Indicators of Catchment Condition in the Intensive Land Use Zone of Australia – Soil acidification hazard

It should be noted that this data is now somwhat dated!

Australia has naturally and widely occurring acid soils, but the extent has been increased by agricultural practices since European settlement, principally through the export of calcium in agricultural products, the use of acid-producing fertilisers, the widespread use of legumes, the leaching of soluble anions (particularly nitrates) below the root zone of annual crops and pastures, and insufficient use of lime to replace lost calcium (SoE, 1998).

Acidification impacts on biophysical condition by producing soils that are suitable only for a narrow range of plants and few crops (which typically prefer a soil pH of 5.5 a 7.0) and limits crop productivity and agricultural flexibility.

Drainage waters have a lower base status and are likely to have low biotic richness.

The Digital Atlas of Australian Soils (1:2M) has been assessed in terms of acid buffering capacity.

The NLWR land-use map (1:1M) has been used to determine areas of intensive agriculture.

Intensive agriculture is defined as cropping and improved pasture practices, as these land-uses tend to involve significant fertiliser use.

Where these land-use practices coincide with areas with an inherently low acid buffering capacity (i.e. most vulnerable to acidification), a soil acidification risk is defined.

The methodology is sound, but data reliability is low.

The indicator assumes that naturally acidic soils are at risk of greater acidity through intensive land-use activities.

This indicator cannot be interpreted unequivocally because land management practices are ignored.

The indicator has not been validated against the assessment question.

The main areas of acidification hazard are in the temperate and Mediterranean climate zones of southern Australia.

The affected areas include most of the ILZ in Western Australia (Albany Coast, Frankland, Donnelly, Blackwood, Busselton, Collie, Murray, Avon, Greenough, Murchison basins) and Victoria (Campaspe, Loddon, Portland), southeastern catchments in South Australia (Glenelg, Fleurieu Peninsula, Myponga and Wakefield).

The tablelands and western slopes of New South Wales show areas of higher acidity hazard in the finer scale assessments.

Tasmania, Queensland and the Northern Territory are rated in the better categories.

Data are available as:

• continental maps at 5km (0.05 deg) cell resolution for the ILZ;
• spatial averages over CRES defined catchments (CRES, 2000) in the ILZ;
• spatial averages over the AWRC river basins in the ILZ.

See further metadata for more detail.