Download Basic Oxidation-Reduction Chemistry - Water

Describing
Redoximorphic
Features
Prepared by:
Mr. Brian Oram
Wilkes University
http://www.water-research.net
Goals of Presentation
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?
Is this motting or
a redoximorphic
feature?
Answer: Both
Is this Mottling or
Redoximorphic Feature
Color variation
is not always a
Redoximorphic
Feature !
Mottled Color Pattern – Variation in Grain Size,
Moisture Content, and Amount of Coatings
What Was the Difference?
Associated with alternating periods
of unsaturated and saturation conditions
with alternating aerobic and anaerobic
conditions.
Associated with alternating periods
of 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 environmentabove 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 Environment
Organic material is consumed by bacteria and the bacteria release hydrogen ions
and electrons (e-). The electron reacts with the oxygen and hydrogen to form
WATER (H20). 02 (air) + 4 e- + 4H+ == 2H20
In this reaction, oxygen is reduced to form water and the carbon or food for the
bacteria is oxidized.
- Anerobic Environment
Organic material is consumed by bacteria and the bacteria release hydrogen ions
and electrons (e-). The electron reacts with the nitrate and hydrogen to cause
Denitrification -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 Structure
Redoximorphic feature associated
with the oxidation and reduction
of iron.
Anaerobic Saturated Conditions
Fe203+4e- +4H+ = 2Fe+2 +3H20
When the soil aerates or as reduced
Iron diffuses, the iron reoxidzes.
Creates Zones of Depletion and Zones
Of Concentration.
How do we use ?
The Answer: Iron – Close UP !
Zone of Depletion- Iron
Reduced and/or Removed
(Gray)
Matrix Color (Predominate Color)
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.
What the Data Means or
Suggests.
Saturated Aerobic
Monitoring Shows Saturated Conditions
Extend To this Zone.
Redoximorphic Features Observed
Saturated and
Anaerobic
Observed Saturated Conditions During
Testing
Describing
Redoximorphic
Features
Prepared by:
Mr. Brian Oram
Wilkes University
http://www.water-research.net