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Salinity is caused by the accumulation of salt in soil or in natural waters. In south east Australia, the most common accumulating salt is sodium chloride (NaCl).
Saline soils do occur naturally (termed primary salinity), however, European settlement has expanded their occurrence (as secondary salinity).
The replacement of perennial native vegetation with annual crops and pastures, and the use of irrigation have both resulted in changes to the water balance as more water moves through the soil. Many areas of Victoria have experienced these changes leading to an increase in the level of saline groundwater. In some areas groundwater levels are high enough to discharge saline water to the soil surface.
Areas discharging saline water, often waterlog, turn saline, support only salt tolerant vegetation, and suffer from soil erosion. It is a problem to agriculture, urban settlement and the natural environment.
Irrigation areas have often acerbated the salinity problem bringing about rising watertables with excess use of irrigation water. This has been termed irrigation salinity. Dryland salinity is the term used for salinity in non irrigated areas although urban salinity is used to describe the influence of rising saline watertable of urban constructions.
Where does the salt come from?
Many areas, such as the Mallee, were once covered by an inland sea. When the sea retreated about 10 million years ago, the sediments it left behind contain large quantities of salt. Many soils in the Mallee region have been derived from these materials.
Salt from the sea is carried inland by strong winds, and falls in rain. As you would expect, salts in rainfall are higher near the coast, decreasing inland. Deposition of windborne salts can range from 30 grams per metre square per year (g/m2/y) close to the coast, down to 5 g/m2/y further inland (Peck, 1980).
Salts are present in rocks and are released by weathering. Many rock types including marine sediments, granites and rhyolites contain high levels of sodium and potassium, which may be mobilised after weathering.
The relation of salinity to groundwater systems
Ground water systems play critical role in the manifestation of salinity in Victoria. A detailed study of their interactions is provided in the report ‘Interaction between groundwater surface systems in northern Victoria’.
Impacts of salinity
Saline soils can have a significant impact on the farm business, the local community and economy, water quality and physical condition of rivers and streams, and it can cause soil structural decline and erosion.
Related Links (external links)
The Federal Department of Sustainability, Environment, Water, Population and Community have a salinity site which provides links to current national activities in the field. Similarly the Federal Department of Agriculture Fisheries and Forestry have a salinity site for further information.
Information about salinity can also be searched through the Australian Academy of Sciences.
The CSIRO have produced a useful Fact Sheet on Salinity in Australia for technical background.
Peck AJ (1980). ‘Salinity: Man’s oldest environmental problem’. Information Service Sheet Number 1-32. CSIRO Publications.