121 CHAPTER 18 WATER POLLUTION Chapter Objectives
Define water pollution. Describe the types and effects of water pollutants. Investigate water quality today. Explain water pollution control. Summarize water legislation.
Key Terms Bioaccumulation Biodegradable Dioxin Disseminate Exacerbate
Hypoxic Leaching Viable Watershed
Concept Review 18.1
Water Pollution
18.2
Clean water is a global priority. Increasing industrialization and livestock production, as well as agricultural runoff, threatens underground water supplies. Pollutants discharged from a specific location are point sources and are easy to monitor and regulate. Nonpoint sources of pollution have no specific location, and are difficult to monitor and regulate. Especially difficult to account for are pollutants that are carried and deposited through the atmosphere.
Types and Effects of Water Pollution
Water pollutants can cause health problems and disrupt ecosystems. The most serious pollutants for human health are pathogenic organisms. o In developed countries, sewage treatment plants eliminate the worst pathogens. o In less-developed countries, sewage treatment is inadequate or lacking altogether.
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18.3
Water quality can be determined by testing the amount of dissolved oxygen in the sample. o Biochemical oxygen demand (BOD) determines how much organic waste is in the water. o Dissolved oxygen (DO) content indicates the health of the aquatic system. Oxygen sag is a measure of bacterial growth and activity; as oxygen levels decline, the desirable fish and organisms are unable to survive, leaving only bacteria and resistant microorganisms. Rivers and lakes that have clean water and low biological productivity are oligotrophic. Eutrophication indicates an increase in nutrient levels and biological productivity. Human activities that increase levels of metals and salts are a serious threat to water quality. These activities include fertilizer runoff, industry, disposal of wastes, and erosion that leads to sedimentation.
Water Quality Today
Only 10 percent of our water pollution comes from industrial point source pollution, due to provisions in the Clean Water Act. The goal of making all U.S. surface waters fishable and swimmable has not yet been accomplished. Canada also has a water act that has seen similar successes. Three-fourths of the water pollution today comes from soil erosion and surface runoff. While global water quality has been improving, some countries, such as India, have two-thirds of all of their surface waters dangerously contaminated. Ninety-five percent of the people living in rural areas in the United States rely on groundwater aquifers for their water supply. In rural areas, fertilizers and pesticides commonly contaminate aquifers. Coastal areas are contaminated by trash and oil more than any other contaminant.
123 18.4
Water Pollution Control
18.5
The best way to control water pollution is not to create it at all. Eliminating lead gasoline additives, reducing the amount of salt used to melt ice on roads, and modifying agricultural practices involving fertilizers and pesticides have resulted in significant reductions. Density of population also plays a role in controlling water pollution. When the density is low, natural processes can control waste recycling. Municipal sewage treatment is used when population density increases. o Primary treatment involves separating the solids from the effluent. o Secondary treatment of the effluent requires bacteria and aeration to decompose the material aerobically. o Tertiary treatment removes plant nutrients to preserve water quality. Wetlands can perform the same function on a smaller scale.
Water Legislation
The Clean Water Act made clean water a national priority. o Land developers who are prohibited from filling in wetlands and industries that want to dump wastes into wetlands and waterways claim this infringes on their rights. o State and local governments oppose the act, as it is an unfunded mandate to clean up sewage and stormwater. The Safe Drinking Water Act regulates water quality in commercial and municipal systems. The Great Lakes Water Quality Agreement established water quality for the Great Lakes. The London Dumping Convention called for the phasing out of ocean dumping.
Class Time: Once students have a firm grasp of the unique qualities of water from the previous chapter, spend 3–5 days examining point and nonpoint source pollution and methods used to clean up water pollution. If possible, include an extra day to take the class to a sewage treatment plant.
Approach and Tips As you continue your discussion on water use and pollution, begin with a review of point source and nonpoint source pollution and their effects on the ecosystem.
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Table 18.1
Contaminants in the water supply affect plants and animals and can move up and be concentrated in the food chain. Review the food chain information covered earlier in the course and discuss bioaccumulation. Government recommendations regarding the types and quantities of fish that are safe to consume is a great basis for the discussion of bioaccumulation and the related impacts on human health. Another good activity is to trace the path of the bubonic plague in London through well water contamination and Dr. John Snow’s research that led to the discovery. Water quality testing is an important laboratory activity that should be included in the course. Commercially packaged kits are available to test BOD, DO, nitrogen and phosphate levels, pH, and others, depending upon your budget and time constraints. These activities also provide another opportunity for students to perform calculations involving decimal points and scientific notation. If time permits, take the class on a field trip to a sewage treatment facility. If this is not possible, students should be able to discuss the process in detail and relate the role of wetlands to the commercial operation. Discuss how plants and microorganisms can be used to clean water through bioremediation and how this technology can be used in domestic as well as hazardous waste treatment situations.
125 End the discussion with the goals of the Clean Water Act and other water quality legislation. Remember that it is very important for students to be able to name and discuss important legislation on both the national and international levels. Table 18.2
Applications Thermal Pollution and Its Effect on Dissolved Oxygen Background: Power plants, both coal and nuclear, produce heat in their production of electricity. This heated water is released into a body of water such as a lake or river. One characteristic of water is that the warmer the water, the less dissolved oxygen the water is able to hold. As the temperature in the lake or river increases, the dissolved oxygen leaves the water and becomes atmospheric oxygen. Though there are no pollutants in the water that the power plants release, this anthropogenic thermal pollution is extremely destructive to the aquatic environment. Purpose: In this lab you will demonstrate the effect of thermal pollution on an aquatic organism, a goldfish, and will evaluate the environmental consequences of such actions on this delicate ecosystem.
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Materials: Goldfish Thermometer Hotplate Ice Dissolved Oxygen Probe Procedure: 1. Put 500 mls of dechlorinated water in to a 1,000 ml beaker. 2. Add one goldfish to the beaker and find the temperature of the water. 3. Using just a few pieces of ice at a time, slowly cool the goldfish down until the temperature of the water is 15° C. 4. Allow the goldfish to calm down and carefully count how many breaths the fish takes in a minute. (Count how many times it opens and closes the operculum, the covering of the gills.) 5. Using the dissolved oxygen probe, record the % dissolved oxygen at 15° C. 6. Place the goldfish on the hotplate and SLOWLY heat it up to 20° C. Using the thermometer slowly stir the water so the goldfish does not lie on the bottom of the beaker and warm up too fast. Once the water has reached 20° C take the beaker off the hotplate and set on the lab table. 7. After allowing the goldfish to settle down, again count how many breaths the fish takes in a minute. 8. Using the dissolved oxygen probe, record the % dissolved oxygen at 20° C. 9. Repeat steps 6 – 8, bringing the temperature to 25° C and 30° C. 10. Do not allow the water to go above 30° C or the fish could be harmed or die. 11. Allow the fish to cool back down to room temperature.
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Analysis: 1. Graph the results below:
Breaths/min
Dissolved Oxygen
15 20 25 30° C °C °C °C 2. What is the relationship between the two lines on the graph above? 3. What is the effect of thermal pollution on aquatic organisms? 4. What does the term anthropogenic mean? 5. What are some ways that each of us could lessen the effect of thermal pollution on a body of water? 6. How might the presence of biological or chemical pollution affect the outcome of the experiment?
128 Common Mistakes and Misconceptions As proven in the lab activity in this lesson, there are many ways that the water can become polluted. I stress to my students that we always think of water pollution as a chemical that gets into the water that might kill the fish, etc. However, thermal pollution because of power plants is a huge environmental problem. Another very common environmental problem is eutrophication, when yard or farm fertilizers cause the algae in a lake or river to over-reproduce. One of the worst problems around the world is sewage in a body of water. This also causes eutrophication, not to mention disease, in rivers and lakes where sewage effluent is not treated. These and other unintended problems can sometimes have a greater effect on the aquatic environment than chemicals being dumped.
Suggested Website Once again, Enviroliteracy has a wonderful section devoted to water issues. It is found at http://www.enviroliteracy.org/category.php/14.html. If going to a sewage treatment plant is not an option, there are many online, interactive ones that you can “tour.” For example http://www.dcwasa.com/about/model_flashcfm (at the bottom click on “view the virtual overview now). There are many others you can find online as well.
Questions 1. “The Clean Water Act has been called the United States’ most successful and popular environmental legislation.” Explain why, and discuss what goals the legislation still needs to work on. 2. Differentiate between point source and nonpoint source pollution. How has the Clean Water Act reduced point source pollution? 3. Explain the process of cultural eutrophication. Differentiate between the positive and negative effects of eutrophication. 4. Diagram and explain the sewage treatment process. How does a wetland serve the same function? Why does the amount of sewage affect the outcome?
