Describing Redoximorphic

Features

Prepared by:Mr. Brian OramWilkes Universityhttp://www.water-research.net

1. What is a redoximorphic feature?

2. What is the difference between mottling and redoximorphic features?

3. How do these features form?

4. What do these features mean and how can we use?

Goals of Presentation

Is this motting ora redoximorphic feature?

Answer: Both

Is this Mottling or Redoximorphic Feature

Color variationis not always aRedoximorphicFeature !

Mottled Color Pattern – Variation in Grain Size, Moisture Content, and Amount of Coatings

What Was the Difference?

Associated with alternating periodsof unsaturated and saturation conditions with alternating aerobic and anaerobic conditions.

Associated with alternating periodsof unsaturated and saturation conditions, variation in moisture, textural variation, but under aerobic

conditions.

Therefore,

• A redoximorphic feature is a feature formed under a set of conditions that indicates that the soil has been saturated and anaerobic for some period of time.

• Does it tell us how long ? Not really!

• The term redoximorphic replaces the old terms: mottles and low chroma colors.

Formation of Redoximorphic Features

• To form redoximorphic features we needed all of the following:

– Decomposable organic material is present.– Bacteria are active (Proper temperature and environment-

above biological zero- > 42 F).– Soil is saturated.– Soil is Anaerobic – stagnant water or water with a low flow.

If one of these factors or conditions are not present –

No Redoximorphic Features Form. The reactions we are going to

discuss are oxidation and reduction reactions.

Oxidation and Reduction Reactions

• Influence Soil Colors

• Control and Influence the amount of Oxygen, Nitrogen, Iron, Manganese, Sulfate, and Carbon in the soil.

• Responsible for denitrification, formation of sulfur or rotten egg odors, and creation of methane gas.

• Formation of features we can use to estimate the depth to saturated and anaerobic conditions and a rough estimate the depth to the water table.

Oxidation and Reduction Reactions

• In these reactions: The electrons from one substance is removed and transferred to another substance.

• Examples:– Aerobic EnvironmentOrganic material is consumed by bacteria and the bacteria release hydrogen ionsand electrons (e-). The electron reacts with the oxygen and hydrogen to formWATER (H20). 02 (air) + 4 e- + 4H+ == 2H20 In this reaction, oxygen is reduced to form water and the carbon or food for thebacteria is oxidized.

- Anerobic EnvironmentOrganic material is consumed by bacteria and the bacteria release hydrogen ionsand electrons (e-). The electron reacts with the nitrate and hydrogen to causeDenitrification -Great We are Getting Rid of Nitrogen. 1 NO3- + 10e- + 12 H+ = N2 (gas) + 6 H20

Oxidation and Reduction Reactions- The Order of Reactions

• As the soil becomes saturated, oxygen is the first ion to be reduced.

• After the soil is saturated and anaerobic, the order of reduction is as follows:

– Nitrates– Manganese (Mn02)– Iron (Fe2O3)– Sulfate– Carbon Dioxide

Therefore – a saturated soil with reduced iron –indicates the oxygen,

nitrate, and manganese has been reduced, but the sulfate and carbon

dioxide is style in an oxidized state.

How can we use this knowledge ????

How do we use ? The Answer: Iron

Prismatic Soil StructureRedoximorphic feature associatedwith the oxidation and reduction of iron.

Anaerobic Saturated ConditionsFe203+4e- +4H+ = 2Fe+2 +3H20

When the soil aerates or as reduced Iron diffuses, the iron reoxidzes.

Creates Zones of Depletion and ZonesOf Concentration.

How do we use ? The Answer: Iron – Close UP !

Matrix Color (Predominate Color)

Zone of Depletion- Iron Reduced and/or Removed (Gray)

Zone of Accumulation (Redder)

These observation indicates the either the soil mass or zones in the soil has areas within the soil that are both saturated for a sufficient period of time for the soil to become anaerobic.

Observed Saturated Conditions During Testing

Redoximorphic Features Observed

Monitoring Shows Saturated Conditions Extend To this Zone.

Saturated andAnaerobic

Saturated Aerobic

What the Data Means or Suggests.

Describing Redoximorphic

Features

Prepared by:Mr. Brian OramWilkes Universityhttp://www.water-research.net