What we may not have seen is that there is time delay between a larger BOD load and the lower dissolved oxygen level. The graphic helped us to see that relationship. Another kind of visualization that may be important looks at relationships over space rather than over time. One of the biological measures pointed to earlier can be used to illustrate those spatial relationships. The IBI is a measure of fish diversity that is the higher the number the more different species of fish we find in the river.
Greater diversity is only possible when there are a minimum of pollution stresses in the stream.
So as pollution levels and the number of pollution sources go up, we would expect the IBI to go down. Examine the map below.