Salinity

The Salinity Crisis

Salinity is literally the salting of the earth. In the natural environment large concentrations of salt have built up

in many areas of the world, through millions of years of rainfall, the deposit of ocean salt carried by the wind and the weathering of rocks. Nature developed ways of preventing this salt from leaching out of the earth; mainly with native vegetation Ð'- its deep-rooted systems helped stop the underground water tables rising to the surface. Human interference has extensively upset this balance. Removing natural vegetation for farming is old as human history, so too is the spread of salinity. Today dryland salinity has become a major worldwide problem.

THE SALINITY PROCESS

The salinisation process is closely linked to changes brought about in the hydrologic cycle by modification to the way water is routed through the landscape. Two fundamentally different reactions occur depending whether one is dealing with irrigation salinisation or dryland salinisation. Both these reactions remobilise salt into the zone of production. These salts were originally stored in either the aquifer or the unsaturated zone between the aquifer and the ground surface. Evaporation concentrations the salts in the near surface zone to levels where plant yield is affected and eventually to levels where halophytic vegetation becomes the dominant species.

For salinisation to occur, it is a necessary condition to have both a hydrologic (with an increase in water flux to the groundwater system) and a source of salt to remobilise to the ground surface. If the salt store is not available, or the rate of flow is high enough to produce a low mass transport rate, then only water logging will eventuate.

Bibliography

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