Define water pollution. Explain how fertilizer in runoff leads to algal blooms and dead zones. Give examples of point-source pollution, and define thermal pollution. Describe how the ocean is being polluted with trash and why ocean water is becoming more acidic.
Lesson Vocabulary • • • • • • • • •
algal bloom dead zone nonpoint-source pollution ocean acidification point-source pollution thermal pollution waterborne disease water pollution wetland
Introduction All living things need water. For most human uses, water must be fresh. Of all the water on Earth, only 1 percent is fresh, liquid water. Most of the rest of Earth’s water is either salt water in the ocean or ice in glaciers and ice caps. Although water is constantly recycled through the water cycle, Earth’s water is in danger. Water pollution is an increasing problem. It occurs when chemicals, sewage, trash, or heat enter water resources. Water pollution is threatening the limited supply of water that human beings and other living things depend on. Already, more than 1 billion people worldwide do not have enough clean, fresh water. With the rapidly growing human population and global climate change, the water shortage is likely to get worse.
Algal Blooms and Dead Zones Water pollution has many causes. One of the biggest causes is fertilizer in runoff. Runoff dissolves fertilizer as it flows over farm fields, lawns, and golf courses. It carries the dissolved fertilizer into bodies of water. More dissolved fertilizer may enter a body of water at the mouth of a river, but there is generally no single point where this type of pollution enters the water. That’s why this type of water pollution is called nonpoint-source pollution. 1
www.ck12.org Algal Blooms
When fertilizer ends up in bodies of water, the added nutrients cause excessive growth of algae. This is called an algal bloom. You can see one in Figure 1.1. The algae out-compete other water organisms. They may make the water unfit for human consumption or recreation.
FIGURE 1.1 Algal bloom
Eventually, the algae in an algal bloom die and decompose. Their decomposition uses up oxygen in the water so that the water becomes hypoxic (“without oxygen”). This has occurred in many bodies of fresh water and large areas of the ocean, creating dead zones. Dead zones are areas where the hypoxic water can’t support life. A very large dead zone exists in the Gulf of Mexico (see Figure 1.2). Nutrients carried into the Gulf by the Mississippi River caused this dead zone. Cutting down on the use of chemical fertilizers is one way to prevent dead zones in bodies of water. Preserving wetlands is also important. Wetlands are habitats such as swamps, marshes, and bogs where the ground is soggy or covered with water much of the year. Wetlands slow down and filter runoff before it reaches bodies of water. Wetlands also provide breeding grounds for many different species of organisms.
FIGURE 1.2 Hypoxic dead zone in the Gulf of Mexico
Point-Source Pollution Unlike runoff, which enters bodies of water everywhere, some sources of pollution enter the water at a single point. This type of water pollution is called point-source pollution. 2
Chapter 1. Water Pollution
Sewage and Other Waste
An example of point-source pollution is the release of pollution into a body of water through a pipe from a factory or sewage treatment plant. Waste water from a factory might contain dangerous chemicals such as strong acids, mercury, or lead. Water from a sewage treatment plant might contain untreated or partially treated sewage. Such pollution can make water dangerous for drinking or other uses. You can learn more about the problem of sewage contaminating the water in U.S. coastal communities by watching this video: http://www.youtube.com/watch?v=r reBKDko6OY
MEDIA Click image to the left or use the URL below. URL: http://www.ck12.org/flx/render/embeddedobject/140781
In poor nations, many people have no choice but to drink water from polluted sources. Drinking sewage-contaminated water causes waterborne diseases, due to pathogens such as protozoa, viruses, or bacteria. Most waterborne diseases cause diarrhea.
If heated water is released into a body of water, it may cause thermal pollution. Thermal pollution is a reduction in the quality of water because of an increase in water temperature. A common cause of thermal pollution is the use of water as a coolant by power plants and factories. This water is heated and then returned to the natural environment at a higher temperature. Warm water can’t hold as much dissolved oxygen as cool water, so an increase in the temperature of water decreases the amount of oxygen it contains. Fish and other organisms adapted to a particular temperature range and oxygen concentration may be killed by the change in water temperature.
Ocean Pollution The ocean is huge but even this body of water is becoming seriously polluted. Climate change also affects the quality of ocean water for living things.
One way that the ocean is becoming polluted is with trash, mainly plastics. The waste comes from shipping accidents, landfill erosion, and the dumping of trash. Plastics may take hundreds or even thousands of years to break down. In the meantime, the waste can be very dangerous to aquatic organisms. Some organisms may swallow plastic bags, for example, and others may be strangled by plastic six-pack rings. You can see some of the trash that routinely washes up on coastlines in Figure 1.3. There are five massive garbage patches floating on the Pacific Ocean. Watch this video to learn more about them: http://www.youtube.com/watch?v=1qT-rOXB6NI
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FIGURE 1.3 Plastic debris in the ocean washes up on shore in the Hawaiian Islands
Ocean water normally dissolves some of the carbon dioxide in the atmosphere. The burning of fossil fuels has increased the amount of carbon dioxide in the atmosphere. As a result, ocean water is also dissolving more carbon dioxide. When carbon dioxide dissolves in water, it forms a weak acid. With higher levels of dissolved carbon dioxide in ocean water, the water becomes more acidic. This process is called ocean acidification. Ocean acidification can kill some aquatic organisms, including corals and shellfish. It may make it more difficult for other aquatic organisms to reproduce. Both effects of acidification interfere with marine food webs, threatening the survival of many aquatic organisms.
Lesson Summary • Water pollution occurs when chemicals, sewage, trash, or heat enter water resources. Water pollution is threatening the limited supply of clean, fresh water that human beings and other living things depend on. • Fertilizer in runoff leads to algal blooms and dead zones in bodies of water. This type of pollution is called nonpoint-source pollution. Point-source pollution includes waste water from factories and sewage treatment plants. Hot water discharge causes thermal pollution. • The ocean is becoming increasingly polluted with trash. Ocean acidification is also occurring because ocean water dissolves some of the excess carbon dioxide in the atmosphere. The more acidic water harms aquatic organisms. 4
Chapter 1. Water Pollution
Lesson Review Questions Recall
1. What is a dead zone? How does it develop? 2. What are wetlands? How do they reduce water pollution? 3. Define thermal pollution, and state when it occurs. Apply Concepts
4. After a month of heavy rain, a formerly clear pond on a golf course is covered with slimy green algae. What do you think happened? Think Critically
5. Compare and contrast point-source and nonpoint-source water pollution. Which type of pollution do you think would be easier to control? 6. Explain the process of ocean acidification. Why does it threaten the survival of many aquatic organisms?
Points to Consider Water is one of our most important natural resources. 1. What is a natural resource? Besides water, what are some other examples of natural resources? 2. What is the difference between renewable and nonrenewable natural resources?
References 1. Cruccone. http://commons.wikimedia.org/wiki/File:River_Cam_green.JPG . CC BY 2.5 2. EPA. http://commons.wikimedia.org/wiki/File:Mississippi_River_basin.jpg . public domain 3. NOAA. http://commons.wikimedia.org/wiki/File:Fish1966_-_Flickr_-_NOAA_Photo_Library.jpg . public domain