Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Secondary salinity and acidity (continued)
Area affected by dryland salinity [L Indicator 3.3]
In 2000 the National Land and Water Resources Audit's dryland salinity assessment defined lands at risk from, and the impacts of, dryland salinity across Australia. This study used known incidences of secondary salinity, information on groundwater depth, and associated soil and topographic factors to provide an estimate of the total area of land at risk from salinisation (Table 27).
|State A||Area (ha)|
|New South Wales||181 000||1 300 000|
|Victoria||670 000||3 110 000|
|Queensland||48 000 B||3 100 000|
|South Australia||390 000||600 000|
|Western Australia||4 363 000||8 800 000|
|Tasmania||54 000||90 000|
|Total||5 706 000||17 000 000|
A NT and ACT excluded, as dryland salinity problems are very minor.
B Partial figure only.
Source: NLWRA (2001a).
Approximately 5.7 million hectares of agricultural and pastoral lands were estimated to have a high potential for developing dryland salinity through shallow water tables. This figure could rise to 17 million hectares by 2050 if effective controls cannot be implemented (NLWRA, 2001a).
The figure of 5.7 million hectares currently at risk is substantially greater than the 2.5-3 million hectares estimated to be are already salted (PMSEIC 1999). Both reports estimate that future secondary salinity will reach a similar 15-17 million hectares by 2050.
These areas are not large compared with the areas affected, for example, by acidification (30-35 million hectares in agricultural crop and pasture lands), but heavily salinised land is almost worthless in commercial farming terms, and rising groundwater salinity is very difficult to control. In addition the 'off-site' or external impacts of salinisation is damaging to freshwater quality, to non-saline ecosystems, and in some cases to whole town infrastructures has alerted governments to the urgency of tackling dryland salinity in a national strategy. Figure 52 shows the extent of the impact from dryland salinity on some of the natural and built assets affected.
Figure 52: Estimated area of vegetation and lengths of streams and roads affected by dryland salinity in Australia, 2000-2050.
Source: NLWRA (2001a)
The NLWRA also estimates that a total of 80 important wetlands, are already affected, and that this number will rise to 130 by the year 2050. Sixty-eight towns are considered to be substantially affected by rising water tables in Western Australia, South Australia, Victoria and New South Wales at present, and this figure will double by 2020 and rise to an estimated 219 towns by 2050.
The NLWRA study provides national and state maps of forecasted areas of land at high risk of dryland salinity. The report describes risk as 'the estimation of the expected amount of harm that will occur to the asset when the condition occurs' (NLWRA 2001a).
Compared with previous maps, the area affected extends far further northward through the full extent of the Great Dividing Range in Queensland, with very significant implications for threats to future water quality in the northern parts of the Murray-Darling Basin
Figure 53: Forecast areas of high risk (predicted) or hazard (estimated) of dryland salinity by 2050 in Australia.
Source: NLWRA (2001a)
The most severely affected area is in south-west Western Australia, but the extent of dryland salinity in Victoria and Queensland are also going to rise significantly in the next 50 years (Table 27).
The most striking new information to come from the recently completed NLWRA salinity assessment (NLWRA 2001a) is that a total of 630 000 ha of remnant vegetation are currently at risk. This is four times the total area of revegetation expected from the national Bushcare project over the period 1997-2001. Eighty wetlands of national significance are also at risk, including several wetlands listed under the Ramsar Convention, such as the Macquarie Marshes.
The NLWRA review concludes that Australia has a continuing and increasing dryland salinity problem because of the scale of land use changes needed, the lag time between implementation and resulting environmental change, and the lack of viable options for farmers to implement recommended land use changes. This last point is predicated on the assumption that landholders will bear the major cost of implementing the needed change, and that the speed of change will be governed by consultative and voluntary actions. However, it is worth remembering that many past land-clearing options were supported by government policies to clear land for economic expansion. Indeed, in some states the purchase of land from the Crown depended on the prospective landholder being able to clear a proportion of the land within a specified time. This poses the interesting question, as to how far the responsibilities of past government actions should be borne by current landholders. While current suggestions and strategies for natural resource management acknowledge the need for public-private sector partnerships and cost-sharing arrangements, the influence of major shifts in government policy towards natural resource use and management has seldom been considered in such discussions (Walker 1994, AACM International 1996, AFFA 1999).