Water Environmental Science Chapter 11. WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Water keeps us alive, moderates climate, sculpts the land, removes

Water

Environmental Science Chapter 11

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• Water keeps us alive, moderates climate, sculpts the land, removes and dilutes wastes and pollutants, and moves continually through the hydrologic cycle.

• Only about 0.02% of the earth’s water supply is available to us as liquid freshwater.


• Comparison of population sizes and shares of the world’s freshwater among the continents.

Figure 14-2Figure 14-2


• Some precipitation infiltrates the ground and is stored in soil and rock (groundwater).

• Water that does not sink into the ground or evaporate into the air runs off (surface runoff) into bodies of water.– The land from which the surface water drains

into a body of water is called its watershed or drainage basin.

Global Water Distribution

• The fresh water we use comes mainly from lakes and rivers and from a relatively narrow zone beneath the Earth’s surface.

Chapter 11 Section 1 Water Resources

Water salinity

• Fresh water Brackish water Saline water Brine

• < 0.05 % 0.05 - 3 % 3 - 5 % >5% < 500 ppm 500 – 30,000 ppm 30 000 – 50,000 ppm > 50,000 ppm

http://en.wikipedia.org/wiki/Fresh_water

http://en.wikipedia.org/wiki/Brackish_water

http://en.wikipedia.org/wiki/Saline_water

http://en.wikipedia.org/wiki/Brine

Fig. 14-3, p. 308

Unconfined Aquifer Recharge Area

Precipitation Evaporation and transpiration Evaporation

Confined Recharge Area

Runoff

Flowing artesian well

Recharge Recharge Unconfined Unconfined AquiferAquifer

Stream Well requiring a pumpInfiltration Water

table LakeInfiltration

Unconfined aquifer

Confined aquiferConfining impermeable rock layer Confining impermeable rock layer

Less permeable Less permeable material such as claymaterial such as clay


• We currently use more than half of the world’s reliable runoff of surface water and could be using 70-90% by 2025.

• About 70% of the water we withdraw from rivers, lakes, and aquifers is not returned to these sources.

• Irrigation is the biggest user of water (70%), followed by industries (20%) and cities and residences (10%).

Water in the United States

• Average precipitation (top) in relation to water-deficit regions and their proximity to metropolitan areas (bottom).


Fig. 14-4a, p. 309

Average annual precipitation (centimeters)

More than 122

Less than 41 81–122

41–81

Watersheds of the World

Case Study: Who Should Own and Manage Freshwater

Resources

• There is controversy over whether water supplies should be owned and managed by governments or by private corporations.

• European-based water companies aim to control 70% of the U.S. water supply by buying up water companies and entering into agreements with cities to manage water supplies.

Groundwater

• Most of the fresh water that is available for human use cannot be seen, as it exists underground.

• Most of the fresh water that is available for human use cannot be seen, as it exists underground.

• When it rains, some of the water that falls onto the land flows into lakes and streams. But much of the water percolates through the soil and down into the rocks beneath.

• Groundwater is the water that is beneath the Earth’s surface.


Aquifers

• An aquifer is a body or rock or sediment that stores groundwater and allows the flow of groundwater. They are an important water source for many cities.

• The water table forms the supper boundary of an aquifer, and most aquifers consist of materials such as rock, sand, and gravel that have a lot of spaces where water can accumulate.

• Groundwater can also dissolve rock formations, filling vast caves with water, creating underground lakes.

Porosity

• Porosity is the percentage of the total volume of a rock or sediment that consists of open spaces.

• Water in an aquifer is stored in the pore spaces and flows form one pore space to another.

• The more porous a rock is, the more water it can hold.


Permeability

• Permeability is the ability of a rock or sediment to let fluids pass through it open spaces or pores.

• Materials such as gravel that allow the flow of water are permeable. Materials such as clay or granite that stop the flow of water are impermeable.

• The most productive aquifers usually form in permeable materials, such as sandstone, limestone, or layers of sand and gravel.


The Recharge Zone

• To reach an aquifer, surface water must travel down through permeable layers of soil and rock. Water cannot reach an aquifer from places where the aquifer is covered by impermeable materials.

• The recharge zone is an area in which water travels downward to become part of an aquifer.

• Recharge zones are environmentally sensitive areas because any pollution in the recharge zone can also enter the aquifer.


TOO LITTLE FRESHWATER

• Cities are outbidding farmers for water supplies from rivers and aquifers.

• Countries are importing grain as a way to reduce their water use.

• More crops are being used to produce biofuels.

• Our water options are:– Get more water from aquifers and rivers,

desalinate ocean water, waste less water.

WITHDRAWING GROUNDWATER TO INCREASE

SUPPLIES• Most aquifers are renewable resources

unless water is removed faster than it is replenished or if they are contaminated.

• Groundwater depletion is a growing problem mostly from irrigation.– At least one-fourth of the farms in India are being

irrigated from overpumped aquifers.

Fig. 14-7, p. 313

Trade-Offs

Withdrawing Groundwater

Advantages Disadvantages

Useful for drinking and irrigation

Aquifer depletion from overpumping

Available year-round

Sinking of land (subsidence) from overpumping

Exists almost everywhere

Polluted aquifers for decades or centuries

Renewable if not overpumped or contaminated

Saltwater intrusion into drinking water supplies near coastal areas

Reduced water flows into surface waters

No evaporation losses

Cheaper to extract than most surface waters

Increased cost and contamination from deeper wells

Groundwater Depletion: A Growing Problem

• The Ogallala, the world’s largest aquifer, is most of the red area in the center (Midwest).

• Areas of greatest aquifer depletion from groundwater overdraft in the continental U.S.


Other Effects of Groundwater Overpumping

• Groundwater overpumping can cause land to sink, and contaminate freshwater aquifers near coastal areas with saltwater.


Other Effects of Groundwater Overpumping

• Sinkholes form when the roof of an underground cavern collapses after being drained of groundwater.


Fig. 14-12, p. 316

Solutions

Groundwater Depletion

Prevention Control

Waste less water Raise price of water to discourage waste

Subsidize water conservation

Ban new wells in aquifers near surface waters

Tax water pumped from wells near surface waters

Buy and retire groundwater withdrawal rights in critical areas

Do not grow water-intensive crops in dry areas

Set and enforce minimum stream flow levels

Fig. 14-13a, p. 317

Provides water for year-round irrigation of cropland

Flooded land destroys forests or cropland and displaces people

Large losses of water through evaporation

Provides water for drinking Downstream

cropland and estuaries are deprived of nutrient-rich silt

Reservoir is useful for recreation and fishing

Risk of failure and devastating downstream flooding

Can produce cheap electricity (hydropower)

Downstream flooding is reduced

Migration and spawning of some fish are disrupted

Case Study: The Colorado Basin – an Overtapped Resource

• The Colorado River has so many dams and withdrawals that it often does not reach the ocean.– 14 major dams and reservoirs, and canals.– Water is mostly used in desert area of the U.S.– Provides electricity from hydroelectric plants

for 30 million people (1/10th of the U.S. population).

Case Study: The Colorado Basin – an Overtapped Resource

• Lake Powell, is the second largest reservoir in the U.S.

• It hosts one of the hydroelectric plants located on the Colorado River.


The Colorado River Basin

• The area drained by this basin is equal to more than one-twelfth of the land area of the lower 48 states.


Case Study: China’s Three Gorges Dam

• There is a debate over whether the advantages of the world’s largest dam and reservoir will outweigh its disadvantages.– The dam will be 2 kilometers long.– The electric output will be that of 18 large coal-

burning or nuclear power plants.– It will facilitate ship travel reducing transportation

costs.– Dam will displace 1.2 million people.– Dam is built over seismatic fault and already has

small cracks.

Dam Removal

• Some dams are being removed for ecological reasons and because they have outlived their usefulness.– In 1998 the U.S. Army Corps of Engineers

announced that it would no longer build large dams and diversion projects in the U.S.

– The Federal Energy Regulatory Commission has approved the removal of nearly 500 dams.

– Removing dams can reestablish ecosystems, but can also re-release toxicants into the environment.

TRANSFERRING WATER FROM ONE PLACE TO ANOTHER

• Transferring water can make unproductive areas more productive but can cause environmental harm.– Promotes investment, jobs and strong

economy.– It encourages unsustainable use of water in

areas water is not naturally supplied.

Case Study: The Aral Sea Disaster

• The Aral Sea was once the world’s fourth largest freshwater lake.


Case Study: The Aral Sea Disaster

• Diverting water from the Aral Sea and its two feeder rivers mostly for irrigation has created a major ecological, economic, and health disaster.– About 85% of the wetlands have been

eliminated and roughly 50% of the local bird and mammal species have disappeared.

– Since 1961, the sea’s salinity has tripled and the water has dropped by 22 meters most likely causing 20 of the 24 native fish species to go extinct.

Residential Water Use

• There are striking differences in residential water use throughout the world. For example, the average person in the United States uses about 300 L of water a day. But in India, the average person uses only 41 L of water everyday.

• In the U.S., only about half of residential water use is for activities inside the home, such as drinking and cooking. The remainder of the water used residentially is used for activities outside the home such as watering lawns.

Chapter 11Section 2 Water Use and Management

Residential Water UseChapter 11

Section 2 Water Use and Management

Water Treatment

• Most water must first be made potable.

• Potable means suitable for drinking.

• Water treatment removes elements such as mercury, arsenic, and lead, which are poisonous to humans even in low concentrations.

• These elements are found in polluted water, but they can also occur naturally in groundwater.


Water Treatment

• A pathogen is a virus, microorganism, or other substance that causes disease.

• Pathogens are found in water contaminated by sewage or animal feces, but can be removed with water treatment.

• There are several methods of treating water to make it potable. A common method includes both physical and chemical treatment.


Drinking-Water

Treatment

Chapter 11

Water Conservation

at Home


Point and Nonpoint Sources of Pollution

Chapter 11 Section 3 Water Pollution

Principal Water Pollutants


Wastewater Treatment Process


DESALTING SEAWATER, SEEDING CLOUDS, AND

TOWING ICEBERGS AND GIANT BAGGIES

• Removing salt from seawater by current methods is expensive and produces large amounts of salty wastewater that must be disposed of safely.– Distillation: heating saltwater until it evaporates,

leaves behind water in solid form.– Reverse osmosis: uses high pressure to force

saltwater through a membrane filter.

DESALTING SEAWATER, SEEDING CLOUDS, AND

TOWING ICEBERGS AND GIANT BAGGIES

• Seeding clouds with tiny particles of chemicals to increase rainfall towing icebergs or huge bags filled with freshwater to dry coastal areas have all been proposed but are unlikely to provide significant amounts of freshwater.

INCREASING WATER SUPPLIES BY WASTING LESS WATER

• We waste about two-thirds of the water we use, but we could cut this waste to 15%.– 65-70% of the water people use throughout the

world is lost through evaporation, leaks, and other losses.

– Water is underpriced through government subsidies.

– The lack of government subsidies for improving the efficiency of water use contributes to water waste.

How Would You Vote?

To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living in the Environment.

• Should water prices be raised sharply to help reduce water waste?– a. No. Poor people, farmers, ranchers, and small

businesses would suffer from price increases. – b. Yes. People would be more likely to conserve

water if it is more expensive.

INCREASING WATER SUPPLIES BY WASTING LESS WATER

• Sixty percent of the world’s irrigation water is currently wasted, but improved irrigation techniques could cut this waste to 5-20%.

• Center-pivot, low pressure sprinklers sprays water directly onto crop.– It allows 80% of water to reach crop.– Has reduced depletion of Ogallala aquifer in

Texas High Plains by 30%.

Fig. 14-18, p. 325

Center pivotCenter pivot

Drip irrigationDrip irrigation

Gravity flowGravity 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.

(efficiency 90–95%)

(efficiency 80%–95%)

Water usually pumped from underground and sprayed from mobile boom with sprinklers.

Fig. 14-19, p. 326

Solutions

Reducing Irrigation Water Waste

• Line canals bringing water to irrigation ditches

• Level fields with lasers

• Irrigate at night to reduce evaporation

• Monitor soil moisture to add water only when necessary

• Polyculture

• Organic farming

• Don't grow water-thirsty crops in dry areas

• Grow water-efficient crops using drought resistant and salt-tolerant crop varieties

• Irrigate with treated urban waste water

• Import water-intensive crops and meat

Solutions: Getting More Water for Irrigation in Developing Countries

– The Low-Tech Approach

• Many poor farmers in developing countries use low-tech methods to pump groundwater and make more efficient use of rainfall.


Fig. 14-21, p. 327

Solutions

Reducing Water Waste

• Redesign manufacturing processes

• Repair leaking underground pipes

• Landscape yards with plants that require little water

• Use drip irrigation

• Fix water leaks

• Use water meters

• Raise water prices

• Use waterless composting toilets

• Require water conservation in water-short cities

• Use water-saving toilets, showerheads, and front loading clothes washers

• Collect and reuse household water to irrigate lawns and nonedible plants

• Purify and reuse water for houses, apartments, and office buildings

• Don't waste energy

Raising the Price of Water: A Key to Water Conservation

• We can reduce water use and waste by raising the price of water while providing low lifeline rates for the poor.– When Boulder, Colorado introduced water

meters, water use per person dropped by 40%.

– A 10% increase in water prices cuts domestic water use by 3-7%.

Solutions: Using Less Water to Remove Industrial and Household

Wastes• We can mimic the way nature deals with

wastes instead of using large amounts of high-quality water to wash away and dilute industrial and animal wastes.– Use nutrients in wastewater before treatment

as soil fertilizer.– Use waterless and odorless composting

toilets that convert human fecal matter into a small amount of soil material.

TOO MUCH WATER

• Comparison of St. Louis, Missouri under normal conditions (1988) and after severe flooding (1993).


TOO MUCH WATER

• Human activities have contributed to flood deaths and damages.


Fig. 14-24, p. 331

Solutions

Reducing Flood Damage

Prevention Control

Preserve forests on watersheds

Strengthen and deepen streams (channelization)

Preserve and restore wetlands in floodplains

Tax all development on floodplains

Build levees or floodwalls along streams

Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry, and recreation

Build dams

SOLUTIONS: USING WATER

MORE SUSTAINABLY

• We can use water more sustainably by cutting waste, raising water prices, preserving forests and wetlands in water basins, and slowing population growth.


Fig. 14-25, p. 333

What Can You Do?Water Use and Waste

• Use water-saving toilets, showerheads, and faucet aerators.

• Shower instead of taking baths, and take short showers.

• Stop water leaks.

• Turn off sink faucets while brushing teeth, shaving, or washing.

• Flush toilets only when necessary.

• Wash only full loads of clothes or use the lowest water-level for smaller loads.

• Use recycled (gray) water for lawn, gardens, house plants, car washing.

• Wash a car from a bucket of soapy water, and use the hose for rinsing only.

• If you use a commercial car wash, try to find one that recycles its water.

• Replace your lawn with native plants that need little if any watering and decorative gravel or rocks.

• Water lawns and gardens in the early morning or evening.

• Sweep or blow off driveways instead of hosing off with water.

• Use drip irrigation and mulch for gardens and flowerbeds.

Documents

Water Environmental Science Chapter 11. WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Water keeps us alive, moderates climate, sculpts the land, removes