ESC110 Chapter Ten Water: Resources and Pollution

ESC110 Chapter TenWater: Resources and Pollution

Chapter Ten Readings & Objectives

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;

Required ReadingsCunningham & Cunningham, Chapter Ten

Water: Resources and Pollution

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

• 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

Chapter Ten Topics

Part 1: Water Resources

REVIEW OF THE HYDROLOGIC CYCLE

Mean Annual Precipitation

Part 2: Major Water Compartments

• 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

Interactions of water with soil.

Aquifers

Recharge zones - areas where surface watersfilter 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, 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 damsEnvironmental Costs

Dams upset natural balance of water systems

Ecosystem LossesLoss of wildlife habitat with impact dependent upon reservoir size and water quality

Displacement of people3 Gorges Dam will force > a millionpeople to relocate

Evaporation, Leakage and SiltationEvaporative 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.

Some dams interesting environmentallyinclude Hetch Hetchy (right), Aswan High, 3 Gorges (previous slide), Glen Canyon (above) and Grand Coulee

To right:sediment hasfilled a lake

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.

• 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.

Part 9: WATER LEGISLATION