A fountain will do all of the things you listed ... just very inefficiently.

I agree with Theo's advice.

You are kind of asking how long you should run 50 electric hot plates to heat your home, compared to running a 98% efficient gas-fired furnace to heat your home.

The electricity to run a 1-HP air pump and good diffusers in your pond would add MUCH more DO to a much greater volume of water, compared to the fountain.

(I say this while liking the look of fountains on manicured ponds. However, the fountain should mostly be considered a "decorative" feature.)