Freshwater Resources

1
Freshwater Resources

• Chapter 15

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Freshwater

• Water that is relatively pure, with very few
  dissolved salts
• Freshwater occurs in
• Lakes, rivers, streams, groundwater, glaciers,
  rainwater, soil, water vapor in the atmosphere
• (In contrast, ocean water is salty because salts
  from land run into it and stay there as surface
  water evaporates.)

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Freshwater

• Only 2.5 of the planets water is freshwater.
• And only 1 of that exists on Earths surface.
• Only 1 part in 10,000 of water is easily
  accessible for drinking and irrigation.

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Where is the Freshwater?

• Rivers and streams
• Wetlands
• Lakes and Ponds
• Groundwater

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Groundwater

• Water beneath Earths surface that did not
  evaporate, flow into rivers, or get taken up by
  organisms
• Groundwater is contained in aquifers, porous
  spongelike layers of rock, sand, or gravel.
• Water table boundary between the upper zone of
  aeration and the lower zone of saturation

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Aquifers

• Confined or artesian aquifer water under
  pressure, trapped within impermeable layers
  (often clay)
• Unconfined aquifer water under less pressure
  no overlying impermeable layer
• Aquifer recharge zone geographic area where
  water infiltrates soil and recharges aquifer

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Groundwater and aquifers
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Freshwater distribution

• Global freshwater distribution is very uneven.
• Rainfall varies from nearly zero up to 1,200
  centimeters (470 inches)/year.
• Canada has 20 times as much water per citizen as
  does China.

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Available freshwater resources

• Nations vary by more than a factor of 100 inches
  of water per capita.

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Available freshwater resources

• Asia has lots of water but very little water per
  capita.
• Australia has lots of water per capita but little
  water overall.

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Water Use

• Consumptive use water is removed from an
  aquifer or surface body, and not returned (e.g.,
  most agricultural, industrial, and residential
  use)
• Nonconsumptive use removal of water is only
  temporary (e.g., passing water through a
  hydroelectric dam)

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Biggest Issue is Depletion and Pollution of
Freshwater
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Solutions for depletion Desalination

• Desalination or desalinization removal of salt
  from seawater to create freshwater
• Perfecting this technology would mean the oceans
  could provide us with unlimited freshwater.
• But so far, it is expensive!
• Most of the worlds 7,500 desalination plants are
  in wealthy oil states of the Middle East, where
  water is scarce enough to make desalination
  economically feasible.

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Solutions for depletion Reducing demand

• In AGRICULTURE
• Use high-efficiency irrigation techniques
• Line irrigation canals to prevent leaks
• Level fields to reduce runoff
• Choose crops appropriate to climate
• Eliminate government subsidies of inappropriate
  crops and methods
• New GM crops?

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Solutions for depletion Reducing demand

• In the INDUSTRIAL and MUNICIPAL sectors
• Shift to processes that save water (and thus
  money)
• Invest in repairing pipe leaks
• Recycle gray wastewater

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Solutions for depletion Reducing demand

• In the RESIDENTIAL sector (what YOU can do)
• Install low-flow faucets and appliances
• Use automatic dishwashers
• Replace lawns with native vegetation
• If you keep lawns, water them at night
• Recycle gray wastewater

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Solutions for depletion Economic approaches

• Market-based strategies
• End government subsidies of inefficient practices
• Make water a commodity whose price reflects its
  costs
• Privatize water supplies
• Decentralize control over water
• Many of these strategies risk increasing the gap
  between rich and poor

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Freshwater pollution

• Over half of the worlds major rivers are
  seriously depleted and polluted, degrading and
  poisoning the surrounding ecosystems, threatening
  the health and livelihood of people who depend on
  them.
• World Commission on Water, 1999
• Groundwater pollution is extensive but invisible,
  a covert crisis.

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Water pollution point and non-point sources
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Urban Runoff organic waste is largest single
pollutant
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Types of pollution Eutrophication

• Excess runoff of nutrients like nitrogen and
  phosphorus leads to blooms of algae or
  phytoplankton
• and then microbial decay that sucks oxygen from
  the water
• (e.g., the hypoxic zone in the Gulf of Mexico)

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Eutrophication
Oligotrophic water body Low-nutrient high-
oxygen conditions
Eutrophic water body High-nutrient, low-oxygen
conditions
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Types of pollution Pathogens

• Waterborne disease from viruses, bacteria, etc.,
  contributes to 5 million deaths per year.
• In 2002, 1.1 billion people were still without
  safe water supplies.
• 2.4 billion people had no sewer or sanitation
  facilities.
• 4/5 of people without sanitation lived in rural
  areas.

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Types of pollution Toxic chemicals

• Many thousands of chemicals we manufacture find
  their way into our water, where some have toxic
  effects.
• Pesticides
• Petroleum products
• Arsenic, lead, mercury, other metals
• Acids from mining runoff and acid precipitation

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Types of pollution Sediment

• Erosion of soil from mining, clear-cutting, real
  estate development, and farming puts sediment
  into waterways.
• There it alters conditions and can kill organisms.

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Types of pollution Heat and cold

• Yes, even heat and cold can pollute!
• Organisms not adapted to the new temperature
  conditions can suffer or die.
• Warm water from power plants decreases
  dissolved oxygen.
• Clearing streamside vegetation also warms
  water.
• Cold water is released below dams, harming
  native fish.

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Indicators of water quality

• Scientists use biological properties to measure
  water quality
• Presence of pathogens disease-causing
  organisms may be present, making water risky for
  drinking

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Indicators of water quality

• Scientists use chemical properties to measure
  water quality
• Nutrient concentrations
• pH waters acidity or alkalinity
• Taste and odor can show presence of certain
  chemical contaminants
• Hardness hard water has high concentrations of
  salts
• Dissolved oxygen content indicates suitability
  for life high D.O. generally good for organisms

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Indicators of water quality

• Scientists use physical properties to measure
  water quality
• Turbidity density of suspended particles
  water with sediments from erosion is turbid
• Color indicates tannins and other chemicals
• Temperature aquatic organisms sensitive to
  temperature warm water holds less dissolved
  oxygen

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Groundwater pollution

• Worse than surface water pollution, because it is
  longer lasting
• (e.g., persistent toxicants get washed out of
  rivers, but remain in groundwater until they
  break down.)

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Groundwater pollution

• Sources are both natural and anthropogenic.

• NATURAL SOURCES
• Arsenic
• Aluminum
• Fluoride
• Nitrates
• Sulfates

• HUMAN SOURCES
• Leaky underground storage tanks (oil, gas,
  industrial chemicals, septic waste)
• Nitrates from fertilizers
• Pesticides
• Pathogens from wells and feedlots
• Contamination from underground hazardous waste
  disposal
• Industrial chemical waste
• Compounds from military sites

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Sources of groundwater contamination
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Pollution prevention

• Drinking water is treated before it reaches your
  tap.
• But it is easier and more cost effective to
  prevent pollution than to mitigate it once it
  occurs.

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What is waste water treatment?

• Municipal and industrial sewage
• Water has been changed because of addition of
  suspended solids, salts, nutrients, bacteria, or
  other oxygen-demanding material

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What is BOD?

• Biological Oxygen Demand the amount of oxygen
  needed by bacteria to decompose the organic
  material in the water
• Indirectly, is a measure of organic matter in
  water
• The higher the BOD, the more organic matter in
  the water

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Waste Water Treatment in Rural Areas

• Septic Tanks
• Problems
• Septic tank is full of solids so bacteria cant
  work (needs to be emptied)
• Leach lines dont release water due to
• Soil compacted, or impermeable, or tree roots
  have clogged the lines

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Waste Water Treatment in Cities

• Centralized Municipal Treatment Plant
• There are 3 steps in the process

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Primary Treatment

• Removes 30 to 40 of the suspended solids and
  organic matter
• Screens remove large pieces of floating organic
  matter
• Grit chambers where sand small stones are
  removed
• Sedimentation tank where smaller particles can
  settle out, forming a sludge. The sludge is
  combed out and transported elsewhere

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Secondary Treatment

• The waster water from the primary treatment goes
  into an aeration tank. Sometimes called
  activated sludge tank. Air may be pumped in.
  Aerobic bacteria consume organic material
• The wastewater than goes into the final
  sedimentation tank
• Waste water is disinfected with chlorine gas
• Water is released into lake, river, ocean or
  recycled

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Advanced Waste Water Treatment

• If the water coming out of the Secondary
  Treatment process still contains pollutants, then
  another level of treatment is required
• Nitrates are removed by charcoal filters
• Heavy metals are removed by sand and grit filters
• Disinfected with chlorine or UV light

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What to do with the treated waste water?

• Discharge in river or ocean
• Use it for irrigating crops, landscape, golf
  courses
• Settling ponds to recharge aquifers

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What to do with the sludge?

• Further decomposition with bacteria also produces
  methane which can be use as fuel source
• Recycle sludge and use to seed in primary
  treatment
• Dry sludge and put in landfill or burn

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What to do with storm drain water?

• Mostly remains untreated and just flows into the
  ocean. Contains oil, metals, pesticides, home
  fertilizers, detergents

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Natural sites of Water Treatment

• Wetlands, marshes serve as natural areas of
  treatment

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• Virtual Water Treatment Plant Tour