Dryland salinity science

Page last updated: Wednesday, 16 November 2016 - 4:29pm

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Salt is a natural component of land, water and ecological systems in Western Australia. Large areas of naturally saline land (primary salinity) were present before European settlement.

Clearing for agriculture has, greatly increased recharge, raised watertables (groundwater levels) and increased the extent of dryland salinity (secondary salinity). An understanding of the groundwater process related to dryland salinity will help design effective management systems.

For a snapshot on salinity and diagnosis refer to the MyCrop salinity fact sheet. More detailed information is provided below.

Salinity development processes

Where does salt come from?

Soil salt comes from three main sources:

  • salt in rainwater derived from the ocean
  • the breakdown of parent rock – a very slow process
  • prehistoric flooding by the oceans – only on discrete areas.

In most of Australia, rainfall is the source of stored salts responsible for salinisation. Salt in rainfall can range from about 20kg/ha/yr (usually in inland areas with low rainfall) to more than 200kg/ha/yr (usually in coastal areas with high rainfall).

Before European settlement and over tens of thousands of years the perennial native vegetation used most of the rainfall, leaving behind the salt to accumulate in the subsoil and regolith (all materials between fresh air and fresh rock).

Stored salt levels

Salt is stored in the landscape when input (through rainfall) exceeds loss through leaching or drainage from the catchment. Where potential evaporation is high and rainfall is low (semi-arid and arid zones), salt falls on the landscape but is not flushed out. It therefore accumulates below the root zone of vegetation.

Accumulation is more noticeable in a flat landscape where there is no clear exit for groundwater or surface water to drain. It also accumulates in landscape sumps where most drainage is internal (i.e. groundwater cannot exit the catchment and moves to a low point such as a salt lake). Accumulation of saline surface water can also create similar features.

Where the regolith is deep, salt storage can rise to thousands of tonnes per surface hectare. With an input of 50kg/ha/yr of salt and limited flushing, 1000t/ha could accumulate in 20 000 years, which is a short timeframe geologically.

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Contact information

Richard George
+61 (0)8 9780 6296
John Simons
+61 (0)8 9083 1128
Paul Raper
+61 (0)8 9780 6295
Russell Speed
+61 (0)8 9956 8561