L5 Water Resources and Water Pollution

Freshwater

is relatively pure and contains

few dissolved salts.

• Earth has a precious layer of water—most

of it saltwater—covering about 71% of the

earth’s surface.

• Water is an irreplaceable chemical with

unique properties that keep us and other

forms of life alive. A person could survive

for several weeks without food, but for only

a few days without water.

wasted

Reducing freshwater waste has

many benefits

• An estimated 66% of the freshwater used

in the world is unnecessarily ___.

• In the United States—the world’s largest

user of water—about half of the water

drawn from surface and groundwater

supplies is wasted.

• It is economically and technically feasible

to reduce such water losses to 15%,

thereby meeting most of the world’s water

needs for the foreseeable future.

blue revolution

We need to use water more sustainably

• Each of us can help bring about

such a “__” by

using and wasting less

water to reduce our water

footprints.

Water pollution

is any change in water

quality that harms humans or other living

organisms or makes water unsuitable for

human uses such as drinking, irrigation,

and recreation.

Point sources

discharge pollutants at specific

locations through drain pipes, ditches, or

sewer lines into bodies of surface water.

• Because point sources are located at specific

places, they are fairly easy to identify, monitor, and

regulate.

Nonpoint sources

are broad, diffuse areas,

rather than points, from which pollutants enter

bodies of surface water or air.

• Difficult and expensive to identify and control

discharges from many diffuse sources.

Agricultural activities

are the leading cause of

water pollution, including sediment from

erosion, fertilizers and pesticides, bacteria

from livestock and food-processing wastes,

and excess salts from soils of irrigated

cropland.

Lakes and reservoirs

are generally less effective

at diluting pollutants than streams.

– Deep lakes and reservoirs often contain stratified

layers that undergo little vertical mixing.

– Little or no flow.

• are more vulnerable than

streams to contamination by runoff or discharge

of plant nutrients, oil, pesticides, and

nondegradable toxic substances such as lead,

mercury, and arsenic.

Groundwater pollution

• groundwater

is a serious threat to

human health.

• Common pollutants such as fertilizers,

pesticides, gasoline, and organic solvents

can seep into groundwater from numerous

sources.

• When __ becomes contaminated,

it cannot cleanse itself of degradable

wastes as quickly as flowing surface water

does.

Flows so slowly that contaminants are not

diluted and dispersed effectively.

– Low concentrations of dissolved oxygen and

smaller populations of decomposing bacteria.

– Usually colder so chemical reactions are

slower.

• It can take decades to thousands of years

for contaminated groundwater to cleanse

itself of slowly degradable wastes.

• On a human time scale, nondegradable

wastes remain in the water permanently.

Groundwater cannot cleanse

itself very well

Flows so slowly that contaminants are not

diluted and dispersed effectively.

– Low concentrations of dissolved oxygen and

smaller populations of decomposing bacteria.

– Usually colder so chemical reactions are

slower.

• It can take decades to thousands of years

for contaminated groundwater to cleanse

itself of slowly degradable wastes.

• On a human time scale, nondegradable

wastes remain in the water permanently.

More-developed countries

• have laws establishing drinking water standards. But most

of the less-developed countries do not have

such laws or, if they do have them, they do not

enforce them.

• usually store surface water in a reservoir to increasing dissolved

oxygen content and allow suspended matter to settle, then pumped water to a purification

plant and treat it to meet government drinking water standards.

Protecting a water supply

Very pure groundwater or surface water sources

need little treatment.

•____ is usually a lot

cheaper than building water purification plants.

• We have the technology to convert sewer water

into pure drinking water. But reclaiming

wastewater is expensive and it faces

opposition from citizens and from some health

officials who are unaware of the advances in this

technology.

clear plastic bottle

Simple measures can be used to purify

drinking water:

– Exposing a ___ filled with

contaminated water to intense sunlight can kill

infectious microbes in as little as three hours.

– The Life Straw is an inexpensive portable

water filter that eliminates many viruses and

parasites from water drawn into

Crude and refined petroleum

reach the ocean from a number of sources and become highly

disruptive pollutants.

– Visible sources are tanker accidents and blowouts at

offshore oil drilling rigs.

– The largest source of ocean oil pollution is urban and

industrial runoff from land, much of it from leaks in

pipelines and oil-handling facilities. At least 37% of

the oil reaching the oceans is waste oil, dumped,

spilled, or leaked onto the land or into sewers by cities

and industries, as well as by people changing their

own motor oil.

15%

• Scientists estimate that current cleanup

methods can recover no more than __ of

the oil from a major spill.

• Preventing oil pollution:

– Use oil tankers with double hulls.

– More stringent safety standards and inspections

could help to reduce oil well blowouts at sea.

– Businesses, institutions, and citizens in coastal areas

should prevent leaks and spillage of even the

smallest amounts of oil.

– Primary and secondary sewage treatment systems

help to reduce water pollution

1. growing shortage of freshwater

2. use water more sustainably

3. Reducing water pollution

Three big ideas

• One of the major global environmental problems

is the __ in many

parts of the world.

• We can ___ by cutting

water waste, raising water prices, and protecting

aquifers, forests and other ecosystems that store

and release water.

• Reducing water pollution requires preventing

it, working with nature to treat sewage, cutting

resource use and waste, reducing poverty, and

slowing population growth.

0.024%

is readily available to us as

liquid freshwater in accessible groundwater

deposits and in lakes, rivers, and streams.

• The rest is in the salty oceans, in frozen

polar ice caps and glaciers, or in deep

underground and inaccessible locations.

earth’s hydrologic cycle

not available to us

• The world’s freshwater supply is continually

collected, purified, recycled, and distributed

in the ___, except when:

– Overloaded with pollutants.

– We withdraw water from underground and

surface water supplies faster than it is

replenished.

– We alter long-term precipitation rates and

distribution patterns of freshwater through our

influence on projected climate change.

Some precipitation infiltrates

the ground and percolates downward through spaces

in soil, gravel, and rock until an

impenetrable layer of rock stops this

groundwater—one of our most important

sources of freshwater.

– The zone of saturation is where the spaces

are completely filled with water.

– The top of this groundwater zone is the water

table.

Aquifers

: underground caverns and porous

layers of sand, gravel, or bedrock through

which groundwater flows—typically movings

only a meter or so (about 3 feet) per year and

rarely more than 0.3 meter (1 foot) per day.

– Watertight layers of rock or clay below such

aquifers keep the water from escaping deeper

into the earth.

aquifer

is a body of rock and sediment that’s saturated—water is in it and around it. And water can move through it. It can be made of sand and gravel, sandstone, sandstone and carbonate, and other rocks. Each is made up of permeable material

Surface water

• is the freshwater from

precipitation and snowmelt that flows across

the earth’s land surface and into lakes,

wetlands, streams, rivers, estuaries, and

ultimately to the oceans.

– Precipitation that does not infiltrate the ground

or return to the atmosphere by evaporation is

called surface runoff.

– The land from which surface water drains into a

particular river, lake, wetland, or other body of

water is called its watershed, or drainage basin.

Surface runoff

Additional information

is the flow of water over the land surface, occurring when rainfall, snowmelt, or other water sources exceed the ground's ability to absorb it (due to saturation, impermeable surfaces, or steep slopes). This water moves across the surface into streams, rivers, lakes, or oceans, playing a key role in the water cycle, erosion, and flood events.

Affluent lifestyles

Worldwide, about 70% of the water we

withdraw each year comes from rivers,

lakes, and aquifers to irrigate cropland,

industry uses another 20%, and residences

10%.

• __ require large amounts of

water.

affluent lifestyles

• ways of living characterized by high income, significant material wealth, and substantial consumption of goods, services, and experiences.

• are also criticized for their large environmental footprint (due to high energy use, travel emissions, and resource consumption) and their role in widening social and economic inequali

1. withdrawing groundwater

2. transporting surface water from one area to another

We can increase freshwater supplies by:

– ___; building dams and reservoirs

to store runoff in rivers for release as needed

–___ ; and converting saltwater to freshwater (desalination)

– reducing unnecessary waste of freshwater

collapse

Withdrawing large amounts of groundwater

causes the sand and rock in aquifers to __.

– This causes the land above the aquifer to subside or

sink (land subsidence), referred to as a sinkhole.

– Once an aquifer becomes compressed by

subsidence, recharge is impossible.

– In addition, land subsidence can damage roadways,

water and sewer lines, and building foundations.

1. Dams

2. reservoirs

1. __ are structures built across rivers to block

some of the flow of water.

• Dammed water usually creates a reservoir, a

store of water collected behind the dam.

• A dam and reservoir:

– ___ -a large natural or artificial lake used as

a source of water supply.

– capture and store runoff and release it as needed

to control floods.

– generate electricity (hydroelectricity).

Desalination.

involves removing dissolved

salts from ocean water or from brackish

water in aquifers or lakes for domestic use

Distillation

involves heating saltwater until it

evaporates (leaving behind salts in solid form)

and condenses as freshwater.

Reverse osmosis

(or microfiltration) uses high

pressure to force saltwater through a

membrane filter with pores small enough to

remove the salt.

Floodplains

Some areas sometimes have too much water

because of natural flooding by streams, caused

mostly by heavy rain or rapidly melting snow.

• A flood happens when water in a stream

overflows its normal channel and spills into the

adjacent area, called a floodplain.

• __, which usually include highly

productive wetlands, help to provide natural

flood and erosion control, maintain high water

quality, and recharge groundwater.

Flowing rivers and streams

can recover rapidly from moderate levels of

degradable, oxygen-demanding wastes

through a combination of dilution and

biodegradation of such wastes by bacteria.

• This natural recovery process does not

work when streams become overloaded

with such pollutants or when drought,

damming, or water diversion reduces their

flows.

Eutrophication

refers to the natural nutrient

enrichment of a shallow lake, estuary, or

slow-moving stream usually caused by runoff of

plant nutrients such as nitrates and phosphates

from surrounding land.

biosphere

The oceans hold 97% of the earth’s water, make up

97% of the ___ where life is found, and contain

the planet’s greatest diversity and abundance of life.

• Oceans help to provide and recycle the planet’s

freshwater through the water cycle. They also strongly

affect weather and climate, help to regulate the earth’s

temperature, and absorb some of the massive amounts

of carbon dioxide that we emit into the atmosphere

• Coastal areas—especially wetlands, estuaries, coral

reefs, and mangrove swamps—bear the brunt of our

enormous inputs of pollutants and wastes into the

ocean.

Volatile organic hydrocarbons

in oil and other

petroleum products kill many aquatic organisms

immediately upon contact.

– Other chemicals in oil form tar-like globs that float on

the surface and coat the feathers of seabirds and the

fur of marine mammals. This oil coating destroys their

natural heat insulation and buoyancy, causing many

of them to drown or die of exposure from loss of body

heat.

agriculture

nonpoint-source water pollution, most of

which comes from ___.

– Reduce soil erosion by keeping cropland

covered with vegetation.

– Reduce the amount of fertilizer that runs off

into surface waters and leaches into aquifers

by using slow-release fertilizer, using no

fertilizer on steeply sloped land, and planting

buffer zones of vegetation between cultivated

fields and nearby surface waters.