Acid Sulfate Soils

​Acid Sulfate Soils (ASS) underlie parts of Tasmania's coastline and some inland locations.

They are natural soils that contain sulfides (mostly iron sulfides), usually in microscopic form. Most of these sulfides were formed by bacterial activity (sulfate reducing bacteria) in underwater sediments over thousands of years. 

Sea water provides a ready source of sulfate sulfur for conversion to sulfides and thus extensive areas of ASS tend to be found on low-lying coastal margins once covered by sea water. As the river deltas and beach ridges advanced seaward and sea levels receded, the sulfur-rich sediments remained and today can be found in coastal plains, wetlands and estuaries.

  Landscapes in High Probability ASS areas   (623Kb)

In an undisturbed and waterlogged state these soils are harmless, but when disturbed and/or exposed to oxygen through drainage, excavation or climate change, a process of oxidation can produce sulfuric acid in large quantities. 

In an undisturbed state these soils are called Potential Acid Sulfate Soils (PASS). Once they are disturbed and start oxidising, they are called Actual Acid Sulfate Soils (AASS). They are collectively referred to as Acid Sulfate Soils (ASS).

After rain and particularly following prolonged dry periods, the sulfuric acid in AASS is released into the surrounding environment. As the acid moves through the soil profile it may 'mobilise' or cause the release of heavy metals and other toxins from the soil, which eventually flow into surrounding waterways. At worst toxic 'slugs' of metal-rich acid runoff can move downstream and flow into estuaries, reducing oxygen levels in the water, significantly decreasing water quality, killing fish and damaging sensitive ecosystems. For example, this process caused extensive environmental damage in NSW in 1987 when flooding mobilised aluminium and acid from disturbed ASS into the Tweed River.

ASS runoff has significant environmental, economic and social impacts on coastal communities. Besides the obvious impacts on the environment such as: 

  • fish kills

  • death of other aquatic organisms

  • the decline of riparian and aquatic vegetation

  • decline or failure of some agriculture, fishery and aquaculture industries

The ecological damage can also affect valuable tourist resources including fishing grounds, swimming areas and other water sports areas. 

Acid discharges can damage infrastructure services and structures such as pipes, foundations, drains, bridges and flood controls.

High levels of iron and manganese may precipitate in receiving waters causing: 

  • ​aesthetic issues

  • staining infrastructure

  • coating aquatic vegetation

  • preventing photosynthesis

  • blocking the gills of aquatic fauna

High levels of some elements such as aluminium and arsenic may also have human health implications.

Acid sulfate soils may also underlie inland areas such as peat bogs, salt lakes and wetlands. If acid sulfate conditions underlie such natural features, disturbance will have a similar effect on the surrounding area as in coastal regions with release of sulfuric acid and reduced oxygen levels in the water. Risks are increased where inland water bodies receive irrigation return water, groundwater or recycled water, as they typically contain elevated sulfate concentrations.

More general information about acid sulfate soils is available in the following publications:

 What are Acid Sulfate Soils? (Pamphlet) (PDF 218Kb)

 What are Acid Sulfate Soils? (Poster) (PDF 374Kb)

Acid Sulfate Soils Management Guidelines​​

The Tasmanian Acid Su​lfate Soil Management Guidelines (PDF) are designed to provide technical and procedural advice to avoid environmental harm from acid sulfate soils (ASS). They can help achieve best practice environmental management through the use of six management principles.

 Acid Sulfate Soil Management Guidelines (PDF 2Mb)

The guidelines have also been designed to help with decision making and provide greater certainty to the construction and agricultural industries, state and local governments and the community in carrying out planning for activities that may disturb ASS. 

It is anticipated that the guidelines will be used by: 

  • consultants

  • earthmoving contractors

  • developers

  • agricultural and aquaculture producers

  • sand and gravel extraction operators

  • community groups

  • administering authorities from state and local government

While the guidelines focus on developments below 20 m AHD the requirement for a management plan should apply wherever significant disturbance of ASS may occur in the State.

  • Section 1 
    Provides an introduction to ASS and why we should be concerned about them, where they occur in Tasmania and the Tasmanian legislation that is relevant to them.

  • Section 2
    Steps through the process of assessing projects which may involve disturbance to ASS, with the aim of determining whether a management plan is necessary for the project.

  • Section 3 
    Outlines the management principles used to guide the development of a management plan.

  • Section 4
    Gives details of management strategies, including avoidance, minimisation and neutralisation.

Other Acid Sulfate Soil Information​​

Information pamphlets for field operators, planners and developers, and the agricultural and aquacultural environments are included below (designed to be printed double-sided and folded):

 Acid Sulfate Soils : Indicators for Field Operators (PDF 258Kb)

 Acid Sulfate Soils : Information for Planners & Developers (PDF 463Kb)

 Acid Sulfate Soils in Agricultural & Aquacultural Environments (PDF 226Kb)

Acid Sulfate Soil Mapping

Acid Sulfate Soil predictive mapping is available for Tasmania on the list website.

Three layers are available which show the landscapes with potential to contain Acid Sulfate Soil in:

  1. Subaqueous Marine and Intertidal

  2. Coastal

  3. Inland environments

Field site information is also available on a seperate layer.

These separate map layers and field site information which includes associated soil core photos, laboratory results, profile description and risk assessment are also available on the list websiteSimply add the ASS layers you want and click using the identify tool to retrieve additional information about the area (polygon) or field site (point).