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Factors contributing to the acid sulfate soil scalding process in the coastal floodplains of New South Wales, Australia

Mark A. Rosicky A C , Leigh A. Sullivan A , Peter G. Slavich B and Mike Hughes B
+ Author Affiliations
- Author Affiliations

A Centre for Acid Sulfate Soil Research, Southern Cross University, Lismore, NSW 2480, Australia.

B New South Wales Agriculture, Wollongbar Agricultural Institute, Bruxner Highway, Wollongbar, NSW 2477, Australia.

C Corresponding author; email:

Australian Journal of Soil Research 42(6) 587-594
Submitted: 16 May 2003  Accepted: 10 May 2004   Published: 17 September 2004


Acid sulfate soil (ASS) scalds are persistently bare areas of land, occurring in the coastal backswamps of New South Wales (NSW), Australia. This study aims to understand why particular areas become ASS scalds, while adjacent areas remain vegetated. Some important soil parameters are compared and field observations are summarised. Soil core sampling in both ASS-scalded land and surrounding areas of permanently vegetated paddocks has demonstrated similar pyrite concentrations and depth occurrence, soil salinity, and soil acidity (pH). As conditions are similar beneath both vegetated and non-vegetated land, there must be some additional factors influencing which areas become denuded. Several disparate (usually human-induced) events were found to cause initial loss of vegetative cover. Once the soil is bare, surface evaporation causes toxic solutes to build up quickly at the soil surface and ASS scalding is perpetuated. Some of the intervening events include fire, flood, flood-scouring, deliberate topsoil removal, surface pyrite oxidation, saltwater inundation of freshwater paddocks, saltwater exclusion from saltmarsh or mangroves, changes to the vegetation regimes, excessive vehicular traffic, and over-grazing. Backswamp management needs to ensure that land underlain by shallow pyritic layers (or with soil-water that is enriched with the toxic by-products of pyrite oxidation) is not laid bare by accident or design. Similar soil chemical conditions underlying both ASS scalds and the surrounding permanently vegetated paddocks suggest that much larger areas are potentially at risk of ASS scalding.

Additional keywords: pyrite oxidation, acid sulfate soil acidity, acid sulfate soil salinity, surface pyrite, subsurface pyrite, backswamp management, backswamp drainage.


This research was funded by the Acid Sulfate Soil Program (ASSPRO), a NSW government initiative, and administered by the Acid Sulfate Soil Management Action Committee (ASSMAC). It forms part of a PhD research project, jointly supervised by Southern Cross University, Lismore, and Agriculture NSW, Wollongbar.


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