What is Salinity?
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What is salinity? The term SALINITY refers to the movement and amount of salt, dissolved in water, though the landscape. Soils and natural water can both become saline, therefore salinity can be described as either soil or water salinity. Salts include sodium chloride (common table salts), calcium carbonate (limestone) and many others. These salts are dissolved by water as it runs over and through rocks and soils.
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Types of salinity
The two main types of salinity are dryland and irrigation salinity. Dryland salinity occurs mostly due to the widespread removal of native deep-rooted trees which caused the watertable to rise. Irrigation salinity occurs because large amounts of water are applied to crops; some of this water enters the ground and causes the watertable to rise. Irrigation has similar effects as that of a large rain event falling on cleared land; there is not enough vegetation to take up the rain so most of it enters the groundwater system.
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Where does it come from?
Rain
Salts can be carried from the sea by strong winds and fall as rain across inland areas. Salt concentration in rainfall is higher nearer to the coast, but still adds a large amount of salt to inland environments. Between 20 and 200 kg/ha of salt can be deposited during a year of average rainfall.
Retreating Seas
Many areas across Australia were once covered by an inland sea. When the sea retreated about 10 million years ago, the sediments that were left behind contained large amounts of salt.
Rocks
Rocks contain salts which are released during the weathering process (water breaking down rocks). Many types of rocks including marine sediments, granites and rhyolites contain high levels of sodium and potassium (salts).
Salts can be carried from the sea by strong winds and fall as rain across inland areas. Salt concentration in rainfall is higher nearer to the coast, but still adds a large amount of salt to inland environments. Between 20 and 200 kg/ha of salt can be deposited during a year of average rainfall.
Retreating Seas
Many areas across Australia were once covered by an inland sea. When the sea retreated about 10 million years ago, the sediments that were left behind contained large amounts of salt.
Rocks
Rocks contain salts which are released during the weathering process (water breaking down rocks). Many types of rocks including marine sediments, granites and rhyolites contain high levels of sodium and potassium (salts).
The cost of salinity
The effects of salinity are broad and include: • reduced productivity capacity of affected land, • degradation of the environment and wildlife habitats, • reduction in the number of plants and animals due to saline soils and water, • deterioration of water quality which limits the use of water for stock and domestic water supplies and increases the cost of water treatment, • loss of production causing social, psychological and economic hardship, • damage to roads, • damage to other infrastructure such as channels and pipes, • damage to water using equipment/machinery. It has been estimated that salinity costs $304 million per year in the Murray Darling basin alone. This figure includes: loss of agricultural production, damage to infrastructure and water quality associated costs (treatment etc). |
Management strategies
There are no easy solutions to this issue and management strategies are complex and long term. There are 4 main areas for revegetation strategies:
- The area planted with trees needs to be significant enough to be a percentage of the catchment
- The arrangement of trees within the catchment (alleys, blocks, wide spaced, etc)
- The location of trees within the catchment (soil type, recharge or discharge area, low or high in the landscape, etc)
- The tree species selected (water use, leaf area index, growth habit, etc).