Cary -- Many thanks for the input and the suggestion about the smaller watergarden diffuser. That could work. I've been concerned for a while about the whole DO trade-off: get the oxygen up and you risk a potentially lethal boost in temprature; but go with stratification and the DO is gone in no time at all from the colder depths ... and the trout are toast.
My pond is marginal trout habitat, to be sure. The spring is steady but really doen't have the volume I would like. Its strong point, according to a local spring expert (this is karst country around here), is that the spring is a deep one, as opposed to a shallow, bluff-type spring that might be adversely affected by droughts and wet seasons. The flip side to that is that the water has almost no dissolved oxygen when it emerges; plus, it is very high in saturated nitrogen -- and total hardness is way up there, too, something like 450 to 500 parts per millions, if memory serves me well.
I'd like to be able to boost DO right up near the spring or near where it enters the pond (about 70-75' away) without bumping the temperature up too much. Unfortunately, there just doesn't seem to be sufficient gradient or fall to create a riffle area that would do any good.
I've discovered a place online that deals in submersible automated data loggers that plot temperature over varying intervals -- and they seem to be fairly reasonable (I'm a retiree and watch my pennies pretty closely!). I guess if I got two data loggers, one could be placed up in the spring channel and another in the zone where the trout hang out in July and August, and that could give me a very good profile of how much temperature gain there is in that span of 100 linear feet or so from the spring to the far end of the trout zone in the pond. That might give me a better picture on where and how to place a small diffuser.
My wife and I have a "grand plan" for the pond that includes putting up a small cabin-style storage building on a little peninsula, bordered on one side where the spring enters. We'll have a new electric line run out there, and then move the aerator to this storage building (it's been up in a shed about 150 yards above and away from the pond). We might also put an old PC in it to receive data from the data loggers ... bold plans, indeed, for a decidely low-tech, non-handy old guy! So, stay tuned.
By the way, that pond depicted in your post is absolutely beautiful! I take it that it's up at a pretty high elevation? -- Mike
