I have to agree on simple obvious facts and without doing PhDs on aeration, the main benefit of bottom aeration is less energy is needed to move water. I have observed that on a typical square shape one acre pond, with just one 9" disc dead center in the deeper area all the pond water was in a slow motion movement. Well located, bubbles will turn your pond over.
Then again, another huge benefit is that oxygen depletion normally starts from the sediments up, and with oxygen depletion, phosphorous, nitrogen, iron & manganese are released from the sediments. Aerating the bottom first makes sense as previously mentioned by Bruce because bubbles will rise and lift the water, in the end, the movement of water has the best benefits as it will pick up the oxygen of the air as well.
Another effect I can suggest for the bubbles is that when they break the surface, which in turns breaks surface tension (imagine a spoon full of water, the top is curved, that is tension) surface tension when water is calm, prevents noxious gases to escape, they need a chimney or a break in the tension. Breaking surface tension alone can be beneficial. A windy day breaks surface tension.
Aeration over no aeration is well described on this animated web site from Agriculture Canada:
http://www.agr.gc.ca/pfra/flash/dugout/en/dugout_e.htm If I had to run a business in aquaculture, I would certainly calculate how much I spend in electricity, fuel or labor to aerate with a surface method. Surface aerators like paddlewheels have certainly a role to play in emergency aeration. A fountain can also aerate, especially if a water feature is the objective.
I believe bottom aeration and surface aeration debate is like Mac or PC debate, it boils down to marketing. On
www.shrimpnews.com objective journalism seem to clearly define that no surface aerating technologies has taken a clear lead. Until now, bottom diffusion is less used because of a higher initial cost and the need to remove for harvesting. I believe that can be offset with the correct technology, especially when the cost of energy is calculated.
As I have observed in my 20 years in the field, there is a lot of folklore around the water, ponds owners are not different. Folklore and tradition are closely knit together and traditionally people will use aeration methods observed at the fish hatchery, mostly surface aerators. It works, but is it the best method?
Saving energy, while doing the maximum of benefits to the fish, water, sediments and microbes should be what pondmeister should strive for. Each pond has a different need but a common ageing process.
Sorry for the long story� correct me if I am wrong�
