Spatial distribution and management of total actual acidity in an acid sulfate soil environment, McLeods Creek, northeastern NSW, Australia

The spatial distribution of total actual acidity (TAA), defined as the total amount of acidity which exists in a soil at the time of sampling, was examined across an acid sulfate soil floodplain in northeastern New South Wales (NSW), Australia. Despite generally uniform soil conditions, there is considerable variation in the amount of acidity, and the amounts of soluble and exchangeable ionic species in the soil profile are positively correlated with this acidity. The surface hydrology of the site has been extensively modified for sugarcane production. It is hypothesised from air photo interpretation and the spatial soil data that variation in TAA is a result of the natural geomorphic environment, and that the current distribution pattern is a remnant of past natural land formation and hydrological processes controlling pyrite oxidation and acidity export. The degree to which land drainage caused the acidity is unclear, but the drainage systems provide the conduit for its increased transfer to estuaries. By investigating the distribution of acidity in the landscape, ‘hotspots’ can be identified and land managers can target these areas. Currently, the acidity is managed by a containment program in which it is kept within the soil profile and discharge into the estuary is minimised. Work is under way to apply emerging technology from the mining industry so that any acidity that enters drains is neutralised prior to discharge from the site.