Geoscience Reference
In-Depth Information
they do underline the speed of deforestation.) In 1990, Australia cleared a further
650,000 ha. According to Anderson (
1995
, p. 12), this amounted to 'more than half
the area cleared in the Amazon Basin'.
The resulting rise of saline groundwater has led to major loss of arable land across
southern Australia. Western Australia had lost 1.6 million ha of farmland to salt
by 1994, equivalent to about one-tenth of the cleared agricultural land in that state,
and is losing an area the size of a football pitch every hour, with concomitant loss
of many hundreds of species of plants unique to that state. In the Murray-Darling
Basin (the agricultural heart of the nation), by 1992, more than 200,000 ha had
been lost to salt. By 1996, South Australia had lost 400,000 ha and Victoria had
lost 150,000 ha of arable land (Commonwealth of Australia,
1996
). Lost agricultural
production was estimated at $500 million each year, but a later audit showed this
to be a gross underestimate. Publication of the
Salinity audit of the Murray-Darling
Basin
in October 1999 (Murray-Darling BasinMinisterial Committee,
1999
), together
with the CSIRO Land and Water Report (
1999
)on
Effectiveness of current farming
systems in the control of dryland salinity
, revealed that more than 2.5 million ha
of former agricultural land in Australia had become unusable because of dryland
salinity. Cost to the Australian economy amounted to at least $1 billion - more than
double previous estimates. Unless current trends can somehow be curbed, more than
15 million ha will be salt affected over the next fifty years. More insidious is the
damage to infrastructure from salt, with more than eighty towns in regional areas now
threatened. The city of Adelaide in South Australia has more than a million people and
depends primarily on the Murray River for its drinking water. In the Murray-Darling
Basin, rising groundwater brings 5 million tonnes of dissolved salt to the surface
each year, with 2 million flowing down the river and 3 million remaining on the land
preventing farming.
Dryland salinization is not the only problem of land degradation facing Australia;
nor are all the areas of saline land a result of human action - many parts of the
continent have been accumulating salt throughout geologically recent times (see
Chapter 22
). Lake Eyre is a case in point. Some of the salt problems are caused by
irrigation, although in general this is well-managed. However, excessive abstraction
of water upstream for growing cotton or rice can seriously deplete the supplies of
freshwater available downstream and can lead to build-up of salt in the distal parts
of drainage basins like the Murray. Much of this salt is cyclic, that is, blown in from
the surrounding oceans, but some comes from times when the sea invaded the land at
intervals during the Neogene.
Another issue is that of localised overgrazing of rangelands in much of central
Australia, coupled with the effects of a change in fire regime on the native plant cover.
Some ingenious methods have been devised in an attempt to separate out the effects of
drought from those primarily caused by overgrazing (Pickup,
1996
; Pickup,
1998
), but
these require detailed ground control calibration to be effective, which is expensive
