Download Chapter 14: Water Resources

Chapter 14: Water Resources
Lesson 1: Earth: The Water Planet
—Where is Our Water?
o As a natural resource, fresh water is renewable.
However, quantities of fresh water on Earth are
limited.
o Water is considered a renewable resource
because the water cycle constantly recycles it.
o Fresh water is water that is relatively pure with
few dissolved salts
 About one half of one percent is fresh, liquid water
that we can use.
—Surface Water
o Surface water is contained within watersheds.
o Surface water = water found on Earth’s surface
o Runoff is water that flows over land and has not
been absorbed into the ground.
o A watershed includes all of the land area that supplies
water to a particular river system.
 Sometimes called drainage basins
 Major watershed regions in the United States include
the Colorado River, Mississippi River, Pacific Northwest,
Great Lakes, Great Basin, California, and Atlantic Slope.
 Watersheds are interconnected, for example the Ohio
River watershed is a part of the Mississippi River
watershed.
 Managing water sustainably requires the cooperation
of everyone living within the watershed.
—Groundwater
o Water found below Earth’s surface is called
groundwater.
o Ground water makes up about one fifth of Earth’s
freshwater supply.
o Ground layers containing pores through which water
can pass are called permeable.
o Layers with few or no pores are called impermeable.
o Water soaks through permeable layers until it reaches
an impermeable layer, then the water begins to fill up
then available spaces.
o Aquifers are sponge-like formations of
rock, sand, or gravel that hold water.
 The zone of aeration is an aquifer’s
upper layer that contains pores
through which water can flow
 The zone of saturation is an aquifer’s
lower layer that contains spaces
completely filled with water
 Water table is the boundary between
the two zones
• Depth is affected by the shape of the
land and the amount of water available.
 Any area where surface water soaks
into the ground and reaches an
aquifer below is called the recharge
zone
o Where the water table naturally rises to the
surface a spring is created.
o Groundwater can burst to the surface as a geyser
o A hole dug into an aquifer to reach groundwater is
called a well.
 Dug deep into the zone of saturation so that it
does not dry out
Lesson 2: Uses of Fresh Water
—How We Use Water
o Fresh water is used for agricultural, industrial, and
personal activities
o Most fresh water is used for agriculture
o Most manufacturing and industrial processes
require water
o When an individual uses water directly (ex:
drinking, laundry) it is referred to as a personal
use.
 Many personal uses occur inside the home, so
they are sometimes called residential uses.
—Using Surface Water
o Because of overuse, surface water resources are
being depleted.
o The process of moving water from its source to
places where humans use it is called water
diversion.
 Ex: irrigation canal
o A dam is any obstruction placed in a river or stream to
block its flow in order to help regulate flow and build
a stable supply of water.
 Create artificial reservoirs – large lakes that store
water for human use.
 Costs include habitat alteration, fisheries decline,
population displacement, sediment capture, loss of
fertile farmland, risk of failure, and lost
recreational opportunities.
 Benefits include clean power generation, crop
irrigation, flood control, shipping, and new
recreational opportunities.
o Drought and overuse have significantly reduced
surface water resources
 Rivers that are heavily diverted can sometimes
run dry
 The Aral Sea in Asia was once the fourth largest
freshwater body on Earth but has lost 90% of
its volume since 1960.
—Using Groundwater
o Ground water is being used, primarily for
irrigation, faster than it can be replenished.
o About 26% of the fresh water used in the US
comes from groundwater and 68% of that is used
for irrigation.
o Most irrigation is very inefficient because a lot of
water is lost to runoff and evaporation.
 Too much water can lead to waterlogging and
salinization
o Withdrawing groundwater faster than it can be
replaced is called groundwater mining.
 Turns groundwater into a nonrenewable
resource
 Many aquifers are being drained as
groundwater is mined
o As aquifers are depleted, water tables drop
 In coastal areas, salt water can move into
aquifers
 The land surface above the aquifer man
subside, or sink
 Causes wetlands to dry up
—Solutions to Freshwater Depletion
o Addressing freshwater depletion will largely depend
on strategies that decrease water demand.
o One strategy is to increase water supply by “making”
more fresh water by removing salt from seawater; this
approach is called desalination, or desalinization.
 Desalination machine
• Heats seawater until the water evaporates, leaving the
salt behind.
• Water vapor is condensed into liquid fresh water
 Filtering
• Water is forced through artificial membranes to
filter out salts
• Most common filtering process is called reverse
osmosis
 Process is expensive, requires a lot of energy,
and produces a concentrated, salty waste.
o To reduce the demand for fresh water, agriculture,
industry, and individuals need to implement water
conservation practices.
 Agricultural solutions
• Selecting climate-appropriate crops
• Drip irrigation systems target individual plants and
introduce water directly into the soil, reducing
water lost to evaporation and runoff.
 Industrial solutions
• Industries are looking at new processes that require
less water
• Some manufacturing plants have made agreements
with cities to recycle their wastewater
• Recycling water within plant processes
 Personal solutions
• Xeriscaping chooses outdoor plants that are
adapted for arid conditions and requires much less
water to maintain landscaping.
• Low-flow toilets, appliances, and faucets can help
reduce water use.
Lesson 3: Water Pollution
—Types of Water Pollution
o There are many different kinds of water pollution,
each with its own sources and effects.
o Point-source pollution comes from distinct locations,
such as a factory or sewer pipe.
o Nonpoint-source pollution comes from many places
spread over a large area, such as runoff from farms,
lawns, and streets.
o Major categories of pollution include nutrient
pollution, toxic chemical pollution, sediment
pollution, thermal pollution, and biological pollution.
o Nutrient Pollution
 Bodies of water that have a high nutrient
content and low oxygen content are called
eutrophic
 Many healthy aquatic ecosystems are
eutrophic, but nutrient pollution by humans
can speed up the eutrophication process with
negative effects
 Eutrophication process
• Occurs naturally when nutrients build up
in a body of water, usually phosphorus
• When nutrients build up, the growth rate
of algae and aquatic plants increases
• More growth leads to more
decomposition as the algae and plants die
• Decomposition requires oxygen, so the
levels of dissolved oxygen in the water
decrease
• The result is a body of water that is high
in nutrients and low in oxygen.
• As a natural process it takes a long time,
sometimes centuries.
 Cultural eutrophication (or artificial eutrophication)
is when nutrient pollution by humans drastically
increases the rate at which eutrophication occurs.
• Phosphorus pollution mostly comes from nonpoint
sources such as phosphorus-rich fertilizers and
detergents carried in runoff or wastewater.
• Wastewater is water that has been used by people in
some way.
• Excess nutrients cause sudden explosions of algal growth
called algal blooms.
o Can be so thick that they cover the water’s surface
and prevent sunlight from reaching plants below
o Toxic-Chemical Pollution
 Toxic chemicals are released during many
industrial and manufacturing processes.
 Can be organic or inorganic chemicals:
• Organic chemicals are found in petroleum, plastics,
pesticides, and detergents.
• Inorganic chemicals include heavy metals such as
mercury, arsenic, and lead.
 Toxic chemicals can poison aquatic animals and
plants as well as cause a wide variety of human
health problems.
o Sediment Pollution
 Sediment transported by rivers and runoff can
harm aquatic ecosystems.
 When large amounts of sediment enter a river it
can cause rates of photosynthesis to decline, food
webs to collapse, and degrade water quality.
 Sediment pollution is the result of erosion
o Thermal Pollution
 Occurs when water temperature is artificially
changed
• When water is used for cooling in industrial
processes it absorbs a lot of heat and is then
returned to its source.
 The warmer water is, the less oxygen it can
hold
 Harms aquatic organisms that cannot tolerate
increased water temperatures or decreased
oxygen
o Biological Pollution
 When disease-causing organisms and viruses,
called pathogens, make their way into our air,
soil, and water, it is called biological pollution.
 Causes more human health problems than any
other type of water pollution
 The best way of decreasing biological water
pollution is to treat water and waste with
chemicals or other substances that kill the
disease-causing organisms.
 Some common pollutants and diseases
•
•
•
•
•
Vibrio cholera bacteria = Cholera
Shigella dysenteriae bacteria = Dysentery
Escherichia coli bacteria = E.coli infection
Giardia lamblie protozoa = Giardiasis
Schistosoma haematobium flatworm =
Schistosomiasis
• Salmonella typhi bacteria = Typhoid fever
—Groundwater Pollution
o It can take decades to clean up groundwater
pollution, so every effort should be made to
prevent it from occurring.
o Some chemicals that are toxic at high
concentrations occur naturally in groundwater.
o Groundwater pollution from human activity is
widespread
 Many pollutants enter groundwater from the
surface
o Chemicals break down much more slowly in
aquifers than they do in surface water.
 Groundwater generally contains less dissolved
oxygen, microbes, minerals, and organic matter,
so decomposition is slower than it is in surface
water or soils.
o The U.S. Environmental Protection Agency has
been working on a nationwide cleanup program to
locate and repair leaky gasoline tanks.
 To prevent future leaks, new sewage and gas
tanks are built with strong materials such as
fiberglass that don’t break down as easily as
the plain steel used in older tanks.
—Ocean Water Pollution
o Oceans are polluted with oil, toxic chemicals, and
nutrients that run off from land.
o Oil pollution
 Major oil spills cause serious environmental
problems
 A lot of oil pollution in the oceans comes from
many widely spread small sources such as
leakage from small boats.
 Naturally occurring deposits on the sea floor
are called oil seepage
• Largest single source of oil in the oceans
 Oil can physically coat and kill marine
organisms and can poison them when ingested.
o Mercury pollution
 Marine pollution can make some fish and
shellfish unsafe for people to eat.
 Mercury is a toxic heavy metal that collects in
the tissues of animals and makes its way up the
food chain by biomagnifications.
• Organisms at high trophic levels can contain high
levels of mercury
 Mercury can cause neurological damage,
especially in fetuses, babies, and children.
o Nutrient pollution
 Increased amounts of nitrogen does the most
damage in oceans
 One type of algal bloom is nicknamed red tide
because the algae produce reddish pigments.
 Some red tides and other harmful algal blooms
release powerful toxins that cause illness and
death among zooplankton, fish, marine
mammals, birds, and humans.
—Controlling Water Pollution
o Government regulation and water treatment are
two ways of decreasing the effects of water
pollution.
o The Clean Water Act
 The Federal Water Pollution Control Act (renamed
the Clean Water Act in 1977) remains the single
most important law to prevent water pollution in
the US
 Made it illegal to release pollution from a point
source without a permit
 Set standards for pollution levels in surface waters
and industrial wastewater
 Funded construction of sewage treatment plants
o Water Treatment
 The EPA set standards for more than 80
drinking water contaminants
 Drinking water Treatment:
1. Filtrations: water is filtered through screen to
remove large solids
2. Coagulation: chemicals added to the water cause
small suspended solids to form clumps that then
also sink to the bottom of the tank.
3. Settling: water flows into large tanks; remaining
solids settle to the bottom and are pumped out.
4. Second Filtration: water is filtered again, usually
by fine grained sand, to remove any remaining
solids.
5. Chlorination: chlorine is added to kill and
remaining harmful organisms.
6. Aeration: air is forced through the water and
bacteria are added to break down organic matter
and remove bad smells.
7. Additional Treatment: additional chemicals may
be added to decrease the mineral content of the
water and fluoride may be added to help prevent
tooth decay.
 Concentrated amounts of wastewater can harm
ecosystems and pose threats to human health.
 In more densely populated areas, sewer
systems carry wastewater from homes and
businesses to centralized treatment locations.
• The treated water, called effulent, is piped into
rivers, reservoirs, or the ocean
• Water that is not released to a body of surface
water is called reclaimed water and might be used
for irrigation or to cool power plants.
 Waste water Treatment:
1. Raw sewage enters the treatment facility
2. Screens and Grit Tank: solid objects and grit are
removed and disposed at a landfill
3. Primary Clarifier: Oils, greases, and solids are
removed; sludge is sent to anaerobic digester.
o The anaerobic digester is a tank full of bacteria
that decompose waste.
• The gas produced is used to generate electricity
• Products used as fertilizer for cropland
4. Aeration Basin: oxygen is added to encourage
bacteria to decompose organic matter; sludge is
sent to anaerobic digester.
5. Secondary Clarifier: remaining oils, greases, and
solids removed; sludge is sent to anaerobic
digester.
6. Filtering and Disinfection: water may be filtered
with coal and sand, disinfected with chlorine or
exposed to UV light
7. Effluent is discharged into waterways
 In rural areas, septic systems are the most
popular method of waste-water disposal.
1. Wastewater runs through a pipe from the house
to an underground septic tank where bacteria
begin to break down wastes.
2. Denser wastes that break down slowly sink to the
bottom of the tank, forming sludge that must be
pumped out.
3. Less-dense wastes that break down slowly, such
as oils, build up at the top of the tank, forming
scum that must be pumped out.
4. Water and wastes that have broken down travel
to a gravel field where microbes decompose the
remaining organic material in the wastewater.
5. Cleansed water eventually makes its way into
aquifers