Ch 15 - Mrs. Fagan's Website · Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings ... publishing as Pearson Benjamin Cummings Ch 15 ... Inc., publishing as

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

PowerPoint® Slides prepared by

Jay Withgott and Heidi Marcum

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Ch 15

Freshwater Resources:

Natural Systems,

Human Impact, and

Conservation

Part 2: Environmental Issues

and the Search for Solutions


Plumbing the Colorado River

• The 2,330 km Colorado River begins in the Rocky Mountains and trickles into the Gulf of California

• Dams and irrigation provide water to millions of people in 7 states

• Las Vegas, Nevada, is growing rapidly, and needs more water

• The other states are allowing Las Vegas to drill for underground water, even though it threatens the area’s ecology and people


Freshwater systems

• Water may seem abundant, but drinkable water is rare

• Freshwater = relatively pure, with few dissolved salts

- Only 25% of Earth’s water is fresh

- Most freshwater is tied up in glaciers and ice caps


Rivers and streams wind through

landscapes

• Water from rain, snowmelt, or springs forms streams, creeks, or brooks

• These merge into rivers, and eventually reaches the ocean

- Tributary = a smaller river slowing into a larger one

- Watershed = the area of land drained by a river and its tributaries


Rivers shape the landscape

• If there is a large bend in the river, the force of the water cuts through the land

- Oxbow = an extreme bend in a river

- Oxbow lake = the bend is cut off and remains as an isolated, U-shaped body of water


A river may shift course

• Floodplain = areas nearest to the river’s course that are flooded periodically

- Frequent deposition of silt makes floodplain soils fertile

• Riparian = riverside areas that are productive and species-rich

• Water of rivers and streams hosts diverse ecological communities


Wetlands include marshes, swamps, and

bogs

• Wetlands = systems that combine elements of freshwater and dry land

• Freshwater marshes = shallow water allows plants to grow above the water’s surface

• Swamps = shallow water that occurs in forested areas

- Can be created by beavers

• Bogs = ponds covered in thick floating mats of vegetation

- A stage in aquatic succession


Wetlands are valuable

• Wetlands are extremely valuable for wildlife

• They slow runoff

- Reduce flooding

- Recharge aquifers

- Filter pollutants

• People have drained wetlands, mostly for agriculture

- Southern Canada and the U.S. have lost more than half of their wetlands


Lakes and ponds are ecologically diverse

• Lakes and ponds are bodies of open, standing water

• Littoral zone = region ringing the edge of a water body

• Benthic zone = extends along the entire bottom of the water body

- Home to many invertebrates

• Limnetic zone = open portions of the lake or pond where the sunlight penetrates the shallow waters

• Profundal zone = water that sunlight does not reach

- Supports fewer animals because there is less oxygen


A typical lake


Lakes vary in their nutrients and oxygen

• Oligotrophic lakes and ponds = have low nutrient and high oxygen conditions

• Eutrophic lakes and ponds = have high nutrient and low oxygen conditions

• Eventually, water bodies fill completely in through the process of succession

• Inland seas = large lakes that hold so much water, their biota is adapted to open water


Groundwater plays a key role

• Groundwater = any precipitation that does not evaporate, flow into waterways, or get taken up by organisms

- Groundwater makes up one fifth of the Earth’s freshwater supply

• Aquifers = Porous sponge-like formations of rock, sand, or gravel that hold groundwater

• Zone of aeration = pore spaces are partially filled with water

• Zone of saturation = spaces are completely filled with water

• Water table = boundary between the two zones

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


A typical aquifer


There are two categories of aquifers

• Confined or artesian = water-bearing, porous rocks are trapped between layers of less permeable substrate (i.e., clay)

- Is under a lot of pressure

• Unconfined aquifer = no upper layer to confine it

- Readily recharged by surface water

• Groundwater becomes surface water through springs or human-drilled wells

• Groundwater may be ancient: the average age is 1,400 years


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 is unequally distributed across Earth’s

surface

• Different regions possess vastly different amounts of groundwater, surface water, and precipitation

• Many areas with high population density are water-poor and face serious water shortages


Water is distributed unevenly in time, too

• Monsoon seasons bring concentrated storms

- Half a region’s annual rain may fall in a few hours

• People erect dams to store water


Climate change will cause water shortages

• Climate change will cause

- Altered precipitation patterns

- Melting glaciers

- Early season runoff

- Intensified droughts

- Flooding

• Increasing probability that there will be still less water for more people


How we use water

• We have achieved impressive engineering accomplishments to harness freshwater sources

- 60 % of the world’s largest 227 rivers have been strongly or moderately affected

- Dams, canals, and diversions

• Consumption of water in most of the world is unsustainable

- We are depleting many sources of surface water and groundwater


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


Different types of water use

• Consumptive use = water is removed from an aquifer or surface water body, and is not returned

• Non-consumptive use = does not remove, or only temporarily removes, water from an aquifer or surface water

- Electricity generation at hydroelectric dams


We have erected thousands of dams

• Dam = any obstruction placed in a river or stream to block the flow of water so that water can be stored in a reservoir

- To prevent floods, provide drinking water, allow irrigation, and generate electricity

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

• Only a few major rivers remain undammed

- In remote regions of Canada, Alaska, and Russia


A typical dam


China’s Three Gorges Dam

• The dam, on the Yangtze River, is the largest in the world

- 186 m (610 feet) high, 2 km (1.3 mi) wide

- Its reservoir stretches for 616 km (385 mi)

- Provides flood control, passage for boats, and electricity


Drawbacks of the Three Gorges Dam

• Cost $25 billion to build

• Is flooding 22 cities and the homes of 1.13 million people

• Submerging 10,000-year-old archaeological sites

• Drowning farmland and wildlife habitat

• Tidal marshes at the Yangtze’s mouth are eroding

• Pollutants will be trapped

• China will spend $5 billion to build sewage treatment plants


Benefits and drawbacks of dams

• Benefits:

- Power generation

- Emission reduction

- Crop irrigation

- Drinking water

- Flood control

- Shipping

- New recreational opportunities

• Drawbacks:

- Habitat alteration

- Fisheries declines

- Population displacement

- Sediment capture

- Disruption of flooding

- Risk of failure

- Lost recreational opportunities


Some dams are being removed

• Some people feel that the cost of dams outweighs their benefits

- They are pushing to dismantle dams

• Rivers with dismantled dams

- Have restored riparian ecosystems

- Reestablished fisheries

- Revived river recreation

• 500 dams have been removed in the U.S.

- Property owners who opposed the removal change their minds once they see the healthy river


Dikes and levees are meant to control floods

• Flooding is a normal, natural process

- Floodwaters spread nutrient-rich sediments over large areas

• Floods also do tremendous damage to property

• Dikes and levees (long, raised mounds of earth) along the banks of rivers hold rising waters in channels

- The U.S. Army Corps of Engineers has constructed thousands of miles of levees

• Levees can make floods worse by forcing water to stay in channels and overflow


We divert – and deplete – surface water

People have long

diverted water to farm

fields, homes, and

cities

The once mighty

Colorado River has

been extensively

dammed and diverted


The Colorado River is heavily diverted

- What water is left after all the diversions comprises just a trickle into the Gulf of California

- On some days, water does not reach the gulf

- Diversion has drastically altered the river’s ecology


The Aral Sea

• Once the fourth-largest lake on Earth

- It has lost more than 80% of its volume in just 45 years

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

• Consequences of a shrinking sea

- 60,000 fishing jobs are gone

- Pesticide-laden dust from the lake bed is blown into the air

- The cotton cannot bring back the region’s economy


Can the Aral Sea be saved?

People may have begun saving the northern part of the Aral Sea


Inefficient irrigation wastes water

• Today, 70% more water is withdrawn for irrigation than in 1960

- The amount of irrigated land has doubled

- Crop yields can double


Most irrigation is highly inefficient

• Only 45% of water is absorbed by crops via “flood and furrow” irrigation

• Overirrigation leads to waterlogging, salinization, and lost farming income

• Most national governments subsidize irrigation

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


Areas where water use exceeds supply


We are depleting groundwater

• Groundwater is easily depleted

- Aquifers recharge slowly

- 1/3 of world population relies on groundwater

• As aquifers become depleted

- Water tables drop

- Salt water intrudes in coastal areas

- Sinkholes = areas where ground gives way unexpectedly

- Some cities (Venice, Mexico City) are slowly sinking

- Wetlands dry up


Will we see a future of water wars?

• 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

• Many nations have cooperated with neighbors to resolve disputes


Solutions can address supply or demand

• We can either increase supply or reduce demand

• Lowering demand

- Politically difficult in the short term

- Offers better economic returns

- Causes less ecological and social damage

• Increasing supply

- Water can be transported through pipes and aqueducts

- It can be forcibly appropriated from weak communities


Desalinization “makes” more water

• Desalinization = the removal of salt from seawater or other water of marginal quality

- Distilling = hastens evaporation and condenses the vapor

- 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, and produces concentrated salty water


The world’s largest reverse osmosis plant

• Near Yuma, Arizona

• Intended to reduce the salinity of irrigation runoff

• Too expensive to operate and closed after 8 months


Agricultural demand can be reduced

• Look first for ways to decrease agricultural demand

- Lining irrigation canals

- Low-pressure spray irrigation that spray water downward

- Drip irrigation systems that target individual plants

- Match crops to land and climate

- Selective breeding and genetic modification to raise crops that require less water


Residential demand can be reduced

• Install low-flow faucets, showerheads, washing machines, and toilets

• Water lawns at night, when evaporation is minimal

• Eat less meat

• Xeriscaping = landscaping using plants adapted to arid conditions


Industrial demand can be reduced

• Shift to processes that use less water

- Wastewater recycling

- Excess surface water runoff used for recharging aquifers

- Patching leaky pipes

- Auditing industries

- Promoting conservation/education


Economic approaches to water conservation

• End government subsidies of inefficient practices

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

• Industrial uses are more profitable than agricultural

- Less developed countries suffer

• Privatization of water supplies

- May improve efficiency

- Firms have little incentive to provide access to the poor

• Decentralization of water control may conserve water

- Shift control to the local level


Freshwater pollution and its control

• Water for human consumption and other organisms needs to be…

- Disease-free

- Nontoxic

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

- They poison surrounding ecosystems

- Threaten the health and livelihood of people

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


Nutrient pollution

• Pollution = the release of matter or energy into the environment that causes undesirable impacts on the health and well-being of humans or other organisms

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

- Leads to eutrophication

• Solutions

- Phosphate-free detergents

- Planting vegetation to increase nutrient uptake

- Treat wastewater

- Reduce fertilizer application


Eutrophication is a natural process, but…

• Human activities dramatically increase the rate at which it occurs


Pathogens and waterborne diseases

• Enters water supply via inadequately treated human waste and animal waste via feedlots

• Causes more human health problems than any other type of water pollution

• Fecal coliform bacteria indicate fecal contamination of water

- The water can hold other pathogens, such as giardiais, typhoid, hepatitis A


Pathogens cause massive human health

problems• Currently, 1.1 billion people are without safe drinking

water

• 2.4 billion have no sewer or sanitary facilities

- Mostly rural Asians and Africans

• An estimated 5 million people die per year

• Solutions:

• Treat sewage

• Disinfect drinking water

• Public education to encourage personal hygiene

• Government enforcement of regulations


Toxic chemicals

• From natural and synthetic sources

- Pesticides, petroleum products, synthetic chemicals

- Arsenic, lead, mercury, acid rain, acid drainage from mines

• Effects include: poisoning animals and plants, altering aquatic ecosystems, and affecting human health

• Solutions:

• Legislating and enforcing more stringent regulations of industry

• Modify industrial processes

• Modify our purchasing decisions


Sediment pollution

• Sediment can impair aquatic ecosystems

- Clear-cutting, mining, poor cultivation practices

- Dramatically changes aquatic habitats, and fish may not survive

- Solutions: better management of farms and forests; avoid large-scale disturbance of vegetation


Thermal pollution

• Warmer water holds less oxygen

- Dissolved oxygen decreases as temperature increases

- Industrial cooling heats water

- Removing streamside cover also raises water temperature

• Water that is too cold causes problems

- Water at the bottom of reservoirs is colder

- When water is released, downstream water temperatures drop suddenly and may kill aquatic organisms


Point and nonpoint source water pollution

• Point source water pollution = discrete locations of pollution

- Factory or sewer pipes

• Nonpoint source water pollution = pollution from multiple cumulative inputs over a large area

- Farms, cities, streets, neighborhoods

• The U.S. Clean Water Act

- Addressed point sources

- Targeted industrial discharge

• In the U.S., nonpoint sources have a greater impact on quality

- Limit development on watershed land surrounding reservoirs


Freshwater pollution sources


Indicators of water quality

• Scientists measure properties of water to characterize its quality

- Biological indicators: presence of fecal coliform bacteria and other disease-causing organisms

- Chemical indicators: pH, nutrient concentration, taste, odor, hardness, dissolved oxygen

- Physical indicators: turbidity, color, temperature


Groundwater pollution is a serious problem

• Groundwater is increasingly contaminated, but is hidden from view

- Difficult to monitor

- Out of sight, out of mind

- Retains contaminants for decades and longer

- Takes longer for contaminants to breakdown in groundwater because of the lower dissolved oxygen levels


Sources of groundwater pollution

• Some toxic chemicals occur naturally

- Aluminum, fluoride, sulfates

• Pollution from human causes

- Wastes leach through soils

- Pathogens enter through improperly designed wells

- Hazardous wastes are pumped into the ground

- Underground storage septic tanks may leak


Agriculture and industries pollute

groundwater

• Agricultural pollution

- Nitrates from fertilizers

- Pesticides were detected in more than half of the shallow aquifers tested

• Manufacturing industries and military sites have been heavy polluters


Legislative efforts reduce pollution

• Federal Water Pollution Control Act (1972)

- Renamed the Clean Water Act in 1977

- Illegal to discharge pollution without a permit

- Standards for industrial wastewater

- Funded sewage treatment plants

• Because of legislation, the situation is much better than it was

• Other nations have also reduced pollution


We treat our drinking water

• Technology has improved our pollution control

• The EPA sets standards for more than 80 drinking water contaminants

- Local governments and private water suppliers must meet

• Before water reaches the user

- It is chemically treated, filtered, and disinfected


It is better to prevent pollution

• It is far better to prevent groundwater contamination than correct it

• Other options are not as good:

- Removing just one herbicide from water costs $400 million

- Pumping, treating, and re-injecting it takes too long

- Restricting pollutants above aquifers would shift pollution elsewhere

• Consumers can purchase environmentally friendly products

- Become involved in local “river watch” projects


Treating wastewater

• Wastewater = water that has been used by people in some way

- Sewage, showers, sinks, manufacturing, storm water runoff

• 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 water

- Solid waste needs to be periodically pumped and landfilled


Municipal sewer systems

• In populated areas, sewer systems carry wastewater

- Physical, chemical, and biological water treatment

• Primary treatment = the physical removal of contaminants in settling tanks (clarifiers)

• Secondary treatment = water is stirred and aerated so aerobic bacteria degrade organic pollutants

- Water treated with chlorine is piped into rivers or the ocean

- Some reclaimed water is used for irrigation, lawns, or industry


A typical wastewater treatment facility


Artificial wetlands

• Natural and artificial wetlands can cleanse wastewater

- After primary treatment at a conventional facility, water is pumped into the wetland

- Microbes decompose the remaining pollutants

- Cleansed water is released into waterways or percolated underground

• Constructed wetlands serve as havens for wildlife and areas for human recreation

- More than 500 artificially constructed or restored wetlands exist in the U.S.


Conclusion

• Obtaining future supplies of freshwater will be an environmental challenge

• With expanding population and increasing water usage, we are approaching conditions of widespread scarcity

• Water pollution is already harming freshwater around the world

• New approaches can help this situation


QUESTION: Interpreting Graphs and Data

What is the relationship between water consumption and the amount of land that is irrigated?

a) Irrigation has grown more

slowly than demand

b) Irrigation and demand

have both increased

c) Growth of demand and

irrigation will slow

d) The U.S. does not follow

this graph


QUESTION: Interpreting Graphs and Data

Which conclusion can you draw from this graph?

From The Science behind the Stories

a) It is more water efficient to

produce vegetables

b) It is more water efficient to

produce meat

c) Vegetable and meat production

are relatively alike in water

consumption

d) There is little correlation

between water consumption and

our diet

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Ch 15 - Mrs. Fagan's Website · Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings ... publishing as Pearson Benjamin Cummings Ch 15 ... Inc., publishing as