Water: A Vital Resource 71% of Earth’s surface is covered with water – 97.5% of this volume is salt water of the oceans and seas – The remaining 2.5% is fresh water – water with a salt concentration of less than 0.1%. 1.97% of fresh water is frozen in ice caps and glaciers 0.5% is located as groundwater 0.03% is surface water (lakes, rivers, streams) or water vapor in our atmosphere.
Hydrologic Cycle Earth’s water cycle, also called the hydrologic cycle consists of – Water rising to the atmosphere through evaporation and transpiration Transpiration – loss of water vapor as it moves from the soil through green plants and exits through leaf stomata. – Water returning to thee land and oceans through condensation and precipitation
Properties of Water Weak attraction known as hydrogen bonding tends to hold water molecules together – Polar molecule – one end is slightly positive, one end is slightly negative Below 32 o F (0 o C) – water freezes; 212 o F, (100 o C) water boils.
Polarity in H 2 O: The Water Molecule O HH ++ -- covalent bond
Penny Activity How many drops of water do you think will fit on a penny? – Write down your hypothesis: _______________ – Write down actual number: ________________ – Draw what your penny looked like : – Why do you think this occurred?
Natural Filter The Hydrologic cycle naturally purifies water – When water in an ocean or lake evaporates, only the water molecules leave the surface; the dissolved slats and other solids remain behind in solution – When water vapor condenses again, it is purified water – except for the pollutants and other aerosols it make pick up from the air Aerosol – microscopic liquid or solid particles originated from land and water surfaces.
Ground Water As precipitation hits the ground, it may either soak into the ground (infiltration) or run off the surface. – The amount that soaks in compared with the amount that runs off is called the infiltration-runoff ratio. Runoff flows over the surface of the ground into streams and rivers, which make their way to the ocean or inland seas. – All the land that contributes water to a particular stream or river is referred to as the watershed
Ground Water Has Two Options – May be held in soil – capillary water Will return to the atmosphere by evaporation through the soil, or through transpiration through plants EVAPOTRANSPIRATION – Percolation Water that is not held in soil is called gravitational water because it trickles down through pores or cracks until it reaches an impervious layer of rock or clay
Ground Water Once gravitational water reaches the impervious rock layer it accumulates – Rock formations that contain groundwater are called aquifers Confined aquifers – has impervious rock layer above water (artesian aquifer) Unconfined aquifer – upper layer coincides with the water table Recharge zone – Area above an aquifer that replenishes the water
Natural Filter As water percolates through the soil, debris and bacteria from the surface are filtered out May also dissolve and leach out certain minerals – In most cases, the minerals that leach into groundwater are harmless Exceptions – sulfide, arsenic
Closure How much of our Earth’s surface is covered with water? How much of that water is salty?
Warm-up Discuss how freshwater is distributed among our earth
Human Impact on the Hydrologic Cycle A large share of the environmental problems we face today stem from direct or indirect impacts on the water cycle. These impacts can be classified into four categories – Changes to Earth’s surface – Floods – Changes to Earth’s climate – Atmospheric pollution – Withdrawals for human use
Water Uses and Sources Nonconsumptive vs. Consumptive – Nonconsumptive Most of the water used in homes and industries Used for washing and flushing away unwanted materials, or for cooling water in electric power generation – The water will be contaminated with wastes and will remain available for human use if adequate treatment is used.
Water Uses and Sources Nonconsumptive vs. Consumptive – Consumptive Example – irrigation The applied water does not return to the water resource – It is allowed to percolate into the ground or return to the atmosphere through evapotranspiration
Water Uses Worldwide Largest use of water is for irrigation (agriculture) – 70% Second is for industry – 20% Third is for direct human use (municipal) – 10% Water use will differ depending on natural precipitation and the degree to which the region is developed
Trends in Population and Freshwater Withdrawals, U.S.
Municipal Water Use and Treatment What is your community’s water source? (field trip to well 11!)
Dams & Reservoirs Pros Ensure year-round supply of water in areas that have seasonal precipitation Reservoirs control flow of water Generation of hydropower Provide flood control Provide recreational activities on reservoirs. Cons Heavy deposition of sediment upstream Disrupts ecosystems Adversely affects fish population Disrupts flow of river downstream Dam failures
Warm Up What is the difference between consumptive and non-consumptive uses of water? List the three main uses for water world wide. Circle the one that takes the most water
Consequences of Overdrawing Groundwater Falling water tables Diminishing surface waters (wetlands) Land subsidence Saltwater intrusion
Ogallala Aquifer Within seven-state High Plans region of the United States – Supplies region with irrigation water More than 3/4ths of the groundwater on earth is stored in this aquifer Takes centuries to recharge aquifer – Considered a nonrenewable aquifer because water is being drawn faster than can be recharged
Saltwater Intrusion In coastal regions, springs of out-flowing ground water may lie under the ocean As long as the water table is high, there is enough pressure in the aquifer so that fresh water will flow into the ocean If water table lowers, pressure is lost and the ocean will flow backwards into the aquifer
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