why bottom fauna is an indicator of water quality?

Answer 1

Bottom fauna live in nearly constant contact with the ground, which infused with the local ground water. Thus, bottom fauna will feel the initial effects of any change in the ground water. Animals higher on the food chain or living physically further from the ground will not feel these effects until they have had more prolonged exposure, or they have eaten the bottom fauna that first became effected. So examining bottom fauna can give you an early indication that something has happened to the water supply.

Answer 2

It is because bottom fauna usually stay in the area they are in and don't move around a lot. If the lake gets too much algae or is being polluted, the decrease in bottom fauna is very noticeable and therefore easy to measure. Scientists throw a square net over a random area and record how much of what fauna was caught in the square area and their relative health from last year, the area of the square area on the bottom remains the the same area year after year. Other fauna in the lake, river, stream etc. are much more mobile and could change there habitat in the region for any number of reasons. While scientists can and do measure fish populations number and health, bottom fauna are the first "red light" that something has changed in the lakes environment. They check for various toxins changes in algae levels etc to see what is changing the quality of the water.

Answer 3

Because of its settlement