The graph below shows the relationship between IBI and the minimum dissolved oxygen (DO) level. Study the graph and answer the questions. Be prepared to explain the correct answers to your group.
- Describe the relationship between DO and IBI - as DO goes down, the IBI ??
- Are there places/times where the relationship does not seem to be consistent? Write those down.
- The reason that the IBI and DO are related in this way is because (choose the best answer and click on the letter):
- The fish are bigger in some areas and use more oxygen.
- When the minimum DO is low, a lot of the fish cannot survive in that part of the stream.
- The minimum DO is higher in places where there are a lot of algae producing oxygen through photosynthesis.
- More trees have been removed in areas with high DO, reducing the amount of leaves that decompose in the water and use up oxygen.
- One major reason that the DO minimum level is lower is:
- There are more trees shading the stream
- There are more fish using more oxygen
- There is less mixing of the water
- There are larger amounts of organic wastes being released in these places
- Oxygen levels can be lower in agricultural areas if:
- There are more trees shading the stream
- Animal wastes get into the stream