A pond with oxygen levels sufficient in the upper layers but lacking it in the bottom layer is known as what?

A pond characterized by sufficient oxygen levels in the upper layers while exhibiting limited or no oxygen in the bottom layer is referred to as a facultative pond. This type of pond supports both aerobic and anaerobic processes. In the upper layers, sunlight promotes photosynthesis, which leads to the production of oxygen. Organisms thrive in this oxygen-rich environment. However, as you move down to the bottom layer, the lack of light and organic matter decomposition result in the depletion of dissolved oxygen, creating an anaerobic condition.

The facultative nature of this pond allows it to effectively process organic waste, utilizing aerobic processes in the upper layers and switching to anaerobic processes in the lower layers, which is beneficial in wastewater treatment applications.

Other types of ponds mentioned, like aerobic ponds, would maintain oxygen levels throughout and not exhibit this stratification. Anaerobic ponds lack oxygen altogether in their entirety, leading to entirely different biological processes. Retentive ponds are not a recognized classification for pond oxygenation and do not reflect the described characteristics of the pond in question.