Tuesday, 11 July 2006

Developing Australian Standards for Analysis of Acid Sulfate Soil—A Step Towards International Standards.

Angus E. McElnea1, Col R. Ahern1, Glenn Barry1, Steven Dobos2, and Leigh A. Sullivan3. (1) Queensland Department of Natural Resources and Mines, Block C, 80 Meiers Rd, Indooroopilly, Queensland, Australia, (2) Dobos & Associates, 6 Pandian Crescent, Bellbowrie, Queensland, Australia, (3) Centre for Acid Sulfate Soil Research, Southern Cross University, PO Box 157, Lismore, Australia

Acid Sulfate Soil (ASS) and sediments have a worldwide distribution, occurring extensively in low-lying areas adjoining coastal and brackish waters. Increasingly, such areas are being subject to agricultural, aquacultural and urban development pressures, with drainage and other disturbances causing oxidation of iron sulfides, leading to severe acidification of soil and water, and concomitant environmental problems. Effective management of these soils is predicated on accurate estimation of their net acid producing potential, which is reliant on appropriate and repeatable laboratory analysis of these often complex and highly variable materials. While the reduced inorganic sulfur content of unoxidised sediments can be assessed by a single determination, such as that provided by the chromium reducible sulfur method, a suite of analytical techniques is needed to analyze, characterize and eventually manage ASS that have started to acidify and produce a variety of oxidation products. Prior to the development of laboratory methods guidelines for ASS, commercial and government laboratories and researchers used a wide variety of methods and approaches to analyze ASS, leading to variable results, confusion for industry and regulators, and poor environmental management outcomes. In order to overcome this uncertainty, a set of guidelines detailing routine methods for use by commercial and government laboratories in Australia have been developed and agreed upon. These methods marry the best aspects of historical approaches to analysis with the latest scientific research. During the development of these laboratory methods, drafts were circulated to over 180 interested scientists and laboratories in Australia and overseas with many of the responses being incorporated in the guidelines. The methods are contained in the current version of the Acid Sulfate Soils Laboratory Methods Guidelines on the Queensland Department of Natural Resources and Mines website (http://www.nrm.qld.gov.au/land/ass) and are free to download. The Guidelines document two decision-tree-based approaches for assessing the net acid producing potential of acid sulfate soils—the Suspension Peroxide Oxidation Combined Acidity and Sulfur (SPOCAS) suite and the Chromium Reducible Sulfur suite. Both these approaches are applicable to the analysis of the spectrum of acid sulfate soils, including highly acidic, oxidized jarositic samples, reduced samples and self-neutralizing sulfidic soils containing shell or other carbonates. That is, the suites allow for the determination of potential acidity, actual acidity, retained acidity and acid neutralizing capacity components in acid sulfate soil samples. From the laboratory results obtained, values for these components are substituted into the appropriate formula, permitting an acid base account (ABA) to be prepared. This allows prediction of net acidity, calculation of appropriate ameliorant application rates and most importantly assessment of risk, leading to better planning and management. The Guidelines are currently being redrafted in a format compatible with Australian Standards. This process is being conducted under the auspices of the Standards Australia Committee EV-009-02-01 whose contribution to the process is gratefully acknowledged. As part of the process of method standardization, six soil samples have been prepared and distributed to laboratories for analysis as part of a sample exchange program. If the methods are approved as Australian Standards, it is intended to pursue their development as ISO or other international standards.

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