Environment and Resource Management

The coastal zone: Acid sulfate soils

Author

Bernard Powell, Department of Natural Resources and Water

Reviewer

Nikki Moore, Environmental Protection Agency

Key findings

Indicators and summary of status


Indicator

Status of indicator

Coastal population growth 2000-05

Queensland continues to experience population growth along the coastline, putting additional pressure on areas of acid sulfate soils. The greatest pressures are being felt in south-east Queensland, with moderate pressure in the Wide Bay, Townsville and Wet Tropics areas. []

Area of land (ha) extremely acidified by acid sulfate soils

Parcels of land acidified by disturbance of acid sulfate soils have been identified along the coastline, but current figures of the affected areas are limited and are underestimates. In south-east Queensland, 8200 ha are known to be acidified. In the Fitzroy-Curtis coast 4650 ha have been found, and in the Mackay Whitsunday region 1200 ha. Although acid 'hotspots' have been observed elsewhere along the coast, their extent and location have not been mapped. []

Number of hotspot areas causing acidified waterways

Not all areas with acidified soils cause the acidification of surrounding waterways and wetlands. However, those that do have a significant impact on the local habitat, fish numbers and biological diversity. Acidified waterways have been confirmed from the Gold Coast to Cairns but information on the number and severity has not been collected or mapped. Where receiving waters for a time mitigate or mask the impacts of acidification through dilution or buffering, this is likely to reduce the assimilative capacity of the waterway to respond to other environmental pressures or climate-related events. []

Number of currently active ERA licences with acid sulfate soil conditions

This information is not accessible from existing databases. However, it is estimated that about 80 Environmentally Relevant Activities (ERA) licences with acid sulfate soil conditions apply to dredging and quarrying activities in the Brisbane district from the New South Wales border to Caboolture. []


Importance

Description and implications

Acid sulfate soils contain iron sulfides such as pyrite. When exposed to oxygen in the air, the pyrite breaks down to form sulfuric acid. With rain, the sulfuric acid, dissolved metals such as aluminium and iron, arsenic and black ooze by-products find their way into adjacent drains, swamps and estuaries, affecting aquatic life.

Acid sulfate soils along the Queensland coast cover an estimated 2.3 million hectares. Only in the past decade have they been recognised as one of the most important environmental issues affecting land use on the coastal lowlands.

Acid sulfate soil disturbance in Queensland has been linked to major fish kills and outbreaks of red spot disease (Aphanomyces invadens) in fish, and to the increased incidence of nuisance algal blooms (Lyngbya majuscula) and disease-carrying, acid-tolerant mosquitoes. It can be a major factor in the deoxygenation of coastal waterways, leading to foul smells, the accumulation of black oozes in drains and the depositing of red iron floc (rust staining) on river banks, plants and boats.

Acid sulfate soils are a major issue for coastal zone agriculture where farming activities have led to the drainage or excavation of low-lying land. Past expansion of the sugar industry and drainage schemes on coastal lowlands have led to unintended off-site impacts that have lasted for decades. In some cases, acidification of soils through lowering of the watertable and spreading of acidifying drain spoil on fields has led to poor sugarcane growth. The expansion of canegrowing into the East Trinity area near Cairns collapsed because of acid sulfate soil problems.

The acid may also attack concrete, steel and road infrastructure (bridges, bitumen, pipes and foundations), leading to faster failure rates and higher maintenance costs. For example, a Sunshine Coast council had to spend over $1 million replacing relatively new pipes that should have lasted 50 years.

In some coastal sands, acid sulfate soil layers can be found deep below the surface. Groundwater extraction and lowering of the watertable can lead to rapid acidification of the acid sulfate soil layer, leading to the acidification of groundwater and dissolution of heavy metals: for example, toxic levels of arsenic in the groundwater have become a major concern in Perth, Western Australia. This serves as a warning that caution should be exercised, and investigations conducted of acidification risk, before accelerated extraction of groundwater from coastal sands is undertaken.

The level of expertise required and the costs to safely remediate already acidified soils, groundwaters and waterways are extremely high and impacts may persist for decades.

Location

Acid sulfate soils are found in low-lying areas generally below 5 m Australian Height Datum (AHD) along the Queensland coast (Figure 6.11). Although these soils or buried sediments are harmless in their natural waterlogged state, when disturbed by excavation or drainage they can generate large quantities of sulfuric acid. Heavy rain can transport the acid into local waterways, causing catastrophic environmental damage.

No statewide statistics are available on the total area of disturbed acid sulfate soils or the number of hotspots causing acidification of waterways. In south-east Queensland alone, the known acidified area of disturbed acid sulfate soils is 8219 ha, representing 11% of the area of acid sulfate soils mapped there (78 000 ha). Mapping programs have revealed 4650 ha of acidified acid sulfate soils in the Fitzroy Statistical Division and 1212 ha in the Mackay Statistical Division. Because these figures are derived from the currently available maps and many gaps remain, they are gross underestimates. With time, additional mapping will allow better estimates of known areas of acidification.


Figure 6.11 Distribution of acid sulfate soils in Queensland
Source: DNRW

Management

If acid sulfate soils are adequately assessed and managed, impacts resulting from their disturbance can be avoided. However, safe remediation of already acidified soils and waterways is usually difficult and expensive, and the community may bear the impacts for decades or more. Since 2002 the Queensland Government has introduced planning policies and regulations that require best practice management of acid sulfate soils, which are reducing the risk of environmental damage and future remediation costs. These build on more general environmental legislation that has been applied to acid sulfate soil issues in a gradually refined way since the late 1990s. The Queensland Government has prepared technical guidelines on the management of acid sulfate soils to support best management practice.

The number of acid sulfate soil management plans required in development applications has grown dramatically since 1994 and industry-based guidelines or codes of practice have also been developed to deal specifically with acid sulfate soils. Major growth areas where acid sulfate soils management has been required include Cairns, Cardwell, Townsville, Yeppoon, Gladstone, the Sunshine Coast, Redcliffe, Bribie Island, Brisbane and the Gold Coast.

Pressure and condition

Population growth

Queensland is the fastest growing state or territory in Australia and pressure for further development on acid sulfate soils continues to intensify as population increases along the coast.

Population growth in Queensland over the three years to 2005 was the largest ever recorded for any consecutive three-year period. Growth in the year to June 2004 of almost 81 000 people is 40% (or about 23 000 people) higher than average levels of growth recorded during the slower second half of the 1990s (58 000 people each year). It is also higher than growth in the first half of the 1990s, when Queensland's population increased by an average of 75 000 people each year. This growth is strongest in coastal areas, particularly in south-east Queensland, which absorbs 80% of the state's new arrivals. A statutory SEQ Regional Plan 2005-2026 now defines an urban footprint to avoid further urban sprawl in coastal and other sensitive areas. This is expected to prove beneficial in minimising acid sulfate soil disturbances.

Population growth is driving the increasingly high value of waterfront land and coastal lowlands where acid sulfate soils commonly occur. Associated infrastructure for development such as ports, roads, bridges, lakes, canals, marinas, rail and underground capital works poses a risk of disturbing these soils. It is estimated that about 80 Environmentally Relevant Activities (ERA) licences with acid sulfate soil conditions apply to dredging and extractive and screening activities in the Brisbane District from the New South Wales border to Caboolture.

The recent drought and consequent pressures on water supply to support the burgeoning south-east Queensland population have led to proposals for accelerated coastal groundwater extraction from the offshore sand islands. Extraction carries the risk of lowering groundwater levels, leading to drying of any acid sulfate soil layers that might be present and acidification of the groundwater. The delivery of the water through a pipe grid to treatment plants also poses a risk of acid sulfate soil disturbance in low-lying coastal localities.

Rural industry expansion

Rural industry expansion onto the coastal lowlands carries with it the risk of disturbingacid sulfate soils. Further sugar cane expansion onto coastal lowlands may lead to the draining of acid sulfate soils whereas the creation of ponded pastures for grazing purposes may disturb and excavate such soils. The aquaculture industry, where it involves the construction of ponds and channels, also carries the risk of disturbing acid sulfate soils.

Response

Government

Since 1995, increasing attention has been paid to the problem of acid sulfate soils, particularly in raising awareness, delivering technical information through workshops and seminars, and offering management options. Levels of communication and collaboration among the private sector, industry groups, state and local government, conservation interests and community groups have been good and are improving.

The Queensland Acid Sulfate Soils Investigation Team (QASSIT) was established in 1995 by the then Department of Natural Resources and Mines (now the Department of Natural Resources and Water). With assistance from the Natural Heritage Trust, industries and local governments, the department has mapped and researched acid sulfate soils, developed improved tests and drainage management, and provided technical guidelines, an information service and a training program.

In 2001 QASSIT worked with the Environmental Protection Agency to develop standard conditions for treatment and management to streamline licensing procedures and provide industry with greater certainty.

In 2002 the Queensland Government released State Planning Policy 2/02: Planning and Managing Development Involving Acid Sulfate Soils (DLGP and DNRM 2002). This policy requires new planning schemes by local governments to take account of acid sulfate soils; it also requires those making new development proposals in high probability areas to undertake assessment and management of acid sulfate soils risk. In the same year, the Queensland Acid Sulfate Soils Management Advisory Committee (QASSMAC), in collaboration with government agencies, released soil management guidelines in the Queensland Acid Sulfate Soil Technical Manual (Dear et al. 2002). These tools are the basis upon which local government manages this issue through the development assessment process.

The policy and management guidelines are cross-referenced to guidelines, plans, codes and procedures that implement the Integrated Planning Act 1997 (Qld), the Fisheries Act 1994 (Qld), the Environmental Protection Act 1994 (Qld), the Vegetation Management Act 1999 (Qld) and the Coastal Protection and Management Act 1995 (Qld).

The most recent addition is the release of acid sulfate soil management measures in the Guidelines for Constructing and Maintaining Aquaculture Containment Structures published by the Department of Primary Industries and Fisheries (2007).

The statutory SEQ Regional Plan 2005-2026, which defines an urban footprint to avoid further urban sprawl in coastal and other sensitive areas, is expected to prove beneficial in minimising new acid sulfate soil disturbances.

Community

The Queensland Acid Sulfate Soils Investigation Team's technical work was complemented in 1996 by the establishment of the Queensland Acid Sulfate Soils Management Advisory Committee (QASSMAC). Members of the committee, which advises the Minister for Natural Resources and Water on acid sulfate soils matters, include representatives of the urban development, extractive and sugar industries, environmental consultants, the Queensland Conservation Council, local governments and affected state government agencies. QASSMAC continues to advise government on stakeholder views and priority actions.

In some regions, natural resource management groups and councils in partnership with the Queensland Government have made successful applications for Natural Heritage Trust funds to support mapping of acid sulfate soils, monitoring of water quality and workshops to raise knowledge and awareness. To date this has occurred at the Gold Coast, the Sunshine Coast, the Rockhampton-Gladstone area, the Mackay-Bowen area and recently in the Cairns area. In some cases local governments have sponsored acid sulfate soil mapping to help deal with particular concerns. For example, Caboolture Shire Council has supported acid sulfate soils mapping because of the ability of such soils to release large amounts of iron into adjacent waterways. Iron is an essential nutrient known to stimulate the growth of nuisance algal blooms such as fireweed (Lyngbya majuscula). In the past decade, Lyngbya blooms have appeared regularly in the adjacent Deception Bay every summer. The alga smothers seagrass habitat and also contains toxins that can cause breathing difficulties and severe blistering of the skin.

References

Dear, S.E., Moore, N.G., Dobos, S.K., Watling, K.M. and Ahern, C.R. 2002, Soil Management Guidelines, Queensland Acid Sulfate Soil Technical Manual, Department of Natural Resources and Mines, Indooroopilly.

DLGP and DNRM 2002, State Planning Policy 2/02: Planning and Managing Development Involving Acid Sulfate Soils, Department of Local Government and Planning and Department of Natural Resources and Mines, Brisbane.

DPI&F 2007, Guidelines for Constructing and Maintaining Aquaculture Containment Structures, Department of Primary Industries and Fisheries, Brisbane.

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Last reviewed 17 May 2011
Last updated 13 February 2008

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