I was talking with a fisheries biologist the other day who stated the following:
"In northern climates I don't recommend winter aeration. The reason for this is that solar energy is absorbed by the dark colored bottom of the pond. Combined with plant and bacterial activity this creates a band of warmer, denser,heavier water on the bottom which is between 36-39 degrees. If you are aerating when the air temperature is less than zero degrees F. you can "supercool" the water that's been brought to the surface to slightly below freezing. This water is then returned to the pond by circulation and you can end up losing this band of warm water that fish such as bluegills and bass like to inhabit. Since cold water in the presence of a healthy plant and algae population is likely to be already high in oxygen why would you bother to use the electricity necessary to aerate a pond in the winter"?
I thought this was an interesting viewpoint, which is probably only applicable to smaller ponds in the northern part of the U.S. and Canada. Does anyone have any comments on this or do you think it's much ado about nothing? I do realize that thick ice covered with several inches of snow can be a contributor to winterkill situations. That notwithstanding the biologist seemed to have a valid argument.
