Redoximorphic

Redoximorphic Features and Microbial Processes: 

Redoximorphic Features and Microbial Processes Presented by: Ray Finocchiaro University of Missouri, Columbia Soil, Environmental, and Atmospheric Sciences

Slide5: 

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.

Redoximorphic Features: 

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.

Importance Of Redox Features: 

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

Where are these features found: 

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)

Redox Chemistry and Hydric Soil: 

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)

Microbial Processes & Redox: 

Microbial Processes & Redox (BIG) (SMALL) OM + soil fauna OM + soil flora Sugars + AA + soil flora + e- + H+ (oxidation) reduced substance + H20 (reduction)

Reduction and Respiration: 

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.

Factors Leading to Reduction in Soils: 

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

Principal Reduction Reactions in Hydric Soils: 

Principal Reduction Reactions in Hydric Soils Denitrification (NO3- – NO2-) Fe and Mn reduction (production of mottles) SO42- reduction (H2S production) CO2, CO32- reduction (CH4)

Fe and Mn Reduction: 

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-

Types of Redoximorphic Features: 

Types of Redoximorphic Features Redox Concentrations Redox Depletions Reduced Matrix

Redox Concentrations: 

Redox Concentrations Bodies of apparent accumulation of Fe and Mn oxides.

Nodules and Concretions: 

Nodules and Concretions Firm to extremely firm irregularly shaped bodies with diffused boundaries.

Masses: 

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

Pore Linings: 

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

Redox Depletions: 

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.

Slide27: 

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

Formation of Redoximorphic Features: 

Formation of Redoximorphic Features

Summary: 

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.