Salinity and water quality
Salinity is a measure of the content of salts in soil or water. Salts are highly soluble in surface and groundwater and can be transported with water movement.
There are two types of salinity:
- Primary salinity — large salt deposits that are a natural feature of vast areas of the Australian landscape, stored deep in soils or as surface salt deposits and salt lakes.
- Secondary salinity — additional salt transported to the soil surface or waterways, increased due to altered land use (vegetation clearance, poor land management, irrigation and industrial practices).
In normal circumstances, the deep roots of native plants absorb most of the water entering the soil before it reaches the salt contained in groundwater below the plant root zone.
Excessive amounts of dissolved salt in water can affect agriculture, drinking water supplies and ecosystem health. Salinity is a significant issue in south-western Australia and in some Murray-Darling Basin regions within New South Wales, Victoria, and South Australia.
Use this guidance to help you understand and manage the effects of salinity on water quality in Australia.
Conditions that lead to salinity
Primary salinity is produced by natural processes such as weathering of rocks or wind and rain depositing salt over thousands of years.
Distribution of salt deposits throughout Australia is uneven, with patterns and impacts of salinity varying due to different topography and the age of the landscapes.
- Eastern regions have more localised incidences of salinity.
- Western regions tend to have salinity that is more pervasively spread across the landscape.
Secondary salinity has occurred with widespread land clearing and altered land use, and may take the form of ‘dryland salinity’ or ‘irrigation-induced salinity’.
- Dryland salinity occurs when deep-rooted native plants are removed or replaced with shallow-rooted plants that use less water. This vegetation imbalance leads to an increase in water passing through soil to groundwater, raising the water table and bringing salt to the surface where it can be left behind as the water evaporates.
- Irrigation-induced salinity occurs when excess water applied to crops travels past the root zone to groundwater, raising the water table and salt to the surface. Salt may also be transported across surface and groundwater systems.
Movement of water across a modified landscape.
Effects of salinity
High concentrations of salt pose hazards for the environment as well as affecting agriculture and infrastructure and therefore, the wider economy.
High levels of salinity in water and soil may cause:
- corrosion of machinery and infrastructure such as fences, roads and bridges
- poor health or death of native vegetation, leading to a decline in biodiversity through dominance of salt-resistant species, potentially altering ecosystem structures
- reduction in crop yields by impairing the growth and health of salt intolerant crops.
Costs of increased salinity can come from impaired agricultural production, a need for additional water treatment, and the more frequent maintenance or replacement of corroded civil and agricultural infrastructure.
Reduced groundcover also makes soil more prone to erosion. Eroded soil can pollute water with increased sediment, threatening:
- high value ecosystems and the plant and animal species they support
- safety of water for both human and animal consumption.
Despite the negative effects of salinity, some aquatic environments have adapted to a range of salt concentrations and can tolerate periods of high salinity.
Due to the complex nature and scale of salinity, a mixture of management responses is usually required. Salinity has been a major land management concern in Australia and various measures have been introduced, including:
- establishing salt interception schemes to divert saline groundwater to evaporation basins
- maintaining the health of wetlands
- planting crops that reduce drainage
- restoring vegetation cover with appropriate native species to control the surfacing of salt.
Management plans specify the best treatments for the circumstances, which are then monitored and reviewed for effectiveness.
Agricultural industries may benefit from employing more efficient farming, irrigation and drainage techniques, and redesigning the timing, volumes and locations of irrigation.
National strategy and guidance
Guidance on salinity management, salinity trigger values, and reducing salinity through adapted irrigation processes is available in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.
All states and territories were involved in developing the National Water Quality Management Strategy and the Australian and New Zealand Guidelines for Fresh and Marine Water Quality and are committed to their ongoing application.
Affected jurisdictions have developed their own salinity management plans or strategies with identified objectives and priority areas for rehabilitation.
Managing salinity in the Murray-Darling Basin is a significant environmental challenge, with implications for water quality, biodiversity, agriculture and the supply of drinking water.
The Basin Salinity Management Strategy 2030 and the Murray-Darling Basin Plan will help to make sure that salt concentration and load targets are met and that water quality will remain fit for purpose by:
- flushing out salt with adequate water flows
- modifying land management practices
- acquiring water entitlements with the objective of returning more water to the environment.
These entitlements become part of the Commonwealth’s environmental water holdings and are managed to restore health of rivers, floodplains and wetlands.
Environmental watering also helps to achieve more natural wetting and drying cycles, flushing out toxicants and salt, and improving water quality.
These measures will benefit aquatic ecosystems, drinking water supplies and irrigation communities.
Biodiversity: the range of interrelated plant and animal taxa and the habitat in which they live.
Ecosystem: specific composition of animals, plants and micro-organisms which interact with one another and their environment.
Groundwater: deposits of water below the land which fill spaces in soil and rock and often contribute to the health of surface water ecosystems.
Primary and secondary salinity: primary salinity occurs naturally and is the result of rainfall interacting with geographical features over thousands of years. Secondary salinity is the result of human land use and either produces more salt or causes primary salinity to rise to the surface of the land.
Salinity: measure of the concentration of total dissolved salts in soil or water, mainly sodium chloride (common table salt).