Tracy I have found the same thing in the summers. MAYBE things are different in the winter?? I don't really know. All I know is trout are supposedly toast at DO levels less than 3 PPM and mine are surviving at .8 PPM.
The lake is at 0.8 PPM. I'm at a loss as to how aeration would lower the DO below this level in the plume. Here's the part that may be missing in the analysis of the DO measures of the summer time plume. While you have established that the DO measurement in the plume is lower than the rest of the BOW, you haven't provided evidence that water in the plume isn't dissolving oxygen and increasing in DO.
I think that it is different in the winter. The dissolution rate of oxygen is greater at colder temperatures particularly when DO is low and well below its potential saturation. In the summer, water brought to the surface continues to dissolve oxygen from air interaction as it spread outs. This can't occur in the winter when the water is frozen and light is prevented from entering the water. It makes perfect sense to me that water near the top of the plume in a frozen snow covered lake carries the most oxygen.
In the end, there must be water with sufficient DO or the trout would die. If we were to agree that the aeration lowers DO instead of increasing it .... then I would agree that there was some factor other than low DO killing the trout when the lake was un-aerated. There are I suppose other possible explanations but the simplest and most plausible to me is that sufficient oxygen from the pumped air dissolved to support the trout.
