Soils 205- General Soils

Lecture 12- Soil aeration/wetlands

I.  Aeration

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    a.  aeration is controlled by:

        1)

        2)

        3)

    b.  characterization of soil aeration

        1)

        2)

        3)

    c.  redox potential- redox potential (Eh) is a measure of the tendency of a substance to accept or donate electrons.  Measured in volts or millivolts. 

        i.  oxidizing agents:

        ii.  reducing agents:

        iii.  role of oxygen- oxygen is a very strong oxidizing agent.  All aerobic respiration requires O2 to serve as the electron acceptor as living organisms oxidize organic carbon to release energy for life.

        iv.  other electron acceptors.  N, Fe, Mn and S are also "redox sensitive" and undergo similar reactions.  The Eh value at which oxidation-reduction occurs varies with the specific substance. 

        v.  significance in soils

        1)  respiration-

        2)  if O2 becomes limiting microorganisms will use alternative electron acceptors. 

        3)  As e- acceptors are depleted, the ability of most organisms to respire (oxidize organic material) and function is inhibited.  This leads to the build up of organic materials.

II.  Wetlands-  Areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated conditions.

    a.  Importance of wetlands:

     b.  Three characteristics of wetlands:

   1)

    2)

    3)

    c.  hydric soils- soils that are saturated near the surface for prolonged periods when soil temperature is high enough for biological activity.  Anaerobic conditions must be present, not just saturation.

        Properties of hydric soils:

        1)

        2)

        3)

Mottles

III.  Wetlands as filters

-removal of excess nutrients

-degradation of many synthetic organic chemicals require alternating aerobic and anaerobic conditions.

- toxic elements such as Se and Cr undergo redox transformations, removing them from water before the water leaves the system