Salinity

Salinity is the accumulation of salt in land and water to a level that damages the natural and built environment. Many parts of the Australian landscape are naturally salty but human activities can cause salt levels to rise.

Salinity and water are inextricably linked. This means salinity is affected by climate variability, which can tend towards extremes in New South Wales.

Salinity usually occurs with other natural resource problems such as decreasing soil and water quality, erosion and loss of native vegetation.

Where does the salt come from?

Salt that accumulates in soil can come from a number of sources:

• rainfall – Airborne salts from ocean spray and pollution are dissolved in atmospheric moisture and deposited on the land when it rains.
• weathering – Minerals that make up rocks break down and release ions that are able to form salts.
• aeolian deposits – Wind picks up and transports dust and salt from soil and lake surfaces and redistributes it across the landscape.
• connate salt – During deposition, salt has been incorporated into marine sediments or, in areas of internal drainage, salt has accumulated over geologic time due to transport and evaporative processes. These areas may later become sources of salt.

Impacts

Salinity affects:

• farms –Salinity can decrease plant growth and water quality, resulting in lower crop yields and degraded stock water supplies. Excess salt affects overall soil health, reducing productivity. It kills plants, leaving bare soil that is prone to erosion.
• wetlands –As salinity increases over time, wetlands become degraded, endangering wetland species and decreasing biodiversity. Where sulfate salts are present, there is an increased risk of acid sulfate soil formation.
• rivers – Increased volume (load) and/or concentration (electrical conductivity or EC) of salinity in creeks and streams degrades town water supplies, affects irrigated agriculture and horticulture, and adversely impacts on riverine ecosystems.
• drinking water – When a source of drinking water becomes more saline, extensive and expensive treatment may be needed to keep salinity at levels suitable for human use.
• buildings, roads and pipes – Salinity damages infrastructure, shortening its life and increasing maintenance costs.
• sports grounds – Salty ground may lose all grass cover, making playing fields unusable.

Costs

Salinity is a costly problem. Dryland and urban salinity costs across the Murray-Darling Basin: an overview and guidelines for identifying and valuing the impacts by S M Wilson (2003) (PDF 2.6MB) put the cost of dryland salinity for the whole of the Murray–Darling Basin at about $305 million a year.

This included costs to agricultural production of $98 million a year and costs to households, industry and commerce of $143 million a year, but not the cost of salinity damage to the environment or cultural heritage.

Causes

Several different salts are responsible for salinity. Generally, sodium, calcium and magnesium combine with chloride, sulfate and carbonate to form salt.

In New South Wales, the most common salt causing salinity is sodium chloride (common table salt). Sodium bicarbonate is also common. It is important to find out what type of salt is causing the problem, as it affects the severity of the impacts and the methods used to manage the problem.

There are several types of salinity each with different causes:

• dryland 
• irrigation 
• urban 
• industrial
• river.

Find out more about different types of salinity and their prevention.

Scale and response times

The scale of groundwater systems affects how quickly salinity problems occur and how long they take to rehabilitate. The scales are:

• local – Salinity is often a local problem, affecting a relatively small area. Groundwater flow paths are usually less than 5 kilometres long and flow in a direction similar to the surface drainage. They respond quickly to recharge events (for example, rainfall). Salinity sites usually respond to remedial actions in the recharge areas within 10 years.
• intermediate – Intermediate groundwater systems store more water than local systems and take longer to fill following increased recharge. Groundwater flow paths are usually between 5 and 50 kilometres. The response times for these systems are generally measured in decades.
• regional – Regional groundwater systems extend over larger areas and go much deeper than local groundwater systems. Groundwater flow direction is usually determined by the regional geology. Regional groundwater systems typically have the following characteristics:
  • long (to hundreds of kilometres) and deep groundwater flow paths
  • very large volumes of stored groundwater
  • a long distance (possibly hundreds of kilometres) between recharge and discharge areas
  • a number of local groundwater systems laying over them
  • mineralised or hot water, such as mineral springs or thermal pools
  • long response times (possibly hundreds of years).

In New South Wales, there are many local, intermediate and regional groundwater systems. The local and intermediate systems predominate where dryland salinity is a problem, particularly in the tablelands and slopes. Regional systems are present in the large riverine plains to the west.