advanced placement environmental science nmsi water and water... · an oxygen sag curve can be used...

ENVIRONMENTAL SCIENCE

Water & Water Pollution Adv

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Student 2014

Water and Water Pollution

Copyright © 2013 National Math + Science Initiative, Dallas, Texas. All Rights Reserved. Visit us online at www.nms.org

Water as a Resource Water covers over seventy percent of the earth’s surface. Several properties of water are responsible for life as we know it.

• Water has a high specific heat allowing for more constant temperatures. Specific heat is the amount of heat per unit mass required to raise the temperature of a substance by 1°C. The specific heat of water is 1 calorie/gram °C.

• Its buoyant nature minimizes the energy spent by organisms in the constant struggle with gravity.

• Aquatic organisms easily obtain dissolved nutrients. No plant or animal can survive without water.

• Water is a major force in weathering. • Water mitigates the world’s climates with its redistribution of solar heat.

The Gulf Stream originates in the Gulf of Mexico. It passes through the Straits of Florida and up along the eastern coast of the United States to the Grand Banks of Newfoundland, Canada, driven northward by southwest winds. Along the way it splits and the part that flows northwest is known as the North Atlantic Drift, which provides temperate waters and warmer climates to the western coastal areas of Europe.

Ninety-seven percent of all water is saltwater or marine. The remaining three percent is fresh water and its distribution is illustrated in figure 11. Water as a resource is used in the United States in the following ways:

• 41% - irrigation (includes water used for growing crops, frost protection, chemical applications, weed control, and other agricultural purposes, as well as water used to maintain areas such as parks and golf courses)

• 38% - energy production (thermoelectric production)

• 11% - industry (fabrication, processing, washing, and cooling, and also includes water used by smelting facilities, petroleum refineries, and industries producing chemical products, food, and paper products)

• 10% - public

The water needed to fill these needs is obtained from several sources.

1 http://ga.water.usgs.gov/edu/waterdistribution.html

Fig. 1



Surface Water consists of streams, lakes, wetlands, and reservoirs. Watersheds (a region from which water drains) feed these bodies of water.

Lake facts: - Largest surface area – Superior (US and Canada) - Deepest and largest volume – Baikal (Russia)

River facts: - Longest – Nile (many) - Largest – Amazon (many)

Reservoirs and man-made lakes are created by dams. These dams not only provide a means for water storage but can also be used to produce electricity through hydroelectric means. Hydroelectric energy production limits greenhouse gas emissions. There are problems associated with the promulgation of dams:

• dams can destroy habitat reducing biodiversity • downstream reduced water quality • blocked fish migration • dams trap sediments • increased water-borne illnesses in reservoir • dams greatly disrupt the flow of rivers.

ex. China's Three Gorges project (Yangtze River) - constructed to produce electricity, increase the Yangtze River's shipping capacity and reduce the potential for floods downstream

Groundwater is water found below the surface. Figure 2 illustrates an aquifer and key terms associated with the surrounding area.

Water Table - the surface of the zone of saturation Aquifer - porous sand, gravel or bedrock through which groundwater flows Recharge area - an area of land through which water passes downward or laterally into an aquifer

Fig. 2



Ninety-five percent of water removed from the Ogallala aquifer (located along the eastern edge of the Rockies) is for irrigation and the removal rate is estimated to be six times greater than the refreshing rate. Problems: Overuse of groundwater can cause land to subside or sink. Removal of freshwater also allows saltwater to intrude into the aquifer. Desalination is another way of producing freshwater. This is accomplished through distillation or reverse osmosis. There are problems associated with desalination, however.

• The process uses large quantities of energy. • The water produced by this method is very expensive. • The process produces large quantities of brine as a by-product.

In order to meet the needs of an ever-growing human population, steps will need to be taken to provide water to the places that need it. However, these projects often prove to be detrimental to the nature and culture of the areas. James Bay Watershed (Canada) and the Aral Sea Project (Russia) are two examples of diverting water. James Bay, at the time of construction, was the world’s largest hydroelectric project. Aral Sea is formerly one of the four largest lakes in the world but has been steadily shrinking since the 1960s after the rivers that fed it were diverted for irrigation projects. It has declined to 10% of its original size. Both of these projects had environmental and cultural casualties. The current water supply could best be protected with conservation practices and more efficient technology. Over sixty percent of the water used throughout the world is wasted through evaporation and leaks. In many developed countries, water is wasted because of its low, government-subsidized prices. Using less water in homes and industry would require municipalities to maintain water lines and eliminate leaks more efficiently. Xeriscaping could replace traditional landscaping. This requires much less water and maintenance. Incentives could also be offered for the installation of more efficient appliances, showers, etc. Using less water in agriculture would consist of changing irrigation practices. Drip irrigation systems are ten percent more efficient than the most efficient center-pivot sprinkler system. Organic farming also uses much less water than conventional framing. Water Pollution Water pollution is classified as any physical, biological, or chemical, change in water that will affect the organisms that live in it or its quality for consumption. Point sources of water pollution have a specific location and are generally to find and control. Non-point sources of water pollution cannot be attributed to one site. This is often associated with agriculture. Water pollution has been divided into several classes.



Organic wastes that deplete dissolved oxygen from water during their bacterial decomposition. The term biological oxygen demand (BOD) is a measure of the oxygen used by microorganisms to decompose this waste. Higher concentrations of waste demands more oxygen and will result in a higher BOD. An oxygen sag curve can be used to illustrate the effects pollution has on streams and rivers. (Fig. 3) Excess nutrients like nitrates and phosphates found in many fertilizers can lead to algal blooms (rapid growth of algae). Once these limiting nutrients are depleted the algae dies and their decomposition leads to the depletion of dissolved oxygen. This often leads to massive fish die offs. Cultural eutrophication is the term used to describe anthropogenic enrichment of lakes or reservoirs that lead to excessive plant growth. Sediments are one of the largest classes of water pollution. They cloud water, which reduces photosynthesis. This in turn disrupts food webs. It also fills in reservoirs and lakes and reduces flow in channels. Thermal pollution is another class of water pollution that is often overlooked. It is the rise in water temperature usually due to the discharge of heat in water used to cool power plants. Thermal shock can weaken organisms and disrupt food chains. Toxic waste, such as pesticides, petroleum products and heavy metals threatens humans and all aquatic organisms. Nonnative species are also genetically polluting many bodies of water. The zebra mussel causes millions of dollars of damage each year in the Great Lakes.

Water pollution is detected in a variety of ways. It can be evaluated through chemical analysis. This includes pH, dissolved oxygen (DO) and nitrate levels. Macro-invertebrates will also indicate the quality of water with the absence and presence of certain species. Another good indicator for the quality of drinking water is the number of coliform bacteria colonies present.

Fig. 3



Preliminary treatment, or screening, is the first step in cleaning wastewater. Bar-screens remove the waste for disposal at a landfill. Following screening, small basins remove before the wastewater is routed to primary treatment. In primary treatment, the incoming flow is slowed in large tanks, which allow the dirt, gravel, and other heavier-than-water components of the waste stream to settle. Grease, oil, and other floatables are also removed here. Both pollutants are pumped into large heated holding silos, called digesters. Odor, resulting mainly from the formation of Hydrogen Sulfide in the incoming sewage lines, escapes the solution at all points of turbulence. These first tanks, or primary clarifiers as they are called, are covered and kept under a constant vacuum, with the gases removed routed through odor reduction equipment. The flow leaving this process is markedly cleaner than the contaminated flow that first appeared at the head of the plant. It is as clean as much of our nation's wastewater was upon discharge to rivers, bays, and oceans, not so long ago. There is still however, about 30 percent of the original suspended solids that were in the plant's influent, and about 70 percent of the original Biochemical Oxygen Demand or BOD, (a measurement of the strength of the pollution). The removal of this final fraction is the job of the secondary treatment process. Secondary treatment What follows next in the plant process is closely akin to sourdough cooking whereby the cook carefully maintains the environment of the sourdough organisms to ensure their survival and availability when he needs them for food preparation. By carefully manipulating the environment, food supply, and population dynamics of the microorganisms in their plant, operators maintain a healthy, manageable biomass, which in turn is happy to feed on incoming waste loads. Since this is a living, breathing, process, it is important not to introduce toxic substances, which can kill these environmental volunteers. Clean Water Services' Source Control Division closely monitors industries in our community to ensure industrial wastes are within the tolerance range of the microorganisms. After gorging themselves on incoming waste, the microorganisms are introduced into settling tanks where they can process their meal. After settling out in these clarifiers, one of two routes is taken. Some will be reintroduced to the feast, while others are sent to be thickened, digested, dewatered, and ultimately trucked to farms across Oregon as a soil amendment. Disinfection The final step in the wastewater treatment process is disinfection.

advanced placement environmental science nmsi water and water... · an oxygen sag curve can be used...

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