Salinisation

1
Salinisation
2
Where?

• Arid and Semi Arid parts of the world that
  receive 25 500 mm of rain per year.
• Where the water table is 2 3 meters below the
  soil, so capillary action can occur.
• Where the rate evaporation far exceeds the rate
  of precipitation.
• Where the base rock is impermeable, so drainage
  is poor keeping the water table high, and not
  allowing saline solution to percolate.

3
What?

• Salts, such as CaCl2 and KCl, are dissolved by
  moisture in the soil.
• Evaporation of moisture in the O horizon (surface
  layer) causes the saline solution to move to the
  surface by capillary action.
• Continued evaporation means that the salt is
  deposited on the surface as a hard crust
• Capillary action happens because of the
  intermolecular attraction between the dry surface
  soil, and the dipolar water molecules

4
Irrigation

• This may induce salinisation, as it causes the
  water table to rise.
• As the water rises through the soil it dissolves
  the salts, and capillary action moves the salt
  water to the surface.
• In rice fields water rises above the surface, and
  evaporates, depositing the salts.

5
Impacts

• River water becomes saline, and may be unfit for
  human consumption - River Colorado, south of
  Hoover Dam.
• Increase in salt causes soil structure to
  collapse and become impermeable.
• Land can support only xerophytes (drought
  resistant plants) and salt tolerant species.
• Bare ground vulnerable to soil
  erosion/desertification

6
San Francisco, California

• Evaporation is rapid, with temperatures of 50
  degrees C.
• Irrigation has caused the water table to rise
  almost to the surface, as there are no drainage
  systems to remove the water.
• Capillary action brings saline moisture to the
  surface, where it evaporates leaving a salt
  crust.
• Due to huge costs, less water is used to flush
  surface salt away, so less salt is removed.

7
Impacts

• The subsoil has become saturated with saline
  water, and the salt accumulates around plant
  roots, so they wither.
• Crop yield has decreased by 10 in parts.
• Some birds eggs do not hatch.
• The embryos of Coots, Grebes and other animals
  are dying, or becoming deformed due to salinium
  poisoning.
• 25 of California has become desert again, as
  little can live on the salinised land.