Drought in South Australia creates soil problems
Dr Paul Shand (Australia)
In South Australia, the staff of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Land and Water 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 drought since the introduction of barrages more than 50 years ago. Lakes, such as Lake Bonney and Lake Yatco, as well as several wetlands formed by the River Murray, are being isolated as one option to generate water savings and help mitigate drought-related problems in the Murray-Darling Basin.
Field observations and chemical analysis confirm the occurrence of both sulphuric materials (pH <4) and sulphidic materials (high sulphide concentrations and pH >4) in a range of ASS subtypes (Fig. 1).
In addition, some areas contain ‘monosulphidic black ooze’, that causes rapid oxygen depletion of lake and drainage waters when the ooze is mixed with oxygenated waters during disturbance (Fig. 2).
Unpleasant smells (‘rotten eggs’), as a result of rotting vegetable matter and the release of gases, have been experienced in these areas of exposed soils when water levels are extremely low or the lakes have been allowed to evaporate fully.
A range of management and remediation options have been proposed for the various ASS subtypes identified in the region. Therefore, a key objective now is to identify the various subtypes of ASS currently formed and predicted when the area continues to be drained, partially drained or reflooded.
| Fast facts • Acid sulphate soils occur naturally in both coastal and inland settings, and are harmless when left undisturbed. • When excavated or drained, sulphides within these soils react with oxygen in the air to form sulphuric acid. • Development, and natural cycles such as drought, can create these changes in the soil environment. • CSIRO’s Atlas of Australian Acid Sulphate Soils, developed in collaboration with the Australian National Committee for Acid Sulphate Soils, will enable informed risk management for planning authorities. |
The newly exposed ASS with sulphuric and sulphidic materials may lead to serious environmental impacts, including acidification, mobilisation of heavy metals, anoxia (that is, the absence of oxygen) and the production of noxious gases.
CSIRO Land and Water researchers are currently providing the following critical information to resource managers, which will help to minimise environmental impacts on surrounding ecosystems and soil and water quality:
- Assessing the risk to more than 50 wetlands, lakes and river channels in Coorong.
- Assessing the 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 infrastructural).
- 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 (for example, aluminium, arsenic, cadmium, lead, selenium and zinc).
- Developing transport models for trace elements, heavy metals and contaminants.
- Developing long-term management and re-flooding strategies.
