Acid sulfate soils
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ACID SULFATE SOILS

How, where and why How they are formed These soils are formed by bacteria under waterlogged conditions and contain sulfides, predominantly iron pyrite. Where they can be found? In Western Australia, acid sulfate soils can be found around the coast from the Northern Territory border through to Esperance. They can be found in water logged environments, where there is a sulfate source, such as low-lying land near the sea, like coastal wetlands, (i.e salt marshes), mangroves and estuaries or coastal saline lakes. Why are acid sulfate soils an issue? When acid sulfate soils are left undisturbed they are harmless. When exposed to air the pyrite oxidises to form sulfuric acid. This results in impacts on agriculture, infrastructure and the environment.

Impacts

Agriculture

Loss of gardens, pasture and horticultural production

• Acidity kills crops, pasture or garden plants
• Nutrients become less available to plants under acidic conditions
• Crops and horticultural products can increase in concentrations of potentially toxic substances which become more available under acidic conditions such as aluminium

Impacts on livestock

• Loss of pasture
• Stock consuming toxic substances such through pasture or drinking acidic water
  • Sulfate: Excess can cause diarrhoea in young animals as well as weight loss
  • Aluminium: Reacts with phosphorous in intestines to form, non-absorbable complex phosphorus deficiency
  • Iron: Decline in body weight, reduced fat and milk yield, worsening of condition of coat. Problems caused when stock drink water and eat pasture with excess iron

Metal or metalloid		Trigger value (low risk)a,b (mg/L)
Aluminium		5
Arsenic		0.5 up to 5c
Berylium		ND
Boron		5
Cadmium		0.01
Chromium		1
Cobalt		1
Copper		0.4 (sheep) 1 (cattle) 5 (pigs) 5 (poultry)
Flouride		2
Iron		not sufficiently toxic
Lead		0.1
Manganese		not sufficiently toxic
Mercury		0.002
Molybdenum		0.15
Nickel		1
Selenium		0.02
Uranium		0.2
Vanadium		ND
Zinc		20

^a Higher concentrations may be tolerated in some situations (details provided in Volume 3, Section 9.3.5)
^b ND = not determined, insufficient background data to calculate
^c May be tollerated if not provided as a food additive and natural levels in the diet are low

Environment and aquaculture

• Discharge of acid and toxic metals can cause death and disease in aquatic animals such as fish, prawns, oysters and marron,
• Aluminium and iron flocculants smothers plant and animals destroying habitat

Infrastructure

Management

Management Options

• Avoid disturbing acid sulfate soils
• Use of agricultural lime to increase pH of affected soils
• Re-cover acid sulfate soils with fresh water (requires careful design to avoid waterlogging and other problems)
• Wide, shallow drains (designed to prevent erosion) that allow surface water to drain away quickly without exposing pyrites

For further information

• Department of Agriculture and Food 9892 8444
• Department of Water 9726 4111
• Department of Environment and Conservation 6364 6500

DEC website:

acidsulphatesoils.environment.wa.gov.au

Water Quality

Australian and New Zealand Guidelines for Fresh and Marine Water Quality October 2000 The Guidelines Volume 1 Chapter 4 Primary industries
www.environment.gov.au/water/quality/ nwqms/volume1.html

Indicators of Acid Sulfate Soils

Salt crystals on the soil Bare Ground Presence of jarosite, a straw-coloured mineral

Iron staining on the ground Iron stains and slimes in water Presence of extremely clear or blue-green coloured water

The Chief Executive Officer of the Department of Agriculture and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.