Chapter 19 Guide Questions

3a. Draw an oxygen sag curve to illustrate what happens to dissolved oxygen levels in streams below points where degradable oxygen demanding wastes are added

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1a. List nine types of water pollutants and give an example of each

1. Infectious agents such as bacteria, viruses, protozoa, human and animal waste, and parasitic worms. 2. Oxygen-demanding wastes such as animal manure. 3. Inorganic chemicals such as water soluble acids, toxic metallic compounds. 4. Organic chemicals such as oil, plastics, and pesticides. 6. Plant nutrients such as nitrate, phosphate and ammonium ions. 7. Sediment, such as soil and silt. 8. Radioactive materials such as radioactive isotopes of iodine, radon, uranium, cesium, and thorium. 9. Heat (thermal pollution), an example of which is excessive heat caused by some kinds of industrial plants.

1b. List three strategies to determine the presence and concentration of water pollutants

A good strategy to determine water quality is to test for the number of infectious agents, such as coliform bacteria, present in a 100 mL sample. Water pollution from oxygen-demanding wastes such as animal manure and plant debris can be determined by measuring the dissolved oxygen in the water. Chemical analysis is also used to determine the presence and concentrations of most inorganic and organic chemicals that pollute water, such as salts or pesticides.

3b. Compare problems of lake water pollution to those of stream pollution

Lakes are more vulnerable than streams to contamination by plant nutrients, oil, pesticides, and toxic substances because of their stratified layers that have little vertical mixing, little flow, and ponds with little water volume. Eutrophication also occurs in lakes, in which nutrients and silt from surrounding land enter the lake. Cultural eutrophication, as a result of sewage treatment plants, fertilizer runoff, and erosion of nutrient-rich topsoil. All of these factors mean that lakes are more vulnerable to contamination. Streams can recover much more rapidly from oxygen-demanding wastes and heat than lakes. Their natural recovery process (due to their constant motion) only works if they are not overloaded with pollutants, and their flow is not reduced in any way by damming, diversion for agriculture, or drought. The time needed for a stream to recover depends on the stream's volume, flow rate, temperature, and pH level. Streams can take more pollution from oxygen-demanding wastes, and because of their flow, can recover faster than lakes, which tend to experience eutrophication (layering of pollutants or nutrients).

2a. Distinguish between point and nonpoint sources of pollution

Point sources discharge pollutants at specific locations through pipes or sewers into bodies of surface water. An example of a point source of pollution is sewage treatment plants, which remove some but not all harmful pollutants before returning the water to surface waterways. Nonpoint sources of pollution cannot be traced to a single source of discharge. Usually nonpoint sources are made of large-land areas that pollute water through runoff. An example of a nonpoint source is surface water runoff from livestock feedlots.

2b. Summarize the availability of clean drinking water for the earth's human population.

The availability of clean drinking water for the human population is abysmal. About 1/4 of people in developing countries do not have access to clean drinking water. For example, in China, it is estimated that 700 million people drink contaminated water, which is a major factor in the drastic increase in liver disease and cancer deaths in China. In Russia, half of the tap water is unfit to drink, and in Africa, 290 million people do not have access to safe drinking water. In many poor villages in developing countries, shallow groundwater wells, polluted river water, and mudholes (used by animals as well) are the main sources of water. In urban slums, people must either drink contaminated water from rivers or buy it from street vendors at exorbitant prices. In short, clean drinking water is not available to a large portion of the earth's human population, and that can contribute to keeping mortality and birth rates high, and high water prices can keep children from getting the education they should have.