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Book: Quantifying Soil Hydromorphology
Published by: Soil Science Society of America

 

This chapter in QUANTIFYING SOIL HYDROMORPHOLOGY

  1.  p. 107-127
    SSSA Special Publication 54.
    Quantifying Soil Hydromorphology

    M.C. Rabenhorst, J.C. Bell and P.A. McDaniel (ed.)

    ISBN: 978-0-89118-949-7

     

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doi:10.2136/sssaspecpub54.c7

A Quantitative Study of Pedogenesis in California Vernal Pool Wetlands

  1. W. A. Hobson and
  2. R. A. Dahlgren
  1. University of California Davis, California

Abstract

Vernal pools are episaturated seasonal wetlands that display all the hydrologic, soil, and vegetation characteristics to be classified as jurisdictional wetlands. The purpose of this study was to correlate soil morphological features with biogeochemical processes in a representative vernal pool catena in the northern Sacramento Valley, near Chico, California. Solid-phase characterization and in situ measurement of redox potential were used to quantify the dominant pedogenic processes. The summit soil, an Aquic Durixerert, has a deeper, more developed profile than the rim or basin soils, both Vertic Duraquolls. The dominant soil processes are ferrolysis, organic matter accumulation, clay formation and translocation, and duripan formation. The cyclic oxidation and reduction of Fe and Mn (ferrolysis) has resulted in seasonally low pH and accelerated mineral weathering above the duripan. The by-products of ferrolysis, soluble bases, silica and metal cations, move downward in the profile and accumulate above the duripan as the pools dry. Oxidation of Fe and Mn creates high-chroma mottles, and near-neutral Mn stains, concretions, and masses. Redoximorphic features are characteristic of this wetland along with low-chroma depletions. The areas of lowest redox potential, the basin and rim, have the most abundant redox features. Organic matter concentrations are highest in the summit surface horizons, diminish with depth in the profile, and decrease laterally to the basin. Organic C pools (kg m−2) above the duripan are greatest in the summit, then rim, and basin. Clay translocation has produced subsurface horizons enriched in clay (42–57%). Duripan formation occurs as illuvial weathering products, dominantly silica with accessory iron oxides and CaCO3, cement subsurface horizons to varying degrees. The duripan and subsurface clay-enriched horizons are essential for maintaining episaturation and nutrient cycling in the upper soil horizons.

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Copyright © 1998. Copyright © 1998 by the Soil Science Society of America, Inc., 5585 Guilford Rd., Madison, WI 53711 USA