Redoximorphic Features and Microbial Processes

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Redoximorphic Features and Microbial Processes

• Presented by Ray Finocchiaro
• University of Missouri, Columbia
• Soil, Environmental, and Atmospheric Sciences

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• What are redoximorphic features, why are they
  used,
• and where are they found.
• Microbial Processes Involved with these
  Features.
• Specific examples of redoximorphic features and
  how
• they are formed.

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Redoximorphic Features

• Formed by the reduction, movement, and oxidation
  of Fe and Mn compounds.
• Various Colors of Gray, Red, Yellow, Brown, and
  Blacks.
• Associated with seasonally saturated and reduced
  soil.
• Most widespread morphological feature formed by
  redox reactions.

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Importance Of Redox Features

• Easy to identify in the field.
• Reliable and long lasting.
• Indicators of Soil Drainage Characteristics.
• Delineate wetlands (U.S. policy)
• 1849 Swamp Act swamp clearing
• 1929 Migratory Bird Conservation Act
• 1972 Clean Water Act (404)
• 1977 Executive Order 11990
• 1985 FSA (Farm Bill / Swampbuster)
• 1988 1993 The National Wetlands Policy Forum

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Where are these features found

• Hydric Soil are wet long enough to periodically
  produce anaerobic conditions, thereby influencing
  the growth of plants.
• Form under a variety of hydrological regimes
  (i.e., permanent seasonal)

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Redox Chemistry and Hydric Soil

• Soil Must be saturated and reduced
• Induces biological chemical processes that
  change the soil from an aerobic and oxidized
  state to anaerobic and reduced state.
• Allows chemical reactions to occur that develop
  the common characteristics found in hydric soils
  (OM, gray colors, H2S, CH4)

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Microbial Processes Redox

• (BIG) (SMALL)
• OM soil fauna OM soil flora
• Sugars AA soil flora e- H
  (oxidation)
• reduced substance H20
• (reduction)

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Reduction and Respiration

• Aerobic (air-rich conditions)
• Oxygen is the main TEA
• Anaerobic
• The major TEA compounds NO3-, MnO2, Fe(OH)3,
  SO42-, and CO2 (theoretically)
• Not all bacteria use the same TEAs but most soils
  contain all microbial species necessary to reduce
  these compounds.

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Factors Leading to Reduction in Soils

• Saturated to exclude oxygen from the soil
• Contain OM that can be oxidized / decomposed
• Microorganisms must be respiring and oxidizing OM
• Stagnant or slow moving water

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Principal Reduction Reactions in Hydric Soils

• Denitrification (NO3- NO2-)
• Fe and Mn reduction (production of mottles)
• SO42- reduction (H2S production)
• CO2, CO32- reduction (CH4)

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Fe and Mn Reduction

• Rates and extent of reduction dependent on forms
  of oxides
• Fe2 (ferrous) highly leachable, when reduced or
  removed allows gray soil colors
• NO3- inhibits reduction of Fe oxides
• Mn reduction can occur with NO3-

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Types of Redoximorphic Features

1. Redox Concentrations
2. Redox Depletions
3. Reduced Matrix

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Redox Concentrations

• Bodies of apparent accumulation of Fe and Mn
  oxides.

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Nodules and Concretions

• Firm to extremely firm irregularly shaped bodies
  with diffused boundaries.

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Masses

• Soft bodies, frequently within the matrix, whose
  shape is variable.

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Pore Linings

• Zones of accumulation that may be either coatings
  on a pore surface or impregnations of the matrix
  adjacent to the pore.

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Redox Depletions

• Bodies of low chroma ( 2) having values of four
  or more where Fe-Mn oxides alone have been
  stripped out or where both Fe-Mn oxides and clay
  have been stripped out.

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Fe depletions are low chroma bodies with clay
contents similar to that of the adjacent matrix.
Fe depletions can occur along pores and in the
matrix.
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Formation of Redoximorphic Features
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Summary

• Red, yellow, browns and black colors are produced
  by the Fe and Mn oxides.
• In anaerobic conditions these oxides can be
  reduced by microbial respiration.
• Once reduced the soil develops the characteristic
  grays (gley) coloring.