Depth of the Mudpuddle

[Don Schaeffer]

https://www.youtube.com/watch?v=rYJobNQWSNw
The 4 inch difference between the top of the water column and the bottom could make a difference in the population of life in the mudpuddle. The upper level is brighter and contains more oxygen than the lower level. In my mudpuddle, the upper level of the water contains floating islands of biofilm. The lower level contains decaying vegetation. How does the depth of the sample affect how much and what kind of organisms can be found?