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.