Water Chapter 15 Water Wars Water shortage Growing population Poor irrigation efficiency Economic competition- importing more grain to reduce need for irrigation water or work out water-sharing agreements with other countries Unique Properties of Water Strong hydrogen bonds Liquid over wide temperature range High heat capacity – changes temperature slowly (moderates climate, used as coolant for car engine & power plants) Large amount of energy needed to evaporate – heat is then released during condensation (helps distribute heat & determine climate zones; evaporation/sweating = cooling process) Dissolves many substances- dissolves nutrients in living tissue, flush waste out of tissues, all-purpose cleanser, helps remove/dilute water-soluble waste Filters out UV radiation that would harm aquatic organisms Bonds – allow capillary action – water can move upward through plants Expands when frozen= ice floats; prevents lakes & streams from freezing solid Available Freshwater Only 0.014% is available for useh Water Cycle Surface runoff- water flowing off the land into bodies of surface water Reliable runoff- amount of run-off that we can generally count on as a stable source of water Watershed (drainage basin)- region from which surface water drains into a river, lake, wetland, or other body of water Groundwater- water stored in spaces in soil & rock Zone of aeration- close to surface; pore space contains mixture of air & water Zone of saturation- lower layers of soil where pore space is filled with water Water table- top of zone of saturation Aquifer- (deep) porous, water-saturated layers of sand, gravel, or bedrock through which groundwater flows Natural recharge- natural replenishment of an aquifer by precipitation, which percolates downward through soil & rock Shortages result from: Removing groundwater faster than it is replenished Some aquifers receive little, if any recharge Water Use Withdrawal- total amount of water removed from lake, river, or aquifer for any purpose Consumptive water use- withdrawn water is not available for reuse in basin due to losses like evaporation, seepage into ground, transportation to another area, or contamination Water Use Population- up 3x Global water withdrawal- up 7x Per capita withdrawal- up 4x Reliable surface runoff used- 34% Used by 2025- 70% (90% if per capita rises too) Irrigation- 70% Industry- 20% Residences & cities- 10% Eastern U.S. Major water use- energy production, cooling, & manufacturing Problems- flooding, occasional urban shortages, pollution Western U.S. Major water use- irrigation Problems- shortage of runoff, low precipitation / high evaporation, recurring prolonged drought Causes of Water Scarcity Dry climate Drought- prolonged period with 70% less precipitation & higher than normal evaporation Dessication- drying of exposed soil due to deforestation or overgrazing Water stress- low per capita availability due to high population relying on limited runoff Increase Freshwater Supply Build dams & reservoirs to store runoff Bring in surface water from another area Desalinization Reduce water waste Import food to reduce water use in crops & cattle Withdraw groundwater Government Ownership - Poor management & efficiency + Strict government oversight + Equal access & fair rates Private Ownership + Funds & management expertise + Improved efficiency, good job - No rate control - Profitable - Sold as a luxary, not basic need Downstream cropland and Flooded land estuaries are destroys forests deprived of or cropland and nutrient-rich silt displaces people Large losses of water through Downstream evaporation flooding is reduced Provides water for year-round irrigation of cropland Reservoir is Can produce Migration and Figure 15-9 useful for recreation and fishing cheap electricity (hydropower) spawning of some fish are disrupted Page 313 Colorado River Dams + Provides electricity from numerous hydroelectric plants + Provides water for 7 states + Multibillion dollar recreational industry (whitewater rafting, boating, fishing, camping, hiking) - Arid area - Legal pacts allocating water supply for US & Mexico - River water rarely makes it to Guld of California - Threatens aquatic spawning - Destroys estuaries - Increases saltwater contaminated coastal aquifers Trade-Offs China’s Three Gorges Dam Advantages Disadvantages Will generate about 10% Floods large areas of of China’s electricity cropland and forests Reduces dependence Displaces 1.9 million people on coal Increases water pollution Reduces air pollution because of reduced water flow Reduces CO2 emissions Reduces deposits of nutrient- rich sediments below dam Reduces chances of downstream flooding for 15 million people Increases saltwater Introduced into drinking water Figure near mouth of river because Reduces river sitting below dam by eroded soil of decreased water flow 15-11 Disrupts spawning and Increases irrigation water migration of some fish below dam Page for cropland below dam High cost 315 Aral Sea Water Transfer Project Shrinking of Aral Sea Regional ecological, economic, health disaster Salinity 3x higher Surface area down 58% 83% water loss Feeder rivers reduced to trickles Eliminates wetlands Birds & mammal species disappeared Extinction of 20 (of 24) native fish species Salt dust settles on wildlife, crops, & other vegetation California Water Transfer Project NORTH SOUTH Degrade Sacramento Need more water to River grow crops Threatens fisheries Lakes shrink = reduced Reduces flushing of populations of ducks, San Francisco Bay gulls, & wading birds pollutants Water sent South is wasted James Bay in Canada - 600 dams & dikes that will reverse or alter flow of 19 giant rivers - Will flood boreal forests & tundra - Displace of indigenous Cree & Inuits + Hydroelectric power Trade-Offs Withdrawing Groundwater Advantages Disadvantages Good source of water for Aquifier depletion from over- drinking and irrigation pumping Sinking of land (subsidence) Available year-round when water removed Polluted aquifiers unusable Exists almost everywhere for decades or centuries Saltwater intrusion into Renewable if not over- drinking water supplies near pumped or contaminated coastal areas Reduced water flows into No evaporation losses streams, lakes, estuaries, and wetlands Cheaper to extract than Increased cost, energy use, most surface waters and contamination from deeper wells Figure 15-15 Page 319 Excessive Withdrawal Unsustainable water mining Limits future food production Increases gap between rich & poor areas Must drill deeper wells, buy larger pumps, & use more electricity Causes sinkholes Saltwater Intrusion Movement of salt water into freshwater aquifers in coastal & inland areas as groundwater is withdrawn faster than it is recharged by precipitation Groundwater becomes unusable Ogallala Aquifer + Transformed vast areas of arid prairie into productive agricultural land - Slows recharge rate - Aquifer is thinner for southern region - Government subsidies increased crop production & increases depletion of aquifer Solutions Groundwater Depletion Prevention Control Waste less water Raise price of water to discourage waste Subsidize water conservation Ban new wells in aquifiers near surface waters Tax water pumped Buy and retire ground- from Wells near water withdrawal rights in critical areas surface water Figure Do not grow water- intensive crops in dry 15-18 areas Set and enforce Reduce birth rates minimum stream flow levels Page 320 Deep Aquifer Concerns: Little known about geological & ecological impacts of using these aquifers No international water treaties govern the rights to & ownership of water that underlies several countries Desalinization - High cost - Large energy requirements - Large amounts of briny waste water - Dumping of waste increases salinity of ocean water (food resources & aquatic life threatened) + Make ocean water or brackish water usable Seeding Clouds Does not work well in very dry areas No scientific evidence of success Introduces large amounts of chemicals into soil & water systems (harms people, wildlife, & agricultural productivity) Ownership of cloud water Iceberg Towing Unsure methods Cost Probably neither (iceberg towing or cloud seeding) would provide significant amounts of freshwater Wasted Water 65-70% of world water is wasted Could be reduced to 15% Causes: Underpricing- government subsidies for irrigation water, electricity, & diesel fuel for farmers to pump water at below-market price Lack of government subsidies for improving efficiency of water use Irrigation Systems Center pivot- uses pump to spray water on crops 80% efficient Uses 25% less water Drip irrigation- microirrigation- above or below ground pipes or tubes deliver water to individual plant roots 90-95% efficient Gravity flow- water flow into ditches from aqueduct or nearby river 60-80% efficient Figure 15-20 Page 324 Center Pivot (efficiency 80% with low- Drip Irrigation pressure (efficiency 90-95%) sprinkler and 90–95% with Gravity Flow LEPA sprinkler) (efficiency 60% and 80% with surge Above- or below-ground pipes valves) or tubes deliver water to Water usually pumped from individual plant roots. underground and sprayed from Water usually comes from an mobile boom with sprinklers. aqueduct system or a nearby river. Solutions Reducing Irrigation Water Waste •Lining canals bring water to irrigation ditches •Leveling fields with lasers •Irrigating at night to reduce evaporation •Using soil and satellite sensorsand computer systems to monitor soil moisture and add water only when necessary •Polyculture •Organic Farming Figure •Growing water-efficient crops using drought- resistant and salt tolerant crops varieties 15-21 •Irrigating with treated urban waste water Page •Importing water-intensive crops and meat 324 Solutions Reducing Water Waste •Redesign manufacturing processes •Landscape yards with plants that require little water •Use drip irrigation •Fix water leaks •Use water meters and charge for all municipal water use •Use waterless composting toilets Figure •Require water conservation in water-short cities •Use water-saving toilets, showerheads, and front- 15-22 loading clothes washers •Collect and reuse household water to irrigate lawns Page and nonedible plants •Purify and reuse water for houses, apartments, and 325 office buildings Reducing Water Used to Remove Waste Use pollution prevention & waste reduction to decrease waste production Ban toxic wastes in municipal sewer system Waterless composting toilet Nutrient-rich sludge returned to soil as fertilizer New sewage treatment methods that recycle nutrients in organic waste material Floods + Fertile soils + Ample water for irrigation + Rivers for transportation & recreation + Flat land suitable for crops, buildings, highways, & railroads - Removal of water-absorbing vegetation Increasing Flood Damage Removal of water-absorbing vegetation Draining wetlands Living on floodplains Pavement & buildings Bangladesh Straighten & deep streams Build levees or floodwalls Build dams Preserve existing wetlands & restore degraded wetlands Identify & manage flood-prone areas Think carefully about where we live Solutions Figure Sustainable Water Use • Not depleting aquifers 15-26 • Preserving ecological health of aquatic systems Page • Preserving water quality • Integrated watershed management 329 • Agreements among regions and countries sharing surface water resources • Outside party mediation of water disputes between nations • Marketing of water rights • Raising water prices • Wasting less water • Decreasing government subsides for supplying water • Increasing government subsides for reducing water waste • Slowing population growth What Can You Do? Water Use and Waste Figure • Use water-saving toilets, showerheads, and faucet aerators • Shower instead of taking baths, and take short showers. 15-27 • Repair water leaks. Page • Turn off sink faucets while brushing teeth, shaving, or washing. 330 • Wash only full loads of clothes or use the lowest possible water-level setting for smaller loads. • Wash a car from a bucket of soapy water, and use the hose for rinsing only. • If you use a commercial car wash, try to find one that recycles its water. • Replace your lawn with native plants that need little if any watering. • Water lawns and garden in the early morning or evening. • Use drip irrigation and mulch for gardens and flowerbeds. • Use recycled (gray) water for watering lawns and houseplants and for washing cars.
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