LOW OXYGEN AND POND AERATION William
A. Wurts, Senior State Specialist for Aquaculture
Kentucky State University Cooperative Extension Program (PDF)
From which I quote:
Sudden death of phytoplankton or algal bloom, "bloom crash", may result from insufficient light (e.g. cloud cover) for photosynthesis, inadequate pond nutrients (a bloom too dense to be supported by available nutrients and oxygen) and/or bloom senescence (the plant cell line becomes too old to continue reproduction). Oxygen is consumed or depleted when dead phytoplankton/algae decay. During the nighttime hours, a dense phytoplankton bloom can remove all oxygen from the water for respiration (to breathe) alone. When a bloom crash occurs, the water appears to have become "black" or clear overnight.
It would seem that certain algae levels are helpful for oxygenating ponds.
I maintain several pet fish ponds. What role does algae play in establishing a healthy pond environment for my fish and other aquatic or semi-aquatic species I might introduce?