Robert Brosa, Highland Park High School, Topeka, KS WATER QUALITY FOR FRESHWATER ORGANISMS Appropriate for grades 8-12. OVERVIEW: In modern day society there are many types and sources of pollution which directly affect the environment. One such type of pollution, which is becoming even more predominate through the construction of nuclear power plants, is that of thermal pollution. Power plants use vast amounts of water which are converted to steam by the thermonuclear reaction. This steam is used to turn the blades of the turbines which turns the generators producing the electricity. The hot water resulting from condensed steam is partially cooled in specially designed towers before it is released again into the environment by means of a reservoir or stream. The temperature of the return water is great enough to raise the temperature of the body of water several degrees. Such increases in temperature could greatly affect the organisms living in the water. PURPOSE: The purpose of this activity is to demonstrate to students the effect increased water temperature has on the amount of dissolved oxygen found in water and in turn upon the gill beat rate of fish. OBJECTIVES: Students will be able to: 1. Describe the proper procedure for observing and recording data. 2. Describe how to use the Winkler method for O2 determination in water. 3. Demonstrate how to graph and interpret data. 4. Discuss what effect increased temperature has on the amount of dissolved oxygen in water and in turn upon the gill beat rate of fish. ACTIVITIES: Equipment needed (for each lab group): cold aerated pond water, 800 ml beaker, minnow, hot plate, Celsius thermometer, ring stand, cork, stirring rod, Hach Dissolved Oxygen test kit, data table, graph paper. Day 1: Step #1 - Place 600 ml. of cold (50C.), well aerated pond water into a 600 ml beaker. Step #2 - Place minnow into beaker and set on hot plate. Step #3 - Suspend Celsius thermometer by means of a ring stand and cork in center of beaker. Step #4 - Allow minnow to quiet down and take the gill beat rate by counting the movement (beat) of the operculum which covers the gills. Take the count for 30 sec. and multiply by 2 to obtain rate per minute and then record count in table of results on work sheet. (By taking the average of 2 or 3 counts you may be more accurate.) Step #5 - Turn on hot plate and heat water slowly while gently stirring. Take a count of the next gill beat rate when the temperature is at 100C. and record data. (You will need to stop the stirring when the beat rate is taken. A double beaker with surrounding water may be used if water heats too quickly.) Step #6 - Repeat steps 4 and 5 at 15, 20, 25, and 30 degrees Celsius, recording your data each time. If the minnow begins to float at the surface or wildly thrash about immediately return to cold water as we do not intend for it to die. Step #7 - Take the recorded data and plot on graph: Gill Beat Rate vs. Water Temperature. Day 2: Step #1 - Same as step #1 above. Step #2 - Without placing minnow into beaker use the cold water sample and your Hach water test kit to determine the amount of dissolved oxygen in parts per million (ppm). Instructions are contained within each kit. All data will need to be recorded on your worksheet. Step #3 - Return the amount of water lost from testing to beaker. Place beaker on hot plate, stir gently, and remove sample for testing when it reaches 100C. Step #4 - Repeat Step #3 and test the amount of dissolved oxygen at 15, 20, 25, and 30 degrees Celsius. (If test kits are in short supply or you do not have enough time to make a test at each 5 degree interval, each lab group may be assigned only a few and the data taken and averaged for the entire class.) Step #5 - Make a graph of Dissolved Oxygen (ppm) vs. Water Temperature. Step #6 - Study each of the graphs which you have made and from your analysis write your conclusion. RESOURCES/MATERIALS NEEDED: All explained above. TYING IT ALL TOGETHER: The balance of nature, as we often hear, is a very delicate one. Each organism has its own specific tolerance levels to many different environmental and human imposed factors. The oxygen level of water is but one of many factors that will determine what species will be present of survive in a freshwater ecosystem. In today's society we need to be more aware of how we effect that balance of nature and weigh carefully the results of our actions and decisions.
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