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of fish, many of which have populations that are now also their water consumption to allow the water supply to
declining. The encouraging news is that some nations have rebound.
regulated the amount of commercial fishing for a given In addition to having available water, it is also important
species of fish or shellfish, such as multiple species of wild that the available water is clean water. The greatest human
salmon in Alaska, and this has allowed the long-term sus- need for water is for agriculture, and this has led to declines
tainable harvest of these species. Unfortunately, commercial in water quality in many parts of the world due to various
fishing for many other species is not effectively regulated pollutants related to agriculture, including excess nutrients,
around the world. In addition, the growth of aquaculture pesticides, and animal waste. We will discuss these water
operations around the world has led to the loss of natural pollution issues, and their solutions, in Unit 8.
coastal habitats in tropical countries. We will have much
more to say about sustainable fishing and aquaculture in Pollination Services
Module 34.
As we noted earlier, pollination of flowers by insects, hum-
Water Availability mingbirds, and bats provides a critical ecosystem support
service for humans. These pollinators also are responsible
The supply of fresh water for humans as an ecosystem ser- for the sexual reproduction of plants in nature. One large
vice has increased globally over the past 50 years, but this concern is the global decline in bees, which is happening
varies a great deal by region. In many parts of the world, due to a combination of habitat loss, parasites, and pesticide
including North Africa, the Middle East, Mexico, and the use. Habitat loss is important because natural habitats pro-
American West, water is being used faster than it can be vide nesting areas for bees and provide natural flowers that
naturally replenished as a result of the increasing demands can sustain bee populations with pollen and nectar when a
of a growing human population. In 2021, for example, nearby agricultural crop is not flowering. Parasites of bees
several reservoirs in the American West experienced their appear to be increasingly common, and this may be due to a
lowest water levels ever recorded as a result of increased decline in bee health due to pesticides in the environment.
drought and record high temperatures. The largest reser- Because pesticides are designed to kill insects that eat crops,
voir, Lake Mead in Nevada and Arizona, supplies water to pesticides can have the unintended consequence of weak-
40 million people across four states and serves to generate ening or killing beneficial insects such as bees. Moreover,
electricity for the region (FIGURE 9.7a). In 2021, a water bees are exposed to multiple pesticides in the environment,
emergency was declared as Lake Mead dropped to a record with the average beehive in the United States containing six
low, falling 43 m (140 feet) and containing only 35 percent different agricultural chemicals. The most complete data on
of the water that it held when initially filled in the 1930s bee populations is from the United States and Europe and
(Figure 9.7b). Such declines are causing the states to reduce both regions are observing declines in both wild species of

400

Lake Mead water elevation (meters above sea level) 350

300

250
0
1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
Year
(a) (b)
FIGURE 9.7 Declining water availability. Lake Mead is a human-made reservoir created by
damming the Colorado River with the Hoover Dam. (a) Since 2000, the lake has steadily declined
in depth due to water use and climate change. (b) In 2021, the lake had dropped 43 m (140 feet)
THIRD PASS
fried_es4e_09_07a_0906 - April 5, 2022
to only 35 percent of its volume. The white rocks along the sides of the lake show the high-water
mark of past decades. (b: BRIDGET BENNET/REUTERS/Newscom)

110 UNIT 2 ■ The Living World: Biodiversity
Uncorrected proofs have been used in this sample.
Copyright © Bedford, Freeman & Worth Publishers.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.

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