Salinity

Salinity Parameters:

• Average ocean salinity is 35ppt - average river water salinity is 0.5ppt or less.

• 35 ppt means that in every kilogram (1000 grams) of seawater, 35 grams are salt.

• Rising water tables can cause salinity. Usually higher near river mouth.

• Death of organisms after 40 ppt.

• O2 less soluble in more salty water.

Salinity and Water Quality

https://www.waterquality.gov.au/issues/salinity

Salinity is a measure of the content of salts in soil or water. Salts are highly soluble in surface and groundwater and can be transported with water movement.

There are two types of salinity:

• Primary salinity — large salt deposits that are a natural feature of vast areas of the Australian landscape, stored deep in soils or as surface salt deposits and salt lakes. Primary salinity is produced by natural processes such as weathering of rocks or wind and rain depositing salt over thousands of years.

Distribution of salt deposits throughout Australia is uneven, with patterns and impacts of salinity varying due to different topography and the age of the landscapes.

• Eastern regions have more localised incidences of salinity.

• Western regions tend to have salinity that is more pervasively spread across the landscape.​

• Secondary salinity — additional salt transported to the soil surface or waterways, increased due to altered land use (vegetation clearance, poor land management, irrigation and industrial practices). Secondary salinity has occurred with widespread land clearing and altered land use, and may take the form of ‘dryland salinity’ or ‘irrigation-induced salinity’.

• Dryland salinity occurs when deep-rooted native plants are removed or replaced with shallow-rooted plants that use less water. This vegetation imbalance leads to an increase in water passing through soil to groundwater, raising the ​water table and bringing salt to the surface where it can be left behind as the water evaporates.

• ​Irrigation-induced salinity occurs when excess water applied to crops travels past the root zone to groundwater, raising the water table and salt to the surface. Salt may also be transported across surface and groundwater systems.

In normal circumstances, the deep roots of native plants absorb most of the water entering the soil before it reaches the salt contained in groundwater below the plant root zone.

Excessive amounts of dissolved salt in water can affect agriculture, drinking water supplies and ecosystem health. Salinity is a significant issue in south-western Australia and in some Murray-Darling Basin regions within New South Wales, Victoria, and South Australia.

Effects of salinity

High concentrations of salt pose hazards for the environment as well as affecting agriculture and infrastructure and therefore, the wider economy.

High levels of salinity in water and soil may cause:

• corrosion of machinery and infrastructure such as fences, roads and bridges

• poor health or death of native vegetation, leading to a decline in biodiversity through dominance of salt-resistant species, potentially altering ecosystem structures

• reduction in crop yields by impairing the growth and health of salt intolerant crops.

Costs of increased salinity can come from impaired agricultural production, a need for additional water treatment, and the more frequent maintenance or replacement of corroded civil and agricultural infrastructure.

Reduced groundcover also makes soil more prone to erosion. Eroded soil can pollute water with increased sediment, threatening:

• high value ecosystems and the plant and animal species they support

• safety of water for both human and animal consumption.

Despite the negative effects of salinity, some aquatic environments have adapted to a range of salt concentrations and can tolerate periods of high salinity.

Changes in salinity

Climate change might lead to more droughts, which make freshwater saltier. This can cause marine algae to invade freshwater ecosystems.