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THERMAL POLLUTION
Thermal pollution is the degradation of water quality by any process that changes ambient water temperature. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. When water used as a coolant is returned to the natural environment at a higher temperature, the change in temperature impacts organisms by (a) decreasing oxygen supply, and (b) affecting ecosystem composition. Urban runoff--stormwater discharged to surface waters from roads and parking lots--can also be a source of elevated water temperatures.

When a power plant first opens or shuts down for repair, fish and other organisms adapted to particular temperature range can be killed by the abrupt rise in water temperature known as 'thermal shock'.

Thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers. This affects fish (particularly their eggs and larvae), macroinvertebrates and river productivity.

Contents [hide] 1 Ecological effects — warm water 2 Ecological effects — cold water 3 Control of thermal pollution 4 See also 5 References

[edit] Ecological effects — warm water Elevated temperature typically decreases the level of dissolved oxygen (DO) in water. The decrease in levels of DO can harm aquatic animals such as fish, amphibians and copepods. Thermal pollution may also increase the metabolic rate of aquatic animals, as enzyme activity, resulting in these organisms consuming more food in a shorter time than if their environment were not changed. An increased metabolic rate may result in food source shortages, causing a sharp decrease in a population. Changes in the environment may also result in a migration of organisms to another, more suitable environment, and to in-migration of fishes that normally only live in warmer waters elsewhere. This leads to competition for fewer resources; the more adapted organisms moving in may have an advantage over organisms that are not used to the warmer temperature. As a result one has the problem of compromising food chains of the old and new environments. Biodiversity can be decreased as a result.

Fish killed in receiving watersIt is known that temperature changes of even one to two degrees Celsius can cause significant changes in organism metabolism and other adverse cellular biology effects. Principal adverse changes can include rendering cell walls less permeable to necessary osmosis, coagulation of cell proteins, and alteration of enzyme metabolism. These cellular level effects can adversely affect mortality and reproduction.

Primary producers are affected by warm water because higher water temperature increases plant growth rates, resulting in a shorter lifespan and species overpopulation. This can cause an algae bloom which reduces the oxygen levels in the water. The higher plant density leads to an increased plant respiration rate because the reduced light intensity decreases photosynthesis. This is similar to the eutrophication that occurs when watercourses are polluted with leached agricultural inorganic fertilizers.

A large increase in temperature can lead to the denaturing of life-supporting enzymes by breaking down hydrogen- and disulphide bonds within the quaternary structure of the enzymes. Decreased enzyme activity in aquatic organisms can cause problems such as the inability to break down lipids, which leads to malnutrition.

In limited cases, warm water has little deleterious effect and may even lead to improved function of the receiving aquatic ecosystem. This phenomenon is seen especially in seasonal waters and is known as thermal enrichment. An extreme case is derived from the aggregational habits of the manatee, which often uses power plant discharge sites during winter. Projections suggest that manatee populations would decline upon the removal of these discharges.

The temperature can be as high as 70° Fahrenheit for freshwater, 80° F for saltwater, and 85° F for tropical fish.[clarification needed]

[edit] Ecological effects — cold water Releases of unnaturally cold water from reservoirs can dramatically change the fish and macroinvertebrate fauna of rivers, and reduce river productivity. In Australia, where many rivers have warmer temperature regimes, native fish species have been eliminated, and macroinvertebrate fauna have been drastically altered and impoverished. The temperatures for freshwater fish can be as low as 50° F, saltwater 75° F, and tropical 80° F.

[edit] Control of thermal pollution Cooling tower at Gustav Knepper Power Station, Dortmund, GermanyIndustrial wastewater In the United States, thermal pollution from industrial sources is generated mostly by power plants, petroleum refineries, pulp and paper mills, chemical plants, steel mills and smelters.[2] [3] Heated water from these sources may be controlled with:

cooling ponds, man-made bodies of water designed for cooling by evaporation, convection, and radiation cooling towers, which transfer waste heat to the atmosphere through evaporation and/or heat transfer cogeneration, a process where waste heat is recycled for domestic and/or industrial heating purposes. Some facilities use once-through cooling (OTC) systems which do not reduce temperature as effectively as the above systems. For example, the Potrero Generating Station in San Francisco, which uses OTC, discharges water to San Francisco Bay approximately 10° C (20° F) above the ambient bay temperature.[4]

Urban runoff During warm weather, urban runoff can have significant thermal impacts on small streams, as stormwater passes over hot parking lots, roads and sidewalks. Stormwater management facilities that absorb runoff or direct it into groundwater, such as bioretention systems and infiltration basins, can reduce these thermal effects. Retention basins tend to be less effective at reducing temperature, as the water may be heated by the sun before being discharged to a receiving stream.[5]

[edit] See also Water cooling Water pollution Water quality

[edit] References ^ Selna, Robert (2009). "Power plant has no plans to stop killing fish." San Francisco Chronicle, January 2, 2009. ^ U.S. Environmental Protection Agency (EPA). Washington, D.C. "Cooling Water Intake Structures - Basic Information." June 2, 2008. ^ EPA. "Technical Development Document for the Final Section 316(b) Phase III Rule." June 2006. Chapter 2. ^ California Environmental Protection Agency. San Francisco Bay Regional Water Quality Control Board. "Waste Discharge Requirements for Mirant Potrero, LLC, Potrero Power Plant." Order No. R2-2006-0032; NPDES Permit No. CA0005657. May 10, 2006. ^ EPA. "Preliminary Data Summary of Urban Storm Water Best Management Practices." August 1999. Document No. EPA-821-R-99-012. p. 5-58. Michael Hogan, Leda C. Patmore and Harry Seidman, Statistical Prediction of Dynamic Thermal Equilibrium Temperatures using Standard Meteorological Data Bases, U.S. Environmental Protection Agency Office of Research and Development EPA-660/2-73-003, August, 1973 E.L. Thackston and F.L. Parker, Effect of Geographical Location on Cooling Pond Requirements Vanderbilt University, for Water Quality Office, U.S. Environmental Protection Agency, Project no. 16130 FDQ, March 1971 Edinger, J.E.; Geyer, J.C (1965). Heat Exchange in the Environment. Edison Electric Institute, New York City, N.Y.. Edward A. Laws, Aquatic Pollution: An Introductory Text, John Wiley and Sons (2000) ISBN 0-471-34875-9

THERMAL POLLUTION(ESSAY)

...pollution is a temperature change in natural bodies of water of that can and often does have negative impacts on the nearby ecosystem caused by human influence. The temperature change can be upwards or downwards. The major sources of thermal pollution are power plants and industrial factories. In most power plants, heat is produced when coal, oil, or natural gas is burned or nuclear fuels undergo fission to release huge amounts of energy. This heat turns water to steam, which spins turbines to produce electricity. After cooling the used steam must be cooled and condensed back into water. To condense the steam, cool water is brought into the plant and circulated next to the hot steam. In this process, the water used for cooling increases 5 to 10 Celsius degrees. Industries such as metalworking use large amounts of water as coolant, and then release this water back into a nearby source, such as a lake or river. The released water then has a higher water temperature than the source of water, which then increases the temperature of that particular body of water. This affects the Aquatic organisms, as they are extremely sensitive to temperature change, in which when subject to this temperature change, like many other animals and plants pose the risk of dying of Thermal Shock. If these organisms die in that particular body of water, it poses a threat of disrupting/damaging the food chain, potentially leading to many other animals dying from starvation or in other instances overpopulation.