Even with the pump drawing water from a depth of only 2', and the flat bottom at ~5.5' down, you still think its too much circulation and that the bottom water will be impacted.

And there is actually quite a bit of organics built up already. Maybe a good 1" layer. The pond is sandwiched between a ~14" diameter maple tree and a ~20" diameter pin oak. And I think every single leaf that falls off one of them trees eventually make it into the pond.

And regarding climate for those unfamiliar with central oh....

I'd say on average we would get a 4-5" ice layer over the farm ponds in the area. (I have a 1 acre farm pond out back, ~8' deep and 60 years old). On the hard cold winters, I have seen ice 10"-12" thick. And then I have seen winters (the last two) where the pond never froze completely over