“Sulfidic sediments” is a term used to describe mud that contains high levels of sulfur that has been converted to sulfide by bacteria. Although they are naturally occurring, human activity has increased their occurrence, particularly in inland aquatic ecosystems. Sulfidic sediments form when sulfate, a naturally occuring part of salt, is reduced to sulfide by anoxic bacteria in the presence of organic carbon and the sulfide reacts with metals within the sediment, (predominantly iron) to form sulfidic minerals such as iron pyrite.

Human activity has increased the occurrence of Sulfidic sediments, particularly in inland aquatic ecosystems.

Sulfidic sediments can adversely affect aquatic ecosystems if they are disturbed. In particular, if sulfidic sediments are exposed to air they can produce enough acid to cause irreversible harm to an ecosystem. In 2002, the pH (a measure of acid) in Bottle Bend Lagoon (a billabong near Mildura in North West Victoria) fell to a value of less than 3 – similar to lemon juice. This caused the death of all the fish in the wetland and all the trees surrounding the wetland.

Acidifciation does not always occur if sulfidic sediments are exposed. There are a number of wetlands in inland Australia with sulfidic sediments which have dried out and have not gone acidic. However, the presence of sulfidic sediments usually means that the water body is usually not in good condition. Often the presence of sulfidic sediments is associated with salinisation.

Sulfidic sediments brochure
Sulfidic sediments in inland wetlands (PDF size =360k) >>

ABC Radio Nationals Bush Telegraph interview with Paula D’Santos from the MWWG and Dr Gavin Rees from MDFRC on Sulfidic Sediments in inland wetlands
Bush Telegraph.mov (size = 2 Meg) >>

(Potential) Acid Sulfate Soils in inland wetlands
Sulfidic Sediments.pdf (PDF size = 1.7 meg) >>