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Notes Chapter 20.1 – 20.2 APES
20.1 What Are the Causes and Effects of Water Pollution?
- Water pollution causes illness and death in humans and other species, and disrupts ecosystems. It
occurs when there is a change in water quality.
- Sources:
• Point:
- Located at specific places
- Easy to identify, monitor, and regulate usually through drain pipes, ditches, or sewer
lines
• Examples: Factories, sewage treatment plants (remove some but not all
pollutants), underground mines, and oil tankers.
• Nonpoint:
- Broad and diffuse areas where rainfall or snowmelt runoff takes pollutants from land
to water sources
- Difficult to identify and control
- Expensive to clean up
• Examples: Runoff of eroded soil and chemicals such as fertilizers and
pesticides from agricultural practices, livestock feedlots, urban streets, parking
lots, and lawns.
- Leading causes of water pollution:
#1) Agriculture activities:
• Sediment eroded from used land
• Fertilizers and pesticides usage from runoff
• Bacteria from livestock and food-processing waste from runoff
• Over salinized soil due to overdrafting water
#2) Industrial facilities
• Inorganic and organic chemicals leaking from pipes and transportation spillages
Ex.) Oil companies like British Petroleum (BP)
#3) Mining
• Erosion and toxic chemicals runoff enter into surface waters or leakages containing
acids from mining drainage ponds/pools
Ex.) Colorado River mining breach
#4) Manmade solid waste
• Plastics used to make products (bottles) containing BPA winding up in rivers and
slowly decaying toxins like BPA
- Ends up in water systems and can even strangulate many aquatic species or
trap their heads within certain containers
- Major water pollutants have harmful effects
- Infectious diseases can develop with water pollution
• Occurs through contaminated drinking and cleaning water
• Estimated 1.6 million people die every year from contaminated water
- Chart of water pollutants and their sources that lead to several diseases:
20.2 What Are the Major Water Pollution Problems in Streams and Lakes?
- Streams and rivers can cleanse themselves of many pollutants if we do not overload them or reduce
their flows by:
• Adding excessive nutrients to lakes from human activities can disrupt their ecosystems, and
prevention of such pollution is more effective and less costly than cleaning it up
• Oxygen sag curve
- Breakdown of biodegradable wastes by bacteria deplete oxygen
- Diagram shows how streams can recover from oxygen-demanding wastes and from the
injection of heated water if they are given enough time and are not overloaded with slowly
degradable/nondegradable pollutants:
- DO levels:
What is biochemical oxygen demand (BOD)?
- Test performed to measure the potential of wastewater and other waters to deplete the
oxygen level of receiving waters.
• Bacteria use oxygen in water to break down and try to filter out the unwanted
material
- The excess oxygen used decreases DO
- Aquatic species and plant life in the area will decrease dramatically (lowers
biodiversity in affected area
- Stream pollution for more-developed countries:
• 1970’s – Beginning of water pollution control laws
- Required industries to reduce or eliminate their point-source pollutants
• Successful water clean-up stories:
- Ohio Cuyahoga River
• Contaminated to the point of flammable water
• Upgraded sewage treatment plants (now cleaner water)
• Fish kills still occur in developed-countries streams mainly by accidental or deliberate release
of toxic inorganic and organic chemicals by:
- Industries and mining operations
- Malfunctioning sewage treatment plants
- Nonpoint runoff of pesticides
- Stream pollution for less-developed countries:
• Half of the world’s 500 major rivers are polluted in these areas for reasons such as:
- Untreated sewage
- Industrial waste
• Can’t afford to build water treatment plants
• Water often used even more for human activities
- Too little mixing and low water flow makes lakes vulnerable to water pollution:
• Less effective at diluting pollutants than streams
- Contain stratified layers that undergo little vertical mixing
- Little or no water flow
- Can take up to 100 years to change the water quality of a lake
- Biological magnification of pollutants is higher (harder to filtrate out)
Cultural eutrophication can sometimes be too much of a good thing:
-Three types of lakes:
• Oligotrophic Lake – deep, usually low in nutrients (little plant growth) and has clear water
- Maintain high DO in the cool, deep-bottom water during late summer to support
cold water fish, such as trout and whitefish
- Sometimes needs to go through the process of eutrophication to maintain an
abundance of aquatic organisms and reach a mesotrophic lake status
• Eutrophic Lake – shallow, usually high in nutrients (large plant growth) and has murky water
- Contain little to no DO and can only support warm water fish like bass and pike
- Can suffer immediately from cultural eutrophication and lead to fish kills with even
further DO loss
• Mesotrophic Lake – medium sized lake, medium nutrients and partially good DO
- Are somewhat clear lakes with pockets of murkiness
- Sport fish (small pike and bass and not as large as eutrophic)
• Cultural Eutrophication: amount of plant nutrients in shallow lakes, estuaries, and slowmoving streams. Involve mostly phosphate and nitrate ions from various sources:
- Sources: Farmland fertilizers, feedlots, parking lots, sewage plants, and mining
sites
• During hot weather or droughts
- Algal blooms appear or increase
- Increased bacteria and anaerobic bacteria (deplete dissolved oxygen)
- Overall, more nutrients
- More nutrients lead to anaerobic bacteria take over and produce highly toxic hydrogen
sulfide and methane
- Not all aquatic species can live in this environment and thus decreases
biodiversity
- Can also provide too much shade for plant growth at bottom of lake leading to
loss of photosynthesis and decreases biodiversity this way as well
• Ways to prevent or reduce cultural eutrophication
- Remove excess amounts of nitrates and phosphates by water treatment plants before
they enter water source
- Ban or limit amount of phosphates in cleaning agents and detergents
• Clean up lakes
- Remove excess weeds
- Use organic herbicides and algaecides to control undesirable plant growth
- Pump in air to control dissolved oxygen levels
- Pollution control programs:
• 1972 – Canada and the United States Great Lakes pollution control program
- Decreased algal blooms
- Increased dissolved oxygen
- Increased fishing catches
- Better sewage treatment plants
- Fewer industrial wastes
- Bans on phosphate-containing household products
• Problems that still exist:
- Raw sewage and biologic pollution
- Nonpoint runoff of pesticides and fertilizers