2. Trout are surviving in the diffuser plume.
It has been posted that in near freezing water a diffuser can affect water 200' away. There is some stuff on Youtube that shows under ice water movement from a single diffuser even farther away than that. This year I measured 1.5PPM 60' or so away from a quad plume and got 1.5PPM. Seems unlikely to me that 30' closer to the plume would have led to DO over 3.0PPM. Also seems unlikely to me that the trout would double in size when confined to living in a 30' circle over the plume.
It seems to me that oxygen exchange from aeration must occur at the top of plume. The surface tension of the bubbles is so high ... probably little exchange occurs there while air is rising. However, at the top of the plume, there would be an air space hollowed under the ice and a lot of turbulence breaking surface tension that would allow for oxygen exchange. The coldest water is near the surface so the oxygenated water would be chilled near the surface. How deep did you take the measurement when 60' away? If it was not in the top 3 or 4 feet, then indications may be deceiving.
At this point you have evidence that O2 is higher 60' from the plume than it is further away from the plume. As to doubling in size ... whatever water is a refuge to trout is also a refuge for their food. If sufficiently concentrated I could see such fantastic growth resulting. The prey items would find the refuge in the same way that trout do ... they would follow the O2 gradient in the direction of increasing O2.
