Transcript Document

ESC110 Chapter Ten
Water: Resources and Pollution
Chapter Ten Readings & Objectives
Required Readings
Cunningham & Cunningham, Chapter Ten
Water: Resources and Pollution
At the end of this lesson, you should be able to
• describe the important sources of water (and the hydrologic
cycle) and the major ways we use it;
• appreciate the causes and consequences of water shortages
around the world and what they mean in people's lives in water
poor communities;
• debate the merits of proposals to increase water supplies and
manage demand;
• apply some water conservation methods in your own life;
• define water pollution and describe the sources and effects of
some major types;
• appreciate why access to sewage treatment and clean water are
important to people in developing countries;
• explain ways to control water pollution, including technological
and legal solutions;
Chapter Ten Key Terms
 aquifers
 biochemical oxygen
demand (BOD)
• coliform bacteria
• consumption
• cultural eutrophication
• discharge
• dissolved oxygen (DO)
content
• eutrophication
• nonpoint sources
• oligotrophic
 oxygen sag
 point sources
 primary treatment
 recharge zones
 renewable water supplies
 residence time
 secondary treatment
 tertiary treatment
 thermal pollution
 total maximum daily
load (TMDL)
 water stress
 watershed
 water table
 withdrawal
Chapter Ten Topics
•
•
•
•
•
•
•
•
•
Water Resources
Major Water Components
Water Availability and Use
Freshwater Shortages and Ways to Increase
Water Supplies
Water Management and Conservation
Water Pollution
Water Quality Today
Pollution Control
Water Legislation
Part 1: Water Resources
REVIEW OF THE HYDROLOGIC CYCLE
Mean Annual Precipitation
Part 2: Major Water
Compartments
Interactions of water with soil.
• Groundwater, after ice, is the
2nd largest reservoir of fresh
water
– Infiltration - Process of water
percolating through the soil
and into fractures and
permeable rocks.
• Zone of Aeration - Upper
soil layers that hold both air
and water.
• Zone of Saturation - Lower
soil layers where all spaces
are filled with water.
• Water Table is at the top of
the Zone of Saturation
Aquifers
Recharge zones - areas where surface waters
filter into an aquifer
• Rivers, Lakes and Streams - Precipitation that does not
evaporate or infiltrate into the ground runs off the surface,
back toward the sea.
• Best measure of water volume carried by a river is discharge.
– The amount of water that passes a fixed point in a given amount of time
(usually expressed as cubic feet per second).
• Wetlands - Play a vital role in hydrologic cycle.
• Lush plant growth stabilizes soil and retards surface runoff, allowing more
aquifer infiltration.
– Disturbance (including urban development) reduces natural waterabsorbing capacity, resulting in floods and erosion in wet periods, and
less water flow the rest of the year.
• The Atmosphere - Among the smallest water reservoirs.
• Contains 0.001% of total water supply.
• Has the most rapid turnover rate.
• Provides a mechanism for distributing fresh water over landmasses and
replenishing terrestrial reservoirs.
Rivers, Lakes, and Wetlands
• Rivers contain a
minute amount of
water at any one
time.
• Lakes contain 100
times more water
than all rivers.
• Wetlands play a vital
role in the
hydrological cycle.
Part 3: Water Availability and Use
• Clean, fresh water is requisite for
human survival.
• Renewable water supplies
consist of surface runoff and
infiltration into accessible
freshwater aquifers (shallow
ground water). These supplies are
most plentiful in the Tropics.
• Picture to the left shows a ditch
being used to divert water for
irrigation of crops. Water rights for
such activities have long been a
source of tension and conflict.
Total water use depends strongly on national wealth and degree of
industrialization, yet the highest consumption rate (measured as water
availability per capita) occurs in countries with moist climates and low
population densities.
Part 4: Freshwater Shortages
• About 25% of the world’s people
lack adequate, clean drinking
water and about 50% lack
adequate sanitation.
• Water stress is a phrase used to
describe countries where water
consumption exceeds by >20%
the available, renewable water
supply
• Widespread water shortages are
predicted by 2025.
Sprinklers (below)
lose large amounts
of water to
evaporation.
Drip irrigation
(above) saves lots
of water but it is not
widely used.
Depleting Groundwater
• Groundwater provides nearly 40% of the fresh water for
agricultural and domestic use in the United States. In many
areas in the U.S., groundwater is being withdrawn from
aquifers faster than natural recharge can replace it.
• Withdrawing large amounts of groundwater in a small area
causes porous formations to collapse, resulting in
subsidence.
– Sinkholes form when an underground channel or cavern
collapses.
– Saltwater intrusion can occur along coastlines where overuse of
freshwater reservoirs draws the water table low enough to allow
saltwater to intrude.
• Ogallala Aquifer (large aquifer in the Central Plains) - water
usage here is the similar to mining for a nonrenewable
resource and the water resource is being depleted rapidly.
• San Joaquin Valley, California - ground surface sinking is
occurring due to excessive groundwater pumping.
Cone of Depression
Ways to Increase Water Supplies
• Building Dams, Canals and Reservoirs
• Seeding Clouds
– Condensation Nuclei
• Towing Icebergs
– Cost
• Desalination
– Most common methods are distillation and reverse
osmosis.
• Three to four times more expensive than most other sources.
Dams trap water in areas of excess and transfer
it to areas of deficit. Listed below are some
political and environmental concerns with dams
Environmental Costs
Dams upset natural balance of water
systems
Ecosystem Losses
Loss of wildlife habitat with impact
dependent upon reservoir size and
water quality
Displacement of people
3 Gorges Dam will force > a million
people to relocate
Evaporation, Leakage and Siltation
Evaporative losses from Lakes Mead
and Powell on the Colorado River is
about one km3 per year (264 billion
gallons)
Dams slow water flow, allowing silt
(nutrients) to drop out
Loss of Free Flowing Rivers
Location of 3 Gorges Dam on the
Yangtze River of southern China
(see case study in text, page 225).
Dams are controversial in terms of environmental costs, justice,
price mechanisms and water policy, sedimentation, evaporative
losses, etc.
To right:
sediment has
filled a lake
Some dams interesting environmentally
include Hetch Hetchy (right), Aswan
High, 3 Gorges (previous slide), Glen
Canyon (above) and Grand Coulee
Part 5: Water Management and
Conservation
• Watershed management
• Sound farming and
forestry practices
• Wetlands conservation
• Domestic conservation
• Water reclamation and
recycling
• Water rights
Domestic Conservation
• Estimates suggest many
societies could save as
much as half of current
domestic water usage
without great sacrifice or
serious change in lifestyle.
– Largest domestic use is
toilet flushing.
• Small volume of waste in
large volume of water.
• Significant amounts of
water can be reclaimed
and recycled (purified
sewage effluent)
Part 6: Water Pollution
Point source pollution source is from drain
pipes, ditches, sewer
outfalls, factories and
power plants - easy to
monitor and regulate
Nonpoint source pollution runoff from farm fields and
feedlots, lawns and gardens,
golf courses, construction
sites, atmospheric deposits no specific location so harder
to monitor and regulate
Types and Results of Water Pollution
• Infectious agents - 25 million deaths a year
• Organic materials - biological oxygen demand (BOD)
increase resulting in oxygen sag
• Plant nutrients - eutrophication, toxic tides
• Metals - mercury and lead poisoning
• Nonmetallic salts - poison seeps and springs
• Acids and bases - ecosystem destabilization
• Organic chemicals - birth defects, cancer
• Sediments - clogged estuaries, death of coral reefs
• Thermal pollution - thermal plume
Infectious Agents
• Main source of waterborne pathogens is untreated and
improperly treated human waste.
– Animal wastes from feedlots and fields is also an important
source of pathogens.
– In developed countries, sewage treatment plants and
pollution-control devices have greatly reduced pathogens.
– Tests for water quality are done for coliform bacteria
(intestinal bacteria). Such tests are easier and cheaper.
• Escherichia coli (E. coli) is the major coliform bacterium
species
Basics for Understanding Environmental
Implications of Oxygen-Demanding Wastes
• Water with a Dissolved Oxygen Content (DOC) content > 6
parts per million (ppm) will support desirable aquatic life,
whereas water with < 2 ppm oxygen will support mainly
detritivores and decomposers.
• Oxygen is added to water by diffusion from wind and waves,
and by photosynthesis from green plants, algae, and
cyanobacteria. Oxygen is removed from water by respiration
and oxygen-consuming processes.
• Biochemical Oxygen Demand (BOD) is the amount of
dissolved oxygen consumed by aquatic microorganisms in
respiration.
• When organic wastes are added to rivers, microorganisms
demand oxygen for respiration used in consuming the
increase in food resource. As a result, DOC levels decline
downstream (oxygen sag) from a pollution source as
decomposers metabolize organic waste materials.
Oxygen sag
Plant Nutrients and Cultural
Eutrophication
• Oligotrophic - Bodies of water
that have clear water and low
biological productivity.
• Eutrophic - Bodies of water that
are rich in organisms and
organic material.
– Eutrophication - Process of
increasing nutrient levels and
biological productivity.
• Cultural Eutrophication Increase in biological
productivity and ecosystem
succession caused by
human activities.
Toxic Tides
• Excessive nutrients support blooms of deadly
aquatic microorganisms in polluted waters.
– Increasingly common where nutrients and
wastes wash down rivers.
• Pfiesteria piscicida is a poisonous dinoflagellate
recognized as killer of fish and shellfish.
Inorganic Pollutants
• Metals
– Many metals such as mercury, lead, cadmium, and nickel
are highly toxic.
• Highly persistent and tend to bioaccumulate in food chains.
– Lead pipes are a serious source of drinking water pollution.
– Mine drainage and leaching are serious sources of environmental
contamination.
• Nonmetallic Salts
– Many salts that are non-toxic at low concentrations can be mobilized by
irrigation and concentrated by evaporation, reaching levels toxic to
plants and animals.
• Leaching of road salts has had detrimental effect on many ecosystems.
• Acids and Bases
– Often released as by-products of industrial processes.
Organic Chemicals
• Thousands of natural and synthetic organic
chemicals are used to make pesticides,
plastics, pharmaceuticals, pigments, etc.
• Two most important sources of toxic organic
chemicals in water are:
– Improper disposal of industrial and household
wastes.
– Runoff of pesticides from high-use areas.
• Fields, roadsides, golf courses
Sediment
• Human activities have accelerated erosion
rates in many areas.
– Cropland erosion contributes about 25 billion
metric tons of suspended solids to world
surfaces each year.
• Sediment can either be beneficial (nourish
floodplains) or harmful (smother aquatic life).
Thermal Pollution
• Raising or lowering water temperatures from normal
levels can adversely affect water quality and aquatic life.
– Oxygen solubility in water decreases as temperatures
increase.
• Species requiring high oxygen levels are adversely affected by
warming water.
• Industrial cooling often uses heat-exchangers to extract
excess heat, and discharge heated water back into
original source.
– Thermal Plume
• Produce artificial environments which attract many forms of wildlife.
Part 7: Water Quality Today
Percentage of
impaired river
miles in the
U.S. by source
of damage
• Areas of Progress
– Clean Water Act (1972) established a National Pollution Discharge System
which requires a permit for any entity dumping wastes in surface waters.
• In 1999, EPA reported 91.4% of all monitored river miles and 87.5% of all
accessed lake acres are suitable for their designated uses.
– Most progress due to municipal sewage treatment facilities.
• Watershed Approach Is Also an Improvement
– 1998, EPA switched regulatory approaches. Rather than issue standards on a
site by site approach, the focus is now on watershed-level monitoring and
protection.
– States are required to identify waters not meeting water quality goals and
develop total maximum daily loads (TMDL) for each pollutant and each listed
water body.
• Persistent Environmental Problems That Remain
– Greatest impediments to achieving national goals in water quality are sediment,
nutrients, and pathogens, especially from non-point discharges.
– About three-quarters of water pollution in the US comes from soil erosion, air
pollution fallout, and agricultural and urban runoff.
• Single cow produces 30 kg manure/day.
– Some feedlots have 100,000 animals.
Groundwater and Drinking water
Pollution
• About half the US population, and 95% of
rural residents, depend on underground
aquifers for drinking water.
– For decades, groundwater was assumed
impervious to pollution. It was considered the
gold standard for water quality.
• An estimated 1.5 million Americans fall ill from
fecal contamination annually.
– Cryptosporidium outbreaks
Groundwater Pollution
Progress and Problems in Other
Countries
• Sewage treatment in
wealthier countries of
Europe generally equal or
surpass the US.
• In Russia, only about half of
the tap water supply is safe
to drink.
• In urban areas of South
America, Africa, and Asia,
95% of all sewage is
discharged untreated into
rivers.
• Two-thirds of India’s surface
waters are contaminated
sufficiently to be considered
dangerous to human health.
Location of Oil Pollution in the Oceans
Part 8: Pollution Control
• Nonpoint Pollution Sources and Land Management
– Reduce nutrient loading thru land use regulations
– Source reduction is cheapest and most effective way to
reduce pollution. To work society must get public and
business leaders to avoid producing or releasing
substances into the environment.
• Studies show as much as 90% less road salt can be used without
significantly affecting winter road safety.
• Soil Conservation
• Banning phosphate detergents
• Sewage Treatment
• Remediation
Sewage Treatment
• Rationale
– More than 500 pathogenic bacteria, viruses, and parasites
can travel from human or animal excrement through
water.
• Natural Processes
– In many areas, outdoor urination and defecation is the
norm.
• When population densities are low, natural processes can
quickly eliminate waste.
• Artificial Wetlands Are a Low Cost Method
– Natural water purification
• Effluent can be used to irrigate crops or raise fish for human
consumption.
Municipal Sewage Treatment
• Primary Treatment - Physical separation of large solids from the
waste stream.
• Secondary Treatment - Biological degradation of dissolved
organic compounds.
– Effluent from primary treatment transferred into trickling bed, or
aeration tank
• Effluent from secondary treatment is usually disinfected (chlorinated) before
release into nearby waterway.
• Tertiary Treatment - Removal of plant nutrients (nitrates and
phosphates) from secondary effluent.
– Chemicals, or natural wetlands.
• In many US cities, sanitary sewers are connected to storm
sewers.
– Heavy storms can overload the system, causing by-pass dumping
of raw sewage and toxic runoff directly into watercourses.
Sewage Treatment
Water Remediation
• Containment methods confine liquid wastes
in place, or cap surface with impermeable
layer to divert water away from the site.
• Extraction techniques are used to pump out
polluted water for treatment.
– Oxidation, reduction, neutralization, or
precipitation.
• Living organisms can also be used effectively
to break down polluted waters.
Part 9: WATER LEGISLATION
• Clean Water Act (1972)
– Goal was to return all U.S. surface waters to “fishable
and swimmable” conditions.
• For Point Sources, Discharge Permits and Best Practicable
Control Technology are required.
– Set zero discharge for 126 priority toxic pollutants.
• Areas of Contention
– Draining or Filling of Wetlands
• Many consider this taking of private land.
– Un-funded Mandates
• State or local governments must spend monies not repaid by
Congress.