Water Pollution Comes from Point and
Nonpoint Sources
• Water pollution
– Change in water quality that can harm
organisms or make water unfit for human
uses
• Point sources
– Located at specific places
– Easy to identify, monitor, and regulate
– Example: offshore oil wells
© Cengage Learning 2015
Water Pollution Comes from Point and
Nonpoint Sources (cont’d.)
• Nonpoint sources
– Broad, diffuse areas
– Difficult to identify and control
– Expensive to clean up
– Example: a logged forest
© Cengage Learning 2015
Water Pollution Comes from Point and
Nonpoint Sources (cont’d.)
• Leading causes of water pollution
– Agriculture activities
• Sediment eroded from the lands
• Fertilizers and pesticides
– Industrial facilities
• Inorganic and organic chemicals
– Mining
• Erosion and toxic chemicals
© Cengage Learning 2015
Fig. 20-2, p. 545
© Cengage Learning 2015
Fig. 20-3, p. 546
Major Water Pollutants Have Harmful
Effects
• Infectious disease organisms
– Contaminated drinking water
– An estimated 1.6 million people die every
year, mostly under the age of five
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Streams Can Cleanse Themselves, If We
Do Not Overload Them
• Dilution
• Biodegradation of wastes by bacteria
takes time
• Oxygen sag curve
– Breakdown of biodegradable wastes by
bacteria depletes oxygen
© Cengage Learning 2015
Stream Pollution in More-Developed
Countries
• 1970s – water pollution control laws
• Successful water clean-up stories
– Ohio Cuyahoga River, U.S.
– Thames River, Great Britain
• Contamination of toxic inorganic and
organic chemicals by industries and mines
© Cengage Learning 2015
Stream Pollution in Less-Developed
Countries
• Half of the world’s 500 major rivers are
polluted
– Untreated sewage
– Industrial waste
• Water often used for human activities
© Cengage Learning 2015
© Cengage Learning 2015
Fig. 20-7, p. 550
Too Little Mixing and Low Water Flow
Makes Lakes Vulnerable to Water Pollution
• Less effective at diluting pollutants than
streams
– Stratified layers
• Little vertical mixing
– Little of no water flow
– Can take up to 100 years to change the water
in a lake
– Biological magnification of pollutants
© Cengage Learning 2015
Cultural Eutrophication Is Too Much
of a Good Thing
• Eutrophication
– Natural enrichment of a shallow lake, estuary,
or slow-moving stream
– Caused by runoff into lake that contains
nitrates and phosphates
• Oligotrophic lake
– Low nutrients; clear water
© Cengage Learning 2015
Cultural Eutrophication Is Too Much
of a Good Thing (cont’d.)
• Cultural eutrophication
– Nitrates and phosphates from human sources
– Farms, feedlots, streets, parking lots
– Fertilized lawns, mining sites, sewage plants
• During hot weather or droughts
– Algal blooms
– Increased bacteria; anaerobic bacteria
– More nutrients
© Cengage Learning 2015
© Cengage Learning 2015
Fig. 20-8, p. 551
Case Study: Pollution in the Great Lakes
• 1960s – many areas with cultural
eutrophication
• 1972 – Canada and the United States
Great Lakes pollution control program
– Decreased algal blooms
– Increased dissolved oxygen
– Increased fishing catches
– Better sewage treatment plants
© Cengage Learning 2015
Case Study: Pollution in the Great Lakes
(cont’d.)
• Pollution control program (cont’d.)
– Fewer industrial wastes
– Bans on phosphate-containing household
products
• Problems still exist
– Raw sewage and biological pollution
– Nonpoint runoff of pesticides and fertilizers
– Atmospheric deposition of pesticides and Hg
© Cengage Learning 2015
Case Study: Pollution in the Great Lakes
(cont’d.)
• Continuing problems
– Urban sprawl and runoff
– Biological pollution
• Zebra mussels
– Atmospheric deposition of pollutants
© Cengage Learning 2015
Ground Water Cannot Cleanse Itself Very
Well
• Source of drinking water for 50% of the
U.S. population and 95 % for the rural
population
• Common pollutants
– Fertilizers and pesticides
– Gasoline
– Organic solvents
– Fracking
•
Pollutants
dispersed
in
a
widening
plume
© Cengage Learning 2015
Ground Water Cannot Cleanse Itself Very
Well (cont’d.)
• Slower chemical reactions in groundwater
due to:
– Slow flow – contaminants not diluted
– Less dissolved oxygen
– Fewer decomposing bacteria
– Low temperatures
© Cengage Learning 2015
Polluted air
Hazardous
waste
injection well
Pesticides
and fertilizers
Coal strip
mine runoff
Deicing
road salt
Pumping
well
Waste lagoon
Gasoline
station
Water
pumping well
Buried gasoline
and solvent
tanks
Cesspool,
septic
tank
Sewer
Landfill
Leakage
from
faulty
casing
Discharge
Accidental
spills
Freshwater
aquifer
Groundwater
flow
© Cengage Learning 2015
Fig. 20-12, p. 554
Case Study: Arsenic in Drinking Water
• Rocks rich in arsenic can contaminate
wells
• Long-term exposure can lead to:
– Skin, lung, bladder cancer and premature
death.
© Cengage Learning 2015
There Are Many Ways to Purify
Drinking Water
• Reservoirs and purification plants
• Process sewer water to drinking water
• Expose clear plastic containers to sunlight
(UV)
• The LifeStraw
• PUR – chlorine and iron sulfate powder
© Cengage Learning 2015
Case Study: Is Bottled Water a Good
Option?
• Bottled water can be useful but expensive. Use of
bottled water can create environmental problems
• The U.S. has some of the world’s cleanest drinking
water
• Bottled water contains about 40% tap water
• 1974 – U.S. Safe Drinking Water Act
– Sets maximum contaminant levels for any
pollutants that affect human health
© Cengage Learning 2015
Ocean Pollution Is a Growing and Poorly
Understood Problem
• Municipal sewage from less-developed
countries are often dumped into oceans
without treatment
• Deeper ocean waters
– Dilution
– Dispersion
– Degradation
© Cengage Learning 2015
Ocean Pollution Is a Growing and Poorly
Understood Problem (cont’d.)
• U.S. coastal waters
– Raw sewage – viruses
– Sewage and agricultural runoff: NO3- and
PO43– Harmful algal blooms
– Oxygen-depleted zones
© Cengage Learning 2015
Ocean Pollution from Oil
• Crude and refined petroleum
– Highly disruptive pollutants
• Largest source of ocean oil pollution
– Urban and industrial runoff from land
• 1989 – Exxon Valdez, oil tanker
• 2010 – BP Deepwater Horizon in the Gulf
of Mexico
© Cengage Learning 2015
Case Study: The BP Deepwater Horizon
Oil-Rig Spill
• Spill from deep-sea oil drilling – 1 mile
deep
– Released 4.9 million barrels of crude oil
– Contaminated vast areas of coastline
– Caused by equipment failure and poor
decisions
• Government developed new standards for
offshore drilling procedures
© Cengage Learning 2015
© Cengage Learning 2015
Fig. 20-19, p. 561
Reducing Surface Water Pollution from
Nonpoint Sources
• Agriculture
– Reduce erosion
– Reduce the amount of fertilizers
– Plant buffer zones of vegetation
– Use organic farming techniques
– Use pesticides prudently
– Institute tougher pollution regulations for
livestock operations
© Cengage Learning 2015
Case Study: The U.S. Experience with
Reducing Point-Source Pollution
• 1972 – Clean Water Act
• 1987 – Water Quality Act
• Experimenting with a discharge trading
policy that uses market forces
• What are some achievements of the Clean
Water Act?
© Cengage Learning 2015
Sewage Treatment Reduces Water
Pollution
• How do septic tank systems work?
• Wastewater or sewage treatment plants
– Primary sewage treatment
• Physical process
– Secondary sewage treatment
• Biological process with bacteria
– Tertiary or advance sewage treatment
• Special filtering processes
• Bleaching, chlorination
© Cengage Learning 2015
Sewage Treatment Reduces Water
Pollution (cont’d.)
• Many cities violate federal standards for
sewage treatment plants
– Federal law requires primary and secondary
treatment
• Exemptions from secondary treatment
• There are health risks of swimming in
water with blended sewage wastes
© Cengage Learning 2015
Manhole cover
(for cleanout)
Septic tank
Gas
Distribution box
Scum
Wastewater
Sludge
Drain field
(gravel or
crushed stone)
Vent pipe
Perforated pipe
© Cengage Learning 2015
Fig. 20-23, p. 565
Primary
Bar screen Grit chamber
Raw sewage
from sewers
Secondary
Settling tank
Aeration tank
Settling tank
Sludge
Activated sludge
Chlorine
disinfection tank
To river,
lake, or
ocean
(kills bacteria)
Air pump
Sludge digester
Sludge drying bed
Disposed of
in landfill or
ocean or
applied to
cropland,
pasture, or
rangeland
© Cengage Learning 2015
Fig. 20-24, p. 566
We Can Improve Conventional Sewage
Treatment
• Remove toxic wastes before water goes to
the municipal sewage treatment plants
• Reduce or eliminate use and waste of
toxic chemicals
• Use composting toilet systems
• Wetland-based sewage treatment systems
– Work with nature
© Cengage Learning 2015
There Are Sustainable Ways to Reduce
and Prevent Water Pollution
• Developed countries
– Bottom-up political pressure to pass laws
• Developing countries
– Little has been done to reduce water pollution
– China
• Small sewage treatment plants
© Cengage Learning 2015