Dissolved Oxygen and Primary Productivity Lab

1. Dissolved Oxygen and Primary Productivity Lab "Why did fish that I kept in an aquarium over my radiator die? An aerator was producing a constant stream of bubbles, so they should have had plenty of oxygen." At the end of this laboratory you should be able to answer this question.

2. Oxygen is necessary for cell respiration in most organisms. Aquatic organisms need oxygen that’s dissolved in the water.

3. Factors that affect dissolved oxygen: • Temperature—As temperature of water increases, its ability to hold dissolved oxygen decreases • Light—As light increases, photosynthetic organisms produce more oxygen • Bacteria and Fungi—As microbes decay organic materials, oxygen is used up • Water motion—Mixing and turbulence (waves, waterfalls, rapids) aerate water, increasing the dissolved oxygen • Salinity—As the salt concentration increases, its ability to hold dissolved oxygen decreases

4. Ideal Conditions for Maximum Dissolved Oxygen

5. Primary Productivity –therate at which plants and other photosynthetic organisms produce organic compounds in an ecosystem. Two aspects of primary productivity:

6. Organic materials are difficult to measure, but we can measure oxygen (or carbon dioxide) instead. • Gross productivity can’t be measured directly since cell respiration (oxygen being used) is always happening along with photosynthesis (oxygen being produced). • We can measure: • Net productivity—O2 production in the light (photosynth) • Respiration—O2 consumption in the dark (no photosynth) • Net productivity + Respiration = Gross Productivity

7. Photosynthesis: 6CO2 + 6H20 + light energy  C6H12O6 + 6 O2

8. Dissolved Oxygen and Temperature Use a nomograph to figure out how much oxygen water can hold at different temperatures (% saturation)

9. 0o 30o

10. Dissolved Oxygen and Light Primary Productivity at varying depths By wrapping water sample bottles with mesh to block light, we can simulate different depths of a lake. Measure the DO of the initial sample and then the DO of each bottle after 24 hrs

11. Light (L) Gross Productivity Dissolved Oxygen Net Productivity Initial (I) Respiration Dark (D) Time

13. A biology student inadvertently removed all the screens and labels from the water-sampling bottles before he measured the amount of dissolved oxygen. When he tested the unidentified bottles, he obtained the results shown below. Label the bottles with the appropriate % light (0, 2, 10, 25, 65, or 100), and figure out gross productivity and net productivity for each bottle (except the 0%).