Managing salinity and caring for the landscape
Lesson Overview
Salt affects millions of hectares of farm land in Australia. Students will examine how dryland salinity occurs, the adverse effects that salt has on our environment and agricultural industry and see the benefit of rehabilitation work.
Australian Curriculum: Humanities and Social Sciences
Geography Biomes and Food Security
- Year 9 - The challenges to food production, including land and water degradation, shortage of fresh water, competing land uses, and climate change, for Australia and other areas of the world (ACHGK063)
Environmental Change and Management
- Year 10 - The human-induced environmental changes that challenge sustainability (ACHGK070)
Biological Sciences
- Year 9 - Ecosystems consist of communities of interdependent organisms and abiotic components of the environment; matter and energy flow through these systems (ACSSU176)
- Year 10 - The theory of evolution by natural selection explains the diversity of living things and is supported by a range of scientific evidence (ACSSU185)
Resources
- Dutch licorice, with varying levels of saltiness. Salty licorice can be purchased from shops specialising in Dutch foodstuffs. Warning: Salty licorice may be produced in factories that also processes dairy or nuts.
- Sticky notes
- Ipad access for research
- Salinity and Water Quality fact sheet
Tuning In
Ask students to view the photographs on the following DAFWA website: Dryland salinity in Western Australia - An introduction.
Give students four sticky notes. Ask them to view each image and write a word or comment in response to each photo. Discuss.
Whole class introduction
Dryland salinity is one of the important environmental threats facing Western Australia's agricultural land, water resource, biodiversity and infrastructure. Dryland salinity (non-irrigated land) is defined as salinity at or near the soil surface causing a reduction in plant growth, reduced water quality and damage to infrastructure.
Sodium chloride (NaCl) is the most often described salt when discussing dryland salinity in Western Australia.
Australian soils have always contained salt. This salt has been deposited into and on Australian soils by rainfall, windborne sea spray and released by rocks as they weather and break down.
Prior to the introduction of agricultural systems in to Western Australia the parts of the landscape that showed the effects of salinity where mostly limited to low lying areas, seeps (which may not be low lying) lakes and wetlands.
The Australian deep rooted native vegetation efficiently used nearly all the available rainfall.
When Europeans removed the native vegetation and replaced it with shallow rooted annual food crops like wheat far less rainfall was used.
This unused rainfall infiltrated the soil, moving downwards, past the roots of annual plants to join the water stored deep in the ground. Overtime the ground began to fill up with water. Groundwater began appearing near or at the surface of the soil in new locations, this is called groundwater table rise.
The rising groundwater carries in it the salts stored in the soil. When the groundwater nears the surface (less than two metres) capillary action and evaporation of the soil water causes the salt to become concentrated in the topsoil.
Combined salinity and waterlogging in the topsoil is toxic to many plants (George et al. 1997) and salinity is often first noticed when trees begin to sicken or die, native vegetation decreases, plant species tolerant to salt will increase in number. The yields of farm crops and pastures are reduced.
In severe cases, bare patches, known as salt scalds, develop with salt obvious on the surface. Where groundwater seepage is apparent, saline areas are referred to as saline seeps or seepage scalds (DAFWA, 2015).