Team+6

Team 6: Sarah, Reed, Jessica, Adam

Dissolved Oxygen and Aquatic Primary Productivity
May 7, 2012

//Part A: Effect of Temperature on Dissolved Oxygen Level of Water//

__**Purpose**__: The purpose of this lab is to measure dissolved oxygen, measure primary productivity, and investigate some factors that can affect the primary productivity of a system.

__**Hypothesis**__: If water holds a greater amount of oxygen at colder temperatures, then the level of dissolved oxygen should be highest at the lowest temperature the algae is exposed to.

__**Materials**__: - 3 BOD bottles - Manganous sulfate - Starch Indicator - Sulfamic Acid - measuring spoon - Alkaline potassium iodide azide - sodium thiosulfate - 2 titration syringes - 2 20 mL sampling vials - thermometer - pipette for titration

__**Methods**__: Please refer to AP Biology Laboratory 12: Dissolved Oxygen and Aquatic Primary Productivity, and follow the Procedure for Activity A

//Table 1: Temperature & Dissolved Oxygen// __**Analysis**__: In this experiment, the constants were the number of drops of manganous sulfate solution (8), number of drops of alkaline potassium solution (8), number of drops of starch indicator solution (8), and uniform size of the BOD bottles and 20mL sampling vials. The independent variable was the water temperature, and the dependent variable was the level of dissolved oxygen in the water sample. The results show a trend of oxygen decrease as temperature decreases. Colder water is supposed to hold more dissolved oxygen, so the results do not make sense. One possible explanation is simply human error. It is highly likely that the amount of sodium thiosulfate used for the titration was not recorded correctly; there was some initial confusion as to whether the amount should be measured in drops or mL. Another possible cause is extra air trapped in the BOD bottles when they were initally filled with water, or turbulence when they were initially filled. This would lead to air being mixed into the water sample and increasing the dissolved oxygen level of the sample. Most likely, both of these possible causes are to some degree responsible for the inconsistency of the results.
 * __Data & Observations__:**
 * Temperature || Group DO ||
 * 10 Degrees Celsius || 1.60PPM ||
 * 20 degrees Celsius || 13.6PPM ||
 * 32 Degrees Celsius || 13 PPM ||

__**Conclusion**__: Since the level of dissolved oxygen did not increase as the water temperature decreased, the hypothesis cannot be supported by the experiment. However, due to the large likelihood of human error being a major factor in the negative outcome of the experiment, it would be highly beneficial for the experiment to be repeated and the new results compared to the results of this experiment.

//Part B: Effect of Amount of Light on Aquatic Primary Productivity//

__**Purpose**__: The purpose of this lab is to measure dissolved oxygen, measure primary productivity, and investigate some factors that can affect the primary productivity of a system.

__**Hypothesis**__: If the temperature and amount of light decrease, then so will the dissolved oxygen levels and productivity of the algae.

**__Materials__**: -7 BOD bottles -algae culture -manganous sulfate -starch indicator -sulfamic acid -measuring spoon -alkaline potassium iodide -sodium thiosulfate -2 titration syringes -2 20mL sampling vials -17 pieces of screening -square of aluminum foil -tape

__**Methods**__: Please refer to AP Biology Laboratory 12: Dissolved Oxygen and Aquatic Primary Productivity, and follow the Procedure for Activity B

**__Data and Observations__**: //Table 2: Group Productivity Data// __8 Screens 7.5 ppm 1.13 9.63__
 * Bottle || DO || Net Productivity || Gross Productivity ||
 * Baseline || 8.5 ppm ||  ||   ||
 * Dark || 0.0 ppm || -8.5 || 0 ||
 * Light (0 screens) || 17.5 ppm || 9 || 0.5 ||
 * 1 screen || 17.0 ppm || 8.5 || 17.0 ||
 * 3 Screens || 5.2 ppm || -3.3 || 5.2 ||
 * 5 Screens || 9.5 ppm || 0.7 || 9.2 ||

__**Analysis**__: The experiment went extremely well and the results were as expected. The independent variable was the amount of light let into each BOD bottle, and the dependent variable was the amount of dissolved oxygen present in the sample. It was found that the completely dark vial wrapped in tin foil had a dissolved oxygen concentration of 0 parts per million (ppm). This is true because without light there is no oxygen being produced, only consumed because the algae is still undergoing respiration. The baseline was 8.5ppm so that was before the period of light began. After 24 hours of light, for the bottle with no screens and one hundred percent of the light reached the inside, the dissolved oxygen was 17.5ppm. This shows that with the most light, this bottle had the most photosynthetic reactions taking place which were far greater than those needed for respiration. As more screens were added to the bottles, the less dissolved oxygen each bottle had. With one screen and sixty-five percent light, that bottle had a dissolved oxygen concentration of 17ppm. Five screens had a DO concentration of 9.5ppm and the bottle with eight screens had 7.5ppm. The only bottle that did not fit the hypothesis was the bottle with three screens because that only had a DO concentration of 5ppm. It is unclear why this happened because three titrations were performed for this bottle and they all said this number. There might have been something wrong with the screens, a bottle may have been mislabeled, the light might have been blocked somewhat before reaching this bottle, or there might have been a higher concentration of algae in the bottle. With all this said, the results do clearly show that as the depth and amount of light decrease, so do the dissolved oxygen levels. __**Conclusion**__: The experiment accepts the initial hypothesis that temperature and light affect the levels of dissolved oxygen and productivity of algae, and that a decrease in light or temperature will cause a decrease in percent dissolved oxygen and productivity. **I attempted to make graphs for both data sets, but I was unsure of how to structure them, what should be placed on which axis, and how the scales would work :( -Sarah