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AP Biology Lab 12: Dissolved O2 and Primary Productivity

Dissolved Oxygen & Primary Productivity

Elizabeth Hawkins

on 5 September 2011

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Transcript of AP Biology Lab 12: Dissolved O2 and Primary Productivity

Hypothesis Introduction Procedure Data/ Observation Analysis/ Conclusion Dissolved Oxygen & Primary Productivity What Is Dissolved Oxygen? Important indicator of water quality
because oxygen is necessary to the
metabolic processes of virtually all
life forms. Aquatic vs. Terrestrial Environment Air contains 95% more oxygen than the water. Water's ability to hold oxygen rapidly decreases
as the water temperature increases. Other Factors That Affect Dissolved Oxygen: 1. Temperature: As water temperature increase, the concentration of dissolved oxygen decreases. 2. Wind: Oxygen is mixed into the water as wind blows across the surface. 3. Turbulence: 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. 4. Trophic State: Amount of nutrients in the water. Two Classification: Eutrophic & Oligotrophic Eutrophic: More shallow, rich in nutrients, and oxygen levels
constantly fluctuate from high to low. Oligotrophic: Oxygen rich, but generally nutrient poor. They are
clearer, deeper , and younger than eutrophic lakes. Oxygen levels are constant. What Is Primary Production? Energy accumulated by plants since
it is the first and basic form of energy storage. The flow of energy through a
community begins with the fixation of
photosynthesis: 12H2O + 6CO2 C6H12O6 + 6O2 + 6H2O How to Measure Primary Production by Using Oxygen Method: Use 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). Part A:
The temperature an aquatic environment is located at influences the dissolved oxygen levels, along with the amount of primary aquatic productivity. Part B:
The amount of light each water samples get exposed to greatly affects the difference in the dissolved oxygen levels. So, the water sample without any screens (exposed to 100% or 65% light) would have the highest dissolved oxygen levels. Part C:
Since living aquatic organisms use up dissolved oxygen in the process of respiration, in return, they also produce dissolved oxygen through photosynthesis. Objectives Measure dissolved oxygen concentration.
Calculate gross productivity, net productivity, and respiration rate.
Demonstrate the importance of oxygen cycles in an ecosystem.
Identify physical & biological factors affecting solubility of dissolved gases in aquatic ecosystems.
Demonstrate the effect of light and nutrients on photosynthesis.
Demonstrate how aquatic organisms are related to dissolved oxygen & what role it plays on their lives. Materials Wear protective equipment – gloves, lab gown, goggles.
Do not leave sample in open air or agitate it.
Use extreme care when working with acid. Safety! Method Part A: Measurement of Dissolved Oxygen Water sample - Pond water
Distilled water
Pipet (many)
Shallow container
Light - sunlight Microscope slide
Compound microscope
Cloth squares, 17
Aluminum foil
BOD bottles, 7
Direct-reading titrator Titration vial
Paper & pen
Paper towels
Manganous sulfate solution
Alkaline potassium iodide azide
Sulfamic acid
Starch indicator solution
Sodium thiosulfate 0°C 20°C 30°C 1. Thoroughly rinsed out a sampling bottle and inserted distilled water, making sure it overflows so that no air bubbles were trapped or inside the bottle. Sealed the bottle with a cap so that no air pockets were created and excess water has been removed. Repeated two more times.

2. Verified the assigned temperatures, 0°C, 20°C, and 30°C, to ensure that it has reached the desired temperature.

3. After verifying the temperatures, placed the three bottles in each designated temperature and left them there for 24 hours. 4. The next day, placed the three bottles in a shallow container and added eight drops of manganous sulfate to the sample bottles. 5. Added eight drops of alkaline iodide to each of the sample bottles, then capped the bottles and mixed by inverting them several times. 6. Allowed the manganous hydroxide precipitate to settle until it came below the shoulder of the bottle. 7. After wearing safety materials, added one scoop of sulfamic acid and mixed by inverting the bottle several times. Then, waited until the sample turned clear yellow as free iodine has been formed. 8. Carefully measured out 20ml of the sample into a titration vial using a pipet. And placed the vial on top of a white sheet of paper to better see the color of the sample.

9. Inserted eight drops of starch indicator to the 20ml sample and observed the bottle as the liquid's color turned from yellow to purple.

10. Placed the cap on the vial and gently swirled to mix. 11. Carefully filled the titration syringe with sodium thiosulfate working solution and inserted the tip of the titration syringe into the hole in the vial cap. 12. While continually swirling the sample, titrated the 20ml sample with sodium thiosulfate working solution. Titrated one drop at a time until the color changed from purple to a colorless solution - this is the titration endpoint where all free iodine had been converted to sodium iodide by the addition of sodium thiosulfate.

13. Determined the concentration of dissolved oxygen in the sample solutions and recorded the values in Table 2 in the Analysis Section. Part B: Measurement of Primary Productivity 1. Obtained seven water sample bottles. One of the bottles served as the initial sample, so labeled the bottle “#1-Initial”. A second bottle served as the dark bottle, so labeled it “#2-Dark”. Labeled the rest of the bottles according to light intensity: “#3-100%”, “#4-65%”, “#5-25%”, “#6-10%”, and “#7-2%”.

2. Carefully filled each bottle with pond water. Same process as #1 in the Part A Method.

3. Wrapped bottle #2 with aluminum foil. And wrapped the rest of the bottles with cloth squares except of bottle #1 according to the chart below. 4. Capped bottles #2 through #7 tightly and laid them down on their sides under the sunlight for about 48 hours. 5. Fixed the sample bottle #1 by performing Steps 4 through 7 as described in the Part A Method, and then kept the #1 bottle at room temperature until processed the other samples. 6. Prepared a wet mount of the pond water and observed it under a compound microscope. And, on a separate sheet of paper, illustrated and identified the organism. 7. After 48 hours, fixed bottles #2 through #7 by performing Steps 4 through 7 as described in the Part A Method.

8. After all bottles were fixed, determined the dissolved oxygen of all samples by performing Steps 8 through 13 in the Part A Method, except recorded the results in Table 3 in the Analysis section of the lab.

9. Calculated the gross and net productivities, respiration rate, and gross productivity (mg C/m3) of the samples and recorded the results in Table 3. Table 2
Dissolved Oxygen Concentration Table 3
Gross and Net Productivity/Respiration Rate Respiration Rate = Initial Bottle (ml O2/L) - Dark Bottle (ml O2/L)
= 0.5 ml O2/L - 0.4 ml O2/L
= 0.1 ml O2/L This table shows the measured dissolved oxygen content at 0°C, 20°C, and 30°C, and the calculated saturation for that. Also, the data shows the relationship of temperature to saturation and dissolved oxygen content. This chart takes the values for dissolved oxygen for different amounts of light and uses it to find
the gross and net productivity. Part C: Aquatic Organism's Impact on Dissolved Oxygen 1. Obtained sample water from tadpole water and observed it under a compound microscope.

2. Identified the organisms and took pictures of them. The temperature affects the solubility of oxygen in water in which that as temperature decreases, solubility increases, and as temperature increases, solubility decreases. They are inversely proportional. Also, if there are too many various minerals in a solution, it can lower the solubility of oxygen in water.

There can be several factors that could influence the dissolved oxygen concentration of a body of water, such as wind, temperature, and altitude. Wind causes oxygen from air to mix into the water, increasing the dissolved oxygen. In lower temperatures, water can store more dissolved oxygen, and decrease the saturation, while increasing the content. And as altitude increases, the dissolved oxygen decreases.

Oxygen is crucial for aquatic organisms that live in lakes because they need oxygen for respiration as organisms consume oxygen and give off carbon dioxide while absorbing food molecules to obtain energy for growth and maintenance. Also, even though aquatic plants and algae consume oxygen, they also produce oxygen in sunlight by the process of photosynthesis.

Furthermore, based on the data table and observation, it can be proved that the sample solutions that were more exposed to sunlight had a higher rate of dissolved oxygen. And the sample solutions that received less sunlight because of the screens, had a lower level of dissolved oxygen. Procedural Errors Possible misreading gradations on the titrator.
Possible miscalculations while recording the information in the data.
Possibility that air bubbles might have been formed in the bottles during the experiment.
May not have received an adequate amount of sunlight, since I did not use the light bulb.
Possibility that the amount of solutions that were inserted were not the same for every bottle.
Maybe lake water might have given a better, or more accurate, result that using pond water.
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