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Acid sulphate soils

Acid Sulphate Soils (ASS) contain iron sulfides (mainly pyrite) which can generate large amounts of sulfuric acid when exposed to air. These soils formed naturally over the last 10,000 years, and are safe unless dug up or drained.

ASS are widespread in our estuarine floodplains and wetlands (including mangrove tidal flats, salt marshes and tea-tree swamps). Before drainage and oxidation, they are termed Potential ASS. Actual ASS are formed when the naturally occurring iron sulfides (pyrite) in the soil become exposed to air (through drainage or excavation) and subsequently oxidise, forming sulfuric acid.


Impacts of Acid Sulphate Soils

Large scale drainage of coastal floodplains for flood mitigation, urban expansion and agriculture has exposed large areas of ASS. Acid leachate, plus the aluminium, iron and the heavy metals which it releases from soils, can cause significant environmental and economic problems. Industries, including commercial fishing and oyster farming, are often directly impacted by acid discharge. Artificial drainage of coastal wetlands and subsequent acidification has also led to large scale loss of wetland biodiversity and habitat for threatened species and migratory birds.

Acid sulphate soils in our area

The Port Macquarie-Hastings local government area has some 57 drainage systems that contribute to acid discharge. Approximately 21,737 hectares of ASS exist in the Hastings and Camden Haven floodplains of which 3580 hectares are considered to be at high risk of producing the majority of acid discharge. These high risk areas also known as 'Hot Spots' include:

  • Partridge Creek
  • Maria River
  • Rawdon Island
  • Rossglen
  • Stewarts River


Remediation Works

Under various grants and Council funding, Council have been undertaking remedial works since 2001. Remedial works aim to contain acid groundwater by means of infilling drains, and installing weirs and to rehabilitate degraded wetlands by restoring the hydrology and promoting revegetation. To date 56 drainage networks have been remediated at a cost $1.5M.

In 2006 the remaining seven artificial drainage networks are to be remediated. The completion of the rehabilitation works will represent a major improvement in estuarine and floodplain health with over 80 per cent reduction in acid discharge and all five ASS 'hot spots' remediated.  Remedial works has also resulted in the rehabilitation of over 940 hectares of scalded wetland and over 5120 hectares of floodplain under voluntary plans of management.


This page was last updated on: 21 January 2016