SoE 2003 > Land > 4.5 Acid sulfate soils

4.5 Acid sulfate soils

Acid sulfate soils are causing severe degradation in many coastal landscapes but a remediation program is targeting the worst-affected areas

NSW has 400,000 hectares of potentially acid sulfate soils in its coastal catchments. Over 260,000 hectares are high-risk areas and more than half of these are used for agricultural production. The largest areas are on the coastal floodplains of northern NSW.

The recognition that acid sulfate soils are a serious environmental problem has been relatively recent. Large-scale fish kills in the late 1980s and early 1990s were the first evidence of the widespread impacts of acidic discharges. In response, the State Government established the Acid Sulfate Soils Management Advisory Committee to oversee and coordinate activities relating to the management of these soils. The committee developed the NSW Acid Sulfate Soils Strategy which employs a whole-of-government approach to address the problem. Components of the strategy include education and awareness, regulatory review, planning controls to address the likely impact of new development on acid sulfate soils, an Acid Sulfate Soils Manual and a program to remediate acid sulfate soil 'hot spots'.

NSW Indicator

Importance of the issue

Many low-lying coastal areas of NSW have potentially acid sulfate soils. These soils contain naturally occurring iron sulfides. If the sulfides are disturbed or exposed to the atmosphere, oxidation produces sulfuric acid which may reach surface waters. Triggers for this process include a lowering of the watertable by human activities, such as drainage, tide and flood mitigation works for new development, excavation or dredging, or natural processes, such as drought (see EPA 2000a). It has been estimated that disturbed acid sulfate soils generate 50,000 tonnes of sulfuric acid in NSW every year (DLWC 2002c).

Acid sulfate soils have a significant impact on the environment, agriculture and other industries. Release of toxic and acidic drainage waters from these soils into estuarine rivers and streams has adversely affected water quality and aquatic ecosystems. These effects have included massive kills of fish and crustaceans, the introduction of fish diseases, such as red spot disease, damage and death to oysters, and the release of heavy metals from contaminated sediments. Acid sulfate soils can also kill or restrict plant growth, e.g. in pastures. They have been responsible for corrosion and deterioration of iron, steel and concrete structures, such as pipes and bridges. Acid sulfate soils cost the NSW fishing industry an estimated $2.2 to $23 million per year (DLWC 2002c). Other industries affected include tourism, aquaculture, cropping, grazing, dairying, extractive industries and urban development. The impacts on the environment and these other industries have not been quantified.

Approximately 400,000 hectares of coastal NSW contain, or are at risk of, acid sulfate soils. Of this, over 260,000 hectares are high-risk areas with 150,000 hectares of these under agricultural production. The largest areas are on the coastal floodplains of northern NSW, particularly the Tweed, Richmond, Clarence, Macleay, Hastings, Manning and Hunter rivers (DLWC 2002e).

It is difficult to estimate the area affected by actual acid sulfate soils as the level of disturbance varies along the coast. However the worst-affected areas or 'hot spots' have been identified and these are shown on Map 4.6. Stretching from the Tweed River to the Shoalhaven, they cover 55,000 hectares of land where disturbance of potential acid sulfate soils has resulted in acid drainage and associated problems. It is important to note that these identified sites do not account for other less-affected areas, nor do they highlight the full potential problem of acid produced and stored in the floodplains.

Map 4.6: Acid sulfate soil priority management areas and areas at risk

Source: Naylor et al. 1998; Davies & Mumby 1999; Tulau 1999a; Tulau 1999b; Tulau 1999c; Tulau 1999d; Tulau 1999e; Tulau 1999f; Tulau 1999g

A less well-known and more restricted form of acid sulfate soil occurs in inland environments and is linked to irrigation or land clearing and rising watertables (Fitzpatrick 1993). Salinity and waterlogging in these 'scalded' discharge areas can lead to the mineralisation of sulfur and iron, transforming once-productive agricultural soils into locally degraded acid sulfate soils (Fitzpatrick 2002). At present, the full extent of inland acid sulfate soils is not known, although these soils have been reported in areas under irrigation near Griffith; the Yass and Macquarie valleys; the mid- and upper Hunter Valley; the Macquarie River catchment (Sullivan et al. 2002b); and near old mining areas, such as Captains Flat in the Southern Highlands.

An emerging issue related to acid sulfate soils in both coastal and inland areas is the presence of monosulfidic black oozes. These highly reactive sediments are often found in the bottom of drains in acid sulfate soil landscapes and can cause rapid and complete deoxygenation of waters when mobilised (Sullivan et al. 2002a). They have been considered a significant contributing factor in the deoxygenation of North Coast rivers, such as the Richmond, and the fish kills that occurred in these areas in 2001 (Sullivan & Bush 2001). Monosulfidic black oozes have also been discovered in inland drainage systems associated with saline areas, which may have serious implications for inland waters and aquatic ecosystems (Sullivan et al. 2002b).

Response to the issue

Under Australia's Ocean Policy, released in 1998, the Coastal Acid Sulfate Soils Program was established specifically to address water quality issues caused by acid sulfate soils (Environment Australia 2000). Funded through the Natural Heritage Trust, the Commonwealth Government allocated $2.6 million under the program for on-the-ground projects to demonstrate techniques that the community, industry and governments can use to manage these soils. In NSW, seven projects have been funded, with additional assistance and contributions from local councils, State Government agencies, community and industry groups, landholders, universities and research organisations. A national cooperative strategy for managing coastal acid sulfate soils was released in August 1999 and endorsed by the NSW Government (SCARM & ARMCANZ 1999).

In NSW, the Acid Sulfate Soils Management Advisory Committee, comprising State and local government, scientific, affected landholder, industry and environmental representatives, has been facilitating a coordinated response to the problem since 1994. The committee developed the NSW Acid Sulfate Soils Strategy which aims to prevent problems by avoiding disturbance of acid sulfate soils; managing disturbances in a manner that does not cause environmental harm; and remediate acid sulfate soil problem areas.

A major component of the strategy has involved local councils ensuring their local environmental plans (LEPs) adequately address the likely impact of new development on acid sulfate soils. Most North Coast councils, where the problem is most serious, have amended or are amending their LEPs to include acid sulfate soil provisions and risk maps. Councils in the Hunter/Central Coast, Metropolitan and South Coast regions have made less progress in this area.

Another major component of the strategy is a remediation program for acid sulfate soil 'hot spots'. Twenty-six priority areas where disturbance of potential acid sulfate soils has resulted in actual (and substantial) acid drainage have been nominated to receive remedial action (see Map 4.6).

Stage 1 of the program is due for completion by June 2004. Over $3 million is being spent to reduce the frequency, intensity and duration of acid discharges from seven hot spots in the Tweed, Clarence, Macleay, Hastings, Manning and Shoalhaven catchments. Table 4.7 describes the remediation projects in each catchment under Stage 1. To date, remediation concept plans agreed to by local committees have been prepared for all Stage 1 hot spots (see also DLWC 2002b). Detailed works programs have been prepared for six sites, and on-the-ground works have commenced.

Table 4.7: Stage 1 of the acid sulfate soil hot spots remediation program

Source: Atkinson 2001

There have been a number of other government activities to manage acid sulfate soils:

• The Acid Sulfate Soils Program has been operating for over five years in NSW and provided more than $3 million to about 70 projects to improve the awareness and management of acid sulfate soils in NSW. These projects have attracted a further $2.5 million investment in acid sulfate soil management from other funding programs and industry sources. The program has funded locally focused extension officers to provide advice to farming communities, assisting them to better understand the off-site impacts of agricultural activities and the means to reduce those impacts.
• Under the NSW Government's Environmental Services Scheme (see Land 4.1), landholders in five coastal areas will receive incentive payments to make land-use changes which bring environmental benefits, including reducing the discharge of acid sulfate soils.
• The Department of Infrastructure, Planning and Natural Resources has prepared 128 coastal acid sulfate soil risk maps, under the Acid Sulfate Soil Risk Mapping Program (Naylor et al. 1998). These have played an important part in enabling a planned response to dealing with these soils. The Department has also mapped the location and dimensions of all drains and engineered waterways within the coastal floodplains of northern NSW, from Tweed Heads to Nabiac. This work is being used to predict a range of outcomes and develop acid sulfate soil management strategies (see also DLWC 2002d).

Industry, as well as government, is taking action to prevent further disturbance of acid sulfate soils. Under a NSW sugar industry program, more than 700 cane farms in NSW have been tested for the soils. In locations where they have been detected, technical staff from the NSW Sugar Milling Cooperative are working with farmers to draft a specific drain maintenance program. In consultation with growers, the Acid Sulfate Soils Management Advisory Committee and State agencies and local government, the Cooperative has developed best practice guidelines for the sugar industry to manage acid sulfate soils (NSW Agriculture 2000). The Australian Tea Tree Industry Association has also adopted a best practice guideline and is promoting responsible development among its members. Similar developments are beginning in the dairy industry (ASSMAC 1999).

Community involvement has been an integral component of many of the projects undertaken to rehabilitate coastal acid sulfate soils. For example, the Macleay floodplain alone has 17 remediation projects with most of the highest risk soils under active management through the efforts of a range of stakeholders. The projects cover approximately 9000 hectares or 28% of the floodplain and are located at Yarrahapinni, Clybucca, Rafferty Drain, Kinchela, Belmore, Upper Maria River–Connection Creek and Frogmore–Darkwater Drains. Local landholders, interested community members and Landcare groups are working together with Kempsey Shire Council, relevant State agencies, drainage boards and Wetland Care Australia (Henderson et al. 2002).

Effectiveness of responses

Concerted efforts have been made over the last decade to improve the management and remediation of acid sulfate soils in NSW, particularly on the North Coast. Community projects to address coastal soils have resulted in greater landholder ownership of the problem and participation in the management of acid sulfate environments. These have also been beneficial environmental outcomes, such as improved water quality and the reinstatement of wetland values (Henderson et al. 2002). An independent review of the Acid Sulfate Soils Program in May 2002 found that its first five years of activity had significantly improved the capacity of floodplain communities to implement alternative water management regimes and facilitate sustainable farming enterprises.

Although much of the remediation is in an early stage, there are indications that improvements have been achieved. For example, the reduced number of fish kills and presence of healthy fish in the Tweed catchment, despite the chronic acid subcatchments locally, suggests progress is being made (NSW Agriculture 2001b).

In areas where the acid sulfate soil problem is greatest, most councils have amended or are amending their local environmental plans (LEPs) to include control provisions on the soils. These measures in are believed to have both slowed the rate of construction of new drainage works and improved the environmental performance of those works which do proceed. Best practice guidelines initiated by industry are also playing an important role in preventing further disturbance of acid sulfate soils.

Monitoring of water quality in acid sulfate soil priority areas is in its early stages and it is difficult to establish any trends. The data is available online as part of the Acid Sulfate Soils Program.

Future directions

The disturbance of potential acid sulfate soils associated with drainage systems, dredging and urban development is a significant ongoing risk factor. Such activities on high-risk acid sulfate soils should be minimised where possible. Prevention of actual acid sulfate soils is extremely important given the magnitude of the environmental and economic impacts and the substantial costs of remediation. Further progress by local councils in adopting appropriate LEPs will be important in preventing their development in the future.

The NSW Government's Acid Sulfate Soils Program will continue to assist in the ongoing remediation of acid sulfate soils in high priority areas. The further development of the Environmental Services Scheme to provide economic incentives for beneficial environmental services could make a significant contribution to managing acid sulfate soils in the future.

Linked issues

2.1 Population and settlement patterns

4.1 Land-use changes

5.1 Freshwater riverine ecosystem health

5.3 Surface water quality

5.5 Groundwater quality

5.6 Marine and estuarine water quality

6.6 Aquatic ecosystems

6.7 Aquatic species diversity

6.9 Aquatic harvesting