Soil Salinity

Salinity in both the rivers and on the land is one of the main and most costly
results of overclearing and irrigation. Salinity is caused by changes in the
delicate balance between surface water and groundwater systems. A small increase
in the infiltration of water from the topsoil to the groundwater, due to
rainfall or irrigation, can result in a dramatic rise in groundwater pressure
and watertable levels.

The trees of the open forests are now replaced by shallow-rooted crops and
pastures which absorb far less water than the native trees. Those trees had been
massive water pumps, sucking up moisture from deep underground and putting it
back into the atmosphere through the evaporation from their leaves. With those
pumps gone, excess rainfall accumulates underground and watertables rise to the
surface, bringing ancient sediments of salt with them, often in heavy
concentrations.

Once exposed to the air and sun, the salts become even more concentrated due to
evaporation, leaving a white crust of salt crystals on the land. Most plants
cannot tolerate the scalding chemical effect of the salt, and so they die. As
they die off, the soil succumbs to erosion and a double dose of salt and
sediment enters nearby rivers and wetlands. In cattle-grazing areas, the animals
often gather at saline seeps to lick the salt, which leads to further erosion.

Salinity affects around 560,000 hectares of the Murray-Darling basin\'s most
productive irrigation lands, mostly in southern New South Wales, and northern
Victoria, and partly in South Australia. This represents more than half the
total irrigation area. In Western Australia, about 250 square kilometres of
agricultural land is going out of production every year because of soil salinity
caused by overclearing of native vegetation.

Category: Social Issues