Lab 12 jm5j

Claudia Bergeron Lab Partners: Janelle

3/14-15/11

Lab 12: Dissolved Oxygen and Aquatic Primary Productivity

Purpose: To measure and analyze the dissolved oxygen concentration in water samples at varying water temperatures, and to measure and analyze the primary productivity of natural waters or lab cultures using screens to simulate the attenuation of light with increasing depth.

Hypothesis: The amount of dissolved oxygen in a solution will be greater the colder the solution is. The amount of dissolved oxygen will be greater if it has more light, provided there are photosynthetic organisms living in it.

Abstract: This experiment proved that temperature affects the ability of water to retain dissolved oxygen (DO). The colder the water is, the more dissolved oxygen the water has. It was proven by using the Winkler method to test the amount of dissolved oxygen in a water sample of 5°C, (which had 2.0mg/l of DO) and 21.5°C (which has 1.28mg/l of DO). This proved cold water has more dissolved oxygen. Then we tested the effect of temperature on DO in pond water by using translucent screens to simulate depth of a pond. We used no screens on one bottle for 100% light, 1 screen on another bottle to simulate 65% light, 3 screens on another bottle to simulate 25% light, 5 screens on another bottle to simulate 10% light, 8 screens on another bottle to simulate 2% light, and aluminum foil on another bottle to simulate no light. The results were the 100% light bottle had 6.4 ml O2/l, the 65% light bottle had 3.8 ml O2/l, the 25% bottle had 4.5 ml O2/l, the 10% bottle had 3.7 ml O2/l, the 2% bottle had 4.0 ml O2/l and the no light bottle had 4.6 ml O2/l. Only the bottle with 100% light had a positive gross productivity (of 1.8 ml O2/l), which meant there was more respiration going on in the pond water then photosynthesis.

Exercise 12A: Dissolved Oxygen and Temperature: Results: Table12.1: Temperature/DO Data Temperature

Domg/ml

%DO

5°C

2.0mg/l

16%

21.5°C

1.28mg/l

19%

These are hypothetical results depicting an accurate representation of what the results would have been if we had the proper equipment. DO stands for dissolved oxygen. These results were obtained through the Winkler method, and then, using a nomogram the percent of dissolved oxygen was found.

Graph 12.1 Temperature’s Effect on Dissolved Oxygen

20%

a. The independent variable: The temperature b. The dependant variable: The percent of dissolved oxygen

19%

Percent of Dissolved Oxygen

18% 17% 16% 15% 14% 5

10

15

20

21.5

Temperature (°C)

Exercise 12:B A Model of Productivity as a Function of Depth in a Lake (day one) Results: Table 12.2: Respiration

Initial DO

9.2mlO2/l

Dark Bottle DO Respiration Rate (Initial – Dark)

4.6 mlO2/l 4.6 mlO2/hr

Day Two: Table 12.3: Individual Data – Productivity of Screen Wrapped Samples # of Screen

% light

DO

6.4 mlO2/l

Gross Productivity (Light Bottle – Dark) 1.8 mg C/m3

Net Productivity (Light Bottle – Initial) -2.8 mlO2/hr

0

100%

1

65%

3.8 mlO2/l

-0.8 mg C/m3

-5.4 mlO2/hr

3

25%

4.5 mlO2/l

-0.1 mg C/m3

-4.7 mlO2/hr

5

10%

3.7 mlO2/l

-0.9 mg C/m3

-5.5 mlO2/hr

8

2%

4.0 mlO2/l

-0.6 mg C/m3

-5.2 mlO2/hr

These results were obtained from a source other then the class. We did not have the screens to perform the experiment. The source obtained these results by performing the Winkler method on bottles wrapped in a certain amount of screens to simulate depth, and it’s effect on dissolved oxygen.

Graph 12.2: Effect of Light on Dissolved Oxygen a. The independent variable: Amount of light allowed to enter 2 bottle by screen Net and Gross 0 b. The dependant Productivity 3 variable: The Net (mg C/m ) -2 2% 10%20%25%30%40%50%60%65%70%80%90% 100% Productivity (pink) -4 and the Gross Productivity (blue) -6 Percent of Light Entering Bottles 4

Questions: 1). What are the three ways primary productivity can be measured? The three ways primary productivity can be measured is by finding the amount of carbon dioxide used, the rate of sugar formation, and the rate of oxygen.

2). What is the relationship between oxygen production and assimilation of carbon? For every mL of O2/L, there is roughtly .536 mg of carbon assimilated. 3). From your graph of the temperature data, what is the effect of temperature on the amount of oxygen that water at different temperatures can hold? The colder the water, the more dissolved oxygen the water can hold. As the water molecules move faster the oxygen can slip away. Warmer water becomes saturated more quickly then cold water, and as it becomes warmer and warmer it can hold less DO. 4). Refer to your graph of productivity and light intensity. At what light intensity do you expect there to be no gross productivity and no net productivity? Based on the graph of productivity and light intensity, there should be no gross productivity at 75% light, and no net productivity at 76% light. 5). A mammal uses only 1 to 2 percent of it’s energy in ventilation (breathing air in and out) while a fish must spend about 15 percent of it’s energy to move water over its gills. Explain this huge difference in their efforts to collect oxygen. A mammal has lungs, which take little energy to operate. They would collapse if it weren’t for the hydrostatic pressure between them and the surrounding chest cavity.

Energy is expended only to fill the lungs with air, rich with oxygen. Fish have to extract the dissolved oxygen in the water, and to do so they have to swim forward so the water rushes over their gills. They have to move forward to gain oxygen, and then separate the oxygen from the water, which takes much more energy then simply expanding the size of a lung by muscle activity and letting the air flow in naturally. 6). Would you expect the DO of water taken in from a stream entering a lake to be higher or lower then the DO taken from the lake itself? Explain. The DO of the stream entering the lake would be lower then the DO in the lake. This is because one of the six factors that effects the DO of water is turbidity: the amount of activity the water is enacting, such as a rushing river. The more turbid the water, the lower the DO is. This is because turbid water causes particles to absorb many of the suns rays, releasing heat in the same fashion that asphalt does. As the heat increases, the capacity to hold dissolved oxygen decreases.

7). Would you expect the DO concentration of water samples taken from a lake at 7:00 a.m. to higher or lower than samples taken at 5:00 p.m. ? The DO concentration should be higher at 5:00 p.m., because it is at the end of the day. Over the course of the day, light goes into the lake, and plants in the lake undergo photosynthesis, creating oxygen and releasing it into the lake. Thus, the net productivity is higher, and the gross productivity is higher because the respiration is being overcome by the amount of photosynthesis going on. At 7:00 the light is just coming out, and in the night the net productivity is very low because there is no light to facilitate photosynthesis. Thus, the gross productivity is low because while organisms are undergoing respiration, no photosynthesis is occurring. However, if it were a place that the sun made the lake very hot and the night made it very cold, it would be able to retain a lot of it’s dissolved oxygen. This would not counteract the dearth of net productivity however. 8). In two identical containers with two identical fish, there is an unequal volume of water. Which fish, A, with more water, or B, with less water, would have more oxygen available to them? Fish B would have more access to oxygen. Because of the unique shape of the glass, fish B is contained in water with a much greater surface area to water ratio, so much more oxygen can diffuse into the small amount of water fish B is in. But, the poor guy has no room to swim. The ideal place for him to be is a tank.

9). What is eutrophication? Research and explain why allowing nitrogen or phosphorus fertilizers to run into a body of water can negatively affect life in it. Eutrophication is the process by which water bodies receive extra nutrients such as nitrates or phosphorus, causing them to grow. Too much nitrogen or phosphorus can cause hypoxia, which is the depletion of dissolved oxygen in water. It does so by increasing the number of phytoplankton blooms, which, while increasing the DO concentration in the day, goes through too much respiration at night so that the gross productivity is detrimentally low to the other organisms in the ecosystem.

Error Analysis: Due to a dearth of equipment, as well as human error during the Winkler method, we were unable to obtain the proper results. The hypothetical results as well, taken from a source (cited) that also mentioned human error in their Winkler method, and were not entirely accurate. Conclusion: Based on our experiment with the temperatures, we found that in our colder temperatures, (5°C) more dissolved oxygen was present in the bottle (2.0mg/l) then in the warmer temperature solution (21.5°C), which had only 1.28mg/l dissolved oxygen. This ed our hypothesis that the colder the water is, the more dissolved oxygen it retains, because warmer water molecules move too fast to hold the oxygen. Our next experiment ed our hypothesis that the more light entering a solution with a photosynthetic organism, the higher the dissolved oxygen. This was ed by our data that the bottle with 100% light, and no depth simulating screens on it had 6.4 ml O2/l, while the 65% bottle with 1 screen had 3.8 ml O2/l, the 25% bottle with 3 screens had 4.5 ml O2/l, the bottle with 5 screens, and 10% light, had 3.7 ml O2/l, and the 2% bottle with 8 screens had 4.0O2/l. The reason this is, is because the more light being ed through the screen, the more light is available for the photosynthetic organisms in the pond water to use. They take the light and turn carbon dioxide and water into organic molecules and oxygen, creating a net productivity of oxygen through this equation: 6CO2 + 6H2O  C6H12O6 +6O2. For every 6 carbon that go in, and every six water molecules, 6 oxygen and a sugar come out. The gross productivity of our bottles was continually increasing because they were under light for 24 hours, so while the microorganisms were undergoing respiration, the photosynthetic organisms were producing more and more oxygen, yielding more oxygen then was used by respiration. Since only the bottle with 100% light had a positive gross productivity of 1.8 ml O2/l, which meant there was more respiration going on in the pond water then photosynthesis. Conclusion 2: Pubic school laboratories are under funded.

Works Cited

"Hypoxia (environmental)." Wikipedia, the Free Encyclopedia. Web. 20 Mar. 2011. .

Chamberlin, Johnnie. "Does the Level of Turbidity Affect the Amount of

Oxygen in Water? | EHow.com." EHow | How To Do Just About Everything! | How To Videos & Articles | EHow.com. Web. 20 Mar. 2011. .

"Ap Sample Lab 12 Dissolved Oxygen." BiologyJunction. Web. 20 Mar. 2011. .