Point-Source Pollution

Transcription

1 Section 3 Objectives Compare point-source pollution and nonpoint-source pollution. Classify water pollutants by five types. Explain why groundwater pollution is difficult to clean up. Describe the major sources of ocean pollution, and explain the effects of pollution on ecosystems. Describe six major laws designed to improve water quality in the United States. Key Terms water pollution point-source pollution nonpoint-source pollution wastewater artificial eutrophication thermal pollution biomagnification Water Pollution You might think that you can tell if a body of water is polluted by the way that the water looks or smells, but sometimes you can t. There are many different forms of water pollution. Water pollution is the introduction of chemical, physical, or biological agents into water that degrade water quality and harm the organisms that depend on the water. Almost all of the ways that we use water contribute to water pollution. However, the two underlying causes of water pollution are industrialization and rapid human population growth. In the last 30 years, developed countries have made great strides in cleaning up many polluted water supplies. Despite this progress, some water is still dangerously polluted in the United States and in other countries. In developing parts of the world, water pollution is a big problem. Industry is usually not the major cause of water pollution in developing countries. Often, the only water available for drinking in these countries is polluted with sewage and agricultural runoff, which can spread waterborne diseases. To prevent water pollution, people must understand where pollutants come from and have access to adequate sanitation facilities. Water pollution comes from two types of sources: point and nonpoint sources. Point-Source Pollution When you think of water pollution, you probably think of a single source, such as a factory, a wastewater treatment plant, or a leaking oil tanker. These are all examples of point-source pollution, which is pollution discharged from a single source. Figure 3.1 lists some additional examples of point-source pollution. Point-source pollution can often be identified and traced to a source. But even when the source of the pollution is known, enforcing cleanup may be difficult. Figure 3.1 leaking septic-tank systems point-source Pollution leaking storage lagoons for polluted waste unlined landfills leaking underground storage tanks that contain chemicals or fuels such as gasoline polluted water from abandoned and active mines water discharged by industries public and industrial waste water treatment plants Point-Source Pollution Point-source pollution comes from a single, easily identifiable source. In this photo, the waste from an iron mine is being stored in a pond. Thomas Del Brase/Photodisc/Getty Images 284 Unit 4: Water, Air, and Land

2 Nonpoint-Source Pollution Nonpoint-source pollution, also known as runoff pollution, comes from many different sources that are often difficult to identify. Figure 3.2 shows common sources of nonpoint pollutants. Other sources might include road salt in northern climates, soil eroded from cleared land, or acid drainage from mine tailings. If any land surface in a watershed is polluted, runoff from a rainstorm can carry the pollution into a nearby river, stream, or lake. Figure 3.3 illustrates some sources of nonpoint pollution. Because nonpoint pollutants can enter bodies of water in many different ways, they are extremely difficult to regulate and control. The accumulation of small amounts of water pollution from many sources is a major issue according to the EPA, nonpoint sources remain the largest source of water quality problems in the United States. Controlling nonpoint sources of pollution depends to a great extent on public awareness of the effects of activities such as spraying lawn chemicals and using storm drains to dispose of used motor oil. Figure 3.2 Nonpoint Sources of Pollution chemicals added to road surfaces (salt and other de-icing agents) water runoff from city and suburban streets that may contain oil, gasoline, animal feces, and litter pesticides, herbicides, and fertilizer from residential lawns, golf courses, and farmland feces and agricultural chemicals from livestock feedlots precipitation containing air pollutants soil runoff from farms and construction sites oil and gasoline from personal watercraft Figure 3.3 Nonpoint-Source Pollution Examples of nonpoint-source pollution include livestock polluting water holes that can flow into streams and reservoirs, oil on a street, which can wash into storm sewers and then drain into waterways, and thousands of watercraft, which can leak gasoline and oil. (l) David Hosking/Photo Researchers, Inc.; (tr) Gary Braasch/Corbis; (br) Corbis Chapter 11: Water 285

3 figure 3.4 Pollutant Types and Sources Type of pollutant Agent Major sources Pathogens Organic matter Organic chemicals disease-causing organisms, such as bacteria, viruses, protozoa, and parasitic worms animal and plant matter remains, feces, food waste, and debris from food-processing plants pesticides, fertilizers, plastics, detergents, gasoline and oil, and other materials made from petroleum mostly nonpoint sources: sewage or animal feces, livestock feedlots, and poultry farms; sewage from overburdened wastewater treatment plants mostly nonpoint sources mostly nonpoint sources: farms, lawns, golf courses, roads, wastewater, unlined landfills, and leaking underground storage tanks Inorganic chemicals acids, bases, salts, and industrial chemicals point sources and nonpoint sources: industrial waste, road surfaces, wastewater, and polluted precipitation Heavy metals lead, mercury, cadmium, and arsenic point sources and nonpoint sources: industrial discharge, unlined landfills, some household chemicals, and mining processes; heavy metals also occur naturally in some groundwater Physical agents heat and suspended solids point sources and nonpoint sources: heat from industrial processes and suspended solids from soil erosion Connect to HISTORY Cryptosporidium Outbreak In 1993, a pathogen called Cryptosporidium parvum contaminated the municipal water supply of Milwaukee, Wisconsin. The waterborne parasite caused more than 100 deaths, and 400,000 people experienced a flulike illness. Cryptosporidium is found in animal feces, but the parasite usually occurs in low levels in water supplies. The outbreak in Milwaukee was probably caused by an unusual combination of heavy rainfall and agricultural runoff that overburdened the city s water treatment plants. FieldStudy Go to Appendix B to find the field study Sources of Water Pollution Principal Water Pollutants There are many different kinds of water pollutants, both natural and man-made. Figure 3.4 lists some common pollutants and some of the sources of each. Agriculture, forestry, grazing, septic systems, recreational boating, industry, urban runoff, construction, physical changes to stream channels, and habitat degradation can all be sources of pollution. Wastewater Do you know where water goes after it flows down the drain in a sink? In urban areas, the water usually flows through a series of sewage pipes that carry it and all the other wastewater in your community to a wastewater treatment plant. Wastewater is water that contains waste from homes or industry. There, water is filtered and treated to make the water clean enough to return to a river, lake, or the oceans. In many rural areas, homes may have individual septic systems, or in some countries, no treatment at all. Treating Wastewater Figure 3.5 illustrates a typical municipal wastewater treatment process. Most wastewater from homes contains biodegradable material, like paper, soap, or body wastes that can be broken down by living organisms. 286 Unit 4: Water, Air, and Land

4 But wastewater treatment plants may not remove all of the harmful substances in water. Some household and industrial wastewater and some storm-water runoff contain toxic substances that cannot be removed by standard methods of treatment. Sewage Sludge The solid material that remains after wastewater treatment is sewage sludge. When sludge contains dangerous concentrations of toxic chemicals, it must be disposed of as hazardous waste. The sludge is often incinerated, and then the ash is buried in a secure landfill. If the toxicity of sludge can be reduced to safe levels, sludge can be used as a fertilizer or combined with clay to make bricks for buildings. Check for Understanding Explain Why is it so expensive to dispose of sewage sludge? Figure 3.5 Wastewater Treatment Process PRIMARY TREATMENT Filtration Wastewater is passed through a large screen to remove solid objects. First Settling Tank Wastewater is sent into a large tank, where smaller particles sink to the bottom and form sewer sludge. The sludge is removed from the water. SECONDARY TREATMENT Aeration Tank Wastewater is mixed with oxygen and bacteria. The bacteria use the oxygen and feed on the wastes. Second Settling Tank Bacteria grown in the aeration tank, as well as other solid wastes, are removed in the form of sludge. Chlorination Chlorine is added to disinfect the water before it is released into a stream, lake, or ocean. Chapter 11: Water 287

5 QUICKLAB Measuring Dissolved Oxygen Procedure 1. Start with three water samples. One water sample should be tap water from a faucet without an aerator. Leave some air space at the top of the bottle. One sample should be collected by submersing the container completely underwater in a larger container, allowing all air to escape from the bottle. Put the lid on the container while it is still underwater. The third sample should be water that has been boiled and allowed to cool. 2. Using a dissolved-oxygen (DO) test kit or electronic DO probe, test the second and third water samples. Record your measurements. 3. Tighten the lid on the first sample. Vigorously shake the sample for one minute. Remove and then replace the lid. Repeat. Uncap the jar quickly and test the sample. Record. Analysis 1. Which sample had the highest dissolved oxygen level? Which had the lowest level? 2. What effect do rapids and waterfalls have on the levels of dissolved oxygen in a stream? What effect would thermal pollution have? Artificial Eutrophication Most natural nutrients in water come from organic matter, such as leaves and animal waste. They are broken down into mineral nutrients by decomposers such as bacteria and fungi. These nutrients flow downstream or settle to the bottom in a process called sedimentation. Nutrients are an essential part of any aquatic ecosystem; too many nutrients can disrupt an ecosystem. When lakes and slow-moving streams contain an abundance of nutrients, they are eutrophic (yoo TROH fik). Eutrophication can be a natural process. When organic matter builds up in a body of water, it will begin to decay and decompose. The process of decomposition uses up oxygen. As oxygen levels decrease, the types of organisms that live in the water change over time. For example, as a body of water becomes eutrophic, plants take root in the nutrient-rich sediment at the bottom. As more plants grow, the shallow waters begin to fill in. Eventually, the body of water becomes a swamp or marsh. Eutrophication is accelerated when inorganic plant nutrients, such as phosphorus and nitrogen, enter the water from sewage and fertilizer runoff. This is referred to as artificial eutrophication. Fertilizer from farms, lawns, and gardens is the largest source of nutrients that cause artificial eutrophication. Phosphates in some laundry and dishwashing detergents are another major cause of eutrophication. Phosphorus is a nutrient that can cause the excessive growth of algae. In bodies of water polluted by phosphorus, algae can form large floating mats, called algal blooms, as shown in Figure 3.6. As the algae die and decompose, most of the dissolved oxygen is used and fish and other organisms suffocate in the oxygen-depleted water. Figure 3.6 Artificial Eutrophication In an effort to limit artificial eutrophication, some states have either banned phosphate detergents or limited the amount of phosphates in detergents. (inset) Getty Images; (br) Nick Hawkes/Ecoscene/Corbis 288 Unit 4: Water, Air, and Land

6 Figure 3.7 Thermal Pollution Fish kills, such as this one in Brazil, can result from thermal pollution. Antonio Scorza/AFP/Getty Images Thermal Pollution If you look at Figure 3.7, you might assume that a toxic chemical caused the massive fish kill in the photo. But the fish were not killed by a chemical spill they died because of thermal pollution. When the temperature of a body of water, such as a lake or stream, increases, thermal pollution can result. Thermal pollution can occur when power plants and other industries use water in their cooling systems and then discharge the warm water into a lake or river. Thermal pollution can cause large fish kills if the discharged water is too warm for the fish to survive. But most thermal pollution is more subtle. If the temperature of a body of water rises even a few degrees, the amount of dissolved oxygen (DO) in the water decreases significantly. As oxygen levels drop, aquatic organisms may suffocate and die. If the flow of warm water into a lake or stream is constant, it may cause the total disruption of an aquatic ecosystem. Groundwater Pollution Pollutants usually enter groundwater when polluted surface water percolates down from the Earth s surface. Any pollution of the surface water in an area can affect the groundwater. Pesticides, herbicides, chemical fertilizers, and petroleum products are common groundwater pollutants. Leaking underground storage tanks are another major source of groundwater pollution. It is estimated that there are millions of underground storage tanks in the United States. Most of the storage tanks located beneath gas stations, farms, and homes hold petroleum products, such as gasoline and heating fuel. As these underground storage tanks age, they may develop leaks, which allow pollutants to seep into the soil and groundwater. Connect to CHEMISTRY Dissolved Oxygen Sufficient levels of dissolved oxygen are critical to the health of aquatic communities. Gaseous oxygen enters water by diffusion from the surrounding air, as a byproduct of photosynthesis, and as a result of the rapid movement (aeration) of water. The amount of oxygen that water can hold is determined by the water s temperature, pressure, and salinity. Slow-moving water tends to have low levels of dissolved oxygen, while rapidly flowing streams have higher levels. Artificial eutrophication and thermal pollution also reduce levels of dissolved oxygen. When dissolved oxygen levels remain below 2 mg/l for several hours, many fish and other organisms suffocate, and massive fish kills can result. Chapter 11: Water 289

7 Connect to MATH Parts per Million Water contamination is often measured in parts per million (ppm). If the concentration of a pollutant is 5 ppm, there are 5 parts of the pollutant in 1 million parts of water. If the concentration of gasoline is 3 ppm in 650,000 L of water, how many liters of gasoline are in the water? The location of aging underground storage tanks is not always known, so the tanks often cannot be repaired or replaced until after they have leaked enough pollutants to be located. Modern underground storage tanks are contained in concrete and have many features to prevent leaks. Other sources of groundwater pollution include septic tanks, unlined landfills, and industrial wastewater lagoons, as shown in Figure 3.8. Cleaning Up Groundwater Pollution Groundwater pollution is one of the most challenging environmental problems that the world faces. As you have learned, groundwater recharges very slowly. The process for some aquifers to recycle water and purge contaminants can take hundreds or thousands of years. Groundwater is also difficult to decontaminate because the water is dispersed throughout large areas of rock and sand. Pollution can cling to the rock and soil, so, even if all of the water in an aquifer were pumped out and replaced with clean water, it would become recontaminated. In 2011, the U.S. government stopped construction of a major oil pipeline because of concerns about polluting the giant Ogallala aquifer. Figure 3.8 Sources of Groundwater Pollution This diagram shows some of the major sources of groundwater pollution. Runoff and percolation transport contaminants to the groundwater. 290 Unit 4: Water, Air, and Land

8 Figure 3.9 Major North American Oil Spills Major North American Oil Spills 1 1 Nantucket, Massachusetts, 6 Prince William Sound, Alaska, Puerto Rico, 7 Caribbean Sea, Atlantic Ocean, 8 Bay of Campeche, Tu xpan, Mexico, ECOFACT Location of Spill ,000 1,500 2,000 2,500 3, Gulf of Mexico, Galveston Bay, Texas, million Barrels of Oil Spilled (in thousands) Ocean Pollution Pollutants are often dumped directly into the oceans. For example, ships can legally dump wastewater and garbage overboard in some parts of the ocean. But at least 85 percent of ocean pollution including pollutants such as oil, toxic wastes, and medical wastes comes from activ ities on land. If polluted runoff enters rivers, the rivers may carry it to the ocean. Most activities that pollute oceans occur near the coasts, where much of the world s human population lives. Sensitive coastal ecosystems, such as coral reefs, estuaries, and coastal marshes, are the most affected by pollution. In many coastal areas, dead zones exist, where excess nutrients from runoff have caused low oxygen levels. ECOFACT Cruise Ship Discharges In one year, ships dump almost 7 billion kilograms of trash into the oceans. About 75 percent of all ship waste comes from cruise ships. According to most international law, cruise ships are allowed to dump non-plastic waste including untreated sewage into the oceans. Increasing public pressure has begun to cause the cruise-ship industry to change this practice, however. Oil Spills Oil spills can occur on land or in water, but are most infamous in oceans. Disasters such as the 1989 Exxon Valdez oil spill in Alaska and the 2010 Deepwater Horizon spill, illustrated in Figure 3.9 make front-page news around the world. Each year, approximately 37 million gallons of oil from tanker accidents are spilled into the oceans. The Deepwater Horizon disaster was notable because of the amount of oil spilled, the great depth at which the spill occurred, and the use of dispersants to keep oil from reaching the coasts. Oil spills can have dramatic ecological effects, but are not the only source of oil pollution in the oceans. Most of the oil that pollutes the oceans comes from nonpoint sources on land. Every year, almost 10 times the amount of oil spilled by tankers enters the ocean from land. Avoiding and responding to all sources of oil pollution are important for protecting ocean ecosystems. Check for Understanding Explain How can limiting nonpoint sources of oil pollution help to keep the oceans clean? Chapter 11: Water 291

9 Figure 3.10 Biomagnification The accumulation of pollutants at successive levels of the food chain is called biomagnification. Water Pollution and Ecosystems Water pollution can cause immediate damage to an ecosystem. For example, toxic chemicals spilled directly into a river can kill nearly all living things for kilometers downstream. But the effects of water pollution can be even more far reaching. Many pollutants accumulate in the environment because they do not decompose quickly and can threaten entire ecosystems. Consider a river ecosystem. Soil tainted with pesticides washes into the river and settles to the bottom. Some of the pesticides enter and are stored in the tissues of bottom-dwelling organisms, such as insect larvae and crustaceans. A small fish eats a hundred of these organisms and in turn, is eaten by a bigger fish. A predatory bird, such as an eagle, eats 10 big fish. Each organism stores the pesticide in its tissues and the concentration of the pesticide that is passed on to the next organism in the food chain increases. This buildup is called biomagnification. Figure 3.10 shows the biomagnification for the pesticide DDT, with alarming consequences for organisms at the top of the food chain. Many U.S. states limit how much fish people can eat from certain bodies of water because of biomagnification. Scientific evidence also indicates that some chemicals that we might not think of as pollutants, like caffeine and human medications, can enter ecosystems and cause health issues for aquatic animals. Figure 3.11 Burning River The Cuyahoga River was so polluted with petroleum and petroleum byproducts that it caught on fire and burned in Cleaning Up Water Pollution In 1969, the Cuyahoga River in Cleveland, Ohio, was so polluted that the river caught on fire as shown in Figure This event was a major factor in the passage of the Clean Water Act of The stated purpose of the act was to restore and maintain the chemical, physical, and biological integrity of the nation s waters. The goal of the act was to make all surface water clean enough for fishing and swimming by This goal was not achieved, however, much progress has been made since the act was passed. The percentage of lakes and rivers that are fit for swimming and fishing has increased by about 30 percent, and many states have passed stricter water-quality standards. Many toxic metals are now removed from wastewater before the water is discharged. The Clean Water Act opened the door for other water-quality legislation, some of which is described in Figure The Federal Water Pollution Act of 1972, which was amended in 2002, was aimed at restoring and maintaining the quality of all U.S. waters. Legislation has improved water quality in the United States, but the cooperation of individuals, businesses, and the government will be essential to maintaining a clean water supply in the future. Bettmann/Corbis 292 Unit 4: Water, Air, and Land

10 Figure 3.12 Federal Laws Designed to Improve Water Quality in the United States 1972 Clean Water Act (CWA) The CWA set a national goal of making all natural surface water fit for fishing and swimming by 1983 and banned pollutant discharge into surface water after The act also required that metals be removed from wastewater Federal Water Pollution Control Act, amended 2002 The objective of this act was to restore and maintain the chemical, physical, and biological integrity of U.S. waters Safe Drinking Water Act (SDWA), amended 1996 This act introduced programs to protect groundwater and surface water from pollution. The act emphasized sound science and risk-based standards for water quality. The act also empowered communities in the protection of source water, strengthened public right-to-know laws, and provided water system infrastructure assistance Comprehensive Environmental Response Compensation and Liability Act (CERCLA) This act is also known as the Superfund Act. The act made owners, operators, and customers of hazardous waste sites responsible for the cleanup of the sites. The act has reduced the pollution of groundwater by toxic substances leached from hazardous waste dumps Water Quality Act This act was written to support state and local efforts to clean polluted runoff. It also established loan funds to pay for new wastewater treatment plants and created programs to protect major estuaries Oceans Act This act created the U.S. Commission on Ocean Policy to develop recommendations for a new coordinated and comprehensive national ocean policy. Section 3 Formative Assessment Reviewing Main Ideas 1. Explain why point-source pollution is easier to control than nonpoint-source pollution. 2. Identify the major types of water pollutants. Suggest ways to reduce the levels of each type of pollutant in a water supply. 3. Describe the unique problems of cleaning up groundwater pollution. 4. Describe the source of most ocean pollution. Is it point-source or nonpoint-source pollution? Critical Thinking 5. Interpreting Graphics Read the description of biomagnification. Draw a diagram that shows the biomagnification of a pollutant in an ecosystem. 6. Applying Ideas What can individuals do to decrease ocean pollution? Write and illustrate a guide that gives at least three examples. Chapter 11: Water 293