Salinity, which has developed by changing land use and management, is called secondary salinity. It is caused by a change in the water balance, leading to more water in the soil and a rising watertable. This mobilises stored salts, which rise with the watertable towards the surface. Clearing for agriculture has been the major cause of secondary salinity in Australia.
The cause of dryland salinity is the changing catchment water balance together with the remobilisation of salt stores, and the indicator of the changing water balance is the rising watertable.
Watertable rises can begin decades before salinity becomes evident at the surface. The process usually starts when the native vegetation is cleared for farming development.
In the vast expanses of flat land throughout Australia there is very little natural runoff to flush salt from the land out to sea. This means that little water escapes to the lower levels of the soil below the surface roots of plants.
The Australian continent has vast quantities of ancient salt and this seeps to the surface particularly during periods of extended drought. The impacts of shallow water tables and saline soils include:
• Salinisation of productive agricultural land
• Saline runoff and base flow to streams and wetlands
• Saline runoff and base flow to on-farm and public water storages
• Degradation of areas of significant dryland and riverine biodiversity
• Deterioration of urban and rural infrastructure - buildings, roads, railways, pavements, aerodromes, bridges, playing fields, parks and gardens, utilities, etc
• Aesthetic deterioration - visual “pollution”, tourism decline.
