Question

Dissolved Oxygen in Aquatic Ecosystems

Dissolved oxygen is oxygen trapped in a fluid such as water. Since many living organisms require oxygen to survive, it is a necessary component of water systems such as streams, lakes, and rivers in order to support aquatic life. The dissolved oxygen is measured in units of ppm (parts per million).

Examine the data in the table below, showing the amount of dissolved oxygen present and the number of fish observed in the body of water from which the sample was taken.

Water Quality vs. Fish Population
Dissolved Oxygen (ppm)	0	2	4	6	8	10	12	14	16	18
Number of Fish Observed	0	1	3	10	12	13	15	15	16	17

a. What general pattern do you observe based on the information in the table?

Answer 1

Dissolved oxygen is very important in sustaining the aquatic life. In this data we can see that as the dissolved oxygen level is increasing, the number of fishes are also increasing. Dissolved oxygen is used by the fishes for respiration and when it is plenty, the water can support more number of fishes. But however, extreme conditions always create troubles. Here also as the dissolved oxygen level increase from 12 to above, there is not much rise in the number of fishes. So there is an optimum range which is best for the fish and during that they seen abundantly. Too low level of dissolved oxygen will simply kill the fish and too high dissolved oxygen (hyper saturated) can cause gas bubble formations in fishes. So the fishes prefer the optimal range ie, around 6-12 ppm as per given data. If we increase the dissolved oxygen further, the number of fishes will reach zero at some point.