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UNIT 4 Water Resources and Pollution
Chapter 13 and 20
Freshwater Is an Irreplaceable Resource That We Are Managing Poorly
• Why is water so important?
• Earth as a watery world: 71%
• Freshwater availability: 0.024%
• Poorly managed resource
• Hydrologic cycle
• Water pollution
Freshwater Is an Irreplaceable Resource That We Are Managing Poorly
• Access to water is – A global health issue– An economic issue– A women’s and children’s issue– A national and global security issue
Freshwater Resources
• Surface water: rivers, lakes, wetlands, estuaries, ocean. -> recharge from runoff
• Groundwater: -> recharge from precipitation ->lateral
recharge: movement of water from rivers and streams.
Fig. 13-3, p. 316
Unconfined Aquifer Recharge Area
Precipitation Evaporation and transpiration Evaporation
Confined Recharge Area
Runoff
Flowing artesian well
Well requiring a
pump Stream
InfiltrationWater table Lake
InfiltrationUnconfined aquiferLess permeable
material such as clay
Confined aquiferConfining impermeable rock layer
Water Equity, Shortages, and Floods
Global usage of groundwater and surface water: • agriculture – 70%• Industry – 20%• Human consumption – 10%
Developing and Developed counties water usageEx: Canada – uses 20% of the world’s liquid water(0.5% of world population)
Asia- uses 30% (60% of world’s population)Water conflicts in the Middle East
Three Major River
Basins in the Middle East
core case study-pg.313
Natural Capital Degradation: Irrigation in Saudi Arabia Using an Aquifer
Water usage in US
• Western half of US = severe water shortage - arid, semi-arid; less precipitation and high evaporation; droughts-uses water withdrawals for irrigation
• Eastern half of US- high level of precipitation; reduced evaporation rate
Fig. 13-4a, p. 317
Average annual precipitation (centimeters)
41–81 More than 122
Less than 41 81–122
Surface Water and Groundwater Depletion
Groundwater Depletion• Overdraft of groundwater can cause sinkholes
or saltwater intrusion (in coastal areas)
• Ogallala aquifer: largest known aquifer– Irrigates the Great Plains– Water table lowered more than 30m– Cost of high pumping has eliminated some of
the farmers– Government subsidies to continue farming
deplete the aquifer further– Biodiversity threatened in some areas
Natural Capital Degradation: Areas of Greatest Aquifer Depletion in the U.S.
Fig. 13-10, p. 323
WYOMINGSOUTH DAKOTA
NEBRASKA
COLORADOKANSAS
OKLAHOMANEW MEXICO
Miles
0
100TEXAS
Saturated thickness of Ogallala Aquifer
Less than 61 meters (200 ft.)61–183 meters (200–600 ft.)More than 183 meters (600 ft.) (as much as 370 meters or 1,200 ft. in places)
0
160Kilometers
Groundwater Over-pumping Has Harmful Effects
• Limits future food production• Land subsidence• Sinkholes • Groundwater overdrafts near coastal
regions– Contamination of the groundwater with
saltwater• Undrinkable and unusable for irrigation
How to protect groundwater resources
• Reduce number of water-intensive crops grown in arid and semi-arid regions;
• Increase the price of water -> discourage waste;
• Implement water conservation practices in residential homes.
• Subsidize water conservation
Surface Water Usage – dams and water transfer projects
Rivers are dammed to create freshwater reservoirs + hydroelectric power
Advantages Disadvantages
No CO2 emissionProvides irrigation and drinking waterFlood controlCheap electricityReservoirs used for recreation
Displace people living behind the damDecreases nutrient-rich silt downstreamFish harvest below dam decreasesDisrupts migration patterns of some fishLoss of water by evaporationUseless after 50 yearsCH4 emissions
Examples of Major Dams
Examples of Major Dams
1. Colorado River Basin-flows from Colorado to Gulf of California- 7 states--water used for drinking (Los Angeles, San Diego, Las Vegas) and irrigation (15 % of US crops)-14 dams -> volume reduction -> not making his way to the Gulf of California or is too salty->> international disputes-> US constructed desalination plants -2 major dams: Hoover Dam (Lake Mead) and Glen Canyon Dam (Lake Powell)
Aerial View of Glen Canyon Dam Across the Colorado River and Lake Powell
The Flow of the Colorado River Measured at Its Mouth Has Dropped Sharply
Examples of Major Dams
2. Three Gorges Dam, China • World’s largest hydroelectric dam and reservoir
• 2 km long across the Yangtze River
• Benefits– Electricity-producing potential is huge– Holds back the Yangtze River floodwaters– Allows cargo-carrying ships
Three Gorges Dam, China
• Harmful effects– Displaces about 5.4 million people– Built over a seismic fault– Rotting plant and animal matter producing
CH4
• Worse than CO2 emissions
Water Transfer Projects1. The Aral Sea - Asia(Uzbekistan)-irrigation canals for cotton and rice fields-loss of volume since 1960s-increase in salinity 7X-> impacted local wetlands;- altered local climate- summers hotter and drier,
winters are colder;- Negative impact on economy – declining
commercially valuable population and decrease crop production
Fig. 13-18a, p. 331
Stepped Art
1976 2006
Ship Stranded in Desert Formed by Shrinkage of the Aral Sea
Water Transfer Projects
2. California Water transfer project- Moves water from N California to S California;- Transfers Water from Water-Rich Areas to Water-
Poor Areas• Water transferred by
– Tunnels– Aqueducts– Underground pipes
• May cause environmental problems
The California Water Project and the Central Arizona Project
Water Transfer Projects
3. China’s water transfer project• South-North Water Transfer Project• Water from three rivers to supply 0.5 billion
people• Completion in about 2050• Impact
– Economic– Health– Environmental
Water Conservation
1. Improve irrigation practices-flood irrigation=pumping large volume of water into agricultural land; H2O flows by gravity into ditches into soil. -Drip irrigation- increase crop yields from 20% to 90%-Center pivot=metal frames rolling on wheels that extend large water pipes out over the crops.
Fig. 13-20, p. 335
Center pivot (efficiency 80% with low-pressure sprinkler and 90–95% with LEPA
sprinkler)Drip irrigation
(efficiency 90–95%)Water usually pumped from underground and sprayed from mobile boom with sprinklers.
Gravity flow (efficiency 60% and 80% with surge valves)
Above- or below-ground pipes or tubes deliver water to individual plant roots.Water usually comes from an aqueduct
system or a nearby river.
Other methods of irrigation water conservation
• Irrigate crops using threated urban wastewater• Irrigate at night• Don’t grow water thirsty crops in arid and semi-
arid regions;• Increase government subsidies for efficient
irrigation practices• Increase polyculture instead of monoculture;• Use soil monitor to irrigate only when needed.
Developing Countries Use Low-Tech Methods for Irrigation
• Human-powered treadle pumps
• Harvest and store rainwater
• Create a canopy over crops: reduces evaporation
• Fog-catcher nets
We Can Cut Water Waste in Industry and Homes
• Recycle water in industry
• Fix leaks in the plumbing systems
• Use water-thrifty landscaping: xeriscaping
• Use gray water
• Pay-as-you-go water use
Fig. 13-23, p. 337
SOLUTIONS
Sustainable Water Use
Waste less water and subsidize water conservation
Preserve water quality
Protect forests, wetlands, mountain glaciers, watersheds, and other natural systems that store and release water
Get agreements among regions and countries sharing surface water resources
Raise water prices
Do not deplete aquifers
Slow population growth
Increasing freshwater supplies
• Desalination-reverse osmosis (microfiltration)-distillation
Some Areas Get Too Much Water from Flooding (1)
• Flood plains – Highly productive wetlands– Provide natural flood and erosion control– Maintain high water quality– Recharge groundwater
• Benefits of floodplains– Fertile soils– Nearby rivers for use and recreation– Flatlands for urbanization and farming
Some Areas Get Too Much Water from Flooding (2)
• Dangers of floodplains and floods– Deadly and destructive– Human activities worsen floods– Failing dams and water diversion– Hurricane Katrina and the Gulf Coast
• Removal of coastal wetlands
Fig. 13-25a, p. 339
Oxygen released by vegetation
Diverse ecological habitat Evapotranspiration
Trees reduce soil erosion from heavy rain and wind
Tree roots stabilize soil
Vegetation releases water slowly and reduces flooding
Forested Hillside
Agricultural land
Stepped Art
Tree plantation
Roads destabilize hillsides
Overgrazing accelerates soil erosion by water and wind
Winds remove fragile topsoil
Agricultural land is flooded and silted up
Gullies and landslides
Heavy rain erodes topsoil
Silt from erosion fills rivers and reservoirs
Rapid runoff causes flooding
After Deforestation
Evapotranspiration decreases
Fig. 13-26, p. 340
SOLUTIONS
Reducing Flood Damage
Prevention Control
Preserve forests on watersheds
Straighten and deepen streams (channelization)
Preserve and restore wetlands in floodplains
Tax development on floodplains
Build levees or floodwalls along streams
Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry
Build dams
Water Pollution Sources and Types
1. Point-source pollution – Located at specific places– Easy to identify, monitor, and regulate– ex: industry, sewage treatment plans, oil spills
from tankers;
2. Non-point pollution –Broad, diffuse areas– Difficult to identify and control– Expensive to clean up
Point Source of Polluted Water in Gargas, France
Nonpoint Sediment from Unprotected Farmland Flows into Streams
Leading Sources of Water Pollution
1. Agriculture – water runoff with sediments, excess fertilizer, pesticides; animal waste (feedlots)
2. Industrial – acids, heavy metals, fertilizers, gasoline, food processing waste, PCBs
3. Mining – sediments and chemicals like arsenic, cyanide, mercury.
Pollution in Streams, Rivers and Lakes
• Dilution – in fast moving rivers
• Biodegradation of wastes by bacteria takes time
• Oxygen sag curve
-occurs in rivers
-bacteria breaks down degradable wastes;
-bacteria depletes the dissolved oxygen in the process.
Fig. 20-5, p. 536
Point source
Pollution-tolerant
fishes (carp, gar)Types of
organisms
Normal clean water organisms
(Trout, perch, bass,
mayfly, stonefly)
Fish absent, fungi,
sludge worms,
bacteria (anaerobic)
Pollution-
tolerant fishes
(carp, gar)8 ppm
Normal clean water organisms
(Trout, perch, bass,
mayfly, stonefly)
Dissolved
oxygen (ppm)
8 ppm
Biochemical
oxygen demand Clean Zone
Recovery Zone
Septic Zone
Decomposition
ZoneClean Zone
Pollution in freshwater lakes
• Less effective at diluting pollutants than streams– Stratified layers
• Little vertical mixing
– Little of no water flow
• Eutrophication
• Oligotrophic lake– Low nutrients, clear water
• Cultural eutrophication
Remediation and Prevention of Cultural Eutrophication
• Prevent or reduce cultural eutrophication– Remove nitrates and phosphates– Diversion of lake water
• Clean up lakes– Remove excess weeds– Use herbicides and algaecides; down-side?– Pump in air
Case Study: Pollution in the Great Lakes (1)
• 1960s: Many areas with cultural eutrophication
• 1972: Canada and the United States: Great Lakes pollution control program– What was done?
• Problems still exist– Raw sewage– Nonpoint runoff of pesticides and fertilizers– Biological pollution– Atmospheric deposition of pesticides and Hg
Case Study: Pollution in the Great Lakes (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?
Water Quality Testing Techniques
1. Physical tests-Temperature-river/stream flow velocity-turbidity – Secchi disk2. Chemical tests-pH-dissolved oxygen-Nitrates/nitrites and phosphates-hardness
Water Quality Testing Techniques
3. Biological test-biological assessment-benthic macroinvertebrates-fish species
Groundwater Pollution
• 50% of US population relies on groundwater for drinking water.
• Sources of pollution: pesticides, fertilizers, gasoline, oil from buried storage or poured directly.
• Characteristics of groundwater:-slow flow rate- 1 foot/day-> contaminants not diluted-low population of decomposing bacteria;-low concentration of dissolved oxygen• Groundwater pollutants:-arsenic: from rock and soil around the aquifer;Mining, ore processing -> cancer of skin, bladder-Nitrate Ions- from fertilizers ->cancer-MTBE (methyl tertiary butyl ether)- gasoline additive -> cancer
Fig. 20-11, p. 542
Polluted air
Hazardous waste injection wellPesticides and
fertilizers
Deicing road saltCoal strip mine
runoffBuried gasoline and solvent tanks
Pumping wellGasoline station Cesspool, septic
tank
Waste lagoon Sewer
Water pumping well
Landfill
Leakage from faulty casing
Accidental spills
Discharge
Groundwater flowUnconfined freshwater aquifer
Confined freshwater aquiferConfined aquifer
Fig. 20-12, p. 543
Leaking tank
AquiferBedrock
Water table
Groundwater flow
Gasoline leakage plume (liquid phase)
Free gasoline dissolves in groundwater (dissolved phase)
Migrating vapor phase
Contaminant plume moves with the groundwater
Water well
Ocean Pollution
• 2006: State of the Marine Environment– 80% of marine pollution originates on land– Sewage– Coastal areas most affected
• Deeper ocean waters– Dilution– Dispersion– Degradation
Ocean Pollution Is a Growing and Poorly Understood Problem
• Cruise line pollution: what is being dumped?
• U.S. coastal waters– Raw sewage
– Sewage and agricultural runoff: NO3- and PO4
3-
– Harmful algal blooms– Oxygen-depleted zones
Fig. 20-15, p. 548
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.
Farms 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.
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.
Closed shellfish bedsClosed
beach Oxygen-depleted zone
A Red Tide
Science Focus: Oxygen Depletion in the Northern Gulf Of Mexico
• Severe cultural eutrophication
• Oxygen-depleted zone
• Overfertilized coastal area
• Preventive measures
• Will it reach a tipping point?
Fig. 20-B, p. 550
Missouri River
Mississippi River Basin
Ohio River
Mississippi River
MSLA
TXMississippi
RiverLOUISIANA
Depleted oxygen
Gulf of Mexico Gulf of Mexico
Oil Pollution in Ocean Waters
Sources• Urban and industrial runoff from land=the largest source
of ocean oil pollution;• Leaks/spills of crude oil and refined petroleum (gasoline)Impact-VOCs(volatile organic compounds) in oil immediately kills larval forms of organisms;-oil reduces buoyancy and insulation in marine mammals and birds -> causing death from loss of body heat or drowning;
Fig. 20-17, p. 551
SOLUTIONSCoastal Water Pollution
Prevention CleanupReduce 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 sewageRegulate coastal
development, oil drilling, and oil shipping Use wetlands, solar-
aquatic, or other methods to treat sewageRequire double hulls for oil
tankers
Preventing and Reducing Water Pollution
• Reduce erosion– Keep cropland covered with vegetation
• Reduce the amount of fertilizers
• Plant buffer zones of vegetation
• Use organic farming techniques
Preventing and Reducing Water Pollution
• Use pesticides prudently/only when needed; use integrated pest management practices
• Control runoff by protecting natural water filtration systems such as wetlands and riparian zones;
• Tougher pollution regulations for livestock operations
• Deal better with animal waste• Increase the use of alternative energy souces to
reduce mercury emissions from coal burning power plants.
Improve Sewage Treatment=reduce water pollution
• Septic tank system
• Wastewater or sewage treatment plants– Primary sewage treatment
• Physical process
– Secondary sewage treatment• Biological process
– Tertiary or advance sewage treatment • Bleaching, chlorination
Fig. 20-18, p. 553
Manhole cover (for cleanout)
Septic tankGas
Distribution boxScum
Wastewater
SludgeDrain field
(gravel or crushed stone)
Vent pipePerforated pipe
Fig. 20-19, p. 554
Sludge
Disposed of inlandfill or ocean or applied to cropland,pasture, or rangeland
Raw sewagefrom sewers
Sludge digester
Sludge drying bed
(kills bacteria)
To river, lake,or ocean
Activated sludge
Air pump
Primary
Grit chamberBar screen Settling tank
Secondary
Chlorinedisinfection tankAeration tank Settling tank
Stepped Art
Further Recommendation for Sewage Treatment
• Separate network of pipes for storm water• Sludge from sewage treatment must be treated
for harmful bacteria, toxic metals, and organic chemicals before used as fertilizers
• Require industries/businesses to remove toxic and hazardous waste before it reaches municipal sewage plants.
• Increase use of natural and artificial wetlands system to treat sewage;
Water Quality Legislation
• Clean Water Act-regulates point-source pollution from municipal sewage facilities, industries and wastewater treatment systems.• Water Quality Act-an amendment to Clean Water Act-encourage separation of storm water and sewer water lines.• U.S. Safe Drinking Water Act-EPA sets standards of maximum containment levels for water pollutants that have a negative health impact for humans.