Process
The soil in Australia naturally contains salt, having accumulated over thousand of years. This salt may come from prevailing winds carrying ocean salt, the evaporation of inland seas, and from weathered parent rocks. Rainfall absorbs this salt on the surface, and carries it down into the subsoil where it is stored in unsaturated soil profiles, until it is once again mobilised by ground water and rising water tables. When this ground water comes closer to the surface, this salt is also brought up. As the water eventually evaporates, it leaves behind all this concentrated salt, resulting in soil salinity. This can be caused by an imbalance in the hydrological cycle, or by irrigation.
Prior to British settlement in 1788, groundwater levels were in equilibrium. Seasonal recharge, and year round utilisation of ground water by deep rooted native vegetation resulted in ground water levels remaining static. Land clearing in Australia has resulted in a loss of this native vegetation, replaced largely by agriculture and pasture crops. These are often annual plants and shallow rooted, and thus, unable to intercept, and adequately absorb stored, and rising ground water. This creates an imbalance in the hydrological cycle, and results in dryland salinity. Salinity is classified as a dissolved salt content of a substance like soil or water. Salinity can prevent crops and other vegetation from growing leaving land empty.
Irrigation is also a contributor to salinity. Firstly, the addition of irrigation acts to simulate rainfall, and if not applied at appropriate levels, can result in the recharge of water tables, and promotes rises in the water table. Secondly, irrigation water itself can contain salts, which are deposited into the soil with its use. This level of salt can range from 0.5 - 2 tonne per hectare per year, and can greatly increase natural salt levels.
Read more about this topic: Salinity In Australia
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