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What is this?
Salt comes in many forms in the natural environment—calcium, magnesium, carbonate, sodium chloride, bicarbonate, and sulphate. Many landscapes are naturally saline, but secondary salinity isn’t so natural, occurring when salts from deep within the earth are dissolved and deposited into soil and water as a result of human activity. This can happen in one of two ways:
Dryland salinity - from removal of deep-rooted plants
In dry regions, deeply-rooted perennial plants, such as shrubs, trees, and grasses, play an important role in regulating groundwater levels. As water is applied to the soil, the plants drink it up and breath it out through a process called evapotranspiration. This ensures that the water table levels stay relatively stable.
But this balance is thrown into chaos when farmers clear the land to gain more space for grazing animals and cultivating food crops. In doing so, they remove the deep-rooted plants and replace them with shallow-rooted annual crops. These plants do not take up as much water as once-plentiful native plants, and as a result, more water remains in the soil.
Over time—up to 30 years—water accumulates in the land, causing the water table to rise. As it does so, it passes through layers of salt and dissolving the deposits that have existed in the land for centuries. The shallow-rooted plants can’t keep up with the rising water levels, which results in rising salt deposits in ever-increasing concentrations in topsoil.
Irrigation salinity - from overirrigation
Much like dryland salinity, irrigation salinity results in a rising water table that brings deep deposits of salt upwards through soil layers. But instead of being caused by land clearing, it results from increased irrigation. As water soaks into the soil, it adds to existing water, raising the water table, bringing salt along for the ride. During periods of irrigation, the water table will lower again, but salt will remain in surface soil, increasing the salt concentration with each irrigation cycle.
What impact does it have?
Contamination of ecosystems with excess salt
Both dryland and irrigation salinity result in similar environmental challenges:
- Groundwater used for human consumption as well as agricultural and industrial applications becomes saline, making it unusable
- Wetlands and bushland ecosystems are damaged, resulting in declines in wildlife biodiversity
- Salt damages houses, pipelines, railways, buildings, roads, and water supply systems
What has been done about it?
Many conservation and regeneration options available
There are many possible steps a community can take to prevent and/or reverse salinity:
- Identify areas where potential for biodiversity loss is significant due to salinity, setting targets to protect and bring back sensitive species
- Protecting key native vegetation species from being cleared and promoting reintroduction of these species in areas affected by salinity
- Limit over-irrigation and the construction of dams in sensitive areas, such as wetlands and watercourses
- Promote environmentally-sound property management planning
- Educate farmers and the public about the risks of increasing salinity
- Construct both surface and sub-surface drainage systems to prevent salinity that results from rising water levels
Is this action working?
Reversing soil salinity a slow process - prevention is easier
Progress in preventing and reversing the effects of salinization is slow and painstaking. Research is beginning to identify ways farmers can continue to cultivate their crops without increasing soil salinity. Planting salt tolerant, deep-rooted plants throughout agricultural lands in one way to see improvements, but like most solutions, it can be costly and requires by-in from farmers and communities alike. Further education of key stakeholders in communities at risk of salinization is required.
Why is this?
Effects of soil salinity take many years to appear
It can take up to 30 years for communities to begin to feel the effects of increasing salinity, making reversal of the problem equally time-consuming. It also requires significant funding. The Australian government, for instance, pledged to spend nearly $8 million on salinization remediation plans to 2008.
Should it continue? On one side, there are those who are against
Without remediation of soil salinity, great problems lie ahead
Without long-sighted solutions, the problem of salinity, including loss of agricultural land, devastation of ecosystems, and the costs associated with damaged property, will continue to increase. In the US, it is estimated that 10 million hectares of land is lost to salinity every year. The challenge is equally serious in Australia.
Environmentalists have been drawing attention to this growing crisis for years, and only after seeing the effects of salinity are individuals and governments coming to terms with the magnitude of the problem. Failure to address salinity could result in widespread crop failures and even more devastating loss of biodiversity.
Should it continue? On the other side, there are those who are all for it
Hydro advocates oppose
There are many who prefer to turn a blind eye to the problem of salinity, especially those with a vested interest in the industries responsible for the consequences. Salinity can increase in the presence of dams and other water reservoirs, making salinity an acceptable cost to advocates of large-scale hydro projects. The damming of the Colorado River, which flows into Mexico, has caused significant increases in the brackish (i.e. saline) quality of the water. Reversing these problems so that those down river can be supplied with high-quality water has been expensive for the US, resulting in costs upwards of several hundred million dollars every year.
Equally challenging is working with farmers who see the very long-range problem of salinity as minor compared to the desire to see short-term financial gains through over-irrigation of crops. Small and large-scale farmers alike struggle with the reality of spending money to prevent a problem that may not occur for decades.