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Wetland Soils

Wetland soils are saturated, flooded or ponded long enough to develop anaerobic conditions in the upper layers of the soil profile. Because of the prolonged period of saturation, anaerobic and/or saturated conditions will influence the genesis of the wetland soil as well as the wetland plant species that grow.

Four conditions are required for a soil to become anaerobic and support reducing reactions (and the development of soil morphological features, if these chemical transformations occur in the soil’s upper layers):

  • the soil must be saturated to the point of excluding atmospheric oxygen
  • the soil must contain a source of organic matter that can be oxidised or decomposed
  • the soil must contain a population of respiring microbes that will oxidise the organic matter
  • the water must be stagnant or slow moving.

Soil morphological indicators are also used to identify a wetland soil. Following is a list of general indicators that may be used:

  • the accumulation of organic matter
  • gleyed soil colours
  • soil mottling
  • iron or manganese segregations
  • oxidising root channels and soil pore linings
  • reduction of sulphur and carbon (for example, acid sulfate soils).
Fig 3 Fig 2 Fig 1

Wetland soil derived from sands. Note the dark, fibrous surface layer showing clear accumulation of organic matter.

Oxidised root channel linings in a soil ped. This morphological feature was observed throughout the top 30cm of a wetland soil.

Aerial roots on a Melalueca spp, suggesting that the surface soils in this wetland remain under anaerobic conditions for many months at a time.

Wetland soils impact directly on other wetland characteristics (for example, water quality, fauna, vegetation), and can be a reflection of the physical processes occurring in the wetland (for example, water inflow, water chemistry, filtering of pollutants). The national soils layer is the Australian Soil Resource Information System, which carries broad scale to point scale information.

 

 

 

 

 

Last updated: 4 July 2008