AP Environmental Science - The Bio Edge - Home · Water! Composed of 2 Hydrogen and 1 oxygen! Exists as solid, liquid or gas! Polar! Forms Hydrogen bond between 2 water molecules!

AP Environmental

Science

Unit OneSunday, August 30, 15

GLOBAL WATER:

RESOURCES and USE

Sunday, August 30, 15

Properties of Water


Water

! Composed of 2 Hydrogen and 1 oxygen

! Exists as solid, liquid or gas

! Polar

! Forms Hydrogen bond between 2 water molecules

! H-bonds define water’s physical properties


Properties of Water:“high heat capacity” hydrogen bonds are strong and as a result can absorb large amounts of energy before the kinetic energy of the molecules increase “high heat vaporization” is similar but relates to breaking bonds

“universal solvent” the polarity of water attracts and surrounds other charged atoms/molecules

“high surface tension, cohesion, adhesion” the charges on water from strong intramolecular bonds between themselves (cohesion) and other charged compounds (adhesion)


“solid form is lighter” water is most dense at 4 degrees Celcius because water expands to form crystalline structure of ice (molecules farther apart)

Water has a “high heat of vaporization” to absorb energy as it changes states/phases.

Sunlight penetrates water to variable depths, permitting photosynthetic organisms to live below the surface.

“polar” unequal sharing of electrons between oxygen and hydrogen atoms

Water can exist in three states/phases: liquid, solid, gas


Importance of Water


Importance of Water! Water is medium for all chemical reactions

solvent, buffer

! Water moderates temps of organisms and their environments

evaporative cooling, insulation, temp moderation

! Water can move between cells, through organisms and the environment

diffusion, osmosis, water cycle, lake turnover


Importance of Water! Cooking & washing

! Agriculture

! Manufacturing

! Mining

! Energy production

! Waste disposal

! Use of freshwater is increasing


Water Cycle


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Hydrologic Cycle


Compartments of Water


Distribution of Water

! Only 2.5% of water on earth is freshwater

! 2% is in the form of ice!

! Only ~0.5% of water on earth is available freshwater


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The Oceans are a Major Water Compartment

• #1. Oceans• The oceans play a major role in moderating

earth’s climate.!Ocean currents moderate the climate by redistributing warm and cold water around the earth like a global ocean conveyor belt.

• 90% of the earth’s biomass is found in the oceans.


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Frozen Water Compartments• #2. Glaciers, Ice, and Snow

!2.4% of world’s water is classified as fresh.- 90% in glaciers, ice caps, and snowfields

" Now, Antarctic glaciers contain nearly 85% of all ice in the world.

" Greenland, together with ice floating around the North Pole, is another 10%.


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Ground Water Compartments" #3. Ground water " Infiltration - process of water percolating through the

soil and into fractures and permeable rocks#Zone of aeration - upper soil layers that hold both air and water

#Zone of saturation - lower soil layers where all spaces are filled with water" Water table - top of zone of saturation

–Locations where surface waters move into the ground are recharge zones

–Places where it flows or seeps out are discharge zones (points)


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Infiltration


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#Zone of aeration - upper soil layers that hold both air and water

#Zone of saturation - lower soil layers where all spaces are filled with water

" Water table - top of zone of saturation

–Locations where surface waters move into the ground are recharge zones

–Places where it flows or seeps out are discharge zones (points)


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• Aquifers - porous layers of sand, gravel, or rock lying below the water table!Artesian - Pressurized aquifer intersects the surface

(water flows without pumping).

• Recharge zones - area where water infiltrates into an aquifer!Recharge rate is often very slow.

- Presently, groundwater is being removed faster than it can be replenished in many areas.


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Lakes and Ponds are Water Compartments

• #4. Lakes and PondsLakes are inland depressions that hold standing

fresh water year-round.!Ponds are generally considered small bodies of

water shallow enough for rooted plants to grow over most of the bottom.

- Both ponds and lakes will eventually fill with sediment, or be emptied by an outlet stream.


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The Atmosphere: Water Compartment

• #5. The Atmosphere!Among the smaller water reservoirs

- Contains < 0.001% of total water supply

- Has most rapid turnover rate

- Provides mechanism for distributing fresh water over landmasses and replenishing terrestrial reservoirs


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Wetlands are Water • #6. Wetlands

!Play a vital role in hydrologic cycle- Lush plant growth stabilizes soil and retards surface runoff, allowing more aquifer infiltration.

#Disturbance reduces natural water-absorbing capacity, resulting in floods and erosion in wet periods, and less water flow the rest of the year.

#Half of U.S. wetlands are gone.


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River & Streams Are Water Compartments

• #7. Rivers and Streams!Precipitation that does not evaporate or infiltrate into

the ground runs off the surface, back toward the sea.

- Best measure of water volume carried by a river is discharge..The amount of water that passes a fixed point in a given amount of time

" Usually expressed as cubic feet per second


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Major Rivers of the World


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Major Water Compartments• The distribution of water across the earth is often

described as interacting water compartments.

• Water may reside briefly in one compartment of stay there for eons.

• The length of time water typically spends in a compartment is called the Residence Time.

• For example, the Average residence time of water in the ocean is about 3,000 years before the water evaporates and enters the hydrologic cycle.!see handout to practice calculating ART


Interactions Between Surface Water and Groundwater

Should be considered part of the same resource.

Nearly all surface water environments have linkages w/ ground water

E.g. withdrawal of groundwater can lower stream flow or lake levels

Pollution can spread from one source to the other

predict linkages for each number on the next slide!



Water: Availability

and UseSunday, August 30, 15

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Water Supplies are Unevenly Distributed

• Rain falls unevenly across the earth’s surface. Some areas receive practically no precipitation and other areas receive heavy rain on a daily basis.

• Three principal factors control global water deficits and surpluses:

!Global atmospheric circulation

!Proximity to water sources

!Topography


Water UseOff-stream use

Refers to water removed from its source for use

May be returned to source after use

Or consumptive use- water enters tissues, product or evaporates during use and not returned

In-stream use

The use of the river for navigation, hydroelectric power, fish and wildlife habitats, and recreation.

Multiple uses can create controversy


Another problem with off stream use is how much water can be removed w/o damaging the stream ecosystem.

E.g. Aral Sea. Diverting water for agriculture caused sea to dry up

Surface area of sea reduces 90% in 50 years

WATER USE





Ancient civilizations constructed canals and aqueducts to transport water

From distant river to where it is needed

In modern civilization water moved from areas of abundant rain and snow fall to areas of high usage

E.g. California moves water from north to south

E.g. New York City has had to obtain water from farther and farther away

TRANSPORTING WATER


Trends in freshwater withdrawals by water-use categories suggests that:

The major uses of water are for irrigation and the thermoelectric industry.

SOME TRENDS IN WATER


Water use by thermoelectric industry decreased slightly in 1980, and stabilized in 1985.

Due to reticulating water for cooling

Water use for irrigation increased from 1950-1980. It decreased and leveled off from 1985-2000

due to better irrigation efficiency, crop type and higher energy costs.

Water for public and rural supplies continued to increase through the period from 1950 to 2000

presumably related to the increase in human population.


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Typical Household Water Use in U.S.



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Water Use is Increasing• Many societies have always treated water as an

inexhaustible resource.

!Natural cleansing and renewing functions of hydrologic cycle do not work properly if systems are overloaded or damaged

!Renewal of water takes time

!Rate at which we are now using water makes conservation necessary


Water: Availability


Water supply

at any point on the land surface depends on several factors in the hydrologic cycle,

precipitation, evaporation, transpiration

Water budget

A model that balances the inputs, outputs, and storage of water in a system.

Precipitation - evaporation = runoff

Runoff- the excess precipitation, in broad terms the water available for human use

WATER SUPPLY: (EX.U.S.)


Amount of water vapor passing over the US every day ~ 152,000 million m3

10% falls as precipitation (66% of which is evaporated or transpired)

Only 34% enters surface or groundwater

WATER SUPPLY: (EX.U.S.)


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• Renewable Water Supplies

!= surface runoff + infiltration into accessible freshwater aquifers

#Readily accessible, renewable supplies are only about 400,000 gal /person/year.

Water Availability


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• Every continent has regions of scarce rainfall due to topographic effects or wind currents.

!The United Nations considers 264,172 gallons per person per year to be the minimum necessary to meet human needs.

!Water Stress occurs when human and ecosystem needs outstrip the renewable water supplies.

Water Scarcity & Stress


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!Withdrawal - total amount of water taken from a source

!Consumption - fraction of withdrawn water made unavailable for other purposes (not returned to its source)

!Degradation - Change in water quality due to contamination making it unsuitable for desired use. Much water that is not consumed is nevertheless polluted.

Water Use


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• Human water use has been increasing about twice as fast as population growth over the past century, but impact varies with location.

!Canada withdraws less than 1% of its renewable supply per year.

! In Israel, groundwater and surface water withdrawals equal more than 100% of the renewable supply. Obviously, this is not sustainable.

!U.S. uses 20% of renewable water/yr.

Quantity of WaterUse


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• Worldwide, domestic water use accounts for about 20% of water withdrawals.!Only about 10% of consumption

- But where sewage treatment is unavailable, water is degraded

• Industry accounts for 20% of global freshwater withdrawals.!Range from 5% to 70% in various locations

- Small proportion is consumed, but degradation is a problem

Domestic & Industrial Water Use


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• Water use is divided into agriculture, domestic use and industrial use.

• Worldwide, agriculture claims about two-thirds of total water withdrawal and 85% of consumption..

!The Aral Sea was once the fourth largest inland body of water in world, but it has now lost 80% of its volume since 1975 as the water was diverted for irrigation of rice and cotton crops.

!Lake Chad is another example. Located in northern Africa, this lake went from 400,000 sq. km to less than 1,000 sq. km.

Agriculture: Largest Consumer of Water


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! Irrigation can be inefficient.

!Flood or furrow irrigation (bad)- Half of water can be lost through evaporation.- Flood irrigation used to remove salts from field, but salt contaminates streams

!Sprinklers have high evaporation. (bad)

!Drip irrigation releases water near roots, conserving water. (good)

Water Use in Agriculture


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Water Withdrawal and Consumption

~60% ~20% ~20%

~World Wide Withdrawals


AP Environmental Science - The Bio Edge - Home · Water! Composed of 2 Hydrogen and 1 oxygen! Exists as solid, liquid or gas! Polar! Forms Hydrogen bond between 2 water molecules!

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