Salinity and turbidity
Salt is a part of the landscape of NSW and some rivers and aquifers have naturally high salinity levels. For example, salinity levels in groundwater aquifers can range from that of rainwater to more than ten times the concentration of sea water. The rate of release of salt into our soils and water sources can be accelerated by tree clearing, intensive irrigation and discharge of saline wastewaters. Mines, industry, sewerage treatment plants and climate fluctuations can also contribute. Over-extraction of water from an aquifer can also cause intrusion from surrounding saline water.
Salinity is the presence of soluble salts and is conveniently measured in water by its ability to transmit an electric current (electrical conductivity or EC). However, the method is not foolproof, and needs to be supplemented with chemical analysis. Water for drinking should ideally have a salt concentration less than 800 μS/cm (microsiemens/centimetre). Levels greater than 1000 μS/cm can cause problems for the irrigation of some crops and can damage aquatic ecosystems.
We have learned that climate can influence stream salinity by causing cyclical mobilisation of salts over decades. Studies suggest that steep catchments in high rainfall areas are less likely to have salinity problems. Flat catchments in low rainfall areas are more vulnerable.
A salinity audit of the Murray Darling Basin published in 1999 predicted that salinity levels were rising and could cause serious problems for water use and the environment within 20 to 50 years. As a result the NSW Government developed the NSW Salinity Strategy in 2000. This recognised that to slow down the increase in salinity, we need to:
- protect and manage our native vegetation
- use our land so that less water goes into the groundwater table
- use water more effectively and efficiently
- use engineering solutions
- make better use of land affected by salt
- focus our efforts on priority salinity hazard landscapes.
The Basin Salinity Management Strategy (BSM2030) sets the direction for salinity management across the Murray Darling Basin for the next 15 years.
The department is also operating and constructing a number of salt interception schemes in south western NSW.
Turbidity is a feature of water that is measured as a water quality indicator in NSW. Increased turbidity can be an issue particularly in the inland areas.
Turbidity refers to how clear the water is – the greater the amount of total suspended solids in the water, the murkier or muddier it appears and the higher the measured turbidity.
In most rivers turbidity increases after rainfall and flooding because of soil erosion and suspension in water. This can then cause sedimentation of rivers and dams as the turbidity settles out. This can smother water plants. The suspended sediments can also absorb and transport microorganisms, nutrients, heavy metals, pesticides and other chemicals.
Turbid water is a problem for country town water supplies – it is difficult and costly to remedy and may create health problems.