Rehabilitation options for inland waterways impacted by sulfidic sediments – Field trials in a south-eastern Australian wetland

Abstract

The accumulation of significant pools of sulfidic sediments in inland wetlands and creeks is an emerging risk for the management of inland waterways. We used replicated plot trials to appraise the viability of various strategies for neutralizing oxidized, acidified sulfidic sediments in a highly degraded wetland. Of the twenty different treatments trialed only addition of calcium hydroxide or calcium carbonate, burning of wood, and planting of Phragmites australis, Typha domingensis and Atriplex nummularia into beds prepared with CaCO3 or P. australis and T. domingensis into beds of sediment and mulch, decreased total actual acidity (TAA) in the top 5 cm of sediment in the first two weeks following treatment. Only the calcium hydroxide treatments and planting of P. australis, T. domingensis and A. nummularia into beds prepared with CaCO3 decreased TAA for a longer period of time (6 months). None of the treatments, except the planting of P. australis into beds prepared with lime, decreased TAA in the 5-30 cm layer of sediments. Therefore, the only effective treatment appears to be the application of highly alkaline ameliorants which need to be transported to the site. A survey of the wetland was undertaken to estimate the total amount of actual and potential acidity stored in the wetland's sediment and overlying water and showed that up to 1200 tonnes of calcium carbonate would be required to neutralise all of the actual and potential acidity in the 10 ha wetland. However, neutralisation of the remaining water in the wetland (about 12.5 ML) would produce approximately 2750 m3 of metal rich sludge (approximately 100 tonnes dry weight) that would require separate disposal.