As you have learned, rivers and oceans can affect and change the land and environment. They change themselves too. We also change them in various ways. Sometimes this benefits us in the short term. But there may be harmful long-term consequences to our actions.

PEOPLE CHANGE RIVERS Sometimes we change the course of a river to help meet our needs. This is called river diversion. Scientists estimate that we will have diverted 70 percent of all the rivers available to us by 2025. The three main types of river diversions are canals, dams, and new river channels.

BUILDING CANALSA canal is a waterway that allows boats to travel where they would otherwise not be able to go. In Europe, canals are an important method for transporting materials. They are also used to supply cities with water. Canals can create environmental benefits, for example, ships use less fuel when they can take a shortcut to their destination. However, canals may also harm the environment. For example, a canal that diverts water from a river can change its flow and alter the local habitats, both in the river and on the land nearby.

BUILDING DAMSA dam is a barrier that is built across a river. As the water passes through the dam, it turns blades on a turbine, which converts the energy from the falling water into electricity. The dam raises the water level behind it. The higher water level widens the river or even creates a new lake. Known as a reservoir, this water can be supplied to farms, industries, and communities.

In 2012, China’s massive Three Gorges Dam was finished (Figure 4.16). It crosses the Yangtze River. The dam generates electricity. It supplies fresh water to nearby cities and to large areas of farmland.

Dams can also have harmful effects. They change the flow and levels of rivers, which can affect erosion. This can also damage the river ecosystems and those that it might feed into, such as wetlands or bogs. Many native species of animals and plants cannot survive. Invasive species may move in.

As well, any people living in what will be the new reservoir area are forced to move away. For example, more than a million people were moved from the area set aside for the reservoir for the Three Gorges Dam.

HOW ARE WE

CHANGING RIVERS AND OCEANS?

river diversion changing the course of a river in order to meet a need

dam a barrier built across a river to control the water’s flow and to create a large supply of water

reservoir a place or area of stored water, such as an artificial lake formed by a dam

canal an artificial waterway built to allow the passage of boats or to divert water

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CREATING NEW RIVER CHANNELSPeople create new river channels to redirect the flow of water from rivers. Sometimes this is done to bring water to farmland. The effects can benefit people living in a region, but there can also be harmful results.

For example, for more than 5 million years, the Aral Sea in Central Asia was the fourth-largest inland sea in the world. It was fed by two rivers. In the 1960s, the government changed the flow of the rivers to irrigate a wide area of farmland. The waters of the Aral Sea began to evaporate, and the sea began to shrink. Salt levels in the sea increased by nine times. All the fish in the sea died because they could not survive in the saltier environment. Part of the seabed became a desert (Figure 4.17). Millions of tonnes of salt from the seabed were carried by wind and rain onto a wide area of pastures and farmlands, harming the local vegetation and crops. In 2005, the country of Kazakhstan began a project to return some water to the sea by building a dam to hold water in the northern section.

FIGURE 4.17 (A)The Aral Sea in 1989, and (B) in 2008 after it shrank. As it shrank, the sea lost a volume of water equal to the waters of Lake Erie and Lake Ontario combined.

I wonder how people weigh the benefits versus the risks before they decide to create new river channels?

FIGURE 4.16 The Three Gorges Dam in Yichang, China I wonder how they controlled the flow of the water while they were building the dam?

A B

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POLLUTING RIVERSHumans also change rivers by polluting them. Water is polluted when people change it in a way that makes it harmful or poisonous for people or other living organisms to use. Pollution can come from many human activities, for example, factories, fertilizers and pesticides washing off lawns and farmers’ fields, and car and airplane exhaust, which is burned gas from an engine. Water pollution harms the whole global environment, including people, wildlife, and plants.

Why should water pollution matter to you? Water pollution kills about 14 000 people a day around the world. This is mostly due to water being contaminated or made impure by sewage. Sewage is the waste liquids from sinks, bathtubs and showers, toilets, and other drains in households, schools, offices, and businesses.

In some communities, sewage is treated, or made safe, from contaminants before it is returned to waterways. In many places, sewage is placed back into waterways without any treatment (Figure 4.18). Untreated sewage that gets into waterways can contain bacteria or viruses. If people consume the water, they can become ill or die. Other living species can also be affected by the poor-quality water.

Why do people pollute rivers if so

much harm is caused? Do the benefits

outweigh the risks?

sewage waste materials carried away from homes and industries through sewers or drains

treated sewage and wastewater that has undergone a process to remove contaminants so that it can be safely returned to the environment

pollute to put harmful substances into the environment

FIGURE 4.18 Discharge from a fertilizer plant spews into the Danube River in eastern Europe.

I wonder who should be responsible for preventing this from happening?

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FOCUS ON

TRY ITSelect an article from a newspaper, magazine, or

blog related to how people are changing rivers

and oceans.

1. Read the article, then ask and answer the four

questions above.

2. Use a graphic organizer to identify patterns

between pieces of information in the article.

For example,

a) Try to find cause and effect relationships in

the article.

b) Try to make a comparison and identify a

pattern in the article.

c) Try to make a connection to ideas in this

chapter or to information that you already

have.

3. Describe the author’s point of view. What

evidence shows this? (You can include

information within the article, as well as

information about the author from the byline.)

4. How will you go about sharing other points of

view on the topic of how people are changing

rivers and oceans?

Interpreting and analyzing information is an

important geographic skill.

INTERPRET INFORMATIONAs you gather and organize information to answer

your research questions, you need to interpret, or

understand, what it means. Some ways you can

do this are by making comparisons, identifying

patterns, or finding connections. Another useful

way to interpret geographic data is to put it in

visual or graphic forms, such as maps, graphs,

diagrams, and tables. Creating visual organizers

helps you identify patterns and relationships

between different pieces of information.

ANALYZE YOUR EVIDENCEYou also have to analyze your evidence, which

means figuring out how it helps answer your

research questions. Some ways to do this are

looking for cause-and-effect relationships and

thinking about the geographic perspectives of

the issue. Another important way to analyze

your evidence is to consider the sources of your

evidence and figure out how the sources will affect

the evidence itself. For example, you should use

sources that are reliable and that can give current

information and ideas about a topic. You need

information from sources that are knowledgeable

about your research topic and that provide good

evidence to support their conclusions.

Information can often be affected by the point of

view of the person or organization that provides it.

A point of view is the way someone looks at a topic

or idea. It affects the way information is selected

and used.

You need to identify the points of view of

your sources. Using information from only one

source with one point of view might limit your

understanding. Considering several sources can

lead to a more reliable conclusion.

INTERPRET AND ANALYZE

Is the information up to date?

Does the source have expertise on the topic?

Does the source present different sides of the issue or only one point

of view?

Does the source provide evidence

to support any conclusions?

You also need to think about your own point of

view and how it might be affecting your conclusion.

Ask the questions shown in Figure 4.19 to analyze

your sources.

FIGURE 4.19 Questions to ask as you analyze sources

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PEOPLE CHANGE OCEANSWhen people harm rivers, the damage flows downstream, to the lower part of the stream or river. Eventually this damage arrives at the ocean.

People also change oceans directly. How we manage our fisheries affects the survival of species and ocean habitats. We are contributing to climate change, which is affecting oceans. We are also polluting oceans.

DESTROYING OCEAN HABITATSPeople’s activities can destroy habitats that border the oceans, such as sea grasses and mangrove swamps. They are also destroying coral reefs. Coral reefs are complex environments. As well as being underwater ridges made of living coral and their skeletons, they are communities of other organisms, such as plants, fish, turtles, starfish, and so on. Coral reefs are home to over one quarter of all marine life on Earth. They are important nurseries for fish and also provide protection during storms. They grow slowly in clear, shallow, warm water. In recent years, reefs in the Pacific and Indian oceans have shrunk by 1550 km2 per year because of human activity.

Loss of habitat happens in several ways, including the following:• Fish nets dragged along the ocean floor

break the coral and disturb sediment. The sediment smothers nearby reefs (Figure 4.20).

• Poor farming practices result in large amounts of soil washing off the land and into oceans. These sediments also smother reefs and sensitive ocean bottoms.

• Tour boats collide with the fragile coral reefs, breaking the coral. Divers may break off chunks of the reef for souvenirs.

• People mine coral to use as road-fill or bricks in new buildings.

• Many kinds of toxins dumped into the ocean or carried there by rivers are poisoning the reefs. Some chemicals, such as nitrogen, are fed on by algae. When the algae multiply in large numbers, they block the sunlight, which the coral needs to grow.

downstream toward the mouth of a stream or river

coral colonies of tiny marine organisms whose secretions form colourful underwater structures

FIGURE 4.20 This coral in Vanuatu, in the South Pacific, is covered in a fishing net.

I wonder what the short-term and long-term consequences of this type of activity are?

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POLLUTING THE OCEANS Today, many ocean beaches around the world are littered with different types of garbage, including plastic bags and bottles (Figure 4.21). The ocean waters and the wildlife that depend on these waters are also being damaged by pollution.

There are four ways pollution ends up in oceans. It is dumped directly into oceans from the land, which is what sometimes happens with sewage, or from ships or ocean drilling rigs. It can also enter the ocean from rivers, from the air, or through natural forces such as tsunamis and hurricanes.

Besides garbage and sewage, there are three other important types of ocean pollution. • Toxic wastes are poisonous chemicals, such as pesticides, and metals,

such as mercury. Many chemicals are used by industries to make products. They are dumped into the water as waste and eventually end up in the oceans. Toxic chemicals can also dissolve out of plastic. Many of these chemicals never break down. As one animal is eaten by another, these chemicals are passed along and become more concentrated. Some animals cannot reproduce or they get sick. Many die from the poisons.

• Farmers put fertilizers on their fields to help their crops grow. Over time, a water system, such as a stream or river, brings the fertilizers to the ocean. These nutrients make algae in the water grow quickly. The algae use up all the oxygen in a zone of water so there is none left for other animals such as fish. There are about 500 of these “dead zones” around the world.

• Oil spills happen when oil tankers or drilling platforms are damaged. Much more oil is released into the water on purpose through ships flushing out their oil tanks. Other sources of oil pollution in oceans are oil-drilling activities and runoff from highways and parking lots.

1. EVALUATE AND DRAW CONCLUSIONS When are river

diversions positive? When are river diversions

negative? Show your ideas in a drawing

with labels.

2. INTERRELATIONSHIPS Make a poster or brochure

to show the effects of the damage being done to

coral reefs.

3. INTERPRET AND ANALYZE Using labelled sketches,

illustrations, or photographs, show two or three

ways people change rivers or oceans. Add a

sentence for each example explaining what you

think are the points of view of the authors of this

resource, and why. Explain what your point of

view is, and why.

CHECK-IN

toxic waste poisonous waste material, usually chemicals, which can cause injury, death, or damage to the environment

FIGURE 4.21 Garbage from the ocean washed up on the beach

I wonder how garbage from one location can end up in another part of the world?

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