Assessment of Acid Sulfate Soil Materials (Phase 2) Craignook wetland, South Australia

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Shand, Paul; Baker, Andrew; Grocke, Sonia Grocke; Smith, Lester; Cozens, Gillian; Fiebiger, Catherine




An initial Phase 1 acid sulfate soil investigation of the Lower Loddon River during December 2008 showed acid sulfate soils to be a priority concern within this wetland complex. Based on Phase 1 recommendations, a Phase 2 investigation was undertaken for the Lower Loddon River to determine the nature, severity and the specific risks associated with acid sulfate soil materials. The river had largely dried during the previous drought conditions with only a series of shallow pools remaining in this reach of the river The 24 hour reactive metals tests were undertaken to determine those metals and metalloids extractable with a moderately strong acid i.e. potentially available from binding sites on soil minerals such as iron (Fe), manganese (Mn) and aluminium (Al) oxides. Although comparisons can be made with soil and sediment quality guidelines, these are defined for total concentrations and not partial extractions. The results showed that concentrations were below the sediment quality guidelines (SQG) and soil ecological investigation levels (EIL) for those elements where guidelines are available. Although the metals and metalloids did not breach sediment quality guidelines and soil ecological investigation level trigger values, the concentrations of some elements were high enough that they may impact water quality if mobilised, particularly for aluminium (Al), iron (Fe) and manganese (Mn). The contaminant and metalloid dynamics tests were undertaken to assess the release of metals during a water extraction, and to assess dynamics in response to saturation over time by incubating soil materials for periods of 1, 7, 14 and 35 days. The degree to which metal and metalloid concentrations exceed ANZECC/ARMCANZ guideline values was used to characterise the degree of hazard. For the Lower Loddon River, aluminium (Al), cobalt (Co) and iron (Fe) were assigned a moderate hazard with concentrations exceeding ANZECC/ARMCANZ environmental protection guidelines by more than 10 times. Arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), vanadium (V) and zinc (Zn) were assigned a low hazard as they breached ANZECC/ARMCANZ environmental protection guidelines by less than 10 times. The dominant control on metal solubility is the pH of the sediments at the time of the extractions. The soils displayed little trend in pH throughout the tests, with some remaining very acidic. Over the duration of the analysis, there was a decrease in Eh. However, this was limited in the very low pH in these samples. The use of environmental flows to protect riparian and floodplain values has been seen as a high priority for the nearby Lower Loddon River catchment, and this is likely to apply to Lower Loddon River also. The river was largely dry at the time of sampling, with only disconnected pools of surface water. The main hazards considered in this study that may impact on wetland values are acidification, contaminant mobilisation and deoxygenation. The wetland has been allocated a high to very high risk rating due to acidification and a high contaminant risk rating for soils. For surface waters, the risk is largely dependent on surface and sub-surface hydrology and is thus scenario dependent. Taking into account the range of likely scenarios, from very low flows (highest risk) to very high flows (lowest risk), the risk to surface waters in the wetland has been allocated medium to very high risk rating for acidification and medium to high risk rating for contaminant mobilisation. The risk associated with deoxygenation was determined as high due to the local presence of monosulfidic black ooze. In designing a management strategy for dealing with acid sulfate soils in the Lower Loddon River, other values and uses of the wetland need to be taken into account to ensure that any intervention is compatible with other management plans and objectives for the wetland. The use of environmental flows to protect riparian



Acid sulfate soil; metal; metalloid; hydrogeochemistry

Environmental Monitoring

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Water for a Healthy Country Flagship Report series ISSN: 1835-095X


Client Report (Author)



Shand, Paul; Baker, Andrew; Grocke, Sonia Grocke; Smith, Lester; Cozens, Gillian; Fiebiger, Catherine. Assessment of Acid Sulfate Soil Materials (Phase 2) Craignook wetland, South Australia. Canberra: MDBA; 2011.

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