 Acid Sulfate Soils Risk Assessment ProjectThe Acid Sulfate Soils Risk Assessment Project aims to assess the spatial extent of, and risk posed by, acid sulfate soils at priority wetlands in the River Murray system, Ramsar wetlands and other key environmental sites in the Murray-Darling Basin and identifies management options. Although a naturally occurring phenomena, acid sulfate soils have become a cause for concern in recent years due to the drought's impact on the drying and wetting cycles of wetlands. The prolonged drought in the Murray-Darling Basin has led to river levels dropping significantly and many wetlands drying out. Long-submerged soils and sediments are being exposed to the air, creating the potential for sulfuric acid production. Following significant flooding or rains, this acid can be released into surrounding waters impacting on the health of the wetland and adjacent waterways. The Murray-Darling Basin Ministerial Council have requested that the Murray-Darling Basin Authority undertake an assessment of the extent of acid sulfate soils in the Basin. This work is being undertaken as the Acid Sulfate Soils Risk Assessment Project. What are acid sulfate soils?Acid sulfate soils are those soils containing iron sulfide minerals (e.g. Pons 1973; Fanning 2002). These soils may either contain sulfuric acid (sulfuric material), or have the potential to form sulfuric acid (sulfidic material), or cause de-oxygenation (monosulfidic material often known as monosulfidic black ooze), or release contaminants when the sulfide minerals are exposed to air (oxygen). Acid sulfate soils form naturally when sulfate-rich water (e.g. saline groundwater, sea water) mixes with sediments containing iron oxides and organic matter. Under waterlogged, anaerobic (oxygen-free) conditions, bacteria convert sulfates to sulfides. These sulfides react with metals to form sulfidic sediments. While this process occurs naturally, changes to the hydrology of inland rivers and wetlands have contributed to the accumulation of these sediments in some areas. If left undisturbed and covered with water, sulfidic sediments pose little threat. When exposed to oxygen, such as under drought conditions, chemical reactions may lead to the generation of sulfuric acid. When these sulfuric sediments are re-wetted and the amount of sulfuric acid produced exceeds the buffering capacity of the system, there is a risk that sulfuric acid may be released into the water, impacting on the health of the wetland. Other risks associated with acid sulfate soils include mobilisation of heavy metals, decrease in oxygen in the water column, and production of noxious gases. These processes can lead to substantial environmental damage and serious impacts on water supplies and human health. Acid Sulfate Soils Risk Assessment ProjectAcid sulfate soils occur in coastal regions as well as in inland aquatic systems. Record-low inflows and river levels in the Murray-Darling Basin in recent years have led to the drying of many permanent wetlands, resulting in the exposure of acid sulfate soils and the risk of acidification in some wetlands. The potential extent and threat posed by inland acid sulfate soils requires assessment. In 2008, the Murray-Darling Basin Ministerial Council requested a Basin-wide assessment of the threat posed by acid sulfate soils to key wetland environments. This assessment, the Acid Sulfate Soils Risk Assessment Project (ASSRAP) aims to assess the spatial extent of, and risk posed by, acid sulfate soils at priority wetlands in the Murray River system, Ramsar wetlands and other key environmental sites in the Murray-Darling Basin, and to identify and assess management and mitigation options. A panel of experts and wetland managers identified which wetlands should be included in the assessment project from the tens of thousands in the Murray-Darling Basin. Selected wetlands include those of ecological significance as well as those that may pose a threat to the surrounding environment if they are affected by acid sulfate soils. The Project involves three levels of assessment - the desktop and rapid assessments, which are aimed at identifying wetlands with an increased likelihood of ASS, and the detailed assessment that is carried out at wetlands identified as a priority through the previous stages. The detailed assessment aims to identify the nature and severity of acid sulfate soils at a wetland, as well as associated risks. A desktop assessment, the first of these assessment levels, was carried out on approximately 19,000 wetlands, which identified almost 1,500 wetlands requiring further investigation. Using a method developed for the Project, these wetlands have now been assessed using a rapid on-ground sampling approach, the second tier of assessment. This rapid on-ground assessment involved field and laboratory measurements of water quality and wetland sediments. The analysis of the collected data determined whether there was a high probability of acid sulfate soils and if the third and final level of assessment was required to conclusively determine the presence and extent of acid sulfate soils and the nature of associated risks. Detailed assessments are currently being carried out by acid sulfate soils scientists in consultation with wetland managers at high priority wetlands in the basin (Figure 1). A detailed assessment protocol has been specifically developed for this project which defines the methods for the comprehensive sampling, field characterisation, laboratory analysis and data presentation. The results of these detailed assessments will allow conclusions to be drawn as to the extent of risk posed by acid sulfate soils to key wetlands of the Murray-Darling Basin.
Figure 1. Location of the wetlands identified for detailed assessment of acid sulfate soils. The wetlands are grouped by regions defined for logistical purposes It is expected that the project will be complete in 2010, following the detailed assessment stage. Completion of the detailed assessment phase of the project will allow more accurate pictures of the distribution, and level of management response required, to be made. ReferencesFanning DS 2002. Acid sulfate soils. pp 11-13. In R Lal (ed.). Encyclopaedia of Soil Science. Marcel Dekker, New York. Pons LJ 1973. Outline of the genesis, characteristics, classification and improvement of acid sulphate soils. In ‘Acid Sulphate Soils. Proceedings of the International Symposium on Acid Sulphate Soils 13-20 August 1972, Wageningen, The Netherlands. I. Introductory Papers and Bibliography.' pp. 3-27. Publication No.18, International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands. Further informationMDBA (2010). Detailed Assessment of Acid Sulfate Soils in the Murray-Darling Basin: Protocols for sampling, field characterisation, laboratory analysis and data presentation. Fitzpatrick, RW, Grealish, G, Shand, P, Simpson, SL, Merry, RH, Raven, MD 2009a ‘Acid Sulphate Soil Assessment in Finniss River, Currency Creek, Black Swamp and Goolwa Channel, South Australia' CSIRO Land and Water Science Report 26/09 (CSIRO, Adelaide) This report, available on the CSIRO website Other useful links:National Water Commission - Minimising environmental damage from water recovery from inland wetlands: Determining water regimes to minimise the impact of sulfidic sediments ASSAY - national acid sulfate soils newsletter Atlas of Australian Acid Sulfate Soils, CSIRO Land and Water |
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, presents the results of research funded by MDBA into acid sulfate soils.
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