At a glance
The distribution of saline soils in Tasmania has increased over the past 200 years due to land management practices such as irrigation and changes to vegetation cover. Salinity is principally located in the Northern and Southern Midlands, Central Highlands and Dorset municipalities.
While Tasmania has some salinity due to natural causes (primary salinity), the main causes of salinity induced since European settlement have been largely due to land use change and, to a lesser extent, irrigation. This type of salinity is called secondary salinity.
Irrigation may cause increased leakage of water below the root zone, mobilising any salt stores and bringing salty water into contact with plant roots. Irrigation with water containing salt may cause salt to build up in the root zone or cause the addition of salt to groundwater, making the situation worse than where high quality water is used.
Land use change (such as clearing native vegetation, altering land use from perennial crops and pasture to annual crops, and the development of urban areas) can result in increased soil salinity due to the removal of perennial vegetation and consequent reduction in rainwater. Unused rainwater, like unused irrigation water, may descend below the root zone and affect the movement of water through the landscape. Salinity may result if this water comes in contact with salt in the soil, geology, or groundwater.
The area of salt-affected agricultural land in 2000 was estimated to be 53,500 ha or 3% of Tasmania's agricultural land (Bastick and Walker 2000). However, this should be considered relative to other land management problems facing Tasmania. For example, it is still a comparatively small area relative to rural tree decline, which is estimated to affect 861,000 ha on private land (Grice 1995).
This 'At a glance' section provides an overview of the salinity issue in Tasmania. More detailed information and references are contained in the Salinity Issue Report. Two indicators are presented in this report: Area Affected By Salinity and Area of Rising Watertables.
Recommendations are provided on Strategic Land Resource Management and Salinity.
- While soil salinity will be an increasing problem in Tasmania, the State is in a position to learn from the experience of other States and benefit from the National Action Plan for Salinity and Water Quality. The National Action Plan aims to build on natural resource management initiatives and bring governments and communities together in planning how to tackle salinity and water quality problems. Tasmania can therefore avoid further exacerbating the problem through prudent land management practices.
- One of the major responses to salinity has been the Tasmanian Salinity Audit (Bastick and Walker 2000). The Audit made several recommendations, including the development of the Tasmanian Salinity Management Strategy. The National Land and Water Resources Audit has worked towards determining the extent and severity of salinity across Australia, and developing methods and programs to manage the issue.
- The Department of Primary Industries, Water and Environment in partnership with key stakeholders has commenced the development of a Tasmanian Salinity Strategy, which is due for completion in early 2004. The Strategy identifies actions required to address salinity within the State.
- The area of salt-affected agricultural land in Tasmania is estimated to increase from 53,500 ha in 2000 to 94,000 ha by 2050 (Bastick and Walker 2000). Half of the 48 catchment areas in the State have undergone some surface water salinity testing. Nineteen of these contained water with levels above 800 µS/cm, the World Health Organisation's highest preferred limit for drinking water. Twelve catchments contained water with levels above 1,500 µS/cm. Adverse ecological effects are likely to occur in aquatic ecosystems if salinity rises above 1,500 µS/cm.
- Salinity is an emerging threat to sustainable agriculture. Annual losses to agriculture in Tasmania are estimated to be $5.4 million. If salinity increases at the estimated rate this figure could rise to $9.4 million by 2050 (Bastick and Walker 2000).
- An emerging salt problem could restrict agribusiness from diversifying into high value, salt sensitive crops using irrigation. It could also affect market perceptions of Tasmania as 'environmentally responsible', influencing market share in export markets linked to quality assurance programs based on sustainability standards.
- Salinity poses a significant threat to some vegetation communities and habitats. Salinity impacts are greatest in the low rainfall areas where there has already been a considerable impact on biodiversity following European settlement. These areas have little remaining native vegetation, and have the highest number of locally extinct plants and animals, and threatened species. The vegetation types considered most threatened by salinity are those that are found on valley floors and low slopes, including native grassland remnants, wetlands and woodlands. These include some of Tasmania's already most endangered vegetation types.
- On a municipal level, the majority (i.e. 20 of the 29 Tasmanian municipalities) show visual signs of salinity. The worst affected areas are Northern Midlands, Southern Midlands, Central Highlands and Dorset, representing 80% of the land thought to be affected by salt in the State.
- Water table trends are an important indicator of salinity potential. If they are too shallow there is a risk from salinisation. In Tasmania, however, there has been very limited groundwater monitoring suitable for assessing groundwater levels and trends. Particular areas of concern are the major irrigation and cropping districts within the State, broad-acre agricultural regions, low lying coastal areas, and any areas with impermeable substrata producing impeded drainage (Dell 2000). A comprehensive, Tasmania-wide, shallow groundwater monitoring network needs to be established.
- There is uncertainty in projections of future increases in salinity. These projections involve assumptions about how to interpret information using the 1992 baseline. Questions remain as to whether an increase in salinity is due to increased detection of land previously affected or an actual increase in salinity.