Australia's Dryland Salinity
Although agricultural development has significantly changed Australian natural systems and landscapes, we have not always appreciated the magnitude and costs to the Australian community of this change. In 1998, the Prime Minister's Science, Engineering and Innovation Council (PMSEIC) emphasised that dryland salinity is a particularly difficult form of degradation to manage:
The time scales over which salinity establishes itself, spreads, and has its effects can be long, but once established it can be very difficult or impossible to contain or reverse. As a consequence, salinity must inevitably continue to get worse in Australia as a result of land use decisions already made. PMSEIC 1998
The consequences of dryland salinity are wide-ranging. They include impacts on soils and agricultural production, stream quality, remnant vegetation, and riparian zones and wetland areas. Salinity is degrading rural towns and infrastructure, crumbling building foundations, roads and sporting grounds. In October 2000, the Prime Minister announced a National Action Plan for Salinity and Water Quality in Australia (Commonwealth of Australia 2000) to be supported and implemented jointly with the States and Territories through the Council of Australian Governments process. This action plan identifies priority actions to address dryland salinity and deteriorating water quality in key catchments and regions. The plan calls for
... decisive salinity and water quality related action to ensure that our land and water management practices will sustain productive and profitable land and water uses as well as our natural environments. Commonwealth of Australia 2000
Hazard/risk assessments
This report provides a synthesis of more detailed information presented in the individual State reports on areas at risk and impacts of dryland salinity. All these reports are available on the Audit Atlas website.
A collaborative program between the National Land and Water Resources Audit (Audit), and State and Territory agencies has produced assessments of extent of dryland salinity risk or hazard at the regional scale across Australia (Table 1). The assessments included information from the recent dryland salinity water resources audit carried out by the Murray Darling Basin Commission (MDBMC 1999).
The definitions of 'hazard' and 'risk' that are most appropriate to the work carried by the Audit are:
hazard: anything that can cause harm to an asset (e.g. salt loads in lands where groundwaters have potential to rise);
risk: estimation of the expected amount of harm that will occur to the asset when a condition occurs (e.g. shallow saline groundwaters under cropland).
'Risk' and 'hazard' are often used as equivalent terms in common language. For ease of reading, 'risk' has been used in narrative text of this document.
Methods
Regional-scale, dryland salinity risk or hazard assessments were undertaken by State agencies using:
- information on groundwater levels and trends;
- known incidence of salinity;
- soil characteristics; and
- topography.
For those States with data on groundwater levels and trends, land units with groundwater within 2 m of surface, or within 2 to 5 m and with well demonstrated rising watertables (except for New South Wales) were classed as being at high risk of dryland salinity. A groundwater level of 2 m was selected in line with documentary evidence that where levels are in the 1 m to 2 m levels, salinisation of the soil occurs adversely affecting crops and native vegetation (Nulsen 1981, Talsma 1963).
The assessments used existing data held by States and were constrained by available data and financial resources, and timeframes. The assessments exposed a number of limitations in the groundwater data quality and coverage across States. Difficulties encountered in applying the same landscape analysis approach across States meant that a range of methods and scales were adopted.
Even where there were perceived to be good quality groundwater data (e.g. in Victoria, south-west Western Australia), the forecasted groundwater levels to 2020 and 2050 are based on straight-line projection of recent trends in groundwater levels. Due to inadequacies in current methods, accurate groundwater surfaces cannot be developed with the existing distributed data. This was also an outcome of the Audit's Salt Scenarios 2020 project focused on the Great Southern region of Western Australia.
Where sufficient groundwater level and trend data were available as in Western Australia, South Australia, Victoria and New South Wales, the assessments have been accepted as risk assessments, as the drivers of dryland salinity have been identified as operating for some time and there is confidence in the understanding of the current and future impacts of shallow water tables.
Where data on groundwater levels and trends are sparse such as in Queensland and Tasmania, assessments were based more on knowledge of land attributes and dryland salinity incidence. Groundwater data were used where available to provide extra confidence in the assessments. In these States the assessments were considered to be hazard assessments as there is less knowledge about the current and likely impacts of shallow watertables on dryland salinity. The existing hazard assessment of the Northern Territory was based mainly on vegetation type, aquifer attributes, landscape and depth of weathering attributes, rather than any trends in groundwater.
The Audit's assessment using groundwater data has identified areas where dryland salinity impacts from shallow groundwaters are known or expected to occur. The hazard assessments have identified those areas where dryland salinity could potentially exist given changes in land use that affect the water balance. This information should not be interpreted as actual areas affected since the assessments are likely to overestimate areal extent particularly in dissected (hilly) landscapes. Rather they identify areas or regions within which dryland salinity occurs or could occur.
Groundwater trend analysis at the scales used will only provide an overview. It is important to recognise that the risk analyses and conclusions presented in this report provide State-wide appreciations of the area at risk and impacts of dryland salinity. Trends at the local level (farm and paddock) can be ascertained from individual bores whose location with respect to landscape position and hydrogeology is well known.
Within these limitations these assessments have for the first time provided an appreciation of dryland salinity area at risk and impacts based on analysis of existing data (particularly groundwater) across all the major agricultural areas of Australia. The assessments have been presented together in Table 1 in order to give an overall picture of dryland salinity in Australia.
Area at risk
Approximately 5.7 million hectares of Australia's agricultural and pastoral zone have a high potential for developing dryland salinity through shallow watertables. Predictions based on groundwater trends, field surveys and landscape characteristics indicate that unless effective solutions are implemented, the area could increase to 17 million hectares by 2050 (Table 1, Figure 1). Most is agricultural land (more than 11 million hectares).
Dryland salinity coincides with those agricultural zones in which natural vegetation has been replaced - often many years ago - with land use systems that do not use water to the same extent as the natural vegetation.
The largest areas of dryland salinity are in the agricultural zone of south-west Western Australia. Groundwater levels in this zone are still rising and over 4 million hectares have areas at risk; an area that could double by 2050. Large areas are also at risk of dryland salinity in South Australia, Victoria and New South Wales, mainly in the Murray Darling Basin where groundwater levels are still rising.
An existing salinity hazard assessment for the Northern Territory (Tickell 1994b) concluded that the overall hazard for the Territory is relatively low. No further assessment was carried out as part of this Audit. Also the bulk of the non-agricultural area of Western Australia, and far western New South Wales were considered to have a very low salinity risk, and were not included.
Although northern Australia has far less dryland salinity than temperate Australia, dryland salinity could become a problem for many catchments with high salt stores if water balance changes led to groundwater rises. In Queensland an estimated 3.1 million hectares is considered to have a high hazard, and more rigorous assessments of the risks under land use are a priority. The extent of salinity in northern Australia can be minimised by preventive management, maintaining water balance by protecting and ensuring vigour in native vegetation.
Table 1.Areas (ha) with a high potential to develop dryland salinity in Australia.
|
State/Territory* |
1998/2000 |
2050 |
|
New South Wales |
181 000 |
1 300 000 |
|
Victoria |
670 000 |
3 110 000 |
|
Queensland |
not assessed |
3 100 000 |
|
South Australia |
390 000 |
600 000 |
|
Western Australia |
4 363 000 |
8 800 000 |
|
Tasmania |
54 000 |
90 000 |
|
Total |
5 658 000 |
17 000 000 |
* The Northern Territory and the Australian Capital Territory were not included as the dryland salinity problem was considered to be very minor.
Figure 1.
This map represents a compilation of dryland salinity risk and hazard mapping for the year 2050. The map shows the broad distribution of areas considered as having either a high salinity risk or a high salinity hazard. In southern Australia where groundwater level and trend data are available, more confident assessments have been possible. However, in northern Australia groundwater data for trend analysis are very sparse or non-existent. In these regions, salinity assessments have been based on the presence of geological, landscape, regolith, land use and climate attributes which are the prime drivers of salinity. This national map provides a basis for identifying those regions where more detailed assessments are warranted, and where land use changes should be targeted if the risks are to be managed.
The bulk of non-agricultural areas in Western Australia, South Australia and western New South Wales were considered to have a very low salinity risk and were not assessed.
Impacts
The processes of dryland salinity can operate at landscape or local scale; impacts can occur on-site (farm scale), elsewhere in the catchment or outside the catchment (downstream). The original cause of the change in water entering the watertable (the main driver of salinity) is often distant from where the salinity occurs.
Dryland salinity as an agent of degradation
The impact of dryland salinity as a resource management issue is greatly increased by its off-site effects, its social and economic consequences and - most importantly - the often high level of inputs required and the long timeframes for management to be effective. Dryland salinity is more pervasive than other degradation issues but is also closely linked to them (e.g. causing soil erosion, eutrophication of streams and loss of riparian zone vegetation). Dryland salinity is difficult to manage because of the lasting nature of its effects on soil and water resources, and on the stability of ecosystems.
The main impact of increasing salinity at the farm level is loss of production and income. Other on-farm effects include the decline in capital value of land, damage to infrastructure, salinisation of water storage, loss of farm flora and fauna, and loss of shelter and shade. These effects are magnified at the regional level, where they have a substantial impact on public resources such as biodiversity, water supplies and infrastructure.
Some of the assets at risk as a consequences of shallow watertables are listed in Table 2, with estimates of their impact predicted to 2050.
Table 2.Summary of assets in areas at high risk from shallow watertables or with a high salinity hazard.
|
Asset |
2000 |
2020 |
2050 |
|
Agricultural land (ha) 1 |
4 650 000 |
6 371 000 |
13 660 000 |
|
Remnant and planted perennial vegetation (ha) 2, 5 |
631 000 |
777 000 |
2 020 000 |
|
Length of streams and lake perimeter (km) 2 |
11 800 |
20 000 |
41 300 |
|
Rail (km)2 |
1 600 |
2 060 |
5 100 |
|
Roads (km)2 |
19 900 |
26 600 |
67 400 |
|
Towns (number)3 |
68 |
125 |
219 |
|
Important wetlands (number) 1, 4 |
80 |
81 |
130 |
Notes:
1 Data from all States, Qld only for 2050.
2 Data from WA, SA, Vic and NSW, Qld only for 2050.
3 Data from WA, SA, Vic and NSW.
4 Including Ramsar wetlands.
5 Much of the remnant and perennial vegetation reported for each State occurs on agricultural lands.
Water resources at risk
The most significant off-site impact of dryland salinity is the salinisation of previously fresh rivers. This affects the supply of drinking and irrigation water, with serious economic, social and environmental consequences for rural and urban communities (e.g. in Western Australia, many of the surface water resources are already too saline for domestic use and further deterioration will challenge future supplies).
Increased salt concentrations also change the habitats of aquatic fauna in wetland, stream and riparian zone systems.
- Predictions from Western Australia show that the length of streams affected by salinity may double over the next 50 years, posing risks for riparian zones and water quality. Surface water resources in the south-west of the State are likely to become more saline.
- In Victoria, a possible three-fold increase in the length of stream or perimeter of reservoir, lake or wetland located in areas of shallow watertable is predicted over the coming 50 years. If these changes are realised, increased saline discharge could be expected into streams and surface water bodies.
- In South Australia, where water resources on the Lower Eyre Peninsula and Kangaroo Island have been degraded by salinity, there is little opportunity for increased industrial, mining or irrigation water supplies. This may have serious consequences for regional development in these areas.
- Nationally, the predicted deterioration in the quality of Murray River water indicates the magnitude of the problem. The salinity audit of the Murray Darling Basin (MDBC 1999) suggested that in the absence of remedial action, the median salinity in the Murray River at Morgan was estimated to increase by about 25% over the next 50 years as a result of increased salt inflows from irrigation and dryland districts. Stream salinity in the Murray exceeds World Health Organization levels for potable water for about 10% of the year. Salinity levels in the Murrumbidgee River are increasing at between 0.8% and 15% each year, depending on where measurements are made.
- The Murray Darling Basin Commission Salinity Audit also suggests that in the upper part of the Basin, the Macquarie, Namoi, Bogan, Lachlan and Castlereagh rivers will exceed the 800 µS/cm (sometimes referred to as EC units) threshold for water within the next 50 years. Some will also exceed the 1500 µS/cm threshold for irrigation within 100 years.
A high correlation between major areas of dryland salinity and areas where the water quality guidelines have been exceeded also occurs (see Figure 2).
Figure 2.Exceedance of salinity guidelines.
Major or significant water quality issues may not be recognised where monitoring coverage of the drainage basin is insufficient. © Commonwealth of Australia
To compile an overview of surface water salinity guideline exceedances within Australia's river basins, the following definitions were used:
- 'major' issues occurred where guideline exceedances were calculated to occupy greater than a third (33%) of a basin area;
- 'significant' issues occurred where guideline exceedances were calculated to occupy greater than 5% but less than 33% of a basin area;
- 'not significant' issues occurred where monitoring coverage was greater than 50% of a basin area; and observed guideline exceedances represented less than 5% of a basin area.
- 'undetermined' issues occurred where monitoring coverage was less than 50% of a basin area; and observed guideline exceedances represented less than 5% of a basin area.
For more detailed information please refer to Australian Water Resources Assessment 2000 (NLWRA 2001).
Agriculture
Broadacre cereal crops and traditional pasture species grown in Australia do not tolerate salt and are seriously affected when salts concentrate within the root zone. Total loss of crop and pasture production occurs where groundwaters are close enough to the surface to discharge or concentrate salts; losses may be restricted to reduced yields where groundwater is deeper.
The assessment has indicated that dryland salinity from shallow watertables potentially threatens production from 4.6 million hectares of agricultural land. Under current land use systems and climate, this is expected to at least double by 2050. These estimates also include some areas - mainly in the temperate zone - with persistent waterlogging from shallow watertables. Although salt is ubiquitous in landscapes in agricultural areas, it is acknowledged that not all of these waterlogged lands will become saline. Much of the area at risk is Australia's most productive land. The greatest impacts are in the Temperate Semi-arid Slopes and Plains agro-ecological region (Williams et al. in press) which includes the wheat-sheep belt in south-west Western Australia. Significant areas of salinity also occur in the crop-pasture zones of New South Wales, South Australia and Victoria. Major irrigation areas of the Murray Darling Basin will be affected by the predicted increases in salt concentrations. The loss of productive lands places a burden on remaining lands. Aggregate productivity can only be maintained by increasing production from unaffected lands and/or developing integrated systems that include saltland production. Higher-yielding crops and additional agricultural inputs are seen as part of the solution but come with their own risks. Innovative land use systems are also seen as part of the solution, but these are still in very early stages of identification and development.
Infrastructure
Large decreases in the lifespan of road pavement occur when groundwater levels rise to within 2 m of the pavement surface. Salt also destroys the properties of bitumen and concrete structures. Road and bridge damage caused by shallow, saline groundwater is a major cost at all levels of government.
- Estimates are that high watertables potentially affect about 34% of State roads and 21% of national highways in south-west New South Wales, with damage costing $9 m each year for classified roads (Douglas 1997).
- Main Roads Western Australia estimated that in 1997, salinity affected 500 km of main roads and that this was likely to double within 20 years (McRobert et al. 1997).
Structures associated with communication and gas pipelines are subject to a similar fate. Wagga Wagga is one of the worst affected towns in New South Wales, experiencing salinity-induced damage to roads, footpaths, parks, sewage pipes, housing and industry (Bugden 1997). Salinity is also present in other provincial cities and towns in New South Wales and Victoria (e.g. Dubbo, Forbes, Cowra, Booroowa, Bendigo) as well as Western Sydney.
Predictions suggest that approximately 30 rural towns in Western Australia will be threatened by rising saline watertables by 2050, leading to damage to roads, recreation facilities and buildings; and difficulties with public utilities such as water supplies and waste management systems. In Victoria, predictions are that more than 60 towns will be at risk from shallow watertables.
Increased flood risks are also a consequence of shallow watertables in Western Australia (Campbell et al. 2000), and this is resulting in increased flood damage to roads, fences, dams, agricultural land and wetlands.
Biodiversity
The greatest threat posed by dryland salinity to biodiversity is from the loss of habitat - both on land and in water. Dryland salinity has severely affected many areas in riparian zones because they occupy the lowest parts of the landscape where much of the saline groundwater is released to the surface. The natural vegetation of such areas has been destroyed or damaged, and this is causing major changes to the landscape and its biodiversity, including destruction of remaining natural habitat in many agricultural areas and fragmentation of wildlife corridors.
In Western Australia, at least 1500 plant species will suffer from dryland salinity, with 450 of these possibly subject to extinction. Fauna species are likely to be reduced by 30%.
The impacts of salinity on aquatic habitats have been less well studied and are more difficult to assess than those on land-based habitat such as woodlands and riparian vegetation.
Approximately 80 important wetlands including those of national and international significance have been affected or are at risk of damage from dryland salinity in all States. Information on the full extent and degree of impacts is very sparse. In the Murray Darling Basin, major wetlands of the Macquarie Marshes, Great Cumbung Swamp, Avoca Marshes and Chowilla Floodplain will suffer impacts from rising salinity.
Remnant vegetation, plantation forest and areas rehabilitated to perennial vegetation in Western Australia, Victoria, South Australia and New South Wales (Table 3) are under threat due to rising watertables. The biggest threat in South Australia is to coastal lowlands of the upper south-east. In Victoria and New South Wales the threats are mainly to remnant and planted vegetation in agricultural lands.
Table 3.Remnant vegetation and plantation forest at risk (ha).
|
State |
Current |
2020 |
2050 |
|
New South Wales |
7 000 |
32 700 |
81 000 |
|
Victoria |
6 000 |
11 800 |
24 300 |
|
Queensland |
n/a |
n/a |
92 000 |
|
South Australia |
18 000 |
22 000 |
25 000 |
|
Western Australia |
600 000 |
710 000 |
1 800 000 |
|
Total |
631 000 |
776 500 |
2 022 300 |
Costs
The full costs of dryland salinity are extremely difficult to estimate and separate from the costs incurred from other types of degradation. Remedial and future costs of dryland salinity have been included in an economic assessment across a range of degradation issues. These will be presented as part of the Audit's Capacity for Change theme report in 2001.
Under the National Dryland Salinity Program, comprehensive guidelines for estimating costs for the range of affected stakeholders have been developed for agriculture, water and infrastructure (Wilson 1999). Estimation of costs associated with losses in biodiversity is complex and methods are not well developed. Preliminary results from a recent study for the Murray Darling Basin Commission in eight priority catchments (Wilson 2000, Ivey ATP 2000) indicate that salinity costs to farmers, local government and government agencies are approximately $251 m a year (Table 4). Further research is being conducted by Wilson and Ivey ATP to refine these preliminary estimates, and these results should be available in March 2001.
Another recent study on financial costs to local government from dryland salinity (Spiller Gibbins Swan and SMEC 2000) for the National Dryland Salinity Program has predicted that if dryland salinity is left unchecked, it will become a major burden on local government finances. Salinity will degrade infrastructure requiring increasing proportions of rate revenue to be allocated to repair and replacement costs. Loss of land value will also reduce local government's ability to raise rate revenue.
Table 4.Total equivalent annual costs to all stakeholders in eight priority catchments in the Murray Darling Basin (Wilson 2000b).
|
Lower estimate ($m/yr) |
Upper estimate ($m/yr) |
Best estimate ($m/yr) |
|
|
Local government |
- |
- |
14.69 |
|
Households |
41.03 |
139.23 |
90.13 |
|
Businesses |
8.45 |
8.96 |
8.71 |
|
State government agencies & utilities |
- |
- |
16.31 |
|
Environment |
? |
? |
? |
|
Agricultural producers |
- |
- |
121.80 |
|
Total |
202.28 |
300.99 |
251.64 |
Conclusions on the constraints to the national assessment
- Coverage of this assessment was constrained to the agricultural regions of Western Australia, South Australia, Victoria and Tasmania; and to the eastern regions of the Murray Darling Basin area in New South Wales; the hazard assessment in Queensland covered the whole State.
- The issues of reporting scale, monitoring bore distribution and density, data quality and availability need to be recognised when interpreting the results of this national assessment. The assessments undertaken by the Audit provide sufficient information to target more detailed regional activities and to scope the impacts of salinity. There are insufficient data to precisely determine dryland salinity outbreak/incidence across Australia. Comparisons between States of `area at risk' should not be undertaken because of the differences in assessment methods.
- The coverage of groundwater data in New South Wales, Queensland, Tasmania and South Australia is inadequate or insufficient as the prime indicator for assessing dryland salinity risk. Data gaps in other States are also significant.
- Assessment of the impacts of dryland salinity and the costs of salinity management have been constrained considerably by the data inadequacies identified in the Audit, and these need to be addressed for future audits.
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