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The water temperature of a river is very important. Many of the physical, biological, and chemical characteristics of a river are directly affected by temperature. Most aquatic organisms have adapted to survive within a certain range of water temperatures. Few organisms can tolerate extremes of heat or cold. Temperature influences the amount of oxygen that can be dissolved in water. Cold water holds more oxygen than warm water. The more oxygen in the water, the more living things it can support. Temperature also influences the rate of photosynthesis by algae and larger aquatic plants. As water temperature rises, the rate of photosynthesis by algae and larger aquatic plants increases. The faster plants grow, the faster plants die. As plants die, they are decomposed by bacteria that consume, or use up, oxygen. Therefore, when the rate of photosynthesis is increased, the demand for oxygen in the water (BOD) is also increased. Temperature influences the metabolic rates of aquatic organisms. Metabolic rate is the speed at which cells conduct the chemical processes of life. Most aquatic animals are cold-blooded. Their metabolic rate is slower in cold water but faster in warm. Therefore, they need more food and oxygen in warm water. They will also release more wastes. Temperature also influences the sensitivity of organisms to toxic wastes, parasites, and diseases. Bacteria and other disease-causing organisms grow faster in warm water. One of the most serious ways humans can harm a river is by causing thermal pollution. Thermal pollution is an increase in water temperature caused by adding warm water to a river. Industries, such as nuclear power plants, may cause thermal pollution by releasing water used to cool machinery. Thermal pollution may also result from storm water running off warm urban surfaces, such as streets, sidewalks and parking lots. People also affect water temperature by cutting down trees. Trees
help shade a river. Water exposed to direct sunlight can be as much as
20°F warmer than water that is shaded. Cutting trees often increases soil erosion. Soil
erosion can contribute to warm water temperatures. Increased amounts of suspended solids
carried by the river make the water cloudy or turbid. Turbid
water absorbs more of the sun's rays which causes the water's temperature to rise.
HOW TO MEASURE TEMPERATURE CHANGE Sampling Procedure: Thermometers are used to measure the change in water temperature between two points- the test site and a site one mile upstream. It is important to match as closely as possible the physical conditions at these sites- current speed, amount of sunlight reaching the water, and the depth of the stream. To reduce errors, the same thermometer should be used at both sites. Check the thermometer before using. Make sure the glass is not cracked and the red fluid is together and not separated. Hold the thermometer towards the top so that the warmth from your hand does not affect the reading. Begin by taking the air temperature in degrees Celsius. Record the air temperature in the appropriate place on the data forms. Temperature testing Procedure:
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