This is just a guess, but if you see 'bubbling,' it may not be a spring; it may just be some air pockets being compressed as the weight of the water squeezes down onto the pond basin, thus causing a slow release of the air or gases.
If you can get a few wood pallets sunk, that will also help with fathead spawning, and it won't be visable from the surface (not that your current floating wood looks bad).
