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Water Resources and Pollution

发布时间:2013-10-23 13:44:13  

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

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?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 dailyload (TMDL)?water stress?watershed?water table?withdrawal









?Water ResourcesMajor Water ComponentsWater Availability and UseFreshwater Shortages and Ways to Increase Water SuppliesWater Management and ConservationWater PollutionWater Quality TodayPollution ControlWater Legislation


Interactions of water with soil.

?Groundwater, after ice, is the

2nd largest reservoir of fresh


?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 Table is at the top

of the Zone of Saturation

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 water-absorbing 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 contain a minute amount of water at any one


?Lakes contain 100 times more water than all rivers.

?Wetlands play a vital role in the

hydrological cycle.

?Clean, fresh water is requisite for human survival.

?Renewable water suppliesconsist 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.

?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


?Widespread water shortages are predicted by


Sprinklers(below) lose large amounts of water to evaporation.

Drip irrigation (above) saves lots of water but it is not widely used.

?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


?Sinkholesform when an underground channel or cavern collapses.

?Saltwater intrusioncan 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.

?Building Dams, Canals and Reservoirs

?Seeding Clouds

?Condensation Nuclei

?Towing Icebergs



?Most common methods are distillationand reverse osmosis.

?Three to four times more expensive than most other sources.

Environmental CostsDams 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 km3per year

(264 billion gallons)

Dams slow water flow, allowing silt

(nutrients) to drop out

Location of 3 Gorges Dam on the Yangtze River of southern China (see case study in text, page 225).

To right:

sediment hasfilled a lake

Some dams interesting environmentally

include Hetch Hetchy (right), Aswan

High, 3 Gorges (previous slide), Glen

Canyon (above) and Grand Coulee

?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


?Significant amounts of water can be reclaimed

and recycled (purified

sewage effluent)

Point source pollution-source is from drain

pipes, ditches, sewer

outfalls, factories and

power plants -easy to

monitor and regulateNonpoint 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

?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

?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


?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

?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.

?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


?Excessive nutrients support blooms of deadly aquatic

microorganisms in polluted waters.

?Increasingly common where nutrients and wastes wash down rivers.

?Pfiesteria piscicidais a poisonous dinoflagellate recognized as killer of fish and shellfish.


?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.

?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

?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).

?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.

?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


?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.

?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

?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


?Two-thirds of India's surface

waters are contaminated

sufficiently to be considered

dangerous to human health.

Location of Oil Pollution in the Oceans

?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



?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.

?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


?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.

?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.

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