National Wetlands Update September 2012
Issue No. 21, September 2012
Action Support Tool for managing sulfidic sediments in inland waterways
Darren Baldwin, Murray-Darling Freshwater Research Centre
Bottle Bend wetland was in poor condition due to
sulphidic sediments for nearly a decade.
There has been growing concern about the risk of disturbance and exposure of sulfidic sediments in Australia's inland waterways, due largely to the drought that affected much of the continent over the last decade. A new tool is available to assist waterway managers to assess and manage actual and potential sulfidic sediments.
Until recently it was thought that acid sulfate soils were solely a coastal problem. However, a number of surveys have shown that they do occur in inland aquatic ecosystems (Murray Darling Basin Ministerial Council (2011) ) and The Environment Protection and Heritage Council and the Natural Resources Management Ministerial Council (2011).
Broadly speaking, sulfidic sediments (or acid sulfate soils) contain or contained reduced inorganic sulfur compounds (mostly elemental sulfur and metal sulfide minerals) at levels that, if disturbed, can lead to environmental harm. They are formed under anaerobic conditions by sulfate reducing bacteria (SRBs). SRBs reduce sulfate to sulfide during anaerobic respiration. The sulfide then reacts with metals to form mineral sulfides.
Sulfidic sediments are relatively harmless if they remain undisturbed and covered by water. However, when disturbed or exposed to oxygen (for example, as a result of a water body drying) sulfidic sediments can cause acidification and deoxygenation of the water column. For example, the pH in Bottle Bend lagoon, near Mildura fell from about eight (slightly alkaline) to less than two (extremely acidic) following partial drying out of the wetland, and remained exceptionally low (below three) for nearly a decade.
In 2007 the National Water Commission in collaboration with Murray-Darling Wetlands Ltd (formerly the Murray Wetlands Working Group), funded the project Minimising environmental damage from water recovery from inland wetlands: Determining water regimes to minimise the impact of sulfidic sediments (potential acid sulfate soils). The principal objective of this project was to provide managers with tools and guidelines, based on the best available science, on how to appropriately manage wetlands in inland Australia to minimise the accumulation of sulfidic sediments and remediate systems that are affected.
One of the outcomes of the project was the development of an Action Support Tool to assist on-ground managers to make operational decisions for waterways that have been or could be affected by sulfidic sediments. The Action Support Tool is a web-based interactive instrument through which the user is guided by answering a series of yes/no questions.
After the series of questions, the tool leads the user to a list of the potential environmental or social issues that may occur at their sites. While acidification is probably the most dramatic effect of disturbing sulfidic sediments, other issues are also important depending on the context. For example, noxious odours may prove to be an important consideration when assessing management interventions in waterways adjacent to population centres. The results page also lists suggested actions that may help to mitigate the risks posed by sulfidic sediments. However, the results are general and the user may also be directed to other useful resources through a series of hyperlinks.
For more information on the Tool or any comments or suggestions for improvement please contact Darren Baldwin at the Murray-Darling Freshwater Research Centre, email@example.com.