State of the Environment

2006

Indicator: LD-04 Area and change in area of exposed soil surface contributing to erosion

Data

In 2001, the National Land and Water Resources Agriculture Assessment undertook a comprehensive assessment of erosion in Australia. The Assessment also provided a summary of estimated tonnage of erosion by different land uses and area currently under each practice in the ILZ.

Summary of erosion by land use for river basins containing intensive agriculture
Land use Area
(km²)		 Total erosion
(t/yr)		 Erosion rate with no conservation practice
(t/ha/yr)		 Rate of acceleration
 Erosion rate* under best practice
(t/ha/yr)
Closed forest 22000 2552000 1 1 N/A
Open forest 228000 6900000 <1 1 <1
Woodland (unmanaged lands) 220000 103400000 5 3 N/A
Commercial native forest production 153000 5800000 <1 1 <1
National parks 86000 76200000 9 1 N/A
Cereals excluding rice 180000 38933000 2 10 <1
Legumes 22000 740000 <1 3
Oilseeds 6000 2382000 4 10
Rice 1500 115000 1; 6
Cotton 4000 2784000 7 11
Sugar cane 5000 18623000 40 57 5
Other agricultural land use 2000 2329000 54 34
Improved pastures 190000 41429000 2 5 N/A
Residual/native pastures 1673500 957939000 6 3 N/A
Total area of river basins containing
intensive agriculture		 2793000 1260126000** 5

Source: National Land and Water Resources Audit 2001, Water-Borne Soil Erosion, Australian Agriculture Assessment 2001, p. 168, Table 5, & Figure 5.7

Total annual Dust Storm Index in relation to total annual rainfall at 46 stations across Australia for the period 1960 to 2004

Total annual Dust Storm Index in relation to total annual rainfall at 46 stations across Australia for the period 1960 to 2004

Source: G.H. McTainsh, J.F. Leys and E.K. Tews 2006, Wind erosion trends for the National State of the Environment Report(2006): data and methods.

What the data mean

Prior to European settlement, there was little bare soil in Australia apart from the areas that were sparsely vegetated in the semi arid and arid regions (NLWRA, 2001, Australian Native Vegetation Assessment, p34). Erosion in pasture lands has doubled from natural conditions, with a five-fold increase for improved pastures. Soil erosion under woodlands and native pastures contributes 86% of total assessed area.

Grazing is the main land use contributing to total soil erosion across assessed river basins, because of the vast areas involved in grazing and their location in northern Australia. Grazed land made up 75% of the NLWRA assessment area and is composed of woodlands as well as pastures which are the basis of the beef industry in northern Australia.

The gross pattern of contemporary soil erosion potential is higher in the north of the continent. This reflects the natural distribution of soil erosion across the continent. Within each climatic zone, areas of significantly accelerated erosion potential have occurred, shown by the ratio of present to pre-European potential.

While the overall erosion rate is low in the cereal belt of Western Australia, it is still many times higher than the very low natural rate. Similar results were found for the cropping belt from Victoria through to Queensland and the extensive grazing lands and tropical croplands of north Queensland.

On average, sheetwash erosion from hillslopes has accelerated by three times the natural rate (Australian Natural Resources Atlas: Land: Soils —erosion and sediments http://audit.ea.gov.au/ANRA/land/land_frame.cfm?region_type=AUS&region_code=AUS&info=soil_erosion).

The Dust Storm Index, calculated by giving weighted values to severe, moderate and local dust storms at recording stations across all states, provides not only an indicator of changes in the severity of dust storms but also a surrogate indicator for the severity of erosion leading to dust storms. Recent data show that in 2002, when rainfall was at its lowest since before 1960, the highest Dust Storm Index since 1966 was recorded. Dust storms were consistently high in the 1960 but, with the exception of another peak with the 1994 drought, have been consistently lower in subsequent decades. Moderate rainfall in 2004 corresponded to a reduction in the index.

Data Limitations

More recent data on quantity of soil lost to erosion across the continent since 2001 are not available.

Issues for which this is an indicator and why

Land — Land condition - Soil stability and quality 

Soil stability is essential to the health of the vegetation growing in it and the other biodiversity inhabiting that vegetation. However, vegetation is also essential to maintaining soil stability.

Area of exposed soil is therefore indicative of both the current and future condition of land.

Other indicators for this issue:

Land — Direct pressure of human activities on the land - Soil loss and loss of soil quality 

As well as being indicative of land condition in relation to soil stability and vegetation, changes in area of exposed soil are indicative of both the pressure of land clearing on the land and of the pressure of soil loss on the land’s capacity to revegetate.

Other indicators for this issue:

Land — Contributions and pressures between the land and inland water - Pressures of changes to the land on inland waters 

Area of exposed soil is an indication of the quantity of unstable soil likely to be available to contribute to runoff to surface waters, impacting as sedimentation on water quality and aquatic biota.

Other indicators for this issue:

Land — Contributions and pressures between the land and the atmosphere - Airborne substances 

Area of exposed soil is an indication of the quantity of unstable soil available to contribute to dust storms affecting air quality and also available to be deposited elsewhere on the land.

Other indicators for this issue:

Inland Waters — Catchment scale influences — Land and vegetation condition - Erosion 

When unstable soil is eroded, it can lead to sedimentation, which can significantly alter the physical habitat of instream environments. Sediment loads in inland water catchments is one measure of the quantity of soil being eroded into waterways.

Other indicators for this issue:

Inland Waters — Catchment scale influences — Land and vegetation condition - Nutrients and sediments - sources and loads 

Area of bare soil is a direct indicator for source and a surrogate indicator for the potential load of sediment available for deposition into inland waters.

Other indicators for this issue:

Inland Waters — Habitat scale influences — Water Quality (for surface and groundwater) - Sediment and turbidity 

Soil erosion also has the potential for downstream impacts on creeks, rivers, reservoirs, lakes, and estuarine and marine environments. Water-borne erosion increases the supply of sediment to rivers. Extent of land subject to erosion is an indirect indicator for the quantity of loose soil available to contribute to turbidity.

Other indicators for this issue:

Key

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