CHAPTER 15

All end of chapter questions due on Tuesday, February 19th

Lecture Outlines

Chapter 15

Environment:The Science behind the Stories

4th Edition

Withgott/Brennan

This lecture will help you understand:• Water’s importance to

people and ecosystems• Water’s distribution• Use and alteration of

freshwater systems• Problems of water supply

and solutions• Problems of water quality

and solutions• How wastewater is

treated

Freshwater systems• Water may seem abundant, but drinkable water is rare• Freshwater = relatively pure, with few dissolved salts

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

Water is renewed and recycled as it moves through the hydrologic cycle

Wetlands are valuable• Wetlands are extremely valuable for wildlife

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

• People have drained wetlands, mostly for agriculture– Southern Canada and the U.S. have lost over half of their

wetlands• In 2006 the Supreme Court told the Army Corps of

Engineers it must create guidelines to determine when wetlands are valuable enough to protect by law

The Colorado River• The Colorado River originates

in the Rocky Mountains– Draining into the Gulf of

California• Its waters chiseled the Grand

Canyon– But it has been reduced to a

mere trickle• Dams provide flood control,

recreation, and hydroelectric power– 30 million people use the

water (7 states) Death of a River

We are depleting surface water• In many places, we are withdrawing water at

unsustainable rates– Reduced flow drastically changes the river’s ecology,

plant community, and destroys fish and invertebrates

The Colorado River often does not reach the Gulf of California

Groundwater plays a key role• Groundwater = water beneath the surface held

in pores in soil or rock– 20% of the Earth’s freshwater supply

• Aquifers = porous, sponge-like formations of rock, sand, or gravel that hold water – Zone of aeration = pore spaces are partly filled with

water – Zone of saturation = spaces are filled with water– Water table = boundary between the two zones

• Recharge zone = any area where water infiltrates Earth’s surface and reaches aquifers

A typical aquifer

The Ogallala Aquifer

• The world’s largest known aquifer

• Underlies the Great Plains of the U.S.

Its water has allowed farmers to create the most bountiful grain-producing region in the world

Water supplies houses, agriculture, and industry

• Proportions of these three types of use vary dramatically among nations– Arid countries use water for agriculture– Developed countries use water for industry

• Consumptive use = water is removed from an aquifer or surface water body and is not returned – Irrigation = the provision of water to crops

• Nonconsumptive use = does not remove, or only temporarily removes, water– Electricity generation at hydroelectric dams

The Aral Sea• 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 from the lake

bed is blown into the air• Cotton cannot save the region’s

economy

Irrigation wastes water• 15–35% of water withdrawals for irrigation are

unsustainable

• Water mining = withdraws water faster than it can be replenished

We are depleting groundwater• Groundwater is easily depleted

– Aquifers recharge slowly– Used by one-third of all people

• As aquifers are mined, water tables drop– Salt water intrudes in coastal areas

• Sinkholes = areas where ground gives way unexpectedly– Aquifers can’t recharge

• Wetlands dry upWhere subsidence is happening

Desalinization “makes” more 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• Desalinization facilities operate mostly in the arid

Middle East– It is expensive, requires fossil fuels, kills aquatic life,

and produces salty waste

Agricultural demand can be reduced• Line irrigation canals• Level fields to reduce runoff• Use efficient irrigation methods

Modern Irrigation methods may save rivers

– Low-pressure spray irrigation sprays water downward– Drip irrigation systems target individual plants

• Match crops to land and climate• Eliminate water subsidies• Selective breeding and genetic modification to

produce crops that require less water• Eat less meat

Residential demand can be reduced• Install low-flow faucets,

showerheads, washing machines, and toilets

• Rainwater harvesting = capturing rain from roofs

• Gray water = wastewater from showers and sinks

• Water lawns at night• We can save hundreds or

thousands of gallons/dayXeriscaping uses plants adapted to arid conditions

Industrial demand can be reduced

• Shift to processes that use less water– Wastewater recycling

• Use excess surface water runoff to recharge aquifers• Patch leaky pipes and retrofit homes with efficient

plumbing• Audit industries• Promote conservation/education

Nutrient pollution• Nutrient pollution from fertilizers, farms, sewage, lawns,

golf courses leads to eutrophication• Fertilizers add phosphorus to water, which boosts algal and

aquatic plant growth• Spreading algae cover the surface, decreasing sunlight• Bacteria eat dead algae, reducing dissolved oxygen• Fish and shellfish die

• Solutions include treating wastewater• Reducing fertilizer application• Using phosphate-free detergents• Planting vegetation to increase nutrient uptake

Eutrophication is a natural process, but…

• Human activities dramatically increase the rate at which it occurs

Pathogens and waterborne diseases• Enter water supplies through inadequately treated

human waste and animal waste from feedlots• Fecal coliform bacteria indicate fecal contamination

– They are not pathogenic organisms– But the water may also hold other disease-causing

pathogens (e.g., giardiasis, typhoid, hepatitis A)• Bacterial pollution causes more human health problems

than any other type of water pollution• Conditions are improving• 86% of people now have safe water

Pathogens cause human health problems

• 1 billion are still without safe water• 2.6 billion have inadequate sewer or sanitary

facilities- Mostly rural Asians and Africans

• Health impacts kill 5 million people per year• Solutions:

- Disinfect drinking water- Treat sewage- Public education to encourage personal hygiene- Government enforcement of regulations protecting food

Make sure to reveiw

• toxic pollution• thermal pollution• sediment pollution

Legislative efforts reduce pollution• Water pollution was worse decades ago

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

– The situation is much better now• The Federal Water Pollution Control Act (1972)

– Renamed the Clean Water Act in 1977– It is illegal to discharge pollution without a permit– Sets standards for industrial wastewater– Funded sewage treatment plants