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Book: Acid Sulfate Weathering
Published by: Soil Science Society of America



  1.  p. 95-108
    SSSA Special Publication 10.
    Acid Sulfate Weathering

    J.A. Kittrick, D.S. Fanning and L.R. Hossner (ed.)

    ISBN: 978-0-89118-905-3


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Genesis, Morphology, and Classification of Acid Sulfate Soils in Coastal Plains1

  1. N. Van Breemen2


Acid sulfate soils form when potentially acid pyritic marshes are drained and tidal influence decreases, either naturally or by man. During oxidation of pyrite to ferrous sulfate, ferric oxide, or jarosite and sulfuric acid, the supply of O2 is ratelimiting. Upon slow oxidation of pyritic soil in situ, buffering by clay minerals, jarosite, and ferric oxide, keeps pace with acid formation, and the pH remains between 3 and 4. Lower pH values may develop with rapid oxidation as in excavated soil and aerated pyritic soil samples. Compared to non-acid marine soils, acid sulfate soils exhibit retarded physical development due to lower evapotranspiration by a less luxuriant vegetation. A well-developed acid sulfate soil shows, from bottom to top, an unoxidized pyritic substratum, a jarositic horizon due to oxidation of ferrous sulfate diffusing upward from oxidizing pyrite, and a horizon high in ferric oxide from hydrolysis of jarosite. As these soils become older and better drained, the jarositic horizon and the pyritic substratum are found at progressively greater depth. The distinction between Sulfaquents and Sulfic subgroups in Soil Taxonomy is practical but sulfidic material and sulfuric horizon need to be redefined.

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Copyright © 1982. Copyright 1982 by the Soil Science Society of America, Inc., 5585 Guilford Rd., Madison, WI 53711 USA