Coasts and Oceans Theme Report

Australia State of the Environment Report 2001 (Theme Report)
Australian State of the Environment Committee, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06751 5

Coastal settlement and development (continued)

Disturbance of coastal acid sulfate soils

Coastal acid sulfate soils (CASS) have, over the last decade, been recognised as contributing to one of the most important water quality issues in coastal lowlands and estuaries. Areas containing disturbed acid sulfate soils have been identified primarily in Queensland and New South Wales, although areas of undisturbed acid sulfate soils are found in all States and the Northern Territory (Figure 19). They underlie coastal estuaries and floodplains where the majority of Australians live. They also underlie significant fish nursery areas and coastal agricultural industries such as sugar cane, dairying and beef.

Figure 19: Indicative distribution of coastal acid sulfate soils in Australia.

 Indicative distribution of coastal acid sulfate soils in Australia

Source: After National Working Party on Acid Sulfate Soils (2000)

No comprehensive mapping of acid sulfate soils has been done to date. However, it is known that potential acid sulfate soils cover approximately 2.3 million hectares in Queensland (EPA 1999a) and over 0.6 million hectares in New South Wales.

In their natural, undisturbed state these soils do not pose a threat to estuarine ecosystems. Their exposure to air, as a result of development and land management practices such as drainage and excavation, generates large quantities of sulfuric acid and other substances, which adversely affects estuarine and coastal ecosystems. Studies in the Richmond River in northern New South Wales estimated over 1000 tonnes of sulfuric acid, 450 tonnes of aluminium and 300 tonnes of iron were released from a 4000-hectare catchment following a major flood in 1994. This acidified a 90-kilometre reach of the river for seven weeks, with the pH falling as low as 2.6 (National Working Party on Acid Sulfate Soils 2000).

There have been significant effects on infrastructure; for example, the Tweed Shire Council in northern New South Wales spent nearly $4 million replacing iron water pipes corroded by acid groundwater.

There is increasing recognition of CASS as a national problem needing a coordinated national approach. A National Strategy for dealing with acid sulfate soils has been developed and is being implemented. Through an initiative of Australia's Oceans Policy, the Coastal Acid Sulfate Soils Program, the Federal Government has allocated approximately $3 million for demonstration projects to assist in the better management of coastal acid sulfate soils. Funding for some eight projects to demonstrate a range of options for the management of coastal soils was announced in September 2000.

State strategies and policies have also been developed; for example:

  • New South Wales established an Acid Sulfate Soils Management Advisory Committee in 1994.
  • Queensland formed an Acid Sulfate Soil Investigation Team in 1995, an Advisory Committee in 1996 and a Strategy in 1999, and
  • Victoria developed the Industrial Waste Management Policy (Waste Acid Sulfate Soils) in 1998.

Where mangroves and low coastal land had been drained for sugar farming in the Tweed River region, acid drainage problems had resulted. However, New South Wales sugar farmers are now self-regulatory, CASS management techniques are widely accepted by the industry and individual farmers, and viable crops are being grown on previously drained CASS. Because of the actions taken, the environmental health of drainage systems running from the majority of Tweed sugar cane farms has improved markedly.