Lecture 06

Environmental Science

Water Resources


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         Water Cycle

 Water is continually moving around, through, and above the Earth as water vapor, liquid water, and ice. In fact, water is continually changing its form. A model used to illustrate process is called the 'Water Cycle". The Earth is pretty much a "closed system," which means that the Earth neither, as a whole, gains nor loses matter, including water. Although some matter, such as meteors from outer space, are captured by Earth, very little of Earth's substances escape into outer space. This is certainly true about water. This means that the same water that existed on Earth millions of years ago is still here. Thanks to the water cycle, the same water is continually being recycled all around the globe.



Water Sources

You can see how water is distributed by viewing these bar charts. The left-side bar shows where the water on Earth exists; about 97 percent of all water is in the oceans. The middle bar shows the distribution of that three percent of all Earth's water that is freshwater. The majority, about 69 percent, is locked up in glaciers and icecaps, mainly in Greenland and Antarctica. You might be surprised that of the remaining freshwater, almost all of it is below your feet, as ground water. No matter where on Earth you are standing, chances are that, at some depth, the ground below you is saturated with water. Of all the freshwater on Earth, only about 0.3 percent is contained in rivers and lakes—yet rivers and lakes are not only the water we are most familiar with, it is also where most of the water we use in our everyday lives exists.

Barcharts of the distribution of water on Earth.

For a detailed explanation of where Earth's water is, look at the data table below. Notice how of the world's total water supply of about 332.5 million cubic miles of water, over 96 percent is saline. And, of the total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of freshwater is in the ground. Thus, surface-water sources (such as rivers) only constitute about 22,300 cubic miles, which is about 1/700th of one percent of total water, yet rivers are the source of most of the water people use.

Estimate of global water distribution:

Water source

Water volume, in cubic miles

Water volume, in cubic kilometers

Percent of fresh water

Percent of total water

Oceans, Seas, & Bays





Ice caps, Glaciers, & Permanent Snow




















Soil Moisture





Ground Ice & Permafrost

























Swamp Water










Biological Water










Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823.


Uses of the World's Fresh Water

According to Miller, 2006- Environmental Science, pg.238, worldwide, we use 70% of the water each year for irrigation, 20% by industries, and 10% by cities and residences.


Oceans          Ocean Zones    El Nino

Oceans cover about 70% of the Earth's surface. The oceans contain roughly 97% of the Earth's water supply.

The oceans of Earth serve many functions, especially affecting the weather and temperature. They moderate the Earth's temperature by absorbing incoming solar radiation (stored as heat energy). The always-moving ocean currents distribute this heat energy around the globe. This heats the land and air during winter and cools it during summer.
      The Earth's oceans are all connected to one another. Until the year 2000, there were four recognized oceans: the Pacific, Atlantic, Indian, and Arctic. In the spring of 2000, the International Hydrographic Organization delimited a new ocean, the Southern Ocean (it surrounds Antarctica and extends to 60 degrees latitude).



Area (square miles)

Average Depth (ft)

Deepest depth (ft)

Pacific Ocean



Mariana Trench, 36,200 ft deep

Atlantic Ocean



Puerto Rico Trench, 28,231 ft deep

Indian Ocean



Java Trench, 25,344 ft deep

Southern Ocean

7,848,300 sq. miles (20.327 million sq km )

13,100 - 16,400 ft deep (4,000 to 5,000 meters)

the southern end of the South Sandwich Trench, 23,736 ft (7,235 m) deep

Arctic Ocean



Eurasia Basin, 17,881 ft deep


The Oceans are salty due to the fact that as water flows over and through the land, it picks up small amounts of mineral salts from the rocks and soil. This very-slightly salty water flows into the oceans and seas. The water in the oceans only leaves by evaporating (and the freezing of polar ice), but the salt remains dissolved in the ocean - it does not evaporate. So the remaining water gets saltier. The oceans and seas contain roughly 5 x 1016 tons of salts. One cubic foot of average sea water contains 2.2 pounds of salt. The oceans are about 3.5% salt (by weight).

Lakes       Lake Turnover

A lake is a body of water or other liquid of considerable size surrounded entirely by land. A vast majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere. Lakes have numerous features in addition to lake type, such as drainage basin, inflow, and outflow, nutrient content, dissolved oxygen, pollutants, pH, and sedimentation.

The change in level of a lake is controlled by the difference between the sources of inflow and outflow, compared to the total volume of the lake. The significant input sources are precipitation onto the lake; runoff carried by streams and channels from the lake's drainage basin area; groundwater channels and aquifers; and artificial sources from outside the drainage basin area. Output sources are evaporation from the lake; surface and groundwater flows; and any extraction of lake water by humans. As climate conditions and human water requirements vary, these will create fluctuations in the lake level.

Lakes can be also categorized on the basis of their richness of nutrients, which typically affects plant growth. Nutrient-poor lakes are said to be oligotrophic and are generally clear, having a low concentration of plant life. Mesotropic lakes have good clarity and an average level of nutrients. Eutrophic lakes are enriched with nutrients, resulting in good plant growth and possible algal blooms. And hypertrophic lakes are bodies of water that have been excessively enriched with nutrients.

Lake turnover occurs due to the unusual relationship between water's temperature and its density. Lakes form layers called thermoclines which are layers of drastically varying temperature relative to depth. Fresh water is most dense at about 4 degrees Celsius (39.2 °F) at sea level. When the temperature of the water at the surface of a lake reaches the same temperature as deeper water (such as during the cooler months in temperate climates), the water in the lake can mix, bringing oxygen starved water up from the depths, and bringing oxygen down to decomposing sediments. Deep temperate lakes can maintain a reservoir of cold water year-round which allows some cities to tap that reservoir for deep lake water cooling.


 Ice and Snow

The vast majority, almost 90 percent, of Earth's ice mass is in Antarctica, while the Greenland ice cap contains 10 percent of the total global ice mass. The ice cap became so large over time because more snow fell than melted. Over the millennia, as the snow got deeper, it compressed and became ice. In many places Greenland’s glaciers on reach to the sea, and contributes to the global water cycle. Climatic factors affect them and during a warmer climate, they can retreat in size at a rate easily measured. Ice is very white, and since white reflects sunlight (and thus, heat), large ice fields can determine weather patterns. Air temperatures can be higher a mile above ice caps than at the surface, and wind patterns, which affect weather systems, can be dramatic around ice-covered landscapes.


Even though the amount of water locked up in glaciers and ice caps is a small percentage of all water on (and in) the Earth, it represents a large percentage of the world's total freshwater. As the data table show, the amount of water locked up in ice and snow is only about 1.7 percent of all water on Earth, but the majority of total freshwater on Earth, about 68.7 percent, is held in ice caps and glaciers.


One estimate of global water distribution

Water source

Water volume, in cubic miles

Water volume, in cubic kilometers

Percent of total water

Percent of total freshwater

Ice caps, Glaciers, & Permanent snow





Total global freshwater





Total global water





Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823.


Rivers    River Pollution

A river is a natural waterway that conveys water derived from precipitation from higher ground to lower ground. Most commonly rivers flow on the surface but there are many examples of underground rivers where the flow is contained within chambers, caves or caverns. In some areas of highly variable rainfall, some rivers carry water only occasionally and may be dry for several years at a time. Water may also be recruited to a river from ground-water sources. Throughout the course of the river, the total volume transported downstream will often be a combination of the free water flow together with a substantial contribution flowing through sub-surface rocks and gravels that underlie the river and its floodplain. For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow.

From their source, all rivers flow downhill, typically terminating in the sea or in a lake. In arid areas rivers sometimes end by losing water to evaporation. River flow may also be lost by percolation into dry, porous material such as sand, soil, or into pervious rock. Excessive abstraction of water for use in industry, irrigation etc can also cause a river to dry before reaching a lake or the sea. The mouth, or lower end, of a river is known by hydrologists as its base level.

The area drained by a river and its tributaries is called drainage basin or watershed. The term "watershed" is also used to mean a boundary between drainage basins, which is also called a water divide.

A river's water is generally confined to a channel, made up of a stream bed between banks. In larger rivers there is also a wider flood-plain shaped by flood-waters overtopping the channel. Flood plains may be very wide in relation to the size of the river channel. This distinction between river channel and flood-plain can be blurred especially in urban areas where the flood-plain of a river channel can become greatly developed by housing and industry.

A river flowing in its channel is a source of considerable energy which acts on the river channel to change its shape and form. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks. In U shaped glaciated valleys, the subsequent river valley can often easily be identified by the V shaped channel that it has carved. In the middle reaches where the river may flow over flatter land, loops (meanders) may form through eroding of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths, if conditions permit. Rivers, whose mouths are in saline tidal waters, may form estuaries. River mouths may also be fjords.

Although the following classes are a useful simplified way to visualize rivers, it is important to recognize there are other factors at work.


Youthful River is a river with a steep gradient that has very few tributaries and flows quickly. Its channels erode deeper rather than wider.

Mature River is a river with a gradient that is less steep than those of youthful rivers and flows more slowly than youthful rivers. A mature river is fed by many tributaries and has more discharge than a youthful river. Its channels erode wider rather than deeper. (Ex: Mississippi River, Ohio River, Thames River)

Old River is a river with a low gradient and low erosive energy. Old rivers are characterized by wide flood plains. (Ex: Tigris River, Euphrates River, Indus River)


Surface water use in the United States

The water in the nation's rivers, streams, creeks, lakes, and reservoirs are vitally important to our everyday life. The main uses of surface water include drinking-water and other public uses, irrigation uses, and for use by the thermoelectric-power industry to cool electricity-generating equipment. The majority of water used for thermoelectric power, public supply, irrigation, mining, and industrial purposes came from surface-water sources. About 74 percent of the freshwater used in the United States in 2000 came from surface-water sources. The other 26 percent came from ground water. Surface water is an important natural resource used for many purposes, especially irrigation and public supply (supplying people with drinking water and for everyday uses).

Ground Water and Aquifers 

The main uses of ground water include irrigation uses, drinking-water and other public uses, and for supplying domestic water to people who do not receive public-supply water. The majority of water used for self-supplied domestic and livestock purposes came from ground-water sources.

Ground water is an important part of the water cycle. There is a hundred times more water in the ground than is in all the world's rivers and lakes. Most of the void spaces in the rocks below the water table are filled with water. Rocks have different porosity and permeability which means that water does not move around the same way in all rocks. Water underlies the Earth's surface almost everywhere, beneath hills, mountains, plains, and deserts. This water may occur close to the land surface, as in a marsh, or it may lay many hundreds of feet below the surface. Water at very shallow depths might be just a few hours old; at moderate depth, it may be 100 years old; and at great depth or after having flowed long distances from places of entry, water may be thousands of years old.

When a water-bearing rock readily transmits water to wells and springs, it is called an aquifer. Wells can be drilled into the aquifers and water can be pumped out. Precipitation eventually adds water (recharge) into the porous rock of the aquifer. Pumping too much water draws down the water in the aquifer and eventually causes a well to yield less and less water and even run dry.


Land Subsidence

Land subsidence occurs when large amounts of ground water have been withdrawn from certain types of rocks, such as fine-grained sediments. The rock compacts because the water is partly responsible for holding the ground up. When the water is withdrawn, the rock compresses and reduces the air spaces. You may not notice land subsidence too much because it can occur over large areas rather than in a small spot, like a sinkhole. That doesn't mean that subsidence is not a big event -- states like California, Texas, and Florida have suffered damage to the tune of hundreds of millions of dollars over the years.

Subsidence is a global problem and, in the United States, more than 17,000 square miles have been directly affected by subsidence. More than 80 percent of the identified subsidence in the Nation has occurred because of exploitation of underground water.


Water Pollution    How a Salt Dissolves

The physical properties of water provide major clues as to its susceptible to becoming polluted. Water is found primarily as a liquid which means it will assume the shape of whatever container is held providing a close contact with the surface of its container. Water is referred to as the “universal solvent” this means that water is able to dissolve many/most substances. This can be affected by temperature and time. Most materials dissolve faster and to a higher concentration as the temperature increases. The greater length of time water has to act on a material the more “opportunity” the material has to dissolve.


Point and Nonpoint Sources

 Water pollution occurs when a body of water is adversely affected due to the addition of materials to the water.  When it is unfit for its intended use, water is considered polluted.  Two types of water pollutants exist; point source and nonpoint source.  Point sources of pollution occur when harmful substances are emitted directly into a body of water.  The Exxon Valdez oil spill best illustrates a point source water pollution.  A nonpoint source delivers pollutants indirectly through environmental changes.  An example of this type of water pollution is when fertilizer from a field is carried into a stream by rain, in the form of run-off which in turn affects aquatic life.  The technology exists for point sources of pollution to be monitored and regulated, although political factors may complicate matters. Nonpoint sources are much more difficult to control.  Pollution arising from nonpoint sources accounts for a majority of the contaminants in streams and lakes.


Types Water Pollution    Acid Deposition      

Sediments include particles of soils, sand, silt, clay, and minerals that wash from the land and settle into creeks and rivers. In large quantities, these substances can kill fish by covering their nests and clogging their gills.

Acid Precipitation occurs in the form of acid rain. Aquatic animals and plants must live in a narrow range of pH. pH is the measure of the acidity of a solution. Acid rain and chemical pollution increases the pH and causes aquatic life to die.

Petroleum Products such as oil, gasoline, and kerosene can find their way into the water from ships, tankers, service stations, oil refineries, and streets. Oil spills kill aquatic life and can make it difficult for oil-soaked birds to fly.

Inorganic Chemicals are found in Mining and manufacturing industries, oil field operations, agriculture, and natural resources often create inorganic chemicals and metal salts that dissolve into water. They destroy fish and other wildlife as well as corrode expensive water treatment equipment.

Human and animal waste that is not properly treated and released into water can spread harmful bacteria and viruses. Sewage can also act as a fertilizer and increase the nutrient level and, as a result, cause damage.      

Fertilizers are used by the agriculture industry. Fertilizer runoff causes large amounts of algae to grow on top of the water. When the algae die, bacteria use it for food. This causes a decrease in oxygen in the water

Organic Wastes are released by sewage treatment plants, food processing plants, paper mills, and leather tanning factories release organic wastes that bacteria feed on. This increases the bacterial population, which in turn consumes more oxygen. This causes the other aquatic wildlife to be deprived of oxygen and die.     

Heated or Cooled Water produced by power plants, reduces the ability of water to dissolve oxygen. Cooled water can cause habitat damage.

Inorganic Compounds such as detergents, pesticides, and other chemicals are often released into waterways. They can be very poisonous in low concentrations.

Pesticides, Herbicides, Fungicides are chemicals are designed to kill or limit the growth of life forms that can be harmful to agriculture. They are often washed into the waterways and prove to be harmful to wildlife.


Wastewater Treatment                   Flush and Tell

Raw sewage includes waste from sinks, toilets, and industrial processes. Treatment of the sewage is required before it can be safely buried, used, or released back into local water systems. In a treatment plant, the waste is passed through a series of screens, chambers, and chemical processes to reduce its bulk and toxicity. The three general phases of treatment are primary, secondary, and tertiary. During primary treatment, a large percentage of the suspended solids and inorganic material is removed from the sewage. The focus of secondary treatment is reducing organic material by accelerating natural biological processes. Tertiary treatment is necessary when the water will be reused; 99 percent of solids are removed and various chemical processes are used to ensure the water is as free from impurity as possible. 




        Clearly, the problems associated with water and water pollution have the capabilities to disrupt life on our planet to a great extent. Congress has passed laws to try to combat water pollution thus acknowledging the fact that water pollution is, indeed, a serious issue. But the government alone cannot solve the entire problem.  It is ultimately up to us, to be informed, responsible and involved when it comes to the problems we face with our water.  We must become familiar with our local water resources and learn about ways for disposing harmful household wastes so they don’t end up in sewage treatment plants that can’t handle them or landfills not designed to receive hazardous materials.  In our yards, we must determine whether additional nutrients are needed before fertilizers are applied, and look for alternatives where fertilizers might run off into surface waters. We have to preserve existing trees and plant new trees and shrubs to help prevent soil erosion and promote infiltration of water into the soil.  Around our houses, we must keep litter, pet waste, leaves, and grass clippings out of gutters and storm drains.  These are just a few of the many ways in which we, as humans, have the ability to combat water pollution.  As we head into the 21st century, awareness and education will most assuredly continue to be the two most important ways to prevent water pollution.  If these measures are not taken and water pollution continues, life on earth will suffer severely.
     Global environmental collapse is not inevitable. But the developed world must work with the developing world to ensure that new industrialized economies do not add to the world's environmental problems. Politicians must think of sustainable development rather than economic expansion. Conservation strategies have to become more widely accepted, and people must learn that energy use can be dramatically diminished without sacrificing comfort.  In short, with the technology that currently exists, the years of global environmental mistreatment can begin to be reversed.




How Can You Help: The Clinton River Watershed an Example of Involvement