeks) indicated that only 31% of the H⁺ applied in the high KHSO₄ treatment reached the mineral soil.

Although increased inputs of H⁺ appear to have little effect on decomposer arthropods, effects of nonacidic SO₄^2– warrant further study.

Key Words: acid precipitation • decomposer arthropods • nutrient cycling • phosphorus

¹ Research sponsored by the Electric Power Res. Inst. (RP 1813-1) for the Office of Health & Environ. Res., U.S. Dep. of Energy, under contract W-7405-eng-26 with Union Carbide Corp. Publication no. 2301, Environ. Sci. Div., ORNL.

² Environ. Sci. Div., Oak Ridge Natl. Lab., Oak Ridge, TN 37830. Current address of senior author: Dep. of Soil Sci., North Carolina State Univ., Raleigh, NC 27695-7619.

Received for publication August 27, 1983.