Geoscience Reference
In-Depth Information
VISUAL CONCEPT CHECK
20.2
Imagine you are flying over the San Joaquin
Valley in California and see this landscape when
you look out the window. What is the best ex-
planation for the whitish area visible in the cen-
ter of the image?
At this point in time, no systematic plan has been imple-
mented to deal with soil salinity in the San Joaquin Valley.
Regardless of the method(s) employed, some kind of soil salt
balance must be achieved for irrigated agriculture to be sus-
tainable in the long term in this critical agricultural zone. Re-
cent modeling of groundwater salt concentrations suggests that
in the near term some kind of soil salt balance can be attained.
The long-term prospects are not as favorable, however, pri-
marily because it appears that salt concentrations in the deep
Central Valley aquifer are slowly rising. These rising concen-
trations will be a problem in the coming decades because this
water supply is used extensively for irrigation. Increasing salt
levels in this aquifer mean that increasingly salty water will
be applied to crops, thereby damaging them and raising soil
salinity levels. Given the need to produce an ever-increasing
amount of food in the future, this potential outcome has seri-
ous implications.
N
Precipitation
mm
in.
3000
120
2000
1000
500
250
50
80
40
20
10
2
Australia
0
250
500 km
Australia is a fascinating country in many ways and has long
been a draw to people throughout the world. It is the largest is-
land on Earth, while at the same time it is a continent about the
size of the contiguous United States (its lower 48 states). Some
of the oldest rocks in the world, dating to about 3.5 billion years
ago, are found in Australia. The Australian continent has been
essentially inert from a geologic perspective for some 60 million
years, which means that some of the oldest and most weathered
soils on the planet occur there. Given its long-term isolation, the
flora and fauna are exotic, with 80% of Australian plants and ani-
mals like the kangaroo, platypus, and koala found nowhere else
on Earth. Some of the most lethal animals on Earth are indig-
enous to Australia, including the salt-water crocodile, trap-door
spider, and box jellyfish. The fantastic Great Barrier Reef fringes
the northeast coast. Among many other unusual things, Australia
has the most salinized soils in the world. Most of the country is
semi-arid to arid, receiving less than 50 cm (20 in.) of precipita-
tion a year (Figure 20.19). The combined effect of low precipita-
tion and ancient soils poor in nutrients produced one of the most
desolate places on Earth, the famed Australian outback.
0
200
400 mi
(a)
(b)
Figure 20.19 Australia precipitation.
(a) Map of average an-
nual precipitation in Australia. Note that most of the country is
semi-arid to arid. (b) Typical scene in the Australian outback. This
landscape is the result of sparse precipitation and ancient soils
that are low in nutrients. Notice the redness of the soils, which
indicates deep weathering of the host sediment.
