What is a salt balance?

A salt mass balance considers the amount of water plus salt entering a system and the amount of water plus salt leaving. When inputs and outputs are in balance, the system is said to be in equilibrium.

Factors influencing these inputs and outputs include the quantities of:

  • rainfall
  • water draining past the root zone
  • water evaporating from discharge areas
  • transpiration from discharge areas
  • surface runoff and groundwater flow away from the discharge area.

The inputs and outputs are also influenced by the salt concentration of:

  • rainfall
  • water draining past the root zone
  • water due to the dissolving of historical salt storage
  • the surface soil due to evaporation
  • soil in the root zone due to the transpiration and the plants exclusion of salt
  • groundwater flowing away from the discharge area.

A change in any one of these inputs or outputs means that other factors must change to bring the system back into balance and reach a new equilibrium.

(Ref: Taylor, S. 1996 Dryland salinity: introductory extension notes, Second Edition, Department of Land and Water Conservation, Sydney, NSW)