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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
SUMMARY
Australian Dryland Salinity Assessment 2000: defining options
It has long been recognised that our land uses-including agricultural development-have significantly changed Australia's landscapes and natural systems. However, we have not always appreciated the magnitude of change in the soil, water and nutrient balances, the resultant degradation, the timeframe for these changes to be slowed or reversed, and the costs to the wider Australian community.
Changes to the Australian landscape have resulted in the widespread and rapidly growing problem of dryland salinity. Farmers were among the first to be affected, through salinisation of rivers and agricultural land. Biodiversity, as well as regional and urban infrastructure, such as water supply, roads and buildings are now also at risk.
Area at risk and impact
The National Land and Water Resources Audit's (Audit) dryland salinity assessment-Australian Dryland Salinity Assessment 2000-has, in collaboration with the States and Territories, defined the distribution and impacts of dryland salinity across Australia. The aggregate values presented below are the best available estimates within the limits of the methods and data used by the State, Territory and research agencies which undertook this risk assessment.
- Approximately 5.7 million hectares are within regions mapped to be at risk or affected by dryland salinity. It has been estimated that in 50 years' time the area of regions with a high risk may increase to 17 million hectares (three times as much as now).
- Some 20 000 km of major road and 1600 km of railways occur in regions mapped to have areas of high risk. Estimates suggest these could be 52 000 km and 3600 km respectively by the year 2050.
- Salt is transported by water. Up to 20 000 km of streams could be significantly salt affected by 2050.
- Areas of remnant native vegetation (630 000 ha) and associated ecosystems are within regions with areas mapped to be at risk. These areas are projected to increase by up to 2 000 000 ha over the next 50 years.
- Australian rural towns are not immune: over 200 towns could suffer damage to infrastructure and other community assets from dryland salinity by 2050.
Information and monitoring constraints
The State assessments have identified a number of significant information and method limitations in our ability to evaluate the exact extent of dryland salinity and the likely effectiveness of management responses. Although groundwater level and trend data are recognised as fundamental requirements in evaluating the size of the problem and the rate at which it is changing, there are major deficiencies in the design and coverage of groundwater monitoring networks. Even in Victoria, Western Australia and South Australia, where monitoring sites have been established, significant gaps limit our ability to evaluate effects of land use responses. Queensland and Tasmania have very limited formal groundwater monitoring systems suitable for assessing dryland salinity.
Groundwater: the key to understanding salinity
When changes occur in the landscape water balance-from tree clearing, loss of vigour in vegetation growth, changes in rainfall pattern-the amount of water entering the watertable (recharge) increases and the rising groundwater mobilises salt and brings it to the surface. Long response and lag times in groundwater level changes - often 100 years or more-mean that salinity is likely to increase even with immediate, widespread action.
In the face of an estimated three-fold increase in the area at risk of dryland salinity over the coming decades, the Audit's assessment concludes that the amount of change needed in the water balance, and therefore in land use, is substantial. The assessment also highlights that in some regions (e.g. northern Australia), protection and prevention management options are still available, implying that northern Australia has potential to avoid degradation from dryland salinity.
Management options in regions already affected by dryland salinity will need to take account of groundwater characteristics. These varying characteristics have been broadly grouped by groundwater flow systems during the Audit's program. Solutions will be based on engineering and innovative farming systems and productive use of saline resources. In many cases, management responses will involve trade-offs between land use patterns and water balance responses. Sometimes, the preferred option will be to `buy time' to allow solutions to be developed. Engineering options are important and may be preferred for protection of key assets. Innovation and research need to seek new farming and land use systems that suit Australian landscapes.
A framework for action
Understanding the way in which groundwater responds to additional water seeping into it from the landscape, and the way in which this excess water is distributed within groundwater systems, provides the key to understanding the processes of salt mobilisation and the responsiveness of systems to change. This knowledge provides the basis for defining management options, so that investment is targeted, actions are appropriate and outcomes are measurable. The Audit's groundwater flow systems classification is based on geological and topographical characteristics, where similar recharge and discharge management activities are likely to lead to similar hydrogeological responses.
Case studies conducted in differing landscapes have provided examples of the use of the groundwater flow system framework across a range of scales. Analysis of the hydrogeological conditions and the modelled behaviour of groundwater flow systems to land use change in each of the case study catchments has confirmed that the concepts could be applied across Australia. In addition the results can also be extrapolated to give broad conclusions about the extent of change required to halt the spread of salinity, and about the lag times between the adoption of changes and evidence of salinity management.
Salinity management requires long-term, well-considered land use strategies underpinned by knowledge about soil, water and vegetation, and integrated with knowledge about groundwater systems so that an appropriate suite of actions may be taken to prevent or remedy impacts of dryland salinity. There is no single solution or quick fix.
The level of assessment and planning needed to develop solutions will depend on the value (not necessarily in dollar terms) of assets to be managed and protected. This assessment will also determine the most appropriate options. Dryland salinity is more than a management problem for landholders: it can only be done through inclusive regional planning with community, science, industry and government working together.
What else do we need to do to move forward?
In meeting the natural resources management challenges associated with dryland salinity we need to:
- recognise that although the rate of salinisation may be able to be slowed or reversed in some areas, in others land and water resources will continue to salinise with major impacts on rural communities and terrestrial biodiversity. Consequently engineering solutions are likely to be required to protect key community assets and infrastructure;
- implement a landscape function approach to the management of on-site and off-site impacts of dryland salinity;
- support the development and use of the groundwater flow system framework both within and across States to maximise exchange of knowledge and understanding of processes, scale and type of interventions required to manage dryland salinity;
- appreciate that targets set need to be based on an understanding of biophysical processes and likely achievability;
- maintain where possible natural water balance processes;
- design new farming and land use systems that manage the salt and water balance;
- enhance existing monitoring systems to better support the assessment and evaluation of outcomes of dryland salinity management programs.
Overall, the Audit's assessment highlights the complex nature of Australia's natural resources and their response to the land use patterns we require to deliver our economic and social well-being. Dryland salinity demonstrates the integrated nature of land use and landscape, the need for our activities to be thought through in the context of Australia's biophysical assets and values, and for salinity solutions to vary, depending on the mix of community needs in any particular region.
The National Action Plan for Salinity and Water Quality agreed by the Commonwealth and States on 3 November 2000 has, as its centrepiece, community-driven action directed at salinity and water quality problems in key catchments and regions. The plan recognises the importance of knowledge and data to underpin management responses and seeks to address this through a range of capacity building activities including research, extension and training. The findings of the National Land and Water Resources Audit are a key input to inform this process and assist with monitoring outcomes.
Detailed information on dryland salinity in Australia is available from the Audit's Australian Natural Resources Atlas.
Dryland salinity
Two broad forms of salinity are recognised in Australia.
- Primary or naturally occurring salinity is part of the Australian landscape, and reflects the development of this landscape over time. Examples are the marine plains found around the coastline of Australia, and the salt lakes in central and western Australia.
Salts are distributed widely across the Australian landscapes. They originate mainly from depositions of oceanic salt from rain and wind. Salt stored in the soil or groundwater is concentrated through evaporation and transpiration by plants. In a healthy catchment, salt is slowly leached downwards and stored below the root zone, or out of the system.
- Secondary salinity is the salinisation of land and water resources due to land use impacts by people. It includes salinity that results from watertable rises from irrigation systems-irrigation salinity- and from dryland management systems-dryland salinity. Both forms of salinity are due to accelerated rising watertables mobilising salt in the soil. There is no fundamental difference in the hydrologic process.
Where the water balance has been altered due to changing land use (e.g. clearing of native vegetation for broad acre farming or grazing) the excess water entering the watertable mobilises salt which then rises to the land surface. Movement of water drives salinisation processes and may move the stored salt towards the soil surface or into surface water bodies.
The extent, causes and management options for irrigation salinity are well understood, and have been an important part of Murray-Darling Basin Commission activities for at least two decades. However, in most States and Territories, dryland salinity has received far less attention and resources, and has not been dealt with nationally in any systematic and coordinated manner until very recently. This report concentrates on dryland salinity in Australia.
Table of Contents for the Australian Dryland Salinity Assessment 2000
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