Interesting - light penetration went up so plankton production of O2 at depth went up while surface O2 stayed the same.

"Why does the clarity change so much week to week:
Ground water flow increases and decreases?
Clear sunny days increase plant oxygen production?
Plankton mini-blooms occurring rapidly over a short time span?
None of the above?
All of the above?
Some other reason?"

All of the above and other reasons , wind , predation by fish on plankton , increase/decrease in nutrients , plankton cycle timing.