AP Biology Lab 12: Dissolved Oxygen & Aquatic Primary Productivity PDF

AP Biology Lab 12 Dissolved Oxygen and Aquatic Primary Productivity April Clark 09/9/10 AP Biology Pd 1/2, Pd 4/5, Pd 8/9 Mrs. Clark’s awesome AP Bio class Abstract: Measurement of Dissolved Oxygen: The...

AP Biology Lab 12 Dissolved Oxygen and Aquatic Primary Productivity April Clark 09/9/10 AP Biology Pd 1/2, Pd 4/5, Pd 8/9 Mrs. Clark’s awesome AP Bio class Abstract: Measurement of Dissolved Oxygen: The purpose of this experiment was to show how temperature affected the amount of dissolved oxygen in an aquatic sample. Water samples were collected at different temperatures and the dissolved oxygen was determined using the Winkler Method. Percent saturation of oxygen was then calculated using a nomograph. Results of the experiment indicated that as the temperature increased, the dissolved oxygen in the sample decreased. Measurement of Primary Productivity: The purpose of this experiment was to demonstrate how light intensity influences primary productivity in an aquatic sample. Water samples were collected and wrapped to simulate different light intensities. One sample was wrapped in foil to simulate a dark sample so respiration rate could be determined. Samples were left overnight under a light. On day 2, the dissolved oxygen of the samples was determined using the Winkler Method. From these results, the net and gross productivity of the samples was calculated. The results of the experiment indicated that the greater the light, the greater the primary productivity. Theory: Dissolved oxygen levels are an extremely important factor in determining the quality of an aquatic environment. Dissolved oxygen is necessary for the metabolic processes of organisms found in water. Terrestrial environments hold over 95% more oxygen than aquatic environments. Oxygen levels in aquatic environments are very vulnerable to even the slightest change. Oxygen must be constantly be replenished from the atmosphere and from photosynthesis. There are several factors that affect the dissolved oxygen levels in aquatic environments. Temperature is inversely proportional to the amount of dissolved oxygen in water. As temperature rises, dissolved oxygen levels decrease. Wind allows oxygen to be mixed into the water at the surface. Windless nights can cause lethal oxygen depletions in aquatic environments. Turbulence also increases the mixture of oxygen and water at the surface. This turbulence is caused by obstacles, such as rocks, fallen logs, and water falls, and can cause extreme variations in oxygen levels throughout the course of a stream. Primary production is the energy accumulated by plants since it is the first and basic form of energy storage. The flow of energy through a community begins with photosynthesis. All of the sun’s energy that is used is termed gross primary production. The energy remaining after respiration and stored as organic matter is the net primary production. The equation for photosynthesis is as follows: 12H2O + 6CO2 → C6H12O6 + 6O2 + 6H2O There are three ways to measure primary production, measure the carbon consumed, measure the glucose produced, or measure the oxygen produced. The oxygen method uses a dark and light bottle to compare the amount of oxygen produced in photosynthesis and used in respiration. Respiration rate is determined by subtracting the dark bottle from the initial bottle. Hypothesis: As temperature increases, dissolved oxygen will decrease. As light intensity increases, primary productivity will increase. Materials: Measurement of Dissolve Oxygen: This part of the lab required BOD bottles, water sample, thermometer, chemicals for the Winkler method, titration vial, syringe, starch, and a nomograph Measurement of Primary Productivity: This part of the lab required BOD bottles, water sample, screens, foil, rubber bands, light source, chemicals for the Winkler method, titration vial, syringe, and starch Procedure: Measurement of Dissolved Oxygen: Water samples were collected from 3 different temperatures in BOD bottles using a specified technique to ensure samples were free of air. The different temperatures are 4˚, 25˚, and 30˚. The samples were fixed and then tested for dissolved oxygen using the Winkler Method. Once the amount of dissolved oxygen was determined, the percent saturation of oxygen of each sample was determined using a nomograph. Measurement of Primary Productivity: Six water samples were collected in BOD bottles using a specified technique to ensure samples were free of air. Each bottle was wrapped according to the directions to simulate different light intensities. The light intensities tested were dark, 100% light, 65% light, 25% light, 10% light and 2% light. The samples were left under a light overnight. On day 2, the samples were fixed and then tested for dissolved oxygen using the Winkler Method. Once the dissolved oxygen was determined, net and gross productivity could be calculated. The baseline dissolved oxygen reading for the calculations came from the results for 25˚C sample from part A. Data/Observations: Measurement of Dissolved Oxygen: Table 1: Temp ˚C Group DO Class DO mg/L Group % Class % mg/L saturation saturation 4 8 8 70 71 22 6 7 70 77 32 6 6 80 92 See attachment for Graph 1 and Graph 2. Measurement of Primary Productivity: Once bottles were fixed, they were not a yellow color which indicates very little dissolved oxygen. Table 2: Bottle Actual DO Manipulated DO Net Productivity Gross Productivity Baseline (initial) 6.7 7.7 X X Dark 7.4 7.4 X X Light 7.6 6.6 1 screen 5.2 6.2 3 screen 6.8 5.8 5 screen 9.1 5.5 8 screen 6.1 5.3 Respiration rate = 4.6 mg O2/L Table 3: See attachment for Graph 3. Analysis/Discussion: Measurement of Dissolved Oxygen: The independent variable was the different temperatures and the dependent variable was the amount of dissolved oxygen or percent saturation of oxygen. The sample at room temperature could be considered the control sample. As the temperature went down, the dissolved oxygen of the sample increased. It was also observed that as the temperature went down, the percent saturation of oxygen went down. Measurement of Primary Productivity: The independent variable was the light intensity and the dependent variable was the primary productivity. The control was the dark samples, since we didn’t expect any photosynthesis to occur in this sample. The data collected showed that overall the primary productivity decrease as light intensity decreased. There were some samples that did not give the results predicted so manipulated data was used. Conclusion: Measurement of Dissolved Oxygen: It was observed that temperature affects the amount of dissolved oxygen in a water sample. As the temperature decreased, the dissolved oxygen increased. The hypothesis was accepted. Any unusual measurements could have been due to technician error, such as incorrect execution of the Winkler Method or allowing over exposure of the water sample to air. The temperatures of the samples may have not been accurate and this could have resulted in similar dissolved oxygen readings. Measurement of Primary Productivity: It was observed that the …. References: MLA style! Make sure you reference your procedure/lab manual