High School Earth Science/Water Pollution

< High School Earth Science

Freshwater and ocean pollution are serious global problems that affect the availability of safe drinking water, human health, and the environment. Waterborne diseases from water pollution kill millions of people in undeveloped countries every year.

Lesson Objectives

Sources of Water Pollution

Water pollution can make our current water shortages even worse than they already are. Imagine that all of your drinking water came from a river polluted by industrial waste and sewage. In undeveloped countries throughout the world, raw sewage is dumped into the same water that undeveloped people drink and bathe in. Without the technology to collect, treat and distribute water, people do not have access to safe drinking water. Throughout the world, more than 14,000 people die every day from waterborne diseases, like cholera which is spread through polluted water.

Even in developed countries that can afford the technology to treat water, water pollution affects human and environmental health.

Water pollution includes any contaminant that gets into lakes, streams, and oceans. The most widespread source of water contamination in undeveloped countries is raw sewage dumped into lakes, rivers and streams. In developed countries, the three main sources of water pollution are:

Types of Water Pollution

Municipal Pollution

Wastewater usually contains many different contaminants. This makes it difficult for the Environmental Protection Agency (EPA) to identify the main source when toxic chemicals are found in wastewater. The pollution coming from homes, stores and other businesses is called municipal pollution (Figure 21.16). Contaminants come from:

Industrial Pollution

Many kinds of pollutants from factories and hospitals end up in our air and waterways (Figure 21.17). Some of the most hazardous industrial pollutants include:

Figure 21.17: Polluted water coming from a factory in Mexico. The different colors of foam indicate various chemicals in the water and industrial pollution.

Agricultural Pollution

Agriculture includes crops, livestock, and poultry farming. Most agricultural contaminants are carried by runoff that carries fertilizers, pesticides, and animal waste into nearby waterways (Figure 21.18). Soil and silt erosion also contribute to surface water contamination.

Figure 21.18: Many types of agriculture add pollutants to groundwater.

Animal wastes expose humans and the environment to some of the most harmful disease causing organisms or pathogens. These include bacteria, viruses, protozoa, and parasites. Pathogens are especially harmful to humans, because they can cause many illnesses including typhoid and dysentery as well as minor respiratory and skin diseases.

You may be surprised to learn that even the fertilizers we use on our lawns and farm fields are extremely harmful to the environment. Fertilizers from lawns and farm fields wash into nearby rivers, lakes and the oceans. Fertilizers contain nitrates that promote tremendous plant growth in the water. Consequences of this accelerated plant growth include:

Every year you can see dead zones, hundreds of kilometers of ocean without fish or plant life (Figure 21.19). These dead zones occur in the Gulf of Mexico and other river delta areas due to water polluted with fertilizers. In 1999, a dead zone in the Gulf of Mexico reached over 7,700 square miles.

Figure 21.19: A dead zone is a large area of water where fertilizer runoff pollutes farms and yards, ultimately killing off aquatic life. The red circles indicate dead zones around the world.

Ocean Water Pollution

Figure 21.20: In some areas of the world, ocean pollution is all too obvious.

Most (80%) of ocean pollution comes as runoff from agriculture, industry, and domestic uses (Figure 21.20). These same kinds of runoff also pollute freshwater. The remaining 20% of water pollution comes from oil spills and people dumping sewage directly into the water.

Coastal pollution can make coastal water unsafe for humans and wildlife. After rainfall, there can be enough runoff pollution that beaches are closed to prevent the spread of disease from pollutants.

A large proportion of the fish stocks we rely on for food live in the coastal wetlands. Coastal runoff from farm waste often carries water-borne organisms that cause lesions that kill fish. Humans who come in contact with polluted waters and affected fish can also experience harmful symptoms. More than one-third of the shellfish-growing waters of the United States are adversely affected by coastal pollution.

Thermal Water Pollution

Thermal pollution is anything that causes water temperatures to rise or fall (Figure 21.21). For example, power plants and other industries often use water to cool equipment. Once the water absorbs heat from a power plant or industry, the heated water is returned to the natural environment at a higher temperature. Cold water pollution can be observed when very cold water is released from reservoirs.

Figure 21.21: The Macquarie perch is now extinct in most of its upland river habitats partially due to thermal pollution by dams.

Why would changing water temperature harm the environment? Fish and other aquatic organisms are often vulnerable to even small temperature changes. Heated water kills fish and other organisms by decreasing oxygen supply in the water. Frigid water has a severe effect on fish (particularly eggs and larvae), macro invertebrates and river productivity.

Lesson Summary

Industrial, agricultural, and municipal sources produce harmful water pollutants such as toxic chemicals, radiological agents, and animal wastes. Thousands of people die from waterborne diseases every year.

Review Questions

  1. What do the initials "EPA" stand for?
  2. What is runoff and why is it a problem?
  3. Who is responsible for reducing water pollution?
  4. Explain what a dead zone is and where you might find one?
  5. What is the leading cause of death for children around the world?

Vocabulary

dead zone
A region hundreds of kilometers wide without fish or plant life due to lack of oxygen in the water.
thermal pollution
Water pollution created by added heat to water.

Points to Consider


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