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.

oWater 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 Watero Surface water is contained within watersheds.o Surface water = water found on Earth’s surfaceo 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.

—Groundwatero 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

oWhere the water table naturally rises to the surface a spring is created.

o Groundwater can burst to the surface as a geysero 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 Watero Fresh water is used for agricultural, industrial, and

personal activitiesoMost fresh water is used for agricultureoMost manufacturing and industrial processes

require water

oWhen 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 Watero 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 Groundwatero 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.

oMost irrigation is very inefficient because a lot of water is lost to runoff and evaporation. Too much water can lead to waterlogging and

salinization

oWithdrawing 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 Depletiono 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 Pollutiono 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 Pollutiono 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 Pollutiono 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.

oMercury 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 Pollutiono 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

oWater 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 facility2. Screens and Grit Tank: solid objects and grit are

removed and disposed at a landfill3. 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