Geoscience Reference
In-Depth Information
Clearly, the Australian people face a critical issue, espe-
cially in the context of a growing population. Australians are
attempting to deal with the problem, specifically with efforts
to restore water and salt balances by controlling groundwater
recharge rates in some areas. In other places, farmers and
ranchers are attempting to reduce the effects of salinization
by planting salt-tolerant trees, such as Saltgrow (a hybrid
eucalyptus tree). These efforts will take a substantial amount
of time, however, which means that the problem of salini-
zation in Australia is going to be chronic for the foresee-
able future and will likely get worse before it gets better.
The potential negative impact that salinization has on wheat
production is magnified if global climate change scenarios
are included in the equation, because most models suggest
that Australia will become even warmer and drier in the fu-
ture. If this is true, then the challenge of producing enough
wheat in Australia is obvious. Stay tuned.
clearing of native vegetation causes local water tables
to rise sufficiently close to the surface that wicking can
occur. This form of salinization is magnified when ir-
rigation causes the water table to rise further. Soil
salinization can also occur when salty irrigated water
evaporates after it is applied to fields, leaving behind
salt deposits.
3.
A major area of soil salinization in the United States is
the San Joaquin Valley in California, which is one of the
most important agricultural regions in the nation.
4.
Extensive soil salinization is also occurring in the agri-
cultural belts of Australia. Soil degradation in these ar-
eas has the high potential to significantly reduce crop
yields such as wheat.
Case 3: Developing
Unconventional Oil Supplies
in North America
The Challenge of Sustainable
Agriculture in Semi-Arid and
Arid Regions
This case study focused on the issue of soil salinization in
semi-arid and arid regions of the world. The factors that
influence the salinization of soils are clearly related to physi-
cal geography and the ways that humans interact with the en-
vironment. Salinization is prone to occur in marginal lands
where people are attempting to farm in an effort to produce
more food. These environments are extremely sensitive to dis-
turbance and modification of the landscape to fit agricultural
needs. Understanding the subsequent salinization of soils that
follows such disturbance requires an appreciation of soils,
groundwater, and evaporation rates. Archaeological evidence
indicates that soil salinization has been a problem since the
dawn of human civilization, resulting in the collapse of past
human societies. The problem remains with us today and will
likely intensify in the future, barring some yet undeveloped
way to deal with soil salts systematically. Given the expected
growth in human population in the coming decades, the likely
loss of farmland or reduced crop yields in salinized areas will
increase the challenge of producing sustainable levels of food
for the world.
The third case study moves away from marginal lands by focus-
ing on some of the challenges we face with regard to petroleum
supplies. As discussed in Chapter 12, the vast majority of en-
ergy required to power our economy is derived from fossil fuels
(coal, gas, petroleum). Of these fuels, people are generally most
familiar with petroleum because they routinely interact with its
refined by-product at the gas pump. Given the importance we
place on freely moving about in our vehicles, people are keenly
aware of price fluctuations, especially if the cost of gas spikes
for a period of time. How many of us understand, however, the
factors involved in maintaining a steady supply of gas to the
American consumer? Certainly, such a discussion could fo-
cus solely on the economic or political factors that influence
the supply and cost of oil. On the other hand, it can be viewed
through the prism of physical geography, which this case study
does, to better understand some of the new issues we face just
to extract oil from the ground.
Oil Supply, Demand, and Geography
As indicated in Chapter 12, the beginning of the modern pe-
troleum era can be traced to the Industrial Revolution in the
mid-1800s. Through the first few decades of industrialization
in the United States, supply easily kept pace with demand. By
1906, for example, U.S. oil production was about 126.5 mil-
lion barrels per year, and extensive fields were discovered in
Texas (Figure 20.23), Oklahoma, and California that expanded
our national supply. During this phase of development and ex-
tending to the recent past, extraction methods can be viewed
simply as an elaborate straw system that sucked oil from res-
ervoirs deep within the ground. During the 1950s petroleum
supplanted coal as the world's dominant fuel source, and the
United States was the world's leading oil producer, yielding
KEY CONCEPTS TO REMEMBER ABOUT
SOIL SALINIZATION
1.
Soil salinization refers to the buildup of salts in soil
and usually occurs in semi-arid and arid regions. It
can occur naturally when salty slopewash accumu-
lates in a depression and evaporates, leaving a salt
crust behind.
2.
Soil salinization can also occur due to agricultural
practices in marginal lands. It can happen when the
