AP Environmental Living in the Environment 18th Edition Chapter 13 (Notes + Study Guide Questions)

What happened in the Colorado River?

• Past 50 Years: A bunch of dams/reservoirs/canals constructed to control flooding a supply electricity.

• A lot of water was drained from it, thus leading to a severe drought.

Severe Drought

A prolonged period in which precipitation is at least 70% lower and evaporation is higher than usual

How much of the Earth’s surface is covered by water?

71%

Freshwater

Water that contains low levels of dissolved salts.

• One of the most important natural capital

• Access to it is a global issue (780 million ppl without access)

How much of the planet’s water supply is readily available to us as liquid fresh water?

0.024%

Earth’s Water Composition

• Saltwater: 96.5%

• Ice caps/glaciers: 1.7%

• Underground Aquifers: 1.7%

• Readily available liquid freshwater: 0.024%

STUDY GUIDE: Groundwater

Freshwater located in the ground.

• Came in as precipitation that infiltrated the ground and percolated downwards until an impenetrable layer of rock stopped it.

STUDY GUIDE: Zone of Saturation

Spaces completely filled with freshwater.

STUDY GUIDE: Water Table

Top of the zone of saturation.

Aquifers

Underground caverns and porous layers of sand, gravel, or rock through which groundwater flows.

How are aquifers replenished?

• Natural Recharge: Precipitation percolating downwards into the aquifer.

• Lateral Recharge: Lakes, rivers, and streams bring in water.

Nonrenewable aquifer

Aquifers that get very little recharge

Surface water

The freshwater from rain and melted snow that flows across the Earth’s land surface and into lakes, wetlands, etc.

Surface Runoff

Precipitation that doesn’t infiltrate the ground (39% of all precipitation)

Watershed or drainage basin

The land in which surface runoff drains into a particular stream, lake, etc.

Hydrologists

Scientists who study water and its movement on Earth.

Reliable Surface Runoff

The remaining 1/3 of surface runoff that is available for human use.

Water Footprint

A rough measure of the volume of freshwater that we use directly and indirectly to support our life.

How much water does the average American use a day?

260 liters (69 gallons)

STUDY GUIDE: Virtual Water

Freshwater that is not direct consumed but is used to produce food and other products.

What are the major uses of groundwater in the United States?

• Cooling of electric power plants (41%)

• Irrigation (37%)

What are the main factors that cause water scarcity?

• Dry Climate

• Drought

• Too many people using a freshwater supply mort quickly than can be replenished

• Inefficient use of groundwater

Scarcity Stress

Measure based on a comparison of the amount of freshwater available with the amount used by humans.

How much of the world’s drinking water is supplied by aquifers?

Half of it

• Huge reliance is leading to many aquifers being unable to replenish themselves.

STUDY GUIDE: What is the Ogallala Aquifer? What states does it cover? What is the current condition of the aquifer?

• The world’s largest known aquifer that supplies 1/3 of all groundwater used in the US.

  • —> Led to the Great Plains being prosperous

• Eight Midwestern States (Wyoming, South Dakota, Nebraska, Colorado, Kansas, New Mexico, Oklahoma, Texas)

• Problem: Slow rate of recharge + Fertilizer Nitrates running off into it

  • High extraction —> Lower water table

STUDY GUIDE: Withdrawing Groundwater Tradeoffs

Advantages

• Useful for drinking/irrigation

• Exists almost everywhere

• Renewable if not overpumped/contaminated

• Cheaper to extract than most surface waters

Disadvantages

• Aquifer depletion from overpumping

• Sinking of land (subsidence) from overpumping

• Some deeper wells are nonrenewable

• Pollution of aquifers lasts decades or centuries

Land Subsidence

Withdrawing large amounts of groundwater —> Sinking aquifers

• This may lead to a sinkhole

Dam

A structure built across a river to control its flow.

• Led to an increase in reliable water use

Reservoir

An artificial lake created by dammed water.

STUDY GUIDE: How can Surface Water Resources be Expanded?

• The use of dams to capture and store surface runoff

  • Help generate energy

  • Help provide half of the water for irrigated cropland

• Reservoir systems

STUDY GUIDE: How can Dams Kill Estuaries?

• Government subsidies —>

  • Inefficient use of irrigation water for growing crops, thus leading to more water withdrawal

• Dams cut water flowing upstream, thus cutting water supplies for affected ecosystems.w

STUDY GUIDE: What is the difference between Confined and Unconfined Aquifers?

• Confined: An impenetrable layer of rock or soil confines the aquifer.

• Unconfined: Not confined by an impenetrable layer of rock.

What are the problems with water transfers?

• While they supply water to dry areas from water-rich areas, they can have:

  • High economic/social costs

  • Large water losses via evaporation and leaks

  • Degraded ecosystems

Desalination

The process of removing dissolved salts from ocean water or from brackish (kind of salty) water in aquifers or lakes.

What methods are used to desalinate?

• Distillation: Evaporation to remove salt

• Reverse Osmosis: High pressures remove salt

What are the problems with desalination?

• High costs

• Kills many marine organisms and uses a lot of energy

• Produces large quantities of salt wastewater

Why is so much freshwater allowed to be lost?

• Cost of freshwater is so low (due to subsidies) that many farmers don’t care about conserving.

• Lack of government subsidies for improving the efficiency of freshwater use.

What is the most inefficient type of irrigation?

• Flood irrigation: Water is pumped from a ground/surface water source via unlined ditches where it flows by gravity to the crops being watered.

• Traditional Spray Irrigation

STUDY GUIDE: What type of irrigation technology is the most efficient?

• Low-energy, precision application (LEPA) sprinklers.

What is the most efficient irrigation method?

• FIRST: Drip (or trickle) irrigation

• SECOND: More crop per drop strategy

  • Uses Center Pivot or LEPA sprinklers

Floodplain

An area in which a flood spills into.

What human activities lead to flooding?

• Removal of water-absorbing vegetation

• Draining of wetlands that naturally absorb water

• Rise in sea levels

How have floods been beneficial?

• Provide nutrient-rich silt

• Recharge groundwater and refill wetlands

How can we reduce flood risks in a manner that is ecologically oriented?

• Less reliance on dams/levees and more on nature’s systems such as wetlands and watershed forests