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Water Pollution. Chapter 20. Water Pollution Comes from Point and Nonpoint Sources. Water pollution Point sources Located at specific places Easy to identify, monitor, and regulate e.g., factories, sewage treatment Nonpoint sources Broad, diffuse areas Difficult to identify and control

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Water pollution l.jpg

Water Pollution

Chapter 20

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Water Pollution Comes from Point and Nonpoint Sources

  • Water pollution

  • Point sources

    • Located at specific places

    • Easy to identify, monitor, and regulate

    • e.g., factories, sewage treatment

  • Nonpoint sources

    • Broad, diffuse areas

    • Difficult to identify and control

    • Expensive to clean up

    • e.g., herbicide runoff, soil erosion

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Water Pollution Comes from Point and Nonpoint Sources

  • Agriculture activities: leading cause of water pollution (Non-point Source)

    • Sediment eroded from the lands

    • Fertilizers and pesticides

    • Bacteria from livestock and food processing wastes

  • Industrial facilities

  • Mining

  • Other sources of water pollution

    • Parking lots

    • Human-made materials (e.g., plastics)

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Major Water Pollutants and StreamsTheir Sources

Infectious agents(e.g., E. coli) – human and animal waste

Oxygen demanding wastes – animal waste & plant debris (stuff that can decompose)

Plant nutrients(e.g., fertilizer) – agricultural fertilizers, animal waste, sewage (treated or untreated)

Sediment(e.g., soil) – land erosion

“Chemicals” (e.g., gasoline; pesticide) – agricultural herbicides and pesticides, oil spills, oil dumping, industry release, household disposal

Heavy Metals(e.g., arsenic, lead, mercury) – unlined landfills, industry release, household disposal

Heat/Thermal(e.g., warming water) – unlined landfills, industry release, household disposal

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20-2 What Are the Major Water Pollution Problems in Streams and Lakes?

  • Concept 20-2A While streams are extensively polluted worldwide by human activities, they can cleanse themselves of many pollutants if we do not overload them or reduce their flows.

  • Concept 20-2B Addition of excessive nutrients to lakes from human activities can disrupt lake ecosystems, and prevention of such pollution is more effective and less costly than cleaning it up.

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Point source and Lakes?

Normal clean water organisms (Trout, perch, bass,

mayfly, stonefly)

Pollution-tolerant fishes (carp, gar)

Fish absent, fungi, sludge worms,

bacteria (anaerobic)

Pollution-tolerant fishes (carp, gar)

Normal clean water organisms (Trout, perch, bass,

mayfly, stonefly)

8 ppm

Types of organisms

8 ppm

Dissolved oxygen (ppm)

Clean Zone

Biochemical oxygen demand

Recovery Zone

Septic Zone

Decomposition Zone

Clean Zone

Fig. 20-5, p. 536

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Stream Pollution and Lakes?

  • 1970s: Water pollution control laws in developed countries

  • Successful water clean-up stories

    • Ohio Cuyahoga River, U.S.

    • Thames River, Great Britain

  • Half of the world’s 500 rivers are seriously polluted (most in developing countries)

  • Untreated sewage & industrial waste discharged directly into streams in developing countries

  • The Ganges River in India

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Low Water Flow and Too Little Mixing Makes Lakes Vulnerable to Water Pollution

  • Less effective at diluting pollutants than streams

    • Stratified layers

      • Little vertical mixing

    • Little of no water flow

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Cultural Eutrophication to Water Pollution

  • Eutrophication – nutrient enrichment of a body of water

  • Cultural eutrophication – human-caused nutrient enrichment of a body of water; results in…

    • More nutrients

    • Algal blooms

    • Increased bacteria

    • Anaerobic bacteria

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Case Study: Pollution in the Great to Water PollutionLakes

  • 1960s: Many areas with cultural eutrophication

  • 1972: Canada and the United States: Great Lakes pollution control program

  • Problems still exist

    • Raw sewage

    • Nonpoint runoff of pesticides and fertilizers

    • Biological pollution (zebra mussels?)

    • Atmospheric deposition of pesticides and Hg

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Case Study: Pollution in the Great to Water PollutionLakes (2)

  • 2007 State of the Great Lakes report

    • New pollutants found

    • Wetland loss and degradation; significance?

    • Declining of some native species

    • Native carnivorous fish species declining

    • What should be done?

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20-3 Pollution Problems Affecting Groundwater, Other Water Sources

  • Concept 20-3A Chemicals used in agriculture, industry, transportation, and homes can spill and leak into groundwater and make it undrinkable.

  • Concept 20-3B There are simple ways and complex ways to purify drinking water, but protecting it through pollution prevention is the least expensive and most effective strategy.

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Ground Water Cannot Cleanse Itself SourcesVery Well

  • Source of drinking water

  • Common pollutants

    • Fertilizers and pesticides

    • Gasoline

  • Pollutants dispersed in a widening plume

  • Slower chemical reactions in groundwater due to

    • Slow flow: contaminants not diluted

    • Less dissolved oxygen

    • Fewer decomposing bacteria

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Leaking tank Sources



Water table

Groundwater flow

Free gasoline dissolves in groundwater (dissolved phase)

Gasoline leakage plume (liquid phase)

Migrating vapor phase

Water well

Contaminant plume moves with the groundwater

Fig. 20-12, p. 543

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Groundwater Pollution



Find substitutes for toxic chemicals

Pump to surface, clean, and return to aquifer (very expensive)

Keep toxic chemicals out of the environment

Install monitoring wells near landfills and underground tanks

Inject microorganisms to clean up contamination (less expensive but still costly)

Require leak detectors on underground tanks

Ban hazardous waste disposal in landfills and injection wells

Pump nanoparticles of inorganic compounds to remove pollutants (still being developed)

Store harmful liquids in aboveground tanks with leak detection and collection systems

Fig. 20-13, p. 545

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Using Laws to Protect Drinking SourcesWater Quality

  • 1972: U.S. Clean Water Act

  • 1974: U.S. Safe Drinking Water Act

    • Sets maximum contaminant levels for any pollutants that affect human health

  • Health scientists: strengthen the law

  • Water-polluting companies: weaken the law

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Is Bottled Water the Answer? Sources

  • U.S.: some of the cleanest drinking water

  • Bottled water

    • Some from tap water

    • 40% bacterial contamination

    • Fuel cost to manufacture the plastic bottles

    • Recycling of the plastic

  • Growing back-to-the-tap movement

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20-4 What Are the Major Water Pollution Problems Affecting Oceans?

  • Concept 20-4A The great majority of ocean pollution originates on land and includes oil and other toxic chemicals and solid wastes, which threaten aquatic species and other wildlife and disrupt marine ecosystems.

  • Concept 20-4B The key to protecting the oceans is to reduce the flow of pollutants from land and air and from streams emptying into these waters.

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Ocean Pollution Is a Growing and Poorly Understood Problem (1)

  • 2006: State of the Marine Environment

    • 80% of marine pollution originates on land

    • Sewage – Land, Cruise Ships

    • Fertilizer and other agricultural runoff

    • Coastal areas most affected

  • Deeper ocean waters

    • Dilution

    • Dispersion

    • Degradation

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Industry Nitrogen oxides from autos and smokestacks, toxic chemicals, and heavy metals in effluents flow into bays and estuaries.

Cities Toxic metals and oil from streets and parking lots pollute waters; sewage adds nitrogen and phosphorus.

Urban sprawl

Bacteria and viruses from sewers and septic tanks contaminate shellfish beds and close beaches; runoff of fertilizer from lawns adds nitrogen and phosphorus.

Construction sites

Sediments are washed into waterways, choking fish and plants, clouding waters, and blocking sunlight.


Runoff of pesticides, manure, and fertilizers adds toxins and excess nitrogen and phosphorus.

Red tides

Excess nitrogen causes explosive growth of toxic microscopic algae, poisoning fish and marine mammals.

Closed shellfish beds

Closed beach

Oxygen-depleted zone

Toxic sediments

Chemicals and toxic metals contaminate shellfish beds, kill spawning fish, and accumulate in the tissues of bottom feeders.

Oxygen-depleted zone Sedimentation and algae overgrowth reduce sunlight, kill beneficial sea grasses, use up oxygen, and degrade habitat.

Healthy zone

Clear, oxygen-rich waters promote growth of plankton and sea grasses, and support fish.

Fig. 20-15, p. 548

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Ocean Oil Pollution Is a Serious Due to Algal Blooms Problem (1)

  • Crude and refined petroleum - highly disruptive pollutants

  • Largest source of ocean oil pollution - urban and industrial runoff from land

  • Large Spills have the potential to be locally overwhelming pollutants.

    1989: Exxon Valdez, oil tanker – Alaska

    2002: Prestige, oil tanker – Spain

    2010: Deepwater Horizon, drill rig – U.S. Gulf Coast

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Ocean Oil Pollution Is a Serious Due to Algal Blooms Problem

  • Volatile organic hydrocarbons

    • Kill many aquatic organisms

  • Tar-like globs on the ocean’s surface

    • Coat animals

  • Heavy oil components sink

    • Affect the bottom dwellers

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SOLUTIONS Due to Algal Blooms

Coastal Water Pollution



Reduce input of toxic pollutants

Improve oil-spill cleanup capabilities

Separate sewage and storm lines

Use nanoparticles on sewage and oil spills to dissolve the oil or sewage (still under development)

Ban dumping of wastes and sewage by ships in coastal waters

Ban ocean dumping of sludge and hazardous dredged material

Require secondary treatment of coastal sewage

Regulate coastal development, oil drilling, and oil shipping

Use wetlands, solar-aquatic, or other methods to treat sewage

Require double hulls for oil tankers

Fig. 20-17, p. 551

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We Need to Reduce Surface Water Pollution from Nonpoint Sources

  • Reduce erosion (Keep cropland covered with vegetation)

  • Reduce the amount of fertilizers

  • Plant buffer zones of vegetation

  • Use organic farming techniques

  • Use pesticides prudently

  • Control runoff

  • Tougher pollution regulations for livestock operations

  • Deal better with animal waste

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Laws Can Help Reduce Water Pollution from Point Sources Sources

  • 1972: Clean Water Act

  • EPA: experimenting with a discharge trading policy (i.e., water pollution cap & trade)

  • How could this differ from similar proposed solutions to carbon emissions?

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Science Focus: Treating Sewage by Working with Nature Sources

  • John Todd: biologist

  • Natural water purification system

    • Sewer water flows into a passive greenhouse

    • Solar energy and natural processes remove and recycle nutrients

    • Diversity of organisms used