Dissolved Oxygen and Aquatic Primary Productivity
Dissolved Oxygen
• In an aquatic environment, oxygen must be dissolved in order to be available for organisms
• You measured the amount of dissolved oxygen in water samples at different temperatures
Results
Dissolved Oxygen Availability
• Oxygen is essential for cellular respiration in most organisms
• Factors that affect the amount of dissolved oxygen in water are:
• Temperature• Photosynthetic activity• Decomposition activity• Mixing and turbulence• Salinity
DO and Temperature
• Nomograph—how much oxygen water can hold (saturation)
Aquatic Primary Productivity• Primary Productivity—rate at which photosynthetic
organisms produce organic compounds– Gross productivity = entire photosynthetic production of
organic compounds– Net productivity = organic materials remaining for next
trophic level (after photosynthetic organisms have used glucose for respiration)
The Lab
• You analyzed the effect of varying amounts of light (various water depths) on primary productivity
• Dissolved oxygen is an easily measured product of photosynthesis and cellular respiration
Productivity and Lake Depth
• You monitored the effect of varying light levels on DO in an algae rich water culture
Initial
Dark
Light
Measuring DO
• You measured DO in the original sample
• Then you measured DO after 24 hours of photosynthesis and respiration under various light
Analysis of Results
Results
Sample Problem
• All screens and labels were removed accidentally. Unidentified bottles, obtained the results shown below.
• The initial oxygen reading for this water was 4 mg O2/l.
