Tuesday, 8 November 2005
9

Long-Term Trace Metal Retention in a Coarse-Textured Forest Soil after a Heavy Biosolids Application.

Julie Forcier, University of Washington, 10511 23rd Ave NE, Seattle, WA 98125

Short-term studies have shown that trace metals added to soils from biosolids applications are retained within soil. This study evaluated trace metal retention in a coarse-textured soil that had 500 Mg ha-1 of biosolids disked into the top 30 cm of soil 29 years ago. Two hypotheses tested were i) total trace metal concentrations are not different for control and biosolids plots below 30 cm; and ii) total trace metal pools are not different for 1990 and 2004 amended soil data. Forest floor and soil samples were collected to a 90 cm depth at the University of Washington's Charles Lathrop Pack Demonstration Forest and analyzed for pH, total C, N, and trace metals. The first null hypothesis rejected Cd at the 45-60 and 60-90 cm depths. At these two depths, Cd averaged 1.0 vs. 5.5 mg kg-1 and 0.5 vs. 4.7 mg kg-1 for control and biosolids plots, respectively. This null hypothesis also rejected Zn at the 30-45 cm depth, with average concentrations of 61.9 vs. 247.5 mg kg-1 in control and biosolids plots, respectively. The second hypothesis rejected Cd and Zn. Differences in Cd pools occurred for 0-30 and 30-45 cm depths. At these two depths, Cd pools averaged 39 vs. 25 kg ha-1 and 0.24 vs. 2.11 kg ha-1 for 1990 and 2004 data, respectively. Differences in Zn occurred at the 30-45 cm depth, with average pools of 18 vs. 230 kg ha-1 for 1990 and 2004 data, respectively. This study shows a gradual movement of Cd and Zn over time; however, even after 29 years, the trace metals are being retained and prevented from leaching into groundwater.

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