The single biggest cause of salinity in Australia is land clearing.
In the figure below, deep rooted native vegetation removes the water added to the system by rainfall, from the soil by transpiration. As a result, the salt cannot dissolve and is locked in the soil in a form that can cause no harm.
By removing the vegetation the water loss from the soil is reduced, as less evaporation/transpiration can take place. The water rises and salt contained in the soil is dissolved. The water being added by rain continues to also raise the water table. This is the cause of dryland salinity.
In the case where water is being added to the system by irrigation (such as on the left side of the bottom figure), this will be the cause of irrigation salinity.
Finally, when this salt affects built structures in residential areas, its called urban salinity.
Over time, as the water table rises, the salty water will reach the surface soil. The water will evaporate and the solid salt is left behind. When salt gets to the surface, very little can grow, and it is very time consuming and expensive to rehabilitate the land.
The best way that salinity can be dealt with is by lowering the groundwater level by either pumping the water out and discharging the water somewhere it cannot cause further harm or by replanting the vegetation so that the roots remove the water and any salt left being is re-solidified and again rendered harmless.
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