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This lecture will help you understand:. Water and the hydrologic cycle Water’s distribution on Earth Freshwater ecosystems Use and alteration of freshwater systems Problems of water supply and solutions Problems of water quality and solutions How wastewater is treated.

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this lecture will help you understand
This lecture will help you understand:
  • Water and the hydrologic cycle
  • Water’s distribution on Earth
  • Freshwater ecosystems
  • Use and alteration of freshwater systems
  • Problems of water supply and solutions
  • Problems of water quality and solutions
  • How wastewater is treated
plumbing the colorado river
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
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
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
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
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 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 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 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
lakes vary in their nutrients and oxygen
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 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
there are two categories of aquifers
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 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
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
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 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
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
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
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
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
china s three gorges 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
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

Power generation

Emission reduction

Crop irrigation

Drinking water

Flood control


New recreational opportunities


Habitat alteration

Fisheries declines

Population displacement

Sediment capture

Disruption of flooding

Risk of failure

Lost recreational opportunities

Benefits and drawbacks of dams
some dams are being removed
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
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
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
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
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
Can the Aral Sea be saved?

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

inefficient irrigation wastes water
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
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
we are depleting groundwater
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
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
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 “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
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
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
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
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
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
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
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
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 and waterborne diseases
pathogens cause massive human health problems
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
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 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
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 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
indicators of water quality
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 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
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
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
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
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 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
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
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
artificial wetlands
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.
  • 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 review

The picture shows a(n) … ?

a) Estuary

b) Wetland

c) Oxbow lake

d) River delta

question review1

The area of a lake that contains open water that does not receive sunlight is called the _______zone.

a) Littoral

b) Benthic

c) Limnetic

d) Profundal

question review2

A confined aquifer is defined as…?

  • An aquifer that traps porous rocks between layers of less permeable substrate
  • An aquifer that traps porous rocks under one layer of less permeable substrate
  • An aquifer with porous rocks resting on bedrock
  • An aquifer with no upper layer
question review3

Arid countries tend to use their water mostly for…?

  • Developing industries
  • Agriculture
  • Households
  • Export to rich countries
question review4

Which of the following statements is not a benefit of dams?

  • Habitat alteration
  • Power generation
  • Crop irrigation
  • Shipping
question review5

Pollution is defined as “the release of matter or energy into the environment that causes ______”?

  • Undesirable impacts on human health
  • Undesirable impacts on other organisms
  • Undesirable impacts on human well-being
  • All of the above are included in the definition
question review6

Which of the following is a nonpoint source of water pollution?

  • A factory
  • Sewer pipes
  • Agricultural fields
  • All are nonpoint sources
question review7

Primary treatment of wastewater includes…?

  • Treating water with chemicals
  • Stirring and aerating water
  • Degradation of wastes by bacteria
  • Physical removal of contaminants
question interpreting graphs and data
QUESTION: Interpreting Graphs and Data
  • Irrigation has grown more slowly than demand
  • Irrigation and demand have both increased
  • Growth of demand and irrigation will slow
  • The U.S. does not follow this graph

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

question interpreting graphs and data1
QUESTION: Interpreting Graphs and Data

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

Which conclusion can you draw from this graph?

From The Science behind the Stories

question viewpoints
QUESTION: Viewpoints

In 2001, angry farmers disobeyed a federal order to divert irrigation water downstream to save endangered species of fish. What should happen to the farmers?

  • Nothing; they need the water for their crops
  • They should be fined for breaking the law
  • They should be paid subsidies so they can continue farming
  • They should be paid to plant different crops that do not require so much water
question viewpoints1
QUESTION: Viewpoints

Should cities in dry areas such as Las Vegas be allowed to increase their populations, so that they will require more water?

  • Yes; it’s not the American way to limit what cities can do
  • Yes, but the people will have to pay the true cost of water
  • Yes, but only if the people are required to use drastic conservation measures
  • No; enough is enough, and cities in arid environments simply cannot continue growing