Water and Water Pollution Chapter 11
Key Concepts • Why is water so important? • How much water is available? • How much water are we using? • What causes water shortages and what can be done? • What causes floods and how can they be avoided? • Sources, types, and risks of water pollution • Preventing and reducing water pollution • Sustainable use of water resources
Groundwater Systems Unconfined Aquifer Recharge Area Evaporation and transpiration Evaporation Precipitation Confined Recharge Area Runoff Flowing artesian well Recharge Unconfined Aquifer Stream Well requiring a pump Water table Lake Infiltration Infiltration Unconfined aquifer Less permeable material such as clay Confined aquifer Confiningimpermeable rock layer Fig. 11-3, p. 239
Annual Precipitation and Water-deficit Regions of the Continental US Fig. 11-4a, p. 240
Annual Precipitation and Water-deficit Regions of the Continental US Average annual precipitation (centimeters) Less than 41 81-22 More than 122 41-81 Fig. 11-4a, p. 240
Annual Precipitation and Water-deficit Regions of the Continental US Acute shortage Shortage Adequate supply Metropolitan regions with population greater than 1 million Fig. 11-4b, p. 240
Water Hot Spots in Western States Wash. N.D. Montana Oregon S.D. Idaho Wyoming Neb. Nevada Colo. Utah Kansas California Oak. N.M. Texas Highly likely conflict potential Substantial conflict potential Moderate conflict potential Unmet rural water needs Fig. 11-5, p. 240
Freshwater Shortages • Causes of water scarcity: dry climate and too many people • Stresses on world’s major river systems • 1 of 6 people have no regular access to clean water • Poverty hinders access to water • Hydrological poverty
Stress on World’s River Basins Europe North America Asia Africa South America Australia Stress High None Fig. 11-6, p. 241
Hydrological Poverty Fig. 11-7, p. 241
Politics and Ethics of Water • Who should pay for the water? • Public or private ownership
Increasing Freshwater Supplies • Dams and reservoirs • Extracting groundwater • Desalination • Reducing water waste • Importing food • Importing water • Catching precipitation
Tradeoffs of Large Dams and Reservoirs Large losses of water through evaporation Flooded land destroys forests or cropland and displaces people Migration and spawning of some fish are disrupted Downstream cropland and estuaries are deprived of nutrient-rich silt Provides water for year-round irrigation of cropland Reservoir is useful for recreation and fishing Can produce cheap electricity (hydropower) Downstream flooding is reduced Fig. 11-8, p. 243
Ecological Services of Rivers N a t u r a l C a p i t a l Ecological Services of Rivers • Deliver nutrients to sea to help sustain coastal fisheries • Deposit silt that maintains deltas • Purify water • Renew and renourish wetlands • Provide habitats for wildlife Fig. 11-9, p. 243
California Water Project and Central Arizona Project CALIFORNIA NEVADA Shasta Lake UTAH Oroville Dam and Reservoir Sacramento River Lake Tahoe Feather River North Bay Aqueduct Sacramento San Francisco Hoover Dam and Reservoir (Lake Mead) South Bay Aqueduct Fresno San Joaquin Valley San Luis Dam and Reservoir Colorado River Los Angeles Aqueduct California Aqueduct ARIZONA Colorado River Aqueduct Santa Barbara Central Arizona Project Los Angeles Phoenix Salton Sea San Diego Tucson Fig. 11-10, p. 244 MEXICO
Shrinking Aral Sea Fig. 11-11, p. 245
Stranded Ship at the Aral Sea Fig. 11-12, p. 245
Tradeoffs of Withdrawing Groundwater Trade-Offs Withdrawing Groundwater Advantages Disadvantages Good source of water for drinking and irrigation Available year-round Exists almost everywhere Renewable if not over- pumped or contaminated No evaporation losses Cheaper to extract than most surface waters Aquifier depletion from over- pumping Sinking of land (subsidence) when water removed Polluted aquifiers unusable for decades or centuries Saltwater intrusion into drinking water supplies near coastal areas Reduced water flows into streams, lakes, estuaries, and wetlands Increased cost, energy use, and contamination from deeper wells Fig. 11-13, p. 246
Aquifer Depletion Groundwater Overdrafts: High Moderate Minor or none Fig. 11-14, p. 246
Saltwater Intrusion into Coastal Water Wells Well contaminated with saltwater Major irrigation well Water table Sea Level Saltwater Fresh groundwater aquifer Seafloor Interface Saltwater Intrusion Interface Normal Interface Fig. 11-15, p. 247
Groundwater Depletion Solutions Groundwater Depletion Prevention Control Raise price of water to discourage waste Tax water pumped from Wells near surface water Set and enforce minimum stream flow levels Waste less water Subsidize water conservation Ban new wells in aquifiers near surface waters Buy and retire ground- water withdrawal rights in critical areas Do not grow water- intensive crops in dry areas Reduce birth rates Fig. 11-16, p. 247
Desalination • Removal of salts from ocean or brackish waters to produce useable water • Distillation method • Reverse osmosis method • Used in 120 countries • Major problems: high cost and a lot of brine wastes • Research is needed
Reducing Water Waste • Benefits of water conservation • Reduce leakage and save water • Water prices, government subsidies, and waste • Improve irrigation • Using less water in homes and businesses
Major Types of Irrigation Systems Drip Irrigation (efficiency 90-95%) Above- or below-ground pipes or tubes deliver water to individual plant roots. Gravity Flow (efficiency 60% and 80% with surge valves) Water usually comes from an aqueduct system or a nearby river. Center Pivot (efficiency 80% with low-pressure sprinkler and 90–95% with LEPA sprinkler) Water usually pumped from underground and sprayed from mobile boom with sprinklers. Fig. 11-17, p. 249
Reducing Irrigation Water Waste 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 • Growing water-efficient crops using drought-resistant and salt tolerant crops varieties • Irrigating with treated urban waste water • Importing water-intensive crops and meat Fig. 11-18, p. 250
Reducing Water Waste 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 • Require water conservation in water-short cities • Use water-saving toilets, showerheads, and front-loading clothes washers • Collect and reuse household water to irrigate lawns and nonedible plants • Purify and reuse water for houses, apartments, and office buildings Fig. 11-19, p. 250
Using Water More Sustainably • Blue revolution • Cut waste • Raise water prices • Drier waste treatment • Preserve forests • Slow population growth
Sustainable Water Use Solutions Sustainable Water Use • Not depleting aquifers • Preserving ecological health of aquatic systems • Preserving water quality • Integrated watershed management • 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 Fig. 11-20, p. 251
What Can We Do? What Can You Do? Water Use and Waste • Use water-saving toilets, showerheads, and faucet aerators • Shower instead of taking baths, and take short showers. • Repair water leaks. • Turn off sink faucets while brushing teeth, shaving, or washing. • 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. Fig. 11-21, p. 251
Flooding After Deforestation of a Hillside Fig. 11-23, p. 253
Flooding After Deforestation of a Hillside Forested Hillside Oxygen released by vegetation Diverse ecological habitat Evapotranspiration Trees reduce soil erosion from heavy rain and wind Agricultural land Steady river flow Vegetation releases water slowly and reduces flooding Leaf litter improves soil fertility Tree roots stabilize soil and aid water flow Fig. 11-23a, p. 253
Flooding After Deforestation of a Hillside After Deforestation Tree plantation Evapotranspiration decreases Roads destabilize hillsides Ranching accelerates soil erosion by water and wind Winds remove fragile topsoil Agriculture land is flooded and silted up Gullies and landslides Heavy rain leaches nutrients from soil and erodes topsoil Rapid runoff causes flooding Silt from erosion blocks rivers and reservoirs and causes flooding downstream Fig. 11-23b, p. 253
Water Pollution • Water is polluted by infectious bacteria, inorganic and organic chemicals, and excess heat. • 1. Water pollution is any chemical, biological, or physical change in water quality that has a harmful effect on living organisms. • 2. Table 11-1 lists the major classes of water pollutants and their major human sources and harmful effects
Water pollution can come from a single source or from a variety of dispersed sources. 1. Point sources discharge pollutants at specific locations through drain pipes, ditches, or sewer lines into bodies of surface water. 2. These sources are easy to identify, monitor, and regulate. 3. Non-point sources are scattered and diffuse and can’t be traced to any single site of discharge. Such things as runoff from croplands, livestock feedlots, etc., are non-point sources. 4. It is difficult and expensive to identify and control these discharges from diffuse sources.
Sources • The leading sources of water pollution are agriculture, industries, and mining. • 1. Agricultural activities are the leading cause of water pollution from erosion, and overgrazing, fertilizers and pesticides and excess slat from irrigated soils. • 2. Industrial facilities are another large source of water pollution and mining is a third source.
One of every five people in the world lack access to safe drinking water. 1. Ninety-five percent of people in developed countries and 74% of people in developing countries have access to clean drinking water. 2. The UN estimates a cost of $23 billion a year for 8-10 years to bring clean drinking water and sanitation to those who do not have it.
Freshwater, Streams, Lakes and Aquifers Pollution • Human activities can overload lakes with plant nutrients that reduce dissolved oxygen and kill some aquatic species. • 1. Natural nutrient enrichment of lakes from runoff is called eutrophication. The amount of natural eutrophication depends on the composition of the surrounding drainage basin. • 2. Natural eutrophication can enrich the abundance of desirable organisms, but cultural eutrophication occurs near urban or agricultural areas and can lead to serious pollution problems.
During hot weather or drought, “blooms” of organisms can reduce lake productivity. 4. Reduced sunlight, and the subsequent decomposition of the “blooms” increase populations of bacteria and decreases dissolved oxygen available. Fish kills can occur and the problem can become so bad that anaerobic bacteria take over.
“Clean Up” • Clean up of lakes includes removing excess weeds, controlling plant growth and pumping air through lakes and reservoirs to avoid oxygen depletion. • Pollution prevention is less expensive than control methods.
Groundwater Pollution: Causes and Persistence • Sources of groundwater pollution • Slow flowing: slow dilution and dispersion • Consequences of lower dissolved oxygen • Fewer bacteria to decompose wastes • Cooler temperatures: slow down chemical reactions • “Degradable” and nondegradable wastes in groundwater
Groundwater Pollution • Groundwater is vulnerable to contamination because it can’t effectively cleanse itself and dilute an disperse pollutants • 1. Spilling gasoline, oil, paint thinners and other organics onto the ground can contaminate groundwater. • 2. Experts rate groundwater pollution as a low-risk ecological problem, it is rated as a high-risk health problem. • 3. Contaminated water in the aquifer will slowly flow along and create a plume of contaminated water.
Contaminants in groundwater are not diluted or dispersed because this water moves usually less than 0.3 meter, or 1 foot per day. 5. Factors such as lower oxygen content, colder temperature of the water and smaller populations of decomposing bacteria mean that cleansing is extremely slow. 6. It can take hundreds of years to cleanse degradable wastes, nondegradable wastes are there permanently.
Lake Pollution • Dilution less effective than with streams • Stratification in lakes and relatively little flow hinder rapid dilution of pollutants • Lakes more vulnerable to pollutants than streams • How pollutants enter lakes • Eutrophication: causes and effects • Oligotrophic and eutrophic lakes • Cultural eutrophication • Preventing or removing eutrophication
Pollution in Streams Normal clean water organisms (trout, perch, bass, mayfly, stonefly) Trash fish (carp, gar, leeches) Fish absent, fungi, sludge worms, bacteria (anaerobic) Trash fish (carp, gar, leeches) Normal clean water organisms (trout, perch, bass, mayfly, stonefly) 8 ppm Types of organisms 8 ppm Dissolved oxygen (ppm) Biological oxygen demand Clean Zone Recovery Zone Septic Zone Decomposition Zone Clean Zone Fig. 11-24, p. 256
Preventing Nonpoint Source Pollution • Mostly agricultural wastes • Use vegetation to reduce soil erosion • Reduce fertilizer use • Use plant buffer zones around fields • Integrated pest management: Only use pesticides when necessary • Use plant buffers around animal feedlots • Keep feedlots away from slopes, surface water and flood zones
Oligotrophic and Eutrophic Lakes Fig. 11-25, p. 257
Groundwater Pollution Polluted air Hazardous waste injection well Pesticides and fertilizers De-icing road salt Coal strip mine runoff Buried gasoline and solvent tank Pumping well Gasoline station Water pumping well Cesspool septic tank Waste lagoon Sewer Landfill Leakage from faulty casing Accidental spills Discharge Unconfined freshwater aquifer Confined aquifer Confined freshwater aquifer Groundwater flow Fig. 11-26, p. 258
Extent of Groundwater Pollution • Not much is known about groundwater pollution • Organic contaminants, including fuel leaks • Arsenic • Protecting groundwater: Prevention is best
Preventing and Cleaning Up Pollution in Groundwater Solutions Groundwater Pollution Prevention Cleanup Find substitutes for toxic chemicals Pump to surface, clean, and return to aquifer (very expensive) Keep toxic chemicals out of the environment Install monitoring wells near landfills and underground tanks Inject microorganisms to clean up contamination (less expensive but still costly) Require leak detectors on underground tanks Ban hazardous waste disposal in landfills and injection wells Pump nanoparticles of inorganic compounds to remove pollutants (may be the cheapest, easiest, and most effective method but is still being developed) Store harmful liquids in aboveground tanks with leak detection and collection systems Fig. 11-27, p. 259