Water Resources and Water PollutionWater Conflicts in the

Middle East

15-1 Water's Importance and Unique Properties

Water covers about 71% of the earth's surface. Organisms are made up mostly of water. Watermolecules are held together by hydrogen bonds, which give water its unique properties. Water has an unusually high heat capacity, is an excellent solvent, filters out some UV radiation, is cohesive, and expands when it freezes.

Water

Animation 1

15-2 Supply, Renewal, and Use of Water Resources

Only a tiny fraction of the earth's water is available as fresh water. (Fig. 15.2) The hydrologic cycle collects, purifies, recycles, and distributes water. Surface runoff from a watershed or drainage basin drains into a stream, lake, or some other body of water. Only about one-third of the world's annual runoff is reliable runoff.

Groundwater located within 1 km of the earth's surface contains more than 100 times all of the freshwater found in rivers, lakes, and reservoirs combined.

Groundwater exists in soil layers: the zone of aeration and the water table, which sits at the top of the zone of saturation. Below this are aquifers, which are replenished through natural recharge. (Fig. 15.3)

Worldwide, about 70% of water use goes to irrigation. (Fig. 14.4)

15-3 Too Little WaterThere are four causes of water scarcity: drought, dry climate, desiccation, and water stress. Currently about 41% of the world's population lives in

countries that are water-scarce or water-stressed. One of six people does not have regular access to fresh water.

15-4 Using Dams and Reservoirs to Supply More Water

Dams increase the annual runoff available for human use but can reduce downstream flow to a trickle and even prevent rivers from reaching the sea.

China's Three Gorges Dam will be the world's largest hydroelectric dam and reservoir. The dam will produce power and reduce flooding, but it also will radically change the region's entireecosystem

.

15-5 Transferring Water from One Place to AnotherTunnels, aqueducts, and underground pipes can transfer water. A massive water-diversion project in part of the former Soviet Union has drasticall shrunk the size of the Aral Sea and created one of the world's most serious ecological and health disasters.

15-6 Tapping Groundwater, Converting Saltwater to Freshwater, Seeding Clouds, and Towing Icebergs

Withdrawing groundwater from an aquifer faster than it can be renewed can lower the water table, deplete the aquifer, and allow contamination of water by salt or chemicals. Desalination requires large amounts of energy and produces large quantities of waste salt. Cloud seeding and towing icebergs are experimental technologies.

15-7 Reducing Water WasteThe world wastes about two-thirds of the water it uses. Charging more for water and implementing government subsidies for improving water efficiency would allow us to reduce waste. More efficient irrigation systems, such as drip irrigation, are used on relatively few of the world's croplands. Xeriscaping and use of gray water can save water in homes and industry.

15-8 Too Much WaterFloodplains are highly fertile and have been settled by people since the beginnings of agriculture. In developed countries, dams, levees, and channelization are used to protect against floodwaters but large-scale flooding can overcome these defenses.

15-9 Solutions: Achieving a More Sustainable Water Future

A "blue revolution" requires irrigating crops more efficiently, using water-saving technologies in industries and homes, and improving and integrating management of water basins and groundwater supplies.

22-1 Types, Effects, and Sources of Water Pollution

The major categories of water pollution are oxygen-demanding wastes, inorganic chemicals, organic chemicals, plant nutrients, radioactive material, and heat. Scientists can test water quality by examining fecal coliform bacteria counts, using bacterial source tracking, doing a chemical analysis, and monitoring indicator species.

The level of dissolved oxygen is related to the amount of oxygen-demanding wastes, because they are broken down by oxygen-requiring bacteria Fig. 22-3 Scientist measure the biological oxygen demand (BOD), the amount of dissolved oxygen consumed by aquatic decomposers. They also use chemical analysis to determine the presence and concentrations of inorganic and organic chemicals that pollute water.

Pollutants from point sources are easy to identify, monitor, and

regulate. It is more difficult to control pollutants from nonpoint sources.

22-2 Pollution of Freshwater Streams

As long as they are not overloaded, flowing bodies of water can recover rapidly from degradable, oxygen-reducing wastes and excess heat through a combination of dilution and bacterial decay. These natural processes do not eliminate slowly degradable and nondegradablepollutants. Water-pollution control laws have improved water quality of streams in most developed countries, but stream-water quality in most developing countries is poor.

Animation: River pollution

22-3 Pollution of Freshwater Lakes

Lakes and ponds are more vulnerable than streams to pollution because they have little flow and contain stratified layers. Eutrophication occurs naturally from runoff surrounding lakes. However, cultural eutrophication threatens many lakes and ponds in urban and agricultural areas.

22-4 Pollution of Groundwater

Prevention is the best approach to groundwater pollution because cleanup is extremely difficult and expensive. Landfills, underground tanks, industrial

waste ponds, and agricultural areas are sources of groundwater pollution.

22-5 Ocean Pollution

The oceans can absorb and break down huge amounts of degradable pollutants, but many coastal areas have become contaminated. Untreated sewage and agricultural waste and acid deposition from the atmosphere can cause harmful algal blooms. Death and decay of alga can cause oxygen-depleted zones. The Black See suffers from both algal blooms and oxygen depletion.

Ocean dumping of dredge spoils, sewage, and debris threatens marine organisms. Oil pollution in the ocean is caused mainly by human activities on land, but also from oil tanker spills and other problems. Most marine life can recover from exposure to crude oil within three years, but exposure to refined oil can take ten years or longer. A variety of methods are used to clean up spills, but none work well on a large spill.

22-6 Preventing and Reducing Surface Water Pollution

The Clean Water Act regulates polluters and sets standards for water quality.

Septic tanks are used to treat sewage wastes from houses in areas not served by municipal sewers and waste treatment plants. Most urban water treatment plants carry out primary sewage treatment and secondary sewage treatment. A few plants also carry out more thorough and expensive advanced or tertiary sewage treatment. (Fig. 22-16) More than half of the sewage sludge produced in the United States is dumped in landfills. There is growing controversy over using contaminated sewage sludge to fertilize food crops.

New methods of treating wastewater by working with nature include ecological systems in which water is cleaned up by passing it through tanks containing cleansing organisms or

through natural or artificial wetlands.

22-7 Drinking Water QualityResearchers have developed several simple and inexpensive ways to purify drinking water in developing countries. The key to improving water quality is preventing pollutants from reaching surface or underground

sources of water.

9-7 Soil Resources: Formation and Types

A mature soil is arranged as a series of soil horizons. This soil profile can be viewed in cross section. Some precipitation percolates through soil layers. This infiltration can cause

leaching.

The relative amounts of clay, silt, sand, and gravel determine soil texture. Other characteristics of soil are soil porosity, soil permeability, and soil structure. Crops generally grow best in

loams.

The acidity or alkalinity of a soil is measured by pH. Soil pH

affects nutrient uptake.

9-8 Soil ErosionThe main agents of soil erosion are flowing water and wind. Human activities can speed up erosion. (Fig. 9.22) In the United States, about one-third of the nation's original topsoil has been displaced, mostly as a result of overcultivation, overgrazing, and deforestation.

Desertification is another serious and growing threat.

Irrigation can cause salinization and waterlogging.

9-9 Solutions: Soil Conservation

Conservation - tillage farming is a method of soil conservation. (Fig. 9-26) Other methods of reducing erosion are terracing, contour farming, strip cropping, alley cropping, establishing windbreaks, and gully

reclamation.

Soil fertility can be improved by crop rotation and by using fertilizers. Organic fertilizers include animal manure, green manure, or compost, and spores of mycorrhizalfungi. Commercial inorganic fertilizers are more commonly used in developed countries. They are easily transported, stored, and applied, but can cause soil problems and pollution.