Theme 3: Human Impacts on Catchments

Topic: Salinity and Land Degradation

What is salinity?

Salinity is a measure of the amount of salt that is dissolved in water, or the level of salt in the soil. Salinity levels of waterways and groundwater are increasing in many areas of Australia. As salty groundwater rises, it damages soil and makes it less useful for farming.

Increased salinity occurs for many reasons. Primary salinity is natural and affects 84,000 hectares of land in SA. Secondary salinity is caused by human actions and affects 326,000 hectares of land in South Australia. The main causes of secondary salinity are, clearing native vegetation for farmland and over-irrigation of crops. If nothing is done, the amount of land in SA affected by secondary salinity is likely to rise to 521,000 hectares by 2050.

Causes of increased salinity of natural waterways and ground water

Primary ('natural') salinity
Primary salinity refers to naturally occurring deposits of salt found in the environment. Three main sources of this salt are:

• Many parts of Australia, including Lake Eyre and the Mallee, were once covered by an inland sea. As the sea retreated, approximately 10 million years ago, large amounts of salt were left behind.
• Salt is deposited from the sea to land by the natural action of the wind. Several kilograms per hectare of salt per year may fall onto some parts of South Australia.
• Certain types of rocks contain salts that are released when the rocks break down by natural weathering. In drier areas, these salts build up in the soil because there is insufficient rainfall to flush them away.

Secondary (human induced) salinity
Since Europeans arrived in Australia, their actions have increased the salt level of groundwater and surface water, which has put at risk more than 5.7 million hectares of land. Causes of secondary salinity include:

• stormwater run-off, collecting salts from roads and other hard surfaces
• salts present in fertilizer, herbicides and pesticides
• salts present in waste discharges such as swimming pool water, manufacturing effluent and sewage effluent
• groundwater collecting salts from the local geology, and
• rising watertable due to land clearing and over irrigation.

All these causes of increased salinity are of concern. The biggest problem is the rising watertable which is dissolving salts from natural soil deposits and releasing them into groundwater and streams. Rising levels of groundwater result primarily from farming practices such as land clearing and over irrigation.

The effects of increased salinity

Rising groundwater and increased salinity is a problem because it damages both the natural and built environment. Four main ways that increased salinity affects our environment follow:

• Destroys habitats - Increased salinity levels in freshwater rivers, creeks or wetlands may kill native plants or animals or make them sick. This can cause species loss in sensitive river and wetland reserves. Scientists estimate that by 2050 more than 20,000km of waterways will be salt-affected.
• Reduces water supplies - Water can become unsuitable for irrigation, stock, drinking or for other home purposes. This is of major concern to communities that rely on a river as their only source of water.
• Restricts farming - More than 5.7 million hectares of land in Australia are at risk of salinity damage. Salty groundwater may seep to the soil-surface, damaging land so that it can no longer be used to grow crops. Even if groundwater does not reach the surface, crop yields can be affected. Scientists estimate that by 2050 more than 17 million hectares of Australian land will be at risk if nothing is done.
• Damages human structures - When humans are forced to use water of higher salinity in their homes, water pipes and hot water systems rust more easily. Buildings, footpaths and roads that are exposed to salty groundwater, crumble. As groundwater rises, more structures will be exposed to this salt and the repair costs will increase. It is estimated that 20,000km of major roads in Australia are at risk of damage from increased salinity. By 2050 more than 200 towns are likely to be affected by salinity.

Measuring salinity

Salt levels, or the salinity of a water, can be measured in various ways, although using a salinity meter is the simplest and fastest method. A salinity meter measures the amount of electricity that passes through a sample of water. Salt water conducts electricity, so a salty sample will give a higher reading on the salinity meter than a freshwater sample. Salinity may be measured in parts per million or milligrams per litre, however, the standard units are the EC (Electrical Conductivity) units.

Student Activity Ideas

• Make salt crystals. Dissolve a very large amount of salt in a bowl of water and allow it to sit very still for up to 6 weeks. More details can be found at this address: www.yourgemologist.com/Kids/Making%20Salt/makingsalt.html
• Investigate the effect that salt water has on the germination of bean seeds. Place several bean seeds on two pieces of cotton wool. Water one with salty water and one with tap water. Observe germination and measure the differences between the shoot growth of both experiments. Present findings in a report. More detailed instructions can be found at this address: www.waite.adelaide.edu.au/school/Soil/projsalt.html

Enquiry Learning

• What are the issues that have led to salinity problems across the county?
• How have irrigation practices compounded salinity problems?
• How does native vegetation clearance contribute to salinity problems?

Internet Resources

Type	Description	Resources Covering the Topic
Easy	Landcare Field Guide website with extensive information on land degradation. Comprehensive, informative and well written. Including: soil erosion, salinity, deterioration of soil structure, soil fertility decline, pest plants and animals, tree, bushland decline.	Landcare Victoria www.netc.net.au/enviro/fguide/
	Sources of water pollution in the Mt Lofty Ranges. Concise summary of main issues, including informative facts, photos and tables. PDF download worth the wait.	Mt Lofty Ranges Watershed Protection Office www.dehaa.sa.gov.au/epa/pdfs/ fact5.pdf
	Natural Advantage: A Blueprint for Sustainable Australia. Comprehensive overview of sustainable development, including salinity issues.	Australian Conservation Foundation www.acfonline.org.au/asp/pages/ publicationtyp.asp?IdPublicationTyp=7
	'Salinity Our Silent Disaster'. Describes the salinity problem facing Australia. A comprehensive and informative overview of the main issues.	ABC www.abc.net.au/science/slab/salinity/ default.htm#Salinity
	What is Salinity? Brief summary of issues.	Environment Australia www.deh.gov.au/land/pressures/ salinity/index.html
	Salinity. Concise explanation of the issues with a diagram.	Qld Department of Natural Resources and Mines www.nrm.qld.gov.au/land/ management/salinity.html
	Salinity. Rising salt destroying native bush and wetlands.	Community Biodiversity Network nccnsw.org.au/member/cbn/projects/ EducationCentre/HI_Sal.html
More Comprehensive	Land degradation. Includes salinity in the Murray-Darling Basin.	Murray-Darling Basin Commission www.mdbc.gov.au/education/ encyclopedia/naturalresources/ env_issues/ water_and_land_salinity.htm www.mdbc.gov.au/naturalresources/ env_issues/land_degradation.htm
	Salinity and water quality in South Australia.	SA Government Department of Water Land and Biodiversity Conservation www.dwlbc.sa.gov.au/salinity/ index.html
	Search this website for excellent information on a range of environmental issues, including dry land salinity. You can select South Australia to locate statistics on a range of issues.	Australian Natural Resource Atlas audit.ea.gov.au/ANRA/land/ land_frame.cfm?region_type=AUS&region_code=AUS& info=soil_erosion
	'Salinity Our Silent Disaster'. Describes the salinity problem facing Australia. A comprehensive and informative overview of the main issues.	ABC www.abc.net.au/science/slab/salinity/ default.htm#Salinity
	Sediment Fact Sheet. Sediment in streams covering the major issues. PDF download worth the wait.	WA Government Water and Rivers Commission www.wrc.wa.gov.au/public/ WaterNotes/pdf/17.pdf
	Land degradation. Comprehensively covers a wide variety of issues.	NSW EPA www.epa.nsw.gov.au/soe/soe2000/ bl/bl_1.htm#bl_1_h008
	Land degradation and salinity.	ABC – Silent Flood www.abc.net.au/learn/silentflood/ edu_ep2.htm
	ABS - Statistics on salinity and land degradation in Australia.	Australian Bureau of Statistics www.abs.gov.au/Ausstats/abs@.nsf/ 94713ad445ff1425ca25682000192af2/ faeb6096cda4d9adca256bdc001223ff!OpenDocument
	Review of soil erosion across Australia. You can select SA and find soil erosion statistics for individual rivers.	Australian Natural Resource Atlas audit.ea.gov.au/ANRA/land/ land_frame.cfm?region_type=AUS&region_code=AUS& info=soil_erosion
	Search the website for information on a range of environmental issues, including dry land salinity. You can select South Australia to locate statistics on a range of issues.	Australian Natural Resource Atlas audit.ea.gov.au/ANRA/land/ land_frame.cfm?region_type=AUS&region_code=AUS& info=soil_erosion
	Salinity - Our Silent Disaster. Describes the salinity problem facing Australia - a comprehensive and informative overview of the main issues.	ABC www.abc.net.au/science/slab/salinity/ default.htm#Salinity
More Complex	Accelerated erosion and loss of surface soil.	Environment Australia State of Environment Report 2001 www.ea.gov.au/soe/2001/land/ land01-1.html#pressures
	Comprehensive report on salinity and land degradation in Australia Implications for biodiversity.	Environment Australia www.environment.sa.gov.au/ biodiversity/pdfs/ salinity_biodiversity.pdf
	Soil acidification in Australia. Clear description of what soil acidification is and a comprehensive review of the issues with statistics, tables and maps.	Environment Australia audit.ea.gov.au/ANRA/agriculture/docs/ national/Agriculture_Soil_Deg.html

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