That accounts for the relationship but not that all 3 were falling while the water cools. Better look and think some more.
Also the ice build has really slowed.
The water had cooled a least a week before the DO levels started to fall in unison.
I believe that both the DO drop and the slowed build in ice are due to the heavy snow cover. Snow cover reduces the light that penetrates the water thus reducing the photosynthesizing ability of plant life. The heavy snow cover also insulates the pond from the cold air temperatures.
A case can also be made that the DO levels are at their peak when the ice cover becomes permanent(for the duration of the current winter). When clear ice builds rapidly it traps excess DO under the ice that will dissipate rapidly if snow cover intervenes in the photosynthesizing process. The peak DO readings were at or above saturation levels during rapid early ice build.
