Sulfur Cycling in Douglas-Fir on a Glacial Outwash Terrace
1982
Stednick, John D.
In a study to determine if a temperate forest site would exhibit accelerated nutrient cycling or increased sulfur accumulation with an increased precipitation input of S, a second-growth Douglas-fir ecosystem (Pseudotsuga menziesii (Mirb) Franco) on a glacial outwash terrace accumulated 2.2 kg ha⁻¹ year⁻¹ of S. Prior to Mount St. Helen's activity, an atmospheric input as precipitation of 8.9 kg ha⁻¹ year⁻¹ of sulfate-S was augmented by an additional 8.1 kg ha⁻¹ year⁻¹ in throughfall. Sulfate-sulfur leaching decreased with increased soil depth: 8.4 kg ha⁻¹ year⁻¹ leached through the forest floor, 10.5 through the A horizon, 6.7 through the B horizon, and 3.2 at 1.5 m in the C horizon. This S budget was not complete, since gaseous forms and movements were not monitored. Sulfate-sulfur mobility accounted for an average 25% of the cation leaching through the soil profile. Sulfur utilization did not measurably change from a similar stand with lower S inputs. The increased SO₄-S input did not accelerate nutrient cycling, rather SO₄-S accumulated in the soil, presumably by sorption. Sulfate-sulfur mobility is defined by the sorption mechanism within the soil.
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