Sulfidic sediments in inland waterways
Waterlines report 55 - September 2011
The Sulfidic sediments in inland waterways report was launched at the Commission's Managing Wetlands Workshop on Tuesday 6 September 2011.
Sulfidic sediments in Australia's inland waterways have recently emerged as a potentially serious environmental problem. They can cause considerable ecological damage, significantly detract from aesthetic values and potentially impact on human health.
The Minimising environmental damage from water recovery in inland wetlands project was designed to determine appropriate wetting and drying strategies in inland wetlands to minimise the formation of sulfidic sediments. It provides environmental water managers with tools and guidelines on how to best manage inland wetlands to prevent the formation of sulfidic sediment, and how to remediate affected systems.
The work was undertaken by the Murray-Wetlands Working Group (MWWG) in collaboration with the Murray-Darling Freshwater Research Centre (MDFRC). The project delivered the following products to assist wetland managers, water planners and policy makers to minimise or ameliorate sulfidic sediments:
- The Waterlines report Sulfidic sediments in inland waterways (Baldwin DS, and Capon SJ 2011) presents a summary of key findings and management recommendations.
- The Action Support Tool for managing sulfidic sediments in inland aquatic ecosystems has been developed to provide guidance on the identification and management of sulfidic sediments in inland aquatic ecosystems. This tool is available on the MDFRC website: www.mdfrc.org.au.
- Project findings provided critical scientific understanding that underpinned the recommendations made in the National guidance for the management of acid sulfate soils in inland aquatic ecosystemspublished by the Department of Sustainability, Environment, Water, Population and Communities in 2011.
The project team determined that once formed, sulfidic sediments are both difficult and costly to effectively manage. Environmental flows have the greatest potential to be used as a proactive tool for preventing the accumulation of harmful levels of sulfidic sediments in inland waterways.
Bend Lagoon. Photo A Brecknell, National Water Commission.
Remediation is costly and time-consuming. A field experiment at Bottle Bend Lagoon, involving the application of 20 treatments aimed at neutralising oxidised sulfidic sediments in a severely degraded wetland, revealed that very few were successful in reducing acidity levels after six months, particularly at sediment depths greater than 5cm. The research also demonstrated that implementation at a wetland scale of any effective treatments, e.g. application of calcium carbonate (aglime), is likely to be prohibitively expensive and logistically challenging.
Findings arising from this work:
- Management of sulfidic sediments should be included as a key objective when determining use of environmental water in Australia's inland river catchments.
- Rehabilitation of waterways affected by sulfidic sediments is not simple and there is no single approach. Each system should be considered on a case-by-case basis, utilising the Action Support Tool developed in this project.
- Use of agriculture chemicals containing sulphate, e.g. gypsum, should be limited as far as possible.
- Monitoring of shallow groundwater composition, especially salinity levels, should be incorporated into wetland and river assessments as an indicator of the potential for the presence or formation of sulfidic sediments.