Explanation:
Type of salinity and their prevention
There are different types of salinity, each with different causes and varying treatment.
Dryland salinity is the accumulation of salts in the soil surface and groundwater in non-irrigated areas. It is usually the result of three broad processes:
groundwater recharge (or deep drainage)
groundwater movement
groundwater discharge.
Often it results from replacing deep-rooted native vegetation with shallower-rooted crops and pastures, which take up less water. Unused rainwater leaks into the ground causing groundwater to rise and dissolve salts stored deep in the soil. The salty water may:
rise to the surface causing waterlogging and/or scalding
emerge at the break of a slope as seeps
flow over the surface or underground into streams and rivers.
Irrigation salinity
Irrigation salinity is the rise in saline groundwater and the build-up of salt in the soil surface in irrigated areas. It is caused by using large volumes of irrigation water that locally raise groundwater levels and mobilise salt. Irrigation salinity is made worse when water used to irrigate is from salty sources.
Irrigation salinity can be controlled by using water efficiently. Crops should receive only the amount of water they can actually use. Reducing water usage in irrigated areas generally requires changes to irrigation infrastructure and technology, and better matching of crops to soil types.
Urban salinity
Urban salinity is a combination of dryland and irrigation salinity processes and is mainly caused by rising groundwater bringing salts to the land surface. The rise in groundwater is caused by blocked or changed natural drainage paths due to:
urban development
over-watering of parks and gardens
leaking pipes, drains and tanks.
In the urban environment, other sources of salt that can contribute to urban salinity include:
effluent
building materials
industrial waste water
fertilisers and chemicals.
Industrial salinity
Many industrial processes have the potential to increase salinity levels in rivers. Examples are:
saline water from mines (working and abandoned) from groundwater seepage and from rainwater coming into contact with mine workings or spoil
discharged cooling water from coal-fired power stations that has been partly evaporated, concentrating the salt content
effluent being discharged.
