Water field study
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    Water field study Water field study Document Transcript

    • Name ____________________________________ Date __________________ A Water Quality Field Study (adapted from Middle School Science with Verneir) Introduction When finding water quality, there are many measurements that can be made. In this experiment, you will measure water temperature, conductivity, pH, and dissolved oxygen. Temperature Water temperatures in streams can range from 0°C in the winter to above 30°C in the summer. Cooler water in a stream is generally considered healthier than warmer water. Problems generally occur when changes in water temperature are noted along one stream on the same day. Conductivity Conductivity values in lakes and streams are typically found to be in the range of 100 to 500 µS/ cm. In areas of especially hard water or high salinity, conductivity values may be as high as 1000 µS/cm. Drinking water usually has conductivity in the 50 to 1000 µS/cm range. Some sample data are listed in Table 2. Conductivity is a measurement of the ability of an aqueous solution to carry an electrical current. An ion is an atom of an element that has gained or lost an electron which will create a negative or positive state. For example, sodium chloride (table salt) consists of sodium ions (Na+) and chloride ions (Cl-) held together in a crystal. In water it breaks apart into an aqueous solution of sodium and chloride ions. This solution will conduct an electrical current. There are several factors that determine the degree to which water will carry an electrical current. 1) the concentration or number of ions; 2) mobility of the ion; 3) oxidation state (valence) and; 4) temperature of the water. Used as a measure of the mineral or other ionic concentration. Conductivity is a measure of the purity of water or the concentration of ionized chemicals in water. pH The best pH range for most aquatic organisms is pH 6.5 to 8.2. The pH values of streams and lakes are usually between pH 7 and 8. Hard water will often have pH values between 7.5 and 8.5. It is used to measure the acidity of liquids represented by a scale of numbers from 0 to 14. The pH of pure water is 7.0, which is neither acidic nor basic. When the pH is less than 7.0 it is identified as acidic; and at a pH greater than 7.0, it is considered basic or alkaline.
    • Aquatic organisms’ ability to survive is reduced if the pH of the water becomes greater than 9.0 or less than 5.0. The pH of water is very important in order to sustain a healthy aquatic ecosystem. The main factors that could affect pH are: 1. Dissolved mineral substances (e.g. hard water-pH greater than 7.0) 2. Aerosols and dust from the air 3. Man-made wastes (e.g. waste from mining operations) 4. Photosynthetic organisms (plants remove carbon dioxide CO2-increasing pH) 5. Underlying rock and soil type in a watershed determines the general pH of the system Toxicity of elements to include metals can affect pH levels dramatically. The level of greater toxicity is when the pH is lower- that is, more acidic. Dissolved Oxygen The dissolved oxygen (DO) is oxygen that is dissolved in water. Therefore, DO analysis measures the amount of gaseous oxygen (O2) dissolved in water. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis. Oxygen is a necessary element to all forms of life. DO is important to fish and other aquatic life. Adequate dissolved oxygen is necessary for good water quality. Natural stream purification processes require adequate oxygen levels in order to provide for aerobic life forms. As dissolved oxygen levels in water drop below 5.0 mg/l, aquatic life is put under stress. The lower the concentration, the greater the stress. Oxygen levels that remain below 1-2 mg/l for a few hours can result in large fish kills. When performing the dissolved oxygen test, only grab samples should be used, and the analysis should be performed immediately. Therefore, this is a field test that should be performed on site. When doing this experiment, you might choose to compare water quality at two or more points on the same stream, in two or more different streams or lakes, or in a lake and a stream that runs into it. 2
    • Name _______________________________________________ Date ___________________________ OBJECTIVES Primary TEKS – 8.11 b, 8.4 a-b Subsequent TEKS – 8.1 a, 8.2 a-e, 8.3 a-c In this experiment, you will: • Compare and contrast water quality between freshwater aquatic systems. • Use Vernier Labquest and probes: • Use a Temperature Probe to measure water temperature. • Use a Conductivity Probe to measure the conductivity of water. • Use a pH Sensor to measure the pH of water. • Use a Dissolved Oxygen sensor to measure dissolved oxygen. • Make visual observations at the test sites of plant, animal, and insect life. • Sample macroinvertibrates populations • Draw a map of your location MATERIALS LabQuest Vernier pH Sensor LabQuest App colorless plastic bottle Temperature Probe plastic cup or beaker Vernier Conductivity Probe Dissolved Oxygen probe Problem Statement How do we determine and compare the health of aquatic systems? Hypothesis __________________________________________________________________________ __________________________________________________________________________ Procedure Part I Measuring Temperature 1. Connect the Temperature Probe to LabQuest and choose New from the File menu. If you have an older sensor that does not auto-ID, manually set up the sensor. 2. Fill the plastic bottle with water taken below the water surface at a point one meter from the shore. CAUTION: Take all necessary precautions to ensure your safety!
    • 3. Measure the water temperature. a. Place the Temperature Probe into the sample. b. Gently move the probe in the water and note the temperature reading on the screen. c. When the temperature stops changing, record the reading in your data table. d. Disconnect the Temperature Probe. Part II Measuring Conductivity 4. Set the Conductivity Probe on the 0–2000 µS/cm position. Connect the Conductivity Probe to LabQuest and choose New from the File menu. If you have an older sensor that does not auto-ID, manually set up the sensor. 5. Measure the conductivity of the same water sample. a. Place the Conductivity Probe into the water. Briefly swirl the probe in the water. b. Once the conductivity reading is steady, record the value in your data table. Part III Measuring pH 6. Disconnect the Conductivity Probe and connect the pH Sensor to LabQuest. Choose New from the File menu. If you have an older sensor that does not auto-ID, manually set up the sensor. 7. Measure the pH of the same water sample. a. Remove the pH Sensor from its protective container and store the container safely aside. b. Rinse the pH Sensor using a plastic cup or beaker and water from the site. c. Place the pH Sensor into the water sample. Briefly swirl the pH Sensor in the water. d. Once the pH is steady, record the reading. Return the pH Sensor to its container. 8. Note and record the clarity (clearness) of the water sample. 9. Make and record other observations (concerning algae, plants, water “critters,” animals, flow rate, etc.) related to water quality at the site. 10. Repeat Steps 1–9 at one or more other sites. Part IV Measuring Dissolved Oxygen 11. Prepare the Dissolved Oxygen Probe for use. a. Remove the blue protective cap if it is still on the tip of the probe. b. Unscrew the membrane cap from the tip of the probe. c. Using a pipet, fill the membrane cap with 1 mL of DO Electrode Filling Solution. d. Carefully thread the membrane cap back onto the electrode. e. Place the probe into a container of water. 12. Plug the Dissolved Oxygen Probe into Channel 1 of the Vernier interface. 13. It is necessary to warm up the Dissolved Oxygen Probe for 5–10 minutes before taking 4
    • Name _______________________________________________ Date ___________________________ readings. To warm up the probe, leave it connected to the interface for 10 minutes. The probe must stay connected at all times to keep it warmed up. If disconnected for a few minutes, it will be necessary to warm up the probe again. 14. Calibrate the probe (see technical info) 15. You are now ready to collect dissolved oxygen concentration data. a. Rinse the tip of the probe with sample water. b. Place the tip of the probe into the stream at Site 1, or intoa cup with sample water from the stream. Submerge the probe tip to a depth of 4-6 cm. c. Click to begin data collection. d. Gently stir the probe in the water sample. Click to begin a 10 s sampling run. Important: Leave the probe tip submerged for the 10 seconds that data is being collected. e. When the sampling run is complete, stop data collection and record the mean dissolved oxygen concentration value on the Data & Calculations sheet. 16. Return to Step 15 to obtain a second reading. When both readings have been taken, rinse the tip of the probe and secure it in the calibration bottle filled with water. Data and Observations Site Temperature (°C) Conductivity (µS/cm) pH Clarity Macroinvertibrates Other observations
    • Map Drawing: Graphs: 6
    • Name _______________________________________________ Date ___________________________ PROCESSING THE DATA 1. How did the water quality at the different sites compare? 2. What differences did you find? Explain the differences. 3. What similarities did you find? Explain the similarities. 4. At which site was the water “best”? Explain why it was the best. 5. What new ideas for testing water quality did you come up with while doing this experiment?
    • EXTENSIONS 1. Test water quality at the same site at different times. 2. Test the effects of rain on water quality. 3. Test water quality at different sites around Tyler, for example between various Middle School test sites. 8