Identifying coastal acid sulfate soils

Management of acid sulfate soils involves identifying them via the ‘sulfur trail’ and ‘acid trail’. According to the NSW Acid Sulfate Soils Manual (p. 27), a management plan is generally required where over 0.03% of oxidisable sulfur is detected per tonne of material or more than 18 moles of H+ per tonne.

The Acid Sulfate Soils Laboratory Methods Guidelines (2004) set out the key methodologies for testing for sulfur and acid levels in soils. These are the Chromium Reducible Sulfur (SCR) suite and the Suspension Peroxide Oxidation Combined Acidity & Sulfur (SPOCAS) suite.

The guidelines use an acid-base accounting method to calculate net acidity of a sample and estimate the quantity of materials required to neutralise the acid.

The hydrogen peroxide (‘fizz‘) test is often used to screen for the presence of oxidisable sulfur. However, this is a qualitative method only that does not estimate the amount of acid that has been or could be produced through the oxidation process. The fizz test is not a substitute for laboratory analysis in the identification of acid sulfate soils for assessment purposes. In fact, it is widely understood that the peroxide test commonly returns false negative and false positive results.

The guidelines also recommend best practice methods for the sampling, handling and transport of soil samples.

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Page last updated: 12 October 2015