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Acid sulfate soil

Acid sulfate soils are widespread along the margins of the NSW coast, in estuarine floodplains and coastal lowlands, including urban areas, farmland, mangrove tidal flats, salt marshes and tea-tree swamps. These soils include those that are producing acid (actual acid sulfate soils) and those that could become acid producing (potential acid sulfate soils).

Acid sulfate soils are widespread along our estuarine floodplains and coastal lowlands. Photo: Mitch Tulau.

Potential acid sulfate soils are naturally occurring soils containing iron sulfides (pyrite). They become actual acid sulfate soils when they are dried, usually because of human activity, and the pyrite is exposed to air. In air, pyrite is oxidised, resulting in production of sulfuric acid.

As a direct result of inappropriate drainage and excavation for urban development and agriculture along the coast of NSW, enough actual acid sulfate soil has been created to generate 50,000 tonnes of sulfuric acid every year. This causes up to $23 million dollars worth of damage to the state's fishing industry each year.

Appropriate planning and management of urban and agricultural land to prevent damage associated with acid sulfate soils is now recognised as an extremely important issue for the NSW coast.

A well informed understanding of acid sulfate soils and their distribution is critical for sustainable use of coastal land. Within the environments containing acid sulfate soils, typical uses of land include urban development, grazing, dairying, sugar cane production, dredging and tea tree plantations. Various aquaculture industries are also located in or near these environments.