Land and Water Link

November 2003

In nature, some things are best left alone, buried well beneath the surface. But housing, marina, and infrastructure developments frequently disturb coastal soils and sediments, sometimes with disastrous consequences. Fish kills, mangrove dieback, algal blooms and many other environmental problems can often be traced back to one thing: the disturbance of coastal acid sulfate soils.

Now, thanks to CSIRO research, the risks posed by these soils can be properly identified and managed. In collaboration with the National Heritage Trust and the Coastal Protection Branch of the South Australian Department for Environment and Heritage, the CSIRO team has produced risk maps of the entire South Australian coast. The results are now freely available, online.

Based on the CSIRO findings, planning policies have been developed at the local and state government level, and adopted by the South Australian Coast Protection Board.

But the Coast Protection Board only has the opportunity to comment when a development is proposed on land that is currently zoned ‘Coastal’, and not all land along the coast has this zoning.

So, as CSIRO team leader Dr Rob Fitzpatrick explains, these policies need to be extended by planning authorities. The South Australian Environment Protection Authority (EPA) recently developed its own guidelines.

Ultimately, it is hoped that all Australian states will adopt coastal planning policies that take into account the risks associated with acid sulfate soils. According to Dr Fitzpatrick the first important steps are now underway.

‘New methods for mapping coastal acid sulfate soils developed by CSIRO Land and Water will form the basis of a national project. We will soon be able to identify the extent and severity of acid sulfate soils along Australia’s coastline.’

An estimated 50,000 square kilometres of coastal acid sulfate soils fringe the continent, containing well over one billion tonnes of the potentially dangerous sulfidic compounds. Systematic risk mapping will pinpoint potential danger zones.

Armed with this information, resource managers in local councils can identify those areas where development is either best avoided, or is going to need some special treatment.

‘The costs associated with treating and rehabilitating acid sulfate soils are enormous’, says Dr Fitzpatrick. ‘In the past, many urban development and infrastructure projects have either stalled or been abandoned altogether. And millions of dollars worth of corroded infrastructure has had to be replaced.’

‘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.’

‘The acid either drains into waterways or reacts with carbonates and clay minerals where they are present in soils and sediments, liberating dissolved aluminium, iron, manganese and heavy metals and metalloids such as copper and arsenic. It is a lethal combination for plants and animals.’

Acid corrosion and soil subsidence damages infrastructure such as roads, concrete and steel pipes, buildings, bridges and culverts. And the environmental consequences can be catastrophic.

Dr Fitzpatrick explains: ‘A rush of acidic water into estuarine or coastal waterways leads to significant kills of fish, crustaceans, shellfish and other aquatic organisms. Even if they are not killed straight away, these creatures are left more vulnerable to infection and disease, either through direct exposure to acid, or the associated heavy metals, aluminium, iron and manganese. Acidic water containing dissolved iron and silica may also trigger algal blooms.’

‘The aquaculture industry suffers, tourism suffers and the economy suffers. And 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.’

A proposal for national risk mapping of acid sulfate soils is currently being considered by the National Land and Water Resources Audit. If approved, the project will allow Dr Fitzpatrick and his CSIRO team to assimilate existing information into a national database, identify and then fill any gaps with new research, using a standard approach.

This will enable informed risk management in coastal regions, both in terms of the maintenance of existing development and future development proposals.

Further information:

A Strategy for Implementing CPB Policies on Coastal Acid Sulfate Soils in South Australia, published in Coastline, No. 33, is available online. (PDF, 3.06Mb) [External link]

CSIRO contact:

Dr Rob Fitzpatrick
Ph: +61-8-8303 8511