新托福TPO3阅读原文(二)Depletion of the Ogallala Aquifer及译文

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二

):Depletion of the Ogallala Aquifer

TPO-3-2

：

Depletion of the Ogallala Aquifer

The

vast

grasslands

of

the

High

Plains

in

the

central

United

States

were

settled by farmers and ranchers in the 1880s. This region has a semiarid climate,

and

for

50

years

after

its

settlement,

it

supported

a

low-intensity

agricultural

economy

of

cattle

ranching

and

wheat

farming.

In

the

early

twentieth

century,

however, it was discovered that much of the High Plains was underlain by a huge

aquifer (a rock layer containing large quantities of groundwater). This aquifer was

named the Ogallala aquifer after the Ogallala Sioux Indians, who once inhabited

the region.

The Ogallala aquifer is a sandstone formation that underlies some 583,000

square kilometers of land extending from northwestern Texas to southern South

Dakota.

Water

from

rains

and

melting

snows

has

been

accumulating

in

the

Ogallala for the past 30,000 years. Estimates indicate that the aquifer contains

enough

water

to

fill

Lake

Huron,

but

unfortunately,

under

the

semiarid

climatic

conditions that presently exist in the

region, rates of addition to

the aquifer are

minimal, amounting to about half a centimeter a year.

The first wells were drilled into the Ogallala during the drought years of the

early 1930s. The ensuing rapid expansion of irrigation agriculture, especially from

the 1950s onward, transformed the economy of the region. More than 100,000

wells

now

tap

the

Ogallala.

Modern

irrigation

devices,

each

capable

of

spraying

4.5

million

liters

of

water

a

day,

have

produced

a

landscape

dominated

by

geometric patterns of circular green islands of crops. Ogallala water has enabled

the

High

Plains

region

to

supply

significant

amounts

of

the

cotton,

sorghum,

wheat, and corn grown in the United States. In addition, 40 percent of American

grain-fed beef cattle are fattened here.

This

unprecedented

development

of

a

finite

groundwater

resource

with

an

almost negligible natural recharge rate

—

that is, virtually no natural water source

to

replenish

the

water

supply

—

has

caused

water

tables

in

the

region

to

fall

drastically. In the 1930s, wells encountered plentiful water at a depth of about 15

meters;

currently,

they

must

be

dug

to

depths

of

45

to

60

meters

or

more.

In

places, the water table is declining at a rate of a meter a year, necessitating the

periodic

deepening

of

wells

and

the

use

of

ever-more- powerful

pumps.

It

is

estimated that at current withdrawal rates, much of the aquifer will run dry within

40 years. The situation is most critical in Texas, where the climate is driest, the

greatest

amount

of

water

is

being

pumped,

and

the

aquifer

contains

the

least

water.

It

is

projected

that

the

remaining

Ogallala

water

will,

by

the

year

2030,

support only 35 to 40 percent of the irrigated acreage in Texas that is supported

in 1980.

The

reaction

of

farmers

to

the

inevitable

depletion

of

the

Ogallala

varies.

Many have been attempting to conserve water by irrigating less frequently or by

switching

to

crops

that

require

less

water.

Others,

however,

have

adopted

the

philosophy that it is best to use the water while it is still economically profitable to

do so and to concentrate on high-value crops such as cotton. The incentive of the

farmers who wish to conserve water is reduced by their knowledge that many of

their neighbors are profiting by using great amounts of water, and in the process

are drawing down the entire region’s water supplies.

In

the

face

of

the

upcoming

water

supply

crisis,

a

number

of

grandiose

schemes have been developed to transport vast quantities of water by canal or

pipeline from the Mississippi, the Missouri, or the Arkansas rivers. Unfortunately,

the cost of water obtained through any of these schemes would increase pumping

costs at least tenfold, making the cost of irrigated agricultural products from the

region uncompetitive on the national and international markets. Somewhat more

promising have been recent experiments for releasing capillary water (water in the

soil)

above

the

water

table

by

injecting

compressed

air

into

the

ground.

Even

if

this

process

proves

successful,

however,

it

would

almost

triple

water

costs.

Genetic

engineering

also

may

provide

a

partial

solution,

as

new

strains

of

drought-resistant

crops

continue

to

be

developed.

Whatever

the

final

answer

to

the water crisis may be, it is evident that within the High Plains, irrigation water

will

never

again

be

the

abundant,

inexpensive

resource

it

was

during

the

agricultural boom years of the mid- twentieth century.

译文：

TPO-3-2

奥加拉拉蓄水层的枯竭

19

世纪

8 0

年代，

在美国中部北美大平原的广阔草原上定居着农场主们和 牧

场主们。这里有着半干旱的气候，在人们定居

50

和小麦种植为主的低密度农业经济。然而，在

20

世纪初，人们发现北美大平原

的大 部地下是巨大的蓄水层

(

含有大量地下水的岩层

)

。这个蓄水层因曾经在这里

定居过的奥加拉拉苏族印 第安人而得名，被称作奥加拉拉蓄水层。

奥加拉拉蓄水层属于砂岩结构，

在从 德克萨斯州西北到南达科塔州南部的地

下绵延了

58.3

万平方公里。雨水和融雪自

3

万年前便开始在 奥加拉拉蓄积。据

估计，

奥加拉拉蓄水层的含水量足以填满休伦 湖，

但不幸的是，

在目前该地区半

干旱 的气候条件下，奥加拉拉蓄水层的蓄水能力极低，每年仅半厘米左右。