In facultative ponds the algae use the inorganic compounds(N,P,CO2) released by aerobic & facultative bacteria for growth using sunlight for energy. They release oxygen into solution that inturn is utilized by the bacteria completing the symbiotic cycle Oxygen also occurs naturally by oxygen transfer ,which is increased by turbulence. There are 2 distinct zones in facultative ponds:Upper aerobic zone - where bacterial (facultative) activity occurs.Lower anaerobic zone – where the solid settle out of suspension to form a sludge that is degraded anaerobic ally These ponds have a complex ecology with many predator-prey association, with phyto- & zooplanktonic forms predominating.