SALINITY

Australia's soils are susceptible to degradation by agricultural activities. One of the most significant causes of soil degradation in Australia is salinity, which poses a serious threat to native species, ecological communities and functioning ecosystems (ANZECC 2001). Salinity occurs when the water table rises, bringing natural salts to the surface; in sufficient quantity, these salts become toxic to most plants.

Salinity has been caused by extensive land clearing in Australia, predominantly for agricultural purposes. European farming practices, which replaced trees or other deep-rooted native vegetation with shallow-rooted crops and pastures that use less water, has resulted in rising water tables which can cause dryland salinity. Dryland salinity is more difficult to remedy than irrigation salinity which is well understood and managed. Land clearance can also lead to soil erosion and, when it results in a changing water balance, to dryland salinity. Soil erosion, which is also linked to overgrazing from livestock and invasive species such as rabbits and goats, can also cause fine particle air pollution.

In 2000, 5.7 million hectares of Australia were assessed as having a high potential to develop salinity. Predictions indicate that unless effective solutions are implemented, the area affected could increase to 17 million hectares by 2050, most of which is agricultural land (more than 11 million hectares) (NLWRA 2001). In 2002, about 20,000 farms and 2 million hectares of agricultural land showed actual signs of salinity (ABS 2002). For many farms, salinity has meant loss of productivity and income.

There are also many off-farm impacts of salinity, the most significant of which appears to be the salinisation of rivers which affects drinking and irrigation water (for example in Western Australia some surface water is already too saline for domestic use) (NLWRA 2001). Other impacts are the damage to infrastructure such as road pavement, bitumen, pipelines and concrete. In 2000, some 1,600 km of rail, 19,900 km of roads, and 68 towns were at risk of damage due to salinity.

Salinity threatens biodiversity through loss of habitat on land and in water. Areas of remnant and rehabilitated native vegetation are under threat in Western Australia, South Australia, New South Wales and Victoria (NLWRA 2001). In the Western Australian wheat-belt, salinity has caused a 50% decrease in the numbers of wetland bird species, and 450 plant species are threatened with extinction through salinity (ANZECC 2001).