WHY ARE

EARTH’S WATER SYSTEMS IMPORTANT?

Without water, there would be no life on Earth. Living things need water to survive. But we use water for more than just survival. We use water to generate electricity. We also use it to make products and to irrigate farmland to grow our food. To irrigate means to artificially supply water to land or plants to help growth. Water is also used as a means of transportation. Ships carry passengers and transport goods all over the world. We also use boats for fun and recreation, for sailing, kayaking, and canoeing. We swim, water-ski, and surf in the water.

irrigate to artificially supply water to land or plants to help growth

FIGURE 4.1 The Ganges River in India has enormous spiritual significance to Hindus.

I wonder why people have spiritual connections with some rivers?

104 UNIT 1: Physical Patterns in a Changing World NEL104 NEL

04_geo7_ch4.indd 104 2014-10-29 3:02 PM

surface runofffrom rivers

evaporationfrom oceans, lakes,

and streams

evaporation fromplants and soil

condensation

precipitation

groundwater

water table

precipitation

Water systems and bodies of water can be used in a political way. They sometimes form boundary lines between countries and regions of the world.

They are also significant to people around the world for other reasons. For example, rivers have been an important part of the traditional way of life for many First Nations, Métis, and Inuit in Canada. The Kwanlin Dün First Nation live along the Yukon River. The river’s banks are lined with meeting places, hunting sites, and burial grounds. The Ganges River in India is sacred to Hindus (Figure 4.1). People bathe in the Ganges as part of religious rituals, use the water to pay tribute to their ancestors, and use the river as part of their funeral ceremonies.

THE WATER CYCLEWater continuously moves through a cycle. As you can see in Figure 4.2, water is always evaporating from the land and water bodies and being moved by winds. Some of it is returned to the land and water bodies by precipitation. Some water is stored in ice or snow or in lakes. Some is stored in the soil or near Earth’s surface as groundwater. Groundwater is water that is held, or flows, beneath Earth’s surface. The upper level of groundwater is the water table. As well, some water on the land drains through rivers toward lakes and oceans, where it can stay for some time.

As water runs off the land, it carries minerals into the ocean. These minerals form salts, which accumulate in the ocean. Lakes are not salty because the minerals are washed to the ocean by the movement of water as the water flows from rivers, to lakes, to oceans.

water systems bodies of water and all their parts

FIGURE 4.2 This diagram shows the journey of water as it moves constantly through the different phases of the water cycle, also known as the hydrologic cycle.

groundwater water that is held or flowing beneath Earth’s surface

water table the upper level of groundwater

CHAPTER 4: Patterns of Rivers and Oceans 105NEL

04_geo7_ch4.indd 105 2014-10-29 3:02 PM

WHERE WE FIND WATERAs you can see in Figure 4.3, most of Earth’s water is found in the oceans. It is salt water. Fresh water makes up only 3 percent of Earth’s water. Much of the fresh water is not available for people to use because it is in ice caps and glaciers or it is deep below the surface as groundwater. Only about 1 percent of all fresh water on Earth is available for 7 billion people to use. Some of this water is found in wetlands, lakes, and rivers. Some of it is within plants and animals. Some available water is in the soil and the atmosphere. This 1 percent of Earth’s water supports the lives of all living things on this planet.

RIVERSRivers are found on all continents except Antarctica. They contain a small percentage of all the fresh water in the world, but it is very important for plants, animals, and people. Rivers shape the land, creating landform patterns such as valleys and canyons. Land also affects rivers. For example, a river flows more quickly down a steep slope.

OCEANSThere is really only one ocean on this planet. The world’s oceans are joined together, and water flows from one ocean to another. It is only for our convenience that we give names to the different parts of the one ocean.

Oceans make up 71 percent of Earth’s surface. As you can see from Figure 4.3, about 97 percent of Earth’s water is in the oceans. As well, the oceans contribute 86 percent of the water that evaporates into the water cycle. However, more water is held in the ocean than is moving through the water cycle. The ocean acts as a storehouse of Earth’s water.

wetlands lowland areas that have plenty of water, such as swamps, marshes, bogs, and lagoons

C04-F02-G07SB

Crowle Art Group

3rd pass

Geography 7 SB

0-17-659048-X

FN

CO

Pass

Approved

Not Approved

Fresh Water

Available Fresh Water

Where is Earth's Water?

All Water

ice caps and glaciers69%

oceans97%

ice and snow73%other4%

rivers0.5%

fresh water3%

groundwater30%

lakes20%

available surface fresh water1%

swamps and marshes2.5%

FIGURE 4.3 This graph shows the proportions of salt water, fresh water, and available fresh water on Earth.

What is one reason that we give

labels to different parts of the ocean?

Where Is Earth’s Water?

106 NELUNIT 1: Physical Patterns in a Changing World

04_geo7_ch4.indd 106 2014-10-29 3:02 PM

THE IMPORTANCE OF SALTMinerals dissolve and are washed from the land and carried by rivers and lakes (Figure 4.4) into the oceans. Water evaporates from the surface of the oceans and returns to the water cycle, but the minerals remain in the ocean, becoming more and more concentrated. These minerals eventually form salt. Some parts of the ocean are saltier than others. The ocean has higher salinity, or saltiness, where there is higher evaporation, for example, near the equator. There is less salinity in the ocean near the poles.

Plants and animals that live in ocean water are adapted to the salinity. Plants that live on the ocean coasts, such as mangrove trees and marsh grass, can tolerate higher levels of salinity than other species. Without rivers, streams, and precipitation supplying the ocean with fresh water, it would become more and more salty—even too salty for fish to survive. The ocean waters would eventually evaporate completely. On page 117, you’ll read more about how something like this happened to the Aral Sea.

1. EVALUATE AND DRAW CONCLUSIONS What is an

important conclusion that you reach after

analyzing Figure 4.3? Explain to someone else

why it is important to know this and how it might

affect your lives.

2. GEOGRAPHIC PERSPECTIVE How does knowing

that all the oceans are joined together help you

understand the impact of a river drying up? Write

a paragraph or create a short presentation to

demonstrate your understanding.

CHECK-IN

salinity the saltiness or dissolved salt content of a body of water

FIGURE 4.4 Here, on the Osa Peninsula in Costa Rica, the mouth of the Rio Claro river empties into the ocean, washing minerals out to sea.

I wonder whether water at the mouth of a river tastes salty?

CHAPTER 4: Patterns of Rivers and Oceans 107NEL

04_geo7_ch4.indd 107 2014-10-29 3:02 PM