Acid sulfate soils: mapping the risk

Mapping acid sulfate soils will enable informed decisions related to risk management of development or changing environmental conditions such as drought.

  • 7 March 2008 | Updated 12 March 2013


Housing, marina, infrastructure and farming developments frequently disturb soils and sediments, sometimes with dramatic consequences.

To assist land managers and developers, CSIRO is leading the Atlas of Australian Acid Sulfate Soils (ASS) project, under the auspices of  the National Committee for Acid Sulfate Soils (NatCASS).

It will identify the extent and severity of ASS in coastal , River Murray and other inland environments.

The problem with acid sulfate soils

Acid Sulfate Soils occur naturally in both coastal (tidal) and inland or upland (freshwater) settings.

Left undisturbed these soils are harmless, but when excavated or drained the sulfides within the soil react with the oxygen in the air, forming sulfuric acid.

This acid, together with associated toxic elements such as heavy metals and other contaminants, can:

  • kill plants and animals
  • contaminate drinking water and food such as oysters
  • corrode concrete and steel.

Land managers need to be able to identify those areas where development is either best avoided, or is going to need some special treatment.

There are already many examples of costly mistakes in Australia involving considerable damage to land, buildings and waterways.

Our research

For decades Dr Rob Fitzpatrick and the team at CSIRO Land and Water have investigated a wide variety of coastal, inland and other (for example, minesite waste rock dumps) acid sulfate soils.

The team have identified many and varied forms of acid sulfate soils and have worked hard to identify, characterise, map and monitor them.

“The impact on biodiversity – both plant and animal – can be irreversible, because the acidic scalds or drain spoils are either devoid of all vegetation or suitable only to acid-tolerant species.”
Dr Rob Fitzpatrick, Pedologist and Research Leader

Field studies have taken place at some 900 degraded sites across Australia and overseas in countries such as China and Iraq.

The more than 8 000 samples that have been retrieved represents the wide range of acid sulfate soils and sediments including:

  • sulfidic materials
  • sulfuric materials
  • gels
  • salt efflorescences
  • salt crusts
  • iron-rich crusts
  • monosulfidic black ooze.

Analytical techniques

In the laboratory, CSIRO researchers have developed and applied various techniques to improve the reliability, accuracy and speed of analysis of acid sulfate soils.

These include:

  • geochemical
  • mineralogical, particularly x-ray diffraction and electron microscopy
  • wet chemical
  • geophysical
  • isotopic methods (S and Pb).

They have also designed experiments to synthesise several minerals under conditions approaching those found in nature.

The team learned to identify and characterise acid sulfate soils in field situations in many different environments across:

  • Australia
  • Iraq
  • Vietnam
  • Brunei
  • southern Africa.

They use specially adapted tools and techniques to model risk potential and predict responses to future land management scenarios.

Risk mapping

While some risk mapping had been undertaken in various locations around Australia, there was a lack of consistency and many large gaps.

In collaboration with NatCASS, CSIRO has developed the Atlas of Australian Acid Sulfate Soils which is available on the Australian Soil Resource Information System (ASRIS) website.

In collaboration with the National Heritage Trust and the Coastal Protection Branch of the South Australian Department for Environment and Heritage, the CSIRO team  also produced risk maps of the South Australian coast in 2002-03.

The results are freely available on the ASRIS website and the Atlas of South Australia website.


Local and state governments around Australia are beginning to respond, producing planning policies and guidelines mindful of the risks associated with acid sulfate soils.

It is hoped that the Atlas of Australian Acid Sulfate Soils will enable informed risk management, both in terms of the maintenance of existing development and the assessment of future development proposals.

Read more about CSIRO Land and Water.