1 Dept of Soil Science, University of Reading, Whiteknights, PO Box 233, Reading, Berkshire RG6 6DW, UK.
2 School of Environmental Science and Management, SCU, PO Box 157, Lismore, NSW 2480, Australia.
3 School of Biological, Earth, and Environmental Sciences, UNSW, Sydney, NSW 2052, , Australia. Email: m.melville@unsw.edu.au
4 National Mapping Division, Geoscience Australia, GPO Box 378 Canberra, ACT 2601, , Australia.
5 Centre for Resource and Environmental Studies, ANU, Canberra, ACT 0200, , Australia.
6 HMC Environmental Services, 2/47 Greenway Drive, South Tweed Heads, NSW, Australia.
7 Condong Sugar Mill, Condong, NSW 2484.
In 1737 Linnaeus named acid sulfate soils (ASS) as Argilla vitriolacea, and in the 1800s the Dutch overcame their extreme acidification caused by drainage of submarine sediments in polders. However in 1989, entomologist Clive Easton had an Australian scientific literature of only three papers when identifying floodplain ASS as the acidity source for the devastating fishkill on the Tweed. Initially we proposed altered hydrology from floodplain drainage as the cause of the ASS oxidation, noting extreme acidity discharge problems when drainage was initiated.
About 50 tonnes/ha of sulfuric acid equivalent is stored across a range of floodplain landuses, but only <0.5 tonnes/ha is discharged annually. More than 70% of this acidity is in the form of oxidisable/hydrolysable dissolved metals. The acidity is sourced <5m from field drains under sugarcane. This information is assisting the NSW cane industry to achieve reduced acidity discharge and self-regulation through changed ASS management.
We now note that the depth and degree of ASS profile oxidation is largely independent of artificial drainage. We also realise that eastcoast uplift by <3m and climate change since present sealevel was reached, can account for natural ASS oxidation. Thus, while artificial drainage may not have caused ASS profile oxidation, it does provide the conduit for enhanced acidity discharge. Therefore, new drainage of backswamp ASS should be avoided and management of existing drained landscapes should focus on avoidance of creating new acidity, maximum retention of existing acidity in the landscape, and better management of acidity discharging in drains.
