According to the National Strategy for the Management of Coastal Acid Sulfate Soils, substantial low-lying coastal areas of the Northern Territory, Queensland and New South Wales are affected by acid sulfate soils (ASS). They are also found along the northern coastline of Western Australia, around Perth, Adelaide and Westernport Bay near Melbourne . In itself, ASS are not necessarily a problem. The problem is that the coastal regions are home to the majority of the Australian population and to various industry and production activities including utility supply, agriculture, aquaculture as well as sand and gravel extraction, which can disturb ASS. Once disturbed and exposed to oxygen, these soils oxidise and produce sulfuric acid. The economic consequences of exposure to ASS have the potential to be significant and can impact on agriculture, fishing, industry, urban development and infrastructure (Photo 1). Loss of product and productivity mainly arises as a direct consequence of the contamination and degradation of water and land .
Photo 1. Characteristic degradation of a concrete bridge pylon in the Pimpama River, southeast Queensland, occurs as the sulfuric acid from acid sulfate soils attacks the carbonate in the concrete, exposing the aggregate ('QASSIT, Qld Department of Natural Resources and Mines').
Economic costs can be incurred in the form of treatment and rehabilitation costs to deal with damage caused by ASS . Given that these soils have a low load bearing capacity, subsidence, particularly of the foundations and earthworks of buildings etc. which may unevenly settle, is a negative impact sometimes associated with ASS. In these situations, costs can be incurred due to additional infrastructure required to ensure the stability of construction. ASS are known also to corrode concrete and steel structures. The Tweed Shire Council (northern NSW), for example, recently spent $4 million replacing acid-corroded iron water pipes situated in an ASS area . Additional costs are incurred from necessary treatment technologies used to prevent the formation of ASS on potential urban development land including housing, resorts, marinas and canal estates. Much of this land attracts a premium price. In Queensland, it is estimated that soil treatments cost in excess of $100 million per annum . Overall, it has been estimated that the cost to industry of managing ASS in Queensland is approximately $189 million per annum .
Relocation costs created during the process of avoiding ASS can also drive up the economic cost of development if it has to be relocated from ASS land to non-ASS land. The process of relocation may result in costs from decreased land values; increased transport costs; loss of income from foregone expansion of industries and loss of amenities. In a more specific example, it has been estimated that testing, treating and monitoring ASS accounts for up to 25% of costs of new subdivisions in Queensland .
Disturbance of ASS affects waterways and the aquatic life they support. As a substantial proportion of Australian fisheries are estuarine dependent or estuarine opportunist, the impact of acid affected water is a major concern to commercial and recreational fishing industries. The immediate effects are manifested as fish kills. These can occur when sulfuric acid is washed into waterways, a situation common following drought-breaking rains. Long-term damage to these industries is likely to result from loss of aquatic habitat, and subsequent changes to the food chain .
Acid water causes skin and gill damage which increases the susceptibility of fish to diseases. For example, in 1995 more than $1 million worth of sea mullet was discarded by the NSW commercial fisheries due to red spot disease (Epizootic Ulcerative Syndrome) . Crustaceans that are not able to escape affected areas are badly affected. It has been estimated that $7million worth of damage has been sustained by Sydney rock oysters from ASS impacts over the last six years . The losses incurred by the NSW fisheries from ASS have been valued at between $2.2-2.3 million per annum . In Queensland it has been noted that millions of dollars have been lost to commercial fisheries due to the destruction of oysters, prawns, fish and fish breeding grounds by ASS .
In addition to this, loss of aquatic habitat areas and the reduced availability of fish targeted by recreational fishers, such as the mangrove jack (Latjanus argentimaculatus) and barramundi (Lates calcarifer), which are dependent on estuarine habitats, is likely to have adversely impacted on tourism. However, no conclusive study has been undertaken.
ASS reduces farm productivity. Sulfuric acid lowers pH which reduces the availability of soil nutrients to plants. In addition, acid reduces the availability of good pasture for grazing, reducing animal productivity and rendering areas bare of vegetation and therefore susceptible to erosion. While estimates have not been provided for the economic cost associated with ASS impacts on agriculture, one report has noted that economically important agricultural industries including dairy farming and sugar cane production are frequently situated on floodplains and estuaries . In addition, swamp pastures, used in periods of drought for grazing, become less viable when impacted by ASS. As agricultural producers in coastal areas are put under increasing pressure to increase their receipts to remain financially viable, they have expanded their activities onto land that would ordinarily be regarded as marginal and which in many cases is located in ASS areas (e.g. Herbert River catchment in north Queensland). The productivity of these systems is threatened by ASS .
While the economic consequences of ASS are substantial, it has been argued that the costs of prevention, in comparison, are minimal. For the most part, the most effective management approach has been to avoid the disturbance of soils in susceptible areas. In the case of agricultural areas, preventative costs largely consist of the opportunity cost associated with using land in a way that does not disturb the ASS and the dissemination of relevant literature to landowners notifying them about at-risk areas and how these areas can be treated or avoided .