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Acid sulfate soils

​​Acid sulfate soils occur naturally in soils that contain sulfate in addition with iron and organic matter. When they remain undisturbed and unexposed to oxygen, acid sulfate soils are not a problem.

Most acid sulfate soils become a problem when the waterlogged soil is allowed to dry, leaving soil exposed to atmospheric oxygen. When exposed to the air, these soils can produce sulfuric acid and often release toxic quantities of iron, aluminium and heavy metals.

1. Typical landscape showing a sulfidic salt-affected and eroded scald in the Tungkillo district of the central Mount Lofty Ranges, SA. 2. Salic Sulfidic Hydrosol soil profile at Gutheries in the Tungkillo district of the central Mount Lofty Ranges, South Australia, 1989.​
Photo showing acid sulfate soil ooze on surface and cross-section showing depth of acid sulfate soil. Copyright CSIRO Land and Water.
Photos: by Rob Fitzpatrick

With monosulfidic black oozes (MBOs), a type of acid sulfate soil, disturbance such as increased water flow while still waterlogged can result in a rapid decrease in the oxygen levels in the water column.

Water and soil quality can be seriously affected by exposing or disturbing acid sulfate soils. This in turn leads to other assets being put at risk. While these potential risks may be significant, resources are available to help you assess and manage the risks.

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