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Chapter17 - Water Supply Use and Management After covering...

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Water Supply, Use, and Management After covering Ch17, you should understand: Hydrologic Cycle Major H 2 O compartments (a.k.a. reservoirs) How much / where H 2 O is available to humans Types of H 2 O use Freshwater shortages & groundwater depletion How to determine a H 2 O budget Water management, conservation, & consequences Increasing H 2 O supplies Cost & pricing mechanisms that conserve H 2 O
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Water Resources Water covers more than 70% of Earth’s surface; most is ocean, 2.5% is fresh ( most FW is ice and glacier ) Hydrologic cycle : movement of H 2 O among different “reservoirs” driven by energy from the sun that creates winds that facilitate evaporation and precipitation Evaporation : when H 2 O molecules change from liquid to vapor (but not necessarily at boiling point). Allows escape of H 2 O in oceans, lakes, land & plants into the air. Only H 2 O evaporates, impurities are left behind Transpiration : when H 2 O evaporates thru leaves; aids in drawing H 2 O up through roots Sublimation : direct change from solid to gas; snow & ice do this VIMP ! VIMP !
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5 Reservoirs of Water on Earth Ocean Ocean Atmosphere Atmosphere aka infiltration precipitation Groundwater Groundwater Surface & soil Surface & soil Ice Ice
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Major Water Reservoirs Oceans contain more than 97% of all liquid water (FW+SW) contain 90% of world’s living biomass moderate earth’s temperature average residence time of water in the ocean is about 3 - 4,000 years Ice, Glaciers, and Snow ~2% of total water largest FW reservoir; 78% of all FW is “locked up” glaciers (mostly Antarctic), ice caps, and snowfields during most recent ice age (12K YBP), one-third of continental landmasses were covered by glaciers Atmosphere smallest reservoir; < 0.001% of total water most rapid turnover rate (~10 days) mechanism for distributing fresh water over landmasses
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Major Water Reservoirs Groundwater Second largest fresh water reservoir; but only 0.5% ! Infiltration : process of water percolating through the soil and into fractures and permeable rocks; some layers are saturated (all pores are filled w/ H 2 O) Water Table : Top of zone of water saturation Aquifer : porous layers of sand, gravel, or rock lying below the water table - Artesian Spring : place where pressurized aquifer intersects the surface; water flows without pumping Recharge Zone : area where water infiltrates into an aquifer; rate is often very slow - Presently, groundwater is being removed in many areas faster than it can be replenished
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Major Water Reservoirs Surface water : Only 0.02% of FW is above ground Rivers and Streams : precipitation that does not evaporate or infiltrate into the ground runs off the surface, back toward the sea - Discharge is the term used to measure amt of water volume carried by a river Lakes
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