Fall 2019 APES chapter 15

Lecture Outlines

Chapter 15

Freshwater Systems and Resources

Withgott/Laposata

This lecture will help you understand:



Water’s distribution and types of freshwater

ecosystems



Use and alteration of freshwater systems



Problems of water supply and solutions



Classes of water pollution and solutions

Central Case Study: Starving the Louisiana

Coast of Sediment



Louisiana loses 65 km

(25 mi

) of coastal wetlands

each year

 These ecosystems support a diversity of animals

 Protect coastal cities from damaging storms



Created by sediments deposited at the end of the

Mississippi River

 The river accumulates material from water flowing off of its 3.2 million km2 _{(1.2 million mi}2_{) watershed}



The wetlands naturally compact, sink, and would

vanish

Case Study: Starving the Louisiana Coast of

Sediment



The Mississippi River has been extensively modified

 The dams slow the water, and the sediment drops out



Levees confine the river, making it deeper and faster

 Sediments shoot out rather then settle in the wetlands



Oil and gas extraction has increased the rate of soil

compaction



Solution: allow water from the Mississippi into the

coastal wetlands rather than shooting it into the Gulf

Freshwater Systems



Water may seem abundant, but drinkable water is

rare



Fresh water



water that is relatively pure, with few

dissolved salts—only 2.5% of total water

 Most is tied up in glaciers, ice caps, and aquifers

Freshwater Systems



Water is renewed and recycled as it moves through

the water cycle

 Precipitation sinks into the ground or runs off into rivers to form lakes or enter oceans

 Rivers interact with ponds, wetlands, and coasts

 Groundwater exchanges with rivers and ponds

Groundwater plays key roles in the hydrologic

cycles

 Surface water  water located atop Earth’s surface

 Groundwater  water beneath the surface held in pores in soil or rock

 20% of the Earth’s freshwater supply

 Aquifers  porous, spongelike formations of rock, sand, or gravel that hold water

 Zone of aeration  pore spaces partly filled with water

 Zone of saturation  spaces are filled with water

 Water table  boundary between the two zones

What do the following mighty bodies of

water have in common?



Aral Sea



Dead Sea



Rio Grande River

Groundwater plays key roles in the hydrologic

cycles



Confined (artesian) aquifer



water-bearing,

porous rocks are trapped between less permeable

substrate (clay) layers

 Water here is under great pressure



Unconfined aquifer



no upper layer to confine it



Groundwater’s average age is 1400 years



The Ogallala Aquifer is the world’s largest known

aquifer

Surface water converges in river and stream

ecosystems



Surface water accounts for just 1% of fresh water



Runoff



water that flows over land

 Water merges in rivers and ends up in a lake or ocean

Surface water converges in river and stream

ecosystems



Watershed

(

drainage basin

)



the area of land

drained by a

river system

(river and its tributaries)



Surface water becomes groundwater through

infiltration



Groundwater becomes surface water through

springs or human-drilled wells

Hydrologic Cycle—Major Aspects

Hydrologic Cycle—Crossword Puzzle

Surface water converges in river and stream

ecosystems



Rivers shape the landscape



Braided river



an interconnected series of

watercourses that run through steep slopes



Meandering river



river in flatter areas

 Water rounding a bend erodes soil from the outer bank

 Sediment is deposited on the inside of the bend

 Rivers form oxbows, areas where river bends become exaggerated

Surface water converges in river and stream

ecosystems



Floodplain



areas nearest to a river’s course that

are flooded periodically

 Frequent deposition of silt makes floodplain soils fertile

 Good areas for agriculture



Riparian



describing riverside areas that are

productive and species-rich

 Damming prevents large floods and river meanders



Rivers and streams host diverse ecological

communities

Lakes and ponds are ecologically diverse

systems

 Lakes and ponds are bodies of open, standing water

 Littoral zone  region ringing the edge of a water body  Rooted aquatic plants grow in this shallow part

 Benthic zone  the entire bottom of the water body  Home to many invertebrates

 Limnetic zone  open portion of the lake or pond where sunlight allows photosynthesis that produces oxygen

 Supports phytoplankton and zooplankton

Lakes and ponds are ecologically diverse

systems



Ponds and lakes may change over time



Oligotrophic

lakes and ponds have low-nutrient and

high-oxygen conditions



Eutrophic

lakes and ponds have high-nutrient and

low-oxygen conditions

 Eutrophication may result from human pollution



Eventually, water bodies may fill completely in

through the process of succession

Freshwater wetlands include marshes,

swamps, bogs, and vernal pools



Wetlands



systems in which the soil is saturated

with shallow standing water with vegetation



Freshwater marshes



shallow water with plants that

grow above the surface



Swamps



shallow water in forested areas



Bogs



ponds covered in thick floating mats of

vegetation

 A stage in aquatic succession

Freshwater wetlands include marshes,

swamps, bogs, and vernal pools



Wetlands are extremely valuable for wildlife

migratory birds each year



They provide valuable ecosystem services

 They slow runoff, reduce flooding, recharge aquifers, and filter pollutants



People have drained wetlands, mostly for agriculture

over half of their wetlands

Human Activities Affect Waterways



Water is crucial for human health as well as farms

and factories



Water is a limited but renewable resource



Withdrawal of water in most of the world is

unsustainable

 We are depleting many sources of surface water and groundwater

Human Activities Affect Waterways



We have achieved impressive engineering

accomplishments to harness fresh water

 60% of the world’s largest 227 rivers have been

Fresh water and human populations are

unevenly distributed across Earth



Different areas possess different amounts of water

availability

 Asia has the most water of any continent but the least water available per person

 Densely populated nations like Pakistan, Iran, India, and Egypt face serious water shortages



Fresh water is also unevenly distributed in time

 Seasonal rains lead to differences in water availability

 India can receive half of its rain in a single monsoon

Fresh water and human populations are

unevenly distributed across Earth



Climate change will worsen conditions in many

region

 Altered precipitation patterns

 Melting glaciers causing early season runoff

 Intensified droughts and flooding



One-third of the world’s major rivers experienced

reduced flow from 1948 to 2004

Water supplies households, industry, and

especially agriculture



Globally, 70% of water is used for agriculture, 20%

for industry, and 10% for residential and municipal

use

 Arid countries use more water for agriculture

 Developed countries use more water for industry



Consumptive use



when water is removed from

an aquifer or surface water body and is not returned



Nonconsumptive use



does not remove, or only

temporarily removes, water

Water supplies households, industry, and

especially agriculture

 Rapid population growth requires more food and clothes

 We use 70% more irrigation water than 50 years ago

 Irrigation can more than double crop yields

 18% of land is irrigated but produces 40% of our crops

 Irrigation is highly inefficient

 Water evaporates in “flood and furrow” irrigation

 Overirrigation leads to waterlogging and salinization  Reducing world farm income by $11 billion

Excessive water withdrawals can drain rivers

and lakes



In many places, we are withdrawing water at

unsustainable rates



Many of the world’s major rivers regularly run dry

before reaching the sea

 The Colorado River often does not reach the Gulf of California, threatening the future of cities and farms that rely on its water

 Reduced flow drastically changes the river’s ecology and plant community and destroys fish and

Excessive water withdrawals can drain rivers

and lakes



The Aral Sea in in present day Uzbekistan and

Kazakhstan was once the fourth-largest lake on

Earth

 It lost 80% of its volume in 45 years

 The two rivers leading into the Aral Sea were diverted to irrigate cotton fields

 60,000 fishing jobs are gone

 Pesticide-laden dust is blown into the air

Excessive water withdrawals can drain rivers

and lakes



Worldwide, 15%–35% of water withdrawals for

agriculture are unsustainable

Groundwater can also be depleted



Groundwater is more easily depleted than surface

water

 Aquifers recharge slowly

 Used by one-third of all people



As aquifers are mined, water tables drop

 In many areas, water tables are falling 1–3 m/year

 Salt water intrudes in coastal areas, making water undrinkable

Groundwater can also be depleted



Sinkholes



areas where ground gives way

suddenly

 Once the soil is compacted, aquifers can’t recharge



Wetlands that get their water from groundwater

Groundwater supplies our bottled water

 Groundwater is being withdrawn for use as bottled water  An average American drinks 29 gallons/year

 Sales topped $15 billion in the United States in 2012

 People drink bottled water for portability, convenience  They think it tastes better or is healthier

 Bottled water is no better than tap water

 It is heavily packaged and travels long distances using fossil fuels

 Energy costs of bottled water are 1000–2000 times greater than those of tap water

People build dikes and levees to control floods

 Flooding  a normal, natural process where water spills over a river’s banks

 Spreading nutrient-rich sediments over large areas

 In the short term, floods damage property

 Levees (or dikes) are the long, raised mounds of earth along the banks of rivers that hold water in channels

 Stop flooding from most rains

 May make floods worse by forcing water to stay in channels, build energy, and then overflow

We divert surface water to suit our needs

 People divert water to farm fields, homes, and cities

 Water from the Colorado River is diverted to Denver, Las Vegas, Los Angeles, and elsewhere

 In China, $62 billion is being spent to move water from the Yangtze to the Yellow River

 Politically strong, water-poor areas forcibly take water from weaker communities

 Los Angeles commandeered water from rural areas,

turning the environment into desert, creating dustbowls, and destroying the economy

 In 1941, it diverted streams that fed Mono Lake

We have erected thousands of dams



Dam



any obstruction placed in a river or stream to

block the flow of water



They create

reservoirs



artificial lakes



Dams are built to prevent floods, provide drinking

water, allow irrigation, and generate electricity

 45,000 large dams have been erected in more than 140 nations

 Tens of thousands of smaller dams have been built

We have erected thousands of dams



Dams produce a mix of benefits and costs



The dam on the Yangtze River is the largest in the

world

 Its reservoir stretches for 616 km (385 mi)

We have erected thousands of dams



However, it cost $39 billion to build

 Flooded 22 cities and the homes of 1.24 million people

 Submerged 10,000-year-old archaeological sites

 Drowned farmland and wildlife habitat

 The tidal marshes at the Yangtze’s mouth are eroding

Some dams are being removed

 Some people feel that the costs of dams outweigh their benefits and are pushing to dismantle dams

 Removing dams will restore riparian ecosystems, reestablish fisheries, and revive river recreation

 The Federal Energy Regulatory Commission (FERC) renews licenses for dams

 If dam costs exceed benefits, the license may not be renewed

 400 dams have been removed in the United States

Wetlands are affected by human manipulations

of waterways



Wetlands are being lost as we divert and withdraw

water, channelize rivers, build dams, etc.



Wetlands have also been widely drained for

agriculture

Wetlands are affected by human manipulations

of waterways



The

Ramsar Convention on Wetlands of

International Importance

(1971) seeks the

conservation and wise use of wetlands in the context

of sustainable development

Solutions to Depletion of Fresh Water



Our use of fresh water has doubled over the last 50

years



We can either increase supply or reduce demand



Increasing supply through intensive extraction is

only a temporary fix

Solutions to Depletion of Fresh Water



Reducing demand is harder politically in the short

term

 International aid agencies are funding demand-based solutions over supply-based solutions

 Offers better economic returns

Desalinization “makes” more fresh water



Desalination

(

desalinization

)



the removal of salt

from seawater or other water of marginal quality

 Distilling  evaporates and condenses ocean water

 Reverse osmosis  forces water through membranes

to filter out salts



Over 2000 desalinization facilities operate around

the world, but there are problems with it

 Is expensive

 Requires large energy inputs (usually fossil fuels)

 Kills aquatic life at the water intakes

Agricultural demand can be reduced

 Agriculture uses the largest amount of water of any use, but a number of measures can be taken to reduce waste

 Line irrigation canals to prevent leaks

 Level fields to reduce runoff

 Use efficient irrigation methods

 Low-pressure spray irrigation sprays water downward

 Drip irrigation systems target individual plants

 Match crops to land and climate

 Eliminate water subsidies

We can lower residential and industrial water

use

 Residential water use can be cut in a number of ways  Install low-flow faucets, toilets, etc.

 Rainwater harvesting  capturing rain from roofs

 Gray water  wastewater from showers and sinks that can be used to water lawns

 Xeriscaping using plants adapted to arid conditions

 Industries and municipalities can save water  Shift to processes that use less water

 Recycle wastewater

 Use surface water runoff to recharge aquifers

Market-based approaches to water

conservation are being debated

 End government subsidies of inefficient practices

 Let the price of water reflect its true cost of extraction

 But since industrial uses are more profitable than

agricultural uses, poorer, less developed countries suffer

 Privatize water supplies: construction, maintenance, management, and ownership

 May improve efficiency

 Little incentive to provide access to the poor

Nations often cooperate to resolve water

disputes

 Freshwater depletion leads to shortages, which can lead to conflict

 261 major rivers cross national borders

 Water is a key element in hostilities among Israel, Palestinians, and neighboring countries

 Conflicts also exist between states in the United States

 Many nations have cooperated with neighbors to resolve disputes

 India has agreements to co-manage rivers with Pakistan, Bangladesh, Bhutan, and Nepal

Freshwater Pollution and Its Control

 People affect aquatic ecosystems and human health when we introduce toxic substances and diseases

 Half of the world’s major rivers are seriously depleted and polluted

 They degrade and poison surrounding ecosystems, threatening the health and livelihood of people

 55% of U.S. streams and rivers are in poor condition

 The invisible pollution of groundwater has been called a “covert crisis”

Water pollution comes from point and

non-point sources

 Pollution  the release of matter or energy that causes undesirable impacts on the health and well-being of

humans or other organisms

 Water pollution comes in many forms and causes diverse impacts

 Point sources  discrete locations of water pollution  Factories, sewer pipes

 Addressed by the U.S. Clean Water Act

 Non-point sources  sources of pollution arising from multiple inputs over larger areas (farms, city streets, neighborhoods)

Water pollution takes many forms



Toxic chemicals

: waterways have become polluted

with toxic organic chemicals of our own making



Pesticides, petroleum products, synthetic chemicals;

arsenic, lead, mercury, acid rain, acid

Water pollution takes many forms



Scientists measure a range of water characteristics

to assess water quality (color, pH, temperature, etc.)



Solutions:

 Issue and enforce more stringent regulations

Pathogens and waterborne diseases



Viruses, protists, and bacteria enter water supplies

through inadequately treated human waste and

animal waste from feedlots



Fecal coliform bacteria indicate fecal contamination

Pathogens and waterborne diseases



Bacterial pollution causes more human health

problems than any other type of water pollution

 Conditions are improving, but 800 million people lack reliable access to safe water

Nutrient pollution



Nutrient pollution from fertilizers, farms, sewage,

lawns, golf courses leads to eutrophication

 Fertilizers add phosphorus and Nitrates to water, which boosts algal and aquatic plant growth

 Spreading algae cover the surface, decreasing sunlight

 Bacteria eat dead algae, reducing dissolved oxygen

Nutrient pollution



Areas of low oxygen can become “dead zones”



Solutions include treating wastewater

 Using phosphate-free detergents

Biodegradable Wastes and Sediment



Introducing large amounts of biodegradable waste

into water decreases dissolved oxygen

 Wastewater  water affected by human activities; can be a source of biodegradable wastes

Biodegradable wastes and Sediment



Clear-cutting, mining, clearing land for housing, and

cultivating farm fields expose soil to erosion



It dramatically changes aquatic habitats



Solutions:

 Better management of farms and forests

Thermal pollution

 Water that is too warm causes problems  Warmer water holds less oxygen

 Dissolved oxygen decreases as temperature increases

 Industrial cooling heats water

 Removing streamside cover raises water temperature

 Water that is too cold also causes problems

 Water at the bottom of reservoirs behind dams is colder

Groundwater pollution is a difficult problem



Most pollution control efforts focus on surface water



Groundwater is increasingly contaminated but is

hidden from view and difficult to monitor

 “Out of sight, out of mind”



Groundwater pollution is harder to address than

surface water pollution

 Rivers flush pollutants out, but groundwater retains contaminants for decades and longer

 It takes longer for contaminants to break down

There are many sources of groundwater

pollution



Some toxic chemicals occur naturally



Pollution from human causes is widespread

 Pathogens enter through improperly designed wells



Leaking underground storage tanks are a source of

carcinogenic pollutants from solvents and gasoline

There are many sources of groundwater

pollution



Leaking radioactive waste also pollutes groundwater

storage tanks at the Hanford Nuclear Reservation in Washington were leaking radioactive waste

 Billions of dollars have been spent on remediation



Agricultural pollution comes from several sources

 Pesticides are in most of the shallow aquifers tested

 Nitrates from fertilizers have caused cancer, miscarriages, and “blue-baby” syndrome

Legislative and regulatory efforts have helped

to reduce pollution



Water pollution was worse decades ago

 Citizen activism and government response resulted in legislation during the 1960s and 1970s

 Rivers and lakes are cleaner now



The Federal Water Pollution Control Act (1972)

 Made it illegal to discharge pollution without a permit

 Set standards for industrial wastewater

Legislative and regulatory efforts have helped

to reduce pollution

 Underfunded and understaffed state and federal regulatory agencies succumbed to pressure by

industries and politicians who received money from them

 Violations of the Clean Water Act have risen to over 100,000 documented violations/year

 10% of Americans are unknowingly exposed to unsafe drinking water

 Government action was taken to help the Great Lakes  The water quality of the lakes has dramatically improved

We treat our drinking water



Technology and government regulation have

improved our pollution control

 Treated drinking water is widespread and successful in developed nations



Before water reaches the user, it is chemically

treated, filtered, and disinfected



The EPA sets standards for over 90 drinking water

contaminants

Wastewater Management and Treatment



Development of wastewater collection and treatment

systems



The pollutants in raw wastewater



Removing the pollutants from sewage



Treatment of sludge

Development of Collection and

Treatment Systems.

1. Before modern waste systems most people got rid of their wastes in an outdoor privy(outhouse).

2. Seepage from the privy often would contaminate the drinking water supply. 3. Due to the fact that they had discovered

the link between illness and sewage they started putting the wastes into the stormwater drains.

5. The first treatment of plants for

sewage in the U.S. were built around 1900.

6. As time went on there were

regulations that made cities separate waste water and storm water into two systems.

7. A major feature of the Clean Water Act of 1972 was to allocate many

billions of dollars of federal money for installing and upgrading both

collection systems and sewage-treatment plants.

8. Most developing countries do not have a good system of waste water

Sewage Management and Treatment

A. The Pollutants in Raw Sewage

1. Raw sewage is about 1000 parts water for every 1 part of waste.

2. A community of 100,000 persons will produce on the order of 1.5 to 2.0

million gallons of wastewater each day. 3. There are four categories of pollutants

in raw sewage and they are as follows: a) Debris and Grit- rags, bags, and

other objects flushed and sand and gravel.

b) Particulate Organic Material-food material from garbage disposal and fecal matter.

Removing Pollutants from Sewage:

Match Technology with Function

Technology

Function

Bar Screen

Particulate organics

Grit Screen

Dissolved organics

Primary Treatment

Dissolved inorganics

d) Dissolved inorganic material-include any nutrients that are in solution.

B. Removing the Pollutants from Sewage 1. Preliminary Treatment

a) In preliminary treatment the large material will be screened out using a bar screen or a

rotating screen and then the waste water will go into a settling tank and the large material will settle out and be removed.

2. Primary Treatment

a) The next step is for the water to go into a primary clarifier where the water moves very slowly in this stage the particulate organic material settles out and is removed.

b) Between 30% to 50% of the total organic material settles out.

c) The oils float to the top and are skimmed off and removed.

3. Secondary Treatment

a) Secondary treatment is also called biological treatment because it makes use of organisms to get rid of bad bacteria and other material. b) In order for this step to work well

there must be plenty of oxygen available to the organisms so that they do not go into anaerobic respiration.

c) One of the old ways that

secondary treatment occurs is by a trickling filter. The trickling filter is a place that there are rocks

covered by organisms that will consume the bad material as the water is sprayed over the rocks and trickle over the rock down to

d) The second way for the

secondary treatment to occur is through activated-sludge

systems. This system works by adding air into a chamber along with sludge that contains good bacteria, the bacteria will

Biological Nutrient Removal



Activated sludge: 3 zones



Conversion of NH

to NO



NO

converted to N gas and released

4. Biological Nutrient Removal

a) Denitrification, the removal of nitrogen can take place by

introducing some bacteria to

change the form of nitrogen into a gas, the gas will then leave the system.

b) Phosphate can be removed by having bacteria eat it and the bacteria become part of the activated sludge.

5. Final Cleansing and Disinfection

a) Waste water final trip is through the sand filters and then being treated with chlorine, ozone or ultraviolet light to kill whatever organisms are left alive.

C. Sludge Treatment Options

1. Raw sludge is 97% to 98% water.

2. There are four methods used to treat the sludge and turn it into organic fertilizer. a) Anaerobic Digestion - is a process

Anaerobic Sludge

Digesters

Methane

b) Composting - is a matter of putting raw sludge mixed with wood chips and placing them in windrows and turning them to get oxygen into the system. During this time of six to eight weeks the good bacteria will decompose the sludge and then the wood chips are taken out of the treated sludge and it can be used as a humus like material.

c) Pasteurization and Drying - may be dewatered and then the sludge cake can be put into drying ovens to kill all the remaining pathogens. This can be sold for humus.

D. Alternative Treatment Systems

1. Using Effluents for Irrigation - Water from secondary treatment could be used for irrigation of parks, golf courses, and farms where the nutrients could be used by the plants.

2. Reconstructed Wetland Systems - Water from secondary treatment can be

released into wetlands to have the nutrients absorbed.

3. Artificial Wetland Systems - Fully

4. Greenhouse Wetland Systems - are artificial wetlands that are designed to work inside a greenhouse and produce food from nutrient rich water. These can be run in any climate.

5. Overland Flow Systems - is an

effective cross between irrigation and wetland systems.

E. Individual Septic Systems

1. Where sewage systems are not available you will need to create a

septic system. Septic systems are made of a tank and a drain field as seen in the following figure.

We treat our wastewater

 Wastewater includes water that carries sewage and that from households, manufacturing, stormwater runoff, etc.

 It is treated before being released into the environment

 Septic systems  the most popular method of wastewater disposal in rural areas

 Underground septic tanks separate solids and oils from wastewater

 The water drains into a drain field, where microbes decompose the pollutants



Aerobic digestion of

solids in septic tank.



Flow of liquids into

drain field for

evaporation,

infiltration, or

irrigation.

We treat our wastewater

 In populated areas, sewer systems carry wastewater to treatment locations

 Primary treatment  physically removes contaminants in settling tanks (clarifiers)

 Secondary treatment  water is stirred and aerated  Aerobic bacteria degrade organic pollutants

 Water is treated with chlorine (and/or ultraviolet light) to kill pathogens

 This water, called effluent, is piped into rivers or oceans

We treat our wastewater



Sludge



solid material resulting from treatment of

wastewater

 Is decomposed microbially in digesters

 Resulting “biosolids” are dried then landfilled, incinerated, or used as fertilizer on cropland



Methane-rich gas created by decomposition can be

burned to generate electricity

Constructed wetlands can aid treatment



Natural wetlands have long filtered and purified

water

 Human-constructed wetlands can do the same thing



After primary treatment at a conventional facility

water is pumped into the wetland

Constructed wetlands can aid treatment



Cleansed water is released into waterways or

percolates underground



They are havens for wildlife and for human

recreation

 The United States has over 500 artificially constructed or restored wetlands

Adiabatic heating/cooling



Adiabatic temperature changes occur when

• Adiabatic temperature changes occur when

 Air is compressed

• Motion of air molecules increases

• Air will warm

• Descending air is compressed due to increasing air pressure

 Air expands

• Air parcel does work on the surrounding air

• Air will cool

Adiabatic heating/cooling



Adiabatic temperature changes occur when

• Adiabatic rates

 Dry adiabatic rate

• Unsaturated air

• Rising air expands and cools at 1˚C per 100 meters (5.5˚F per 1000 feet)

Adiabatic heating/cooling



Adiabatic temperature changes occur when

• Adiabatic rates

 Wet adiabatic rate

• Commences at condensation level

• Air has reached the dew point

• Condensation is occurring and latent heat is being liberated

• Heat released by the condensing water reduces the rate of cooling

Processes that lift air



Orographic lifting

• Elevated terrains act as barriers

• Result can be a rainshadow desert



Frontal wedging

• Cool air acts as a barrier to warm air

Processes that lift air



Convergence

where the air is flowing

together and rising (low pressure)



Localized convective lifting

• Localized convective lifting occurs where

Conclusion



Obtaining future supplies of fresh water requires

citizen action, legislation and regulation, technology,

economic incentives, and education



With expanding population and increasing water

usage, we are approaching conditions of widespread

scarcity



Water pollution is already harming health,

economies, and societies of both rich and poor

nations

QUESTION: Review

The picture shows a(n)

a) braided river.

b) meandering river.

c) oxbow.

QUESTION: Review

The area of a lake that rings the edge and contains

rooted plants is called the _______ zone.

a) littoral

b) benthic

c) limnetic

QUESTION: Review

An unconfined aquifer is defined as

a) an aquifer that traps porous rocks between layers of less permeable substrate.

b) an aquifer that traps porous rocks under one layer of less permeable substrate.

c) an aquifer with porous rocks resting on bedrock.

QUESTION: Review

Why do governments subsidize irrigation?

a) It promotes food self-sufficiency.

b) Governments have to or food could not be grown.

c) Governments want to lower water tables.

QUESTION: Review

Which of the following statements

about dams is NOT true?

a) They change habitat.

b) They generate electrical power.

c) They have created more farmland upstream.

QUESTION: Review

Which of the following is a point source of water

pollution?

a) A factory

b) Roads

c) Agricultural fields

QUESTION: Review

Which of the following types of water pollution causes

the most severe human health problems?

a) Nutrient pollution

b) Pathogens

c) Toxic chemicals

QUESTION: Review

Which statement regarding using artificial wetlands to

treat wastewater is NOT correct?

a) Water first undergoes primary treatment.

b) Microbes decompose pollutants.

c) Cleansed water cannot be released into waterways.

QUESTION: Viewpoints

During times of drought, conflicts erupt between

farmers (who need water for irrigation) and ecologists

(who want water left in rivers to protect wildlife). Who

should have the highest priority?

a) Farmers; they need the water for their crops.

b) Wildlife; animals will die without water.

c) Farmers should be paid subsidies to withdraw water from other places.

QUESTION: Weighing the Issues

Should cities in dry areas, such as Las Vegas, be

allowed to increase their populations, so that they will

require more water?

a) Yes; it’s un-American to limit what cities can do.

b) Yes, but make the people pay the true cost of water.

c) Yes, but only if the people are required to use drastic conservation measures.

d) No; enough is enough, and cities in arid

QUESTION: Interpreting Graphs and Data

Which nation has the largest desalination capacity?

a) Japan

b) Russia

c) Saudi Arabia