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This article in SSSAJ

  1. Vol. 52 No. 6, p. 1801-1807
    Received: July 13, 1987

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Sequential Extraction of Iron, Manganese, Aluminum, and Silicon in Soils from Two Contrasting Watersheds1

  1. R. W. Arnseth * and
  2. R. S. Turner
  1. Science Applications Int. Corp., P.O. Box 2501, 800 Oak Ridge Turnpike, Oak Ridge, TN 37831
    Environmental Science Division, Oak Ridge Nat. Lab., P.O. Box 2008, Oak Ridge, TN 37831-6038



Soil samples from two contrasting forested watersheds on the U.S. Department of Energy Oak Ridge Reservation in Oak Ridge, TN, were chosen for selective extraction of organics, Fe, Mn, and aluminosilicates. The extracts were analyzed for Fe, Mn, Al, and Si, and the results were evaluated in terms of pedogenic processes. The clay mineralogy was determined on a subset of the samples. Differences between the watersheds were observed in clay mineralogy and in the vertical distribution of extractable Mn. Walker Branch soils, developed on Knox Group carbonates, exhibit vertical flow paths capable of transporting soluble Mn deep in the profile before precipitation. Physically separated zones of Mn and Fe precipitation are observed in Walker Branch cores wherein mid-depth maxima in citrate-bicarbonate-dithionite (CBD)-extractable Fe are not mimicked in the Mn-specific extractable Mn profiles. Melton Branch soils, developed on shaly carbonates of the upper Maryville Limestone, with shaly residua persisting to the surface in some areas, retain a structure that obstructs vertical flow, forces lateral flow, and provides microenvironments for water stagnation. When these microenvironments experience periodic desiccation and oxidation, Fe- and Mn-oxyhydroxides are precipitated and coprecipitated. Therefore, clay mineralogy reflected differences in parent material whereas differences in the distribution of extractable Mn-oxyhydroxides probably reflect the distribution of soil microenvironments conducive to Mn accumulation and oxidation with implications for soil water flow patterns.

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