How are biological oxygen demand and depth related?
Biological Oxygen demand increases with accumulation of decaying organic matter in a water system. This means that BOD is highest where there is high concentration of decomposing organic matter in that system.


  What is the relation between biological oxygen demand (BOD) and depth?


The answer may vary as in some cases organic matter floats on upper columns of water and can be decomposed readily by aerobic microorganisms manifesting an increased BOD. 

However, this study   which was conducted using waste water from stabilization ponds (depths ranging from 0-5m) shows that there is an increase in the Biological Oxygen Demand with increasing depth and this can be attributed to the settling down of organic matter in these ponds.