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Acid sulfate soils along the River Murray, Lake Alexandrina and Lake Albert

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CSIRO Land and Water Staff have recently shown that the River Murray, adjacent wetlands and the Lower Lakes (Alexandrina and Albert) close to the Murray Mouth are being seriously impacted by a combination of low water levels and the presence of Acid Sulfate Soils (ASS). The Lower Lakes and the floodplains below Lock 1 at Blanchetown are undergoing their first major drying phase since the introduction of barrages more than 50 years ago. The isolation of Lakes (e.g. Bonney and Yatco) and several wetlands from the River Murray is currently being used as an option to generate water savings and help mitigate drought-related problems in the Murray-Darling Basin. Field observations and chemical analysis confirm occurrence of both sulfuric materials (pH < 4) and sulfidic materials (high sulfide concentrations and pH > 4) in a range of ASS Subtypes (Figure 1).

In addition, some areas contain ‘monosulfidic black ooze’ (MBO), which causes rapid oxygen depletion of lake and drainage waters when the ooze is mixed with oxygenated waters during disturbance (Figure 2).  Unpleasant smells have been experienced in these areas of exposed soils when water levels are extremely low or allowed to evaporate to dryness due to rotting vegetable matter and release of gases (e.g. ‘rotten egg smell’).

A range of management and remediation options have been proposed for the various ASS subtypes identified in the region. Hence, a key objective is to identify the various subtypes of ASS currently formed and predicted when the area continues to be drained, partially drained or reflooded.

The newly exposed ASS with sulfuric and sulfidic materials may lead to serious environmental impacts including acidification, mobilisation of heavy metals, anoxia and the production of noxious gases. CSIRO Land and Water Staff is currently providing the following critical information to resource managers, which will help to minimise environmental impacts on surrounding ecosystems, soil and water quality:

  • Assessing risk to more than 50 wetlands, lakes, in river channels and Coorong.
  • Assessing risk of dredging ASS in lakes and in river channels.
  • Developing criteria to assess severity, potential severity and spatial extent (ASS maps) of ASS risk (ecological, human and infrastructures).
  • Determining trigger levels for intervention and remediation.
  • Developing criteria for monitoring ASS and water quality.
  • Assessing the presence and potential mobilization of trace elements and heavy metals (e.g. Al, As, Cd, Pb, Se, Zn).
  • Developing transport models for trace elements, heavy metals and contaminants.
  • Developing long term management and re-flooding strategies.

Further information

Recent Reports

To see more publications, go to CSIRO Land and Water's online publications database and type'acid sulfate soils' into the Search in Title/Abstract field. Also tick 'View online publications only' to see items available online.

Acid Sulfate Soil Maps

The following two sets of Acid Sulfate Soil maps have been produced showing the spatial distribution of the wide range of ASS Subtypes when the water levels were:

Plus 0.5 mAHD (i.e. pre-drought level):

Minus 0.5 mAHD (i.e. February 2008 level):

Acid Sulfate Soil with sulfuric material near Swanport adjacent to the Murray River Acid Sulfate Soil with sulfuric material near Swanport adjacent to the Murray River
Acid Sulfate Soil with sulfuric material near Swanport adjacent to the Murray River

Figure 1 Acid Sulfate Soil with sulfuric material near Swanport adjacent to the Murray River (top left), which shows extensive cracking and accumulation of white and yellow Na-Mg-Fe-Al-sulfate-rich minerals or salt efflorescences (below left) where soil pH is about 2.5 (ph < 4) and formed after drainage because watertable levels have dropped below 40 cm in June 2007 (top right) and are now below 90 cm in November 2007 - due to current drought conditions - exposing large sections of riverbank and wetlands that once contained high levels of unoxidised iron sulfides (pyrite).  Sulfidic material (pH>4), which contains unoxidised pyrite, occurs below the water table shown (top right).

Figure 2 - Monosulfidic black ooze (MBO) material in Acid Sulfate Soil exposed in a shallow backswamp

Figure 2 Monosulfidic black ooze (MBO) material in Acid Sulfate Soil  exposed in a shallow backswamp / wetlands (e.g. Paiwalla wetland adjacent to the River Murray). MBO in water is able to remove most of the oxygen from the water

Contact: Rob Fitzpatrick
Ph: (08) 8303 8511