Question

To measure primary production of algae in a stream, you place two sealed chambers in the stream, each enclosing the sediments as well as the water above them. One chamber is covered with black tape (blocking all light) while the other is transparent to light.

You measure dissolved oxygen (DO) before and after a 24-hour incubation. DO in the light chamber increases by 30 mg/m2 while DO in the dark chamber decreased by 10 mg/m2.

What is the estimated Re for the stream?

Answer 1

Answer:

The estimated Re for the stream is 10 mg/$m^{2} /day$

Explanation:

Re is the short form for ecosystem respiration. It is the sum total of the respiration being carried out by all the living organisms occupying a particular ecosystem.

Respiration in itself is a process during which the energy locked in food consumed by living organism is unlocked and made available for proper functioning of the organism. The process can happen both in the presence or absence of oxygen.

When respiration occur in the presence of oxygen, it is referred to as aerobic respiration and it is represented by the following equation;

         $C_6H_1_2O_6 + 6O_2 -----------> 6CO_2 + H_2O + Energy$

On the other hand, a respiration that occur in the absence of oxygen is termed anaerobic respiration or fermentation and it is represented by the equation;

         $C_6H_1_2O_6 ---------> 2C_2H_5OH + 2CO_2 + Energy$

Hence, for aerobic respiration, the amount of oxygen consumed per unit time gives an indication of the rate of respiration.

In the light exposed chamber, the process of photosynthesis is taking place concurrently with the process of respiration. Photosynthesis is process during which photosynthetic organism utilize raw materials such as carbondioxide and water to manufacture glucose. It can viewed as the opposite of aerobic respiration and represented thus;

        $6CO_2 + H_2O + Energy ---------> C_6H_1_2O_6 + 6O_2$

Dissolved oxygen (DO) in the light exposed chamber increased because the rate of photosynthesis was more than the rate of respiration. Hence, the rate at which oxygen is being produced outweighs the rate at which it is being consumed.

However, photosynthesis cannot take place in the covered chamber because light is necessary for photosynthesis to take place. Therefore, only respiration can take place in this chamber. As a result, the decrease in the amount of DO observed after incubation is as a result of aerobic respiration.

10 mg/$m^{2} /day$ is an estimated ecosystem respiration rate because only aerobic respiration is considered. There is a likelihood some anaerobic respiration might be taking place in the sealed, covered chamber.