Primary Productivity of the JBS Pond (Laughing Lake)
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9/28/08 Data

The primary productivity of an ecosystem is defined as the rate at which organic materials (carbon-containing compounds) are stored.  Only those organisms possessing photosynthetic pigments can utilize sunlight to create new organic compounds from simple inorganic substances.  Green plants obtain carbon for carbohydrate synthesis from the carbon dioxide in the water or in the air according to the basic equation for photosynthesis:
6CO2 + 6H2O ---->  C6H12O6 + 6O2

The rate of carbon dioxide utilization, the rate of formation of organic compounds, or the rate of oxygen production can be used as a basis for measuring primary productivity.  A measure of oxygen production over time provides a means of calculating the amount of carbon that has been bound in organic compounds over a period of time.  For each milliliter of oxygen produced, approximately 0.536 milligrams of carbon has been assimilated.
productivity

One method of measuring the rate of oxygen production is the light and dark bottle method.  In this method, the DO concentrations of samples of ocean, lake, pond, or river water or samples of laboratory algal cultures can be measured and compared before and after incubation in light and darkness.  The difference between the measurements of DO in the initial and dark bottles is an indication of the amount of oxygen that is being consumed by respiration by the organisms in the bottle.  In the bottles exposed to light, the biological processes of photosynthesis and respiration are occurring; therefore, the change over time in DO concentration from the initial concentration is a measure of net productivity.  The difference over time between the DO concentration in the light bottle and the dark bottle is the total oxygen production and therefore an estimate of gross productivity.  See the figure below

productivity 2


September 26, 2008

Condition
Dissolved Oxygen
Dissolved Oxygen

Net
Productivity

Gross Productivity
Without Elodea
With Elodea
Without Elodea
With Elodea
Without Elodea
With Elodea
Initial Bottles

11

11
N/A
N/A
N/A
N/A
Dark Bottles
4
2
N/A
N/A
N/A
N/A
100% Light
9
12
-2
1
5
10
65% Light
5
10
-6
-1
1
8
25% Light
4
6
-7
-5
0
4
10% Light
4
8
-7
-3
0
6
2% Light
3
4
-8
-7
-1
2

*Lighting conditions were done artificially in the lab using screens. Bottles were under constant light for 24 hours.